Resistance of silicon carbide refractories to the action of carbon monoxide,alkalis, and slag

Conclusions The effect of alkalis, slag, and carbon monoxide on silicon carbide and nitride was studied at elevated temperatures up to 1550°C. It was established that silicon carbide is destructed most rapidly at 1200°C under the action of the investigated factors. The properties of silicon nitride virtually do not change on heating up to 1400°C in the presence of carbon monoxide; one observes a slight decrease in the nitrogen content of the system only at 1550°C and an increase in the silicon content in the 1200–1550°C range due to the dissociation of Si₃N₄ and the formation of Si₂ON₂.At 1200 °C, carbon monoxide and alkalis significantly influence the property variation of the silicon carbide refractories containing a silicon nitride-based binder only during the first 2 h of holding; this is confirmed by the abrupt decrease of the open porosity and the apparent density during this period. Further increase in the holding period up to 16 h does not have a significant effect on the variation of the properties of the products owing to the protective glassy coating formed on the refractory surface as a result of partial oxidation of SiC. Our studies confirmed that the silicon carbide refractories containing a silicon nitride binder possess a high degree of stability under aggressive conditions.Translated from Ogneupory, No. 2, pp. 1–4, February, 1988.     

Main causes of refractory wear in the shaft of a blast furnace and means of improving the resistance

Conclusions During service, refractories in a blast furnace shaft are saturated by components of the batch, change their properties and phase composition, and acquire a zoned structure which reduces the resistance to the complex action of the physicochemical and thermomechanical destructive factors.The wear of the shaft is a maultistaged cyclic process, including the saturation of the refractories through the pores, joints, and cracks by liquid and gaseous components of the batch and the gaseous medium, the decomposition of mullite and the formation of new compounds and glass — mainly potassium phyllitic and nepheline compounds — solution and reduction of the new compounds, and abrasion of the reaction products by the batch materials.We recommended for the lining of the shaft shoulders and the bottom and upper parts of the hearth the use of dense kaolin refractories containing 41–42% Al₂O₃ and with an open porosity of 8–12%, the technology for which is being introduced at the Chasov-Yar Refractories Combine.Translated from Ogneupory, No. 4, pp. 41–45, April, 1980.     

Refractories for continuous casting of low carbon rimmed steel

Conclusions The compound proportioning device designed by the All-Union Institute of Refractories from an aluminous nozzle containing 80–82% alumina with a porosity of 18–23% and a corundum insert containing 97% alumina with a porosity of not more than 18% satisfies the requirements of continuous casting of low-carbon rimmed steel of the type 05–08KP.Investigations led to the determination of a range of refractories for steel casting and intermediate ladles permitting satisfactory casting in continuous casting plant of low carbon rimmed steel of the type 05–08KP from 140-ton ladles in four shanks with a casting time of about 1.5 h.Translated from Ogneupory, No. 8, pp.4–12, August, 1967.     

Fireclay refractories for service in reducing conditions

Conclusions The Chasov-Yar Refractories Combine has organized the production of firebrick of 57 standard sizes for lining the shafts of furnaces used for direct reduction of iron oxides.Tests of brick with an open porosity of up to 16% and up to 1.5% Fe₂O₃ showed that they are resistant to reducing conditions in a current of CO at 500°C for 500 h. These refractories have been in use since 1983 at OÉMK in the linings of shaft furnaces used for reduction firing of nodules. During service the working layer of the refractories becomes saturated with fine dust from the nodules, become densified and worn due to abrasion. The pores of the refractory are saturated with a small amount of finely dispersed carbon.A TU 14-8-606-90 standard specification is being prepared — Refractory fireclay shapes for constructing shaft furnaces used for nodule metallization. The bricks will be designated ShPSh-41.Translated from Ogneupory, No. 5, pp. 33–34, May, 1991.     

Impregnation of a periclase-chromite lining with nickel matte

Results of an investigation of periclase-chromite linings in contact with matte (sulfide-metallic melt) in shaft melting of oxidized nickel ores are presented. It is shown that the sulfide components of matte, preferentially iron sulfide, impregnate the refractory, whereas the metal (21.9–23.1% Ni, 1.38–1.45% Co, 73.3–76.1% Fe, and 0.8–1.0% S) remains in the gaps between bricks. Chemical analysis data show that the sulfide-impregnated refractory contains 5.1–9.5% S, 9.8–27.9% Fe, 1.8–7.5% Ni, 0.09–0.15% Co, which markedly decreases the heat engineering parameters of the refractory and the entire lining. The results clarify the mechanism of failure of refractories and the formation of skull.Translated from Ogneupory, No. 6, pp. 28–29, June, 1995.     

More efficient utilization of alumina in refractories production

Conclusions An investigation was carried out of ways of utilizing commercial alumina more efficiently in refractories production by improving the composition of the products and the technology of their manufacture. Commercial alumina should be used mainly for the production of mullite refractories from synthetic mullite and of corundum refractories containing 90–99% Al₂O₃. Commercial alumina must be used for the production of spinel and spinel-containing refractories.More extensive use should be made of the alumina-containing waste from chemical plants for the production of refractories with a low mullite content, of ramming compounds, fusioncast refractories, and electrofused spinel as a substitute for chromite in roof bricks. To produce refractories with a higher Al₂O₃ content than can be achieved with kaolin more extensive use should be made of natural alumina-containing starting materials.Some mullite and corundum refractories should be produced with low porosity by using high molding pressures, actively sintering starting materials, and hydrostatic molding.Translated from Ogneupory, No. 8, pp. 33–39, August, 1978.     

Impregnating periclase refractories with water-soluble coal-tar bonds

Conclusions A study was made of the properties of a new carbon-containing material-noncarcinogenic water-soluble coal-tar bond (VOKS) with a high coke residue and low viscosity. We determined the conditions and parameters for effective impregnation of periclase refractories with the new material, in particular tiles for the gate valves of steel-casting ladles.By impregnating the tiles with VOKS, up to 2% of residual carbon was introduced into the refractory, which reduced the open porosity of the articles by factors of 2–7.Translated from Ogneupory, No. 1, pp. 26–29, January, 1982.     

Changes in the properties of aluminosilicate refractories under prolonged reducing conditions

Conclusions Studies of corundum and aluminosilicate refractories of dense and granular structures in an atmosphere of hydrogen and dissociated ammonia at 1200, 1500, and 1700°C in periods of 175 and 50 h showed that the resistance of the products increases with an increase in the alumina concentration and density. The maximum resistance is exhibited by corundum products. In the aluminosilicate refractories there is some additional sintering of the material with the separation of mullite and glass. Simultaneously on the surface of the specimens we detected deeper mineralogical changes, accompanied by the decomposition of the mullite, with the formation of corundum, silicon monoxide, and glass.The changes in the phase composition are accompanied by a change in the structure, and an increase in the creep. Considering that a reduction in the temperature of 100°C causes a reduction in the creep by approximately a half [26], it can be recommended that corundum refractories should be used (under a load of 2 kg/cm²) in a reducing atmosphere at temperatures of up to 1550–1600°C, sillimanite up to 1450–1500°C, kaolin and chamotte (high-grog) up to 1300°C, with a reduction in the load and an increase in the density, the temperature of application for the products examined, especially corundum, can be increased.Translated from Ogneupory, No.5, pp.26–32, May, 1972.     

Quartz glass-base unfired Refractories

Conclusions Quartz-glass-base increased heat-resistance unfired quartz refractories were produced having after hardening a compressive strength of 24–26 MPa and an open porosity of 14.3–14.5%. Their strength may be increased by heat and moisture treatment. Such refractories do not lose strength in the whole range from 110 to 1300°C and are promising for the steel and construction material industries.Translated from Ogneupory, No. 8, pp. 34–37, August, 1985.     

Porous magnesia refractories

Summary Permeable, relatively strong, highly refractory material with a porosity of 30–60% and about 98% MgO was produced from magnesia.By varying the grain sizes of the aggregate, the ratio of aggregate and bond, the amount and grading of the combustible, it is possible to regulate the properties of the porous goods over wide limits.Porous periclase refractories have a high refractoriness, gas permeability and low thermal conductivity, and can be used as heat insulation at high temperatures if not subject to heavy loads and sharp changes in temperature; they are suitable for use as filters in aggressive conditions where a basic highly refractory material is needed.     

Using increased fabrication pressures for making articles from certain electrofused highly refractory materials

Conclusions The porosity of refractories made from fused materials can be greatly reduced (to 10–13%) by using increased fabrication pressures and coarse grained bodies with low quantities of finely milled bond (10–15%).The densification mechanism in the coarse-grained bodies consists in breaking up the large grains and redistributing them. The requirement for maximum density of packing in selecting the grain-size composition of the bodies is of first rate importance.The maximum fabrication pressure should not exceed the values at which the critical density is reached.Translated from Ogneupory No.6, pp.49–53, June, 1972.     

Influence of synthetic primary slag on fracture of kaolin refractories for blast-furnace stacks

Conclusions Investigations of the reaction of kaolin refractories with synthetic slag have shown that under isothermal conditions erosion of sintered kaolin refractories with a porosity of 12% by slag increases with a decrease in its basicity from 1.8 to 0.65. The corrosiveness of the slag increases with an increase in temperature from 1300 to 1500°C and with an increase in the FeO content; with an increase in the density of the refractory, its erosion by the slag decreases; the contact zone between the refractory and the synthetic slag has a complex mineral composition and consists of anorthite, pyroxene, magnetite, dicalcium ferrite, corundum, ferriferous spinellide of complex composition, etc; reaction of fused kaolin refractories with the slag is observed only at their contact, with formation of anorthite, magnetite, manganous spinel, and complex spinellides in the slag.Translated from Ogneupory, No. 1, pp. 37–42, January, 1980.     

Wetting of aluminosilicate refractories with cast iron

Conclusions The magnitude of the wetting angle of molten cast iron on aluminosilicate refractories depends on the structure, phase composition, and physicochemical properties of the solid material and the melt. An increase in the temperature from 1140 to 1500°C causes the wettability of the refractories by molten cast iron to increase as a result of the increase in the content and chemical activity of the liquid phase in the refractory.An increase in the open porosity of sintered kaolin refractories from 8 to 16% results in a decrease in the wetting angle of cast iron at 1350 and 1500°C from 122 to 108° and from 119 to 102°, respectively; at 1140°C the wetting angle increases with the open porosity.The largest wetting angles of cast iron occur on high-density mullite and kaolin refractories containing a minimum of glass phase.Translated from Ogneupory, No. 5, pp. 35–38, May, 1978.     

Vibro-cast periclase refractories of a grainy structure and some of their properties

Conclusions We have studied the process of obtaining vibro-cast periclase refractories based on fine- and coarse-grained molding systems using a low-concentration solution of HCl as the binder.Using a combined experimental and calculation method based on the use of a cone, we have carried out studies to optimize the production parameters of the vibro-casting process.The materials obtained in the initial (unfired) state are characterized by fairly high strength (_comp=12–30 MPa) and can be used as refractory concretes.The process of sintering the materials was studied and it is shown that their properties are comparable with the normal periclase refractories of a grainy structure. After firing at 1550–1600°C the refractories show virtually no additional shrinkage and their true porosity is 19–23%, ultimate compressive strength 30–60 MPa, and ultimate bend strength 12–26 MPa.The results were proved industrially. Large details of the smelting unit of induction furnaces were manufactured and successfully tested.Translated from Ogneupory, No. 8, pp. 9–15, August, 1986.     

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.     

Refractories from fused magnesite-chromite in the lining of a nickel converter

Conclusions Refractories based on a fused magnesite-chromite material are 33–35% more durable than ordinary magnesite-chromite refractories. Their erosion depends to a slightly greater extent on spalling than on chemical dissociation. A relation exists between the pattern of impregnation with the converter melts and the development of cracks in the refractory.The durability of the converter lining can be increased still further by increasing the density of the refractories.Translated from Ogneupory, No. 6, pp. 28–32, June, 1977.     

Periclase-spinel refractories from beneficiated materials

Conclusions Magnesite and magnesite-chromite powders obtained on the basis of beneficiated Satkinsk magnesite using the flotation method can be employed for making periclase-spinel refractories similar in quality to products of grade PShSO and PShSP. For such refractories there is typically an increased refractoriness under load of 2 kg/cm², which on average equals 1640–1670°C.The periclase-spinel products made from beneficiated materials contain 4–5% silicates instead of 8–12% in the refractories obtained from ordinary powders. In the high-temperature fired periclase-spinel refractories made from beneficiated materials we note the formation of high-quality structures containing about 50% direct intergranular bonds between the highly refractory minerals. In the structural elements of such refractories there is a predominance of intergranular bond of the type periclase-secondary spinel-periclase.Translated from Ogneupory, No. 2, pp. 10–14, February, 1973.     

Use of semiacid clay of the Kuznetsk Basin

Conclusions Izhmorsk clays can be classed as kaolinite-hydrated micaceous raw materials (monothermite) with a large impurity-content of quartz. The properties of these clays are similar to those of Barzassk clays, and the two materials can be mineralogically classed as the same type.The Izhmorsk clays were used to obtain specimens of semiacid products with an apparent porosity of 18–23%, having a finely porous structure, and a compressive strength of 300–500 kg/cm².Since they are similar to the Barzassk semiacid clays that were studied in industrial conditions at KMK, we can consider Izhmorsk clays to be suitable for producing refractories.The basic condition for producing semiacid refractories, when employing the method normally used for firebrick, is careful observation of the firing cycle, which will ensure completion of mullite formation, while maintaining the quartz in the crystalline phase and the production of finely porous structures in the materials.Industrial testing of semiacid refractories in various conditions should be organized as a means of extending the application, and of solving the problem of using, semiacid products.An all-round exploitation of the Barzassk source of fireclays and the Izhmorsk source of sands is required in conjunction with the use of the large resources of semiacid raw materials with the basic refractory clays and sands.Translated from Ogneupory, No.3, pp. 11–17, March, 1968.     

The service of regenerator checkers in open hearth furnaces

Summary An effective way of increasing the life of checkers is to increase the height of the structure made of chrome-magnesite brick to 10–12 courses. This reduces the average melting time, increases furnace output by 5–7%, and reduces the oil consumption by 7%.The dust settling on the refractory has a typically high content of iron oxides. At normal checker temperatures (not above 1400°C) the surface of the refractories forms friable, dusty deposits. With a rise in temperature in the regenerator the dust sinters, partly fuses, and sticks to the refractory. This cake is removed by blowing the checkers.Investigation of the refractories after service confirms that the phase changes,in the reaction layer of the brick, take place mainly owing to the action of iron oxides of the dust on the refractory. Fusing of firebrick is also intensified by oxides of iron contained in the dust.The mineral formation and destruction processes are greatly affected by the changing composition of the gaseous atmosphere, which is confirmed by the formation of mixed crystals of magnetite and haematite in the crusts and reaction zones of the refractory.Of the refractories tested in the checkers, the best was chrome—magnesite.To explain the possibility of increasing the life of checkers, experiments should be made using forsterite brick of high quality in the 15 top courses of the checkers using the Cowper system of building the checkers.     

Reaction between refractories and slag and oxidizing steel

Conclusions Scale, removed from the lining of a heating furnace reacts weakly at 1200–1450°C with corundum, high-alumina, chromite, chrome-magnesite, forsterite, and carborundum refractories.Directly in the process of formation, the scale reacts actively with corundum, high-alumina, chromite, forsterite, and chrome-magnesite refractories, and adheres strongly to them. Carborundum refractories in an oxidizing atmosphere at 1200–1500°C are not wetted and do not react with the scale and the oxidizing metal.Under experimental oxidizing conditions, corundum refractories with zero porosity must be considered to be the most resistant to the action of the scale immediately after its formation.Translated from Ogneupory, No. 4. pp. 23–28, April, 1968.