Molten Salt Synthesis Of MgAl₂O₄ Spinel And Preparation Of Porous Spinel Material

Molten salt synthesis of MgAl2O4 spinel powder and preparation of porous spinel material were investigated in single and compound molten salts system by using industrial alumina, activeα-Al2O3 and light calcined MgO at the temperature below 1200℃, the influence of fluorides was studied as well. The results show that:(1) The formation temperatures of magnesium aluminate spinel in molten salt media are strongly affected by the melting points temperature (or eutectic points temperature) of the molten salt systems. Generally, the lower melting (or eutectic) points temperature of the molten salt systems, the lower formation temperature of MgAl2O4 spinel.(2) Compound salts systems showed more effective than single salt systems as reaction media for synthesis of magnesium aluminate spinel (for instance: KCl-LiCl more effective than LiCl and KCl, NaCl-KCl more effective than KCl and NaCl). Industrial alumina has higher reactivity than activeα-Al2O3 as starting material for molten salt synthesis of spinel powder. The fluorides showed great accelerating effects on the formation of MgAl2O4, and may deeply decrease the reaction temperature.(3) The porosity of porous spinel materials prepared by using industrial alumina and light magnesia as raw materials in molten salt is highter than that by using activeα-Al2O3 and light magnesia as raw materials. NaCl-KF0.04, KCl-KF0.04, NaCl-KCl-KF0.04 molten salt systems are more favorable to the synthesis of porous spinel material. The ratio of salts to oxides strongly affect apparent porosity and bulk density of porous spinel material, the higher ratio of salts to oxides gives higher apparent porosity and lower bulk density, and lower crushing strength of samples. Crushing strength increased with the increase of firing temperature, but there is no evidential correlation between firing temperature and porosity or bulk density of the porous samples.(4) The porosity of porous corundum-spinel material prepared by using activeα-Al2O3, light magnesia and tabular corundum as raw materials decreased with the increase of addition amount of tabular corundum aggregations.