Refractories and Industrial Ceramics最新文献

The physicochemical and thermophysical properties and phase composition of heat-resistant ceramic materials synthesized based on the Al₂O₃–SiO₂–TiO₂ system were studied. The influence of modifying additives such as RO₂ (ZrO₂, SnO₂, CeO₂, and MnO₂) on the sintering and phase formation processes of ceramic materials was studied. Samples of mullite-thialite ceramics modified with SnO₂ and CeO₂ in the amounts of 5% and 7.5%, respectively, were characterized by water absorption from 0.2 to 2.2% and CLTE in the range 2.4 × 10^–6 – 3.2 × 10^–6 K^–1. The developed materials could withstand greater than 70 heating and cooling cycles and could be used to work under conditions of sudden temperature changes.

Materials with a layered perovskite-like structure of the Aurivillius phase type are important for technology fields such as magnetoelectronics and photocatalysis. Features of phase formation during the synthesis of nano- and macrocrystalline materials based on Bi₆Fe₂Ti₃O₁₈ with the five-layer Aurivillius phase structure are described. Samples were characterized by powder XRD, DSC/TG, dilatometry, and SEM/EDX. The temperatures of the beginning of formation, the Curie point, the beginning of decomposition and activation of sintering of the obtained materials, and the value of the coefficient of linear thermal expansion were determined. The technological possibility of controlling the dispersion of the obtained materials by changing the synthesis conditions is shown.

Many problems arising at the development of a mathematical model of critical regimes of two-phase flows are connected with the necessary account for differently directed motion of particles at all levels of the channel simultaneously. These problems were solved by developing a discrete-stationary model of the process. Recurrent equations allowing us to determine solid phase distribution both in ordinary conditions and in optimal separation regimes were derived and solved.

The article provides results of a study of alumina ceramic production based on domestic grades of alumina: GN, GÉF, GK-1, GRT. The different initial state of alumina of different grades in terms of purity and fineness is reflected in the shape and size of granules of pressed powders and in alumina ceramic physical and mechanical properties. Use alumina of domestic producers did not provide preparation of high-quality alumina ceramics. The maximum attainable apparent density value of fired ceramic did not exceed 3.80 – 3.84 g/cm³. Overseas alumina brands Almatis CT 3000 SG and Nabalox 713-10 NM (Germany) have high purity, fineness and an α-Al₂O₃ content of more than 99.0 wt.%, which ensures production of alumina ceramics with a high apparent density at 3.94 – 3.96 g/cm³ and can be used for production of alumina ceramics with a high level of physical and engineering properties.

Technological aspects of the synthesis of heat-resistant ceramics in the NiO–YSZ system using an oxidizable Ni-based cermet composite, including testing the use of additive synthesis technology to enable the production of items of complex shape, have been studied. The key functional characteristics of the materials were determined based on the results of the synthesis. In particular, oxidation of prototypes was found to be accompanied by a volume increase of the ceramics by ~10%.

The alumina ceramics with high compressive strength were prepared by pressureless sintering, and the kaolinite and calcium carbonate were added as Al₂O₃–SiO₂–CaO sintering aids. The effects of sintering temperature on the volume shrinkage, bulk density, water absorption and compressive strength of the alumina ceramics were studied. The phase composition, crystal cell parameters, average grain size and microstructure of the ceramic were analyzed by XRD, SEM and EDS. The results show that the lattice tends to packed with the increase of sintering temperature. The bonding between grains is the most compact after sintering at 1700°C. The volume shrinkage increases with the increase of sintering temperature. The water absorption of alumina ceramics after sintering at 1700°C reaches the minimum value of 0.06%. The bulk density and compressive strength increase first and then decrease with the increase of sintering temperature. At 1700°C, optimized mechanical properties of alumina ceramics is obtained, with a bulk density of 3.80 g/cm³ and a compressive strength of 1323 MPa.

The article presents the description of slags produced by the Klyuchevskaya Concentrating Plant; samples of metallic chromium, ferrochrome, and ferrotitanium slag are described. In addition, the chemical composition of slag used for producing high-alumina refractory cement, physical and mechanical properties of cement obtained by remelting metallic chromium slags, and charge compositions during the remelting of metallic chromium slags are described. Finally, the scheme of covering the bottom of the dump truck body is discussed.

This article presents theoretical information about high-temperature plastic deformation (creep), as well as criteria for its evaluation. Results of practical determination of creep of high-purity periclase refractory material are provided. The basic parameters (apparent activation energy, exponential load ratio) describing the process are determined. Influence of temperature and load changes on the process of high-temperature plastic deformation is studied.

Hard alloys are successfully used as friction units under exposure to high loads, aggressive and abrasive media. However, despite all the advantages of traditional hard-alloy materials, slide bearings based on them demonstrate low performance in case of insufficient or no lubrication. The addition of graphite to a nickel-containing hard alloy increases the operating time under the dry friction conditions and improves the load-bearing capacity in the presence of a lubricant, as well as the thermal conductivity of the material.

The article shows the effect of ultra-high pressing load of 1,8 GPa at 1850°C during spark plasma sintering, compaction pressures of 1,56 and 2,12 GPa at 1080 and 1150°C, respectively during explosive sintering of ceramic and metallic powder mixtures on the phase composition, microstructure, grain sizes of crystalline phases, relative density, linear shrinkage, microstructural features of boundary layers, microcracks paths, physico-mechanical properties of mullite–(Ti,Cr,V,Mo)(C,N)–c-ZrO₂–β-Si₃N₄–c–BN–Mo–V–Cr and mullite–(Ti,Cr,V,Mo)(C,N)– β-Si₃N₄–B₄C–Mo–V–Cr samples. Synthesized powders Ti(C_0.7N_0.3), β-Si₃N₄, B₄C, h-BN are characterized by different crystallization intensity of phases Ti(C_0.7N_0.3), β-Si₃N₄, B₄C, and h-BN, respectively. Spark plasma-sintered c-ZrO₂ at 1400°C shows intensive crystallization of the c-ZrO₂ phase, as well as crystalline, uniform and dense microstructure. The samples sintered by spark plasma method at ultra-high pressing load of 1,8 GPa show intensive mullitization, crystallization of (Ti,Cr,V,Mo)(C,N), β-SiAlON, c-ZrO₂, γ-Si₃N₄, and c-C₃N₄ phases, more crystalline, uniform and densely sintered microstructures, polydisperse grains of crystalline phases at 1850°C unlike the samples produced by the explosive sintering. The samples sintered by different methods differ by density, homogeneity, path, width of the boundary layers of ceramic phases, and propagating microcracks across these boundary layers, resistance to cracking, as well as different values of physico-mechanical properties.