Frontiers of Materials Science (v.2, #3)

The studies of the thermo-mechanic principles and the kinetic analysis of MnS precipitation behavior in oriented electrical steels conducted in the last dozen years have been summarized. The problems and insufficiency in the fields concerning nucleation theory of MnS precipitation, the relationship between the precipitation and dynamic recrystallization of the matrix as well as the influence of high-energy boundary precipitation on the pinning effect of the boundary migration were discussed. Suggestions were proposed to modify researches concerning the initial position density for MnS nucleation, the mutual interaction between the precipitation and the dynamic recrystallization as well as the kinetic principles of precipitation nucleation on grain boundaries with different boundary energy, which would complete the related theory of MnS precipitation behaviors.
Keywords: oriented electrical steel; MnS; precipitation; dynamic recrystallization; Goss orientation

The understanding of interfaces and interaction of organic molecules and inorganic materials are the important issues in biomineralization. Experimentally, it has been found that amino acids (AA) can regulate the morphology of hydroxyapatite (HAP) crystals significantly. In this study, molecular dynamics simulation is employed to investigate the detailed adsorption behavior of polar, ionic, and hydrophobic AA on the {100} face of HAP at the atomic level. The results indicate that various AA are adsorbed on the HAP crystal surface mainly by amino and carboxylate groups at the specific sites. Multiple interaction points are found for polar and ionic AA. The adsorbed AA molecules occupy the Ca and P sites of the HAP surfaces which may inhibit and regulate the HAP growth. The adsorbed amino acid layer can also change the interfacial hydration layer and influence the transportation of ions in and out of HAP, which may be another strategy of biological control in biomineralization.
Keywords: hydroxyapatite (HAP); adsorption; amino acid (AA); interfacial structure

The shell structure of the Bivalvia has been observed with the use of optical and electron microscopes since the early 1900’s. The prismatic structure is one of the more attractive shell structures in bivalved mollusks. This structure is composed of the aggregation of polygonal prisms arranged densely. Each prism is made of small calcite crystallites arranged perpendicular to a growth shell surface. Organic materials, named organic sheaths, accumulate around prisms and stain well with heamatoxylin-eosin.The Bivalvia, which make prismatic structures, are divided into two groups. One group has the inner shell layer made up of a nacreous structure, and the other has the inner shell layer made up of a foliated structure. The aragonite prismatic layer and the prismatic layer are closely related to each other, as is the aragonite prismatic layer to the composite prismatic one.
Keywords: Bivalvia; shell structure; prismatic structure; prism; calcite; organic sheath

Preparation of alginate-gelatin capsules and its properties by Xiao-yan Li; Xi-guang Chen; Cheng-sheng Liu; Chen-guang Liu; Yu-ping Xue (253-260).
Capsules based on alginate and gelatin prepared by extrusion method could increase the cell numbers of Lactobacillus casei ATCC 393 to be 108 CFU·g−1 in the wet state of the capsules. The capsules were spherical, smooth-surfaced and non-aggregated with a diameter of (4.0 ± 0.3) mm. The behavior of the samples were quite similar at low relative humidity (33%, 52%) and the ratio of weight change reached 93%. Four kinds of capsules in simulated gastric fluid (SGF) exhibited shrinkage while the beads eroded accompanied with slight swelling in simulated intestinal fluid (SIF). The pH values affected the stability of the capsules and with the increase in pH, the capsules changed from shrank then swelled and finally, broke into pieces. The capsules behaved differently under different ion intensities and the introduction of gelatin weakened the stability of capsules compared with the alginate ones. Cells of L. casei ATCC 393 could be continuously released from the capsules in the simulated gastrointestinal tract (GIT) and the release amounts and speeds in SIF were much higher and faster than those in SGF.
Keywords: capsule; alginate; gelatine; Lactobacillus casei ATCC 393

Release of lysozyme from electrospun PVA/lysozyme-gelatin scaffolds by Dong-zhi Yang; Yu-hua Long; Jun Nie (261-265).
This article describes an electrospinning process in fabricating ultra fine fibers with core-shell structure. A biodegradable polymer, poly(vinyl alcohol) (PVA), was used as the shell; lysozyme was a kind of antioxidant; and gelatin were used as the core.Morphology and microstructure of the ultra fine fibers were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analysis. As a comparison, composite nanofiber PVA/lysozyme-gelatin blend was prepared by a normal electrospinning process. In vitro drug release behaviors of the nanofibrous membranes were determined in phosphatebuffered saline (PBS) solution. It was found that core-shell nanofibers PVA/lysozyme-gelatin obviously exhibit higher initial release rates compared to that of PVA/lysozymegelatin blend nanofibers. The current method may find wide application in controlled release of bioactive proteins and tissue engineering.
Keywords: gelatine; lysozyme; release; core-shell; electrospinning

On the growth morphous of capillaries and tissue in porous silk fibroin films by Lun Bai; Bao-qi Zuo; Guo-ping Guan; Li-xing Dai; Yong-zhen Chen; Zheng-yu Zhou; Jian-mei Xu; Zhen-yu Wu (266-270).
In this study, the porous silk fibroin film (PSFF) is implanted into the body of a rat. Ten days later, the growing state of the capillaries in the material was observed, and the growing law of the capillaries in porous material is discussed to better understand the growing state of the peripheral tissue and cells around the material. The fact that the PSFF creates a beneficial environment for the growth of the capillaries in the tissue is confirmed, and the good growing states of the new skeleton muscle and the hypodermal tissue are also observed. This provides basic experimental results for the design of the PSFFs, which is a new medical biomaterial.
Keywords: porous silk fibroin film (PSFF); tissue regeneration; growth of the capillaries; growth of the skeleton muscle

Stable waterborne polyurethane/organic clay latex was synthesized by ultrasonically-assisted mixing with different clay content. Fourier transform infrared (FT-IR) spectra showed that the interaction between NH and C=O was enhanced with low content organic clay loaded. X-ray diffraction (XRD) results implied that the layered organic clay was exfoliated and the crystallization of the hard domain in the waterborne polyurethane (WPU) matrix was enhanced. Transmission electron microscopy (TEM) images show that the layered clay was exfoliated by WPU molecule. The tensile test shows that the mechanical properties were improved by loading organic clay and the desired addition was 1 wt.%.
Keywords: waterborne polyurethane (WPU); organic clay; WPU/clay nanocomposites

Immobilizing collagen type I to TiO2 film for improvement of biocompatibility by Xiao-song Jiang; Jun-ying Chen; Nan Huang (276-280).
In this work, using a bio-chemical modification method, collagen type I was immobilized on the TiO2 film surface by a silane coupling reagent of aminopropyltriethoxysilane. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were used to investigate the characteristics of the modified TiO2 film. The thrombus formation ability of the films was studied by in vitro platelet adhesion test. Furthermore, the biological behavior of cultured human umbilical vein endothelial cells (HUVECs) onto different films was investigated by in vitro HUVECs cultured experiment. The results show that the modification can improve the biocompatibility of TiO2 film for applications of biomedical microcoil hemangioma treatment, etc.
Keywords: collagen type I; TiO2 film; platelets; endothelial cells

Recycling cobalt from spent lithium ion battery by Zhi-dong Xia; Xiao-qian Xie; Yao-wu Shi; Yong-ping Lei; Fu Guo (281-285).
Spent lithium ion battery is a useful resource of cobalt. In this paper, cobalt was recovered by a chemical process based upon the analysis of the structure and composition of the lithium ion battery. X-ray diffraction results show that cobalt oxalate and cobaltous sulfate have been obtained in two different processes. Compared with the cobaltous oxalate process, the cobaltous sulfate process was characterized by less chemical substance input and a cobalt recovery rate of as much as 88%. A combination of these two processes in the recycling industry may win in the aspects of compact process and high recovery rate.
Keywords: spent lithium ion battery; recycling; precipitation process; distillation process

The luminescence lifetime of the 0.01 mol.%-0.1 mol.% Er3+- and 0–20 mol.% Y3+-codoped Al2O3 powders prepared at a sintering temperature of 900°C in a non-aqueous sol-gel method has been investigated to explore the enhanced mechanism of photoluminescence properties of the Er3+-doped Al2O3 by Y3+ codoping. For the 0.1 mol.% Er3+-Y3+-codoped Al2O3 powders, the measured lifetime of Er3+ gradually increases with increasing Y3+ concentration. Consequently, codoping with 20 mol.% Y3+ leads to an increase in the measured lifetime from 3.5 to 5.8 ms. By comparing the measured lifetime for different Er3+ concentrations in the Al2O3 powders, the radiative lifetime of both the Er3+-doped and the Er3+-Y3+-codoped Al2O3 powders is estimated to be about 7.5 ms. Infrared absorption spectra indicate that Y3+ codoping does not change the-OH content in the Er3+-Y3+-codoped Al2O3 powders. The prolonged luminescence lifetime of the 4I13/2 level of Er3+ in Er3+-doped Al2O3 powders by Y3+ codoping is ascribed to the decrease in the energy transfer rate between the Er3+ ions and the Er3+ and -OH, respectively, due to the suppressed interaction between Er3+ ions.
Keywords: Er3+-doped Al2O3 ; luminescence lifetime; Y3+ codoping; sol-gel method

Enhanced cycle stability of spinel LiMn2O4 by a melting impregnation method by Hao Qi; Gao-shao Cao; Jian Xie; Xin-bing Zhao (291-294).
Spinel LiMn2O4 particles were successfully coated with CuO, MgO, ZnO, Al2O3 and CeO2 by a melting impregnation method. Except for the CeO2-coated sample, all the others exhibit better cycling stability than bare LiMn2O4 at room temperature and at 55°C. Among these samples, the ZnO-coated sample shows the best cycling stability. A capacity of 100 mA·h·g−1 still remained after 100 cycles at 55°C while the bare LiMn2O4 retains a capacity of only 80 mA·h·g−1 after the same number of cycles. The improvement in the cycling stability is attributed to the suppressed Mn dissolution caused by HF.
Keywords: spinel lithium manganate; melting impregnation; cathode material; lithium-ion batteries

Investigation of cube-textured Ni-7at.%W alloy substrates for YBa2Cu3O7−δ coated superconductors by Dan-min Liu; Fei Hao; Jiu-xing Zhang; Yan-cao Hu; Mei-ling Zhou (295-300).
Ni-7at.%W alloys were fabricated by powder metallurgy process. After heavy cold-rolling and recrystallization annealing, sharp cube-textured Ni-7at.%W substrates were obtained. Deformation and recrystallization textures of Ni-7at.%W alloys were studied systematically. It was found that intermediate annealing during the process of cold-rolling is beneficial to the formation of a cube texture in the Ni-7at.%W substrate.
Keywords: coated superconductor; recrystallization; cube texture; Ni-W alloys

In order to control the length of tunnels within Al foil etched in HCl-H2SO4 solutions, the influence of on-off control of the DC on growth and passivation of tunnels has been investigated. From SEM of oxide replicas of tunnels, it was found that, in a given etchant solution at a special temperature, the longest tunnel length depended only on the turn-on interval of DC, and the number of pits was determined by the total electricity of the DC. The corresponding mechanism is that the potential of Al foil changed rapidly at the point of the switch of DC by the result according to the anodic polarization curve and potential-time (E-t) response curves. The moment the DC was switched on, the potential increased immediately over pitting potential, leading to nucleation of pits at the surface and growth of tunnels at special lengths. When the DC was switched off, the potential rapidly decreased to a passive state, leading to the cessation of nucleation and the death of tunnels. Therefore, the longest tunnel length can be controlled and a non-piercing layer can be obtained. Furthermore, consequent etching of Al foil by the on-off control of the DC is beneficial for maintaining a good mechanical strength.
Keywords: tunnel length; growth and passivation; on-off controlling DC; a non-piercing layer; mechanical strength

Semi-solid thixo casting structure of aluminum alloy and relevant assistant analysis with the help of computer simulation by Yi-tao Yang; Jian-fu Wang; Meng Chen; Heng-hua Zhang; Guang-jie Shao (306-310).
The relationship between structure morphology of semi-solid aluminum alloy die-casting sample and filling condition was studied. By systematical structure analysis and computer simulation of the filling process, the quantitative relationship between microscopic morphology (such as solid fraction, grain size and shape) and formation state was studied. The results showed that the billet microstructure must have fine and round grains for the die-casting of complex shapes. It is necessary to optimize injection speeds to escape the non-uniform distribution of the solid fraction in complex and changeable mold cavity.
Keywords: semi-solid; solid fraction; computer simulation

In the present article, the theoretical calculations of the phonon dispersion curves (PDCs) of five alkali metals viz. Li, Na, K, Rb, Cs and their four equiatomic sodium-based binary alloys viz. Na0.5Li0.5, Na0.5K0.5, Na0.5Rb0.5 and Na0.5Cs0.5 to second order in a local model potential is discussed in terms of the realspace sum of the Born von Karman central force constants. Instead of the concentration average of the force constants of pure alkali metals, the pseudo-alloy-atom (PAA) is adopted to directly compute the force constants of the four equiatomic sodium based binary alloys and was successfully applied. The exchange and correlation functions due to the Hartree (H) and Ichimaru-Utsumi (IU) are used to investigate the influence of the screening effects. The phonon frequencies of alkali metals and their four equiatomic sodium-based binary alloys in the longitudinal branch are more sensitive to the exchange and correlation effects in comparison with the transverse branches. The PDCs of pure alkali metals are found in qualitative agreement with the available experimental data. The frequencies in the longitudinal branch are suppressed rather due to IU-screening function than those due to static H-screening function.
Keywords: alkali metals; sodium based equiatomic alloys; phonon dispersion curves (PDCs); exchange and correlation functions

During deformation, the orientation of a grain influences not only the deformation mechanisms (slip or twinning) and the specific selection of activated slip or twinning systems for that grain, but also the kinetics of different types of transformation. Schmid factor analysis was applied to determine the orientation dependency of deformation mechanisms in magnesium alloys AZ31 in this work. The orientation changes after the operation of the specific deformation mechanisms were also calculated based on Sachs model. It was found that different deformation mechanisms proceeded differently according to theoretical predictions. Basal slip occurred when basal planes of grains were tilted toward ND around TD. Prismatic slip dominated when basal planes were approximately perpendicular to TD. Calculation results also indicated that the operating of pyramidal 〈a〉 slip can not be neglected. {10 $$ ar 1 $$ 2} twinning was favorable when basal planes were approximately normal to RD and {10 $$ ar 1 $$ 1} twinning was analyzed to be related to the grains with basal orientations. The operating of 〈a + c〉 slip could greatly suppress the activating of twinning by our Schmid factor analysis. Basal orientations with TD and RD scattering can favor basal slip and tension twinning, respectively, after the operation of compression twinning based on the Schmid factor calculations.
Keywords: magnesium alloy; deformation; Schmid factor orientation; Sachs model

Thermal decomposition studies of CuInS2 by Sunil H. Chaki (322-325).
Single crystals of copper indium disulphide (CuInS2) have been successfully grown by the chemical vapour transport (CVT) technique using iodine as the transporting agent. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were carried out for the CVT grown CuInS2 single crystals. It was revealed that the crystals are thermally stable between the ambient temperature (300 K) and 845 K and that the decomposition occurs sequentially in three steps. The kinetic parameters, e.g., activation energy, order of reaction, and frequency factor were evaluated using non-mechanistic equations for thermal decomposition.
Keywords: single crystal; CVT single crystal growth; TGA; DTA

The initial pitting behaviors of 30CrMnSi steel in 0.05 mol/L NaCl + 0.5 mol/L NaHCO3 solution was studied using electric speckle pattern interferometery (ESPI) and electrochemical noise (EN). Results show that the bright speckles and sharp fluctuation of electrochemical signals occurred at the same time. The EN curve shows that there are three stages during the pitting process — the induction stage (0–50 s), the incubation stage (50–300 s) and the initiative stage (300–512 s).
Keywords: 30CrMnSi steel; pitting; ESPI; EN

Effects of TiO2/Al ratio on the microstructures and mechanical properties of in situ Al2O3/TiAl based composites were investigated. The results indicate that the as-sintered products consist of grains of nearly lamellar α2 + γ structure with a dispersion of randomly oriented Al2O3 particles. A 43.9Ti-38.6Al-17.5TiO2-nNb2O5 system was compared to 57.46Ti-36.78Al-5.76TiO2-nNb2O5 system. The lamellar spacing of the products increases and the α2 phase volume decreases with decreasing TiO2/Al ratio. For each system, as the volume of α2 phase increases, the average lamellar spacing decreases. Strength increases with an increasing TiO2/Al ratio due to the amount of α2 phase. Al2O3 phase increases with increasing TiO2/Al ratio. Toughness increases with decreasing TiO2/Al ratio. When the Nb2O5 content is smaller than 6 wt.%, the lamellar spacing plays an important role in toughness than the Al2O3 content. When the Nb2O5 content is larger than 6 wt.%, the Al2O3 content exhibits significantly increases the values of toughness than lamellar spacing.
Keywords: titanium aluminides; microstructure; mechanical properties