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Materials (cement stone samples) in the CaO-K2O-SO3-H2O system with the target phase compositions, including syngenite K2Ca(SO4)2·H2O and calcium sulfate dihydrate CaSO4·2H2O, were prepared from powder mixtures of calcium sulfate anhydrite CaSO4, and/or calciolangbeinite K2Ca2(SO4)3, and potassium sulfate K2SO4 via hydration reactions at a water/powder ratio within an interval of 0.5–0.9. It was revealed that samples with contents of 25, 50, 75 and 100 mol% of syngenite K2Ca(SO4)2·H2O demonstrated a nonlinear dependence of their respective microstructures on their phase compositions. The microstructures of samples with phase compositions of 25 and 75 mol% of syngenite K2Ca(SO4)2·H2O consisted of pillar crystals. The microstructures of samples with phase compositions of 50 and 100 mol% of syngenite K2Ca(SO4)2·H2O consisted of plate crystals. An explanation of microstructure formation was set forth, taking into account equilibria of the dissolution–crystallization processes during cement stone formation. Materials obtained in the CaO-K2O-SO3-H2O system consisting of biocompatible and resorbable (soluble in water) phases can be recommended for testing as potential substances for bone defect treatments.

Mixture of abramis brama (freshwater bream), carassius carassius (crucian carp), and sander lucioperca (pike perch) scales was used for the preparation of fish scale powder containing about 26.5 wt. % of removed when heating components preferably of organic nature, and 63.5 wt. % of mineral components. Fish scale powder enriched with inorganic components was prepared from washed, dried, and ground fish scale mixture using vibration sieving. Inorganic powders consisting of hydroxyapatite and magnesium whitlockite were obtained via heat treatment of this fish scale powder at 800-1000 oC. Particles of these inorganic powders consisted of sintered grains with dimensions less than 100 nm after heat treatment at 800 oC, less than 200 nm after heat treatment at 900 oC, and 100-500 nm after heat treatment at 1000 oC. Fish scale powder enriched with inorganic components as well as heat-treated inorganic powders consisting of hydroxyapatite and magnesium whitlockite can be recommended for the production of different materials such as ceramics or composites.

Synthesis from mixed-anionic aqueous solutions is a novel approach to obtain active powders for bioceramics production in the CaO-SiO2-P2O5-Na2O system. In this work, powders were prepared using precipitation from aqueous solutions of the following precursors: Ca(NO3)2 and Na2HPO4 (CaP); Ca(NO3)2 and Na2SiO3 (CaSi); and Ca(NO3)2, Na2HPO4 and Na2SiO3 (CaPSi). Phase composition of the CaP powder included brushite CaHPO4‧2H2O and the CaSi powder included calcium silicate hydrate. Phase composition of the CaPSi powder consisted of the amorphous phase (presumably containing hydrated quasi-amorphous calcium phosphate and calcium silicate phase). All synthesized powders contained NaNO3 as a by-product. The total weight loss after heating up to 1000 °C for the CaP sample—28.3%, for the CaSi sample—38.8% and for the CaPSi sample was 29%. Phase composition of the ceramic samples after the heat treatment at 1000 °C based on the CaP powder contained β-NaCaPO4 and β-Ca2P2O7, the ceramic samples based on the CaSi powder contained α-CaSiO3 and Na2Ca2Si2O7, while the ceramics obtained from the CaPSi powder contained sodium rhenanite β-NaCaPO4, wollastonite α-CaSiO3 and Na3Ca6(PO4)5. The densest ceramic sample was obtained in CaO-SiO2-P2O5-Na2O system at 900 °C from the CaP powder (ρ = 2.53 g/cm3), while the other samples had densities of 0.93 g/cm3 (CaSi) and 1.22 (CaPSi) at the same temperature. The ceramics prepared in this system contain biocompatible and bioresorbable phases, and can be recommended for use in medicine for bone-defect treatment.

Ceramic samples based on b-calcium pyrophosphate b-Ca2P2O7 were prepared using firing at 900, 1000, and 1100 oC from powders of g-calcium pyrophosphate g-Ca2P2O7 with preset molar ratios Ca/P=1; 0,975 and 0,95. To prepare powders of g-calcium pyrophosphate g-Ca2P2O7 with preset molar ratio Ca/P=1; 0,975 and 0,95 powder mixtures based on 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, dried, disaggregated in acetone, and heat-treated at 600 oC. The phase composition of powder mixtures after treatment if planetary mill in aqua medium included both brushite CaHPO4⋅2H2O or monetite CaHPO4, and starting salts. The phase composition of all powder mixtures after disaggregation in acetone in planetary mill included monetite CaHPO4 and starting salts. After heat treatment at 600 oC according to the XRD data phase composition of all powder mixtures was presented by g-calcium pyrophosphate g-Ca2P2O7. The grain size of ceramics increased both with the growth of firing temperature and with decreasing of molar ratio Ca/P of powder mixtures. Calcium polyphosphate (t melt =960–968 oC) formed from monocalcium phosphate monohydrate Ca(H2PO4)2⋅H2O acted like a liquid phase sintering additive. It was confirmed by tests in vitro, that prepared ceramic materials with preset molar ratio Ca/P=1; 0,975 and 0,95 and phase composition presented by b-calcium pyrophosphate b-Ca2P2O7 according to XRD data were biocompatible and could maintain bone cells proliferation.

Lomonosov Moscow State University, 119991, Russia, Moscow Leninskie Gory, 1 E-mail: t3470641@yandex.ru Manuscript received online 20 October 2020, revised and accepted 31 October 2020 Uniform dark grey colored powders of β-calcium polyphosphate β-Ca(PO3 )2 with fine particles (2–4ṷm) modified with amorphous carbon were prepared using heat treatment of monocalcium phosphate monohydrate Ca(H2 PO4 )2 .H2O after treatment in water solution of lactic acid CH3 CHOHCOOH under mechanical activation using planetary mill. Prepeared dark grey coloured powders of calcium polyphosphate can be used as a multifunctional additive in technology of porous calcium phosphate ceramics using stereolithographic printing as a molding method of semi-finished items.

Thermal plasma processing of carbon sources using a plasma jet with high heat capacity is one of the most promising methods for the synthesis of new materials. This paper describes the low-temperature deposition of carbon nanomaterials by remote plasma-enhanced chemical vapor deposition (PECVD) in the absence of catalysts. The remote PECVD process differs from conventional and direct PECVD process in two ways: (a) only a subset of the process reactants and/or diluents are directly plasma excited; and (b) thin film deposition takes place on a substrate that is outside of the plasma glow region. In conventional CVD methods, carbon is produced from the decomposition of carbon sources such as hydrocarbons, carbon monoxide, alcohols, and so on, over a metal catalyst. The unavoidable metal species remaining in carbon nanomaterials would lead to obvious disadvantages for property characterization and application exploration. Despite sustained efforts, it is still an intractable problem to remove metal catalysts completely from carbon nanomaterials samples without introducing defects and contaminations. Good reactor design allowed to overcome problems of chemical and structural purity, and poor process robustness in terms of phase composition of product from run to run. For the synthesis of graphene materials, carbon black, carbon nanotubes, nanowires we used the thermal plasma generator which is a high current divergent anode-channel DC plasma torch. The experiment involved a simultaneous input of hydrocarbons (methane, propane, butane, acetylene) with the plasma forming gas (helium, argon, nitrogen) into the plasma torch, wherein heating and decompositions occurred in the plasma jet and in the region of the arc discharge, followed by condensation of the synthesis product on metallic surfaces. The deposition rate was varied with distance from the plasma. Consumption of carbon source, plasma forming gas and plasma torch power were changed independently from each other. For the experimental conditions the electric power of plasma torch was set up to 40 kW. Regularities of formation of carbon thread-like nanostructures and graphene in the course of hydrocarbons pyrolysis in thermal plasma without participation of catalytic particles were studied by means of electron microscopy, X-ray diffraction, IR-spectrometry and thermogravimetry. Depending on the pyrolytic synthesis parameters, different proportions of crystal carbon and soot may be obtained. It has been demonstrated that the phase composition is varied by hydrocarbons flow rate, plasma forming gas pressure and dc plasma torch power. It has been established through the experiments that carbon nucleation is volumetric and proceeds according to the model of explosive soot formation.