本研究採用非晶質奈米氮化矽摻雜氧化釔之奈米粉體作為起始原料，利用碳熱還原處理與火花電漿燒結技術製備單一相奈米氮化矽陶瓷，並以摻雜氧化釔及氧化鋁之非晶質奈米氮化矽粉體作為對照組，探討奈米碳黑添加量與助燒結劑之組成，對於單一相奈米氮化矽陶瓷的微觀結構與機械性質的影響。
首先討論摻雜不同含量(2 wt%與6 wt%)氧化釔作為助燒結劑之奈米氮化矽的燒結行為，實驗結果顯示：摻雜2 wt%氧化釔之奈米氮化矽粉末經火花電漿燒結過後，由於液相的生成量不足，試樣並無法緻密；較多摻雜量的6 wt%氧化釔之奈米氮化矽粉末則能生成足夠的液相量，使氮化矽完成α→β相變化，進而完全緻密。由於奈米粉體比表面積過大，容易在表面殘留過多的氧而形成二氧化矽，故於燒結體內皆可發現許多氧氮化矽生成，除了造成燒結體機械性質降低，微結構也顯示有許多大尺寸之微米尺寸晶粒生成，經分析確定此微米尺寸晶粒大多為氧氮化矽，而氮化矽仍保持奈米尺寸。
接著藉由碳熱還原處理將摻雜6 wt%氧化釔之奈米氮化矽粉體中過多的氧含量去除，並與摻雜6 wt%氧化釔與8 wt%氧化鋁之奈米氮化矽粉體相比較。研究顯示：碳熱還原處理可有效地降低粉體中的氧含量，且減少二氧化矽對於液相量的貢獻，因此收縮曲線有往高溫移動的趨勢；其中在碳黑添加量3 wt%(含氧化釔之試樣)與6 wt%(含氧化釔及氧化鋁之試樣)以上時能有效抑制第二相氧氮化矽生成，形成單一相氮化矽。
此外，經碳熱處理後，由於粉體彼此相異的液相系統，形成不同組成的起始粉體，並造成燒結體燒結時不同的液相溶質濃度，產生微觀結構的差異；含有較多α相氮化矽的含氧化釔起始粉體，傾向形成高長寬軸比的氮化矽晶粒，為次微米/奈米結構；而擁有較多β相氮化矽的含氧化釔及氧化鋁起始粉體，較低的表面能使晶粒成長受到抑制，形成等軸狀的奈米結構。
機械性質方面，經碳熱處理後之燒結體，含氧化釔試樣由於晶粒有較大的長寬軸比，因此有較佳的韌性性質；含氧化釔及氧化鋁試樣則由於具有奈米尺寸的微觀結構，因此有較佳的硬度性質。此外，由於晶粒尺寸降低與第二相的消除，耐磨耗性質可有效地提升，其中具有良好的高溫玻璃相性質的含氧化釔試樣，有最佳的磨耗性質，磨耗率由未經碳熱處理的4.07 × 10-5 mm3/Nm大幅降低至碳熱處理後的2.16 × 10-5 mm3/Nm，降低幅度達到53.1%。

An amorphous nano-Si3N4 doped with Y2O3 was used as starting powders and treated by carbothermal reduction treatment (CRT) to remove excess oxygen. As a reference, amorphous nano-Si3N4 doped with Y2O3 and Al2O3 was also used as a starting material. The aim of this work is to fabricate fully densified Si2N2O phase-free Si3N4 nanoceramics by combining CRT and spark plasma sintering (SPS). The effects of different carbon black contents and sintering additives on microstructural evolution and mechanical properties of sintering bulks were investigated.
First, we developed the densification behavior of nano-Si3N4 doped with Y2O3. When decreasing the amount of sintering additive from 6 wt% to 2 wt%, there is less liquid phase formation and is hard to complete the α-β phase transformation and then get full densification. Because In liquid-phase sintering, the liquid provides the vehicle for rapid mass transport and thus rapid densification. The nano-Si3N4 doped with 6 wt% Y2O3 can achieve full densification but there is too much secondary phase formation, because nanosized powder generally contains a significant amount of oxygen, which results in the secondary crystalline Si2N2O phase in the sintering bulks.
After performing CRT, the formation of secondary phase was effectively suppressed at calcination temperature of 1400°C and fully densified Si2N2O phase-free β-Si3N4 nanoceramics were fabricated when adding 3 wt% (with Y2O3) and 6 wt% (with Y2O3 and Al2O3) carbon black. However, when adding too much carbon black will reduce the formation of SiO2, which reducing the amount of liquid phase and α-β phase transformation cannot complete.
For microstructure, a nanostructure were observed in the specimens with Y2O3 and Al2O3 and a submicron/nanostructure with Y2O3. Due to different liquid systems, α-β phase transformation of nano-Si3N4 with Y2O3 and Al2O3 was more pronounced than that with Y2O3, for the same calcination temperature. Therefore, nano-Si3N4 with Y2O3 and Al2O3 has higher β phase content of initial powder than that with Y2O3 and can minimize the driving force for grain growth.
For mechanical properties, the elimination of Si2N2O and different microstructures can effectively enhance the mechanical properties, such as hardness, toughness and wear properties. The wear rate of Si2N2O phase-free Si3N4 nanoceramics contained Y2O3 has been decreased to 53.1% (from 4.07 × 10-5 mm3/Nm to 2.16 × 10-5 mm3/Nm) compared to the specimen without CRT.

[1] Z. Krstic and V. D. Krstic, "Silicon nitride: the engineering material of the future," Journal of Materials Science, vol. 47, pp. 535-552, 2012.
[2] F. L. Riley, "Silicon nitride and related materials," Journal of the American Ceramic Society, vol. 83, pp. 245-265, 2000.
[3] G. G. H. Deeley, J.M. Moore, N.C., "Dense Silicon Nitride," Powder Metallurgy, vol. 8, pp. 145-151, 1961.
[4] A. Tsuge, K. Nishida, and M. Komatsu, "Effect of Crystallizing the Grain‐Boundary Glass Phase on the High‐Temperature Strength of Hot‐Pressed Si3N4 Containing Y2O3," Journal of the American Ceramic Society, vol. 58, pp. 323-326, 1975.
[5] S. Boskovic, L. Gauckler, G. Petzow, and T. Tien, "Reaction sintering forming beta-Si3N4 solid solutions in the system Si, Al/N, O. I- Sintering of SiO2-AlN mixtures," Powder Metallurgy International, vol. 9, pp. 185-189, 1977.
[6] M. J. Hoffmann, "High-Temperature Properties of Yb-Containing Si3N4," in Tailoring of Mechanical Properties of Si3N4 Ceramics. vol. 276, M. Hoffmann and G. Petzow, Eds., ed: Springer Netherlands, pp. 233-244, 1994.
[7] J. Wallace and J. Kelly, "Grain growth in Si3N4," Key Engineering Materials, vol. 89, pp. 501-508, 1993.
[8] H. Klemm, "Silicon Nitride for High‐Temperature Applications," Journal of the American Ceramic Society, vol. 93, pp. 1501-1522, 2010.
[9] H. Gleiter, "Nanostructured materials: basic concepts and microstructure," Acta materialia, vol. 48, pp. 1-29, 2000.
[10] R. Vassen and D. Stöver, "Processing and properties of nanophase non-oxide ceramics," Materials Science and Engineering: A, vol. 301, pp. 59-68, 2001.
[11] A. Chokshi, A. Rosen, J. Karch, and H. Gleiter, "On the validity of the Hall-Petch relationship in nanocrystalline materials," Scripta Metallurgica, vol. 23, pp. 1679-1684, 1989.
[12] J. H. Kim, B. Venkata Manoj Kumar, S. H. Hong, and H. D. Kim, "Fabrication of silicon nitride nanoceramics and their tribological properties," Journal of the American Ceramic Society, vol. 93, pp. 1461-1466, 2010.
[13] M. HOTTA and J. HOJO, "Nanostructure control of liquid-phase sintered Si3N4 ceramics by spark plasma sintering," Journal of the Ceramic Society of Japan, vol. 117, pp. 1302-1305, 2009.
[14] K. Matsuhiro and T. Takahashi, "Physical properties of sintered silicon nitride controlled by grain boundary chemistry and microstructure morphology," in MRS International Meeting on Advanced Materials, 1 st, Tokyo, Japan, pp. 11-15, 1989.
[15] E. T. Turkdogan, P. M. Bills, and V. A. Tippett, "Silicon nitrides: Some physico-chemical properties," Journal of Applied Chemistry, vol. 8, pp. 296-302, 1958.
[16] A. Zerr, G. Miehe, G. Serghiou, M. Schwarz, E. Kroke, R. Riedel, et al., "Synthesis of cubic silicon nitride," Nature, vol. 400, pp. 340-342, 1999.
[17] D. Hardie and K. Jack, "Crystal structures of silicon nitride," 1957.
[18] P. Šajgalík, Z. Lenčéš, and M. Hnatko, "Nitrides," Ceramics Science and Technology. Volume 2: Materials and Properties, pp. 59-89, 2010.
[19] R. C. Sangster, "FORMATION OF SILICON NITRIDE: FROM THE 19 TH TO THE 21 ST CENTURY," Materials Science Foundations, p. 948, 2005.
[20] A. I. H. Committee, Engineered Materials Handbook: Ceramics and glasses: ASM International, 1991.
[21] G. Terwilliger and F. Lange, "Pressureless sintering of Si3N4," Journal of Materials Science, vol. 10, pp. 1169-1174, 1975.
[22] R. Grun, "The crystal structure of-Si3N4: structural and stability considerations between-and-Si3N4," Acta Crystallographica Section B: Structural Crystallography and Crystal Chemistry, vol. 35, pp. 800-804, 1979.
[23] P. Dörner, L. J. Gauckler, H. Krieg, H. L. Lukas, G. Petzow, and J. Weiss, "Calculation of heterogeneous phase equilibria in the SiAlON system," Journal of Materials Science, vol. 16, pp. 935-943, 1981.
[24] C. Brosset and I. Idrestedt, "Crystal structure of silicon oxynitride, Si2N2O," Nature, vol. 201, p. 1211, 1964.
[25] W.-Y. Ching, "Electronic Structure and Bonding of All Crystalline Phases in the Silica–Yttria–Silicon Nitride Phase Equilibrium Diagram," Journal of the American Ceramic Society, vol. 87, pp. 1996-2013, 2004.
[26] Z. K. Huang, P. Greil, and G. Petzow, "Formation of silicon oxinitride from Si3N4 and SiO2 in the presence of Al2O3," Ceramics International, vol. 10, pp. 14-17, 1984.
[27] M. Ohashi, S. Kanzaki, and H. Tabata, "Processing, Mechanical Properties, and Oxidation Behavior of Silicon Oxynitride Ceramics," Journal of the American Ceramic Society, vol. 74, pp. 109-114, 1991.
[28] R. Larker, "Reaction Sintering and Properties of Silicon Oxynitride Densified by Hot Isostatic Pressing," Journal of the American Ceramic Society, vol. 75, pp. 62-66, 1992.
[29] W. Y. Ching and S.-Y. Ren, "Electronic structures of Si_{2}N_{2}O and Ge_{2}N_{2}O crystals," Physical Review B, vol. 24, pp. 5788-5795, 1981.
[30] K. White, F. Yu, and Y. Fang, "In situ Reinforced Silicon Nitride — Barium Aluminosilicate Composite," in Handbook of Ceramic Composites, N. Bansal, Ed., ed: Springer US, pp. 251-275, 2005.
[31] C. P. Doǧan and J. A. Hawk, "Microstructure and abrasive wear in silicon nitride ceramics," Wear, vol. 250, pp. 256-263, 2001.
[32] K. Kijima and S.-i. Shirasaki, "Nitrogen self-diffusion in silicon nitride," The Journal of Chemical Physics, vol. 65, pp. 2668-2671, 1976.
[33] K. Negita, "Effective sintering aids for Si3N4 ceramics," Journal of Materials Science Letters, vol. 4, pp. 755-758, 1985.
[34] K. Negita, "Ionic radii and electronegativities of effective sintering aids for Si3N4 ceramics," Journal of Materials Science Letters, vol. 4, pp. 417-418, 1985.
[35] W. D. Kingery, "Densification during Sintering in the Presence of a Liquid Phase. I. Theory," Journal of Applied Physics, vol. 30, pp. 301-306, 1959.
[36] J. Weiss, "Silicon Nitride Ceramics: Composition, Fabrication Parameters, and Properties," Annual Review of Materials Science, vol. 11, pp. 381-399, 1981.
[37] H. Hausner, G. L. Messing, S. Hirano, and D. K. Gesellschaft, Ceramic powder processing science: proceedings of the second international conference, Berchtesgaden (Bavaria) FRG, October 12-14, 1988: Deutsche Keramische Gesellschaft, 1989.
[38] G. Woetting, H. Feuer, and E. Gugel, "The Influence of Powders and Processing Methods on Microstructure and Properties of Dense Silicon-Nitride," Silicon Nitride Ceramics, vol. 287, pp. 133-146, 1993.
[39] R. W. Rice and W. J. McDonough, "Hot-Pressed Si3N4 with Zr-Based Additions," Journal of the American Ceramic Society, vol. 58, pp. 264-264, 1975.
[40] J. S. Vetrano, H. J. Kleebe, E. Hampp, M. J. Hoffmann, M. Rühle, and R. M. Cannon, "Yb2O3-fluxed sintered silicon nitride," Journal of Materials Science, vol. 28, pp. 3529-3538, 1993.
[41] J. Kim and C. Kim, "Effects of ZrO2 and Y2O3 dissolved in zyttrite on the densification and theα/β phase transformation of Si3N4 in Si3N4-ZrO2 composite," Journal of Materials Science, vol. 25, pp. 493-498, 1990.
[42] T. Ekström, L. K. L. Falk, and E. M. Knutson-Wedel, "Pressureless-sintered Si3N4-ZrO2 composites with Al2O3 and Y2O3 additions," Journal of Materials Science Letters, vol. 9, pp. 823-826, 1990.
[43] G. Wötting, B. Kanka, and G. Ziegler, "Microstructural Development, Microstructural Characterization and Relation to Mechanical Properties of Dense Silicon Nitride," in Non-Oxide Technical and Engineering Ceramics, S. Hampshire, Ed., ed: Springer Netherlands, pp. 83-96, 1987.
[44] M. J. Hoffmann and G. Petzow, Tailoring of mechanical properties of Si3N4 ceramics: Kluwer Academic, 1994.
[45] C.-M. Wang, X. Pan, M. J. Hoffmann, R. M. Cannon, and M. Riihle, "Grain Boundary Films in Rare-Earth-Glass-Based Silicon Nitride," Journal of the American Ceramic Society, vol. 79, pp. 788-792, 1996.
[46] F. Lange, S. C. Singhal, and R. Kuznicki, "Phase Relations and Stability Studies in the Si3N4‐SiO2‐Y2O3 Pseudoternary System," Journal of the American Ceramic Society, vol. 60, pp. 249-252, 1977.
[47] F. Lange, "Importance of phase equilibria on process control of Si 3 N 4 fabrication," in Ceramics for High-Performance Applications III Reliability. Proc. 6 th Army Materials Technology Conference held at Orcas Island, Washington, 10-13 July, 1979. Edited by Lenoe, E. M., p. 275, 1983.
[48] A. Wereszczak, T. Kirkland, K. Breder, M. Ferber, and P. Khandelwal, "High temperature dynamic fatigue performance of a hot isostatically pressed silicon nitride," Materials Science and Engineering: A, vol. 191, pp. 257-266, 1995.
[49] K. Faber and A. Evans, "Crack deflection processes—I. Theory," Acta Metallurgica, vol. 31, pp. 565-576, 1983.
[50] K. Faber and A. Evans, "Crack deflection processes—II. Experiment," Acta Metallurgica, vol. 31, pp. 577-584, 1983.
[51] P. F. Becher, "Microstructural design of toughened ceramics," Journal of the American Ceramic Society, vol. 74, pp. 255-269, 1991.
[52] P. F. Becher, C. H. Hsueh, P. Angelini, and T. N. Tiegs, "Toughening Behavior in Whisker‐Reinforced Ceramic Matrix Composites," Journal of the American Ceramic Society, vol. 71, pp. 1050-1061, 1988.
[53] F. Van Dijen, A. Kerber, U. Vogt, W. Pfeifer, and M. Schulze, "A Comparative Study of Three Silicon Nitride Powders, Obtained by Three Different Syntheses," Key Engineering Materials, vol. 89, pp. 19-28, 1993.
[54] J. Szepvolgyi, F. L. Riley, I. Mohai, I. Bertoti, and E. Gilbart, "Composition and microstructure of nanosized, amorphous and crystalline silicon nitride powders before, during and after densification," Journal of Materials Chemistry, vol. 6, pp. 1175-1186, Jul 1996.
[55] M. Peuckert and P. Greil, "Oxygen Distribution in Silicon-Nitride Powders," Journal of Materials Science, vol. 22, pp. 3717-3720, 1987.
[56] K. Okada, K. Fukuyama, and Y. Kameshima, "Characterization of Surface-Oxidized Phase in Silicon-Nitride And Silicon Oxynitride Powders by X-Ray Photoelectron-Spectroscopy," Journal of the American Ceramic Society, vol. 78, pp. 2021-2026, 1995.
[57] S.-C. Zhang and W. R. Cannon, "Preparation of Silicon Nitride from Silica," Journal of the American Ceramic Society, vol. 67, pp. 691-695, 1984.
[58] S. J. P. Durham, K. Shanker, and R. A. L. Drew, "Carbothermal Synthesis of Silicon Nitride: Effect of Reaction Conditions," Journal of the American Ceramic Society, vol. 74, pp. 31-37, 1991.
[59] H. Arik, S. Saritas¸, and M. Gündüz, "Production of Si3N4 by carbothermal reduction and nitridation of sepiolite," Journal of Materials Science, vol. 34, pp. 835-842, 1999.
[60] H. Arik, "Synthesis of Si3N4 by the carbo-thermal reduction and nitridation of diatomite," Journal of the European Ceramic Society, vol. 23, pp. 2005-2014, 2003.
[61] M. Belmonte, J. González-Julián, P. Miranzo, and M. Osendi, "Spark plasma sintering: A powerful tool to develop new silicon nitride-based materials," Journal of the European Ceramic Society, vol. 30, pp. 2937-2946, 2010.
[62] Z. A. Munir, D. V. Quach, and M. Ohyanagi, "Electric current activation of sintering: a review of the pulsed electric current sintering process," Journal of the American Ceramic Society, vol. 94, pp. 1-19, 2011.
[63] Z. Munir, U. Anselmi-Tamburini, and M. Ohyanagi, "The effect of electric field and pressure on the synthesis and consolidation of materials: A review of the spark plasma sintering method," Journal of Materials Science, vol. 41, pp. 763-777, 2006.
[64] M. Tokita, "Mechanism of spark plasma sintering," in Proceedings of the International Symposium on Microwave, Plasma and Thermochemical Processing of Advanced Materials, ed S. Miyake and M. Samandi, JWRI, Osaka Universities, Japan, pp. 69-76, 1997.
[65] E. Rabinowicz, Friction and Wear of Materials, 2nd edition ed.: John Wiley & Sons, Inc., 1995.
[66] J. F. Archard, "Contact and Rubbing of Flat Surfaces," Journal of Applied Physics, vol. 24, pp. 981-988, 1953.
[67] N. P. Suh, "Citation Classic - The Delamination Theory of Wear," Current Contents/Engineering Technology & Applied Sciences, pp. 16-16, 1981.
[68] K. Kato, "Tribology of Ceramics," Wear, vol. 136, pp. 117-133, Feb 1990.
[69] A. G. Evans and E. A. Charles, "Fracture Toughness Determinations by Indentation," Journal of the American Ceramic Society, vol. 59, pp. 371-372, 1976.
[70] G. Woetting, H. Feuer, and E. Gugel, "The influence of powder and processing methods on microstructure and properties of dense silicon nitride," in MRS Symp. Proc., Boston, p. 146, 1993.
[71] K. Plucknett, "Hot isostatic pressing of silicon nitride based ceramics," University of Warwick, 1990.
[72] C. P. Dogan and J. A. Hawk, "Microstructure and abrasive wear in silicon nitride ceramics," Wear, vol. 250, pp. 256-263, 2001.
[73] C. P. Gazzara and D. R. Messier, "Determination of Phase Content of Si3n4 by X-Ray-Diffraction Analysis," American Ceramic Society Bulletin, vol. 56, pp. 777-780, 1977.
[74] D. S. Park, H. J. Choi, B. D. Han, H. D. Kim, and D. S. Lim, "Effect of Si2N2O content on the microstructure, properties, and erosion of silicon nitride-Si2N2O in situ composites," Journal of Materials Research, vol. 17, pp. 2275-2280, 2002.
[75] S. M. Johnson and D. J. Rowcliffe, "Mechanical properties of joined silicon nitride," Journal of the American Ceramic Society, vol. 68, pp. 468-472, 1985.
[76] M. L. Mecartney, R. Sinclair, and R. E. Loehman, "Silicon Nitride Joining," Journal of the American Ceramic Society, vol. 68, pp. 472-478, 1985.
[77] L. Junting, Z. Kaifeng, W. Guofeng, and H. Wenbo, "Fabrication of fine-grained Si3N4-Si2N2O composites by sintering amorphous nano-sized silicon nitride powders," Journal of Wuhan University of Technology-Mater. Sci. Ed., vol. 21, pp. 97-99, 2006.
[78] F. Lange, "Fracture Toughness of Si3N4 as a Function of the Initial α‐Phase Content," Journal of the American Ceramic Society, vol. 62, pp. 428-430, 1979.
[79] W. Dressler, H.-J. Kleebe, M. J. Hoffmann, M. Rühle, and G. Petzow, "Model experiments concerning abnormal grain growth in silicon nitride," Journal of the European Ceramic Society, vol. 16, pp. 3-14, 1996.
[80] R. Wills, S. Holmquist, J. Wimmer, and J. Cunningham, "Phase relationships in the system Si3N4-Y2O3-SiO2," Journal of Materials Science, vol. 11, pp. 1305-1309, 1976.
[81] U. Kolitsch, H. J. Seifert, T. Ludwig, and F. Aldinger, "Phase equilibria and crystal chemistry in the Y2O3–Al2O3–SiO2 system," Journal of Materials Research, vol. 14, pp. 447-455, 1999.
[82] T. Jawhari, A. Roid, and J. Casado, "Raman-Spectroscopic Characterization of Some Commercially Available Carbon-Black Materials," Carbon, vol. 33, pp. 1561-1565, 1995.
[83] T. P. Mernagh, R. P. Cooney, and R. A. Johnson, "Raman-Spectra of Graphon Carbon-Black," Carbon, vol. 22, pp. 39-42, 1984.
[84] G. Chollon, "Oxidation behaviour of ceramic fibres from the Si-C-N-O system and related sub-systems," Journal of the European Ceramic Society, vol. 20, pp. 1959-1974, 2000.
[85] V. G. Kesler, S. G. Yanovskaya, G. A. Kachurin, A. F. Leier, and L. M. Logvinsky, "XPS study of ion-beam-assisted formation of Si nanostructures in thin SiO2 layers," Surface and Interface Analysis, vol. 33, pp. 914-917, 2002.
[86] J. Dusza, P. Šajgalik, Z. Bastl, V. Kavečanský, and J. Ďurišin, "Properties of β-silicon nitride whiskers," Journal of Materials Science Letters, vol. 11, pp. 208-211, 1992.
[87] M. Hnatko, P. Šajgalı́k, Z. Lenčéš, D. Salamon, and F. Monteverde, "Carbon reduction reaction in the Y2O3–SiO2 glass system at high temperature," Journal of the European Ceramic Society, vol. 21, pp. 2797-2801, 2001.
[88] C. Balázsi, F. S. Cinar, O. Addemir, F. Wéber, and P. Arató, "Manufacture and examination of C/Si3N4 nanocomposites," Journal of the European Ceramic Society, vol. 24, pp. 3287-3294, 2004.
[89] M. Kitayama, K. Hirao, M. Toriyama, and S. Kanzaki, "Modeling and simulation of grain growth in Si3N4—I. Anisotropic Ostwald ripening," Acta Materialia, vol. 46, pp. 6541-6550, 1998.
[90] T. Nishimura, M. Mitomo, H. Hirotsuru, and M. Kawahara, "Fabrication of silicon nitride nano-ceramics by spark plasma sintering," Journal of materials science letters, vol. 14, pp. 1046-1047, 1995.
[91] M. Mitomo, H. Hirotsuru, H. Suematsu, and T. Nishimura, "Fine‐Grained Silicon Nitride Ceramics Prepared from β‐Powder," Journal of the American Ceramic Society, vol. 78, pp. 211-214, 1995.
[92] D. R. Clarke, "On the Equilibrium Thickness of Intergranular Glass Phases in Ceramic Materials," Journal of the American Ceramic Society, vol. 70, pp. 15-22, 1987.
[93] J. L. Huang, Z.-H. Shih, H.-H. Lu, and C.-Y. Chen, "The effects of post heat-treatment on the microstructure and fracture behaviors of Yb< sub> 2</sub> O< sub> 3</sub>-doped Si< sub> 3</sub> N< sub> 4</sub>," Materials chemistry and physics, vol. 63, pp. 116-121, 2000.
[94] M. Belmonte, P. Miranzo, M. I. Osendi, and J. Gomes, "Wear of aligned silicon nitride under dry sliding conditions," Wear, vol. 266, pp. 6-12, 2009.
[95] H. Hyuga, M. I. Jones, K. Hirao, and Y. Yamauchi, "Influence of Rare-Earth Additives on Wear Properties of Hot-Pressed Silicon Nitride Ceramics under Dry Sliding Conditions," Journal of the American Ceramic Society, vol. 87, pp. 1683-1686, 2004.