The role of in situ formed lamellar Mg‒Al hydrotalcite on densification of high-chrome castables for coal gasifier

The gasifier is a critical component in coal gasification technology, enabling the efficient and environmentally friendly utilization of coal resources. However, premature failure of aluminum phosphate-bonded high-chrome bricks in the gasifier has been observed due to phosphate migration in reducing atmospheres, which exacerbates slag penetration and thermal spalling. In this study, hydratable alumina-bonded high-chrome castables were prepared, and the effect of active magnesia on their properties was investigated. Hydrates were characterized using X-ray diffraction, Fourier transform infrared, thermogravimetry‒differential scanning calorimetry, and scanning electron microscopy analyses. The results revealed that an appropriate amount of active magnesia could accelerate the hydration of hydratable alumina, promoting the formation of micro-nano-sized lamellar Mg‒Al hydrotalcite. This effectively filled the pores within the castables, thereby improving their properties. During heat treatment, the micro-nano-sized Mg‒Al hydrotalcites decomposed into micro-nano-sized MgAl₂O₄ spinel, which readily reacted with Cr₂O₃ to form Mg(Cr, Al)₂O₄ spinel solid solutions. This phenomenon facilitated sintering at 1600°C, optimizing the internal structure and ultimately leading to enhanced mechanical properties and improved slag resistance.