Abstract
Rapid-setting magnesium monophosphate cementitious materials were prepared by mixing calcined magnesium oxide (MgO) powder with an aqueous solution of diammonium phosphate (ADP) at 24°C. The activation energy for the curing reaction of the cement paste was determined to be 30.29 kcal/mole, and at age 1 hr the compressive strength was ≈900 psi (6.2 MPa). X-ray diffraction studies of the cured cement indicated that the major reaction product was magnesium orthophosphate tetrahydrate [Mg 3(PO 4) 2·4H 2O]. Magnesium ammonium phosphate hexahydrate [MgNH 4PO 4·6H 2O] and Mg(OH) 2 were also detected. Subsequent heating of the cement to 1300°C resulted in the conversion of the three compounds to a single phase of anhydrous magnesium orthophosphate [Mg 3(PO 4) 2]. The resultant product had a compressive strength of 7000 psi (48.23 MPa) and was thermally stable in air at temperatures >1000°C.
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