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Materials Development in α-Sialon Ceramics
Mitomo Mamoru,Xie Rong-Jun,Hirosaki Naoto The Korean Ceramic Society 2006 한국세라믹학회지 Vol.43 No.8
The solid solutions of ${\alpha}-Si_3N_4$, i.e. ${\alpha}$-sialons, are represented by a general formula of $M_x(Si,Al)_{12}(O,N)_{16}$, in which metal ions (M) dissolve into interstitial sites to stabilize the structure. Processing methods for the fabrication of ${\alpha}/{\beta}$-sialon composites, ${\alpha}-sialon/{\beta}Si_3N_4$ composites, refractory or tough ${\alpha}$-sialon ceramics have been developed to tailor the mechanical properties. Translucent and photoluminescent properties have been investigated recently. A number of applications of ${\alpha}$-sialon ceramics as engineering and optical ceramics are also presented.
Materials Development in α-Sialon Ceramics
Mamoru Mitomo,Rong-Jun Xie,Naoto Hirosaki 한국세라믹학회 2006 한국세라믹학회지 Vol.43 No.8
The solid solutions of α-Si3N4, i.e. α-sialons, are represented by a general formula of M x(Si,Al)12(O,N)16, in which metal ions (M)dissolve into interstitial sites to stabilize the structure. Processing methods for the fabrication of α/β-sialon composites, α-sialon/β-Si3N4 composites, refractory or tough α-sialon ceramics have been developed to tailor the mechanical properties. Translucent andphotoluminescent properties have been investigated recently. A number of applications of α-sialon ceramics as engineering andoptical ceramics are also presented.
Fabrication of Heat-Resistant Silicon Carbide Ceramics by Controlling Intergranular Phase
Kim, Young Wook,Lee, Sung Hee,Nishimura, Toshiyuki,Mitomo, Mamoru,Lee, Je Hun,Kim, Doh Yeon Trans Tech Publications, Ltd. 2005 Key engineering materials Vol.287 No.-
<P>The effect of glassy-phase, using AlN and Lu2O3 as sintering additives, on the microstructure and mechanical properties of liquid-phase-sintered, and subsequently annealed SiC ceramics was investigated. The microstructure was strongly influenced by the sintering additive composition, which determines the intergranular phase (IGP). The average thickness of SiC grains increased with increasing the Lu2O3 /(AlN + Lu2O3) ratio, whereas the average aspect ratio decreased with increasing the molar ratio. The homophase and heterophase boundaries of the SiC ceramics were completely crystalline in all specimens. The room temperature (RT) strength decreased with increasing the molar ratio whereas the RT toughness showed a minimum at the molar ratio of 0.6. The best results at RT were obtained when the molar ratio was 0.2. The flexural strength and fracture toughness of the ceramics were >700 MPa and ~6 MPa.m1/2 at RT. The high temperature strength was critically affected by the chemistry, especially the content of Al in the IGP. The best strength at temperatures ³ 1500oC was obtained when the molar ratio was 0.5. Flexural strengths of the ceramics at 1500oC and 1600oC were 610 ± 80 MPa and 540 ± 30 MPa, respectively. The beneficial effect of the new additive compositions (Lu2O3-AlN) on high-temperature strength of SiC ceramics was attributed to the crystallization or removal of IGP and introduction of Al into SiC, i.e., removal or reduction of Al content from the IGP, resulting in an improved refractoriness of the IGP.</P>
Kim, Y.W.,Chun, Y.S.,Nishimura, T.,Mitomo, M.,Lee, Y.H. Elsevier Science 2007 Acta materialia Vol.55 No.2
The effect sintering additives comprising AlN and Re<SUB>2</SUB>O<SUB>3</SUB> (Re=Sc, Lu, Yb, Er and Y) in a 2:3 molar ratio on the high-temperature strength of liquid phase-sintered and subsequently annealed SiC ceramics was investigated. Clean SiC-SiC boundaries and clean SiC-junction phase boundaries without the amorphous inter-granular phase (IGP) were observed in Sc<SUB>2</SUB>O<SUB>3</SUB>-, Lu<SUB>2</SUB>O<SUB>3</SUB>- and Yb<SUB>2</SUB>O<SUB>3</SUB>-doped SiC ceramics. Clean SiC-SiC boundaries and SiC-junction phase boundaries with the amorphous IGP were also observed in Er<SUB>2</SUB>O<SUB>3</SUB>-doped SiC ceramics. The amorphous IGP was present in both SiC-SiC and SiC-junction phase boundaries in Y<SUB>2</SUB>O<SUB>3</SUB>-doped SiC ceramics. The high-temperature strength was not dependent on the crystalline nature of the IGP and junction phases, but was dependent on the chemistry of these phases. Lu<SUB>2</SUB>O<SUB>3</SUB>-, Er<SUB>2</SUB>O<SUB>3</SUB>-, Sc<SUB>2</SUB>O<SUB>3</SUB>- and Y<SUB>2</SUB>O<SUB>3</SUB>-doped SiC maintained their room-temperature strengths up to 1600, 1500, 1400 and 1400<SUP>o</SUP>C, respectively. However, Yb<SUB>2</SUB>O<SUB>3</SUB>-doped SiC manifested a drastic degradation in strength at 1400<SUP>o</SUP>C. Thus, clean boundaries and/or crystallization of junction phases did not always lead to the hoped-for increase in strength at temperatures above 1400<SUP>o</SUP>C.