Sintering of Ultrafine Silicon Powder

Abstract

The sintering behavior of compacts of ultrafine silicon powder (0.02 to 0.1 μm particle size) was investigated. Two sintering modes occur: normal sintering associated with densification and subnormal sintering without densification. The micro‐structure developed in normal sintering has a fine grain size (0.05 to 0.3 μm) and fine porosity; the grains contain stacking faults and twins. The microstructure developed in subnormal sintering exhibits larger grains (∼1 μm in size) and coarse pores. Green densities >42% of theoretical and temperatures >1100°C are required for densification. Densification follows an exponential time and temperature dependence with an activation energy of 470 kJ/mol, indicating bulk diffusion as the transport mechanism. Grain‐boundary diffusion is thought to be inhibited by grain‐boundary oxide films. The carbon phase‐separates into discrete amorphous regions and is thought to have little effect on sintering behavior.