Abstract: To address the challenges associated with the agglomeration of magnesia and its poor dispersion stability in sol systems,the effects of the sodium pyrophosphate additions (0-2.5 mass%),suspension pH (7.9-11.5),and ultrasonic dispersion time (0-20 min) on the dispersity and stability of the magnesia powder were investigated.Subsequently,SiO₂-coated magnesia powders were prepared using sodium silicate as the raw material through the sol-gel method.The influence of the coating time (1-9 h),coating temperature (55-95 ℃),suspension pH (7.5-11.3),and sodium silicate solution mass fraction (1%-5%) on the surface properties of the powders was studied.The results indicate that within certain ranges (the sodium pyrophosphate addition <1.5%,the pH <11.5,and the ultrasonic dispersion time <5 min),the dispersity of the magnesia powders improves with the above parameter values increasing;while at the sodium pyrophosphate addition >1.5% and ultrasonic dispersion time >5 min,the dispersity gradually deteriorates.After being coated with SiO₂,as the coating time prolongs,the coating temperature increases from 55-65 ℃,or the pH rises,the dispersity of the magnesia powders first increases and then decreases.Generally,under the following conditions:coating time of 7 h,coating temperature of 65 ℃,pH of 10.5,and sodium silicate solution mass fraction of 5%,the magnesia powder exhibits the optimal dispersity,with d₅₀=45.2 μm,d₉₀=70.5 μm,and the minimum specific surface area of 792 m²·kg^-1.

Key words: magnesia, sol-gel method, SiO₂ coating, coating time, coating temperature

摘要： 针对氧化镁易团聚且无法在溶胶体系中实现均匀分散等问题,首先探究了焦磷酸钠添加质量分数(0~2.5%)、悬浮液pH(7.9~11.5)及超声分散时间(0~20 min)对氧化镁粉体分散性与稳定性的影响;随后以硅酸钠为原料,采用溶胶-凝胶法,通过调控包覆时间(1~9 h)、包覆温度(55~95 ℃)、悬浮液pH(7.5~11.3)及硅酸钠溶液质量分数(1%~5%),研究了上述参数对SiO₂包覆氧化镁粉体表面特性的影响。结果表明:当焦磷酸钠添加量小于1.5%(w),pH小于11.5,超声分散时间小于5 min时,氧化镁粉体的分散性随上述参数的增大而提升;当焦磷酸钠添加量大于1.5%(w),超声分散时间超过5 min时,氧化镁粉体分散性逐渐降低;采用SiO₂包覆氧化镁后,随着包覆时间的延长,包覆温度(55~65 ℃)的升高以及pH的增大,氧化镁粉体分散性均先增强后降低。综上所述,当包覆时间为7 h,包覆温度为65 ℃,pH稳定在 10.5,硅酸钠溶液质量分数为5%时,氧化镁粉体的分散性最佳,其d₅₀为45.2 μm,d₉₀为70.5 μm,比表面积降至最小值792 m²·kg^-1。

关键词: 氧化镁, 溶胶-凝胶法, SiO₂包覆, 包覆时间, 包覆温度