Properties of refractories produced from synthetic magnesia

Conclusions The sinterability, open porosity, and cold-crushing strength of magnesite and magnesite-chromite specimens processed from magnesia powders (96–97% MgO) are improved with a decrease in the size of the periclase grains in the powder and with an increase in the firing temperature and do not depend on the percent and composition of the silicates and on the B₂O₃ content of the magnesia powder.The high-temperature bending strength of both types of refractories increases with a decrease in the B₂O₃ content of the magnesia powder. The creep resistance of the magnesite specimens increases with the ratio CaO/SiO₂ in the magnesia powder while the creep resistance of the magnesite — chromite specimens does not depend on this index.The indices of the open porosity and strength of the magnesite and magnesite — chromite specimens were optimal when they were produced with magnesia obtained by the bicarbonate method from dolomite.To produce dense and strong magnesite refractories from magnesia, they should be fired at a temperature not below 1700°C. The firing temperature of magnesite — chromite refractories should not be below 1750°C.Translated from Ogneupory, No. 6, pp. 53–57, June, 1978.     

Refractory articles based on the ZrO2-Y2O3(Nd2O3)-Cr2O3 systems

The nature of interactions in compositions of stabilized ZrO₂—rare-earth chromite at 1750°C and the technical properties of specimens of zirconia-chromite refractories are investigated. It is shown that the use of induction melting for stabilizing the cubic modification of ZrO₂ is very effective if the material is intended for the production of conducting ceramics with high thermomechanical characteristics.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 8, pp. 8–12, August, 1996.     

Strain and Fracture of a Ceramic Based on Lanthanum Chromite

The bending behavior of a ceramic — a lanthanum chromite-based solid solution La_{1 – x} Ca_xCrO₃ (x = 0.025) doped with 5 – 40 wt.% Y₂O₃ — is studied in the temperature range of 20 – 1400°C. At 20°C the composition with 5 – 10 wt.% Y₂O₃ is strained inelastically and exhibits relatively superior mechanical properties in comparison to compositions containing 20 – 40 wt.% Y₂O₃. These compositions are prone to brittle fracture within the linear elastic strain. Based on the strain and fracture characteristics of lanthanum chromite at 20°C, its mechanical behavior at high temperatures is predicted.     

Effect of rare-earth chromites on sintering of magnesia

The effect of neodymium, cerium, lanthanum, and yttrium chromites, added in amounts of not more than 8%, on the sintering of magnesia in air and in vacuum has been studied. On addition of rare-earth chromites, the initial magnesia is sintered to a density of 0.98. By their sintering action, these chromites fall into the following sequence: neodymium chromite — lanthanum chromite — yttrium chromite — cerium chromite. The highest density (0.98 – 0.99) and the lowest porosity (1–2%) are obtained on addition of 2% of neodymium chromite to magnesia. The process of sintering of magnesia is accompanied by an increase in the size of periclase crystals from 12 to 38–56 µm.Translated from Ogneupory, No. 1, pp. 2–4, January, 1994.     

Service of chrome — Forsterite products in the vertical channels and roofs of slaggers and regenerators of open-hearth furnaces

Conclusions Following industrial testing of thermal-shock resistant chrome -forsterite refractories in 400 ton open-hearth furnaces we established that it is possible to use them completely for replacing magnesite — chromite products in the roofs of slaggers and regenerators, and chrome — magnesite products in the structure of vertical channels.The use of chrome-forsterite products in the structure of the roofs and the walls of the lower structure of open-hearth furnaces would reduce the consumption of magnesite — chromite and chrome — magnesite products and have a substantial saving effect.Translated from Ogneupory, No. 2, pp. 22–31, February, 1970.     

Calculation of expenditure norms for periclase-chromite items used to lay slag chamber arches in open-hearth and two-vessel furnaces

Actual data collected during a lengthy operating period are used to construct models giving expenditure norms for periclase — chromite items in slag chamber arches of open-hearth and two-vessel furnaces. The models allow for the furnace capacity and the repair category during the period between cold repairs and give objective estimates of the absolute expenditure of items for this laying element in groups of open-hearth furnaces. For two-vessel furnaces the share of periclase — chromite in the laying of slag chamber arches is taken into account.Translated from Ogneupory, No. 6, pp. 28 – 30, June, 1994.     

Magnesite refractory with a high CaO content

Conclusions Chromite, added in amounts of 10% to dolomitic magnesite containing 8.35% CaO by bonding with it completely during firing, is an effective stabilizer.An increase in the chromite content of the batch of more than 10% lowers the quality of the refractory.The hydrothermal treatment of the calcined dolomitic magnesite with 10% chromite accelerates the process of hydrating the free CaO and disperses the material, which helps the refractory to sinter during firing.The proposed technique provides for combined grinding and firing of a mixture of dolomitic magnesite with chromite, excludes aging of the body, reduces the firing temperature of the body and increases the quality of the refractory compared with the periclase-spinel technique.The calcium oxide in dolomitic magnesite with the addition of 10% chromite is bonded mainly with theCr₂O₃ into calcium oxychromite 9CaO · 4CrO₃ · Cr₂O₃ and the ferric oxide is introduced into the lattice of the periclase with the formation of a solid solution. With 30% chromite in the batch 3CaO · 2CrO₃ · 2Cr₂O₃ is formed, and the ferric oxide enters the magnesio-ferrite.Calcium oxychromite, existing in the refractory with 10% chromite and being a secondary phase, at its fusing temperature (>1250–1290°C) reversibly converts to calcium monochromite with a fusing temperature of 2170°C, which explains the increase in the refractoriness under load.     

Refractories of a fused periclase-chromite material for the wall lining of 100-ton arc furnaces

Conclusions The durability of a wall lining in 100-ton arc furnaces of MKhVP type refractories based on fused periclase—chromite material is 20–30% higher than that of a lining constructed of periclase—spinel brick produced from sintered magnesite and chromite ore.The chemical inertness, high resistance to attack by corrosive media, and the low content of low-melting silicates in the MKhVP refractories ensure that the rate of zone formation in the bricks is slow and the durability of the lining high.Bricks of fused periclase—chromite can be recommended as refractories for the wall lining of the arc furnaces of the Oskolsk Metallurgical Combine now being constructed.These refractories should also be subjected to testing in the roof lining of arc furnaces.Translated from Ogneupory, No. 7, pp. 26–30, July, 1978.     

Surface properties and catalytic performance of La1−xSrxCrO3 perovskite-type oxides for CO and C3H6 combustion

Catalytic CO oxidation and C₃H₆ combustion have been studied over La_1−xSr_xCrO₃ (x = 0.0–0.3) oxides prepared by solid-state reaction and characterised by X-ray diffraction (XRD), nitrogen adsorption (BET analysis) and X-ray photoelectron spectroscopy (XPS). The expected orthorhombic perovskite structure of the chromite is observed for all levels of substitution. However, surface segregation of strontium along with a chromium oxidation process, leading to formation of Cr⁶⁺-containing phases, is produced upon increasing x and shown to be detrimental to the catalytic activity. Maximum activity is achieved for the catalyst with x = 0.1 in which mixed oxide formation upon substitution of lanthanum by strontium in the chromite becomes maximised.     

Research in the production of periclase-chromite refractories from beneficiated raw materials

Conclusions Laboratory and technological investigations of periclase-chromite refractories produced from beneficiated starting materials were carried out for the purpose of defining more precisely the required grainsize distribution of the starting components of the mix. The structural characteristics (the nature of the porosity, the development of a fragmented macro- and microstructure, and the formation of a direct intergranular bond) were analyzed in relation to the composition and grain-size distribution of the mix.The process of the formation of direct chrome-spinel-periclase bonds depends primarily on the firing temperature. The degree of the development of direct bonds can be regulated, however, by varying the composition of the mix in addition to which the process can be intensified by adding some of the chromite to the fine-ground part of the mix and increasing the proportion of coarse-grained chromite. An increase in the molding pressure and a decrease in the upper limit of the coarseness of the granular chromite also contribute to the formation of direct bonds.To ensure that the properties of the refractories, more particularly the thermal-shock resistance, are as required and that the standard specifications for the Cr₂O₃ content are met the proportion of the granular chromite in the mix must be 10–15% and that of the fine-ground component 5–10%. It will be necessary to verify the compositions in production conditions and to investigate the durability of the refractories in service.Translated from Ogneupory, No. 7, pp. 30–38, July, 1978.     

Concentration of chromite from the Kempersayi deposit by magnetic separation

Conclusions Serpentines which accompany different varieties of Kempersayi chromites are endowed with higher magnetic susceptibility than chromite ore due to the presence of microscopic magnetite veinlets. Serpentine grains without magnetite inclusions as well as calcite and quartz are non-magnetic.A concentration procedure for chromite ore from the Kempersayi deposit has been elaborated and verified under semi-industrial conditions. This procedure consists of magnetic separation in two stages, i. e. at a magnetic field strength of 5000 and at 11000 oersted.The concentration of chromite ore from the Kempersayi deposit according to the above procedure permits a decrease of SiO₂ (from 6.1 to 2.5% and CaO (from 1.3 to 0. 7%) and an increase of Cr₂O₃ (from 51.7–52.3 to 55.6%). The yield of the concentrate amounted to 82.8% and the extraction of chromium oxide to 89.5%.     

Estimation of the Combustion and Detonation Parameters for Hydrocarbon Gas Hydrates

Calculated combustion and detonation parameters for methane—oxygen (air)—H₂O and acetylene—oxygen (air)—H₂O mixtures are presented. The values of the critical detonation–initiation energy are estimated as applied to methane and acetylene hydrates.     

Concentration dependences of elastooptic coefficients of germanate glasses containing lead and bismuth oxides

Concentration dependences of elastooptic coefficients of lead — bismuth — germanate glasses with compositions from virtually the entire range of glass formation in the system PbO — Bi₂O₃ — GeO₂ are investigated. Partial elastooptic coefficients of the oxide ingredients of the investigated glasses are determined. The results are interpreted with consideration of the nature of the elastooptic interaction in glasses subjected to uniaxial stress. The data can be used for designing compositions of optical media for the light and acoustic lines of acoustooptical devices.Translated from Steklo i Keramika, No. 4, pp. 11–14, April, 1995.     

Periclase-chromite refractories from fused materials

Conclusions Experiments were carried out to obtain high-grade fused chromite-periclase. It is shown that during the melting of batch consisting of raw magnesite and chromite ore we eliminate the process of reducing the chromite ore to metallic ferrochromium, which adversely affects both the content of Cr₂O₃ in the fused material, and also the commerical appearance of the resulting refractories. We developed a technology for preparing periclase-chromite refractories with chromite-periclase constituents. The goods obtained possess good physicoceramic properties and a low content of silicates.The articles thus prepared were used to make the linings of the most critical parts of converters, Kivset unit in PZhV furnaces, which allowed an increase to be made in the duration of campaigns for these units of 1.5–2 times.Translated from Ogneupory, No. 3, pp. 41–44, March, 1985.     

Effect of phosphoric acid concentration on some properties of finely milled refractory materials

Conclusions The concentration of phosphoric acid seriously affects the setting, weakening, and sintering of the finely milled refractory materials.Increasing the acid concentration boosts the setting rate of alumina, MgO·Al₂O₃, chromite, electrocorundum, dunite, and dinas, but hardly affects the setting of MgO, Cr₂O₃, magnesite, zircon, and quartzite.The materials that were studied are almost unaffected at 800°C. Increasing the concentration of H₃PO₄ improves the sintering of alumina, MgO·Al₂O₃, chromite, zircon, and dinas, but impairs the sintering of MgO, Cr₂O₃, magnesite, electrocorundum, dunite, and quartzite.Translated from Ogneupory, No.3, pp. 40–43, March, 1968.     

Hydrogen Permeability of Borosilicate Glasses

Borosilicate glass-forming compositions R₂O – B₂O₃ – SiO₂ – R_aO_b (R — Li, Na, K; R_a — Zn, PbO) are investigated. A correlation-regression analysis of the criteria (the silicate modulus, the oxygen number, the structure cohesion factor, the relative molar volumes of the components) affecting the hydrogen permeability of glasses is carried out. The tendency for permeability variations depending on the component composition and the above specified criteria is identified.     

On the mechanism of the electrochemical reduction of the La(III)—alizarin complexone complex with and without F in (CH2)6N4---HNO3

The mechanism of the electrochemical reduction of the La(III)—alizarin complexone(L) complex with and without F⁻ at the mercury electrode was investigated in (CH₂₆N₄---HNO₃(pH4.3). The reaction scheme can be written as follows: For La(III)—alizarin complexone system, in the solution: at the electrode:

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For La(III)—alizarin complexone—F⁻ system, in the solution: at the electrode:

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where L′ and L″ are the products of the reduction of L in these complexes adsorbed on the surface of the electrode.     

Physicochemical studies and purifying of drainage in refractories plants

Conclusions The main contaminating component of drain waters is the dust suspension of clay, grog, chromite and magnesite.Coagulation followed by standing is recommended as the basic method for purifying drain waters. The cheapest regent for coagulation is CaO, and it is also possible to use Al₂ (SO₄)·18H₂O in combination with CaO.Translated from Ogneupory, No.3, pp.30–32, March, 1967.     

Nitrate distribution and accumulation in an Ustochrept soil profile in a long term fertilizer experiment

Distribution and accumulation of NO₃—N, down to 210 cm depth, in the soil profile of a long term fertilizer experiment were studied after 16 cycles of cropping (maize-wheat-fodder cowpea). The application of fertilizer N without P and K or in combination with only P resulted in higher NO₃—N concentration in the soil profile than the application of N with P and K. With an annual application of 320 kg N ha^–1 alone, a peak in NO₃—N accumulation occurred at 135 cm soil depth. However, with the application of NPK, no peak in NO₃—N distribution was discernible and its content at most of the sampling depths was either less than or equal to N and NP treatments. The annual application of 10 tons farm yard manure (FYM) per ha along with NPK resulted in a relatively lower NO₃—N content in the sub soil. The amount of NO₃—N accumulation in the soil profile decreased as the cumulative N uptake by the crops increased. Application of fertilizer amounts greater than that of the recommended (100% NPK) resulted in low percent N recoveries in crops and greater NO₃—N accumulation in the soil profile.     

Optimizing the composition of thermal-shock resistant ceramics based on magnesium chromite

Conclusions Using the method of mathematical planning of experiments the optimum composition of thermal-shock resistant ceramics based on magnesium chromite was established: the total ratio of the molar parts of magnesia and chromium oxide in the batch equals 0.6; the ratio of the magnesium oxide-chromium oxide in the dispersed constituent of the batch equals 2.0; the size of the grains of the coarse fraction (chromium oxide) is located within the range 0.25–0.6 mm.The resulting material on the basis of magnesium chromite possesses high values for thermal-shock resistance, and also factors (K_1c, _p and _ef) characterizing destruction. The specimens have an adequately low porosity value and are acceptable for design ceramics in terms of the physical and mechanical properties, and the thermal expansion coefficient.Translated from Ogneupory, No. 5, pp. 8–11, May, 1989.