Cost-effective manufacture and synthesis mechanism of ferrosilicon nitride porous ceramic with interlocking structure

Abstract

To realize cost-effectively manufacture of high-performance Si3N4 porous ceramic, a ferrosilicon nitride porous ceramic with an optimized interlocking structure was synthesized by flash combustion synthesis using FeSi75 powder as raw material. And the technology has been improved in many ways to ensure stable industrial production. The theoretical combustion temperature of FeSi75 in N2(g) is up to 4608K, while Si3N4 is unstable. Both adding diluent and designing the preheat temperature of nitrogen are taken to control synthesis temperature below 1600 °C. During synthesis, the Fe–Si liquid phase and SiO(g), which are essential for the selective growth of elongated columnar β-Si3N4 and whisker α-Si3N4 respectively, are formed firstly. Then, nitriding proceed in multiple ways. N diffuses through Fe–Si(l) and reacts with Si to form β-Si3N4, and the growth of elongated β-Si3N4 in Fe–Si liquid follows the dynamic ripening model, which is very fast and effective. Thus, an interlocking structure composed of elongated β-Si3N4 with an aspect ratio above 20 is reached. There is also an indirect nitridation reaction, that is, FeSi75 preferentially reacts with trace O2 in atmosphere to form SiO(g), which is further nitrided to form needle-like α-Si3N4. Needle-like α-Si3N4 is interspersed in the well-developed columnar β-Si3N4, making the structure stronger. Fe finally exists in the form of Fe3Si, which binds the surrounding elongated Si3N4 to form a sea-urchin like unit, making the structure more stable and strengthened. Through control of these reactions, optimizations in microstructure are reached, and the annual output of has reached 25,000 tons. The reaction model is established.