S. V. Kazakov

A study of the high-temperature transformations of periclase-carbon refractories using the method of X-ray spectral microanalysis

Etude des transformations a haute temperature des refractaires periclase-carbone par la methode de microanalyse spectrale a rayons X

Optimization of the composition and the properties of the plastic bodies for obtaining silicon carbide products

ConclusionsBased on the simplest concepts regarding the filler-plasticizer system, we derived an expression relating the ratio of the quantities of the filler and the plasticizer to the densities of the filler and the plasticizer under the condition of dense packing; a scheme of optimizing the composition of the plastic bodies was shown.It was shown that the Cpl/CSiC ratio is determined by the mechanism of the evolution of the final structure of the silicon carbide products during the siliconizing firing process. The methods of controlling the apparent density of the filler and the density of the plasticizer were examined.We developed a plastic body requiring a lower forming load; the content of the primary silicon carbode in the original charge of the body could be brought up to 94%; the products obtained using this body possess a combination of high strength and electrophysical properties.

Structure and electrical conductivity of polycrystalline silicon carbide

ConclusionsUsing the methods of optical and electron microscopy and EPR, we identified and determined the electrophysical characteristics of SiC′ and SiC″ in self-bonding polycrystalline silicon carbide. It was established that the relative content of SiC″ can differ from the content of the carbide-former depending on the prevailing mechanism of formation of SiC″ (reaction sintering or recrystallization). The temperature dependence of the specific electrical conductance (conductivity) of the fired polycrystalline silicon carbide materials was calculated in the 20–1500°C.

Investigating sintering of magnesia obtained by chemical beneficiation

ConclusionsA study was made of the sintering behavior of samples of magnesium oxide obtained by chemical purification. The magnesia obtained by the nitrate method is a low sinter-active material. The density of the material after firing at up to 2400°C equals about 3.0 g/cm3. Partial hydration of the material improves the sintering results. The magnesia obtained by the ammonium-sulfate technology is an active material which when fired yields a densely sintered product with a density of 3.3–3.4 g/cm3.

Effect of certain transition-metal oxides on the structure and properties of periclase-chromite refractories

ConclusionsThe solubility of the oxides of the transition metals in fused chromium spinellide decreases in the following order: iron oxide, manganese oxide, vanadium oxide, and titanium oxide. This series corresponds to the well known series [12] of increasing atomic volumes of the elements.When firing the periclase-chromite systems based on the chromium spinellides containing the oxides of the transition metals, the migration of these metals into periclase decreases in the following order: iron → manganese → vanadium.It was revealed that the addition of manganese oxide to iron-free chromium spinellide decreases its microhardness. However, in this case, the addition of manganese oxide does not affect the other properties of the specimens.

Effect of iron oxides on the service life of periclase-spinellide refractories

ConclusionsThe conducted tests showed that low-silica periclase-spinellide refractories having an excess iron content in the chromium-containing component are not suitable for use because of their rapid slag-induced chemical corrosion.In continuously operating metallurgical units where splitting of the lining due to the action of the slags is not a decisive factor, it is advisable to use refractories having the optimum content of iron oxides for the formation of a homogeneous spinellide matrix.In units operating cyclically under the most severe conditions (for example, in the ASEA-SKF type installations), the periclase-spinellide products in which the spinellide having the minimum content of iron oxides acts as a fused synthetic chromium-containing component are suitable since they exhibit the best high-temperature thermomechanical properties and stability.

Structure of the calcareous gunite-coatings of the linings of converters

ConclusionsA study of the structure of the calcareous gunite coatings before and after bringing them into contact with a lime-fayalite melt showed that due to the effect of high temperatures, a dense refractory coating forms at the surface of the lining. The obtained coating corresponds to the lime-periclase refractories with respect to composition. It exhibits high slag resistance, thermal shock resistance, and mechanical strength and improves the service life of the converters. The optimum specific consumption of oxygen was determined for carrying out guniting.The obtained results form a basis for improving the properties of the calcareous gunite coatings of the converter linings.

Microstructure and chemical composition of the phases of the fused low-silica chromite-periclase materials

In order to produce chromite (chrome)-periclase bearing refractories having a low silica content, one makes use of beneficiated concentrates of chromium ores or synthetic chromiumbearing materials [i, 2] Which require presintering or prior melting because of the fine dispersion of the products of benefieiation and synthesis. It was previously shown [3, 4] that fused materials can exhibit significant differences in the structure and that ferrochromium has a negative effect on the service properties of the products.

Phase and chemical analysis of a fused refractory based on bauxite concentrate

ConclusionsBased on a bauxite concentrate, we obtained a mullite-bearing refractory exhibiting high-temperature strength. The refractory materials produced by melting the bauxite concentrate with alumina and silica additions show the presence of solid solutions of mullite whose basicity was quantitatively evaluated using chemical and IR-spectroscopic methods.The conducted studies confirm the assumption (hypothesis) that the polymorphic modification of aluminum oxide having the structure of mullite m-Al2O3 can crystallize at high cooling rates that are close to quenching rates and, also, at a high Al2O3 content (99.9%). The IR absorption spectrum and the refractive index of the suggested phase have been determined. IR-spectroscopic analysis of the glass phase showed the presence of aluminum atoms having tetrahedral and octahedral coordination in this phase.