Combustion synthesis, powder treatment, dispersion and tape casting of lanthanum strontium manganite

Abstract

Lanthanum strontium manganite La0.84Sr0.16MnO3 (LSM) powder was prepared by combustion synthesis, using a concentrated solution of nitrates of lanthanum, strontium, and manganese as oxidiser, and critic acid as fuel. The as formed powder was found to be crystalline LSM consisting of porous agglomerates of fine particles, and exhibited about 7% total weight loss on heating up to 1100°C. Dispersion conditions for wet grinding of the powder agglomerates calcined at 1100°C were evaluated from zeta potential and viscosity studies. A maximum zeta potential of -35 mV was noted at a pH of 11, while pseudoplasticity of the slurry decreased with decreasing solid concentration. Powder with d50 of around 3 μm and free of agglomerates of size greater than 10 μm was formed by wet grinding. Further calcination of this powder at 1350°C improved the solids loading in the slurry. The tape cast slurry composition was optimised for minimum content of binder, plasticiser, and water with acceptable pseudoplasticity to form flexible and flat tapes. The dried tapes cut to required sizes were subjected to controlled binder burnout followed by sintering in the range 1350-1450°C. The sintered flat specimens exhibited densities in the range 65-80% of theoretical, and open porosities in the range 35-20%, with a homogeneous distribution of pore phase in the matrix.