Preparation of anhydrous dicalcium phosphate, DCPA, through sol–gel process, identification and phase transformation evaluation

Anhydrous dicalcium phosphate, CaHPO4, DCPA, as a member of the series of calcium phosphates, has considerable biological importance to the biomineralization processes in bones and teeth, and has found practical applications in dental cements and restorative materials. This compound, can reconstruct hard tissues because of high solubility in vivo in comparison with many of the other calcium phosphate compounds. In this work, Ca-deficient DCPA was synthesized through sol–gel process as a new method. Ca(NO3)2 · 4H2O and H3PO4 were employed as precursors and identified by XRD, FTIR and SEM spectroscopic techniques. The later technique makes the elemental analysis possible. The measured Ca/P molar ratio suggests, Ca1−x(H2PO4)2x(H2PO4)1−2x (x = 0.02, 0.04 and 0.07) formula for the synthesized compounds. The effect of aging time and heat treatment (sintering stage) on phase purity and phase transformations of products were systematically studied. The minimum necessary aging time for Ca-deficient DCPA preparation was 24 h. From X-ray patterns of powders sintered at different temperatures, the sintering temperature of Ca-deficient DCPA was confirmed to be 300 °C. According to the experimental results, varying the temperature from 300 to 1000 °C gave different stable phases as products: Ca-deficient DCPA at 300 °C, hydorxyapatite (Ca5(PO4)3OH, HA) at 600 °C and β-tri calcium phosphate (β-Ca3(PO4)2, β-TCP) at 1000 °C.