KINETIC-ANALYSIS OF COMBUSTION SYNTHESIS OF LEAD MAGNESIUM NIOBATE FROM METAL CARBOXYLATE GELS

A combustion synthesis route was developed for direct crystallization of perovskite lead magnesium niobate (PMN) from metal carboxylate gels , Direct PMN formation is attributed to a homogeneous cation distribut ion in the gel and the rapid heating during exothermic gel decompositi on in oxidizing atmospheres, The maximum bed temperature and gel decom position rate are determined by the combined influence of chemical kin etics, heat, and mass transfer, It is shown that there is a temperatur e window between 700 degrees and 750 degrees C which favors direct PMN formation, whereas pyrochlore formation is favored below 650 degrees C and PbO volatilization occurs above 800 degrees C, The effects of ki netic and transport parameters including oxygen partial pressure, gas flow rate, and bed geometry on PMN formation are discussed on the basi s of a thermal ignition model for heterogeneous reactions.