Low-cost high-yield synthesis of nanosize powders of Si-based nitrides and carbides by CO_2 laser induced gas phase reactions

摘要

Amorphous Si_3N_4, Si/N/C and crystalline SiC nano-powders, 5-50 nm in mean diameter, with yields of 40-120 g/h were synthesized via laser induced gas phase reactions of low cost hexamethyldisilazane (HMDS) and NH_3 (or H_2). Reaction flame temperatures, which were controlled by the total gas flow rate, greatly influenced powder composition and crystallinity. Amorphous Si_3N_4 powders (96 wt percent) were obtained at 1000 deg C from HMDS + NH_3; beta-SiC (93 wt percent) was formed at 1600 deg C with H_2. Amorphous Si/N/C powders with various N/C ratios (0.1-6) were synthesized at various temperatures. The main impurities in the powders were the organo-ligands such as NH_x- and CH_x (x= 1-3) whose existence also resulted in a strong surface absorption of oxygen.