Vinylphosphonic acid-modified calcium aluminate and calcium silicate cements: Fid-Bau Portal

Vinylphosphonic acid-modified calcium aluminate and calcium silicate cements

Sugama, T. / Mora, R.N. jun.

Cementitious materials in terms of calcium phosphate cements(CPC) were prepared through the acid-base reaction between vinylphosphonic acid (VPA) and calcium aluminate cement (CAC) reactants or calcium silicate cement (CSC) reactants at 25 deg C. Using CAC, two factors were responsible for the development of strength in the cements: one is the formation of an amorphous calcium-complexed vinylphosphonate (CCVP) salt phase as the reaction product, and the other was the high exothermic reaction energy. Because the formation of CCVP depletes the calcium in the CAC reactants, (Al2O3)(xH2O) gel was precipitated as a by-product. CCVP-> amorphous calcium pyrophosphate hydrate (CPPH) and (Al2O3)(xH2O) -> gamma-AlOOH phase transitions occured in the CPC body autoclaved at 100 deg C. Increasing the temperature to 200 deg C promoted the transformation of CPPH into crystalline hydroxyapatite (HOAp). In the VPA-CSC system, the strong alkalinity of CSC reactant with its high CaO content served in forming the CPPH reaction product which led to a quick setting of the CPC at 25 deg C. Hydrothermal treatment at 100 deg C resulted in the CPPH -> HOAp phase transition, which was completed at 300 deg C for both the VPA-CAC and VPA-CSC systems, and also precipitated the silica gel as by-product. Although the porosity of the specimens was one of the important factors governing the improvement of strength, a moderately mixed phase of amorphous CPPH and crystalline HOAp as the matrix layers contributed significantly to strengthening of the CPC specimens.