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.     

Refractories based on fused pe riclase — Chromite material for vacuum steel refining plants

Conclusions The relevant technology was developed and production has started of high-quality refractories based on a high-density fused periclase —chromite material.The refractories are characterized by a low content in silica and silicates, well-developed direct bonds between the high-refractoriness minerals, and high indices for density, cold-crushing strength, thermal strength, refractoriness under a load, and in-vacuo stability to the action of slag and steel melts and the gases. The most favorable combination of properties was achieved when using starting materials of high-purity, fused periclase-chromite with a maximum grain size of 5 mm, batches with a low content of fine-ground components, high specific molding pressures, high firing temperatures, and long holding times at the peak temperature.The refractories are designed for the lining of the pipe, bottom, and walls of the chamber of equipment for vacuum steel refining and can be used with good results in the lining of converters, electric-arc and plasma furnaces, and other installations for melting high-temperature materials.Translated from Ogneupory, No. 8, pp. 5–12, August, 1976.     

Corrosive Interaction between Slags High in Copper and Nickel Oxides and Periclase,Periclase-Chromite,and Chromite Refractories

A mechanism of corrosive interaction between periclase-chromite, periclase, and chromite refractories and molten copper (I) oxide and slag melts containing copper oxide and nickel oxide has been studied. The refractories in question are shown to be insufficiently resistant to slag attack typical of smelting technologies for converting nickel-containing copper sulfide mattes into blister copper. __________ Translated from Novye Ogneupory, No. 8, pp. 41 – 47, August, 2005.     

Obtaining magnesia and periclase refractories from bischofite from the volgograd deposits

Conclusions Experimental work was carried out to obtain from bromine liquors of bischofite of the Volgograd deposits magnesium oxide, using low capacity industrial equipment for chemical purification of magnesite, including a recuperator, a tank-collector, a spray-reactor, a cyclone, an absorption column, spray traps, a vacuum pump, and a filter press.We worked out the parameters for the processes of boiling off the liquor, thermohydrolysis of the magnesium chloride, absorption of the hydrogen chloride with the production of hydrochloric acid, washing and leaching the hydrolytic magnesium oxide, and filtration of the resulting magnesium hydroxide. During the reprocessing of the liquor containing the bischofite, using this technology, without preliminary purification to remove boron and sulfates, we obtained magnesium hydroxide with a high purity level (98.5–99.5% MgO on the calcined weight).It is shown that the magnesium hydroxide thus obtained is a high-quality raw material for the production of fused and sintered periclase with a purity of 98–99.5% MgO. The technology of sintering, including carbonization of the magnesium hydroxide, hot palletizing without bond, and firing at moderate temperatures, ensures the production of densely sintered periclase. Tiles with inserts made from fused periclase of high purity with a clear anisotropic structure facilitate the casting of two heats through the gate valves.The results obtained can serve as the starting data for the development of specifications (TLZ) and planning the production of magnesium oxide from the debrominized bischofite liquors at the Volgograd site using the thermohydrolysis method. We need to solve the problem of the use of the 20% HCl that is obtained.Translated from Ogneupory, No. 1, pp. 27–30, January, 1988.     

Influence of mechanical activation of basic refractories and mixtures on sintering

Conclusions Mechanical activation leads to partial breakdown of the crystalline structures of refractory materials, conferring a higher reaction state on them. This is manifest as a reduction in the temperature range in which the magnesite and dolomite undergo conversions during heating, and also in the greater degree of exposure of the periclase and chrome concentrate.The porosity of the clinker obtained from activated sintered periclase with (CaO + SiO₂) >3.5%, fused periclase obtained from magnesite calcined in a shaft furnace, raw magnesite and periclase-skin, is reduced by more than an order compared with the original. It is considerably less for periclase-chromite skin, is reduced by more than an order compared with the original. It is considerably less for periclase-chromite skin, sintered periclase with (CaO + SiO₂) <3.5%, fused periclase-chromite, and periclase obtained from Kul'dursk brucite.To determine the possibility of applying these results in production conditions, research is now being conducted to select effective production activators, e.g., equipment with an elastic deformable working component.The authors would like to thank N. B. Kusin'sh, G. I. Vikulina, G. N. Bondarenko, and A. P. Kima for assistance in completing this work.Translated from Ogneupory, No. 3, pp. 14–17, March, 1993.     

Production technology of high-density periclase-spinel roof materials

Conclusions High-density periclase-spinel refractories can be produced from a body of magnesite powder containing 94–96% magnesium oxide and Kempirsai chromite by high-pressure molding and high-temperature firing in a tunnel kiln. The product is strong with good thermal stability and high onset temperature of deformation under a load. The structure of the refractory is improved as a result of the formation of a large proportion of direct intergranular bonds between the periclase and spinel.It is planned to produce experimental industrial-scale batches of periclase-spinel roof refractories and to subject them to trials in the roof of open-hearth furnaces in continuous operation.Translated from Ogneupory, No. 8, pp. 39–44, August, 1973.     

Wear of high-fired periclase-spinel refractories in the roof of a double-bath steel-melting furnace

Conclusions Periclase-spinel products prepared from magnesite powders which are pure in chemical composition and beneficiated Kempirsaisk chromite possess an increased resistance (30% higher than in ordinary periclase-spinel brick) during service in the roof of a double-bath steel-melting furnace, operating with oxygen blow in the bath. Their wear in general occurs as a result of the fusion of the working surface. The mechanism of this wear is explained by the metasomatic processes which lead almost to complete replacement of the periclase and chrome-spinel by ferritic spinels.The increase in the resistance of the experimental periclase—spinel refractories is helped by the structure with the direct bond between the grains which retards the access of silicates and slags inside the textural elements. This exerts a favorable influence on the change in structure of the refractory during service, especially in the transition zone in which additional sintering and crack formation leading to scaling of the experimental refractory hardly develops.On the basis of the results of the research we recommend that refractory enterprises set up various technological production lines for making periclase-spinel products from pure Satkinsk magnesite powders (94–96% magnesium oxide) and beneficiated Kempirsaisk chromite (59–60% chromium oxide) using high-temperature firing in a tunnel klin. The use of high fired periclase-spinel products with a direct bond between the grains would increase the resistance of the roofs of metallurgical furnaces operating with the use of oxygen and increasing their outputs.Translated from Ogneupory, No. 5, pp. 28–33, May, 1973.     

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.     

Experience with the use of mullite-corundum refractories in the roofs of electric-steel furnaces

Conclusions The resistance of mullite-corundum roof articles, as for periclase chromite, is due to the absorption of melt products from the working region of the furnace and the action of one-sided, high-temperature heating, but in view of the considerable difference in the physicochemical properties the use of the first in the central zone of the roof, subjected to the most severe working conditions, is more desirable than the second.The use of mullite corundum roof bricks, structurally reinforced with nonisometric grains of fused mullite, instead of periclase-chromite refractories will provide an increased roof life, both during the melting of stainless and ballbearing steels, without a change in the structure design; the increase amounts to 25–35%.Translated from Ogneupory, No. 4, pp. 43–46, April, 1986.     

Development of a resistant spherical packing for service in nitrogen at 1650°C

Conclusions The action of scale on periclase, spinel, corundum, periclase-chromite, and chromite-periclase specimens (production and laboratory) at 1650°C in commercially pure nitrogen was investigated.A method was developed for production of periclase, spinel (aluminomagnesia), and periclase-chromite spherical packings by the pelletizing method. It was shown that pelletizing of fused periclase and of mixtures based on it is possible only with the addition during vibrogrinding of a surface-active hydroxylated alcohol-base alkyl phosphate paste in a quantity of 0.1% and alternate moistening of the powder being pelletized with a suspension of glycerine residue in silica sol and a solution of lignosulfonate and methyl cellulose.Tests were made of the action of scale on pellets of all of the compositions at 1650°C in commercially pure nitrogen under load and without load. The preferable spherical packing materials for service under such conditions are periclase with a density of not less than 3.12 g/cm³, corundum with zero porosity, and spinel of stoichiometric composition with a density of not less than 3.36 g/cm³. In addition, the use of periclase-chromite with a density of not less than 3.32 g/cm³ is possible.Translated from Ogneupory, No. 3, pp. 5–10, March, 1989.     

Sintering magnesium oxide obtained by the chemical beneficiation of magnesite

Conclusions A quantitative relationship was established for sintering chemically beneficiated magnesite and a method of obtaining the MgO; we also established the parameters of hydrolysis of the magnesium chloride, the quantity of residual volatiles, the temperature and rate of thermal activation of residual volatiles, the temperature and rate of thermal activation of the magnesium oxide, not washed, and washed to get rid of the calcium impurities, and also the completeness of the hydration of the magnesium oxide during leaching.A production flow line is proposed for obtaining from the enriched material sintered periclase clinkers differing in density and degree of purity.Translated from Ogneupory, No. 7, pp. 43–50, July, 1982.     

Microstructure of Periclase

The microstructure of magnesia grains obtained from coarse crystalline and cryptocrystalline magnesites and from seawater and brines is illustrated and the influence of the amount and type of impurities on the development of periclase is discussed. The factors which affect direct peri-clase-periclase bonding in basic brick are reviewed; the microstructural effects of additions of sesquioxides are shown. The complex reactions between periclase and chromite spinel are considered with reference to direct periclase-chromite bonding. The formation of secondary periclase is briefly described.     

The effect of composition of granular and dispersed constituents of magnesite-chromite and periclase-spinel products on their properties and behavior under the action of iron oxides

Conclusions The composition of the dispersed and granular constituents greatly affect the properties of periclase-spinel and magnesite-chromite articles.With the introduction of chromite in the dispersed phase of the articles, the refractoriness under load may be increased by about 70°. The spalling resistance is also increased.Magnesite-chromite articles with the introduction of part of the chromite in the dispersed phase has much less tendency to embrittlement under the action of iron oxides even with a higher total content of chromite than articles containing chromite only in the granular part.With a reduction in the content of chromite in the granular part (so that the total content of chromite in the article does not exceed 25–30%) we can get quite a satisfactory life for the articles in regard to the embrittling action of the iron oxides.The manufacture of refractories of this type may also prove to be favorable with the use of magnesites with a somewhat higher content of calcium oxide.High physicochemical factors for the articles may be obtained by making the periclase-spinel articles with the addition of aluminous materials in the dispersed or granular phase.Comparative study of the properties shows that the periclase-spinel articles compared with the magnesite-chromite (with one and the same composition of dispersed phase) has a higher refractoriness under load, a lower porosity, lower gas permeability, and a much lower tendency to embrittlement under the action of iron oxides, although the spalling resistance of periclase-spinel refractories, as is well known, is lower.Translated from Ogneupory, No. 1, pp. 44–52, January, 1966.     

Effect of calcium oxide on the hydration activity of the powders of electrical-engineering periclase

Conclusions The hydration activity of the periclase powders depends to a significant extent on the hydration of free calcium oxide. The hydration resistance of the powders can be increased by fixing calcium oxide in the hydration-resistant compounds with silicon and magnesium oxides.It is also necessary to decrease the specific surface of the periclase powders for decreasing their ability to absorb moisture.Translated from Ogneupory, No. 8, pp. 9–12, August, 1988.     

Influence of free chromium oxide on some properties of ceramics made of lanthanum chromite

Conclusions The stability of the properties of materials made of lanthanum chromite is determined primarily by their original porosity, and to a less degree by the content of free chromium oxide. An increase in the stability of the properties may be obtained by using a material with the minimum content of free chromium oxide, and the maximum possible density.The change in the porosity of the material on the basis of electrofused lanthanum chromite containing free chromium oxide, during use at high temperatures, is connected with the predominant removal of the chromium oxide and the completion of sintering of the material with volatilization of the Cr₂O₃.The dynamics of the mass loss of lanthanum chromite depend not only on the nature of the volatilization (congruent or incongruent) but also on the material's porosity.Translated from Ogneupory, No. 1, pp. 26–29, January, 1989.     

Periclase-spinel products based on sintered materials for vacuum treatment of steel outside the furnace

Conclusions A technology was developed for periclass-spinel, low-silica chrome-concentrate (SiO₂ <1.5%) and sintered periclase (MgO 91–92%, SiO₂ < 3%). As regards the resistance in the walls of the metal zone of circulation vacuum equipment, these refractories are not inferior to PKhP periclase-chromite goods made from fused materials.In the production of PShKh articles it is recommended that titanium additives be used to ensure sintering of the chrome-concentrate to a low porosity, and to stabilize the properties of goods made with it.It is desirable to make wider tests of these refractories in vacuum units of different types. The introduction of PShKh articles based on sintered materials in the walls instead of PKhP articles should reduce the consumption of scarce fused materials for vacuum treatment and cut the costs of the linings.Translated from Ogneupory, No. 7, pp. 32–36, July, 1991.Deceased.     

Chemical Resistance of Refractories to AI and AI-Mg Alloys

The chemistry of the reaction between molten aluminum alloys and some refractory oxides is discussed. High-alumina brick containing 85, 94, and 99% Al₂O₃ periclase brick, and magnesia spinel brick were immersed for 48 hours in three aluminum alloys containing 0, 2.4, and 7.7% magnesium, respectively. All brick were discolored, although most of the discoloration disappeared after reheating at 1000°C in an oxidizing atmosphere. Only the 85 and 94% brick, which contained silica, showed permanently darkened reaction rims. X-ray diffraction analysis of these darkened areas showed that the alloy containing 7.7% magnesium caused periclase formation in the rim whereas the alloy containing 2.4% magnesium produced spinel. Commercial aluminum caused only a decrease in the mullite content of the darkened area. Magnesia spinel and periclase were unaffected by all the alloys tested.     

Fused forsterite refractory material

Conclusions The possibility in principle is shown of obtaining pure forsterite by electric-arc melting of natural magnesium orthosilicate.It was established that the oxides of iron, chromium, silicon, and manganese reduce easily and are concentrated in a ferroalloy the content of which is 6–8%. The product of fusion of dunite is 95–98% forsterite and an insignificant quantity of iron containing siliceous glass.Parts produced from fused dunite have quality indices significantly exceeding the indices of those produced from fired dunite.Translated from Ogneupory, No. 8, pp. 31–34, August, 1985.     

Microhardness of fused periclase

Conclusions The microhardness of fused periclase has been studied. It is shown that the microhardness of periclase is significantly affected by defects in the structure, in particular, by the dislocation density and the presence of impurity oxides.When fused periclase is heat-treated at 1000–1400°C which reduces the dislocation density by approximately two orders of magnitude, the microhardness of periclase is decreased. The reduction in the microhardness helps to increase the electrical resistance of the periclase as a result of both a decrease in the dislocation density and also, obviously, of the change in the packing density of the particles if the electrical resistance is measured in tubular electric heaters.The reduction in the microhardness helps to improve the ease of pressing of the refractory articles manufactured using fused periclase.Translated from Ogneupory, No. 4, pp. 10–13, April, 1984.     

Oxidative transformations of acetonitrile on a La-Ce/MgO catalyst

In the interaction with air or a methane-air mixture in the presence of a ctalyst containing lanthanum and cerium oxides supported on magnesium oxide (periclase), acetonitrile underwent redox transformations that mainly resulted in carbon oxides. Acrylonitrile and propionitrile were also detected in the reaction products. The products of the oxidative dimerization of acetonitrile were formed to an insignificant extent.