Investigation of setting reaction in magnesium potassium phosphate ceramics with time resolved infrared spectroscopy

Crucial information on reaction products in magnesium potassium phosphate ceramics, essential for material design, is lacking. Setting reaction has been followed with time resolved infrared spectroscopy, supported by 2D correlation spectroscopy. We found evidence of a first amorphous orthophosphate precursor, possibly MgKPO4·H2O, forming early, and of a second intermediate amorphous phase, more structurally similar to MgKPO4·6H2O, forming later. Crystallization of MgKPO4·6H2O occurs from this last phase. Presence of amorphous Mg(OH)2 and magnesium phosphates identified as precipitates from diluted suspensions, was excluded. This complex set of parallel reactions, bears analogies with reaction of zinc phosphate cements and is consistent with recent NMR results.