Seeded silicon nitride powders obtained by carbothermal reduction—nitridation of diatomite and various sources of carbon

Abstract

In this paper, the effects of the addition of silicon nitride seeds on the phase composition, particle size, and shape of silicon nitride powders obtained by carbothermal reduction-nitridation were studied. Environmentally friendly natural raw material, diatomaceous earth, was used as a Si precursor. Three different carbon sources were used: activated carbon, carbonized sucrose, and carbon cryogel as reducing agents in the molar ratio C/SiO2 = 5. To obtain better-quality Si3N4 powder, the commercial α-Si3N4 powder was added into starting mixtures as seeds in four different quantities. The X-ray diffraction, specific surface area, infrared spectroscopy with Fourier transform, and scanning electron microscopy were employed to characterize the obtained powders. Sucrose as a carbon source enables a major reduction of SiO2 and the onset of β-Si3N4 crystallization at a lower temperature (1350 °C) as well as the complete absence of diatomaceous earth relics. It indicates that the carbothermal reduction-nitridation takes place faster in contrast to the other two carbon sources.