ИСТИНА

This work is aimed at creating biocompatible ceramic materials in CaO-P2O5, CaO-P2O5-Na2O and CaO-P2O5-K2O systems, by heat treatment of green powder products (cement stone) formed from highly loaded hardening suspensions. The following reactions were used to calculate the composition of starting powder mixtures: Ca3(C6H5O7)2•4H2O + 3Ca(H2PO4)2•H2O + 5H2O → 6CaHPO4•2H2O + 2H3C6H5O7 (1) Ca3(C6H5O7)2•4H2O + 3NaH2PO4 + 2H2O → 3CaHPO4 • 2H2O + Na2HC6H5O7 + NaH2C6H5O7 (2) Ca3(C6H5O7)2•4H2O + 3KH2PO4 + 2H2O → 3CaHPO4 • 2H2O + K2HC6H5O7 + KH2C6H5O7 (3) Calcium citrate tetrahydrate (Ca3(C6H5O7)2•4H2O) and calcium dihydrogen phosphate monohydrate (Ca(H2PO4)2•H2O), sodium dihydrogen phosphate (NaH2PO4) and potassium dihydrogen phosphate (KH2PO4) powders were used as components of the starting powder mixtures with the molar ratio corresponding to the reaction equations (1-3). Powder mixtures were homogenized in a planetary mill in an acetone medium for 15 minutes. Then the resulting powder mixtures were mixed with water at a water-solid ratio (w/s) = 0.5 by weight. A latex form was filled with the resulting paste and prepared samples were left for hardening and drying at the air for a week. The phase composition of cement stone samples based on Ca3(C6H5O7)2•4H2O and Ca(H2PO4)2•H2O, Ca3(C6H5O7)2•4H2O and NaH2PO4, Ca3(C6H5O7)2•4H2O and KH2PO4 was represented by brushite (CaHPO4•2H2O), monetite (CaHPO4) and unreacted Ca3(C6H5O7)2•4H2O and Ca(H2PO4)2•H2O, NaH2PO4, KH2PO4 respectively. The presence of unreacted salts is associated with the incompleteness of the reactions 1-3 during the process of chemical bonding. Cement stone samples with phase composition including monetite, sodium citrate, potassium citrate, citric acid and non-reacted components, were annealed in the furnace in the temperature range of 500-1000oC with an exposure of 2 hours for obtaining ceramics. During heat treatment, the components in the cement stone are subjected to thermal destruction, and the resulting components interact with each other. The phase composition of the ceramic materials was investigated using X-ray diffraction data analysis. After annealing of cement stone based on Ca3(C6H5O7)2•4H2O and Ca(H2PO4)2•H2O at 500oC phase composition of the ceramic materials was represented by γ-Ca2P2O7 and γ-Ca(PO3)2. In the temperature range of 700-900oC γ-Ca(PO3)2 and γ-Ca2P2O7 phases passed into a higher-temperature modifications (β-Ca(PO3)2 and β-Ca2P2O7). And after annealing at 1000oC the phase composition of ceramics was presented only with β-Ca2P2O7. Heat treatment of cement stone based on Ca3(C6H5O7)2•4H2O and NaH2PO4 500oC resulted in the formation of a phase composition that included the phases β-CaNaPO4 and Ca10(PO4)6(OH)2. At 700oC, in addition to β-CaNaPO4 and Ca10(PO4)6(OH)2, the phases of double calcium – sodium pyrophosphate Na2CaP2O7 and tricalcium phosphate β-Ca3(PO4) were formed. After firing at 900 oC, only the β-CaNaPO4 phase was detected in the ceramic according to X-ray diffraction data. After firing of cement stone based on Ca3(C6H5O7)2•4H2O and KH2PO4 at 500oC the phase composition of the samples was represented by the phases β-CaKPO4, Ca10(PO4)6(OH)2 and β-Ca3(PO4)2. After firing in the temperature range of 700-900oC, CaKPO4 passes into a higher-temperature modification-α-CaKPO4, and the phases of double calcium – potassium pyrophosphate K2CaP2O7 and potassium-substituted tricalcium phosphate Ca10K(PO4)7 were also observed. After firing at 900oC, only the α -CaKPO4 phase was detected in the ceramic according to X-ray diffraction data. The resulting material based on β-Ca2P2O7, β-CaNaPO4, and β-CaKPO4 which has the ability to slowly dissolve, can be used in regenerative medicine for the treatment of bone defects. This work was supported by Russian Foundation for Basic Research (project No 18-29-11079).