Calcium Phosphate Cements Prepared by Acid–Base Reaction

Abstract

We investigated the characteristics of calcium phosphate cements (CPC) prepared by an exothermic acid–base reaction between NH 4 H 2 PO 4 ‐based fertilizer (Poly‐N) and calcium aluminate compounds (CAC), such as 3CaO · Al 2 O 3 (C 3 A), CaO · Al 2 O 3 (CA), and CaO · 2Al 2 O 3 (CA 2 ), in a series of integrated studies of reaction kinetics, interfacial reactions, in‐situ phase transformations, and microstructure development. Two groups were compared: untreated and hydrothermally treated CPC specimens. The extent of reactivity of CAC with Poly‐N at 25°C was in the following order: CA > C 3 A ≫ CA 2 . The formation of a NH 4 CaPO 4 · x H 2 O salt during this reaction was responsible for the development of strength in the CPC specimens. The in‐situ phase transformation of amorphous NH 4 CaPO 4 · x H 2 O into crystalline Ca 5 (PO 4 ) 3 (OH) and the conversion of hydrous Al 2 O 3 gel →γ‐AIOOH occur in cement bodies during exposure in an autoclave to temperatures up to 300°C. This phase transformation significantly improved mechanical strength.