Silicon-based non-oride structural ceramics sing quartz sand and clay minerals low-priced pure and fine Si,N4 powder. The diimide pro oroducts are achievable 4, 55 Highly pure pow- cess is industrially used to process Sian, por ders can be produced by applying synthetic ders for advanced applications tarting materials derived from pyrolytic or Owing to the predominantly homogeneous ol- gel reactions nucleation, the reaction of SiCa or SiH4 with The liquid phase reaction of SiCl4 and NH3 NH3 in the gas phase provides fine and pure forming Si(NH)2 has been firstly performed by Si, powders with large specific surfaces Persoz in 1830 and has been investigated in (2-20 m" g)and high sintering activities detail by Blix and Wirbelauer, 7 Glemser and Similar to the liquid phase reaction of Sicl4 Naumann and Mazdiyasni and Cooke 9 later. with NH,(see eqn(3))amorphous Si3n4 pre- Billy showed that the ammonolysis of Sicla cursors are formed which have to be thermally under these conditions results in a polymerized converted to crystalline Si, N4. The use of the polysilicon diimide low priced Sicla requires the extraction of the n SiCl+6n nh C-RT [Si(NH)2I by-product NHCl(see eqn (3)). In contrast to this only H2 is evolved during the ammonolysis +anNeCI (3) of the expensive and spontaneous inflammable During the subsequent calcination the gener- (in air)SiHa. The synthesized amorphous pre- ated silicium diimide transforms into an amor- ceramic compounds are crystallized to mainly phous Si,N, accompanied by the evolution of -SiaNa at temperatures between 1200 and NH, or N,/Hz. At temperatures above 1200 C 1500C under nitrogen. Both methods are used the diffusion controlled crystallization to in industry to process commercially availab a-Si, n takes place possessing an activation Si,, qualities to produce engine and turbine energy of 306 kJ mol parts. In Table 1 the properties of some com mercially available Si3N4 powders are summa rized [SI(NH)]. 1200-1400°C a-Si3N +N2+3H 3 SILICON CARBIDE (SiC)-INTRINSIC The particle morphology, particle size and STRUCTURAL PROPERTIES AND phase composition is determined by the pro- SYNTHESIS cessing parameters such as temperature, reac tion time and impurities. 2. 0. The liquid phase The fundamental structural elements of the reaction of SiCl, with NH, gives extraordinary various polytypes of Sic are covalently(88% Table 1. Characteristics of commercially available Si, N,-powders derived from diffe measurements by the authors Powder type SN-E10 SN-ESP Grade GP LC 12-SX A200 Production process Liquid phas Liquid pha Gas phase Direct diimide nitridation Manufacturer Ube Industries, Ube Industries, H C Starck, H.C. Starck, Toshiba Ceramics, Tokyo Tokyo Berlin Tokyo Impurities(wt%) 18-21,(15) 0 <0001 <001 <0005 <0002 <0002 pecinc surtace are (98) Mean particle size 05,(055) 05,(079) 06,(048) 阝-SiN4(wt%) 5,(41) <10,(64)Silicon-based non-oxide structural ceramics 17 using quartz sand and clay minerals low-priced products are achievable? 4"55 Highly pure pow￾ders can be produced by applying synthetic starting materials derived from pyrolytic 53 or sol-gel 52 reactions. The liquid phase reaction of SIC14 and NH3 forming Si(NH)2 has been firstly performed by Persoz 56 in 1830 and has been investigated in detail by Blix and Wirbelauer, 57 Glemser and Naumann 58 and Mazdiyasni and Cooke 59 later. Billy" showed that the ammonolysis of SiCI4 under these conditions results in a polymerized polysilicon diimide. nSiC14 + 6nNH30°C-- RT) [Si(NH)2], +4nNH4C1. (3) During the subsequent calcination the gener￾ated silicium diimide transforms into an amor￾phous Si3N 4 accompanied by the evolution of NH3 or NJH2. At temperatures above 1200°C the diffusion controlled crystallization to ~-Si3N461 takes place possessing an activation energy of 306 kJ moli 1200-- 14OO°C -- [Si(Nn)2], , ) ~-Si3N4 n pure and fine Si3N4 powder. The diimide pro￾cess is industrially used to process Si3N4 pow￾ders for advanced applications. Owing to the predominantly homogeneous nucleation, the reaction of SiCl4 or SiH4 with NH3 in the gas phase provides fine and pure Si3N4 powders with large specific surfaces 64"65 (2-20m 2 g-') and high sintering activities. Similar to the liquid phase reaction of SiCl4 with NH~ (see eqn (3)) amorphous Si3N4 pre￾cursors are formed which have to be thermally converted to crystalline Si3N 4. The use of the low priced SiCl4 requires the extraction of the by-product NH4C1 (see eqn (3)). In contrast to this only H2 is evolved during the ammonolysis of the expensive and spontaneous inflammable (in air) Sill4. The synthesized amorphous pre￾ceramic compounds are crystallized to mainly ~-Si3N 4 at temperatures between 1200 and 1500°C under nitrogen. Both methods are used in industry to process commercially available Si3N 4 qualities to produce engine and turbine parts. In Table 1 the properties of some com￾mercially available Si3N4 powders are summa￾rized. +N2+3H2 (4) The particle morphology, particle size and phase composition is determined by the pro￾cessing parameters such as temperature, reac￾tion time and impurities. 62"63 The liquid phase reaction of SiCl4 with NH3 gives extraordinary 3 SILICON CARBIDE (SIC) -- INTRINSIC STRUCTURAL PROPERTIES AND SYNTHESIS The fundamental structural elements of the various polytypes of SiC are covalently (88% Table 1. Characteristics of commercially available Si3N4-powders derived from different production processes. () Means measurements by the authors Powder type SN-E I O SN-ESP Grade G P LC 12-SX A 200 Production process Liquid phase Liquid phase Gas phase Direct Carbothermal diimide diimide nitridation reduction Manufacturer Ube Industries, Ube Industries, H.C. Starck, H.C. Starck, Toshiba Ceramics, Tokyo Tokyo Berlin Berlin Tokyo Impurities (wt%) O <2 (1.1) (1.0) 1.1-1.6 1.8-2.1, (1.5) 2.0 C <0-2 <0.2 <0.05 <0.2 0.9 CI < 0-01 0.01 < 0.1 < 0.001 -- Fe < 0.01 0.01 < 0.01 < 0.008 0.007 A1 < 0-005 -- < 0.004 < 0.005 0.2 Ca < 0-005 < 0.002 < 0.002 < 0.002 0.01 Specific surface area (9.8) (7.5) (12.2) (21.4) -- (m 2 g ') Mean particle size ds,, (#m) fl-Si3N4 (wt%) 0.5, (0.55) (0.64) 0.5, (0.79) 0.6, (0.48) 0.9 <5, (4.1) (<3) <10, (6.4) s8, (5-6) 2