Resistance of blast furnace refractories to the action of aggressive reactants under conditions of an oxidizing gaseous atmosphere

Conclusions Investigations have been made of the resistance of ShPD-41, ShPD-39, and ShUD-37 chamotte refractories to the action of K₂CO₃, Fe₂O₃, blast furnace dust, and initial and final blast furnace slags under conditions of an oxidizing atmosphere. The investigation results showed that iron oxides and slag break down these refractories at 1400–1500°C. Dense ShPD-41 refractory is more resistant to the action of the reactants.The most resistant to the action of slags and iron oxides at 1400–1500°C are silicon carbide refractories with binders of silicon nitride and oxynitride.Translated from Ogneupory, No. 7/8, pp. 24–27, July–August, 1992.     

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.     

Lining fireboxes in a high-pressure steam boiler

Conclusions The service conditions of the lining in high-pressure steam boilers with gas turbine blowing are characterized by a heating temperature above 1500–1550°C on the working surface and repeated sharp changes in temperature at rates of up to 100 deg/min during heating and up to 85 deg/min during cooling. In these conditions it is advisable to use silicon carbide refractories which are the most heat-resistant.The developed designs for the refractory linings to go into the fireboxes of high-pressure boilers have satisfactory heat-insulating properties. Owing to the combination of silicon carbide products with the ramming body, the choice of the most optimum product shape, and making them from silicon carbide with a complex oxynitride bond, such linings are very resistant and recommended for wide use.Translated from Ogneupory, No.2, pp. 18–23, February, 1970.     

Some properties of refractories based on clinkers with various concentrations of calcium oxide

Conclusions We have studied the properties of the refractories prepared from periclase-lime clinkers with a CaO concentration of 2 to 60%. It is established that as the concentration of CaO is increased, the rate also increased at 1500–1650°C; the degree of dissolution of the refractories in slag is reduced; and in connection with this, their wear resistance is also lowered when tested under conditions simulating, in a first approximation, normal production conditions.The wear-resistance of the fired, pitch-impregnated refractories is higher than for the resin-bonded refractories of the same composition; this is the result of their greater density and strength at the test temperatures. The stability of the resin-bonded refractories made from synthetic clinker with 20% CaO is roughly 20% higher and that of the pitchimpregnated fired refractory 40–50% higher than the resistance of the resin-magnesite refractories normally used in production.Translated from Ogneupory, No. 5, pp. 43–48, May, 1981.     

Sialon-containing silicon carbide refractories

Conclusions We worked out the technology of sialon-containing silicon carbide refractories for lining the shafts of blast furnaces. It was shown that addition of MgO in combination with the waste products of the oxides of the rare-earth elements improves the strength and the other properties of the products fired at 1550°C in nitrogen atmosphere.The sialon-containing silicon carbide refractories exhibit a high resistance to the action of slags and are recommended for lining the lower portion of the shaft and the bosh of blast furnaces.Translated from Ogneupory, No. 5, pp. 6–8, May, 1992.     

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.     

Deformation characteristics of silicon carbide and chamotte refractories

Conclusions It was established that silicon-carbide refractories with bonds of silicon nitride and oxynitride, and also self-bonded silicon carbide articles possess 2–3 times higher elasticity moduli compared with chamotte (firebrick) refractories.The anisotropy of the elasticity modulus determined in the longitudinal and transverse directions of the refractories is markedly higher (anisotropy coefficient n=2.28–2.49) than for chamotte refractories (n=1.22).In high-temperature conditions (1600–1650°C) the compressive strength of SiC refractories is about 28 N/mm², and the tensile strength 2.1 N/mm², i.e., the compressive strength is about 10 times higher than the tensile.At room temperature the strength of SiC refractories is double that of chamotte, while at 1200–1400°C this difference increases to 10 times.Silicon carbide self-bonded articles at high temperatures possess the highest strength properties, which confirms the effectiveness of using them in service under the action of abrasive forces.A new method was developed for determining the deformation and strength characteristics of refractories on the UITS-0.5/2.5 test machine.A method was developed for obtaining tension and compression diagrams from the results of tests for pure and longitudinal-transverse bending.Translated from Ogneupory, No. 7, pp. 8–13, July, 1989.     

Statistical regularities of the effect of slag activity on the slag corrosion of chamotte refractories in various media

Statistical regularities of the effect of slag basicity and the mass fraction of FeO in the slag in oxidizing and reducing media and in vacuum at 1500–1600°C on the slag corrosion of chamotte ladle refractories are investigated. It is shown that slag penetration and corrosion in the refractories depend mainly on the mass fraction of FeO in the slag, and the slag resistance decreases in the following order: oxidizing medium reducing medium vacuum.Translated from Ogneupory, No. 2, pp. 22 – 23, February, 1996.     

Cast (Self-Flow) Ceramic Castables. 4. Spreadability of Molding Systems and Some Properties of Mullite – Silicon Carbide Ceramic Castables

The rheological properties of molding systems are shown to depend on the spreadability of the mixture under the action of its own mass; some of the factors influencing the self-flow are determined, namely, the moisture content, the content of the filler, and the temperature of the mixture. The described self-flow castables based on a mullite HCBS and a SiC filler have a porosity of 18% after drying and 16 – 16.5% after heat treatment. Their ultimate bending strength is 45 MPa and the ultimate compressive strength is 110 MPa, which is higher than those of the known refractories of similar compositions. The temperature of 4% deformation of mullite – silicon carbide refractory heat treated at 1350°C and having C _Vf = 0.4 is 1710 – 1720°C, which is 70 – 80°C higher than that of a similar material molded by pressing and heat treated at 1500°C.     

Mullite-alumina refractories with combined nitride-containing binders

Formation of a combined nitride-containing binder for mullite-alumina refractories is studied. An optimal combination is found to consist of 80% crystalline silicon, 10% silicon carbide, and 10% aluminum, magnium, or zirconium oxide. Mullite-alumina refractories with selected binders showed high resistance to the effects of slag, alkali, and iron.Translated from Ogneupory, No. 6, pp. 9–13, June, 1994.     

Industrial development of vibroimpact molding of silicon carbide refractories

Conclusions A technology was developed for the vibrocompaction of silicon carbide refractories. The efficiency of the process was confirmed in industrial conditions.The properties achieved by vibrocompaction in silicon carbide refractories and their uniformity of distribution appreciably exceeds similar characteristics for tamped, and to some extent pressed, refractories.Vibromolding equipment is very simple in design, of low metal content, low power rating and cost, and can be used to obtain product qualities at pressures of 1–2 kg/cm² that are achieved in pressing only by pressures of about 1500 kg/cm².The use of vibrocompacted silicon carbide slabs in the porcelain industry as kiln furniture increased the inter-repair periods for shelf cars for firing pottery.Translated from Ogneupory, No. 8, pp. 7–12, August, 1970.     

Stability of silicon nitride heated in air and in carbon monoxide

Conclusions Silicon nitride oxidizes in air at 1100–1500°C mainly with the formation of silica. An addition of NaF contributes to oxidation of the silicon nitride to silicon oxynitride.In a coke filling silicon nitride decomposes at 1450–1550°C into oxynitride and cubic silicon carbide.Additions of CaF₂ and MgO contribute to the conversion of the silicon nitride in a carbon monoxide atmosphere into the silicon oxynitride at 1550°C.Translated from Ogneupory, No.6, pp. 33–39, June, 1967.     

Resistance of silicon carbide referactories to the effect of aluminum melt and aluminum chloride vapor

Silicon carbide refractories with binders of silicon nitride and silicon oxynitride are compared with dense aluminum silicate refractories. It is shown that silicon carbide refractories possess high stability in aluminum melts and vapors of aluminum chloride, whereas aluminosilicate refractories are severely damaged under these conditions. Silicon carbide refractories with a binder of silicon nitride possess the highest resistance to the effect of the tested aggressive factors and are recommended for operation in aluminum melts and gaseous aluminum chloride media.Translated from Ogneupory, No. 12, pp. 2–5, December, 1995.     

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.     

Silicon carbide refractories with a sialon binder

An investigation concerning molding of silicon carbide refractories with a sialon binder was carried out. It is shown that the alumina-containing component plays an important role in the synthesis of the sialon binder. A corundum addition to the composition of silicon carbide refractories ensures higher parameters for the refractory as compared to a mullite addition. With an increase in the content of crystalline silicon the strength of silicon carbide refractories grows sharply due to the increased amount of -sidalon. Refractories with elevated contents of sialon in the binder have better resistances to alkali, slag, and molten metal than refractories with binders containing silicon nitride.Translated from Ogneupory, No. 4, pp. 2–4, April, 1995.     

Relationship between the oxidation resistance and the high-temperature strength of silicon carbide materials

Conclusions Oxidation is the reason for the decrease in the ultimate strength of the self-bonded silicon carbide at temperatures exceeding 1000°C.Recrystallized silicon carbide possesses high oxidation resistance and retains its initial strength up to 1400°C.Translated from Ogneupory, No. 5, pp. 25–28, May, 1985.     

Change in structure and some properties of industrial aluminosilicate refractories under prolonged anneals at high temperatures

Conclusions A study was made of the change in the structure and some properties of aluminosilicate refractories after prolonged heat processing at 1350–1500°C. The changes in the structure of the refractories occur mainly after heating at 1500°C, and consist in the redistribution of the glassy phase and some increase in the mullite crystals. In the fireclay refractories there was an increase in the quantity of glass phase, because of which its porosity sharply diminished.The change in the structure in aluminosilicate refractories is much lower than in pure-oxide materials, so the properties of these refractories after prolonged heating hardly change.Translated from Ogneupory, No. 6, pp. 27–30, June, 1970.     

Synthesis of Al2O3-SiC powder from electroceramics waste and its application in low-carbon MgO-C refractories

Composite additives are an efficient means to improve the high-temperature stability and slag resistance of low-carbon MgO-C refractories. In this work, Al₂O₃-SiC powder was firstly synthesized from electroceramics waste by carbon embedded method at 1500°C, 1550°C, and 1600°C for 4 h, and then the as-synthesized Al₂O₃-SiC powder was used as an additive to low-carbon MgO-C refractories. The effects of its addition amounts of 0, 2.5 wt.%, 5.0 wt.%, and 7.5 wt.% on the properties of the refractories were investigated in detail. It was found that increasing the heat treatment temperature is beneficial to the phase conversion of mullite and quartz to alumina and silicon carbide in the electroceramics waste. Furthermore, the addition of Al₂O₃-SiC powder effectively improves the performance of low-carbon MgO-C samples, and the formation of spinel dense layer and high-viscosity isolation layer is the internal reason for the improvement of the oxidation resistance and slag resistance of low-carbon MgO-C samples. This work provides ideas for the reuse of electroceramics waste and presents an alternative strategy for the performance optimization of low-carbon MgO-C refractories.     

Strength of magnesia refractories in combined thermal cyclic and mechanical loading of them

Conclusions As the result of laboratory tests of periclase-chromite refractories produced by different methods (MKhS, MKhV, and MKhVP) under the combined action of thermocyclic and mechanical loads possibilities were revealed of the most effective use of them in relation to the service conditions of plasma and electric arc furnace linings. The results of production tests of MKhS, MKhV, and MKhVP refractories at various furnace lining operating temperatures agree with the laboratory data and make it possible to draw the following conclusions:MKhS parts, as the most heat resistant, may be used successfully in heating the furnace lining working surface to 1700–1750°C, which corresponds to a temperature on the boundary of spalling of the refractory of 1400–1500°C.An increase in the lining operating temperature to 1800–1900°C (1550–1650°C on the boundary of spalling) requires the use of refractories with a combination of such properties as heat resistance and high-temperature strength. These requirements are met to the greatest degree by MKhV parts.In the future for large tonnage plasma and electric arc furnaces with high mechanical loads MKhVP high-strength parts may be recommended for the lining. However, for successful use of these parts it is necessary to aim to increase their heat resistance.Translated from Ogneupory, No. 5, pp. 43–47, May, 1985.     

Mullite-corundum refractories with silicon carbide for linings of transportable mixers

Investigations of the technology of mullite-corundum refractories containing silicon carbide and used for linings of transportable mixers are described. It is shown that an addition (10%) of silicon carbide to a mullite-corundum mixture ensures a high slag resistance. Mixers lined with mullite-corundum refractories with silicon carbide have shown high service properties, namely, 720 pourings of cast iron with 5 hot repairs. Translated from Ogneupory, No. 3, pp. 26–29, March, 1995.