The Preparation Of MgCr₂O₄ Spinel Made By Molten-salt Method And Its Application In Fuel Gas Filter

Molten salt method is recently developed as a novel synthetic method for inorganic materials. Based on one or more low melting point salts as a reaction medium, which can be dissolved by the appropriate solvent, the reaction is easily carried out via the media and pure product can be obtained after filtering and washing. Due the advantages of the simple process, low cost and synthetic temperature, short reaction time and high stability in chemical compositions, molten salt method has been widely applied in different fields, such as in the synthesis of high melting point oxide powders, electronic ceramic powders and other functional powder materials.MgCr2O4 spinel powders were synthesized in NaCl and KCl molten salt media. The effects of different raw materials, such as heating temperature, holding time and different molten salt kinds on the performances of the products have been studied. The results indicated shows that both the chromic oxide and chromic salt can be combined with crystal magnesium and calcium carbonate to produce octahedral MgCr2O4 spinel. The materials--MgCl2·6H2O,CaCO3,Cr2O3,NaCl,KCl being heated under 900℃for 5hours, the crystal size distribution of MgCr2O4 spinel becomes equal in a octahedral form and such crystals grow complete. By contrast, the crystals of MgCrO4 spinel produced by Cr(NO3)3.9H2O and CrCl3.6H2O become octahedral, incomplete and irregular in form. With increase in heating process temperature and delay in soaking time, the crystallinity of MgCr2O4 spinel improves and crystal size increases, too. And MgCr2O4 spinel growth features Ea=10.01 KJ/mol in medium of NaCl fused salt. Through molten-salt method the produced cellular MgCr2O4 spinel ceramics can be used as the carrier of automobile exhaust katalyst, standard both in form and in grid size. And the cellular MgCr2O4 spinel has the advantage of more pores, even pore width and large surface area. Therein, the celluar magne siochromic can so evenly absorb and preserve the automobile exhaust katalyst as to provide conditions for perfect exhaust purified effect.