Refractories and Industrial Ceramics最新文献

Structural changes in cerium dioxide on heating in a vacuum in the range 25 – 1600°C, in air in the range of 25 – 1500 °C, and during successive annealing in the range of 1600 – 2100°C in air, followed by water quenching, are studied. In the CeO_2–x crystal lattice the F ⟶ F¹ phase transformation in a vacuum proceeds in the range of 1100 – 1600°C; in addition, at 1200°C, X-ray lines of the C-type Ce₂O₃ phase appear. The thermal expansion coefficient of phases of the fluorite type F and F¹ in the range of 25 – 1500°C in air, as well as phases of the fluorite type F, F¹ and type C Ce₂O₃ in the range of 25 – 1600°C are determined in a vacuum and their dependence on the change in oxygen content in the CeO_2–x crystal lattice is found. Kinetic conditions for reduction of cerium dioxide in a vacuum and oxidation in air are different. The cubic structure of the fluorite type F CeO_2–x, when specimens are heated in air, is preserved up to 1800°C with the content of anionic vacancies, and at 1900°C the transformation F ⟶ F¹ occurs. Formation of loops, edge and screw dislocations within the structure of cerium dioxide grains after specimen annealing in the range of 1900 – 2100°C in air are discovered for the first time. Decomposition of the structure F¹ into cerium oxide phases of types F and C proceeds at 2100°C along the height and boundaries of screw dislocations. It is found that fragments of the C-type phase of cerium oxide are located in loops over the height of screw dislocations, which indicates movement and evaporation of these fragments. During specimen oxidation at 1600°C in air, a black-colored type C Ce₂O_3–x phase in a gradient of different concentrations moves along certain trajectories to opposite grain boundaries, abuts against dislocation loops, bends them, and is oxidized to phases F¹ and F. Within the structure of polycrystalline cerium dioxide, during heating in a vacuum and in air, certain concentrations of defects control phase transformations.

The results of grinding powdered and solid zirconium and aluminum oxides in various grinding units, i.e., ball, planetary, and bead mills, are presented. The grinding materials were PSZ-5.5Y brand partially yttrium-stabilized zirconium dioxide (USA) and Almatis CT 3000 GS brand alumina with an α-phase content of >99.0 wt.% (Germany). The use of bead mills with ZrO₂ grinding balls of dimensions 0.6 – 0.8 mm with an M:W ratio of 1:4 and a specific grinding energy of 0.6 – 0.8 kW was advisable to obtain high-purity and ultrafine oxide powders. Solid-phase sintering of the oxide powders was activated and the densities of the ceramic materials increased for aluminum oxide from 3.50 – 3.78 g/cm³ and for zirconium oxide from 5.40 – 5.89 g/cm³ if the ultrafine state of the initial oxide powders was achieved.

The article considers a method for activating cement hardening processes using nanomaterials due to the magnitude of their surface energy: when injected into concrete, nanoparticles dump it as they tend to transition to a stable state. Such activity leads to a significant gain in strength and hardness, resulting in high-strength concrete. It is shown that such an effect can be achieved by surface impregnation of concrete with sols (colloidal solutions) based on SiO₂ nanoparticles. It is feasible to start impregnation from day three of hardening under normal conditions. At this time, the main heat generated as a result of cement’s intrinsic exothermic hardening reaction has already been released into the ambient, and the introduction of additional energy will not cause a shift in equilibrium towards slowing down the hardening processes in accordance with the Le Chatelier’s principle. The article also presents the results of physicochemical studies of concrete after hardening to clarify this effect.

Premature decommissioning of a steel-teeming ladle lining due to critical localized damage, which significantly reduces lining functional properties, is one of the most acute problems in modern metallurgy. The main type of products used for steel-teeming ladle lining is periclase-carbon. In order to improve corrosion resistance and resistance to thermomechanical loads, additional additives, such as spinel, and high alumina CMA cement, are introduced into periclase-carbon products. In this article the effect of calcium aluminate-based additive on the properties of periclase carbon refractories is investigated. It is assumed that there is a potential for formation of magnesium aluminate spinel (MA) in periclase-carbon products with calcium-aluminate additives during heat treatment. Fused periclase is used as the raw material, the carbon component is represented by natural flaky graphite in an amount of 10 wt.%, and a combined binder. An additive based upon calcium aluminates is introduced, with a fractional size from 0 to 3 mm, while the amount of main fractions of fused periclase is reduced by the corresponding amount of the additive introduced. The compressive strength, apparent porosity, and bending strength values before and after coking firing are analyzed. The thermal coefficient of linear expansion, phase composition and microstructure of the products are also investigated.

The purpose of the work was to obtain a heat-resistant binder with the addition of metakaolin from mineral and man-made raw materials of the Aral Sea region. The results of preparing alumina cement using kaolin, limestone, and alumina-containing waste were presented. Effective compositions of alumina cement in the kaolin-limestone-alumina-containing waste system were developed. The preparation of metakaolin with its subsequent addition during clinker grinding was investigated to improve the physicomechanical properties of a heat-resistant binder. The reliability of the results was confirmed using modern physicochemical methods.

Improvement of plasma deposition wear-resistant coatings technology is demonstrated. At the same time, special attention is paid to one of the most important parameters, i.e., thickness of a functional layer, since when using plasma deposition methods it has a significant impact on coating quality, as well as functionality and productivity of the process. Based upon planning an experiment, mathematical models are developed that make it possible to establish a relationship between coating thickness and plasma spraying process production parameters. Results of analyzing the dependences obtained show that coating thickness is most affected by plasma torch arc current strength.