KINETICS OF SILICON MONOXIDE AMMONOLYSIS FOR NANOPHASE SILICON-NITRIDE SYNTHESIS

Silicon monoxide vapor generated from Si/SiO2 mixed-powder compacts wa s used with NH3 to synthesize silicon nitride in a tubular how reactor operated at temperatures in the range of 1300 degrees-1400 degrees C. The ammonolysis of SiO with excess NH, was very rapid, yielding three different types of silicon nitride at different longitudinal location s in the reactor: amorphous nanophase powder of an average size of abo ut 20 nm, amorphous whiskers of a few micrometers in diameter, and alp ha-polycrystals. The amorphous products mere heat-treated for crystall ization at temperatures between 1300 degrees and 1560 degrees C in a s tream of dissociated NH3, N-2, or N-2/H-2 mixture gas, When dissociate d NH3 was used, nanophase powder was crystallized at 1300 degrees C. T he yield of nanophase silicon nitride from SiO varied from 13% to 43%, depending on operating conditions.