Refractories and Industrial Ceramics最新文献

The results of studies into high and super refractory materials for use in the Cowper heaters of high-temperature pulsed installations are presented. It is shown that long-term operation of corundum refractories (up to 1.5 years) at temperatures of 1750 – 1800°C has an insignificant effect on the thermophysical properties of the material. The materials and designs of the packing and lining elements of Cowper heaters for different layers and temperatures are selected. The gas flow velocity, which ensures a fixed position of the ball packed bed, is determined. The efficient packing design improves heat transfer and reduces the Cowper dimensions by a factor of 3.75.

Experimental results for structure formation of a ceramic composite of the Al₂O₃–ZrO₂ system with formation of reinforcing strontium hexaaluminate (SrAl₁₂O₁₉) during firing are presented. Lamellar crystals of SrAl₁₂O₁₉ are shown to be uniformly distributed in the composite structure, the strength of which is increased by 30% if SrAl₁₂O₁₉ is synthesized during firing of the ceramic with pre-synthesized strontium zirconate (precursor) introduced into the charge. Introduction of pre-synthesized SrAl₁₂O₁₉ into the composite charge followed by mixing and grinding does not harden the composite.

Electrodynamic properties of composite (BeO + TiO₂)-ceramics in the frequency range 8 – 12 GHz are studied. An increase in ceramic sintering temperature from 1823 to 1933 K after introducing TiO₂ micro- and nanopowders into BeO mixtures makes it possible to influence the efficiency of (BeO + TiO₂)-ceramics as an absorbing component of microwave radiation by increasing the modulus of imaginary and real parts of the dielectric constant. Additional reduction annealing in a hydrogen atmosphere at 1073 K further changes the ceramic electrical conductivity and enhances the effect of its ability to absorb UHF-radiation.

Refractories widely used in metallurgy and power engineering operate under constant dynamic impacts. In this regard, it is proposed to use elements of modal analysis to diagnose refractories. A test bench for diagnosing refractories has been developed, its approbation has been carried out, and the feasibility of using the proposed method to improve the quality of refractory materials has been shown.

The express method for evaluating the porous structure of ceramic materials was refined by replacing a smooth change in gas pressure with a stepwise change. After determining the average radius, the maximum radius was determined using the pressure drop until only one chain of gas bubbles remained. The average coordination number for the solid phase and the coefficient of capillary tortuosity were calculated. The experimental and calculated mean radii are in good agreement, whereas the tortuosity coefficients differ.

The results of studying the possibility of producing fire-resistant phosphate glue based on aluminosilicate and high-alumina industrial waste are presented. Using the methods of physico-chemical analysis, the phase composition of cured adhesive structures was studied, and the change in the composition after drying and firing was analyzed. Disperse-filled fire-resistant liquid adhesives were obtained that remain stable for at least 90 days. The main properties of adhesive refractory compositions are provided. The maximum application temperature of such materials was found to be 1700°C.

In the presented research, the heat distribution on the contact surfaces of the brake system of a drilling rig was studied using thermal simulation. The friction temperature distribution model on contact surfaces was obtained using the finite element method in COMSOL Multiphysics 5.5. As a prototype, the mobile drilling rig designed for drilling wells with a depth of up to 3000 m was included in the model. The brake systems of drilling rigs usually use a steel disc and a pad made of a composite material. In this study, a pair of steel and a new asbestos-free organic composite was selected. Based on the selected parameters, the thermal model was used to determine the temperature distribution mechanism along the contact surface of the disc and the brake pad. The highest friction temperature was observed during the first 2 – 4 sec of the braking cycle.

This paper presents the results of studies on silicon carbide production by self-propagating high-temperature synthesis. To provide the necessary energy for the process, the synthesis was performed using magnesium-thermal reduction of silicon dioxide in an argon atmosphere. This study was characterized by the use of carbon fibers as a carbon source. It was determined that during magnesium-thermal synthesis, hexagonal particles with a size of 1 – 2 μm and a thickness of approximately 0.2 – 0.3 μm were mainly formed. X-ray phase analysis showed the predominant formation of a cubic syngony of silicon carbide.

Microstructure defects arising in the manufacture of oxide ceramics based on aluminum oxide were studied. Several common problems arising in the manufacture of ceramic materials from fine-grained starting powders with high sintering activity as well as differences in the optimal properties of materials intended for use at high and moderate temperatures were considered. Samples of ceramic materials of the mullite–corundum system modified with zirconium dioxide were obtained by co-deposition of the initial powders followed by their grinding, pressing, and sintering. The fracture surfaces of samples were examined on a scanning electron microscope to study defects in the microstructure of powder ceramics. Characteristic defects in the microstructure were identified. The reasons for their appearance were explained. Possible ways to solve the problems of degradation of the properties of oxide ceramic materials were proposed based on technical literature data and the experimental results.

The manufacturing processes and mechanical properties of ceramics based on fused corundum and an organic aluminum(hafnium binder were studied. Samples of ceramics with the composition Al₂O₃/HfO₂ were prepared. The features of the sintering process of the ceramic materials and their heat-treatment modes were studied. The quality of the front layer was assessed. The tensile strength in bending of the manufactured ceramic samples was tested. The microstructure of the ceramics consisted of grains of fused corundum, the surface of which was uniformly covered with a film of Al₂O₃–HfO₂ binder. The tensile strength in bending of the ceramic samples with an Al–Hf binder ranged from 1.1 to 5.5 MPa, which meets the requirements for industrial ceramic casting molds.