All-ceramic multilayer composite ytterbium doped yttrium aluminum garnet (Yb:YAG) laser gain medium with doping concentration distribution of 0-5-10-15-20-15-10-5-0 at.% Yb ions was successfully fabrication by the technique of c
Combustion synthesis of b-silicon carbide (SiC) powders was accomplished at a nitrogen pressure lower than 2 MPa. The combination of mechanical activation and chemical stimulation was effective in enhancing the reactivity of Si powder reactants, which was responsible for the reduction in the minimum nitrogen pressure normally required for the combustion synthesis of SiC. Nanosized b-SiC powders with spherical particles were synthesised at nitrogen pressure as low as 1 MPa. The combustion synthesised SiC powders have a narrow particle size distribution in the range of 50-100 nm and could be hot pressed to 99?1% theoretical density with 10 wt-%Y 2 O 3 and AlN as additives.
Combustion synthesis of Ti 3 SiC 2 was carried out in air with Si 3 N 4 , SiC, and Si as Si sources respectively, and the effect of Si source on the phase composition of the products was investigated. With Si 3 N 4 as Si source, the major product was TiC x N 12x and no Ti 3 SiC 2 was synthesised. When SiC and Si were used, Ti 3 SiC 2 was synthesised. Such effect of Si source is thought to be connected with the formation mechanism of Ti 3 SiC 2 , where the presence of a Ti-Si melt is required. The combustion synthesis was also performed under high gravity condition instead of common gravity. The apparent density of the product prepared under high gravity was y60% higher than that obtained under normal gravity. It is proposed that, the high gravity can facilitate the permeation of Ti-Si melt and enlarge the interface between the melt and carbide phases, which is helpful for the formation of Ti 3 SiC 2 .
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