Refractories and Industrial Ceramics最新文献

The article shows the effect of an ultra-high pressing load of 1,20 GPa at 1800°C during spark plasma sintering, compaction pressure of 2,30 GPa at 1260°C during the explosive sintering of the particles of solid solutions of ceramic and metallic phases with the additive of oxide powders mixture, NiCr on the phase composition, microstructure, grain size of the crystalline phases, relative density, linear shrinkage, microstructural features of the boundary layers, microcrack paths, physico-mechanical properties of mullite–c-ZrO₂–c-BC₂N–NiCr–V–Mo–Zr–W and mullite–c-ZrO₂–c-BC₂N–NiCr–Cr–Mo–Nb–Ta. Spark-plasma sintered c-ZrO₂ at pressing load 35 MPa and temperature 1400°C, g-BC₂N at pressing load 60 MPa and temperature 1600°C show evoluted crystallization of the c-ZrO₂ and g-BC₂N phases, respectively, crystalline, uniform, dense microstructures. Samples sintered by the spark-plasma method at an ultra-high pressing load of 1,20 GPa at 1800°C show evoluted mullitization, crystallization of c-ZrO₂, c-BC₂N, NiCr, β-V, Mo, W, Zr, β-Cr, Mo, Nb, Ta phases, more crystalline, more uniform and more densely sintered microstructures, variously dispersed grains of the crystalline phases. Samples sintered by both methods differ by the relative density, linear shrinkage, density, uniformity, width, path and moving microcracks across these boundary layers, crack resistance and values of physico-mechanical properties.

Polymorphic transformations of the first and second kind of the type C ordered cubic structure into the type C¹ disordered structure were found during heating of samples of Y₂O₃ oxide grade (99.990%) for phosphors in the range 500 – 1100°C in air and vacuum. The phase transformations proceeded without changing the chemical composition of oxygen in yttrium oxide. The mechanism of these transformations was determined. The chemical composition of oxygen in cubic C¹ Y₂O₃ was stable up to 1750°C in air and up to 1500°C in vacuum. The change in the chemical composition of Y₂O_3–x with respect to the oxygen content in the C¹ type cubic phase was studied. This structure was stable up to 2200°C in air and up to 1800°C in vacuum. The disordered type C¹ phase decomposed at these temperatures into the ordered type C_x phase and a monoclinic type B phase. It was theoretically substantiated and experimentally confirmed for the first time that when samples were heated in the range 2100 – 2200°C in vacuum and the oxygen stoichiometry deviated to the composition YO_1.37, the type C_x cubic phase decomposed into two cubic phases: type F with anionic vacancies and lattice parameter a = 0.5265 nm (space group Fm3m) and type C¹¹ cubic phase with color centers and lattice parameter a = 1.0652 nm (space of group Ia3). The refractive indices of these phases were determined. The type F and C¹¹ phases were stable when heated in air to 1300°C. The yttrium oxide samples were oxidized in air in the range 1300 – 1400°C to the composition Y₂O₃. The energy of oxygen migration into the yttrium oxide lattice was determined. The diffusion rate of oxygen during oxidation was calculated. The diffusion rate was found to depend on the temperature of oxidation and holding.

A method for producing a composite sorbent with a honeycomb structure (a system of parallel directed permeable pores) for capturing platinum aerosols in high-temperature catalytic processes is proposed. The composite sorbent is prepared from cordierite ceramics with the addition of active calcium oxide. The calcium oxide precursor is introduced into the molding mass as calcium carbonate powder or by impregnating the matrix material with a solution of calcium nitrate. The mechanism of synthesis of the composite sorbent is investigated. Its physicochemical properties are given. Pilot tests of composite sorbents in an industrial reactor have shown its resistance to technological conditions of ammonia conversion and the ability to capture platinum catalyst aerosols.

The paper discusses a method for obtaining a ceramic material composition for further use in investment casting. Prototypes of Al₂O₃ ceramics based on electrocorundum and silica-free binders were produced. The quality of the front layer was assessed. The manufactured samples were tested. It was revealed that the mechanical properties of the obtained ceramic materials did not meet the required ones, which led to measures aimed at improving the mechanical characteristics of the ceramics, in particular, the use of sintering additives.

The entropy parameter is key when analyzing the properties of mass systems. This concept was first formulated in thermodynamics and then extended to many areas of knowledge. The concept of entropy for two-phase flows in separation modes was also reasonably formulated. Analysis of the connection between this entropy and other parameters characterizing the critical two-phase flow allowed us to determine a statistical identity for this process, which constitutes a balance between the potential and kinetic energy of various parameters characterizing the two-phase flow. This relationship connects all the main separation parameters determined from the consideration of the mass process, including also entropy. On this basis, it was possible to develop an in-depth theory of the process and create an adequate experimental methodology for calculating separation results and methods for optimizing it.

A study of a two-stage method for the formation of nanostructured Ni₃Fe is presented. Nanostructured Ni₃Fe hollow microspheres were synthesized by ultrasonic spray pyrolysis (URP) from a mixture of aqueous solutions (10 wt.%) of nickel(II) and iron(III) nitrates. In the first stage, hollow microspheres with diameters in the range 0.5 – 10 μm were formed from a mixture of Ni and Fe oxides. The second stage involved metallization of a mixture of Ni and Fe oxides in a tube furnace in a hydrogen atmosphere. X-ray diffraction (XRD) data of the final product showed the presence of the Ni₃Al phase and a crystallite size close to 40 nm. Scanning and transmission electron microscopy revealed the hollow morphology of the studied Ni₃Fe microspheres. Their walls were assembled from crystallites with diameters of 30 – 60 nm.

The efficiency of using a mechanoacoustic method for preparing a multicomponent charge for producing ceramics from highly dispersed aluminosilicate raw materials is evaluated. The influence of ultrasonic dispersion and mechanical activation on the dispersed phase structural state is evaluated using x-ray diffraction analysis based upon changes in the size of particles and crystallites that make up an aggregate. It is established that with the help of mechanoacoustic treatment in powder represented by a mixture of differently active particles it is possible to achieve maximum structural homogeneity by reducing the size of local inhomogeneities. It is shown that use of montmorillonite as an additive to a charge in combination with mechanical-acoustic treatment reduces the sintering temperature and makes it possible to prepare ceramic with a more uniform structure and high strength.

Since the early 1950s, aluminum titanate has attracted attention as a basis for the creation of high-temperature heat-resistant materials. This is due to a combination of a number of useful properties, the nature of which lies in the characteristics of the crystal structure and behavior of aluminum titanate when heated. The article generalizes information regarding the phase diagram and crystal structure of aluminum titanate.

Including sulfide ore beneficiation tailings in sulfide ore processing is mainly ascribed to their use in the construction industry. In addition to dump products, various other wastes are formed during processing of sulfide ore materials, and these wastes are sent into circulation for pyrometallurgical processing. This study proposes a device for thermal beneficiation of gold-containing sulfide ore materials using a tubular purge grate. Gas purging through the holes of hollow rings, which are arranged in a staggered order, will evenly distribute bubbles throughout the volume of the slag melt and also evenly mix it. Gas purging of only the molten slag will reduce energy consumption.

Introduction of ash-slag into the ceramic composition as a desiccant, which is a non-shrinkable material, contributes to a more uniform moisture distribution within a sample and its effective removal during drying. This also has a positive effect on ceramic product molding and drying processes. Ash-slag must be introduced into ceramic masses to reduce shrinkage during drying, increase moisture conductivity, however, it should be borne in mind that this reduces the ceramic product strength under compression. Optimum compositions for effective drying contain 20 – 24 % ash slag. A regression analysis method is used to predict the results that are not provided in an experiment.