Inorganic Materials最新文献

Pycnometric methods of characterization of the pore structure of solids, based on density measurements, provide data on the pore size distribution. Here we report results of open porosity determination via weighing of a dry sample, followed by evacuation and saturation with distilled water at atmospheric pressure; via pressure infiltration with water using a manostat system; and by mercury intrusion porosimetry. We have studied porous nickel samples prepared by a powder metallurgy process involving sintering of green compacts consisting of mixtures of nickel nanopowder and ammonium bicarbonate (NH₄HCO₃) powder as a pore former, with volume fractions of 80 and 20%, respectively. The particle size ranges of the pore former were 63–125, 140–200, and 250–315 μm. For the three methods used to determine open porosity, we theoretically evaluated the size of pores accessible to infiltrating liquid. The results demonstrate that, in the case of saturation with water after evacuation, the liquid can penetrate only pores more than 3 μm in size. Moreover, in the case of porous structures with a large fraction of submicron pores, the open porosity determined via saturation with distilled water after evacuation is considerably underestimated. The larger the fraction of small pores in the material, the larger the underestimation. The difference between the open porosity values obtained via pressure infiltration with water and by mercury porosimetry is insignificant. We demonstrate that, of the three porosity determination methods, only saturation with distilled water after evacuation cannot be used to analyze structures with submicron pores. The results we obtained can be useful in designing porous functional materials and articles with a tailored pore structure.

We have studied the effect of small Cr₂O₃ and Cr³⁺ additions on the optical properties of high-purity alumina-based powders and photocurable slurries for 3D printing. The polymerization depth of the slurries has been shown to strongly depend on the amount of the coloring additive in the Al₂O₃ powders. Using digital light processing (DLP) 3D printing followed by high-temperature sintering, we have obtained thin-walled planar samples of high-density periodic-structure ceramics and studied their microstructure and luminescence properties. Their photoluminescence spectrum contains a sharp strong line in the red spectral region, at 694 nm (characteristic line of ruby). The luminescence decay curves showed single-exponential behavior with a decay time of ~3.7 ms.

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.

A high-voltage power supply, along with an X-ray tube, is one of the main components of X-ray machines widely used in studying the structure of materials, estimating the internal structure of components and mechanisms, and nondestructive testing of technological processes. In monoblock devices, an X-ray tube and power supply are located in a common housing, while in cable-type setups, an X-ray emitter with the tube and a power supply are connected by a high-voltage cable. In this study, the results of creation of a stabilized high-voltage power supply for X-ray tubes as a part of a cable-type machine are reported. The electric circuits and design of the power supply based on a full-bridge voltage inverter built on power bipolar transistors are developed. The output voltage and power of the source are adjusted through the pulse width modulation of the rectified mains voltage applied to the primary winding of a high-voltage transformer. The use of a solid-state compound with increased thermal conductivity has made it possible to limit the design to forced air cooling of the source and place it within the Rack Mount standard dimensions (4U form factor). The experience of the power supply operation at a large industrial enterprise has shown that its electrical and dimensional parameters provide the possibility of successful use in X-ray machines for structure control of materials.

The study of the causes of destruction of power equipment is necessary for their elimination or limitation, as well as for the development and improvement of methods of technical diagnostics. The latter is especially important, since accidents or unplanned shutdowns of power equipment cause great economic damage. Standard methods of technical diagnostics in assessing the residual life of equipment include mechanical testing of samples cut out of equipment parts, determination of their chemical composition, structural studies, and fractography of the metal. Both fractures of samples specially cut for mechanical testing and surfaces of destruction that occurred during operation are studied. The danger of developing hydrogen embrittlement in metals is well known. The presence of brittle fracture areas or facets is usually associated with hydrogen-induced destruction or hydrogen embrittlement. Direct measurements of the concentration of hydrogen dissolved in metal samples are not regulated by standards; therefore, diagnostics of the development of hydrogen embrittlement is only qualitative. Our studies show that standard approaches are insufficient for technical diagnostics of the pipes of heating surfaces of boiler equipment. Hydrogen accumulation during operation may not have visible signs of corrosion or structural changes. It was found that hydrogen and external thermomechanical load induce anisotropy of mechanical and structural properties of steels of pipes of heating surfaces. As a result, the nature of destruction of samples cut from pipe walls depends on the orientation of test loads relative to the main axes of the stress tensor of operational (working) loads. The obtained experimental data allow us to conclude that, when establishing the causes of accidents and examining working heat exchangers in order to assess their residual life, it is necessary to additionally measure the distribution of the concentration of dissolved hydrogen in the metal and mechanically test ring samples.

We describe binders and impregnating mixtures based on chelated organoalumoxanes, which are used as precursors to highly thermally stable matrices and protective coatings. Using the polymer impregnation and pyrolysis (PIP) process, we have fabricated Al₂O_3f/Al₂O₃ ceramic-matrix composites. Ceramic micropowders resulting from pyrolysis of the precursors have been shown to have an advantageous effect on the microstructure and properties of the material. We have studied the microstructure and density of Al₂O_3f/Al₂O₃ composites produced using chelated organoalumoxane-based binders and impregnating mixtures. The relative density of the composites, 3.1 g/cm³, considerably exceeds the initial density of the porous preform: 2.5 g/cm³.

The calcium strontium germanate Ca₃Sc₂Ge₃O₁₂ has been prepared by solid-state reaction, by firing a stoichiometric mixture of CaO, Sc₂O₃, and GeO₂ in air at temperatures from 1273 to 1623 K. Using X-ray diffraction data for single-phase samples, we have determined the unit-cell parameter of Ca₃Sc₂Ge₃O₁₂ crystals (garnet structure, sp. gr. Ia(bar {3})d, a = 12.508(48) Å, V = 1956.92(2) ų). The heat capacity of polycrystalline samples has been determined in the range 320–1050 K using differential scanning calorimetry. The results have been used to calculate thermodynamic functions of the calcium strontium germanate.

For manufacturing parts operating under complex conditions of cyclic loading, as well as products with stable dimensions, materials with minimal manifestations of inelastic properties are required. To study them, it is necessary to conduct specialized narrow-focus tests using machines and installations with appropriate experimental techniques. This paper presents the design of an electromagnetic installation for fatigue and frequency stability testing operating in a self-oscillating mode, in which the cyclic loading frequency is always equal to the natural frequency of oscillations of a sample. The installation control system contains two closed loops—for excitation of self-oscillations and for the oscillation amplitude stabilization. The sample is loaded by electromagnetic force and unloaded owing to the elastic forces of the material. This work presents a technique and algorithms for calculating the stresses of samples of various geometric shapes to assess changes in the amplitude–frequency characteristics. A calculated relationship is established between the force applied to the sample and its displacement at the point of force application, followed by determining the stress by the known force. The results of calibration tests for the static loading mode of samples are presented and the forces acting on the sample (external, inertia, elasticity) are estimated taking into account the maximum stress and maximum deformation amplitude. Static and cyclic loading modes are compared. The frequency characteristics are obtained when testing steel samples according to the proposed method. An analysis of the experimental results of tests with breaks during cyclic loading and continuous tests is carried out. It is shown that breaks in cyclic tests lead to an abrupt increase in frequency, while such jumps are absent during continuous tests. At the same time, a comparative analysis of the results of the considered types of tests showed that the total frequency deviation for the entire operating cycle is approximately the same in both cases. It is shown that the increase in frequency after rest is random and does not depend on the number of operating cycles.

We have studied water vapor absorption by the α-phase of zinc pyrophosphate, Zn₂P₂O₇, at 25°C. This compound has been found to be highly hygroscopic owing to the formation of a crystalline hydrate with the composition Zn₂P₂O₇∙5H₂O. Removal of its water of crystallization has been shown to occur in three steps, starting at 60°C and reaching completion at 400°C. The phase composition of the dehydration product depends on heat treatment temperature. Below 500°C, we observe considerable amorphization and predominant formation of γ-Zn₂P₂O₇, whereas phase-pure α-Zn₂P₂O₇ can be obtained as a result of annealing at temperatures above 600°C.

This paper examines how the gypsum-containing waste processing procedure influences the degree of rare-earth metal (REM) extraction from the waste. Gypsum-containing waste from the production of phosphoric acid was treated with aqueous solutions of various acids in the temperature range 25–140°C at solid : liquid ratios from 1 : 1 to 1 : 3. The results demonstrate that the largest REM extraction from phosphogypsum can be reached by treating with hydrochloric or nitric acid at the boiling point of the aqueous solution of the acid. Nitric acid is preferable because, after the acid treatment, the gypsum contains a large amount of nitrates, which can be used as agricultural fertilizers. Treatment of phosphogypsum at elevated temperatures and pressures leads to dissolution of a larger amount of gypsum, without increasing the REM yield. The highest economic efficiency of REM extraction from phosphogypsum is ensured by a solid : liquid ratio of about 1 ; 2, treatment temperature of 103–105°C, and cascade time no more than 10 min.