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We present a solid-state nuclear magnetic resonance (NMR) spectroscopy study of the local 31 P and 1 H environments in monetite [CaHPO 4 ; dicalcium phosphate anhydrous (DCPA)], as well as their relative spatial proximities. Each of the three 1 H NMR peaks was unambiguously assigned to its respective crystallographically unique H site of monetite, while their pairwise spatial proximities were probed by homonuclear 1 H– 1 H double quantum–single quantum NMR experimentation under fast magic-angle spinning (MAS) of 66 kHz. We also examined the relative 1 H– 31 P proximities among the inequivalent P1, P2 and H1, H2, H3 sites in monetite; the corresponding shortest internuclear 1 H– 31 P distances accorded well with those of a previous neutron diffraction study. The NMR results from the monetite phase were also contrasted with those observed from the monetite component present in a pyrophosphate-bearing calcium phosphate cement, demonstrating that while the latter represents a disordered form of monetite, it shares all essential local features of the monetite structure.

We report the synthesis and the characterization of dicalcium phosphate anhydrous (DCPA, CaHPO4) crystals prepared using a hydrothermal process. To prepare an aqueous solution containing Ca2+ and HPO42− ion precursors, we dissolved calcium nitrate tetrahydrate and ammonium phosphate dibasic, respectively, in deionized water at room temperature without adding a hydroxide precursor. The pH value was set to about 3.5. The structure and the morphology of the as-grown DCPA crystals were investigated using synchrotron X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and transmission electron microscopy. Disk-shaped microcrystals with rectangular surfaces were observed. The (001) atomic planes of the triclinic monetite structure were aligned along the surface normal direction. We also found that the individual DCPA crystals were single crystals with well-aligned mosaic domains. The full width at half maximum of the φ-scan at off-specular (-1-12) Bragg peaks was approximately 0.061°. This indicated that the atomic positions of the DCPA crystals in the in-plane direction were highly ordered.

Ceramic samples based on β-calcium pyrophosphate β-Ca2P2O7 were prepared from powders of γ-calcium pyrophosphate γ-Ca2P2O7 with preset molar ratios Ca/P = 1, 0.975 and 0.95 using firing at 900, 1000, and 1100 °C. Calcium lactate pentahydrate Ca(C3H5O3)2⋅5H2O and monocalcium phosphate monohydrate Ca(H2PO4)2⋅H2O were treated in an aqua medium in mechanical activation conditions to prepare powder mixtures with preset molar ratios Ca/P containing calcium hydrophosphates with Ca/P = 1 (precursors of calcium pyrophosphate Ca2P2O7). These powder mixtures containing calcium hydrophosphates with Ca/P = 1 and non-reacted starting salts were heat-treated at 600 °C after drying and disaggregation in acetone. Phase composition of all powder mixtures after heat treatment at 600 °C was presented by γ-calcium pyrophosphate γ-Ca2P2O7 according to the XRD data. The addition of more excess of monocalcium phosphate monohydrate Ca(H2PO4)2·H2O (with appropriate molar ratio of Ca/P = 1) to the mixture of starting components resulted in lower dimensions of γ-calcium pyrophosphate (γ-Ca2P2O7) individual particles. The grain size of ceramics increased both with the growth in firing temperature and with decreasing molar ratio Ca/P of powder mixtures. Calcium polyphosphate (t melt = 984 °C), formed from monocalcium phosphate monohydrate Ca(H2PO4)2⋅H2O, acted similar to a liquid phase sintering additive. It was confirmed by tests in vitro that prepared ceramic materials with preset molar ratios Ca/P = 1, 0.975, and 0.95 and phase composition presented by β-calcium pyrophosphate β-Ca2P2O7 were biocompatible and could maintain bone cells proliferation.

A novel form of anhydrous dicalcium phosphate CaHPO4 (monetite) is synthesized hydrothermally and characterized by single crystal X-ray diffraction. It crystallizes in the orthorhombic space group Ccm21 with a = 6.242(1) Å, b = 6.994(2) Å, c = 7.003(3) Å, V = 305.73(16) Å3 and it has four independent unit formulas in the unit cell (Z = 4). A three-dimensional crystal structure can be described by HPO4n infinite zigzag chains linked by Ca–O bonds. The comparison to the crystal structures of other polymorphs is given.