Ceramics in the Ca2P2O7–Ca(PO3)2 System Obtained by Annealing of the Samples Made from Hardening Mixtures Based on Calcium Citrate Tetrahydrate and Monocalcium Phosphate Monohydrate

Abstract: Calcium phosphate ceramics in the Ca2P2O7–Ca(PO3)2 system was obtained by annealing of hardened samples formed from highly loaded suspensions (HLS). HLSs included water and a homogenized powder mixture of calcium citrate tetrahydrate Ca3(C6H5O7)2 ⋅ 4H2O and monocalcium phosphate monohydrate Ca(H2PO4)2 ⋅ H2O. The latter was taken in the amount providing the molar ratio of Ca/P = 1 in the powder mixture, as well as at a molar ratio of Ca/P < 1 so that the excess of monocalcium phosphate monohydrate Ca(H2PO4)2 ⋅ H2O provided the formation of the calcium polyphosphate Ca(PO3)2 phase upon annealing. The samples were molded by extrusion of the HLS through a die with a diameter of 2 mm by sandwiching powder cords. After hardening and drying, the phase composition of all obtained samples included brushite CaHPO4 ⋅ 2H2O, monetite CaHPO4, monocalcium phosphate monohydrate Ca(H2PO4)2 · H2O, and octacalcium phosphate Ca8(HPO4)2(PO4)4H2O. According to the XRD data, the phase composition of all ceramic samples after annealing in a range of 800–1000°C included calcium β-pyrophosphate β-Ca2P2O7, and a ceramic sample obtained from a powder mixture with the highest excess of monocalcium phosphate monohydrate Ca(H2PO4)2 · H2O additionally included tromelite Ca4P6O19. Hardening HLSs containing water and a homogenized powder mixture of calcium citrate Ca3(C6H5O7)2 · 4H2O and monocalcium phosphate monohydrate Ca(H2PO4)2 · H2O can be used for layer-by-layer extrusion molding. The resulting calcium phosphate ceramics with lowered sintering temperature can be used for the design of a resorbable matrices of tissue engineering constructs. © 2020, Pleiades Publishing, Ltd.