Tailoring the microstructure of reaction-sintered alumina/lanthanum hexaaluminate particulate composites

The aim of this study was modification of the microstructure and adjustment of the porosity in alumina/lanthanum hexaaluminate particulate composites, by altering the lanthanum hexaaluminate content, for the further development of new materials that can be applied in several technological processes. The amount of lanthanum hexaaluminate was varied from 2.8 to 80 vol.% in particulate composites. As a novel approach to develop homogenously distributed dense and porous alumina/lanthanum hexaaluminate particulate composites, a carbonate co-precipitation method was applied to produce lanthanum aluminate-coated alumina particles. For the coating process itself, a surface charge adjustment called ‘electrostatic attraction’ was utilised. Subsequent reactive sintering of the calcined-coated particles caused the in situ formation of lanthanum hexaaluminate platelets inside the alumina matrix. The prepared composite powders, as well as the sintered samples, were characterised by FE-SEM, TEM, XRD, dilatometry, and mercury porosimetry. The results revealed that the uniform distribution of the low amount of lanthanum hexaaluminate prohibited the grain growth of alumina matrix and resulted in denser microstructures, whereas the increase in the lanthanum hexaaluminate content yielded more porous microstructures.