In this paper, we present results of a study on the possibilities of the mechanochemical synthesis of copper-substituted hydroxyapatite with the replacement of calcium cations by copper cations. During the synthesis, various reagents—sources of copper cations—were used. It was found that the nature of the carrier of the doping cation plays an important role in the formation of the structure of Cu-substituted apatite. It was established that a single-phase material forms most efficiently when copper (II) phosphate is employed; however, even this reagent did not allow the introduction of a large amount of copper into the hydroxyapatite crystal lattice. Out of 10 calcium cations in the unit cell of hydroxyapatite, no more than two could be replaced by copper cations. A further increase in the copper concentration led to the formation of an amorphous product. The degree of copper substitution in hydroxyapatite increases as the oxidation state of copper increases. The thermal stability of the hydroxyapatite with the highest degree of substitution was studied. It was shown that the presence of copper cations significantly decreases the stability of hydroxyapatite. In a temperature range of 550–750 °C, it is gradually decomposed to form a mixture of rhombohedral Ca2.57Cu0.43(PO4)2 and CuO. The FTIR spectrum of Ca2.57Cu0.43(PO4)2, which is a copper-substituted β-Ca3(PO4)2, was first studied.

The results of calculations of the substitution of calcium atoms for zinc in the structure of hydroxyapatite using density functional theory methods using hybrid functionals in the supercell model are presented. Changes in the parameters and volume of the unit cell, energy bands and energy of formation of substitutions with increasing number of substitutions in different positions of calcium (Ca1 and Ca2) are analyzed in comparison with experimental data. A proportional decrease in the parameters and volume of the cell with an increase in the number of substitutions has been established, and a more complex behavior of various cell parameters has been revealed, which is a consequence of the violation of the original symmetry. Electronic energy levels were found to depend on the zinc concentration and the positions of the calcium ions being replaced. In this case, the band gap Eg of hydroxyapatite experiences a jump of 0.6–0.8 eV with the introduction of one zinc ion per supercell, and then decreases and reaches values below the initial Eg value by 0.5–0.6 eV for substitutions in Ca1 positions, and by 0.8–0.9 eV for substitutions in Ca2 positions. It has been shown that the energy of substitution has a complex dependence on the concentration of the substituent and the replacement of calcium ions with zinc occurs predominantly in the Ca2 position over the entire concentration range. An analysis of changes in interatomic distances during the process of relaxation to the equilibrium state at different zinc concentrations was carried out. We revealed formation of bonds between zinc atoms and nearby oxygen anions, which violates the original symmetry of hydroxypatite structures. The data obtained are important for understanding the structural changes that occur during substitution, as well as for understanding and predicting the properties of synthesized biocompatible materials.

The feasibility of soft mechanochemical synthesis was studied here for hydroxyapatite with various types of substitution. It was shown that this method allows obtaining hydroxyapatites substituted with copper or iron cations and hydroxyapatites cosubstituted with zinc cations and silicate groups. Thermal stability of the synthesized samples was evaluated. It was found that to preserve phase homogeneity of the material, the temperature during the preparation of ceramic products and coatings should not exceed 600–800 °C. An exception is the hydroxyapatite where a hydroxyl group is expected to be replaced by a copper cation during the synthesis at a degree of substitution x = 0.5. For this sample, the temperature of the the heat treatment can be increased to 1100–1200 °C because copper cations return to the hydroxyapatite crystal lattice at these temperatures, and the material becomes single-phase.

The doping of hydroxyapatite with various substituent ions can give this material new and useful properties. Nonetheless, local distortions of structure after doping can change the properties of the material. In this work, the thermal stability of copper-substituted hydroxyapatite synthesized by the mechanochemical method was investigated. In situ diffraction analyses showed that copper ion diffusion during the heating of Cu-substituted hydroxyapatite promotes phase transformations in the substituted hydroxyapatite. The behavior of copper ions was studied in samples with ratios (Ca + Cu)/P = 1.75 and 1.67. It was found that in both cases, single-phase Cu-substituted hydroxyapatite with the general formula Ca10−xCux(PO4)6−y(CO3)y(OH)2−yOy is formed by the mechanochemical synthesis. When heated at approximately 600–700 °C, the lattice loses copper cations, but at higher temperatures, CuO diffusion into the hydroxyl channel takes place. Cuprate-substituted hydroxyapatite with the general formula Ca10(PO4)6(OH)2−2x(CuO2)x forms in this context. At 1200 °C, the sample is single-phase at (Ca + Cu)/P = 1.75. Nonetheless, slow cooling of the material leads to the emergence of a CuO phase, as in the case of (Ca + Cu)/P = 1.67, where the material contains not only CuO but also Cu-substituted tricalcium phosphate. In the manufacture of ceramic products from Cu-substituted hydroxyapatite, these structural transformations must be taken into account, as they alter not only thermal but also biological properties of such materials.

— We have examined the feasibility of mechanochemically stimulated thermal synthesis of lithium monoaluminates from a boehmite + lithium carbonate mixture with the use of a semicommercial scale ball mill. The effect of mechanical pretreatment of the mixture of boehmite and lithium carbonate on the solid-state reaction between them has been studied using thermogravimetry, in situ X-ray diffraction, room-temperature X-ray diffraction, specific surface area measurements, and particle size analysis. The results demonstrate that mechanical pretreatment of such a mixture with an Al : Li atomic ratio of 1 : 1 in a semicommercial ball mill at a vial rotation rate of 120 rpm for 58 h, followed by heat treatment in air for 4 h at 950°C, allows phase-pure gamma-lithium aluminate to be prepared.

The work shows that single-phase hydroxyapatite doped with zinc or copper ions can be obtained using a solid-phase mechanochemical synthesis after 30 min of processing the reaction mixture in a planetary ball mill. To understand the mechanism of incorporating doping elements in the apatite structure, two substitution reactions have been investigated, namely replacement of the calcium and hydroxide ions with copper or zinc ions. The research has shown that, in the synthesized material, the dopant ions mainly take the sites of calcium ions. The degree of substitution can be up to 2 mol of substituent per mol of hydroxyapatite. The obtained samples can be used to produce medical bioresorbable items and coatings with antibacterial properties.

It has been shown that mechanical activation of a boehmite + lithium carbonate mixture with an Al : Li atomic ratio of 5 : 1 in an AGO-2 planetary activator at a centrifugal acceleration of 40g and milling times from 1 to 10 min and subsequent heat treatment of the mechanically activated mixture for 2 h at 900°C ensure the formation of fine-particle phase-pure lithium pentaaluminate with a specific surface area from 15 to 25 m2/g. We consider a scheme of the processes involved in the mechanically stimulated thermal synthesis of lithium pentaaluminate.

— We have found conditions for the synthesis of fine-particle phase-pure α-LiAlO 2 via heat treatment of a mechanically activated mixture of gibbsite and lithium carbonate in air. The results demonstrate that, to synthesize α-LiAlO 2 , the mechanical activation of the reaction mixture should cause no gibbsite amorphization and heat treatment in air should be performed in the range 650–700°C.

The influence of the conditions of preliminary mechanical activation of a mixture of gibbsite and lithium carbonate in a planetary-type activator and the conditions of subsequent heat treatment on the phase composition of lithium aluminates is studied. It is shown that for the formation of γ-LiAlO2 it is necessary that at the stage of mechanical activation of the mixture an almost complete amorphization of aluminum hydroxide occurs, and the air heat treatment is carried out at a temperature above 750 °C. Thermal treatment of a mechanically activated mixture in the atmosphere with the partial water vapor pressure of below 1 Pa allows the synthesis of γ-LiAlO2 without significant amorphization of aluminum hydroxide at above 600 °C. For the synthesis of α-LiAlO2 preliminary mechanical activation should not lead to the amorphization of aluminum hydroxide, and the process of heat treatment in the air should be carried out at temperatures below 700 °C. The mechanism of formation of highly dispersed lithium aluminates during mechanical activation and subsequent heat treatment of a mixture of gibbsite and lithium carbonate is discussed.

It is shown that the phase composition of lithium aluminates formed when aluminum hydroxide in the form of gibbsite interacts with lithium carbonate in their mixture with Al: Li atomic ratio of 5: 1 depends on the duration of a preliminary mechanical activation of the mixture and on the temperature of the subsequent thermal treatment. A thermal treatment of the starting mixture at temperatures exceeding 800°C yields LiAl5O8 with a substantial admixture of α- and γ-LiAlO2. Raising the duration of the mechanical activation to 5 min and more makes it possible to obtain highly dispersed single-phase LiAl5O8 with a specific surface area larger than 20 m2 g–1

Using thermogravimetry, in situ X-ray diffraction, room-temperature X-ray diffraction, specific surface area measurements, and particle size analysis, we have studied how preliminary mechanical activation of a mixture of aluminum hydroxide and lithium carbonate in an AGO-2 planetary mill and subsequent heat treatment of the mixture influence the synthesis of fine-particle nanostructured gamma-lithium monoaluminate. We have proposed a scheme of the structural changes accompanying the synthesis of gamma-lithium monoaluminate.

This paper examines the structural and particle size characteristics of lithium carbonate after mechanical processing in an AGO-2 planetary activator, followed by heat treatment. Milling increases the specific surface area of lithium carbonate, changes the aggregate size distribution, reduces the crystallite size, increases the lattice strain in the material, and changes the monoclinic cell parameters. Subsequent heat treatment of the mechanically activated samples in the range 25–500°C is accompanied by recrystallization of the material: its specific surface area and lattice strain decrease, the crystallite size increases, and its unit-cell parameters change.

The changes in the dielectric properties of steatite ceramic before and after irradiation were studied. The characteristic vibrational frequency ω0 affects the change in the properties of the ceramic, which is important for devices operating in the presence of radiation. It was found that the permittivity of ceramic increased after irradiation. The structure of the material and the sintering temperature of the ceramic determine the relaxation region of the material.

An influence of the conditions of the mechanical activation of aluminium hydroxide and lithium carbonate mixture in the planetary type activator APF and of the conditions of subsequent thermal treatment upon the phase composition, morphology and dispersity level of lithium gamma-monoaluminate (gamma-LiAlO2) is considered. Potentialities are demonstrated concerning the use of the gamma-LiAlO2 synthesized for obtaining the matrix electrolyte for a fuel element with molten carbonate electrolyte as well as within a separator for thermal lithium batteries.