Inorganic Materials最新文献

We have studied the effect of α-Al₂O₃ powders added as sintering aids (15 wt %) on the hardness and porosity of Al₂O₃–3YSZ ceramics. The alumina powders were synthesized via combustion of aluminum nitrates or by solution combustion synthesis (SCS) with the use of glycine and urea as organic reducing agents. The use of aggregates of submicron alumina particles that remained intact after SCS was shown to prevent preparation of high-density ceramics. After sintering at 1550°C, the relative density of the ceramics was 75 to 85% on account of considerable closed porosity. The microhardness of the ceramics ranged from 1 to 11.1 MPa and correlated with the variations in their density and porosity. A reference sample, containing pure-grade alumina additions, had the highest relative density, 98%, without closed porosity.

This paper reports the preparation of cast iron aluminides from thermite-type highly exothermic mixtures at atmosphere pressure in air. We have studied general aspects of combustion during the synthesis process and evaluated the ingot yield of the synthesized iron aluminides and the relative weight loss of the starting mixture components and final products in the combustion process. The chemical and phase compositions of three synthesized cast phase-pure iron aluminides—Fe₃Al, FeAl, and Fe₂Al₅—have been determined, their microstructures have been studied, and their microhardness has been measured.

This paper presents results on the synthesis, phase composition, and optical properties of Al₅O₆N aluminum oxynitride doped with Fe ions in a broad concentration range: from 0.01 to 5.0 at % (relative to aluminum). All of the samples, prepared by firing mixtures of Al₂O₃, AlN, and Fe₂O₃ at a temperature of 1750°C in flowing nitrogen, consisted of almost phase-pure γ-AlON, with small amounts of aluminum nitride and unidentified phases. The band gap E_g of AlON:Fe depends on Fe concentration and ranges from 5.76 to 5.88 eV. We have identified AlON:Fe luminescence due to native defects and extrinsic emission centers and measured the luminescence intensity of emission bands as a function of Fe concentration in AlON. The presence of Fe in AlON leads to an increase in optical absorption and a decrease in intrinsic luminescence intensity in the material.

We have developed a technique for the synthesis of CeO₂ nanopowder with the use of a powdered cellulose (PC)/Ce(NO₃)₃/NaCl composite. It comprises the following steps: preparation of PC/Ce(NO₃)₃/NaCl, burnout of the cellulose template (600°C), and removal of the sodium chloride via washing with water. Using IR and UV spectroscopies, X-ray diffraction, and electron microscopy, we have assessed the effect of sodium chloride concentration in the parent composite on the physicochemical properties of the resulting CeO₂. The material prepared from PC/Ce(NO₃)₃/NaCl consisted of two types of CeO₂ particles: particles 15–40 nm in diameter (forming irregularly shaped structures) and particles 1.5–2.2 nm in diameter. These latter formed the surface of spherical aggregates ranging in size from 30 to 200 nm. Increasing the amount of NaCl in PC/Ce(NO₃)₃/NaCl has been shown to cause an increase in the fraction of spherical aggregates in the nanopowders. The size of the spherical aggregates and that of the particles aggregated on their surface are essentially independent of the amount of sodium chloride in the parent composite. The nanopowder prepared without sodium chloride (PC/Ce(NO₃)₃) consisted of only particles of the former type. In the material prepared from PC/Ce(NO₃)₃/NaCl, cerium dioxide was present in the form of cerianite and amorphous phase. A tendency has been found for the content of the amorphous phase in CeO₂ to increase as the amount of sodium chloride in PC/Ce(NO₃)₃/NaCl increases. If the parent composite was free of NaCl, no amorphous phase was formed. No Ce(III) has been detected in the material prepared from PC/Ce(NO₃)₃/NaCl, as distinct from that prepared from PC/Ce(NO₃)₃. Increasing the amount of sodium chloride in PC/Ce(NO₃)₃/NaCl increases the thickness of the hydroxyl–hydrate shell in the nanopowder. The carbon-containing impurities identified in the nanopowders have been shown to be the result of sorption from the ambient atmosphere. The catalytic activity of CeO₂ nanopowder for hydrogen peroxide decomposition as a model reaction rises in proportion to the increase in the amount of sodium chloride in the parent composite.

The thermodynamic properties of RuTe₂ have been determined for the first time using electromotive force (emf) measurements in the Ag–Ru–Te system. The thermodynamic properties have been evaluated from the temperature dependence of the emf measured on an all-solid electrochemical cell with a common gas space, corresponding to the virtual chemical reaction 4Ag + RuTe₂ = 2Ag₂Te + Ru. The measurements have been performed in the temperature range 747–884 K. As a result, the following standard thermodynamic properties of formation of RuTe₂ from its constituent elements at 298.15 K and 1 bar (10⁵ Pa) are recommended: Δ_fG° = –126.9 kJ/mol, S° = 94.94 J/(mol K), and Δ_fH° = –136.6 kJ/mol. The thermodynamic properties of RuTe₂ are compared to literature data for compounds isostructural with it: ruthenium disulfide and ruthenium diselenide.

Using the climbing image nudged elastic band (CI-NEB) method, we have calculated activation energies of reaction of H₂ with an oxygen molecule preadsorbed on the (011) In₂O₃ surface, resulting in the formation of a water molecule or hydroxyl group. In the latter process, one hydroxyl results from bonding of OH to a surface metal atom, and another, from bonding of hydrogen to lattice oxygen. Calculations show that the activation energies of these reactions differ little, 0.99 and 0.98 eV, respectively, but the thermodynamically favorable process is hydroxylation of the surface.

A new technique has been proposed for the synthesis of metal-containing exfoliated graphite: by expanding a mixture of expandable graphite with metal (Fe³⁺, Co²⁺, and Ni²⁺) nitrates and a reducing agent (melamine). Heat treatment of such a mixture in an inert (nitrogen) atmosphere at 900°C leads to the formation of exfoliated graphite, with fine metallic alloy (FeCo, FeNi, FeCoNi, or CoNi) particles located on its surface. The exfoliated graphite samples thus prepared have low loose bulk density (down to 6 g/L) and high saturation magnetization (up to 41.2 emu/g).

Transmission of Ni²⁺-doped multicomponent glasses in the TeO₂–ZnO–Bi₂O₃ system has been studied by optical spectroscopy. The spectra of the glasses contain three strong absorption bands, peaking at 0.43, 0.80, and 1.32 μm. We evaluated the specific absorption coefficient of a particular glass matrix containing a certain amount of Ni²⁺. At a wavelength of 0.80 μm, it is 15.9 ± 1.3 cm^–1/wt %. In addition, we obtained its spectral dependence throughout the transmission window of the glass and estimated the integrated absorption coefficient of the glass in the wavenumber range 3600–16 500 cm^–1: 10.6 ± 0.5 cm^–2/ppm.

We have studied the effect of crystallite size on the magnetic properties of GaSb–MnSb alloys prepared by the sealed-ampule method. Using the Debye–Scherrer method, optical microscopy, and electron microscopy, we have demonstrated that raising the cooling rate from 0.1 to 60°C/s reduces the crystallite size of MnSb in 59 mol % GaSb + 41 mol % MnSb eutectic alloy and 30 mol % GaSb + 70 mol % MnSb hypereutectic alloy by a factor of ~10. The decrease in crystallite size is larger in the case of the eutectic composition. The crystallite size of MnSb has been shown to determine the magnetic properties of the alloys. The alloys are ferromagnets and reducing their crystallite size changes the behavior of their magnetoresistance and raises their Curie temperature. The eutectic material obtained at a cooling rate of 60°C/s has a negative magnetoresistance, which attests to spin polarization in the alloy. The corresponding saturation field is 0.13 T. The electrical resistance of the alloys is a linear function of temperature both in the absence of a field and in a magnetic field. The composites obtained at the higher cooling rate have a more uniform distribution of their constituent phases, which is important for application of such materials in the fabrication of spin-polarized granular structures.

The theory of fuzziness is an important area of modern theoretical and applied mathematics. The methodology of the theory of fuzziness is a doctrine of organizing activities in the field of development and application of the scientific results of this theory. We discuss some methodological issues of the theory of fuzziness, i.e., individual components of the methodology in the area under consideration. The theory of fuzziness is a science of pragmatic (fuzzy) numbers and sets. Ancient Greek philosopher Eubulides showed that the concepts of “Heap” and “Bald” cannot be described using natural numbers. E. Borel proposed to define a fuzzy set using a membership function. A fundamentally important step was taken by L.A. Zadeh in 1965. He gave the basic definitions of the algebra of fuzzy sets and introduced the operations of intersection, product, union, sum, and negation of fuzzy sets. The main thing he did was demonstration of the possibilities of expanding (“doubling”) mathematics: by replacing the numbers and sets used in mathematics with their fuzzy counterparts, we obtain new mathematical formulations. In the statistics of nonnumerical data, methods of statistical analysis of fuzzy sets have been developed. Specific types of membership functions are often used— interval and triangular fuzzy numbers. The theory of fuzzy sets in a certain sense is reduced to the theory of random sets. We think fuzzy and that is the only reason we understand each other. The paradox of the fuzzy theory is that it is impossible to consistently implement the thesis “everything in the world is fuzzy.” For ordinary fuzzy sets, the argument and values of the membership function are crisp. If they are replaced by fuzzy analogs, then their description will require their own clear arguments and membership functions, and so on ad infinitum. System fuzzy interval mathematics proceeds from the need to take into account the fuzziness of the initial data and the prerequisites of the mathematical model. One of the options for its practical implementation is an automated system-cognitive analysis and Eidos intellectual system.