Lanthanum Chromite Powders Of Doped Lithium Synthesis And Sintering Tissue Performance

Ionic radius, tolerance factor and electronegative difference were calculated to select doping element and its content according to a theory of materials design. Lithium-doped lanthanum chromites (LaCr_1-yLi_yO₃) with perovskite-type structure could be synthesized by the solid reaction, the Pechini method and the combustion method respectively. It was found that the lattice parameters, calculated by a least squares refinement procedure, decreased with the Li content. The solid solubility of Li in lanthanum chromites is limited between 0.2 and 0.25 .Structure and thermal decomposition of polymeric precursors was analyzed by infra-red spectrum (IR), thermogravimetric analysis (TG), differential scanning calorirnetry (DSC) and X-ray diffractometer (XRD), respectively. The results indicated that the gelating process of the Pechini method was in accord with that of the combustion method: the chelate is formed when mixing citric acid with metal ions dispersed uniformly in solution, and polyreaction and esterification between chelete and ethylene glycol takes place, then gel is dried to form the dry-gel during heating. The glycol as disperser is advantageous to form more uniform stable gel, but disadvantageous to thermal decomposition of the dry-gel due to excessive carbon inducted. The difference between the two methods is thermal decomposition of the dry-gel. The transformation of the intermediate phase mainly depends on gentle decomposition and calcination by several steps during the decomposition course of Pechini method at a high temperature. The higher the heating rate, the better is the dispensability of the final particles, but the poorer is the uniformity of particle size. Both decomposition of organic component and formation of the final powders can be completed by one step during severe combustion synthesis. The subsidiary oxidant, NH₄NO₃, can make combustion more complete and combusting speed more quick owing to self-decomposition and formation of oxygen at high temperature. On basis of the process studied systematically, the optimum key parameters, that is, content of citric acid and ethylene glycol, drying and calcination temperature, heating rate, were...