Amorphous-crystalline transformation control on the microstructural evolution of magnesium phosphate cements

Magnesium phosphate cements are chemically-bonded ceramics exhibiting high strength and good adhesive properties. In-situ investigation of the reaction of Mg-K phosphate cements, indicated that microstructural evolution is controlled by a cement densification process entailing amorphous-to-crystalline transformation during hardening. Owing to the replacement of the amorphous fraction with a material of higher density, possessing elongated crystal habit, an increase in porosity with time occurs, at variance with previous models. The beneficial effect provided by the developed interlocked lath-shaped microstructure, constituted by crystals embedded in the amorphous matrix, prevails over the detrimental role of the increased porosity, explaining the increase in mechanical strength.