Inorganic Materials最新文献

The need to study the thermophysical properties of molding materials for foundry production using mathematical and computer methods is due to the rapid change in the binding components in these materials. The composition and, accordingly, the properties of the molding material, consisting of sand and binders, change when the casting mold is heated after pouring molten metal. The ambiguity of the composition of the sand-based mixture and the many influencing factors are reasons to doubt the suitability of those experimental properties that were obtained by measurements on small standard samples for computer simulation of manufacturing technologies for large-sized castings. The purpose of this work is to develop an algorithm for refining the thermophysical properties of non-metallic materials that are used in casting molds and cores. The refinement of the thermophysical properties as coefficients of the nonlinear heat equation was performed by solving the inverse heat conduction problem using the Levenberg–Marquardt method. The peculiarity of the method is that in iterations it refers to the results of solving the direct heat conduction problem, where the non-stationary temperature field is calculated. The direct problem of nonlinear heat conduction during the solidification of a casting in a sand mold was solved using the LVMFlow program. Real information about the temperature field during the solidification of Al-Si alloy in a sand mold was obtained in a full-scale experiment using thermocouples. The accuracy of temperature measurements by thermocouples was analyzed in relation to the technological processes of sand casting, depending on the dimensions of the casting and the melting temperature of the casting alloy. Thermocouples with chromel-constantan electrodes were recommended for experimental determination of temperature fields in aluminum alloy castings. An algorithm has been developed that changes the thermophysical properties so that the temperature field measured by thermocouples in an experiment on the solidification of a casting in a sand mold becomes equal to the calculated temperatures obtained by simulating the identical casting process in the LVMFlow program. The developed algorithm ensures the correct construction of the Jacobi matrix and is implemented in the SciLab software environment. The approach proposed in this work makes it possible to adjust the computer model of the casting technology according to the thermophysical properties of the mold materials, which leads to a reduction in the development time for technologies and tooling.

In modern industry, additive technologies (AT) are being rapidly implemented for the production of materials and products. A significant interest is represented by the Wire Arc Additive Manufacturing (WAAM) technology, which is due to the relatively low cost of equipment and deposited material, as well as a sufficient level of knowledge regarding welding processes. The growth of metallic layers and the manufacture of volumetric parts of various geometric shapes in this case is achieved through wire deposition. Among the deposited materials for three-dimensional printing, chromium-nickel steels have gained wide popularity. Considering the specifics of complex structural and shape-forming processes during the implementation of WAAM, there arises a need for additional research into the structure and properties of the obtained materials. Therefore, the aim of this work is to apply modern nondestructive testing methods for structural degradation during uniaxial tension of ER308LSI steel produced by the electric arc additive manufacturing method. Metallographic and magnetic studies were conducted, and an analysis of changes in microhardness during the deformation of samples cut along and across the printed layers was performed. The features of the structural degradation stages during uniaxial tension and the corresponding behavior of the magnetic parameters of the material were analyzed. It was established that uniaxial tension of samples manufactured using the WAAM method leads to the formation of a large number of structural defects in the form of deformation bands, discontinuities, and microcracks, the appearance of which is accompanied by significant changes in yield strength, microhardness, and coercive force (H_c). On the basis of the obtained H_c values, a magnetic anisotropy parameter (A_magn) was introduced, reflecting the nature of changes in coercive force in samples cut both along and across the direction of deposition. However, the nature of such changes for longitudinally and transversely cut samples (relative to the deposited layers) differs. The results of this work can be applied to the diagnostic tasks of assessing the deformed state of products obtained using the WAAM technology.

Indium oxide–graphene (In₂O₃/Gr) composites (2.0 and 4.0 wt % graphene) have been prepared by sol–gel synthesis and the microstructure and gas-sensing properties of the composites (in the composition of single-electrode ceramic sensors) have been studied. The composites have the form of heterogeneous systems formed by the In₂O₃ phase ranging in crystallite size from 7 to 12 nm and the graphene phase. The microstructure of the composites has been shown to depend on the fabrication process. The In₂O₃/Gr-based sensors have higher sensitivity to reducing (CH₄) and oxidizing (NO₂) gases than do In₂O₃-based sensors and shorter response and recovery times. Possible causes of their better gas sensitivity are the formation of spatially separated positively and negatively charged regions, which leads to electron concentration redistribution in individual phases; the increased defect density in the indium oxide and graphene phases in the composite; and the large specific surface area of graphene.

Abstract—A porous intermetallic/ceramic interpenetrating phase composite has been produced by self-propagating high-temperature synthesis (SHS) in samples of the Ni–Al–Ti–B model system. The starting mixture was prepared using composite granules (with the composition 3Ni + Al) produced by mechanical activation and a mixture of titanium and boron powders (with the composition Ti + 2B). The SHS process was run in the combustion regime. Two main chemical reactions occurred in the combustion wave: between aluminum and nickel in the granules and between titanium and boron in the mixture around the granules. Combustion was accompanied by the formation of a porous TiB₂ skeleton around the granules, into which molten nickel aluminides infiltrated from the granules. The solid phase of the SHS product contained interpenetrating fine-grained intermetallic and diboride skeletons. The composite had appreciable porosity on different scales.

We have developed a technique for controlling internal structure parameters (specific surface area, pore volume, and pore size) of spherical amorphous silica particles by varying the synthesis temperature. The particles have been prepared through hydrolysis of tetraethyl orthosilicate in an ethanol–water–ammonia mixture in the presence of cetyltrimethylammonium bromide at temperatures from –20 to 50°C. We have studied the morphology and adsorption structure properties of the synthesized materials and demonstrated the effect of reaction mixture temperature on the particle formation mechanism. The synthesized particles, 500–1100 nm in diameter, contain pores 3 to 50 nm in size up to 0.8 cm³/g in volume, with a specific surface area of up to 1000 m²/g. The particles prepared below room temperature have a core/shell structure.

The ternary system NaF–KF–MgF₂ has been divided into simplexes by a geometric method and a phase tree has been constructed, which has a linear structure and comprises four stable triangles separated by three stable secants. The phase tree has been used to predict the number and composition of crystallizing phases for stable elements of the system. Chemical interaction in the ternary system has been described using the ion balance method. The compounds located on the binary sides of the composition triangle have made it possible to obtain quadrangles with diagonals whose intersection points correspond to exchange reactions—main reactions in the system. Experimental data obtained by thermogravimetry confirm that reactions occur on the sides and in the composition triangle.

Steel S690QL is intended for welded heavily loaded structures: lifting beams, traverses, trailers for heavy haulers, and others. This work presents the results of a study on the mechanical properties and microstructure of S690QL steel produced in Russia and abroad, as well as the ductile properties of welded samples at different temperatures. Atomic emission spectroscopy methods, tensile testing, impact toughness testing, and microstructural analysis were used. Hardness was determined using the Vickers method. It was established that the chemical composition of both steels is practically identical. The impact toughness values of samples made from domestic S690QL exceed those of the foreign counterpart, particularly in the metal that has not undergone welding processes (the impact toughness for Russian steel in this zone was 200 J/cm² at –40°C, which exceeds that of the foreign steel in the same zone by almost 80%). The brittle–ductile transition temperatures for the weld joint zones of Russian S690QL were determined. For the zones of melted metal and thermal influence, this temperature was –40°C. In all zones of the weld seam of the test welded joints made from both steels, a similar microstructure was observed. The hardness in the studied samples showed close values and similar variations across the zones of the weld joints. The obtained results can be used in machine engineering for the certification and design of welded structures, primarily for the Arctic zone.

A comparative analysis of the computational complexity of exact algorithms for estimating linear regression equations has been carried out using the least absolute deviations method. The aim of this study is to compare the computational efficiency of exact algorithms for descent along nodal straight lines and algorithms based on solving linear programming problems. To do that, the algorithm of gradient descent along nodal straight lines and algorithms for solving the equivalent primal and dual linear programming problems using the simplex method have been discussed. The computational complexity of the algorithms for implementing the least absolute deviation method in solving the primal and dual linear programming problems has been estimated. The average time for determining regression coefficients using the primal and dual linear programming problems and the average time for gradient descent along nodal straight lines have been compared in Monte Carlo statistical experiments. It is shown that both options are significantly inferior to the gradient descent along nodal straight lines in both the computational complexity of the algorithms and the computation time. The advantage of the algorithm for descent along nodal straight lines increases by two orders of magnitude or more with an increase in the sample size.

Two new ternary intermetallic compounds, Yb₂Pt₃Si₂ and Yb₃Pt₅Si, have been identified in the Yb–Pt–Si system in the composition region from 0 to 42 at % silicon and from 20 to 43 at % ytterbium. Using Rietveld refinement of X-ray powder diffraction data, we have determined crystallographic parameters of the new compounds. Yb₂Pt₃Si₂ has an orthorhombic structure (Sc₂Pt₃Si₂ structure type, sp. gr. Pbam). The Yb₃Pt₅Si compound crystallizes in a body-centered orthorhombic structure (Ce₃Pd₅Si structure type, sp. gr. Imma). Phase equilibria in the 850°C isothermal section of the Yb–Pt–Si system have been studied in the above composition region.

Optimal conditions have been found for lime treatment of diatomite from the Jradzor deposit (Armenia) which ensure that the resulting calcium metasilicate hydrate has a large specific surface area, high adsorption capacity, and good filtration performance. Differential thermal analysis, IR spectroscopy, and X-ray diffraction have been used to identify the mechanism underlying the formation of a C–S–H(I) calcium metasilicate hydrate during lime treatment of diatomite. Water and benzene vapor adsorption isotherms have been used to assess adsorptive and structural properties of the C–S–H(I) calcium metasilicate hydrate and calculate parameters of its pore structure. It is shown that C–S–H(I) calcium metasilicate hydrate can be effectively used as a filtration material and adsorbent.