Rare earth phosphates are known to possess very high melting points in the range 1900–2000 °C and have excellent thermal phase stability. Hence, they are considered excellent candidates to produce high refractory materials. Alumina-LaPO₄ composites are thermally stable and LaPO₄ successfully controls the grain growth of alumina, thus leading to enhanced thermomechanical properties.

This work deals with the shape forming of alumina-LaPO₄ composites by a colloidal filtration route. A LaPO₄ powder was synthesised by mechanochemical milling from lanthanum nitrate and di-hydrogen ammonium phosphate precursors. A commercial coarse alumina was used to obtain mixtures with 20, 30, and 40 wt.% of monazite phase (A80, A70, and A60, respectively). The starting powders and the mixtures were attrition milled and its effect on the physicochemical properties was studied, focusing on the particle size and shape, as well as the colloidal behaviour as a function of pH and adsorbed polyelectrolytes. The optimisation of the dispersing conditions was studied by measuring the rheological behaviour of concentrated suspensions of the mixtures. Suspensions of alumina and alumina-monazite prepared to a solids loading of 40 vol.% were slip cast in plaster moulds. Green cast bodies were characterized through densities determination and microstructural observations. Sintering treatments were studied in order to obtain dense materials.

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