Inorganic Materials: Applied Research最新文献

The structure and some mechanical properties of electrolytic chromium coatings deposited on the inner surface of the fuel cladding made of EP823-Sh ferritic-martensitic steel were studied. It was shown that the optimal temperature of the electrolytic bath for deposition of hard dense coatings without cracks is 30–35°C at a current density of 0.15–0.18 A/cm². At higher temperatures, finely dispersed columnar chromium crystals are deposited, texture appears, and microcracks are formed, which reduces the protective properties of the coating. Nanohardness, elastic modulus, elastic limit, ultimate relative deformation, tensile fracture limit, and abrasive wear resistance of the coatings are determined.

The influence of organic (acetic acid, citric acid, and diethylene glycol) and inorganic (nitric acid and ammonia) plasticizing agents on the properties of alumina supports has been studied. Alumina supports were investigated using methods of elemental CHNS analysis, X-ray diffraction (XRD), low-temperature nitrogen adsorption–desorption, temperature-programmed desorption of NH₃ (TPD-NH₃), and FT-IR spectroscopy of adsorbed pyridine. The mechanical strength of the samples has been determined. The variation of the plasticizing agent had a significant impact on the textural characteristics of the obtained supports. The use of an aqueous ammonia solution as a plasticizing agent led to an increase in the pore volume in the support and an increase in the pore portion of 13–50 nm by 4–16 times compared to other samples. In the case of the alumina support plasticized with diethylene glycol there is a decrease in pore volume in the sample by almost 2 times compared to the sample plasticized with ammonia, which is explained by an increase in the proportion of pores smaller than 7 nm by 9–35%. No significant influence of the plasticizing agent on the concentration of acid sites of alumina was observed. Among the studied series, a sample of alumina prepared with the addition of nitric acid stood out. The results of TPD-NH₃ and IR spectroscopy of adsorbed pyridine show a decrease in the concentration of Lewis acid sites (LAS) for this sample compared to the other samples.

Abstract—Composite materials based on a mixture of calcium phosphates and polysaccharides (sodium alginate, chitosan, and hyaluronic acid) have been synthesized. Their properties can be adjusted by varying the filler/matrix ratio and drying temperature. The composition and morphology of samples and their degradation in a tris-buffered saline solution and a model SBF solution have been studied. It was found that a calcium phosphate layer is formed on the surface of samples in the SBF solution, which indicates the bioactivity of the samples. At the same time, a gradual transition of calcium ions from the surface of the material into the solution was observed in the tris-buffer medium.

Abstract—This work is devoted to the study of the influence of complex modification on the microstructure of complex-alloy hypereutectic silumin of the Al–Si–Cu–Mg–Ni–Mn system. The task of the work was to determine the phase composition of the alloy in the cast state. The analysis of literature and multicomponent phase diagrams was carried out. The phase composition was studied using scanning electron microscopy (SEM), energy-dispersive X-ray spectral microanalysis, and X-ray phase analysis (XRD) of the studied alloy. Various modifying elements and their modifying mechanisms are considered. For modification of complex-alloy hypereutectic silumin the following additives were used: K₂TiF₆ and K₂ZrF₆ salts, complex-modifying fluxes (CMFs), a tableted refining-modifying preparation (RMP), and a phosphorus-containing ligature. The effect of complex modification on the coefficient of thermal linear expansion (CTLE), hardness, and microhardness of primary silicon of complex-alloy hypereutectic silumin was assessed. Microstructural studies of the effect of complex modification on the sizes of primary and eutectic silicon were conducted. The studies showed that the use of complex modification is a relevant direction for improving the structure of complex-alloy hypereutectic silumins and increasing their properties.

Manganites La_0.7Sr_0.3Mn_0.9Fe_0.05Me_0.05O_3+γ (Me = Sc, Co) with different oxygen content (γ < 0, γ = 0, γ > 0) were synthesized. Corresponding values of γ were obtained by annealing of sintered samples at different oxygen pressures: 10^–8, 10^–1, 10⁵ Pa, respectively. All synthesized manganites have rhombohedral structure and are characterized by small value of microdistortions, which is associated with the formation of modulated structures. Microstructure of the samples is quite dense, with an average crystallites diameter of 3.9 ± 1.6 μm for scandium-containing manganite and 3.1 ± 1.3 μm for (Fe,Co)-substituted manganite. Unit cell parameters and electromagnetic characteristics of the latter indicate the presence of Co³⁺(3d ⁶) ions in its composition. (Fe,Sc)-containing manganites have lower magnetization values, Curie points and a significantly lower metal-semiconductor transition temperature compared to those containing iron and cobalt. Current–voltage (I–V) characteristics of La_0.7Sr_0.3Mn_0.9Fe_0.05Sc_0.05O_3+γ and La_0.7Sr_0.3Mn_0.9Fe_0.05Co_0.05O_3+γ manganites with negative deviation from oxygen stoichiometry and stoichiometric exhibit negative differential resistance of S-type in certain temperature ranges, and I–V characteristics of (Fe,Co)-substituted manganite in magnetic field contain two S-shaped sections. Threshold switching fields and maximum values of negative differential resistance modulus of I–V characteristics at different temperatures are determined. (Fe,Sc)-substituted manganite with an excess oxygen content at 190–200 K exhibits voltage stabilization effect. I–V characteristic of (Fe,Co)-substituted manganite annealed in oxygen does not contain the sections with negative differential resistance. Mechanisms of the formation of current-voltage characteristics of various types are considered.

The physics of modifying the mechanical properties of synthetic fibers during treatment in a capacitive coupling plasma (ССP) discharge at reduced pressure is considered. The dependence of the tensile strength limit of various types of fibers on the composition of the plasma-forming gas, as well as on the duration of the treatment, has been determined. It was found that a mixture of argon and propane-butane allows for the greatest increase in tensile strength for all types of synthetic fibers studied.

The influence of fibrous basalt content on the crystallization patterns of composites based on high-density polyethylene was investigated. The crystallization process was studied using the stepwise dilatometry method within the temperature range of 20–210°C. The fibrous basalt content in the HDPE composition was varied between 1 and 20 wt %. The dependence of the specific volume of the composites on temperature was examined by dilatometric analysis. The results of analysis allowed for the identification of first-order phase transitions, the second-order phase transitions (glass transition temperature), and the free and occupied specific volumes of the composites. The studies showed that fibrous basalt is distributed within the free volume of the polymer matrix, which is primarily located in the interspherulitic amorphous region. The kinetic patterns of crystallization of the composites were studied in Kolmogorov–Avrami coordinates, establishing that the mechanism of crystalline formation growth during continuous nucleation largely depends on the content of fibrous filler. In particular, it was determined that the initial high-density polyethylene and composites with filler content of 1–5 wt % are characterized by a three-dimensional spherulitic type of crystal growth; composites with fibrous filler content of 10–15 wt % exhibit a lamellar type of crystal growth; and samples with filler content of 20 wt % show a rodlike type, which is the simplest type of crystalline growth.

One of the main problems limiting effective operation of electronic devices is overheating. In order to provide effective heatsink in many applications, dielectric polymer composite materials should be used. Excellent dielectric and thermal properties, minimal thermal expansion considered, they should also provide stable properties throughout all temperature range of operation. In the present paper, temperature dependencies (25–200°C range) of thermal conductivity, heat capacity, thermal diffusivity, and thermal expansion coefficient of hexagonal boron nitride/phenol-formaldehyde resin are considered. Most important dielectric properties—permittivity and dielectric loss tangent, were also measured. Filler volume fraction varied from 5 to 85%. Thermal diffusivity at highest filler fraction was 3.4 mm²/s (25°C, ca. 2300% improvement over neat polymer), thermal conductivity—7.5 and 16.4 W/(m K) in orthogonal directions being stable up to 200°C. Agari-Uno model parameters (including filler anisotropic thermal conductivity) best fitting the system under study have been calculated. Conclusions on material composition providing optimal thermal, dielectric and thermo-mechanical properties for heatsink bulk thermal management electronic-grade composite, are made.

The spraying of a WC–Co–Cr powder suspension in a tower spray dryer was investigated in order to determine the most suitable apparent viscosity of the suspension for achieving a productive flow of the suspension, whose productivity is evaluated by the maximum content of agglomerates after spray drying. The maximum content of agglomerates of the required fraction is determined by subsequent shrinkage during sintering. After sintering and sieving, the powder is suitable for deposition of wear-resistant coatings by the gas-flame spraying method. An analysis of the starting materials was carried out in terms of the particle size and bulk density for preliminary mixing of the suspension; the optimal amount of added liquid relative to the dry material was determined with subsequent measurement of the apparent viscosity of the resulting suspensions. The apparent viscosities of the suspensions and agglomerate particle sizes after spraying in the drying and granulating unit were measured. The dependencies of the granule size on the apparent viscosity of the suspension during agglomeration in the drying and granulating unit were obtained. The maximum content of the required fraction was achieved at an apparent viscosity of 20.07 s. Agglomeration of composite materials by spray drying enabled us to obtain spherical particles of the specified fraction that are suitable for further compaction and subsequent spraying of the powder composite material onto parts for protection against wear and corrosion.

Injection-thermal treatment (ITT) of MIS structures in the mode of stepwise increase in high-field injection current density bounded by the value of J_b, at which no noticeable processes of irreversible charge degradation of the gate dielectric and its interface with the semiconductor occur, is under consideration. The charge density injected into the gate dielectric during ITT should provide the revealing of samples with external defects. It is established that injection-thermal treatment allows one to significantly reduce the density of external defects in the dielectric film of MIS structures and exclude most of the samples with a small charge injected until the breakdown. It is shown that, after injection-thermal treatment, the reliability of MIS structures and devices based on them is determined mainly by internal defects of the dielectric film; this significantly improves the reliability indicators of MIS devices.