Study On Preparation Of Oxide Powders Used As High Temperature Structural Ceramics Via Solid State Reaction At Low-heating Temperature

Magnesium aluminum spinel (MgAl2O4) and yttrium aluminum garnet (YAG) could be used as high temperature structural ceramics. Properties, synthesis methods of MgAl2O4 and YAG, characteristic, developing process, principles and research progress of the solid state reaction at low-heating temperature are introduced in this paper.MgAl2O4 precursor was synthesized via solid state reaction at low-heating temperature by using AR basic aluminum acetate and magnesium nitrate as starting materials, and citric acid as complex former. MgAl2O4 powders are formed by calcining the precursor. YAG was synthesized via the same method using AR basic aluminum acetate and yttrium nitrate as starting materials. Composition and thermo-decomposing process of precursor, combustion of citric acid, synthetic reaction of and MgAl2O4 and YAG was studied by using IR spectrum and TG/DTA analysis. The product powders were characterized with XRD, BET, SEM and TEM. Dependence of MgAl2O4 performance on the calcination temperature, the amount of citric acid and the precursor radiated by microwave was studied. Dependence of YAG performance on surface active agent was studied in this paper also. Lattice imperfection, sintering character of MgAl2O4 and Nd:YAG has been discussed. Kinetics of grain growth of MgAl2O4 and YAG has been calculated.The results show that precursor was intensive mixed through solid state reaction at low-heating temperature.MgAl2O4 spinel forms only at 700℃for 3 h. The crystallized mass was a mixture of ordered and disordered phases of MgAl2O4 spinel. Pure Y3AI5O12 began to form only at 800℃and intermediate phases were not detected. Well-crystallized and even granular MgAl2O4 and YAG could be obtained when heightening the temperature.When the amount of citric acid agrees with the ratio of n(C6H8O7):n(Mg+Al)= 1:1, the specific surface area of MgAl2O4 spinel could reach 160m2/g. The precursor which was direct radiated by microwave could synthesize MgAl2O4 spinel that has bigger grain size and has no-lattice imperfection. The precursor which was radiated by microwave-assisted use SiC as microwave absorption material could synthesize MgAl2O4 spinel that has worse crystallinity. The spinel powders are nanometer powders that have better recrystallization behavior and could improve the sintering densification of spinel ceramics. Lower calcine temperature of powders has better sintering activity. With Nd(NO)3·nH2O as raw material could synthesize Nd:YAG powders. The amount of Nd3+ could reach 3%. Lattice dilatation happened in the product powders. These powders have small grain size and better dispersibility.