[1] Mohammed NA, Daher AM. Preparation of high-purity zirconia from zircon: An anion-exchange purification process. Hydrometallurgy. 2002;**65**(2-3): 103-107. DOI: 10.1016/S0304-386X (02) 00042-7

[2] Han H, Zhu J. Surface science studies on the zirconia-based model catalysts. Topics in Catalysis. 2013;**56**:1525-1541. DOI: 10.1007/s11244-013-0156-5

[3] Blumenthal WB. The Chemical Behavior of Zirconium. Princeton, NJ: D. Van Nostrand Company Inc.; 1958. 58 p.

[4] Selby JH. The industrial uses of zircon and zirconia, and the radiological consequences of these uses. In: Proceeding of International Symposium. Seville, Spain. Vienna: IAEA; 2007. p. 95

[5] Elkady MY, Mohmed AM, Daher AME, Wafaa H, Saleh WH, Negam S, et al. Preparation of La2Zr2O7 ceramic from Egyptian black sand. Journal of Radiation Research and Applied Sciences. 2018;**11**(1):37-42. DOI: 10.1016/j.jrras.2017.10.005

[6] Singh Y. Rare earth mineral deposits in Indian context. Society of Earth Scientists Book Series. Cham, Switzerland: Springer; 2020. pp. 137-178. DOI: 10.1007/978-3-030-41353-8\_2

[7] Moussa MO, Kouidri S, Rached H, Haid S, Beloufa N, Ouadha I, et al. Theoretical investigation on the optoelectronic properties of ZrxSi1 xO2 tetragonal hypothetical alloys from zircon family. Applied Physics A. 2022; **128**:231. DOI: 10.1007/s00339-022- 05362-x

[8] El Barawy KA, El Tawil SZ, Francis AA. Alkali fusion of zircon sand. Transactions of the institution of mining and metallurgy (section C). Mineral Processing and Extractive Metallurgy. 2000;**109**(1):C49-C56

[9] Yamagata C, Andrade JB, Ussui V, Limai NB NB, José OA, Yamagata PC. High purity zirconia and silica powders via wet process: Alkali fusion of zircon Sand. Materials Science Forum. 2008; **591-593**:771-776

[10] Song J, Fan JF, Liu JC, Liu R, Qu JK, Qi T. A two-step zircon decomposition method to produce zirconium oxychloride: Alkali fusion and water leaching. Rare Metals. 2020;**39**(4): 448-454. DOI: 10.1007/s12598-015-0537-y

[11] Murti CFK, Aldila H, Triwikantoro E. Particle size analysis of the synthesised ZrO2 from natural zircon sand with variation of pH deposition using alkali fusioncoprecipitation method. Material Science Forum. 2019;**966**:89-94. DOI: 10.4028/ www.scientific.net/MSF.966.89

[12] Septawendar R, Sutardi S, Karsono U, Sofiyaningsih N. A low-cost, facilem on production of nano zirconia and silica from local zircon in a large scale using a sodium carbonate sintering technology. Journal of The Australian Ceramic Society. 2016;**52**(2): 92-102

[13] El Tawil SZ, El Barawy KA, Francis AA. Cubic zrconia from zircon sand by firing with CaO/MgO mixture. Journal of the Ceramic Society of Japan. 1999;**107**(3):193-198

[14] Zhang J, Wang L, Jiang D. Decomposition process of zircon sand concentrate with CaO-NaOH. Rare Metals. 2012;**31**(4):410. DOI: 10.1007/ s12598-012-0529-0

[15] Bidaye AC, Venkatachalam S. Studies on the chlorination of zircon: Part I. static bed investigations. Metallurgical and Materials Transactions. 1999;**30B**:205

[16] Poernomo H, Sajima Pusporini ND. Synthesis of zirconium oxychloride and zirconia low TENORM by zircon sand from landak West Kalimantan. Journal of Physics: Conference Series. 2020; **1436**:012106. DOI: 10.1088/1742-6596/ 1436/1/012106

[17] Wilks PH, Ravinder P, Grant CL, Pelton PA, Downer RJ, Talbot ML. Plasma process for zirconium dioxide. Chemical Engineering Progress. 1972;**68** (4):82-83

[18] Butterman WC, Foster WR. Zirconium stability and ZrO2-SiO2 phase diagram. American Mineralogist. 1967;**52**: 880

[19] Rendtorffabc NM, Suárezabd G, Conconiac MS, Singhe SK, Agliettiabd EF. Plasma dissociated zircon (PDZ) processing; influence of the Zr:Si ratio in the composition, microstructure and thermal recrystallization. Procedia Materials Science. 2012;**1**:337-342

[20] Ananthapadmanabhan PV, Sreekumar KP, Iyer KV, Venkatramani N. Plasma thermal dissociation of Indian zircon. Journal of Alloys and Compounds. 1993;**196**(1–2): 251-254

[21] Yuan Z, Li W, Liu J, Luo M, Liu J. Production of zirconia from zircon using a plasma-rotating furnace. Scandinavian Journal of Metallurgy. 2004;**33**:189-192

[22] Kaiser A, Lobert M, Telle R. Thermal stability of zircon (ZrSiO4). Journal of the European Ceramic Society. 2008;**28**: 2199-2211

[23] Suzuki M, Sodeoka S, Inoue T. Structure control of plasma sprayed zircon coating by substrate preheating and post heat treatment. Materials Transactions. 2005;**46**(3):669-674

[24] Ananthapadmanabhan PV, Lusvarghi L, Yugeswaran S. Zircon dissociation in air plasma through low power transferred arc plasma torch. Ceramics International. 2014;**8**:68. DOI: 10.1016/j.ceramint.2014. 08.068

[25] Syamprasad U, Bhattacharjee S, Galgali RK, Mohapatra BK, Mohanty BC. Studies on plasma dissociation of Indian zircon in a specially developed plasma reactor. Journal of Materials Science. 1992;**27**(7):1762-1766

[26] Manikandana S, Kuberana A, Yugeswaranb S, Ananthapadmanabhana PV, Pandiyarajc NK, Shajana XS, et al. Silicafree zirconia from zircon mineral by thermal plasma processing. Materials and Manufacturing Processes. 2021; **36**(2):88-199. DOI: 10.1080/10426914. 2020.1832681

[27] Gole JL, Prokes SM, Stout JD, Glembocki OJ, Yang R. Unique properties of selectively formed zirconia nanostructures. Advanced Materials. 2006;**18**:664

[28] Zhuiykov S, Miura N. Development of zirconia-based potentiometric NOx sensors for automotive and energy industries in the early 21st century: What are the prospects for sensors. Sens. Actuators B Chemical. 2007;**121**(2): 639-651. DOI: 10.1016/j.snb.2006.03.044

[29] Wilk RM, Wallace JM, Anthony GD, Wilk GD, Wallace RM, Anthony JM. High-κ gate dielectrics: Current status and materials properties considerations high- gate dielectrics: Current status and materials properties considerations. Journal of Applied Physics. 2001;**89**(10): 5243-5274. DOI: 10.1063/1.1361065

*Zirconia: Synthesis and Characterization DOI: http://dx.doi.org/10.5772/intechopen.111737*

[30] Jin XJ. Martensitic transformation in zirconia containing ceramics and its applications. Current Opinion in Solid State & Materials Science. 2005;**9**: 313-318. DOI: 10.1016/j.cossms.2006. 02.012

[31] Gupta S, Noumbissi S, Kunrath MF. Nano modified zirconia dental implants: Advances and the frontiers for rapid osseointegration. Medical Devices and Sensors. 2020;**3**:1-8. DOI: 10.1002/ mds3.10076

[32] Carlos E, Martins R, Fortunato E, Branquinho R. Solution combustion synthesis: Towards a sustainable approach for metal oxides. Chemistry - A European Journal. 2020;**26**(42): 9099-9125. DOI: 10.1002/chem. 202000678

[33] Branquinho R, Santa A, Carlos E, Salgueiro D, Barquinha P, Martins R, et al. Solution combustion cynthesis: Applications in oxide electronics. In: Developments in Combustion Technology. London, UK: IntechOpen; 2016. DOI: 10.5772/64761

[34] Boopalan K, Vijayaraghavan R, Chidambaram K, Mudali UMK, Raj B. Preparation and characterization of nanocrystalline zirconia powders by the glowing combustion method. Journal of the American Ceramic Society. 2010; **93**(11):3651-3656. DOI: 10.1111/ j.1551-2916.2010.03947.x

[35] Matias ML, Carlos E, Branquinho R, do Valle H, Marcelino J, Morais M, et al. A comparison between solution-based synthesis methods of ZrO2 nanomaterials for energy storage applications. Energies. 2022;**15**:6452. DOI: 10.3390/en15176452

[36] Lim HS, Ahmad A, Hamzah H. Synthesis of zirconium oxide

nanoparticle by sol-gel technique. AIP Conference Proceedings. 2013;**1571**:812. DOI: 10.1063/1.4858755

[37] Suciua C, Gageab L, Hoffmanna AC, Moceanb M. Sol–gel production of zirconia nanoparticles with a new organic precursor. Chemical Engineering Science. 2006;**61**:7831-7835

[38] Zhou H, Pu S, Huo J, Cao W, Wang B, Li J. Facile corrosion synthesis and sintering of disperse pure tetragonal zirconia nanoparticles. Ceramics International. 2016;**42**:15005-15011. DOI: 10.1016/j.ceramint.2016.06.148

[39] Meetei SD, Singh SD. Hydrothermal synthesis and white light emission of cubic ZrO2: Eu3+ nanocrystals. Journal of Alloys and Compounds. 2014;**587**: 143-147. DOI: 10.1016/j.jallcom.2013. 10.159

[40] Noh HJ, Seo DS, Kim H, Lee JK. Synthesis and crystallization of anisotropic shaped ZrO2 nanocrystalline powders by hydrothermal process. Materials Letters. 2003;**57**:2425-2431. DOI: 10.1016/S0167-577X(02)01248-X

[41] Nath S, Biswas A, Kaur PP, Sarma LS, Sur UK, Ankamwar BG. Synthesis of mesoporous nanocrystalline zirconia by surfactant-assisted hydrothermal approach. Journal of Nanoscience and Nanotechnology. 2018; **18**(8):5390-5396. DOI: doi.org/10.1166/ jnn.2018.15362

[42] Gonell F, Portehault D, Julián-López B, Vallé K, Sanchez C, Corma A. One step microwave-assisted synthesis of nanocrystalline WOx–ZrO2 acid catalysts. Catalysis Science & Technology. 2016;**6**:8257-8267. DOI: 10.1039/x0xx00000x

[43] Majedi A, Davar F, Abbasi A, Ashrafi A. Modified sol–gel based nanostructured zirconia thin film: Preparation, characterization,p and corrosion behavior. Journal of Inorganic and Organometallic Polymers and Materials. 2016;**26**:932-942. DOI: 10.1007/s10904-016-0394-7

[44] Huang Z, Han W, Feng Z, Qi J, Wu D, Wei N, et al. The effects of precipitants on co-precipitation synthesis of yttriastabilized zirconia nanocrystalline powders. Journal of Sol-Gel Science and Technology. 2019; **90**:359-368. DOI: 10.1007/s10971-019- 04947-y

[45] Jaenicke S, Chuah GK, Raju V, Nie YT. Structural and morphological control in the preparation of high surface area zirconia. Catalysis Surveys from Asia. 2008;**12**:153-169. DOI: 10.1007/ s10563-008-9048-2

[46] Huang HJ, Wang MC. The phase formation and stability of tetragonal ZrO2 prepared in a silica bath. Ceramics International. 2013;**39**:1729-1739. DOI: 10.1016/j.ceramint.2012.08.019

[47] Li X, Wang Y, Xiong X, Liu HB, Wu N, Liu R. Microstructure and synthesis mechanism of dysprosiastabilized zirconia nanocrystals via chemical coprecipitation. Ceramics International. 2020;**46**(9): 13331-13341. DOI: 10.1016/j.ceramint. 2020.02.112

[48] Dahanayake U, Karunaratne BS. Preparation of zircon (ZrSiO4) ceramics via solid state sintering of ZrO2 and SiO2 and the effect of dopants on the zircon yield. Solid State Ionics. Advanced Materials for Emerging Technologies. 2006:146-153. DOI: 10.1142/<PHONE_NUMBER>104\_0017

[49] Averu AC, Biel LV, Medeiros JLB, De Souza J. Comparative study of the

diffusibility of a nickel alloy composed by Ni-Cr-Fe. International Journal of Engineering Research & Technology (IJERT). 2016;**5**(12):IJERTV5IS120261

[50] Aytimur A, Kocyigit S, Uslu I. Calcia stabilized ceria doped zirconia. Nanocrystalline ceramic. Journal of Inorganic and Organometallic Polymers. 2014;**24**:927-932. DOI: 10.1007/ s10904-014-0064-6

[51] Ahmed T, Ren H, Noman M, Shahid M, Liu M, Ali MA, et al. Green synthesis and characterization of zirconium oxide nanoparticles by using a native Enterobacter sp. and its antifungal activity against bayberry twig blight disease pathogen Pestalotiopsis versicolor. Nano Impact. 2021;**21**:10028. DOI: 10.1016/j.impact.2020.100281

[52] Bansal V, Rautaray D, Ahmad A, Sastry M. Biosynthesis of zirconia nanoparticles using the fungus Fusarium oxysporum. Journal of Materials Chemistry. 2004;**1**(4):3303-3305. DOI: 10.1039/B407904C

[53] Al-Zaqri N, Muthuvel A, Jothibas M, Fahad AA, Alharthi A, Mohana V. Biosynthesis of zirconium oxide nanoparticles using Wrightia tinctoria leaf extract: Characterization, photocatalytic degradation and antibacterial activities. Inorganic Chemistry Communications B. 2021;**127**: 108507. DOI: 10.1016/j. inoche.2021.108507

[54] Kumari N, Sareen S, Verma M, Sharma S, Sharma A, SohalbHS MSK, et al. Zirconia-based nanomaterials: Recent developments in synthesis and applications. Nanoscale Advances. 2022; **4**:4210-4236. DOI: 10.1039/ D2NA00367H

[55] Merten D, Broekaert JAC, Brandtc R, Norbert JJ. Analysis of ZrO2 powders by

*Zirconia: Synthesis and Characterization DOI: http://dx.doi.org/10.5772/intechopen.111737*

microwave assisted digestion at high pressure and ICP atomic spectrometry. Journal of Analytical Atomic Spectrometry. 1999;**14**:1093-1098

[56] Chen S, Li J, Lu D, Zhu S. Study on the simultaneous determination of different volatile elements in high purity zirconium dioxide by in situ matrix removal and ETV-ICP-MS. Atomic Spectroscopy. 2016;**37**(1):13-18

[57] Degueldre C, Favarger PF, Bitea C. Zirconia colloid analysis by single particle inductively coupled plasma– mass spectrometry. Analytica Chimica Acta. 2004;**518**(1-2):137-142

[58] Stefanov P, Stoychev D, Stoycheva M, Ikonomov J, Ts M. XPS and SEM characterization of zirconia thin films prepared by electrochemical deposition. Material D. Chemistry. 2000; **30**(1):628-631

[59] Routray BCS, Mohanty R, Swain R, Sahu S, Mishra BR. Preparation and characterisation of zirconia nanomaterials prepared from zircon minerals. Journal of The Institution of Engineers (India): Series E. 2021;**102**(1):87-95. DOI: 10.1007/s40034-020-00201-1

[60] Zhu LQ, Fang Q, He G1, Liu M, Zhang LD. Microstructure and optical properties of ultra-thin zirconia films prepared by nitrogen-assisted reactive magnetron sputtering. Nanotechnology. 2005;**16**:2865-2869. DOI: 10.1088/ 0957-4484/16/12/022

[61] Azdad Z, Marot L, Moser L, Steiner R, Meyer E. Valence band behavior of zirconium oxide, photoelectron and auger spectroscopy study. Scientific Reports. 2018;**8**:16251. DOI: 10.1038/s41598-018-34570-w

[62] Lackner P, Zou Z, Mayr S, Diebold U, Schmid M. Using

photoelectron spectroscopy to observe oxygen spill over to zirconia. Physical Chemistry Chemical Physics. 2019;**32**: 1-9. DOI: 10.1039/C9CP03322J

[63] Barkadze G, Jeurgens PLH, Mittemeije EJ. Valence-band and chemical-state analyses of Zr and O in thermally grown thin zirconium-oxide films: An XPS study. Journal of Physical Chemistry C. 2011;**115**(40):19841-19848. DOI: 10.1021/jp206896m

[64] Deshmane VG, Adewuyi YG. Synthesis of thermally stable, high surface area, nanocrystalline mesoporous tetragonal zirconium dioxide (ZrO2): Effects of different process parameters. Microporous and Mesoporous Materials. 2012;**148**(1): 88-100. DOI: 10.1016/j. micromeso.2011.07.012

[65] Sidhua GK, Kaushik AK, Ranac S, Bhansali S, Kumar R. Photoluminescence quenching of zirconia nanoparticle by surface modification. Applied Surface Sciences. 2015;**334**:216-221. DOI: 10.1016/j.apsusc.2014.10.036

[66] Ashkarran AA, Afshar SAA, Aghigh SM, kavianipour M. Photocatalytic activity of ZrO2 nanoparticles prepared by electrical arc discharge method in water. Polyhedron. 2010;**29**:1370-1374. DOI: 10.1016/j. poly.2010.01.003

[67] Fillit R, Homerin RP, Schafer RJ. Quantitative XRD analysis of zirconiatoughened alumina ceramics. Journal of Materials Science. 1987;**22**:3566-3570. DOI: 10.1007/BF01161460

[68] Wang J, Yin W, He X, Wang Q, Guo M, Chen S. Good biocompatibility and sintering properties of zirconia nanoparticles synthesized via vaporphase hydrolysis. Scientific Reports. 2016;**16**:35020. DOI: 10.1038/srep35020 [69] Manoharan D, Loganathan A, Kurapati V, Nesamony VJ. Unique sharp photoluminescence of size-controlled sonochemically synthesized zirconia nanoparticles. Ultrasonics Sonochemistry. 2015;**23**:174-185. DOI: 10.1016/j.ultsonch.2014.10.004

[70] Harris DC, Bertolucci MD. Symmetry and Spectroscopy: An Introduction to Vibrational and Electronic Spectroscopy. 1st ed. New York, NY, USA: Oxford University Press; 1978

[71] Narayana DKL, Rao SV, Rao DN. Spectroscopic investigation of fs laserinduced defects in polymer and crystal media. Laser-Induced Damage in Optical Materials: Proc. of SPIE. 2012:8530

[72] Pezzotti G, Porporati AA. Raman spectroscopic analysis of phasetransformation and stress patterns in zirconia hip joints. Journal of Biomedical Optics. 2004;**9**(1):372-384. DOI: 10.1117/ 1.1647547

[73] Clarke DR, Adar F. Measurement of the crystallographically transformed zone produced by fracture in ceramics containing tetragonal zirconia. Journal of the American Ceramic Society. 1982;**65**: 284-288

[74] Basahel S, Ali TT, Mostafa MMM, Katabathini N. Influence of crystal structure of nanosized ZrO2 on photocatalytic degradation of methyl orange. Nanoscale Research Letters. 2015;**10**(1):73. DOI: 10.1186/s11671-015- 0780-z

[75] Shia F, Lib Y, Wanga H, Zhang Q. Fabrication of well-dispersive yttriumstabilized cubic zirconia nanoparticles via vapor phase hydrolysis. Progress in Natural Science: Materials International. 2012;**22**(1):15-20. DOI: 10.1016/j. pnsc.2011.12.003

[76] Ada P, Falkowski P, Miazga A, Konopka K, Szafran M. Fabrication of ZrO2-Ti composites by slip casting method. Archives of Metallurgy and Materials. 2016;**61**(2B):1095-1100. DOI: 10.1515/amm-2016-0184

[77] Darmawan BA, Fisher JG, Trung DT, Sakthiabirami K, Park S. Two-step sintering of partially stabilized zirconia for applications in ceramic crowns. Materials. 2020;**13**(8):1857. DOI: 10.3390/ma13081857

[78] Anjum DH. Characterization of nanomaterials with transmission electron microscopy. IOP Conference Series: Materials Science and Engineering. 2016:146

[79] Siddiqui MRH, Al-Wassil AI, Al-Otaibi AM, Mahfouz RM. Effects of precursor on the morphology and size of ZrO2 nanoparticles, synthesized by solgel method in non-aqueous medium. Materials Research. 2012;**15**(6):986-989. DOI: 10.1590/S1516-14392012005 000128

[80] Liu J, Mir AH, He G, Danaie M, Hinks J, Donnelly S, et al. In-situ TEM study of irradiation-induced damage mechanisms in monoclinic-ZrO2. Acta Materialia. 2020;**199**:429-442

[81] Salih SI, Salih WB, Hamad HS. Preparation and investigation of some mechanical properties of unsaturated polyester resin reinforced by hybrid nanoparticles. The Iraqi Journal For Mechanical And Material Engineering. 2018;**18**(2):331-338

[82] Lee M, Son JS, Kim K, Kwon T. Improved resin–zirconia bonding by room temperature hydrofluoric acid etching. Materials. 2015;**8**:850-866. DOI: 10.3390/ma8030850

#### **Chapter 4**

### Processing of Zirconia

*Ghassan Albarghouti and Sojood Mahmoud Farhan Darwish*

#### **Abstract**

This chapter starts with an introduction, including zircon, zircon structure, zirconia ceramics and their structures as they exhibit a distinct crystal structure at various temperatures while maintaining the same chemical composition. Then the properties of zirconia including mechanical, tribological, and electrical properties and thermal conductivity, were discussed. Zirconia's properties offer excellent resistance to corrosion and chemicals. When compared to other high-tech ceramic materials, zirconia is very robust at room temperature. The processing of zirconia was explained, starting with the purification of zirconium compounds followed by powder processing of zirconia, colloidal processing of zirconia, additive manufacturing, and zirconia treatments. Zirconia ceramics are processed from their raw ingredients in order to modify and enhance their physical and chemical characteristics and make them more suitable for use in future processes and in the production of finished goods. Various analysis methods of zirconia, including powder processing and sintering, microstructural analysis, phase characterization, mechanical testing, and tribological characterization were discussed. The last section in the chapter discusses the nano zirconia (ZrO2 nanoparticles). In addition to photocatalytic and piezoelectric uses, dental and optical coatings, nano zirconia has additionally been employed as a catalyst in a variety of organic interactions. It appears in the cubic, tetragonal, and monoclinic structural phases.

**Keywords:** zirconia, structure, properties, processing, analysis, 3D printing

#### **1. Introduction**

#### **1.1 Zircon**

Zircon, which is frequently found in highly silicic stones and contains significant quantities of certain trace elements, is regarded as a resistant auxiliary mineral. It is also a helpful instrument for tracking melt compositional alterations throughout magma development [1]. The quantity of Zr in the principal minerals is often negligible in comparison to that housed by zircon, and there is disagreement on the presence of zircon at boundaries of grains vs. the amount hidden as inclusions within different minerals [2]. Zirconium silicate is another name for the mineral zircon (ZrSiO4). It results from the extraction and processing of historical heavy mineral sand and is most typically found in coastal placers or dune deposits across the world [3]. Zirconium silicates are abundant in essence, along with presence under hydrothermal circumstances (between 300 and 550°C) which seems to have received a lot of interest [4].

The global output of zircon is around 1.1 million t/a, with the majority of it coming from Australia and South Africa. The most important use of zircon is represented by ceramics sector [3]. Zircon may be treated to make zirconia by melting the sand at extremely high temperatures to yield molten zirconium oxide (ZrO2) [5].

It is debatable how zircons behave in suprasolidus metamorphic environments. Experimental findings suggest zircon growth occurs throughout prograde metamorphism in melt-bearing systems, but computational modeling only anticipates zircon development upon cooling and melt crystallization. Zircon in high-pressure zones and elevated temperatures metamorphic rocks is a probable by-product of inconsistent melting events. However, knowledge of how zirconium, a crucial structural component of zircon, is distributed among the numerous products and reactants that occur during incongruent partial melting is still limited. A fresh source of Zr may become accessible to zircon formation after heating under suprasolidus under certain circumstances, or Zr may redistribute from already-existing zircon [2].

#### **1.2 Zircon structure**

Zircon is a mineral that is an orthosilicate accessory. Its chemical formula is ZrSiO4 (Z = 4) with the space group *I*41/*amd*. The zircon structure is made up of chains of consecutive, edge-shared SiO4 and ZrO8 polyhedra that pass along the c axis. The structure is rather wide; it incorporates "channels" of evidently vacant sixfold sites that run in corresponding direction to the {001} orientation and can accommodate big amount of non-formula components [6].

The edges of the ZrO8 triangular dodecahedra are coupled in a zigzag manner across the {100} dimensions. The structure shown in **Figure 1** accounts for the most prevalent three-dimensional behavior of zircon as well as the uncertain cleavage along {110}. Natural zircon incorporates non-formula elements at all times [7]. On the other hand, large cations (U, Th, Y, lanthanides, Hf) often replace Zr in the eightfold dodecahedral position, however, smaller cations may be placed in the sixfold location [8].

#### **1.3 Zirconia ceramics**

For several reasons, zirconia-based ceramics are the most researched and demanding materials. Zirconia (zirconium dioxide, ZrO2), popularly known as "ceramic steel", offers outstanding hardness, strength, and fatigue resistance, as well as good wear characteristics and biocompatibility [9].

Zirconium oxide, silicon nitride, and aluminum oxide are a few frequently employed ceramics that have exceptional chemical and physical qualities including high hardness, high strength, high toughness, and corrosion resistance [1]. Zirconium oxide, on the other hand, outperforms silicon nitride and aluminum oxide in terms of abrasion resistance, toughness, and service temperature [10].

Zirconia is a significantly highly versatile transition metal oxide frequently applied in ceramics, electrolytes for solid-oxide fuel cells and semiconductor technology [11]. The finest qualities come from zirconia stabilized with Y2O3. A crystallographic change on a ZrO2 surface limits fracture formation once is subjected to stress [12].

Baddeleyite, a naturally existing zirconia, is found in igneous rocks such as carbonatite. South Africa was the major producer of baddeleyite until 2002, but these plants have since closed, leaving the Kola Peninsula area of the Russian Federation as the only commercial source of this mineral. The majority of zirconia presently

accessible is made using zircon (34,000 t/a), with a relatively minor natural source by the Russian Federation (6000 t/a) [3].

Zirconia ceramics are traditionally processed using turning, milling, and grinding techniques. These techniques have significant drawbacks, including inadequate productivity and inevitable manufacturing damage, which make it difficult to achieve sufficient quality of the surface. But sandblasting and acid etching have a tendency to pollute the component's surfaces or alter their physical and chemical characteristics. In order to get an immaculate finish and undo surface and subsurface damage from earlier preparation, polishing can significantly enhance the surface quality [10].

#### **1.4 Zirconia structure**

There are three different types of zirconia crystal structures: Cubic, tetragonal, and monoclinic. It is possible to achieve high structural stabilization by combining ZrO2 and associating to other metallic oxides like ZrO2—MgO, ZrO2—CaO, or ZrO2—Y2O3 [13]. However, recent research emerged to be more concentrated on zirconia—yttria ceramics, which can be recognized by their fine-grained in the micro range classified as Tetragonal Zirconia Polycrystals (TZP) [14].

At high temperatures (>2370°C), a cubic zirconia also known as (c-ZrO2) fluorite crystal configuration with a unit cell of face-centered cubic (fcc) and a (space group Fm-3m) form. A numerous atom of Zr is linked to eight oxygens to create the fcc cube and the oxygen atoms are arranged along the cube's diagonals [15]. Furthermore, the fluorite structures of the monoclinic and tetragonal are deformed as seen in **Figure 2**.

**Figure 2.**

*The three ZrO2 polymorphs are shown in a schematic in the following order: (a) cubic, (b) tetragonal, and (c) monoclinic [16].*

At intermediate temperatures (1200–2370°C), the structure is transferred to tetragonal (*P*42/*nmc*), while at low temperatures (<950°C), the structure is monoclinic (*P*21/ *c*) [16]. Throughout thermal cycling, undoped zirconia reveals the following phase transitions [17]:

$$\text{cm-ZrO}\_2 \overset{1170^\circ \text{C}}{\underset{950^\circ \text{C}}{\rightleftharpoons}} \text{t-ZrO}\_2 \overset{2370^\circ \text{C}}{\underset{950^\circ \text{C}}{\rightleftharpoons}} \text{c-ZrO}\_2 \overset{2650^\circ \text{C}}{\underset{950^\circ \text{C}}{\rightleftharpoons}} \text{Liiquid} \tag{1}$$

#### **2. Properties of zirconia**

In relation to their usage, this section describes the many varieties and characteristics of zirconia materials. Due to the following qualities, zirconia has recently been the subject of substantial inquiry in the scientific literature:

#### **2.1 Mechanical properties**

Recent studies showed that mechanical parameters including hardness, grain size, and fracture toughness, as seen in **Table 1** have an important bearing on slide wear resistance of bulk ceramics [18]. Zirconia has mechanical properties that are on par with stainless steels. Its traction resistance might be in the 900–1200 MPa range, and it has a 2000 MPa compression tolerance [19]. 3Y-TZP dentistry zirconia incorporates alumina (Al2O3) as a strain-hardening promoter, resulting in great opacity and exceptional mechanical qualities [20].

Although the sintering of ZrO2 stabilized with Y2O3 is substantially more complex, this is the primary type of zirconia recognized for present medical usage. Surface treatments have the potential to alter the physical characteristics of zirconia. Furthermore, prolonged wetness contact may have a negative impact on its assets. The term for this is zirconia aging. Surface grinding can also diminish toughness. The mechanical characteristics of zirconia might deteriorate as it ages. Mechanical forces and moisture exposure are essential for speeding up this process [20].

Due to transition toughening, ZrO2 has the ability to achieve extremely high toughness. It is regarded as a strong contender for numerous cutting tool applications as well as a biomedical material. Nevertheless, the intrinsic fragility of these substances remains the primary bottleneck. This issue has been addressed by developing suitable composites. Novel materials, including carbon nanotubes and fiber-like structures, have been produced in recent years. The fibrous character of the

#### *Processing of Zirconia DOI: http://dx.doi.org/10.5772/intechopen.112121*

**Table 1.**

*Thermal, electrical, and mechanical properties of zirconia [18].*

toughening components may result in increased fracture toughness. Furthermore, compared to the other two non-metallic additions, carbon's electrical conductivity allows for additional electrical qualities to be helpful [21].

Using Eq. (2), it is possible to conduct a three-point bending test and a biaxial flexure test to assess flexural capacity and can be examined using a universal testing device (Autograph AG-X).

$$\sigma = \frac{-\mathbf{0}.2387 \mathbf{P}(\mathbf{X} - \mathbf{Y})}{\mathbf{b}^2} \tag{2}$$

where the center's highest tensile stress is σ (in MPa), the total load producing the rupture is P (in N), and the cross-section of the test piece at the fracture point is b (in mm) [22].

Meanwhile, fracture toughness (KIC) test can be performed using the single-edge pre-cracked beam technique and can be measured by applying Eq. (3). Where **B** represents the material length (in m), **W** represents the sample width (in m), and **a** represents the pre-crack length; **P** represents the breaking force (N), and **S** represents the support span (m) [22].

$$K\_{IC} = \left(\frac{P \times S}{B \times W^{3/2}}\right) \times \left\{\frac{3}{2} \left(\frac{a}{W}\right)^{\frac{1}{2}} \times Y \left(\frac{a}{W}\right)\right\} \tag{3}$$

#### **2.2 Tribological properties**

Zirconia ceramics have been extensively researched as a wear resistant material for engineering fields throughout the last few years. The kind of Hall-Petch law governs the connection between wear resistance and grain size in tetragonal zirconia ceramics. As a result, it is reasonable to predict that nano-structured zirconia coatings will have more wear resistance than standard zirconia. Friction and wear tests may sometimes be performed on an MM-200 wear tester's block-on-ring configuration. As seen in **Figure 3**, the stationary zirconia-coated blocks are

**Figure 3.** *The block on ring test [23].*

pressed up against a moving stainless steel. The tester provides the friction coefficient immediately. Additionally, wear frequencies can be calculated by dividing the wear mass loss by the force implemented, sliding distance, and material density [24].

Throughout wear testing, the surface morphology, particularly big pores, may result in excessive stress concentration and fracture development, resulting in poor resistance. Additionally, it is shown that, as evidenced by Eq. (4), the wear rate of polycrystalline ceramics matched an exponential function. In which **1/K0w** represents the TZP substance wear resistance with no pores (in N.m/mm<sup>3</sup> ) and **P** represents porosity.

$$\frac{1}{k\_w} = \frac{1}{k\_{0w}} \exp\left(-2\Im P\right) \tag{4}$$

Eq. (4) above illustrates that decreasing the porosity of zirconia ceramics resulted in enhanced wear resistance. The existence of gaps reduces the probability of grain boundary sliding, which delays or prevents the occurrence of plastic deflection [24].

#### **2.3 Electrical properties and thermal conductivity**

Zirconia additionally has a high degree of flexibility, a superior conductivity, a poor thermal conductivity, and a strong corrosion resistance as seen in **Table 1** [18]. Because of that, zirconia is utilized in many applications at various high temperatures, such as fuel cells and thermal barrier coatings [18]. Monoclinic zirconia was demonstrated at 1000°C to be an amphoteric semiconductor in a prior work. When oxygen pressures are high (10�<sup>6</sup> to a value of 1 atm), the most common defects are fully ionized zirconium holes, which produced exceptionally well, implying charge transfer via a thermally induced hopping mechanism [25].

On the other hand, at ambient temperature, zirconia in its monoclinic phase has a thermal conductivity of 7.2 Wm�<sup>1</sup> K�<sup>1</sup> . However, at high temperature (1100°C) zirconia begins to have very poor heat conductivity (1.2–2.6 Wm�<sup>1</sup> K�<sup>1</sup> ), making it an ideal candidate for thermal barrier (TBC) coatings [26]. However, the volume variation (5%) caused by phase transformation at elevated heat as well as during cooling the apparatus limits the use of zirconia in aggressive environments. The crumbling of the zirconia-based components is caused by phase transformation and volume change [27].

Yet, when the temperature rises, the phase transition (**Figure 4**) occurs, resulting in structural failure and fractures in the coat. This would be prevented by enriching the zirconia matrix with yttria, which stabilizes the zirconia at high temperatures. Some Zr4+ cations are substituted by Y3+ during this stabilizing procedure [29]. To preserve charge balance, one oxygen gap is formed for every two replacing Y3+ cations. Because of the presence of voids, YSZ is valuable not only for TBCs but also as an electrolyte in oxygen sensors and solid-oxide fuel cells (SOFC) [30].

This kind of stabilization not only assists in preventing phase change but also reduces the thermal conductivity of YSZ, for example, from 1.42 W/m�K (at ambient temperature) to 1.35 Wm�<sup>1</sup> K�<sup>1</sup> at 1200°C since c-phase zirconia exhibits less thermal conductivity than m-zirconia [27].

Zirconia is also a metal oxide which is composed of a weak base and a weak acid and is one of the ceramic semiconductors. Because of its crystalline structure, it can be

**Figure 4.** *Thermal conductivity of ZrO2 [28].*

an insulator utilized as an n-type semiconductor or a high-resistance ceramic. The forms of the nanocrystals determine the potential uses for them. Oxygen sensors, fuel cell electrolytes, and gate dielectrics have all been employed with spherical ZrO2 [31].

#### **3. Processing of zirconia**

This section discusses the purification process of zircon, followed by stating various methods for zirconia processing (thermal dissociation, chlorination, additive manufacturing, and colloidal processing) depending on the characteristics asked for and the purpose or the industry that asks for a zirconia supply.

#### **3.1 Purification of zirconium compounds**

For usage in the electronics sector and the creation of partly stabilized zirconia, highly pure zirconia is commonly used today. A large portion of the world's zirconia supply found naturally as ZrSiO4 [32].

By caustic fritting of zircon sand, the zirconium nitrate solution is obtained. Caustic fritting was accomplished with the aid of magnesium hydroxide carbonate and magnesium oxide. These additives reduce the quantity of soluble silica in nitric acid by less than 1000 ppm. With no additional ingredients, caustic fritting produces some nitric acid-soluble silica, which is eliminated by dehydrating with sulfuric acid [32].

Other procedures currently are utilized to extract zirconia from zircon generally by including heat or chemical disintegration of zircon to provide zirconia and silica. But even so, the resulting zirconia needs to be purified through additional chemical processing. A financially appealing method of producing zirconia is the thermal dissociation of zircon, which results in a combination of zirconia and silica. The dissociated zircon result can be leached either with a strong base, like sodium hydroxide

#### *Processing of Zirconia DOI: http://dx.doi.org/10.5772/intechopen.112121*

(NaOH), to breakdown the silica and end up leaving zirconia or with a strong acid, like sulfuric acid (H2SO4), to solubilize the zirconia and produce a zirconium salt, leaving non-soluble silica. Zirconia may be created using the caustic-leach technique with a purity of up to 99.5%. Still, it must undergo subsequent chemical treatment, usually including dissolving the zirconia in acid to attain greater purity zirconia [32].

In reality, however, acid-leaching precipitates are gel-like, challenging to filter, and enclose numerous contaminants. Because of this, the basic sulfate precipitation using zirconium sulfate solution is favored, even though it is challenging to regulate the circumstances. To precipitate the basic sulfate, sulfuric acid or a sulfate salt is frequently added after the zirconium sulfate is converted to zirconium oxychloride. It has been discovered that creating zirconium compounds with good quality, including zirconia, is feasible by precipitating zirconium from zirconium sulfate solution at a low pH [32].

It is desired to utilize a zirconium sulfate solution with a zirconium level of more than 75 g/L and a sulfate content of more than 180 g/L. The ammonia source is introduced to the aqueous zirconium sulfate solution throughout the procedure of the present invention till the solution's pH value is between 0.1 and 2.5. Whenever the pH is in the interval of 1.0 to 2.0, it is preferable to stop adding the ammonia source. The zirconium compositions created using the procedure of the present invention are white, compressible, unrestricted, finely dispersed substances after washing and drying [32].

#### **3.2 Chlorination**

Chlorinating impure zirconia in the presence of carbon is among the best ways to create highly pure zirconia. To purge contaminants from the ZrCl4, partial solidification and sublimation procedures are performed in the range of temperature between 623 and 673 K. Additionally, highly pure ZrO2 is created by the interaction of pure solid ZrCl4 with water steam. Another crucial stage in the industrial scale of titanium and zirconium is chlorination in the presence of carbon. In the temperature range of 1000 K–1100 K, chlorine and ZrO2 do not really thermodynamically interact, and a reducing agent like carbon is necessary to complete the process. Consequently, the process is known as carbochlorination [33].

By determining the variation in the free energy of the different reactions, it is possible to know why a reducing agent is required. By creating a low oxygen potential environment, the existence of carbon atoms lowers the inclination of the production of oxides and stimulates the creation of chlorides. It has been discovered that between 1075 K and 1275 K, the following reaction (CO2 + C = 2CO) moves more slowly than during the chlorination process of ZrO2 with a <sup>Δ</sup>G of 4.6 kJ mol<sup>1</sup> at 1000 K to a 22.0 kJ mol<sup>1</sup> at 1100 K [34]. On the other hand, thermodynamically speaking, reaction 1 cannot take place at 1100K but other reactions may. It's possible that reaction (ZrO2 + C + 2Cl2 = ZrCl4 + CO2) with a <sup>Δ</sup>G of 248.3 kJ mol<sup>1</sup> and reaction (CO2 + C = 2CO) will produce reaction (ZrO2 + 2C + 2Cl2 = ZrCl4 + 2CO) with a ΔG of 270.4 kJ mol<sup>1</sup> .

#### **3.3 Colloidal processing of zirconia**

During lower sintering temperatures, high-density zirconia structures with decently crystal frames and improved mechanical characteristics may be created using fine nanocrystalline 3Y-TZP powders. However, throughout most of the production of the 3Y-TZP nanocrystalline initial crystals, significant agglomeration takes place [35]. The outer surface of the colloidal matter is decreased by agglomerates, which consist of networks of particles linked by van der Waals forces [36]. Ultimately, accumulation could lead to the development of undesirable variabilities, including defects, fractures, and porous surfaces with big granules, which can impair the mechanical capabilities of zirconia structures. As a result, attempts must be considered to prevent agglomeration due to consolidation. Powders are merged in greenish structures with the necessary shapes using various consolidation techniques, such as solid free-form manufacturing, wet slip casting, dry isostatic and uniaxial pressing. A slip casting is a common colloidal procedure that creates structures with a significant density and few harmful variabilities. By adjusting the intensity of the attracting and repelling interparticle interactions between zirconia particles, steady solutions with high particle dispersion may be created, which are necessary for reducing the production of agglomerates [37]. An electric double surface is produced by generating comparable charges on the interfaces of suspended particles of sufficient size [36].

CAD/CAM, which denotes computer-aided engineering and production, is one way to create zirconia copings and frames. An automatic manufacturing process using a software power tool follows the editing of a 3D model on a screen in the CAD/CAM manufacture of zirconia. There are two methods for creating CAD/CAM zirconia foundations: pre-sintered blanks can be "soft-machined" or completely sintered blanks can be "hard-machined". These foundations have undergone high-quality procedures to produce homogeneous material structures with little to no cavities, defects, or fractures. A binder is blended with partly stabilized zircon powder (silicone oxide 0.02%, yttrium oxide >4%, hafnium oxide >1%, zirconium dioxide 96%, aluminum oxide 1%) to create zirconia [38].

Well-dispersed zirconia solution has just been subjected to direct coagulation casting (DCC) and gel casting are two innovative methods for treating colloidal materials to produce greenish particles [39]. DCC focuses on creating ceramic components closer to their final form from suspensions of ceramic particles in concentration solutions. It combines the DLVO concept with colloidal ceramic formation. The saturated suspension is disrupted by the decomposition generating base, electrolyte, and acid, whether to boost the ionic strength or to let the pH reach the ceramic powder isoelectric point framework [35, 36].

#### **3.4 Powder processing of zirconia**

Because of their acceptable mechanical qualities, minimal neutron absorption cross-section, and superior corrosion tolerance, zirconium that concentrates on alloys has been employed extensively in industrial power stations.

Nevertheless, because zirconium has a great melting point (>1800°C) and a significant attraction for H, O, and other contaminating atoms, it is challenging to produce zirconium workpieces using standard methods. AM will make it easier to produce complex parts that are employed in a variety of industrial applications. The quality of the finished products, however, is heavily dependent on the raw powders. When used in the AM process, powders with desirable morphological properties display improved rheological properties and more optimum particle packing. Research on producing sphere powder from commercial products like Ti64 has advanced significantly. Spherical metal components have been created using various techniques, such as Electrode Induction Melting Gas Atomization, Plasma Atomization, Plasma Rotating Electrode Process, Plasma Spheroidization (most flexible approach), and Vacuum Induction Melting Inert Gas Atomization [40].

#### **3.5 Additive manufacturing (AM)**

3D printing technology commonly referred to as additive manufacturing techniques, opens up new possibilities for material shaping by increasing design flexibility, accelerating production, and minimizing waste and expense. The revolutionary possibilities of using these technologies to produce technical ceramics have been widely acknowledged, despite the ceramic industry's slower adoption of 3D printing technology than the polymer and metal industries. Stereolithography (SLA), one of the several 3D printing technologies currently accessible, offers advantages in the areas of printing resolution and precision, which—along with the exceptional efficiency of exterior coating—make it the ideal suitable AM technology for constructing ceramics [41]. The greatest range for achieving uniform mixing, according to an investigation by Jang et al. on the synthesis of zirconia employing DLP additive manufacturing, was 58 vol% of zirconia by volume. The 3-point bending durability improves as the volume fraction rises. The research did note that the viscosity rose quickly to 56 vol% [42]. SLA technique is built on the layer-by-layer polymerization of a liquid photocurable monomer incorporating ceramic particles; more specifically, it uses a beam of UV laser that shifts from one location to another while tracking the photo-polymerized pattern [43].

A near fabrication path to the manufacture of progressed ceramics with extremely complicated geometries is provided by additive manufacturing (AM). It does not involve the original building of a mold, making it a quick-response solution for engineers and designers to create new items [44].

A possible method for creating intricately shaped ceramic components with high accuracy is digital light processing (DLP) [43]. A different type of SLA utilizes a UV projector as the light source for treating an entire resin layer by layer, improving the speed of the process. Due to the variety of utilizations for which this material can be applied, including restorative dentistry and frameworks, fuel cells for monolithic support, tooling and blades, and other precision parts for various applications, including mechanical and thermal ones, 3D-printed zirconia is becoming more and more popular among technical ceramics [44].

DLP, which has excellent printing resolution, a high interfacial polish, and a rapid building process, is becoming increasingly popular for manufacturing ceramic components. However, compared to traditional ceramic processing, DLP is still in its developing phase [44].

Making completely dense, defect-free ceramics with characteristics equal to those of materials treated using traditional technologies is considered a difficult task. This requires the supervision of numerous manufacturing steps, including printing optimization techniques, the slurry preparation, and the sintering heating cycles. Nevertheless, even though DLP and SLA are established for zirconia 3D printing technologies, most articles briefly discuss the mechanical characteristics of the resulting materials [43] within the beginning, zirconia green entities are created for the specimen preparation using a heavily zirconia-loaded slurry on a DLP 3D printer utilizing a UV light with a wavelength of 405 nm. In **Figure 5**, a diagram of the DLP printing principles is displayed. For all builds, the depth can be adjusted at 25 μm. For further characterization and assessment, a variety of zirconia green bars, disks, and parts are acquired.

**Figure 5.** *Diagram illustrating the DLP printing principles [39].*

The extra slurry is then washed off the artificial green parts in an ultrasonic bath. The debinding and sintering then performed in a tubular furnace with an air flow [44].

#### **3.6 Thermal dissociation/calcination**

Calcination is the practice of heating a substance at 400, 600 and 800°C without allowing it to fuse to affect changes in its physical or chemical composition [45]. Electrospinning, a newly improved combination of the ceramic precursor zirconium acetylacetonate and the bond polymer polyacrylonitrile, may be utilized to create zirconia incorporating nanofibers. It is discovered that the steps that follow the ceramic precursor conversion occur simultaneously with the transformation of electrospun zirconium acetylacetonate/polyacrylonitrile fibers into zirconia nanofibers:

$$\text{Zr}(\text{C}\_{5}\text{H}\_{7}\text{O}\_{2})\_{4} \rightarrow \text{ZrO}(\text{OH})(\text{CH}\_{3}\text{COO})\_{3} \rightarrow \text{ZrO}(\text{CH}\_{3}\text{COO})\_{2} \rightarrow \text{t}-\text{ZrO}\_{2} \rightarrow \text{t} \tag{5}$$

$$-\text{ZrO}\_{2} + \text{m}-\text{ZrO}\_{2} \rightarrow \text{m}-\text{ZrO}\_{2}$$

Fibers are heated in two stages; first, they are heated to a temperature of 500°C with a heat rate of 1°C/min, and subsequently to a specified temperature with a heat rate of 5°C/min, calcining them at various temperatures between 500 and 1300°C for 1 hour. A low-temperature profile was adopted for the first annealing stage to ensure the sensitive removal of the ceramic precursor's breakdown products and binding polymer to minimize fiber breaking [46].

Additionally, furnaces for manufacturing glassware have often been built using and repaired with zircon refractories. Its breakdown tendency is a crucial zircon property that might affect furnace and glass performance. A decrease in the proportion of aluminum, titanium, iron, and alkali is necessary to lessen the rate of zircon deterioration [47].

Generally, the below process may be used to describe zircon dissociation:

*Processing of Zirconia DOI: http://dx.doi.org/10.5772/intechopen.112121*

$$\text{ZrSiO}\_4 \rightarrow \text{3ZrO}\_2 + \text{SiO}\_2 \tag{6}$$

where zircon is transformed into zirconia and silica, often by thermal methods at a temperature of around 1676°C. Zirconia acquires a tetragonal shape at 1173°C, whereas underneath this temperature, it exists as a monoclinic phase [47].

Zirconia precipitates are calcined at 800°C for 2 hours (h) in the air, which changes the monoclinic crystal structure and improves the crystallinity as well as the dimensions of the precipitate. Additionally, it was noted that zirconia with a cubic and tetragonal structure undergoes a partial transformation from its monoclinic state. In additional research, acidic and ammoniacal zirconium chloride solutions in different concentrations were used to create nanoscale zirconia precipitates at temps between 110 and 150°C for times ranging from 1 to 4 hours [48].

#### **3.7 Zirconia treatments**

Surface treatment to form a strong chemical connection with such composite resin is one method for successfully mending chemically inert zirconia foundations. Consequently, the effectiveness of dental restorations is determined by the adhesiveness of zirconia and composite resin.

It is extremely hard to chemically or physically change the zirconia ceramic surfaces because of its superior stiffness and chemical inertness to avoid corrosion [49]. In addition, unlike other types of ceramics, such as glass, zirconia is not etchable, making it difficult to carry out the adhesion processes [50]. According to earlier research, sandblasting significantly enhanced the ceramic surface's wettability, surface energy, and roughness. Because of this, the resin cement is retained by microinterlocking due to the bonding area's enhancement [49].

However, implant technology has been working hard to change zirconia in terms of morphological and bioactive features essential for suitable cell interaction and differentiation throughout most of the neighboring bone healing. Numerous physicochemical techniques have been utilized to improve zirconia properties, such as PVD, grit blasting, laser treatment, PVD, micro-machining, and CVD [51].

Although it has been asserted that zirconia pretreatment techniques like tribochemical silica coating, sol-gel processes, silicon nitride hydrolysis, and vapor-phase deposition technique increase resin adherence to zirconia, the long-term bond performance of tribochemical silica coating is in doubt. Condensed silanol layers produced by the sol-gel technique and hydrolyzed from tetraethyl orthosilicate are prone to cracking when heated, and coatings produced by silicon nitride hydrolysis or vapor-phase deposition require complex equipment and take a long time, making them unsuitable for use in clinical settings. With 5% HF inscription for 90–120 seconds at a pressure of 0.3 Mpa, a new glass ceramic spray deposition (GCSD) approach has recently been described to increase the zirconia bond strength. It is possible to create an extremely thin layer that does not alter the zirconia's physical characteristics by spraying glass-ceramic powders over zirconia surfaces which are subsequently sintered [52].

#### **3.8 Powder sintering**

During sintering, powder components are condensed and go under consolidation at a high temperature but still below their melting temperature. A particle substance is transformed into a rigid, compact design. Somewhere at macro scales, changes in geometry, dimension changes (shrinkage), and density variation may be seen, as well as changes in mechanical qualities like mechanical strength (as a result of shrinkage) [53].

To achieve a greater compactness and performance, more machined and sintering operations are required [44]. However, these existing techniques methods have a variety of drawbacks, including the inability to produce highly complex geometry because of the common usage of molds, their increased price, and their prolonged processing times. Furthermore, machining ceramic materials is challenging due to their extraordinary hardness and brittleness. Additionally, flaws and unwanted shrinkages may also be produced in the ceramic parts [54].

DLP-produced sintered ceramic components may have shrinkage problems. An effective way to address them is to scale the CAD/CAM model appropriately for each axis before printing to account for shrinks [44]. Through DLP, a single layer of material is first made, and by repeating this process, a body with three dimensions is developed. The three-dimensional cross-linked polymer that makes up the green body has ceramic fragments caught inside it. The components are then cleaned, debonded, and sintered to create the final thick ceramic part. This technique makes it possible to create intricate three-dimensional ceramic structures with excellent precision and creative freedom [55].

The microstructure changes throughout sintering, and this development is characterized by a rise in grain compaction and rearrangement and cohesive bonds among granules develop in the early stages. Because of the mass transmission, the bonds between particles expand as the sintering process continues. Surface and grain boundary diffusion are often the primary mass transport modes in sintering. Surface tension and bonds'stresses cause particle attraction, which causes the system to contract. The decrease and occasionally the actual eradication of material porosity is a result of neck development and shrinking [53].

Owing to the possibility of the ceramic material's cracking or breaking, thin restorations for minimally invasive dentistry might be challenging to create employing the subtractive method. In addition, subtractive manufacturing usually results in significant cutting tool usage and significant volumes of generated waste (zirconia powder) after milling. Additionally, zirconia's resilience and lifetime are improved by surface treatment and adhesive bonding with primers [55].

#### **4. Analysis methods**

#### **4.1 Microstructural analysis**

For microstructural characterization, Raman microanalysis can be demonstrated. On the other hand, for studying the chemical composition, high vacuum X-ray energy dispersive microanalysis, X-ray photoelectron spectroscopy (XPS) are usually used. XPS is accelerated under a voltage of 14 kV, emission of current of o.2 A, pressure of 10<sup>9</sup> mbar, energy resolution of 0.30 eV, maximum power of 2.8 kW, sampling area of 6 0.5 mm sampling area, and around 90° take-off angle. Finally, to charge compensation, an electron flood gun works at 4 eV. All spectra can be shown and recorded on the binding energy with an excellent resolution of 150 eV pass energy [56].

#### *Processing of Zirconia DOI: http://dx.doi.org/10.5772/intechopen.112121*

In order to recognize and define the pattern of the tetragonal (which can be demonstrated by 145 and 262 cm<sup>1</sup> Raman shift) and monoclinic (by 180 and 190 cm<sup>1</sup> Raman shift) ZrO2 phases just at the surface area, then the cervical collar that is prepared for XRD investigation is examined. The following requirements are used to conduct a Raman microscope: 100 m slit, Ar laser (532 nm), 10 mW at the sample, a grating of 1800 grit/mm, a confocal hole of 1000 μm, and a sampling duration of 10s.

The microscope's optical system independently finds and examines three locations at every implant surface site (collar/root). 20 35 m regions are chosen and examined at 5 m increments with a 5 s scan time in order to map the monoclinic ZrO2 phase [56].

#### **4.2 Phase characterization**

For morphological analysis, LV-SEM is used. And for the roughness, optical profilometry is used. In X-ray diffraction (XRD), a sample from each implant is embedded in epoxy resin and sliced into longitudinal sections using a microtome while being continually cooled by water to test for the presence of tetragonal and monoclinic ZrO2 phases across the whole implantation. The materials are smoothed using SiC paper and polished using 3 M diamond paste, and then for 3 minutes, ultrasonic cleaning in distilled water is applied [56]. The zirconia X-ray diffraction spectra is displayed in **Figure 6**. Their X-ray diffraction patterns may identify zirconia's monoclinic and metastable tetragonal phases [57].

The threaded portions of the implants' 3D surface roughness characteristics are evaluated using optical profilometry. At 10–100 magnification, an optical profiler may be utilized to look at the gap between two subsequent implant threads. The roughness metrics of a 3D surface, including arithmetic mean deviation (Sa), root average square deviation variance (Sq), and max peak to valley altitude (Rt) are then measured using Veeco Vision software [56].

**Figure 6.**

*Diagrammatic representation of the parameters (L, W, and H) change along the zirconia DLP pathway [44].*

#### **4.3 Mechanical testing**

Using the techniques specified in **Table 2** at ambient temperature, the mechanical characteristics, including fracture toughness, Vickers hardness, and flexural strength, are thoroughly studied. A Weibull assessment of the tensile and flexural data is thus carried out to determine the possibility that zirconia would rupture. By employing the single-edge V-notched beam (SEVNB) technique and indentation, correspondingly, the fracture toughness value (KIC) is assessed (**Table 3**) [44].

It is crucial to pick a reference based on the actual indentation fracture morphology since the selection of the equations also depends upon the type of crack. A femtosecond laser is used to construct an incredibly sharp V-notch (0.5 m, indicated by a red dashed line as seen in **Figure 7**) to measure fracture toughness accurately [49, 58, 59].

**Figure 7** shows how U-grooves are created at particular thicknesses using a reduced-speed blade and diamond rims with a 200 m thickness under irrigation water. A 2.9 W femtosecond laser is now being used to create a crisp V-notch just at the bottom of the U-grooves. With a repeating rate of 100 kHz, the femtosecond lasers produced 290 fs linearly polarized pulses at 515 nm [50, 58].

#### **5. Future perspectives of zirconia**

#### **5.1 Nano zirconia**

Nano solids, which are tiny structures of ZrO2, have been extensively proposed. ZrO2 on a nanoscale, which exhibits better mechanical properties and superior biocompatibility, is frequently included into many technologies utilized in tissue engineering and dental applications [51]. Even though sophisticated powder synthesis processes can generate nano-sized particles [60–62]. Nano zirconia also showed a promising future for fuel cell applications. Cubic ZrO2 nanoparticle production is challenging because of the range of phases that the reactions create. In a previous study, a simple precipitation method was established to adjust the form and crystallinity of cubic (Arkelite) and monoclinic (baddeleyite) zirconia nanoparticles. The

**Table 2.**

*Zirconia's carbochlorination reactions and the change in Gibbs free energy [34].*

#### *Processing of Zirconia DOI: http://dx.doi.org/10.5772/intechopen.112121*

**Table 3.**

*Investigation techniques for mechanical properties [44].*

#### **Figure 7.** *XRD spectra of zirconia [57].*

manufactured cubic and monoclinic zirconia can be put into the Nafion® membrane to increase the fuel cell's efficiency. The polytetrafluoroethylene backbone and perfluorinated ether sidechain are characteristics of the proton conductor electrolyte Nafion®. Additionally, due to the transpiration of water that leads the membrane to buckle, Nafion® loses conductivity at a higher temperature of 100 C [31].

Toward the latter situation, the rise in clinical defects in the dental sector has been noticed owing to veneer chipping due to pressure accumulation throughout fabrication. Additionally, the use of ceramics' nanocrystalline structure has gained the interest of engineers since they strengthen their resistance to low-temperature deterioration (LTD) [63].

Current efforts involve synthesizing nanoparticle agglomerates within 30 mm aggregates. The high-velocity oxy-fuel (HVOF) method can be subjected to spray nano-zirconia powders made in radio frequency (RF) plasma. This method employs relatively low flame temperatures (<3000°C) to ensure that the particles are only a little heated. The nano-zirconia particle-reinforced coatings are examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The effects of the post-spray treatment on the coatings are investigated [62].

Wet-chemical synthesis techniques, such as co-precipitation, hydrothermal synthesis, and sol–gel preparation, are primarily used to manufacture nano-ZrO2 powders. The physical approach cannot achieve nanoscale results, and the gas-chemical process is too expensive to be repeated in a real-world setting [64].

The nanoparticles'surfaces are treated with various surfactants that have different attaching head groups and carbon chain lengths. Because of their distinct nature and properties, quantum dots (QDs) fall within the special category of nanomaterials. A QD is defined as an individual semiconducting nanocrystal that ranges in dimension from 2 to 10 nm. Several techniques, including soot vapor deposition, microwave synthesis, laser ablation or chemical oxidation of graphite, and graphite oxidation heat-induced oxidation of a molecular precursor, can be used to create QDs. In recent research, scientists devised a simple approach for producing a highly effective photocatalytic composite by adsorbing carbon quantum dots (CQDs) onto the surface of ZrO2 NPs as demonstrated in **Figure 8**. The developed

#### **Figure 8.**

*(A) Diagrammatic representation of SEVNB samples. (B) Equipment for creating a razor-sharp V-notch using a blade [49, 58].*

**Figure 9.** *TEM pictures of ZrO2 nanoparticles with CQD embellishments [65].*

photocatalyst could be useful for the rapid fading of textile colors. The composite's production method, which entailed calcination of an ammonium citrate solution, is used to make QDs. Then, using a conventional solvent-based chemical method, produced QDs are adsorbed onto the surface of ZrO2 NPs with ultrasound assistance **Figure 9** [65].

Other studies show another development regarding a nano-structured glasszirconia in order to increase the resilience of the interface between dental zirconia substrate and veneered porcelain. A new SiO2–Li–Al–O3 material to create a glasszirconia nanostructure, prepped (SLA) glass was infiltrated through the outermost layer of fully sintered dental zirconia [66].

#### **6. Conclusions**

Zirconia has been indicated and used in various industries including, dentistry, glassware, and electronics. This comes from different reasons especially, its mechanical, electrical, thermal conductivity, and tribological properties. Due to the high demand, zirconia supply had to be produced after purifying zirconium compounds by chemical processing using acids or bases. Different processes might be performed to produce pure zirconia, such as chlorination under a high-temperature range between 623 K and 673 K, colloidal processing of zirconia, and additive manufacturing which uses a 3D printing technology with high precision and resolution. Zirconia's microstructure is analyzed by XPS and X-ray energy, phase characterization by XRD, and Mechanical properties are tested analyze the fracture toughness and flexural strength. The uses of zirconia have been constantly increasing over the last years, and the most discussed structures are nano zirconia integrated with other systems such as CQDs to enhance its characteristics.

#### **Conflict of interest**

The authors declare no conflict of interest.

### **Author details**

Ghassan Albarghouti\* and Sojood Mahmoud Farhan Darwish Birzeit University, Ramallah, Palestine

\*Address all correspondence to<EMAIL_ADDRESS>
© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### **References**

[1] Yan LL, He ZY, Beier C, Klemd R. Zircon trace element constrains on the link between volcanism and plutonism in SE China. Lithos. 2018;**320–321**:28-34. DOI: 10.1016/j.lithos.2018.08.040

[2] Yakymchuk C. Prograde zircon growth in migmatites. Journal of Metamorphic Geology. 2023;**2023**

[3] Selby JH, Committee ZM, Africa S. The industrial uses of zircon and zirconia, and the radiological consequences of these. Atomic Energy. 2007;**51**:1-14

[4] Ferreira P, Ferreira A, Rocha J, Soares MR. Synthesis and structural characterization of zirconium silicates. Chemistry of Materials. 2001;**13**(2): 355-363

[5] Yugeswaran S, Selvarajan V, Dhanasekaran P, Lusvarghi L. Transferred arc plasma processing of mullite-zirconia composite from natural bauxite and zircon sand. Vacuum. 2008; **83**(2):353-359

[6] Klinger M, Kempe U, Pöpl A, Böttcher R, Trinkler M. Paramagnetic hole centres in natural zircon and zircon colouration. European Journal of Mineralogy. 2012;**24**(6):1005-1016

[7] Mineralogical Studies on Zircon [Internet]. 2009. Available from: https:// www.researchgate.net/publication/ 277093078

[8] Aia MA. Journal of the Electrochemical Society. 1967; **114**(4):367

[9] Bona AD, Pecho OE, Alessandretti R. Zirconia as a dental biomaterial. Materials. 2015;**8**(8):4978-4991

[10] Li X, Huang J, Cao Q, Liao Y, Feng M. Investigation on polishing the concave surface of zirconia ceramics with magnetic compound fluid enhanced by hydration reaction. Magnetochemistry. 2023;**9**(3):74

[11] Tyagi B, Sidhpuria K, Shaik B, Jasra RV. Synthesis of nanocrystalline zirconia using sol-gel and precipitation techniques. Industrial and Engineering Chemistry Research. 2006;**45**(25): 8643-8650

[12] Manicone PF, Rossi Iommetti P, Raffaelli L. An overview of zirconia ceramics: Basic properties and clinical applications. Journal of Dentistry. 2007; **35**(11):819-826

[13] Piconi C, Maccauro G. Zirconia as a ceramic biomaterial. Biomaterials. 1999; **20**(1):1-25

[14] Herr C, Rizo-gorrita M, Maza-solano S, Serrera-figallo M, Torres-lagares D, Yttria-stabilized CADCAM, et al. A Review on CAD/CAM Yttria-Stabilized Tetragonal Zirconia. 2022

[15] Cadi-Essadek A, Roldan A, de Leeuw NH. Density functional theory study of the interaction of H2O, CO2 and CO with the ZrO2 (111), Ni/ZrO2 (111), YSZ (111) and Ni/YSZ (111) surfaces. Surface Science. 2016;**653**:153-162

[16] Evans AG, Marshall DB, Burlingame NH. Transformation toughening in ceramics. Advances in Ceramics. 1981;**3**(190144):202-216

[17] Basu B. Toughening of yttriastabilised tetragonal zirconia ceramics. International Materials Reviews. 2005; **50**(4):239-256

[18] Rahmawati F, Permadani I, Syarif DG, Soepriyanto S. Electrical properties of

various composition of yttrium dopedzirconia prepared from local zircon sand. International Journal of Technology. 2017; **8**(5):939-946

[19] Saridag S, Tak O, Alniacik G. Basic properties and types of zirconia: An overview. World Journal of Stomatology. 2013;**2**(3):40

[20] De Souza RH, Kaizer MR, Borges CEP, Fernandes ABF, Correr GM, Diógenes AN, et al. Flexural strength and crystalline stability of a monolithic translucent zirconia subjected to grinding, polishing and thermal challenges. Ceramic International. 2020; **46**(16):26168-26175. DOI: 10.1016/j. ceramint.2020.07.114

[21] Hvizdoš P, Puchý V, Duszová A, Dusza J, Balázsi C. Tribological and electrical properties of ceramic matrix composites with carbon nanotubes. Ceramics International. 2012;**38**(7): 5669-5676

[22] Tanaka H, Maeda T, Narikiyo H, Morimoto T. Mechanical properties of partially stabilized zirconia for dental applications. Journal of Asian Ceramic Societies. 2019;**7**(4): 460-468

[23] Tong Z, Ma Q, Ni Y, Mei T, Li J, Dong G. Tribological properties of carbon fabric reinforced phenolic-based composites containing CNTs@MoS2 hybrids. Journal of Materials Science. 2019;**54**(23):14354-14366

[24] Chen H, Zhang Y, Ding C. Tribological properties of nanostructured zirconia coatings deposited by plasma spraying. Wear. 2002;**253**(7–8):885-893

[25] Vest RW, Tallan NM. Electrical properties and zirconia: 11, Tetragonal Defect Structure of Phase and Inversion [26] Venkataraj S, Geurts J, Weis H, Kappertz O, Njoroge WK, Jayavel R, et al. Structural and optical properties of thin lead oxide films produced by reactive direct current magnetron sputtering. Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films. 2001;**19**(6):2870

[27] Clarke DR, Levi CG. Materials design for the next generation thermal barrier coatings. Annual Review of Materials Research. 2003;**33**:383-417

[28] Raza M. Oxygen vacancy stabilized zirconia (OVSZ); synthesis and properties What drives the phase formation of reactively sputtered transition metal oxide films ? View project. Available from: https://www.re searchgate.net/publication/315142103

[29] Gautam C, Joyner J, Gautam A, Rao J, Vajtai R. Zirconia based dental ceramics: Structure, mechanical properties, biocompatibility and applications. Dalton Transactions. 2016; **45**(48):19194-19215

[30] Mistarihi Q, Umer MA, Kim JH, Hong SH, Ryu HJ. Fabrication of ZrO2 based nanocomposites for transuranic element-burning inert matrix fuel. Nuclear Engineering and Technology. 2015;**47**(5):617-623

[31] Sigwadi R, Mokrani T, Dhlamini M. The synthesis, characterization and electrochemical study of zirconia oxide nanoparticles for fuel cell application. Physica B Condensed Materials. 2020; **2020**:581

[32] Ngian KF, Hartshorn AJ, Jenkins DH. Process for the Purification of Zirconium Compounds. Vol. 191989

[33] Movahedian A, Raygan S, Pourabdoli M. The chlorination kinetics of zirconium dioxide mixed with carbon black. Thermochimica Acta. 2011;**512**(1– 2):93-97

[34] Landsberg A, Hoatson CL, Block FE. The Chlorination Kinetics of Zirconium Dioxide in the Presence of Carbon and Carbon Monoxide

[35] Rami ML, Meireles M, Cabane B, Guizard C. Colloidal stability for concentrated zirconia aqueous suspensions. Journal of the American Ceramic Society. 2009;**2009**

[36] Aboras M, Muchtar A, Azhari CH, Yahaya N, Mah JCW. Enhancement of the microstructural and mechanical properties of dental zirconia through combined optimized colloidal processing and cold isostatic pressing. Ceramic International. 2019;**45**(2):1831-1836. DOI: 10.1016/j.ceramint.2018.10.072

[37] Lange FF. Densification of powder compacts: An unfinished story. Journal of the European Ceramic Society. 2008; **28**(7):1509-1516

[38] Ardekani KT, Ahangari H, Leila F. Marginal and internal fit of CAD/CAM and slip-cast made zirconia copings. Journal of Dental Research, Dental Clinics, Dent Prospects. 2012;**6**(2):42-48. Available from: http://dentistry.tbzmed. ac.ir/joddd

[39] Xie Z, Ma J, Xu Q, Huang Y, Cheng YB. Effects of dispersants and soluble counter-ions on aqueous dispersibility of nano-sized zirconia powder. Ceramics International. 2004; **30**(2):219-224

[40] Kaga T, Application F, Data P, Andrews PE, Melvyn J. United States Patent (19). 1991;(19)

[41] Fu X, Zou B, Xing H, Li L, Li Y, Wang X. Effect of printing strategies on forming accuracy and mechanical

properties of ZrO2 parts fabricated by SLA technology. Ceramics International. 2019;**45**(14):17630-17637

[42] Kang JH, Sakthiabirami K, Kim HA, Hosseini Toopghara SA, Jun MJ, Lim HP, et al. Effects of UV absorber on zirconia fabricated with digital light processing additive manufacturing. Materials. 2022; **15**(24)

[43] Coppola B, Schmitt J, Lacondemine T, Tardivat C, Montanaro L, Palmero P. Digital light processing stereolithography of zirconia ceramics: Slurry elaboration and orientationreliant mechanical properties. Journal of the European Ceramic Society. 2022;**42** (6):2974-2982

[44] Sun J, Chen X, Wade-Zhu J, Binner J, Bai J. A comprehensive study of dense zirconia components fabricated by additive manufacturing. Additive Manufacturing. 2021;**2021**:43

[45] Saikumari N, Dev SM, Dev SA. Effect of calcination temperature on the properties and applications of bio extract mediated titania nano particles. Scientific Reports. 2021;**11**(1)

[46] Rodaev VV, Razlivalova SS, Zhigachev AO, Vasyukov VM, Golovin YI. Preparation of zirconia nanofibers by electrospinning and calcination with zirconium acetylacetonate as precursor. Polymers (Basel). 2019;**11**(6)

[47] Pavlik RS, Holland HJ, Payzant EA. Thermal Decomposition of Zircon Refractories

[48] Saricimen H, Ul-Hamid A, Quddus A. Effect of calcination on nanoscale zirconia produced by high temperature hydrolysis. Protection of Metals and Physical Chemistry of Surfaces. 2015; **51**(5):803-811

[49] Li R, Wang C, Ma SQ, Liu ZH, Zang CC, Zhang WY, et al. High bonding strength between zirconia and composite resin based on combined surface treatment for dental restorations. Journal of Applied Biomaterials and Functional Materials. 2020;**2020**:18

[50] Russo DS, Cinelli F, Sarti C, Giachetti L. Adhesion to zirconia: A systematic review of current conditioning methods and bonding materials. Dentistry Journal. 2019;**7**

[51] Schünemann FH, Galárraga-Vinueza ME, Magini R, Fredel M, Silva F, Souza JCM, et al. Zirconia surface modifications for implant dentistry. Materials Science and Engineering C. 2019;**98**:1294-1305

[52] Shen D, Wang H, Shi Y, Su Z, Hannig M, Fu B. The effect of surface treatments on zirconia bond strength and durability. Journal of Functional Biomaterials. 2023;**14**(2)

[53] Rojek J, Nosewicz S, Maździarz M, Kowalczyk P, Wawrzyk K, Lumelskyj D. Modeling of a sintering process at various scales. In: Procedia Engineering. Vol. 2017. 2017. pp. 263-270

[54] Grossin D, Montón A, Navarrete-Segado P, Özmen E, Urruth G, Maury F, et al. A review of additive manufacturing of ceramics by powder bed selective laser processing (sintering/melting): Calcium phosphate, silicon carbide, zirconia, alumina, and their composites. Open Ceramics. 2021;**2021**:5

[55] Patil A, DJ D, Bomze D, Gopal V. Wear behaviour of lithography ceramic manufactured dental zirconia. BMC Oral Health. 2023;**23**(1):276. Available from: h ttps://bmcoralhealth.biomedcentral.com/a rticles/10.1186/s12903-023-02974-4

[56] Zinelis S, Thomas A, Syres K, Silikas N, Eliades G. Surface characterization of zirconia dental implants. Dental Materials. 2010;**26**(4):295-305

[57] Zhang QH, Feng YQ, Shi-Lu D. Preparation and Characterization of Zirconia-Silica and Zirconia-Magnesia Supports for Normal-Phase Liquid Chromatography

[58] Yang J, Huang Y, Meier LP, Wyss H, Tervoort E, Gauckler LJ. Direct coagulation casting via increasing ionic strength. In: Key Engineering Materials. Trans Tech Publications Ltd; 2002. pp. 631-636

[59] Xu J, Gan K, Yang M, Qu Y, Wu J, Yang J. Direct coagulation casting of yttria-stabilized zirconia using magnesium citrate and glycerol diacetate. Ceramics International. 2015; **41**(4):5772-5778

[60] Strecker K, Ribeiro S, Hoffmann MJ. Fracture toughness measurements of LPS-SiC: A comparison of the indentation technique and the SEVNB method. Materials Research. 2005;**8**

[61] Ćorić D, Renjo MM, Ćurković L, Žmak I. Indentation Fracture Toughness of Y-TZP Dental Ceramics

[62] Li H, Khor KA, Kumar R, Cheang P. Characterization of hydroxyapatite/nano-zirconia composite coatings deposited by high velocity oxyfuel (HVOF) spray process. Surface and Coating Technology. 2004;**182**(2–3): 227-236

[63] Kocjan A, Pouchly V, Shen Z. Processing of zirconia nanoceramics from a coarse powder. Journal of the European Ceramic Society. 2015;**35**(4): 1285-1295

[64] Hu C, Sun J, Long C, Wu L, Zhou C, Zhang X. Synthesis of nano zirconium oxide and its application in dentistry.

*Processing of Zirconia DOI: http://dx.doi.org/10.5772/intechopen.112121*

Nanotechnology Reviews. 2019;**8**(1): 396-404

[65] Ratnayake SP, Mantilaka MMMGPG, Sandaruwan C, Dahanayake D, Murugan E, Kumar S, et al. Carbon quantum dots-decorated nano-zirconia: A highly efficient photocatalyst. Applied Catalysis A: General. 2019;(570):23-30

[66] Zhou M, Zhang X, Zhang Y, Li D, Zhao Z, Wang Q, et al. Construction of nanostructured glass-zirconia to improve the Interface stability of dental bilayer zirconia. Nanomaterials. 2023; **13**(4)

Section 4