Inorganic Materials最新文献

We consider the effect of mechanical activation on the particle size and strain of natural sphalerite particles and demonstrate that mechanical activation of the mineral for 20 min in a high-energy planetary mill reduces the crystallite size to 20 nm and that in this process the lattice strain in sphalerite reaches 0.73–0.85%. Thermogravimetry, calorimetry, and mass spectrometry have been used to study sphalerite oxidation processes during nonisothermal heating to a temperature of 1000°C in flowing air before and after mechanical activation. Mechanical activation of sphalerite has been shown to lead to a slight increase in the rate of sulfate formation, a decrease in the temperature and enthalpy of the thermal effects involved, and release of sulfur dioxide as a product of interaction with oxygen starting at a temperature of 150°C.

A process has been developed for the preparation of ultrafine amorphous precursors (starting mixtures) differing in the ratio of Er:YAG to 20Bi₂O₃–60B₂O₃–20BaO. Using selective laser sintering, we have demonstrated the feasibility of producing functional glass-ceramics—with a crystalline phase consisting of yttrium erbium aluminum garnet and an yttrium erbium borate—from the synthesized precursor. The chemical and phase transformations during heat treatment of the precursor were analyzed using differential scanning calorimetry and X-ray diffraction, and changes in the macrocomposition of the glass-ceramics at characteristic synthesis temperatures were assessed by inductively coupled plasma atomic emission spectroscopy. The results demonstrate that the ultrafine precursor we used is potentially attractive for the fabrication of optical integrated circuits by selective laser sintering.

Information on the exciton sizes in bulk copper, silver, zinc, cadmium, mercury, tin, and lead sulfides has been summarized using data on the effective masses of charge carriers and permittivity. The possible impact of exciton size effects on the electronic (optical) properties of these sulfides in the nanosized (nanocrystalline) state has been considered.

Nanosized NiFe₂O₄ and ZnFe₂O₄ were synthesized by the citrate combustion method. The nanopowders were characterized by elemental analysis and powder X-ray diffraction; size, dispersion, and morphological features were determined. It was established that the nanopowders of the synthesized ferrite spinels (average particle size 38 ± 3 nm for NiFe₂O₄ and 49 ± 3 nm for ZnFe₂O₄) are effective catalysts for the oxidation reaction of methylene blue dye (degradation efficiency 92% for nickel ferrite and 95% for zinc ferrite). The observed dependence of the catalytic activity of nanosized ferrites on the type of illumination is more pronounced for nickel ferrite (a 2.5-fold increase in the reaction rate constant and a 31% increase in the degradation efficiency).

The wettability and work of adhesion of the Ge₂₈Sb₁₂Se₆₀ glass melt to stainless steel grades AISI 201 and AISI 430 with a conventional and nitrided surface, titanium and a tungsten carbide alloy YG8 in the temperature range of 480–530°C was studied. It was found that nitriding of the stainless steel surface leads to a 2–3-fold decrease in the adhesion of chalcogenide melts to the stainless steel surface. Among all the considered structural materials, the maximum adhesion of the Ge₂₈Sb₁₂Se₆₀ glass melt is observed to AISI 201 stainless steel, the minimum to AISI 430 nitrided steel.

A new technique has been developed for the synthesis of dimolybdenum pentaboride nanoparticles via reaction between molybdenum powder and amorphous boron in the molar ratio 2 : 5 after mechanochemical activation in argon. The reaction was run in ionic salt melts with various compositions at temperatures of 750, 800, and 850°C in a hydrogen atmosphere. Using X-ray diffraction, X-ray energy spectrometry, simultaneous thermal and elemental analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, and specific surface area measurements, we demonstrate that the use of ionic melts makes it possible to obtain nearly spherical single-phase Mo₂B₅ particles ~30 nm in average diameter only at a reaction time of at least 28 h. The particles have a rhombohedral structure with unit-cell parameters a = 0.3007–0.3015 nm and с = 2.090–2.095 nm.

Photoionization cross-sections of atomic shells are essential for studying the electronic structure of materials using X-ray photoelectron spectroscopy. In the chemical bonding of lanthanoids with other atoms, electrons from both the ground-state configurations and excited states participate. However, existing tables only include photoionization cross-sections for the ground-state configurations of lanthanoids. In this work, photoionization cross-sections were calculated for both the ground and, for the first time, the excited states of lanthanoid atoms for photon energies of 1253.6 and 1486.6 eV. The calculations were based on relativistic wavefunctions of the self-consistent field obtained using the Dirac–Fock method. The application of these results to experimental X-ray photoelectron spectra of lanthanoid compounds is discussed, exemplified by the experimental spectrum of CeO₂ and the first calculated spectrum of cluster Ce₆₃O₂₁₉.

The technological foundations for producing the MAX phase Nb₂AlC by the method of self-propagating high-temperature synthesis (SHS) from powdered mixtures of Nb + Al + C with an energy additive Mg + Mg(ClO₄)₂ have been developed. As a result of the synthesis, a multiphase powder is formed, containing the target phase Nb₂AlC and secondary phases NbC, Nb₂C, AlNb₂, MgO, and MgAl₂O₄. It has been shown that the phase composition of the product and the yield of the target phase are controlled by the carbon content in the charge. Reducing the carbon content in the charge relative to its stoichiometric ratio leads to a decrease in the niobium carbide content in the product. Optimal component ratios have been determined to obtain, after acid leaching, a powder containing ~82 wt % Nb₂AlC.

The structure of contacts was determined, and a method was developed for applying them to nanostructured thermoelectric materials. Contacts were formed by the chemical solution deposition (CSD) of nickel or cobalt on catalytically active surfaces from alkali solutions using hypophosphite ions as reducing agents. The nickel and cobalt CSD films 5 to 8 µm thick form continuous uniform coatings that contain at least 82 wt % metals and 7.4 to 9.1 wt % phosphorus. The phosphorus enhances the barrier properties of the contacts. The resistivity of cobalt and nickel films was 10 × 10^–8 and 12×10^–8 Ω m, respectively. The contacts had a high adhesive strength (up to 20 MPa) and low contact resistivity (at a level of 10^–9 Ω m²) and were thermally stable up to 600 K.

The thermodynamic modeling of the GaI₃–Se and ZnI₂–Se systems was carried out by the equilibrium constant method in the temperature range of 200–500°C. The equilibrium degrees of conversion of iodides to Ga₂Se₃ and ZnSe were found to be 21 and 0.7%, respectively. Molecular iodine was the major component of the vapor phase in both systems. A preparation method of Ga₂Se₃, ZnSe, and ZnGa₂Se₄ by the reaction of GaI₃ and ZnI₂ with selenium in an evacuated quartz reactor with two temperature zones was developed. The selective withdrawal of iodine from the reaction melt made it possible to attain a practical yield of selenides of 86–90% at 450°C. The residual content of iodine in the products was 0.2–1 at %.