Reaction Mechanism of Mineralizers Ferrosilicon Nitride and Calcium Carbonate in Silica Bricks

Silica bricks only used the combined mineralizer of calcium hydroxide and iron scale in the early domestic production. It is feasible and necessary to explore novel mineralizers to improve the performance of silica bricks. In this paper,novel silica bricks were prepared with ferrosilicon nitride and calcium carbonate as mineralizers instead of calcium hydroxide and iron scale. The prepared silica bricks have good properties, and the content of tridymite with 2% ferrosilicon nitride and calcium carbonate added reaches 62% and 65%, respectively. The effects of ferrosilicon nitride and calcium carbonate on the formation of tridymite in silica bricks were investigated by X-ray diffraction and scanning electron microscopy. The results show that in the silica brick with ferrosilicon nitride as mineralizer, Si₃N₄ network formed by the intertwined columnar Si₃N₄ in the sea urchin-like structure ferrosilicon nitride protects Fe and Fe₃Si through its oxidation reaction, thereby achieving a higher FeO/Fe₂O₃ ratio and a lower liquid formation temperature in the FeO–Fe₂O₃–SiO₂ ternary phase. The FeO/Fe₂O₃ ratio in the liquid phase fluctuates at a high temperature, and then the constant change of the solubility of tridymite in the saturated liquid phase promotes the crystallization of tridymite due to the reducibility of Fe, Fe₃Si and Si₃N₄. When calcium carbonate is used as a mineralizer of silicon brick, the formation temperature of the liquid phase in the brick is increased to 1436 ℃. Before that, the reactions in the bricks are mainly the decomposition of calcium carbonate and the transformation from β-quartz to α-quartz and to metastable α-cristobalite. The increase of the formation temperature of the liquid phase does not reduce the content of tridymite in the brick, and the content of glass phase in the brick is less than that in the brick with iron mineralizer.