Densi cation and crystallisation behaviour of Si–B–O–N ceramics prepared by hot pressing with organic precursors

Powders of Si–B–O–N prepared by organometallic polymeric precursor were hot pressed into ceramics at different temperatures. Experimental results indicated that density of ceramics increased slowly with increasing temperature before 1400°C, and increased rapidly after 1400°C. Density of ceramics sintered at 1600°C was 2.11 g cm^-3, which was the highest in this system. Amorphous silicon oxynitride decomposed when sintered at temperatures higher than 1600°C. Differential scanning calorimetry and X-ray diffraction analyses results showed that the amorphous Si–B–O–N began to crystallise at 1350°C and only h-BN precipitates was detected. Observations using SEM showed that particles precipitated at 1400°C were close to equiaxial crystals, however, particles precipitated at 1600°C were well developed platelets. The growth mechanism of precipitates was step like epitaxial growth. Crystals in ceramics sintered at 1700°C were quite small and adhered by molten silica.