Inorganic Materials最新文献

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.

The study of the crystal structure and properties of multicomponent interstitial alloys helps obtain new materials with improved properties. In this paper, we report a study of the crystal structure and microhardness of bulk samples of Ti_xMo_1–xC_yN_z interstitial alloys differing in concentrations of their constituent elements. Samples were prepared by self-propagating high-temperature synthesis and homogenized by annealing at 2600 K for 8 h, followed by furnace-cooling. According to neutron diffraction data, the alloys have a face-centered cubic crystal structure in which the Ti and Mo atoms substitute for each other and occupy position 4b at random, and the C and N atoms also substitute for each other and occupy octahedral position 4a. Using X-ray diffraction data, we determined the crystallite size, dislocation density, and lattice strain in the alloys by the Rietveld method. The microhardness of the samples was determined by the Vickers method. The crystallite sizes determined by the Williamson–Hall method and using the Scherrer formula were found to differ significantly, but in both cases the crystallite size, dislocation density, and lattice strain increase with increasing component concentration in the composition of the alloys. With increasing carbon content, the crystallite size and lattice strain of the alloys decrease, whereas the dislocation density rises. With decreasing crystallite size and increasing dislocation density, the microhardness of the alloys shifts to higher carbon content. As the crystallite size and lattice strain decrease and the dislocation density rises in response to changes in the composition of the Ti_xMo_1–xC_yN_z alloys, their microhardness rises by a factor of 1.5–2 in comparison with binary titanium carbide and nitride. The present results can be helpful for application of interstitial alloys in tool making and high-temperature engineering.

We have studied the kinetics of small cracks in 316L steel specimens produced by selective laser melting and demonstrated structural sensitivity of such cracks forming at process-induced defects in the early stage of fatigue. They propagate predominantly along fusion boundaries, and their growth rate is lower at melt pool boundaries. An increase in the opening of arrested cracks leads to the formation of a plastic zone at their tips and deformation localization, followed by a decrease in crack opening and further growth as the number of cycles increases. Alternation of small crack arrest and growth reflects in the kinetic diagram of fatigue fracture, which has growth rate thresholds with the spacing between them approaching the scan step in the steel preparation process. The diagram can be described by Paris’s equation with identical exponents for the growth of short and long cracks. The fatigue curve we constructed was compared to fatigue curves of 316L steel produced by a conventional and an additive method. We demonstrate that, like fatigue curves reported for 316L steel in the literature, the curve we plotted lies far below the fatigue curve of the steel produced by a conventional process. At the same time, optimization of specimen preparation conditions and subsequent heat treatment make fatigue characteristics of the “additive” steel more similar to those of steel produced by a conventional process. We have studied macro- and microrelief of fracture surfaces of specimens, identified stable and accelerated crack propagation stages, evaluated crack lengths corresponding to these stages on fracture surfaces, and described predominant fracture mechanisms in each stage. The observed knee point in the fatigue curve of the steel was shown to be accompanied by an increase in damage to the lateral surface of the specimens with increasing stress amplitude and a transition to a more ductile fracture surface microrelief, which can be accounted for by a change from a plane strain state to a plane stress state of the material of the specimen at the macrocrack tip.

We demonstrate the feasibility of constructing the dependence of the effective separation factor β on the degree of distillation (g) and temperature (at known values of the vapor pressure of the substance being evaporated, the Peclet number at its melting point, the activation energy for impurity diffusion, and the initial separation factor β₀) via construction of the dependence of condensate purity on g at a given β₀ and Peclet numbers corresponding to a series of temperatures under consideration. We present calculation of such a dependence for a beryllium-based model material as an example and examine its typical features.

We have studied structural and ion-conducting properties of a nanoceramic (Pb_0.67Cd_0.33)_0.825Sr_0.175F₂ solid solution (CaF₂ structure, sp. gr. (Fmbar {3}m)). Nanocrystalline powders were prepared by mechanochemical synthesis using two types of starting mixtures. One mixture was prepared using melted PbF₂, CdF₂, and SrF₂ individual fluorides, and the other, using a prefused Pb_0.67Cd_0.33F₂ solid solution and SrF₂. The way in which the starting mixture was prepared was found to have no effect on the formation and properties of the ternary solid solution. The lattice parameter of the (Pb_0.67Cd_0.33)_0.825Sr_0.175F₂ solid solution was determined to be a = 5.778 and 5.772 Å in the case of the former and latter starting mixtures, respectively. Using X-ray diffraction data, the average crystallite size of the nanopowders was estimated at several tens of nanometers. Nanoceramics were prepared by cold-pressing the powders. Their density was 80% of the X-ray density of the solid solution (6.89 g/cm³). Annealing at 500°C for 2 h increased the density of the ceramics to 90%. The ionic conductivity σ_dc of the as-prepared and annealed nanoceramics was determined to be 2.5 × 10⁻⁶ and 1.2 × 10⁻⁵ S/cm, respectively. The σ_dc of the annealed nanoceramic is 20% lower than that of a single crystal with the same composition.