Inorganic Materials最新文献

This review is concerned with the synthesis of tricalcium phosphates and hydroxyapatites doped with silver, strontium, zinc, magnesium, iron, copper, manganese, gadolinium, potassium, sodium, and silicate ions or codoped with two of the above ions; the preparation of related ceramics, calcium phosphate cements, and composites with polymers that are used in medicine (methylcellulose, sodium alginate, polyvinylpyrrolidone, and polylactide); and investigation of their phase composition, microstructure, and behavior in simulated body fluid.

PbTe, SnTe, and Pb_0.75Sn_0.25Te single crystals have been grown and their electrical conductivity and thermoelectric power have been measured in the range 90–300 K before and after annealing. The results demonstrate that the conductivity of unannealed PbTe and Pb_0.75Sn_0.25Te crystals, its variation with temperature, and its type are determined mainly by structural defects formed during crystal growth and sample preparation, which can be eliminated by annealing. The electrical properties of unannealed and annealed SnTe crystals are determined mainly by acceptor vacancies on the tin site, whose concentration reaches 10²⁰ to 10²¹ cm^–3.

Nanocrystalline undoped and Sr²⁺-doped YFeO₃ has been prepared by sol–gel synthesis. Its structure and elemental composition have been determined by X-ray diffraction and X-ray microanalysis. Thin films of the synthesized nanopowders have been produced on the surface of silicon substrates by spin coating. Surface resistivity measurements in air and in the presence of the gases to be detected have demonstrates that the materials thus prepared have a sensor response to NH₃ and CO. The concentration of the gases was 50 ppm, and the sensor signal exceeded 50%.

Carbon nanotubes can be used as active matrices for accommodation and transfer of biomodeling components. It seems likely that the application area of such systems can include reactions ensuring aerobic and peroxide oxidation of hydrocarbons. Here, we report a study of iron-containing multiwalled carbon nanotubes (Fe@MWCNTs) and manganese glycinate dihydrate ([NH₂CH₂COO]₂Mn∙2H₂O) as an active catalytic system for aerobic oxidation of hydrocarbons. The synthesized starting compounds were identified using infrared spectroscopy, electron microscopy, and elemental analysis. Aerobic oxidation of cumene was used as a model test reaction. The results demonstrate that, taken alone, each compound increases the reaction rate by 10–12 times in comparison with a control sample, whereas in the case of the joint use of Fe@MWCNTs and manganese glycinate dihydrate the reaction rate rises many times, reaching 373 mm³ O₂/min. We have proposed a scheme of the oxidation process, which describes the observed synergistic effect. The use of such catalytic systems is of interest for further research in the field of bioinorganic catalysis.

Fe:ZnSe single crystals are promising materials for mid-infrared (4–5 μm) lasers. Here we present thermodynamic analysis of the vapor phase growth of Fe:ZnSe single crystals by a modified free growth method. Doping with Fe atoms was performed during the growth process. The single crystals were grown from sublimates of the binary compounds ZnSe and FeSe placed in separate source compartments. Vapors of the starting materials were directed to a single-crystal seed in the growth zone through calibrated orifices. Calculations were performed for physical transport in a helium atmosphere. We took into account three main steps of the growth process: vaporization of the starting materials in the source compartments, transport of the vapor to the growth zone, and crystal growth on the seed. The rate of the growth process was assumed to be limited by mass transport from the source to the growth zone, controlled by the geometric dimensions and mutual arrangement of the elements of the growth ampule. The experimental data on the dopant concentration are compared to the calculation results. The proposed growth technique is shown to ensure preparation of single crystals up to 8 cm³ in volume, with a Fe concentration of up to 5 × 10¹⁸ cm^–3.

The thermophysical properties of the PbFe_0.5Ta_0.5O₃ relaxor ferroelectric have been studied in the temperature range 150–800 K. We have revealed anomalies in its heat capacity, thermal diffusivity, and thermal conductivity in the region of the broad ferroelectric transition at T_C ≈ 275 K, the Burns temperature T_B ≈ 690 K, and an intermediate temperature T* ≈ 380 K. The anomalous behavior of heat capacity in the temperature range 200–700 K has been shown to be due to three-level states (Schottky anomaly). We have examined prevailing phonon mechanisms of heat transport in the multiferroic with a nanopolar structure. The anomalous behavior of its thermophysical properties in the temperature range T_B > T > T_C has been attributed to the growth and changes in the system of reorientable nanopolar regions. We have demonstrated that studies of thermophysical properties allow one to determine all characteristic temperatures of relaxor ferroelectrics, related to the formation of a nanopolar structure and its variation with temperature. The results of this study are discussed in combination with structure data.

Electrically conductive carbon nanomaterials possessing high mechanical and tribological properties are in high demand for a wide range of applications. In the context of the potential usage, functional characteristics of composite materials produced by HPHT sintering of shock-synthesized nanopolycrystalline diamond powders have been investigated for the first time. Nanodiamonds powders with narrow and polydisperse granulometric distributions were sintered both without a binder and after infiltration with copper and silicon at pressures of 8–9 GPa and temperatures up to 1600°C. The binder-less sintered nanodiamond compacts are characterized by a hardness up to 33 GPa, electrical conductivity of ~6600 Sm^–1, and a friction coefficient on hardened steel as small as 0.07. Silicon infiltration leads to somewhat smaller conductivity (~190 Sm^–1), but produces compacts with hardness increased up to 48 GPa, improved mechanical properties and a low friction coefficient (~0.04). Copper infiltration sintering generally replicates functional properties of the compacts without a binder. However, in contrast to composites with copper, the compacts obtained without a binder and infiltrated with silicon demonstrate semiconductor-type conductivity, favorable for high-temperature applications. The sintering parameters are readily accessible with modern instrumentation, thus opening opportunities for broad use of compacts based on shock-synthesized polycrystalline nanodiamonds, for example, in miniature sliding bearings and electrical contacts working in severe conditions.

This study presents the results of an investigation into the hot pressing of optical magnesium oxide (MgO) ceramics from powders synthesized via the self-propagating high-temperature synthesis (SHS) method. A preprocessing technique for industrially produced raw materials is proposed to adjust their impurity composition to a level sufficient for obtaining high-quality optical ceramics. The addition of 1 wt % LiF as a sintering aid to the SHS precursor enables the fabrication of MgO ceramics with a thickness of 1.5 mm, achieving near-theoretical transmittance across the material’s transparency range (0.2–9.5 µm). It is demonstrated that even a small amount of LiF (as low as 0.125 wt %) significantly enhances the transparency of the ceramics; however, it also leads to a substantial reduction in thermal conductivity within the studied temperature range (25–300°C). The thermal conductivity of MgO ceramics without the sintering aid is measured at 67.7 W/(m K) at room temperature. The microhardness of the fabricated ceramic samples remains largely unaffected by the LiF content in the precursor, with values ranging from 9 to 11 GPa.

Extrapolation of available experimental data for AnO₂ (An = Th, U–Bk), represented on a unified binding energy scale on which E_b(O 1s) = 529.9 eV, has been used to evaluate bond lengths and An 4f electron binding energies in AnO₂ (An = Cf–Lr). The bond lengths thus found are in qualitative agreement with results obtained in the ionic approximation, and the An 4f electron binding energies have been determined with an uncertainty of ±0.4 eV, which is an order of magnitude smaller than that in available reference values. The results obtained on the structure of the actinide dioxides are needed for relativistic calculations of valence band X-ray photoelectron spectra of AnO₂, and the An 4f electron binding energies are needed for constructing quantitative schemes of molecular orbitals in AnO₂. These data will be useful for understanding general aspects of the formation of specific features of the electronic structure and chemical bonding in the AnO₂ (An = Th–Lr) series.

In this paper, we report the preparation of titanium carbide from mineral concentrate by plasma synthesis, without chemical isolation of TiO₂, a major oxide component. Chemical and phase analysis data for synthesis products are used to discuss chemical reactions occurring during plasma treatment of a starting mixture of the concentrate and a carburizer. We describe a model for the destructuring of mixed compounds in the mineral concentrate and synthesis of titanium carbide. As a local power source, we use an experimental setup comprising an indirect electric arc plasma source and microwave generator. The specific enthalpy of the plasma jet reaches ~3 kJ/g at a weight-average velocity of up to 10 m/s, and additional exposure to a microwave field makes it possible to raise the plasma energy and process temperature. In this manner, high-purity stoichiometric titanium carbide has been prepared. Plasma processing has been demonstrated to be a promising approach for the preparation of titanium carbide nanoparticles from titanium-containing mineral concentrates.