Kenmare Resources

Kenmare Resources plc is a mining company headquartered in Dublin, Republic of Ireland. It is listed on the London Stock Exchange and Euronext Dublin under the ticker KMR. Kenmare is one of the world's largest mineral sands producers and the Company owns and operates the Moma Titanium Minerals mine. Moma is one of the world's largest titanium minerals deposits, located 160 km from the city of Nampula in Mozambique, Africa.
Kenmare is the world’s fourth largest producer of titanium feedstocks (ilmenite and rutile), which are primarily used to make titanium dioxide (Ti02) pigment. Ti02 pigment impart whiteness and opacity in the manufacture of paper, paint and plastics. The Company is responsible for 7% of global supply of titanium feedstocks at current production levels and this is expected to grow to 10% once Kenmare has completed the third of its three growth projects to increase ilmenite production to 1.2 million tonnes per annum (plus associated co-products).
History.
Kenmare was incorporated in Ireland in 1972 under the name Kenmare Oil Exploration Limited. After several years of oil exploration, the Company re-registered as a public limited company under the name Kenmare Oil Exploration Plc on 5 June 1985. On 28 July 1987, the Company changed its name to Kenmare Resources plc and in 1994 it was listed on the main market of the London Stock Exchange and the main market of the Irish Stock Exchange (now Euronext Dublin).
In 1987, the company acquired 50% of the licence for the Congolone heavy mineral sands deposit in Mozambique and during 1989, Kenmare's holding increased to 95%.
Separately, the Company operated the Ancuabe graphite mine from 1994 until 1999 when it was placed on care and maintenance due to a fall in graphite prices.
Kenmare's drilling of the Congolone deposit resulted in measured mineral resources of 167 million tonnes of ore at grade 3.3% heavy minerals, containing a recoverable 4 million tonnes of ilmenite and associated co-products rutile and zircon. In 1996, BHP became a joint venture partner with Kenmare in the development of the Congolone deposit. Over the coming years, BHP would begin appraising the Namalope, Pillivi and Mualadi deposits and identify new heavy minerals deposits, which would ultimately become the main focus of the mining project. Following the closure of some of BHP's Titanium feedstocks operations, the joint venture agreement was dissolved in 1999 and by 2001 Kenmare had acquired the exclusive rights to the deposit.
Work began constructing the mine in October 2004. Production began in 2007 and Kenmare exported its first ilmenite from Moma in December 2007. Commercial production commenced in 2009.
A settling pond adjacent to the Moma Mine breached its southern wall on 8 October 2010. A non-toxic discharge of water, sand and clay flowed through the nearby village of Topuito, leaving one 4-year-old child missing. Mining at Moma is undertaken using dredges and floating concentrator plants. Once the minerals are extracted, sand and clay tailings are deposited behind the plants through a series of settling ponds. The accident occurred when a containment wall on one of these settling ponds failed during the early hours of the morning. Mining resumed the following month after some 300 homes had been rebuilt. Kenmare extensively reviewed the berm system, which surrounds the containment ponds and implemented design changes provided by independent engineering firms to prevent any future incidents.
Operations.
The Company's principal asset is the Moma Titanium Minerals Mine, located in Moma, Nampula Province, Mozambique. It has been in production since late 2007. In 2019 the Mine produced 892,900 tonnes of ilmenite (plus associated co-products) and this is expected to increase to 1.2 million tonnes per annum once the third of the Company’s three growth projects, the relocation of Wet Concentrator Plant (WCP) B, is complete.
The mine produces 7% of the world's titanium feedstocks (ilmenite and rutile), which are predominantly used in the production of titanium dioxide pigment favoured for its whiteness and opacity in paper, paint and plastics.
The Moma Mine also produces zircon, an important raw material in the manufacture of ceramics and mineral sands concentrates, which is used in various clean technology applications.
The mine is estimated to have a mine life of over 100 years at current production levels, with over eight billion tonnes of Mineral Resources in various ore zones. The current mine plan extends to beyond 2040.
The Mine has a low environmental impact, with 90% of its power requirement in 2019 sourced from hydropower. No chemicals are used in Moma’s mining or processing operations and Kenmare employs a progressive rehabilitation strategy in order to return mined land to local communities in a timely manner.
At the end of 2019, the Mine employed over 1,420 people and 96% were Mozambican. In 2019 the Mine received a five star NOSA accreditation for health, safety and environmental management for the fourth consecutive year.
The total proved and probable ore reserves under the Namalope, Pilivili, and Nataka mining concession are estimated as at 31 December 2019 at 1,584 million tonnes, grading 2.7% ilmenite, 0.18% zircon and 0.060% rutile, containing 43 million tonnes of ilmenite, 2.9 million tonnes of zircon and 0.95 million tonnes of rutile. The total ore resource (excluding reserves) held by the Group under a combination of exploration licences and mining concessions is estimated as at 31 December 2019 at 6.4 billion tonnes, grading 2.4% ilmenite, 0.16% zircon and 0.052% rutile, containing 150 million tonnes of ilmenite, 10 million tonnes of zircon and 3 million tonnes of rutile.
Kenmare Moma Development Association.
In 2004 Kenmare established a not-for-profit development association called the Kenmare Moma Development Association. The association's objective is to implement development projects in the Moma Mine’s host communities, with the three key focuses of economic development and livelihoods, healthcare development and education development.
Since its inception, some of the association's initiatives have included drilling water boreholes to provide clean drinking water for more than 24,000 people, building over 30 classrooms for local schools, constructing a community health centre including a maternity unit and pharmacy, and building a technical school for vocational development.
Products.
The Moma Mine's primary product is ilmenite (accounting for 68% of revenue in 2019), with the associated co-products of primary zircon (22% of revenue), concentrates including mineral sands concentrate (7% of revenue), and rutile (3% of revenue).
Kenmare is the world’s fourth largest producer of titanium feedstocks (ilmenite and rutile), which are primarily used to make titanium dioxide (Ti02) pigment. Ti02 pigment impart whiteness and opacity in the manufacture of paper, paint, plastics and multiple other ‘quality of life’ items like inks, pharmaceuticals, and cosmetics. The Company is responsible for 7% of global supply of titanium feedstocks at current production levels and this is expected to grow to 10% once Kenmare has completed the relocation of WCP B to increase ilmenite production to 1.2 million tonnes per annum (plus associated co-products).
The Moma Mine also produces zircon, which is an important raw material for the ceramics industry, and mineral sands concentrate, which is used in various clean technology applications.
Ilmenite is a common accessory mineral in igneous rocks, sediments, and sedimentary rocks in many parts of the world. Apollo astronauts found abundant ilmenite in lunar rocks and the lunar regolith. Ilmenite is a black iron-titanium oxide with a chemical composition of FeTiO3. Ilmenite is the primary ore of titanium, a metal needed to make a variety of high-performance alloys. Most of the ilmenite mined worldwide is used to manufacture titanium dioxide, TiO2, an important pigment, whiting, and polishing abrasive.
Ilmenite is the main source of titanium dioxide, which is used in paints, fabrics, plastics, paper, sunscreen, food and cosmetics. Kenmare produces 7% of the world's titanium feedstocks (ilmenite and rutile).
Zircon is a zirconium silicate mineral with a chemical composition of ZrSiO4. It is common throughout the world as a minor constituent of igneous, metamorphic, and sedimentary rocks. Zircon is present in most soils and clastic sediments. Zircon-rich sediments are mined and the recovered zircon is used to produce zirconium metal and zirconium dioxide. These are used in a wide variety of manufactured products and industrial processes. Zircon is mainly consumed as an opacifier, and has been known to be used in the decorative ceramics industry.
Rutile is a titanium oxide mineral that is most commonly found in granites, pegmatites, and metamorphic rocks. It is also found in sands derived from the weathering of these rocks. Rutile also forms as slender crystals within quartz and micas. It is a common mineral in the alluvial sands that are dredged for magnetite and ilmenite. Rutile is used as a coating on welding rods. It is also used as an ore of titanium, a metal used where light weight and high strength are needed. Some rutile is used in the production of pigments for paints.
In Q4 2018 Kenmare introduced a new product stream called mineral sands concentrate, which contains monazite. Monazite is a rare phosphate mineral with a chemical composition of . It usually occurs in small isolated grains, as an accessory mineral in igneous and metamorphic rocks such as granite, pegmatite, schist, and gneiss. These grains are resistant to weathering and become concentrated in soils and sediments downslope from the host rock. When in high enough concentrations, they are mined for their rare earth and thorium content. Monazite is an important source of thorium, cerium, and other rare elements. Often mined as a byproduct from heavy mineral deposits. Kenmare despatched its first shipment of mineral sands concentrate from the Moma Mine in Q2 2019.
Markets.
Kenmare's products are raw materials used in the production of many consumer products. The market for ilmenite, zircon and rutile is a substantial one – the titanium feedstocks industry is worth US$4.5 billion per year and the zircon industry is worth US$1.7 billion per year.
Demand for Kenmare’s products is heavily linked to the performance of the global economy. Ti02 pigment is a ‘quality of life’ item and consumption of it grows as income levels increase. Kenmare also expects to benefit from emerging supply constraints. The Company believes that current product prices are not high enough to incentivise new greenfield projects to be built, which means that over time, demand for titanium feedstocks will exceed the available supply. This is expected to support product prices.
Kenmare's sales profile is geographically diverse with the Company selling its products to customers operating in more than 15 countries globally. In 2019, 58% of the Company’s revenue was attributable to Asian markets, 27% to European markets and 15% to the rest of the world.
Expansion plans.
In August 2018, Kenmare announced three development projects that together have the objective of increasing Moma’s production to 1.2 million tonnes per annum of ilmenite, plus associated co-products, on a sustainable basis. This represents a 35% increase compared to 2019 ilmenite production. The Company says that its development projects will also deliver margin expansion, with Moma’s largely fixed costs spread over higher production volumes. This will position Kenmare in the first quartile of the industry revenue to cost curve.
The first of the three development projects, the WCP B upgrade, was undertaken in 2018. It had the objective of increasing WCP B’s capacity by 20% from 2,000 tph to 2,400 tph. The project was completed on time and for a capital cost of US$10 million, 35% less than the original budget of US$16 million.
The second project was the construction of a third mining plant, named WCP C, and this work was primarily undertaken during 2019. The project budget was US$45 million. WCP C produced its first heavy mineral concentrate, which is then separated into Kenmare’s four final products, in February 2020. The project experienced some delays due to the late delivery of the concentrator by the contractor, but Kenmare expects WCP C to achieve its nameplate capacity in Q2 2020.
The third project is the relocation of WCP B to the high grade Pilivili ore zone. The move was scheduled to take place in Q3 2020, once WCP B has completed its mine path in Namalope, however in April 2020 Kenmare said the timing is uncertain due to the COVID-19 pandemic.
Prior to the current development programme, the last major expansion decision was taken in 2010. Against the backdrop of a bottleneck in global supply and a very favourable product market, Kenmare announced that it was going to undertake a major expansion of the mine. The goal of the expansion was to raise production by 50%. As the project was being developed, the market cycle turned.
The mine briefly suspended operations in June 2015 in the face of industrial action by employees unhappy about the company's cost-cutting measures. Successful negotiation between the union, the Company and the Ministry of Labour had resulted in agreement on somewhat less drastic measures involving fewer layoffs than originally announced. The industrial action was not organized by the union. Operations resumed in early July 2015.
By late 2015 the mine had fallen into financial crisis due to a worldwide drop in mineral prices. Flooding in northern Mozambique was also causing power outages in the Moma District region. Prices for titanium ingots fell by about a third between 2012 and 2015. This led Kenmare to undertake a capital raising and restructuring in mid-2016, raising US$275 million and reducing its debt by 74%. As a result, the Company’s balance sheet was significantly stronger, with a robust cash position and a manageable debt position.
Iluka attempted takeover.
In June 2014, following media speculation in Australia, both Iluka and Kenmare Resources announced that Iluka had made an approach to Kenmare, based on a paper transaction, regarding a possible takeover. No formal offer was made, although a number of prices were put forward.
The process carried on over an extended period, during which Iluka returned with a lower offer. The Iluka approaches failed to attract support from Kenmare's largest shareholder and Iluka ultimately ended the process in December 2015.
Oman investment and restructuring.
As Iluka was announcing its decision to withdraw from takeover talks, Kenmare management announced that the State General Reserve Fund (SGRF) of Oman had indicated an interest in investing $100 million, based on an overall restructuring arrangement being accepted by shareholders. The deal which would ultimately be agreed, saw the SGRF invest $100 million of an overall $275 million refinancing of the Company, which closed in mid-2016. Lenders to the Company agreed to substantially reduce debt. The overall impact of the restructuring was to leave the company with a substantially strengthened Balance Sheet, placing the Company on a firm financial footing.
Return to profit and announcement of dividend.
Since the completion of the Mine expansion, production and shipments have risen to record levels. Production in 2017 was just short of 1m tonnes. Kenmare reported a return to profit in 2017. Full year profits after tax of $19.4m were reported by the Company. In 2019 Kenmare delivered US$92.6 million in earnings before interest, taxes, depreciation, and amortization, and US$44.8 million profit after tax.
On October 16, 2018, Kenmare announced its dividend policy and indicated dividend payments would commence in 2019. The dividend policy committed to pay a minimum of 20% of profits after tax as shareholder returns from 2019, subject to market conditions.
In October 2019, Kenmare paid a maiden dividend of USc2.66 per share, which was an interim dividend and based on the Company’s H1 2019 Results. In May 2020, Kenmare paid a final dividend of USc5.52 per share, resulting in a 2019 full year dividend of USc8.18 per share. This was in line with the dividend policy.
Kenmare says that it expects to pay increased shareholder returns following the completion of the WCP B move.


Guyanaite

Guyanaite (CrOOH) is a chromium oxide mineral that forms as an intergrowth with other chromium oxide minerals known as bracewellite (CrOOH) and grimaldiite (CrOOH) as well as eskolaite (Cr2O3) which in early findings were nearly indistinguishable from one another. These oxides formed so closely as intergrowths with one another that they were initially, and erroneously, identified as a single definite mineral previously known as merumite. Because of its complex history and the previously undiscovered nature of these chromium oxide polymorphs, the relevance of any information found in many early experiments involving the mineral formerly known as merumite in regard to guyanaite is unknown and it is implied that in any further reference of merumite it will have been composed of a mineral assemblage including guyanaite. The rare occurrence and complexity from intergrowth of naturally occurring guyanaite hinders experimental work, leading to laboratory synthesized samples which help to better experiment with the minerals.
Composition.
Guyanaite has a chemical formula of Cr3+O(OH), it was first identified primarily by means of X-ray powder diffraction and chemical data and has been confirmed in recent studies by means of X-ray diffraction, optical reflectance, and infrared absorption (IR) spectroscopy. It is both trimorphous with, and shares an exact chemical formula with both bracewellite and grimaldiite which are also chromium oxides, differing only in their mineralogical structure being orthorhombic with space group Pnnm, orthorhombic with space group Pbnm, and hexagonal with space group R3m, respectively. It is formed from the parent compound of CrO2 by means of one of two processes. The first process for the conversion of CrO2 into CrOOH occurs through a reduction of CrO2 in the presence of H2O and a reductant (oxalic acid or steel) resulting in the chemical equation of (2CrO2 + H2O → 2CrO(OH) + O2). The second process is an oxidation of the chromium ion using a solution as a solvent. Such a reaction is represented by the chemical equation (3CrO2 + 2NaOH → Na2CrO4 + 2CrO(OH)).
Structure.
The identical chemical composition of guyanaite and other polymorphs of chromium oxide requires that the structure of the mineral become the primary characteristic in defining each mineral and differentiating them from one another, making it the single most significant attribute of guyanaite. Laboratory synthesized samples are identified by their separate crystal forms and denoted as α-CrOOH (grimaldiite), ß-CrOOH (guyanaite), and Γ-CrOOH (bracewellite). Guyanaite has an orthorhombic crystal structure, a space group of Pnnm, and has point group 2/m2/m2/m. Its cell dimensions are a = 4.857 Å , b = 4.295 Å , c = 2.958 Å and the structure is based upon a hexagonal closest packing of oxygen atoms parallel to (101) while edge-sharing CrO6 octahedra form along [001] connected by oxygen-corners which forms layers of octahedral parallel to (101). Simply put, the Cr atoms are each surrounded by six oxygen atoms, and short hydrogen bonds are located in a mirror plane perpendicular to the c-axis. These bonds in neighboring planes are aligned in opposite directions to one another resulting in a lower level of symmetry than the parent compound.
Studies done in order to clarify the hydrogen bonding effect and determine if a hydrogen-centered model or hydrogen off centered model represented them best determined there to be no significant difference between either of the models due to the hydrogen-bond distance being so close to the critical distance.
Physical properties.
Because of the high level of difficulty in obtaining a pure mineral sample of guyanaite, experimentation is carried out on samples of a known complex composition which is determined by x-ray and optical studies. The complex intergrowth of chromium oxide minerals results in poor samples for analyzing physical properties such as hardness, measured density, cleavage, habit, and luster giving incomplete data and an inability to determine values for each. A number of “merumite” grains shown to be almost entirely guyanaite by means of x-ray diffraction do however have a yellow-brown streak. The other known physical properties vary greatly based on which one of the two major locations this mineral is found. Samples from Guyana are distinguished by the brown, red, and sometimes green color of prismatic crystals as much as .1 mm long and a light-green to greenish-black variety is occasionally found forming in prismatic microcrystalline aggregates where samples from the Otokumpu mine in Finland occur as aggregates of golden-brown to greenish-brown fibers which replace smaller crystals of eskolaite that are less than 1.0 mm in size.
Geologic occurrence.
Guyanaite as well as its polymorphs were discovered first in eskolaite from within alluvial shingle deposits of the Merume River in what was British Guiana where they occurred as fine-grained aggregates with one another. They were described as small rounded shingles in close association with quartz. Its presence with free gold, pyrophylite rosettes, and double-terminated quartz crystals also implies that these occurrences come from hydrothermal origins. It also occurs in Finland in sulfide-rich veins cutting skarnified quartzites at the Outokumpu mine where it developed as fibrous pseudomorphs. Mineral associations include carbonate minerals, zinc-bearing chromite, rutile, uraninite, nolanite, graphite, zircon, titanite, and corundum as well as in chromium-rich tremolite skarns, metaquartzites, and chlorite veins. Due to its rare geologic occurrence much of experimental guyanaite is synthesized in a laboratory.
Special characteristics.
Guyanaite has never played a significant historical or political role in any way primarily due to its relative isolation, rarity and abundance in very insignificant amounts. As an ore it had unfavorable views on its economic value and potential due to its low abundance and as a result has never held any significant role in industry or commerce. Although recently there have been experiments aimed at incorporating chromium oxides such as guyanaite for cathode materials in rechargeable lithium batteries, as cells created with chromium oxides may give a more efficient charge-discharge process compared with current technology, although no mention is made of the economic viability of using guyanaite and its polymorphs as opposed to current technology.
Geographic location.
Guyanaite as well as its polymorphs were discovered first in deposits of the Merume River in what was British Guiana and is currently known as Guyana. It is found most abundantly in the upper branches of Director Creek which is a small tributary of the Merume River flowing into the Mazaruni River. The nearest populated area is a government rest-house and hydroplane stop called Kamakusa of which the Merumite area is roughly southwest. The largest strip of merumite in Guyana along the base of the Robello Ridge consisting of Roraima-like sandstones, conglomerates and volcanic ash with the entire deposit located within a low-lying swampy and forested terrain which is contained between scarps of the Roraima formation and extensive talus slopes. The relatively small area in which the minerals are found indicates a local origin as well as indications of mild hydrothermal activity within the surrounding ridge rocks. The only other significant source of guyanaite occurs in the Outokumpu mine in Finland and despite the fact that it is a copper ore mine there was an estimated seven-million tons of metallic chromium alongside the copper, serpentine, and skarn rocks found within the mine.


Hydrogenacetylenedicarboxylate


Osmium dioxide

Osmium dioxide is an inorganic compound with the formula OsO2. It exists as brown to black crystalline powder, but single crystals are golden and exhibit metallic conductivity. The compound crystallizes in the rutile structural motif, i.e. the connectivity is very similar to that in the mineral rutile.
Preparation.
OsO2 can be obtained by the reaction of osmium with a variety of oxidizing agents, including, sodium chlorate, osmium tetroxide, and nitric oxide at about 600 °C. Using chemical transport, one can obtain large crystals of OsO2, sized up to 7x5x3 mm3. Single crystals show metallic resistivity of ~15 μΩ cm. A typical transport agent is via the reversible formation of volatile OsO4:
Reactions.
OsO2 does not dissolve in water, but is attacked by dilute hydrochloric acid. The crystals have rutile structure. Unlike osmium tetroxide, OsO2 is not toxic.


Epitaxial graphene growth on silicon carbide

Epitaxial graphene growth on silicon carbide (SiC) by thermal decomposition is a method to produce large-scale few-layer graphene (FLG).
Graphene is one of the most promising nanomaterials for the future because of its various characteristics, like strong stiffness and high electric and thermal conductivity.
Still, reproducible production of Graphene is difficult, thus many different techniques have been developed.
The main advantage of epitaxial graphene growth on silicon carbide over other techniques is to obtain graphene layers directly on a semiconducting or semi-insulating substrate which is commercially available.
History.
The thermal decomposition of bulk SiC was first reported in 1965 by Badami. He annealed the SiC in vacuum to around 2180 °C for an hour to obtain a graphite lattice. In 1975, Bommel et al. then achieved to form monolayer graphite on the C-face as well as the Si-face of hexagonal SiC. The experiment was carried out under UHV with a temperature of 800 °C and hints for a graphene structure could be found in LEED patterns and the change in the carbon Auger peak from a carbided character to a graphite character.
New insights in the electronic and physical properties of graphene like the Dirac nature of the charge carriers, half-integer quantum Hall effect or the observation of the 2D electron gas behaviour were first measured on multilayer graphene from de Heer et al. at the Georgia Institute of Technology in 2004.
Still, the Nobel Prize in Physics ″for groundbreaking experiments regarding the two-dimensional material graphene″ in 2010 was awarded to Andre Geim and Konstantin Novoselov. An official online document of the Royal Swedish Academy of Sciences about this awarding got under fire. Walter de Heer mentions several objections about the work of Geim and Novoselov who apparently have measured on many-layer graphene, also called graphite, which has different electronic and mechanical properties.
Emtsev et al. improved the whole procedure in 2009 by annealing the SiC-samples at high temperatures over 1650 °C in an argon environment to obtain morphologically superior graphene.
Process.
The underlying process is the desorption of atoms from an annealed surface, in this case a SiC-sample. Due to the fact that the vapor pressure of carbon is negligible compared to the one of silicon, the Si atoms desorb at high temperatures and leave behind the carbon atoms which form graphitic layers, also called few-layer graphene (FLG). Different heating mechanisms like e-beam heating or resistive heating lead to the same result. The heating process takes place in a vacuum to avoid contamination. Approximately three bilayers of SiC are necessary to set free enough carbon atoms needed for the formation of one graphene layer. This number can be calculated out of the molar densities.
Today's challenge is to improve this process for industrial fabrication. The FLG obtained so far has a non-uniform thickness distribution which leads to different electronic properties. Because of this, there's a demand for growing uniform large-area FLG with the desired thickness in a reproducible way. Also, the impact of the SiC substrate on the physical properties of FLG is not totally understood yet.
The thermal decomposition process of SiC in high / ultra high vacuum works out well and appears promising for large-scale production of devices on graphene basis. But still, there are some problems that have to be solved. Using this technique, the resulting graphene consists of small grains with varying thickness (30–200 nm). These grains occur due to morphological changes of the SiC surface under high temperatures. On the other side, at relatively low temperatures, poor quality occurs due to the high sublimation rate.
The growth procedure was improved to a more controllable technique by annealing the SiC-samples at high temperatures over 1650 °C in an argon environment.
The desorbed silicon atoms from the surface collide with the argon atoms and a few are reflected back to the surface. This leads to a decrease of the Si evaporation rate. Carrying out the experiment under high temperatures further enhances surface diffusion. This leads to a restructuring of the surface which is completed before the formation of the graphene layer. As an additional advantage, the graphene domains are larger in size than in the initial process (3 x 50 μm2) up to 50 x 50 μm2 .
Of course, the technology always undergoes changes to improve the graphene quality. One of them is the so-called confinement controlled sublimation (CCS) method. Here, the SiC sample is placed in a graphite enclosure equipped with a small leak. By controlling the evaporation rate of the silicon through this leak, a regulation of the graphene growth rate is possible. Therefore, high-quality graphene layers are obtained in a near-equilibrium environment.
The quality of the graphene can also be controlled by annealing in the presence of an external silicon flux. By using disilane gas, the silicon vapor pressure can be controlled.
Crystallographic orientation between the SiC and graphene layers.
SiC is bipolar and therefore the growth can take place on both the SiC(0001) (silicon-terminated) or SiC(000) (carbon-terminated) faces of 4H-SiC and 6H-SiC wafers. The different faces result in different growth rates and electronic properties.
Silicon-terminated face.
On the SiC(0001) face, large-area single crystalline monolayer graphene with a low growth rate can be grown. These graphene layers do have a good reproducibility. In this case, the graphene layer grows not directly on top of the substrate but on a complex formula_1 structure. This structure is non-conducting, rich of carbon and partially covalently bonded to the underlying SiC substrate and provides, therefore, a template for subsequent graphene growth and works as an electronic ″buffer layer″. This buffer layer forms a non-interacting interface with the graphene layer on top of it. Therefore, the monolayer graphene grown an SiC(0001) is electronically identical to a freestanding monolayer of graphene. Changing the growth parameters such as annealing temperature and time, the number of graphene layers on the SiC(0001) can be controlled
. The graphene always maintains its epitaxial relationship with the SiC substrate and the topmost graphene, which originates from the initial buffer layer, is continuous everywhere across the substrate steps and across the boundary between regions with different numbers of graphene layers.
The buffer layer does not exhibit the intrinsic electronic structure of graphene but induces considerable n-doping in the overlying monolayer graphene film.
This is a source of electronic scattering and leads therefore to major problems for future electronic device applications based on SiC-supported graphene structures.
This buffer layer can be transformed into monolayer graphene by decoupling it from the SiC substrate using an intercalation process.
It is also possible to grow off axis on 6H-SiC(0001) wafers. Ouerghi obtained a perfect uniform graphene monolayer at the terraces by limiting the silicon sublimation rate with N2 and silicon fluxes in UHV at an annealing temperature of 1300 °C.
A growth on the 3C-SiC(111) face is also possible. Therefore, annealing temperatures over 1200 °C are necessary. First, the SiC loses silicon atoms and the top layer rearranges in a SiCformula_2 structure. A loss of further silicon atoms leads to a new intermediate distorted stage of SiCformula_3 which matches almost the graphene (2 x 2) structure. Losing the residual silicon atoms, this evolves into graphene. The first four layers of cubic SiC(111) are arranged in the same order as SiC(0001) so the findings are applicable to both structures.
Carbon-terminated face.
The growth on the SiC(000) face is much faster than on the SiC(0001) face
. Also the number of layers is higher, around 5 to 100 layers and a polycrystalline nature appear. In early reports, the regions of graphene growths have been described as ″islands″ since they appear on microscopy images as pockets of graphene on the substrate surface.
Hite et al. however found out, that these islands are positioned at a lower level than the surrounding surface and referred them as graphene covered basins (GCBs). The suggestion is, that crystallographic defects in the substrate act as nucleation sites for these GCBs. During the growth of the graphene layers, the GCBs coalesce with each. Because of their different possible orientations, sizes and thickness, the resulting graphene film contains misoriented grains with varying thickness. This leads to large oriental disorder. Growing graphene on the carbon-terminated face, every layer is rotated against the previous one with angles between 0° and 30° relative to the substrate. Due to this, the symmetry between the atoms in the unit cell is not broken in multilayers and every layer has the electronic properties of an isolated monolayer of graphene.
Evaluation of number of graphene layers.
To optimize the growth conditions, it is important to know the number of graphene layers. This number can be determined by using the quantized oscillations of the electron reflectivity. Electrons have a wave character. If they are shot on the graphene surface, they can be reflected either from the graphene surface or from the graphene-SiC interface. The reflected electrons (waves) can interfere with each other. The electron reflectivity itself changes periodically as a function of the incident electron energy and the FLG thickness. For example, thinner FLG provides longer oscillation periods. The most suitable technique for these measurements is the low-energy electron microscopy (LEEM).
A fast method to evaluate the number of layers is using optical microscope in combination with contrast-enhancing techniques. Single-layer graphene domains and substrate terraces can be resolved on the surface of SiC. The method is particularly suitable for quick of the surface.
Applications.
Furthermore, epitaxial graphene on SiC is considered as a potential material for high-end electronics. It is considered to surpass silicon in terms of key parameters like feature size, speed and power consumption and is therefore one of the most promising materials for future applications.
Saturable absorber.
Using a two-inch 6H-SiC wafer as substrate, the graphene grown by thermal decomposition can be used to modulate a large energy pulse laser. Because of its saturable properties, the graphene can be used as a passive Q-switcher.
Metrology.
The quantum Hall effect in epitaxial graphene can serve as a practical standard for electrical resistance. The potential of epitaxial graphene on SiC for quantum metrology has been shown since 2010, displaying quantum Hall resistance quantization accuracy of three parts per billion in monolayer epitaxial graphene. Over the years precisions of parts-per-trillion in the Hall resistance quantization and giant quantum Hall plateaus have been demonstrated. Developments in encapsulation and doping of epitaxial graphene have led to the commercialisation of epitaxial graphene quantum resistance standards
Other.
The graphene on SiC can be also an ideal platform for structured graphene (transducers, membranes).
Open problems.
Limitations in terms of wafer sizes, wafer costs and availability of micromachining processes have to be taken into account when using SiC wafers.
Another problem is directly coupled with the advantage. of growing the graphene directly on a semiconducting or semi-insulating substrate which is commercially available. But there's no perfect method yet to transfer the graphene to other substrates. For this application, epitaxial growth on copper is a promising method. The carbon's solubility into copper is extremely low and therefore mainly surface diffusion and nucleation of carbon atoms are involved. Because of this and the growth kinetics, the graphene thickness is limited to predominantly a monolayer. The big advantage is that the graphene can be grown on Cu foil and subsequently transferred to for example SiO2.


Reference materials for stable isotope analysis

Isotopic reference materials are compounds (solids, liquids, gasses) with well-defined isotopic compositions and are the ultimate sources of accuracy in mass spectrometric measurements of isotope ratios. Isotopic references are used because mass spectrometers are highly fractionating. As a result, the isotopic ratio that the instrument measures can be very different from that in the sample's measurement. Moreover, the degree of instrument fractionation changes during measurement, often on a timescale shorter than the measurement's duration, and can depend on the characteristics of the sample itself. By measuring a material of known isotopic composition, fractionation within the mass spectrometer can be removed during post-measurement data processing. Without isotope references, measurements by mass spectrometry would be much less accurate and could not be used in comparisons across different analytical facilities. Due to their critical role in measuring isotope ratios, and in part, due to historical legacy, isotopic reference materials define the scales on which isotope ratios are reported in the peer-reviewed scientific literature.
Isotope reference materials are generated, maintained, and sold by the International Atomic Energy Agency (IAEA), the National Institute of Standards and Technology (NIST), the United States Geologic Survey (USGS), the Institute for Reference Materials and Measurements (IRMM), and a variety of universities and scientific supply companies. Each of the major stable isotope systems (hydrogen, carbon, oxygen, nitrogen, and sulfur) has a wide variety of references encompassing distinct molecular structures. For example, nitrogen isotope reference materials include N-bearing molecules such ammonia (NH3), atmospheric dinitrogen (N2), and nitrate (NO3−). Isotopic abundances are commonly reported using the δ notation, which is the ratio of two isotopes (R) in a sample relative to the same ratio in a reference material, often reported in per mille (‰) (equation below). Reference material span a wide range of isotopic compositions, including enrichments (positive δ) and depletions (negative δ). While the δ values of references are widely available, estimates of the absolute isotope ratios (R) in these materials are seldom reported. This article aggregates the δ and R values of common and non-traditional stable isotope reference materials.
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Common reference materials.
The δ values and absolute isotope ratios of common reference materials are summarized in Table 1 and described in more detail below. Alternative values for the absolute isotopic ratios of reference materials, differing only modestly from those in Table 1, are presented in Table 2.5 of Sharp (2007) (a text freely available online), as well as Table 1 of the 1993 IAEA report on isotopic reference materials. For an exhaustive list of reference material, refer to Appendix I of Sharp (2007), Table 40.1 of Gröning (2004), or the website of the International Atomic Energy Agency. Note that the 13C/12C ratio of Vienna Pee Dee Belemnite (VPDB) and 34S/32S ratio of Vienna Canyon Diablo Troilite (VCDT) are purely mathematical constructs; neither material existed as a physical sample that could be measured.
In Table 1, "Name" refers to the common name of the reference, "Material" gives its chemical formula and phase, "Type of ratio" is the isotopic ratio reported in "Isotopic ratio", "δ" is the δ value of the material with indicated reference frame, "Type" is the category of the material using the notation of Gröening (2004) (discussed below), "Citation" gives the article(s) reporting the isotopic abundances on which the isotope ratio is based, and "Notes" are notes. The reported isotopic ratios reflect the results from individual analyses of absolute mass fraction, aggregated in Meija "et al." (2016) and manipulated to reach the given ratios. Error was calculated as the square root of the sum of the squares of fractional reported errors, consistent with standard error propagation, but is not propagated for ratios reached through secondary calculation.
Reference terminology.
The terminology of isotopic reference materials is not applied consistently across subfields of isotope geochemistry or even between individual laboratories. The terminology defined below comes from Gröening "et al." (1999) and Gröening (2004). Reference materials are the basis for accuracy across many different types of measurement, not only the mass spectrometry, and there is a large body of literature concerned with the certification and testing of reference materials.
Primary reference materials.
Primary reference materials define the scales on which isotopic ratios are reported. This can mean a material that historically defined an isotopic scale, such as Vienna Standard Mean Ocean Water (VSMOW) for hydrogen isotopes, even if that material is not currently in use. Alternatively, it can mean a material that only ever existed theoretically but is used to define an isotopic scale, such as VCDT for sulfur isotope ratios.
Calibration materials.
Calibration materials are compounds whose isotopic composition is known extremely well relative to the primary reference materials or which define the isotopic composition of the primary reference materials but are not the isotopic ratios to which data are reported in the scientific literature. For example, the calibration material IAEA-S-1 defines the isotopic scale for sulfur but measurements are reported relative to VCDT, not relative to IAEA-S-1. The calibration material serves the function of the primary reference material when the primary reference is exhausted, unavailable, or never existed in physical form.
Reference materials.
Reference materials are compounds which are carefully calibrated against the primary reference or a calibration material. These compounds allow for isotopic analysis of materials differing in chemical or isotopic composition from the compounds defining the isotopic scales on which measurements are reported. In general these are the materials most researchers mean when they say "reference materials". An example of a reference material is USGS-34, a KNO3 salt with a δ15N of -1.8‰ vs. AIR. In this case the reference material has a mutually agreed upon value of δ15N when measured relative to the primary reference of atmospheric N2 (Böhlke "et al.," 2003). USGS-34 is useful because it allows researchers to directly measure the 15N/14N of NO3− in natural samples against the standard and report observations relative to N2 without having to first convert the sample to N2 gas.
Working standards.
Primary, calibration, and reference materials are only available in small quantities and purchase is often limited to once every few years. Depending on the specific isotope systems and instrumentation, a shortage of available reference materials can be problematic for daily instrument calibrations or for researchers attempting to measure isotope ratios in a large number of natural samples. Rather than using primary materials or reference materials, a laboratory measuring stable isotope ratios will typically purchase a small quantity of the relevant reference materials and measure the isotope ratio of an in-house material against the reference, making that material into a working standard specific to that analytical facility. Once this lab-specific working standard has been calibrated to the international scale the standard is used to measure the isotopic composition of unknown samples. After measurement of both sample and working standard against a third material (commonly called the working gas or the transfer gas) the recorded isotopic distributions are mathematically corrected back to the international scale. It is thus critical to measure the isotopic composition of the working standard with high precision and accuracy (as well as possible given the precision of the instrument and the accuracy of the purchased reference material) because the working standard forms the ultimate basis for accuracy of most mass spectrometric observations. Unlike reference materials, working standards are typically not calibrated across multiple analytical facilities and the accepted δ value measured in a given laboratory could reflect bias specific to a single instrument. However, within a single analytical facility this bias can be removed during data reduction. Because each laboratory defines unique working standards the primary, calibration, and reference materials are long-lived while still ensuring that the isotopic composition of unknown samples can be compared across laboratories.
Isotopic reference materials.
Traditional isotope systems.
The compounds used as isotopic references have a relatively complex history. The broad evolution of reference materials for the hydrogen, carbon, oxygen, and sulfur stable isotope systems are shown in Figure 1. Materials with red text define the primary reference commonly reported in scientific publications and materials with blue text are those available commercially. The hydrogen, carbon, and oxygen isotope scales are defined with two anchoring reference materials. For hydrogen the modern scale is defined by VSMOW2 and SLAP2, and is reported relative to VSMOW. For carbon the scale is defined by either NBS-19 or IAEA-603 depending on the age of the lab, as well as LSVEC, and is reported relative to VPDB. Oxygen isotope ratios can be reported relative to either the VSMOW or VPDB scales. The isotopic scales for sulfur and nitrogen are both defined for only a single anchoring reference material. For sulfur the scale is defined by IAEA-S-1 and is reported relative to VCDT, while for nitrogen the scale is both defined by and reported relative to AIR.
Hydrogen.
The isotopic reference frame of Standard Mean Ocean Water (SMOW) was established by Harmon Craig in 1961 by measuring δ2H and δ18O in samples of deep ocean water previously studied by Epstein & Mayeda (1953). Originally SMOW was a purely theoretical isotope ratio intended to represent the mean state of the deep ocean. In the initial work the isotopic ratios of deep ocean water were measured relative to NBS-1, a standard derived from the steam condensate of Potomac River water. Notably, this means SMOW was originally defined relative to NBS-1, and there was no physical SMOW solution. Following the advice of an IAEA advisory group meeting in 1966, Ray Weiss and Harmon Craig made an actual solution with the isotopic values of SMOW which they called Vienna Standard Mean Ocean Water (VSMOW). They also prepared a second hydrogen isotope reference material from firn collected at the Amundsen-Scott South Pole Station, initially called SNOW and later called Standard Light Antarctic Precipitation (SLAP). Both VSMOW and SLAP were distributed beginning in 1968. The isotopic characteristics of SLAP and NBS-1 were later evaluated by interlaboratory comparison through measurements against VSMOW (Gonfiantini, 1978). Subsequently, VSMOW and SLAP were used as the primary isotopic reference materials for the hydrogen isotope system for multiple decades. In 2006 the IAEA Isotope Hydrology Laboratory constructed new isotopic reference materials called VSMOW2 and SLAP2 with nearly identical δ2H and δ18O as VSMOW and SLAP. Hydrogen isotope working standards are currently calibrated against VSMOW2 and SLAP2 but are still reported on the scale defined by VSMOW and SLAP relative to VSMOW. Additionally, Greenland Ice Sheet Precipitation (GISP) δ2H has been measured to high precision in multiple labs, but different analytical facilities disagree on the value. These observations suggest GISP may have been fractionated during aliquoting or storage, implying that the reference material should be used with care.
Carbon.
The original carbon isotope reference material was a Belemnite fossil from the PeeDee Formation in South Carolina, known as the Pee Dee Belemnite (PDB). This PDB standard was rapidly consumed and subsequently researchers used replacement standards such as PDB II and PDB III. The carbon isotope reference frame was later established in Vienna against a hypothetical material called the Vienna Pee Dee Belemnite (VPDB). As with the original SMOW, VPDB never existed as a physical solution or solid. In order to make measurements researchers use the reference material NBS-19, colloquially known as the Toilet Seat Limestone, which has an isotopic ratio defined relative to the hypothetical VPDB. The exact origin of NBS-19 is unknown but it was a white marble slab and has a grain size of 200-300 micrometers. To improve the accuracy of carbon isotope measurements, in 2006 the δ13C scale was shifted from a one-point calibration against NBS-19 to a two point-calibration. In the new system the VPDB scale is pinned to both the LSVEC Li2CO3 reference material and to the NBS-19 limestone (Coplen "et al.", 2006a; Coplen "et al.," 2006b). NBS-19 is now also exhausted and has been replaced with IAEA-603.
Oxygen.
Oxygen isotopic ratios are commonly compared to both the VSMOW and the VPDB references. Traditionally oxygen in water is reported relative to VSMOW while oxygen liberated from carbonate rocks or other geologic archives is reported relative to VPDB. As in the case of hydrogen, the oxygen isotopic scale is defined by two materials, VSMOW2 and SLAP2. Measurements of sample δ18O vs. VSMOW can be converted to the VPDB reference frame through the following equation: δ18OVPDB = 0.97001*δ18OVSMOW - 29.99‰ (Brand "et al.," 2014).
Nitrogen.
Nitrogen gas (N2) makes up 78% of the atmosphere and is extremely well mixed over short time-scales, resulting in a homogenous isotopic distribution ideal for use as a reference material. Atmospheric N2 is commonly called AIR when being used as an isotopic reference. In addition to atmospheric N2 there are multiple N isotopic reference materials.
Sulfur.
The original sulfur isotopic reference material was the Canyon Diablo Troilite (CDT), a meteorite recovered from Meteor Crater in Arizona. The Canyon Diablo Meteorite was chosen because it was thought to have a sulfur isotopic composition similar to the bulk Earth. However, the meteorite was later found to be isotopically heterogeneous with variations up to 0.4‰ (Beaudoin "et al.," 1994). This isotopic variability resulted in problems for the interlaboratory calibration of sulfur isotope measurements. A meeting of the IAEA in 1993 defined Vienna Canyon Diablo Troilite (VCDT) in an allusion to the earlier establishment of VSMOW. Like the original SMOW and VPDB, VCDT was never a physical material that could be measured but was still used as the definition of the sulfur isotopic scale. For the purposes of actually measuring 34S/32S ratios, the IAEA defined the δ34S of IAEA-S-1 (originally called IAEA-NZ1) to be -0.30‰ relative to VCDT. These fairly recent changes to the sulfur isotope reference materials have greatly improved interlaboratory reproducibility (Coplen & Krouse, 1998).
Organic molecules.
A recent international project has developed and determined the hydrogen, carbon, and nitrogen isotopic composition of 19 organic isotopic reference materials, now available from USGS, IAEA, and Indiana University. These reference materials span a large range of δ2H (-210.8‰ to +397.0‰), δ13C (-40.81‰ to +0.49‰), and δ15N (-5.21‰ to +61.53‰), and are amenable to a wide range of analytical techniques. The organic reference materials include caffeine, glycine, "n"-hexadecane, icosanoic acid methyl ester (C20 FAME), L-valine, methylheptadecanoate, polyethylene foil, polyethylene power, vacuum oil, and NBS-22.
The information in Table 7 comes directly from Table 2 of Schimmelmann "et al". (2016).
Non-traditional isotope systems.
Heavy isotope systems.
Isotopic reference materials exist for non-traditional isotope systems (elements other than hydrogen, carbon, oxygen, nitrogen, and sulfur), including lithium, boron, magnesium, calcium, iron, and many others. Because the non-traditional systems were developed relatively recently, the reference materials for these systems are more straightforward and less numerous than for the traditional isotopic systems. The following table contains the material defining the δ=0 for each isotopic scale, the 'best' measurement of the absolute isotopic fractions of an indicated material (which is often the same as the material defining the scale, but not always), the calculated absolute isotopic ratio, and links to lists of isotopic reference materials prepared by the Commission on Isotopic Abundances and Atomic Weight (part of the International Union of Pure and Applied Chemistry (IUPAC)). A summary list of non-traditional stable isotope systems is available here, and much of this information is derived from Brand "et al." (2014). In addition to the isotope systems listed in Table 8, ongoing research is focused on measuring the isotopic composition of barium (Allmen "et al.," 2010; Miyazaki "et al.," 2014; Nan "et al"., 2015) and vanadium (Nielson "et al.", 2011). Specpure Alfa Aesar is an isotopically well-characterized vanadium solution (Nielson "et al.", 2011). Furthermore, fractionation during chemical processing can be problematic for certain isotopic analyses, such as measuring heavy isotope ratios following column chromatography. In these cases reference materials can be calibrated for particular chemical procedures.
Table 8 gives the material and isotopic ratio defining the δ = 0 scale for each of the indicated elements. In addition, Table 8 lists the material with the 'best' measurement as determined by Meija "et al." (2016). "Material" gives chemical formula, "Type of ratio" is the isotopic ratio reported in "Isotope ratio", and "Citation" gives the article(s) reporting the isotopic abundances on which the isotope ratio is based. The isotopic ratios reflect the results from individual analyses of absolute mass fraction, reported in the cited studies, aggregated in Meija "et al." (2016), and manipulated to reach the reported ratios. Error was calculated as the square root of the sum of the squares of fractional reported errors.
Clumped isotopes.
Clumped isotopes present a distinct set of challenges for isotopic reference materials. By convention the clumped isotope composition of CO2 liberated from CaCO3 (Δ47) and CH4 (Δ18/Δ13CH3D/Δ12CH2D2) are reported relative to a stochastic distribution of isotopes. That is, the ratio of a given isotopologue of a molecule with multiple isotopic substitutions against a reference isotopologue is reported normalized to that same abundance ratio where all isotopes are distributed randomly. In practice the chosen reference frame is almost always the isotopologue with no isotopic substitutions. This is12C16O2 for carbon dioxide and 12C1H4 for methane. Standard isotopic reference materials are still required in clumped isotope analysis for measuring the bulk δ values of a sample, which are used to calculate the expected stochastic distribution and subsequently to infer clumped isotope temperatures. However, the clumped isotope composition of most samples are altered in the mass spectrometer during ionization, meaning that post-measurement data correction requires having measured materials of known clumped isotope composition. At a given temperature equilibrium thermodynamics predicts the distribution of isotopes among possible isotopologues, and these predictions can be calibrated experimentally. To generate a standard of known clumped isotope composition, current practice is to internally equilibrate analyte gas at high temperatures in the presence of a metal catalyst and assume that it has the Δ value predicted by equilibrium calculations. Developing isotopic reference materials specifically for clumped isotope analysis remains an ongoing goal of this rapidly developing field and was a major discussion topic during the 6th International Clumped Isotopes Workshop in 2017. It is possible that researchers in the future will measure clumped isotope ratios against internationally distributed reference materials, similar to the current method of measuring the bulk isotope composition of unknown samples.
Certifying reference materials.
Overview.
The certification of isotopic reference materials is relatively complex. Like most aspects of reporting isotopic compositions it reflects a combination of historical artifacts and modern institutions. As a result, the details surrounding the certification of isotopic reference materials varies by element and chemical compound. As a general guideline, the isotopic composition of primary and original calibration reference materials were used to define the isotopic scales and so have no associated uncertainty. Updated calibration materials are generally certified by IAEA and important reference materials for two-point isotopic scales (SLAP, LSVEC) were reached through interlaboratory comparison. The isotopic composition of additional reference materials are either established through individual analytical facilities or through interlaboratory comparisons but often lack an official IAEA certification. There are certified values for most of the materials listed in Table 1, about half of the materials listed in Tables 2–7, and few of the materials in Table 8.
Primary and original calibrations.
The agreed-upon isotopic composition of primary reference and the original calibration materials were generally not reached through interlaboratory comparison. In part this is simply because the original materials were used to the define the isotopic scales and so have no associated uncertainty. VSMOW serves as the primary reference and calibration material for the hydrogen isotope system and one of two possible scales for the oxygen isotope system, and was prepared by Harmon Craig. VSMOW2 is the replacement calibration standard and was calibrated by measurements at five selected laboratories. The isotopic composition of SLAP was reached through interlaboratory comparison. NBS-19 is the original calibration material for the carbon isotope scale made by I. Friedman, J. R. O’Neil and G. Cebula and is used to define the VPDB scale. IAEA-603 is the replacement calibration standard and was calibrated by measurements at three selected laboratories (GEOTOP-UQAM in Montreal, Canada; USGS in Reston, USA; MPI-BGC in Jena, Germany). The isotopic composition of LSVEC was reached through interlaboratory comparison. IAEA-S-1, the original calibration material for the sulfur isotope scale and still in use today, was prepared by B. W. Robinson.
International Atomic Energy Agency.
IAEA issues official certificates of isotopic composition for most new calibration materials. The IAEA has certified isotopic values for VSMOW2/SLAP2 and IAEA-603 (the replacement for the NBS-19 CaCO3 standard). However, the isotopic composition of most reference materials distributed by IAEA are established in the scientific literature. For example, IAEA distributes the N isotope reference materials USGS34 (KNO3) and USGS35 (NaNO3), produced by a group of scientists at the USGS and reported in Böhlke "et al." (2003), but has not certified the isotopic composition of these references. Moreover, the cited δ15N and δ18O values of these references were not reached through interlaboratory comparison. A second example is IAEA-SO-5, a BaSO4 reference material produced by R. Krouse and S. Halas and described in Halas & Szaran (2001). The value of this reference was reached through interlaboratory comparison but lacks IAEA certification. Other reference materials (LSVEV, IAEA-N3) were reached through interlaboratory comparison and are described by the IAEA but the status of their certification is unclear.
National Institute of Standards and Technology.
As of 2018 NIST does not provide certificates for the common stable isotope reference materials. As seen at this link showing the light stable isotope references currently available from NIST, this category includes all of the isotopic references critical for isotopic measurement of hydrogen, carbon, oxygen, nitrogen, and sulfur. However, for most of these materials NIST does provide a report of investigation, which gives a reference value that is not certified (following the definitions of May "et al." (2000)). For the above examples of USGS34 and USGS35, NIST reports reference values but has not certified the results of Böhlke "et al." (2003). Conversely, NIST has not provided a reference value for IAEA-SO-5. As seen at this link, NIST does certify isotopic reference materials for non-traditional "heavy" isotopic systems including rubidium, nickel, strontium, gallium, and thallium, as well as several isotopic systems that would normally be characterized at "light" but non-traditional such as magnesium and chlorine. While the isotopic composition of several of these materials were certified in the mid-1960s, other materials were certified as recently as 2011 (for example, Boric Acid Isotopic Standard 951a).
Uncertainty and error in reference materials.
Uncertainty in absolute isotope ratios.
Because many isotopic reference materials are defined relative to one another using the δ notation, there are few constraints on the absolute isotopic ratios of reference materials. For dual-inlet and continuous flow mass spectrometry uncertainty in the raw isotopic ratio is acceptable because samples are often measured through multi-collection and then compared directly with standards, with data in the published literature reported relative to the primary reference materials. In this case the actual measurement is of an isotope ratio and is rapidly converted to a ratio or ratios so the absolute isotope ratio is only minimally important for attaining high-accuracy measurements. However, the uncertainty in the raw isotopic ratio of reference materials is problematic for applications that do not directly measure mass-resolved ion beams. Measurements of isotope ratios through laser spectroscopy or nuclear magnetic resonance are sensitive to the absolute abundance of isotopes and uncertainty in the absolute isotopic ratio of a standard can limit measurement accuracy. It is possible that these techniques will ultimately be used to refine the isotope ratios of reference materials.
δ-scales with two anchoring reference materials.
Measuring isotopic ratios by mass spectrometry includes multiple steps in which samples can undergo cross-contamination, including during sample preparation, leakage of gas through instrument valves, the generic category of phenomena called 'memory effects', and the introduction of blanks (foreign analyte measured as part of the sample). As a result of these instrument-specific effects the range in measured δ values can be lower than the true range in the original samples. To correct for such scale compression researchers calculate a "stretching factor" by measuring two isotopic reference materials (Coplen, 1988). For the hydrogen system the two reference materials are commonly VSMOW2 and SLAP2, where δ2HVSMOW2 = 0 and δ2HSLAP2 = -427.5 vs. VSMOW. If the measured difference between the two references is less than 427.5‰, all measured 2H/1H ratios are multiplied by the stretching factor required to bring the difference between the two reference materials in line with expectations. After this scaling, a factor is added to all measured isotopic ratios so that the reference materials attain their defined isotopic values. The carbon system also uses two anchoring reference materials (Coplen "et al.", 2006a; 2006b).


Chromium(III) nitrate

Chromium(III) nitrate describes several inorganic compounds consisting of chromium, nitrate and varying amounts of water. Most common is the dark violet hydrated solid, but an anhydrous green form is also known. Chromium(III) nitrate compounds are of a limited importance commercially, finding some applications in the dyeing industry. It is common in academic laboratories for the synthesis of chromium coordination complexes.
Structure.
The relatively complicated formula - [Cr(H2O)6](NO3)3•3H2O - highlights the complicated structure of this material. The chromium centers are bound to six water ligands, and the remaining volume of the solid is occupied by three nitrate anions and three molecules of water of crystallization. Such complicated formulas typify hydrated metal salts.
Properties and preparation.
The anhydrous salt forms green crystals and is very soluble in water (in contrast to anhydrous chromium(III) chloride which dissolves very slowly except under special conditions). At 100 °C it decomposes. The red-violet hydrate is highly soluble in water. Chromium nitrate is used in the production of alkali metal-free catalysts and in pickling.
Chromium nitrate can be prepared by dissolving chromium oxide in nitric acid.


Dichlorobis(triphenylphosphine)nickel(II)

Dichlorobis(triphenylphosphine)nickel(II) is a metal phosphine complex with the formula NiCl2[P(C6H5)3]2. It is a dark blue crystalline solid. It is used as a catalyst for organic synthesis.
Synthesis and structure.
Dichlorobis(triphenylphosphine)nickel(II) is a commercially available reagent. The blue isomer is prepared by treating hydrated nickel chloride with triphenylphosphine in alcohols or glacial acetic acid:
When allowed to crystallise from chlorinated solvents, the tetrahedral isomer converts to the square planar isomer.
The square planar form is red and diamagnetic. The phosphine ligands are trans with respective Ni-P and Ni-Cl distances of 2.24 and 2.17 Å. The blue form is paramagnetic and features tetrahedral Ni(II) centers. In this isomer, the Ni-P and Ni-Cl distances are elongated at 2.32 and 2.21 Å.
As illustrated by the title complexes, tetrahedral and square planar isomers coexist in solutions of various four-coordinated nickel(II) complexes. Weak field ligands, as judged by the spectrochemical series, favor tetrahedral geometry and strong field ligands favor the square planar isomer. Both weak field (Cl−) and strong field (PPh3) ligands comprise NiCl2(PPh3)2, hence this compound is borderline between the two geometries. Steric effects also affect the equilibrium; larger ligands favoring the less crowded tetrahedral geometry.
Applications.
The complex was first described by Walter Reppe who popularized its use in alkyne trimerisations and carbonylations. Dichlorobis(triphenylphosphine)nickel(II) is a catalyst in Suzuki reactions as an alternative to the traditional palladium(0) catalysts because nickel is cheaper and more abundant. It is not a full substitute since nickel has different catalytic properties than palladium.


Epitizide

Epitizide is a diuretic. It is often combined with triamterene.


Isotopes of zinc

Naturally occurring zinc (30Zn) is composed of the 5 stable isotopes 64Zn, 66Zn, 67Zn, 68Zn, and 70Zn with 64Zn being the most abundant (48.6% natural abundance). Twenty-five radioisotopes have been characterised with the most abundant and stable being 65Zn with a half-life of 244.26 days, and 72Zn with a half-life of 46.5 hours. All of the remaining radioactive isotopes have half-lives that are less than 14 hours and the majority of these have half-lives that are less than 1 second. This element also has 10 meta states.
Zinc has been proposed as a "salting" material for nuclear weapons. A jacket of isotopically enriched 64Zn, irradiated by the intense high-energy neutron flux from an exploding thermonuclear weapon, would transmute into the radioactive isotope 65Zn with a half-life of 244 days and produce approximately 1.115 MeV of gamma radiation, significantly increasing the radioactivity of the weapon's fallout for several years. Such a weapon is not known to have ever been built, tested, or used.


Fluckite

Fluckite is an arsenate mineral with the chemical formula CaMnH2(AsO4)2·2(H2O).
Fluckite's mineral crystallography is triclinic meaning it has three axis of different length and three different interior angles that do not equal 90°. Because fluckite possesses three axes with different angles and lengths it is an anisotropic mineral. This means that it has more than one optic axis. This mineral is a member of the P space group meaning that it can be rotated 360° degrees and inverted to obtain the original figure. Optically, this mineral has positive biaxial birefringence, which can be shown obtaining an interference figure that is blue in the upper right and lower left quadrants of the figure while looking down the c- axis. Fluckite possesses moderate optical relief which is the degree to which the mineral stands out from the mounting medium.
Occurrence.
Fluckite was first described in 1980 for an occurrence in the Gabe-Gottes Mine in Haut-Rhin, Alsace, France, and named for mineralogist Pierre Fluck of Louis Pasteur University in Strasbourg, France. The mineral was found in at a depth of . It occurs as a post-mine phase on carbonate gangue. It occurs in association with native arsenic, tennantite, skutterudite, sainfeldite, pharmacolite, villyaellenite, picropharmacolite, calcite, dolomite, ankerite and quartz.


Germanide

A germanide is any binary compound of germanium and a more electropositive element. The composition of most germanides is analogous to that of the corresponding silicides and does not follow formal valence rules. The germanides of alkali and alkaline earth metals, are readily decomposed by water and acids to give germanium hydrides; most germanides of the transition metals resist the action of acids and alkalies. The main method of producing germanides is the melting or sintering of the components.


Turbo-Hauser bases

"Turbo"-Hauser bases are amido magnesium halides that contain stoichiometric amounts of LiCl. These mixed Mg/Li amides of the type R2NMgCl⋅LiCl are used in organic chemistry as non-nucleophilic bases for metalation reactions of aromatic and heteroaromatic substrates. Compared to their LiCl free ancestors "Turbo"-Hauser bases show an enhanced kinetic basicity, excellent regioselectivity, high functional group tolerance and a better solubility.
Preparation.
Typically "Turbo"-Hauser bases are prepared by reacting an amine with a Grignard reagent or by mixing a lithium amide with stoichiometric amounts of MgCl2.
Commonly used "Turbo"-Hauser bases.
"i"Pr2NMgCl·LiCl, "i"Pr-"Turbo"-Hauser base
TMPMgCl·LiCl, TMP-"Turbo"-Hauser base, also called "Knochel"-Hauser Base (TMP = 2,2,6,6,tetramethylpiperidino)
Structure.
So far not many structures of "Turbo"-Hauser bases are known. Generally, they show a complex temperature and concentration dependent behaviour in solution.
This is why it is not easy to crystallize Hauser bases and their "Turbo" variants.
Solid State Structure.
The "i"Pr-"Turbo"-Hauser base crystallizes as a dimeric amido bridged contact ion pair (CIP). Due to the high steric demand of the TMP ligand the dimerization process is sterically hindered. This is why the TMP-"Turbo"-Hauser base crystallizes as a monomeric CIP.
In both structures LiCl coordinates to the magnesium amides.
Solution Structure.
Although there is a great deal of information on the utility of these reagents, very little is known regarding the nature of "Turbo"-Hauser bases in solution. One reason for that lack of information is that ("Turbo")-Hauser bases show a complex behaviour in solution.
In 2016, "Neufeld et al." showed via Diffusion-Ordered Spectroscopy (DOSY) that at room temperature and high concentrations (0.6 M) the solid state structure of dimeric ["i"Pr2NMgCl·LiCl]2 remains in solution. At lower concentrations the equilibrium is on the side of the monomeric species. Both, dimer and monomer are co-coordinated by LiCl. At temperatures below -50°C LiCl gets separated from the magnesium amide in sense of a stable [LiCl]2 dimer solvated by four THF molecules.
The solid state structure of TMPMgCl·LiCl remains almost completely in THF solution independently of temperature and concentration. Due to the high steric demand of the TMP ligand and its flexible rotation in solution, the THF molecule gets separated from the magnesium cation. The result is an unsaturated magnesium side that could explain the enhanced reactivity and selectivity of TMPMgCl·LiCl.
"Knochel et al." proposed that LiCl increases the reactivity of "Turbo"-Grignard compounds RMgCl·LiCl (R = alkyl, aryl or vinyl) by giving the reactive bimetallic monomer a magnesiate character in sense of a solvent separated ion pair (SSIP) [Li(THF)4]+ [RMg(THF)Cl2]−.
In case of the above mentioned "Turbo"-Hauser bases where the alkyl group of a Grignard is replaced by an amido group (R = R'2N−) this hypothesis could not be confirmed because no SSIP [Li(THF)4]+ was detectable.
LiCl has been shown to increase solubility of RZnX reagent as well. Without LiCl, organozinc reagent remains on surface of zinc particle. With LiCl organozinc reagent forms a RZnX-LiCl complex, which is more soluble in THF.
Reactions.
In contrast to "Turbo"-Grignard compounds that are used for highly efficient Br/Mg exchange reactions, "Turbo"-Hauser bases are used as effective deprotonation reagents of functionalized aromatics. After deprotonation, the intermediate product (a "Turbo"-Grignard) can selectively be functionalized via addition of an electrophile (e.g. I2, -CHO).
Reactivity.
"Turbo"-Hauser bases are used as metalation/deprotonation reagents, like for example organolithiums. However, lithiated compounds are only stable at low temperatures (e.g. -78 °C) and competing addition reactions (like e.g. Chichibabin reactions) can occur. In contrast the magnesium compounds have more covalent and therefore less reactive metal-ligand bonds. Additionally, the whole magnesium amide complex is stabilized by LiCl. This is why "Turbo"-Hauser bases display a higher functional group tolerance and a much greater chemoselectivity at high and low temperatures.
"i"Pr2NMgCl·LiCl can show a different reactivity compared to TMPMgCl·LiCl. "Armstrong et al." showed that the TMP-"Turbo"-Hauser base easily metalates ethyl-3-chlorobenzoate in the C2 position, while the same reaction carried out with the "i"Pr-"Turbo"-Hauser base resulted in no metalation at all. Instead, an addition-elimination reaction occurs.
Another difference in reactivity was shown by "Krasovskiy et al." with the deprotonation of isoquinoline in THF solution. While TMPMgCl·LiCl required only 2h and 1.1 equivalents, "i"Pr2NMgCl·LiCl needed 12h and 2 equivalents for comparable metalation.
On the one hand the different reactivity can be attributed to the higher kinetic basicity of the TMP compound compared to its homologous "i"Pr-"Turbo"-Hauser base. On the other hand, the contrasting behaviour should also be reflected in the different aggregation state of both "Turbo"-Hauser bases in THF solution (monomer vs. dimer, see chapter above).
Generally, in organolithium chemistry monomeric species display the most active kinetic species. This could explain why reactions of the monomeric TMP-"Turbo"-Hauser base are much faster than that of dimeric "i"Pr-"Turbo"-Hauser base.
"Neufeld et al." suggested that the highly regioselective ortho deprotonation reactions of TMPMgCl·LiCl could stem from a sufficient complex-induced proximity effect (CIPE) between the bimetallic aggregate and the functionalized (hetero)aromatic substrate.


Stibine

Stibine (IUPAC name: stibane) is a chemical compound with the formula SbH3. A pnictogen hydride, this colourless gas is the principal covalent hydride of antimony, and a heavy analogue of ammonia. The molecule is pyramidal with H–Sb–H angles of 91.7° and Sb–H distances of 170.7 pm (1.707 Å). This gas has an offensive smell like hydrogen sulfide (rotten eggs).
Preparation.
SbH3 is generally prepared by the reaction of Sb3+ sources with H− equivalents:
Alternatively, sources of Sb3− react with protonic reagents (even water) to also produce this unstable gas:
Properties.
The chemical properties of SbH3 resemble those for AsH3. Typical for a heavy hydride (e.g. AsH3, H2Te, SnH4), SbH3 is unstable with respect to its elements. The gas decomposes slowly at room temperature but rapidly at 200 °C:
The decomposition is autocatalytic and can be explosive.
SbH3 is readily oxidized by O2 or even air:
SbH3 exhibits no basicity, but it can be deprotonated:
Uses.
Stibine is used in the semiconductor industry to dope silicon with small quantities of antimony via the process of chemical vapour deposition (CVD). It has also been used as a silicon dopant in epitaxial layers. Reports claim the use of SbH3 as a fumigant but its instability and awkward preparation contrast with the more conventional fumigant phosphine.
History.
As stibine (SbH3) is similar to arsine (AsH3); it is also detected by the Marsh test. This sensitive test detects arsine generated in the presence of arsenic. This procedure, developed circa 1836 by James Marsh, treats a sample with arsenic-free zinc and dilute sulfuric acid: if the sample contains arsenic, gaseous arsine will form. The gas is swept into a glass tube and decomposed by means of heating around 250 – 300 °C. The presence of arsenic is indicated by formation of a deposit in the heated part of the equipment. The formation of a black mirror deposit in the cool part of the equipment indicates the presence of antimony.
In 1837 Lewis Thomson and Pfaff independently discovered stibine. It took some time before the properties of the toxic gas could be determined, partly because a suitable synthesis was not available. In 1876 Francis Jones tested several synthesis methods, but it was not before 1901 when Alfred Stock determined most of the properties of stibine.
Safety.
SbH3 is an unstable flammable gas. It is highly toxic, with an LC50 of 100 ppm in mice.
Toxicology.
The toxicity of stibine is distinct from that of other antimony compounds, but similar to that of arsine. Stibine binds to the haemoglobin of red blood cells, causing them to be destroyed by the body. Most cases of stibine poisoning have been accompanied by arsine poisoning, although animal studies indicate that their toxicities are equivalent. The first signs of exposure, which can take several hours to become apparent, are headaches, vertigo, and nausea, followed by the symptoms of hemolytic anemia (high levels of unconjugated bilirubin), hemoglobinuria, and nephropathy.


Wakefieldite

Wakefieldite ((La,Ce,Nd,Y)VO4) is an uncommon rare-earth element vanadate mineral. There are four main types of wakefieldite- wakefieldite-(La), wakefieldite-(Ce), wakefieldite-(Nd), and wakefieldite-(Y), depending upon the dominant rare-earth metal ion present. Wakefieldite has a Mohs hardness ranging from 4 to 5. Wakefieldite forms crystals of tetragonal structure. In terms of crystal structure, it is the vanadate analog of the rare-earth phosphate mineral xenotime. Unlike xenotime, it is more favorable for wakefieldite to contain the lighter rare-earth elements over the heavier ones. Due to the lanthanide contraction, the heavier rare earths have smaller ionic radii than the lighter ones. When the phosphate anion is replaced by the larger vanadate anion, the tetragonal crystal system preferentially accommodates the larger light rare-earth elements.
Wakefieldite was first described for an occurrence in the Evans Lou mine, St. Pierre de Wakefield, Quebec, Canada and later designated Wakefieldite-(Y).
Wakefieldite-(Ce) was first described as "kusuite" for its type locality in the Kusu deposit, SW of Kinshasa, Zaire. It was renamed in 1977 as the Ce analog of wakefieldite-Y.
Wakefieldite-(La) was first described in 2008 for an occurrence in the Glücksstern mine, Gottlob Hill, Friedrichroda, Thuringia, Germany.
Wakefieldite-(Nd) was first described in 2008 at the Arase mine, Kami city, Kōchi Prefecture, Shikoku Island, Japan.


Zinc ammonium chloride

Zinc ammonium chloride is the inorganic compound with the formula (NH4)2ZnCl4. It is the ammonium salt of tetrachlorozincate. It used as a flux in the process of hot-dip galvanizing.
Uses.
Steel to be galvanized passes through an acidic cleaning process to remove iron oxide "mill scale". After this process, the surface of the steel is very active and oxide layers begin forming immediately upon exposure to the atmosphere. Zinc ammonium chloride flux in aqueous solution is applied to the steel to reduce any oxides that are formed and/or inhibit them from forming altogether. This allows the molten zinc in the proceeding galvanizing step to maximally adhere to and alloy with the surface of the steel.
Precautions.
Zinc ammonium chloride is a Class 9 hazardous material (Miscellaneous) according to the U.S. DOT.


Dipotassium cyclooctatetraenide

Dipotassium cyclooctatetraenide, sometimes abbreviated K2COT, is an organopotassium compound with the formula K2C8H8. It is a brown solid that is used as a precursor to cyclooctatetraenide complexes, such as uranocene (U(C8H8)2). Analogs of K2C8H8 are known with ring substituents, with different alkali metals, and with various complexants.
Preparation and structure.
Potassium cyclooctatetraenide is formed by the reaction of cyclooctatetraene with potassium metal:
The reaction entails 2-electron reduction of the polyene and is accompanied by a color change from colorless to brown.
The structure of K2(diglyme)C8H8 has been characterized by X-ray crystallography of the derivatives with diglyme complexed to the potassium cations. The C8H8 unit is planar with an average C-C distance of 1.40 A.


Borocarbonitrides

Borocarbonitrides are two-dimensional compounds that contain boron, nitrogen, and carbon atoms in a ratio BCN Borocarbonitrides are distinct from B,N co-doped graphene in that the former contains separate boron nitride and graphene domains as well as rings with B-C, B-N, C-N, and C-C bonds. These compounds generally have a high surface area, but borocarbonitrides synthesized from a high surface area carbon material, urea, and boric acid tend to have the highest surface areas. This high surface area coupled with the presence of Stone-Wales defects in the structure of borocarbonitrides also allows for high absorption of CO2 and CH4, which may make borocarbonitride compounds a useful material in sequestering these gases.
Electrical.
The band gap of borocarbonitrides range from 1.0–3.9eV and is dependent on the content of the carbon and boron nitride domains as they have different electrical properties. Borocarbonitrides with a high carbon content have lower bandgaps whereas those with higher content of boron nitride domains have higher band gaps. Borocarbonitrides synthesized in gas or solid reactions also tend to have large bandgaps and are more insulating in character. The wide range of composition of boronitrides allows for the tuning of the bandgap, which when coupled with its high surface area and Stone-Wales defects may make boronitrides a promising material in electrical devices.
Synthesis.
Solid state reaction.
A high surface area carbon material such as activated charcoal, boric acid, and urea are mixed together and then heated at high temperatures to synthesize borocarbonitride. The composition of the resulting compounds may be changed by varying the concentration of the reagents as well as the temperature.
'Gas phase synthesis.
In chemical vapor deposition, boron, nitrogen, and carbon precursors react at high heat and are deposited onto a metal substrate. Varying the concentration of precursors and the selection of certain precursors will give different ratios of boron, nitrogen, and carbon in the resulting borocarbonitride compound.
Borocarbonitride composites.
Borocarbonitride can also be synthesized by random stacking of boronitride and graphene domains through covalent interactions or through liquid interactions. In the first method, graphene and boron nitride sheets are functionalized and then are reacted to form layers of borocarbonitride. In the second method, boron nitride and graphite powder are dissolved in isopropanol and dimethylformamide, respectively, and then sonicated. This is then exfoliated to isolate borocarbonitride layers.


Unhexnilium


Vanadyl nitrate

Vanadyl nitrate, also called vanadium oxytrinitrate or vanadium oxynitrate is a compound of vanadium in the +5 oxidation state with nitrate groups and oxygen. The formula is VO(NO3)3. It is made from dinitrogen pentoxide and vanadium pentoxide. It is a nitrating agent, adding nitro groups to aromatic compounds such as benzene, phenol, chlorobenzene, anisole, acetanilide, benzoic acid, ethyl benzoate, and toluene.
Production.
Vanadyl nitrate can be made by soaking vanadium pentoxide in liquid dinitrogen pentoxide for durations around two days at room temperature. The yield for this method is about 85%.
Purification can be done by vacuum distillation.
Vanadyl nitrate can also be made from vanadyl trichloride VOCl3 and dinitrogen pentoxide.
Properties.
Vanadyl nitrate is a pale yellow liquid. It is viscous but can be poured.
VO(NO3)3 molecules have a distorted pentagonal bipyramid shape. The whole molecule has a Cs mirror symmetry. The vanadium oxygen double bond is in the same plane as a nitrate group roughly opposite. The other two nitrate groups are at about an 83° angle from the doubly bonded oxygen. The three nitrate groups are planar. Each nitrate is connected to the vanadium atom via two oxygen atoms, but one is closer than the other. The nitrate opposite the oxygen is quite asymmetric, but the mirror image nitrate groups have more equal oxygen bond lengths.
Vanadyl nitrate can dissolve in water, but cannot be recrystallized, instead a polymeric oxide precipitates. Nitric acid is formed as a result of the reaction with water.
Solvents include dichloromethane, nitromethane, carbon tetrachloride, cyclohexane, trichlorofluoromethane. It is probably incompatible with amines, aromatic hydrocarbons, and ethers.
Vanadyl nitrate is stable under nitrogen, ozone or oxygen. The liquid is indefinitely stable at room temperature, unlike some other transition metal nitrates that decompose to nitrogen oxides. Over 80 °C it decomposes slowly.
Vanadyl nitrate can form a solid pale yellow adduct with boron trifluoride. An adduct is also formed with acetonitrile.
When mixed with petrol or l-hexene, or other unsaturated hydrocarbons, vanadyl nitrate ignites. It does not ignite with hexane. It reacts with paper rubber and wood, and ignites many organic solvents.
It can be used to nitrate various organic compounds at high yield when diluted with dichloromethane. Nitrotoluene, methyl benzoate and benzoic acid are nitrated by prolonged exposure over a few days. Benzonitrile does not react. Benzene, toluene, tert-butylbenzene, halo-benzenes, "ortho"-nitrotoluene, anisole, phenol and acetanilide are all rapidly nitrated within 30 minutes at room temperature.
The ultraviolet spectrum of the liquid shows an absorption band peaking at 208 nm with a shoulder at 242 nm. At 55 °C the gaseous vanadyl nitrate has absorption bands also at 486, 582 and 658 nm in the visual light spectrum. Liquid vanadyl nitrate has absorption lines in the infrared at 1880, 1633, 1612, 1560, 1306, 1205, 1016, 996, 965, 895, 783, 632, 457, 357, 301, 283, 234, 193, 133, 93 and 59 cm−1. Gaseous vanadyl nitrate has absorption bands at 775, 783, 786, 962.5, 994.4, 997.5, 1000.5, 1006.2, 1012, 1016.3, 1020, 1198, 1211, 1216.3, 1564, 1612, 1629, 1632, 1635, 1648 and 1888 cm−1. Many of these bands are due to stretching in nitrogen–oxygen bonds, but 1016.3 cm−1 is due to the double vanadium–oxygen bond. 786 is due to out of phase wagging in N-O, and 775 is due to deformation in O-N=O in the mirror plane.
Related compounds.
Hexammino-vanadium nitrate.
Hexammino-vanadium nitrate V(NH3)6.(NO3)3 was claimed to be formed by reacting hexamino vanadium trichloride with nitric acid. However doubt is cast on the existence of hexammino complexes of vanadium.
Vanadyl (IV) nitrate.
Vanadyl (IV) nitrate VO(NO3)2 is made from vanadyl sulfate and barium nitrate, or vanadyl chloride and silver nitrate. It forms a blue solution, but cannot be crystallized, instead forming vanadium pentoxide when evaporated. Another method to make it as green blue needles is via vanadium pentoxide, oxalic acid and dilute nitric acid at 90 °C, but the solid form is not confirmed.
Mononitratodioxovanadium.
Vanadium metal reacts with dinitrogen tetroxide with an acetonitrile catalyst at 0 °C to yield mononitratodioxovanadium(V), VO2NO3, a brick red solid. Mononitratodioxovanadium easily dissolves in water to make an orange solution, but this is unstable forming a deep brown gel after a day. VO2NO3 cannot be crystallized from the solution, instead vanadium pentoxide results when a solution is evaporated. Also if VO2NO3 is heated at 350 °C, vanadium pentoxide solid is left behind.
Infrared absorption at 9.8 to 10 μm indicates vanadium to oxygen bonds are present, and absorption at 7.25 μm indicates nitrate. Very weak absorption at 12.19 μm shows a very small quantity of ionic nitrate exists, so this compound is mostly covalent.


Chemical series


YF-73

The YF-73 was China's first successful cryogenic liquid hydrogen fuel and liquid oxygen oxidizer gimballed engine. It was used on the Long March 3 H8 third stage, running on the simple gas generator cycle and with a thrust of . It had four hinge mounted nozzles that gimbaled each on one axis to supply thrust vector control and was restart capable. It used cavitating flow venturis to regulate propellant flows. The gas generator also incorporated dual heat exchangers that heated hydrogen gas, and supplied helium from separate systems to pressurize the hydrogen and oxygen tanks. The engine was relatively underpowered for its task and the start up and restart procedures were unreliable. Thus, it was quickly replaced by the YF-75.
History.
In October 1970 the Beijing Aerospace Propulsion Institute was tasked with developing a prototype rocket engine burning liquid hydrogen and liquid oxygen. They settled on a pump-fed gas generator design. The prototype was successfully fire tested for 20 seconds on January 25, 1975. In March of the same year, China officially initiated the "Project 311" do initiate the engineering work on the first Chinese cryogenic engine, which was named YF-73. It had its debut on April 8, 1984, when it sent the first geosynchronous communications satellite experiment, the Dong Fang Hong 2 to geosynchronous orbit. It flew 13 times with 3 failures and was last used on May 26, 2000. It was replaced by the more capable YF-75 which enabled to increase payload from to over and significantly increased reliability.


Unhexbium


Tin(II) 2-ethylhexanoate

Tin(II) 2-ethylhexanoate or tin(II) octoate or stannous octoate (Sn(Oct)2) is a compound of tin. Produced by the reaction of tin(II) oxide and 2-ethylhexanoic acid, it is a clear colorless liquid at room temperature, though often appears yellow due to impurities, likely resulting from oxidation of Sn(II) to Sn(IV).
It is sometimes used as a polymerization catalyst, such as for the production of polylactic acid.


Carbon flaw

A carbon flaw is a blemish present within a diamond crystalline form of carbon, usually seen as a black spot. The blemish may be microscopic or visible to the naked eye. The spots are undesirable imperfections since they can be seen more easily than other flaws. It is worth noting that, while diamonds are composed of purely carbon, the black spot flaws could be other inclusions (foreign matter) such as olivine, garnet, pyrite, silica, calcite, and iron oxides.
Appearance.
Carbon flaws can come in many different appearances. They can range in size from specks so small they can barely be seen with the a magnifying glass to spots and clusters clearly visible to the naked eye. A carbon flaw can appear as a sharply defined spot or as an amorphous cloud, like a shadow in the stone. The appearance of a spot usually indicates an inclusion of uncrystallized carbon, but a cloudy carbon flaw is indicative of improper or irregular crystallization. Carbon flaws can also appear as small, fuzzy dots, somewhere between a speck and a cloud. Another common carbon flaw appears as a black shard or needle through the stone.
These flaws are regarded as undesirable in any stone, though the appearance of carbon flaws is more notable in white stones. The presence of these flaws can severely impact the value of the stone, despite its carat weight. Most flaws that do not affect the clarity or brilliance of the diamond are usually seen as ugly and will drive buyers away from a stone. The flaws that affect brilliance make it difficult to sell a stone at any price.
Formation.
The reason for the formation of carbon flaws is largely unknown. It is theorized that, though the material was exposed to the same conditions of heat and pressure as the rest of the crystal, there may be some other factor not evenly distributed throughout the carbon that formed the diamond. Many chemical actions happening simultaneously could possibly cause carbon in the solution to surround particles that escaped the solvent. Another theory is that diamonds are formed by the slow accretion of crystals. That means that the crystal structure forms and grows around a single nucleus of the element and that nucleus can be excluded from the crystallization process. The nucleus is then surrounded by crystallized diamond and becomes a carbon flaw. The nuclei are theorized to be other common forms of carbon such as graphite or carbonado, though they could be an amorphous carbon structure.
Effect on strength.
A carbon flaw in a diamond has a severe impact on strength. Any inclusion in a diamond is a weak point in the crystalline structure and will make the stone more prone to breakage. Specifically, if a cloud forms too close to the surface of the diamond, or the diamond is cut to close to a flaw, it will appear as a crack in the surface. Flaws near or on the surface of a diamond also appear a rough patches and are usually removed when the diamond is being cut for sale. A small crack in the surface of the diamond caused by an extensive flaw in the crystalline structure it makes the diamond prone to further cracking. Diamonds flawed in that way are liable to crack under a modest sudden change in temperature or a sharp blow.


Uranium pentachloride

Uranium pentachloride is an inorganic chemical compound composed of uranium in the +5 oxidation state and five chlorine atoms.
Preparation.
Uranium pentachloride can be prepared from the reaction of uranium trioxide with carbon tetrachloride, with a previously prepared amount of the compound serving as a catalyst.
It can also be prepared from the reaction between uranium tetrachloride and chlorine in a fluidized bed reactor at 550 °C.
Properties.
Uranium pentachloride is available as red-brown microcrystalline powders or black-red crystals with metallic sheen. It is very hygroscopic and decomposes into uranium hexachloride and uranium tetrachloride when in water or heated. There are two crystalline forms, each of which has the uranium atom in an octahedral geometry among six chlorine atoms. Usually, it is in the α-form, which has a monoclinic crystal structure with space group "P"21/"n". The β-form is triclinic with space group "P".
The gaseous form has C4v symmetry.


Planar hexacoordinate carbon

Planar hexacoordinate carbon in chemistry describes a molecular geometry featuring a planar arrangement of carbon with six surrounding atoms. No actual chemical compounds having this particular hexacoordinate configuration have been reported but quantum mechanical methods have demonstrated that these molecules are a possibility. Examples of molecules investigated with computational methods are the B6C dianion, the CN3Be3+ ion, the CO3Li3+ ion and the CN3Mg3+ ion. A simulated Be2C monolayer is reported to consist of quasi-planar hexacoordinate carbon atoms.
On the other hand, experimental research has confirmed that the pentagonal-pyramidal hexamethylbenzene ion, C6(CH3)62+, contains a hexacoordinate carbon atom. Furthermore, a heptacoordinate carbon atom has been predicted to be involved in a stable hexagonal-pyramidal configuration of tropylium trication, (C7H7)3+.


Potassium hydrogen phthalate

Potassium hydrogen phthalate, often called simply KHP, is an acidic salt compound. It forms white powder, colorless crystals, a colorless solution, and an ionic solid that is the monopotassium salt of phthalic acid. KHP is slightly acidic, and it is often used as a primary standard for acid–base titrations because it is solid and air-stable, making it easy to weigh accurately. It is not hygroscopic. It is also used as a primary standard for calibrating pH meters because, besides the properties just mentioned, its pH in solution is very stable. It also serves as a thermal standard in thermogravimetric analysis.
KHP dissociates completely in water, giving the potassium cation (K+) and hydrogen phthalate anion (HP− or Hphthalate−).
And then as a weak acid hydrogen phthalate reacts reversibly with water to give hydronium (H3O+) and phthalate ions.
KHP can be used as a buffering agent in combination with hydrochloric acid (HCl) or sodium hydroxide (NaOH) depending on which side of pH 4.0 the buffer is to be.
KHP is also a useful standard for total organic carbon (TOC) testing. Most TOC analyzers are based on the oxidation of organics to carbon dioxide and water, with subsequent quantitation of the carbon dioxide. Many TOC analysts suggest testing their instruments with two standards: one typically easy for the instrument to oxidize (KHP), and one more difficult to oxidize. For the latter, benzoquinone is suggested.


Vanadiocarpholite

Vanadiocarpholite (Mn+2V+3AlSi2O6(OH)4) is straw yellow to brown silicate mineral. It crystallizes in the orthorhombic crystal system. It is the vanadium rich variety of carpholite (Mn+2Al2Si2O6(OH)4).
Discovery and occurrence.
It was first described in 2005 for an occurrence in the Molinello Mine, Graveglia Valley, Genova Province, Liguria, Italy. It occurs in chert in a manganese ore deposit as vein fillings in silicified wood.
Chemical composition.
It consists of:


Unpentseptium