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In recent years, development of periclase-carbonaceous refractories has been receiving particular attention. There are numerous patented compositions of such refractories that have certain common features: the presence of periclase (sintered and melted), a carbon-based component (graphite, coke, etc.), a carbonaceous binder, and additives (antioxidants, etc.). The previously developed resin-magnesite refractories can be classified as one of the forms of periclase-carbonaceous refractories because their quality depends mainly on the presence of a periclase-carbonaceous network resulting from the transformations of the binder based on coal tar or pitch during the heating process [i].We studied the properties of the systems (compositions) based on fused periclase in combination with new carbonaceous binders: water soluble coal tar binders (WCTB) and resol (bakelite) type phenolic resins. In contrast to the conventional binders, these binders can be advantageously used for preparing the bodies without preheating (the bodies made using the conventional carbonaceous binders are blended at a temperature exceeding 120~It is considered that the new binders are not inferior to pitch with respect to coke residue [2].Sidorov et al. [2] determined the properties of WCTB. In the form of a powder having a particle size 95%) of the 2-0.5 mm, minus 0.5 mm, and vibration milled fractions in the 50:20:30 ratio. The bodies were prepared in edge-runner mixing mills and the binders were added to the granular portion of the charge. We found that in order to obtain the bodies suitable for compaction, it is sufficient to add 5% WCTB solution; in the case of more viscous phenolic resins, we tried out additions ranging from 5 up to 10%. Experimental specimens were compacted at a pressure of I00 MPa; thereafter, they were dried at I00-150~ and were heat-treated in the protective CO atmosphere in a special furnace developed at the pilot plant of VostlO at 500~ with a dwell of 20 h (heating time up to the given temperature: 4 h) or by placing the specimens in coke powder charge and using a furnace having Silit heating elements at 750~ for 4 h (heating rate 25 ~ .tThe evaluated properties of the specimens are given in Table 2.After drying at i00 and i50~ all the materials exhibit high compressive strength (>40 MPa) and low open porosity. After heat-treating in the protective atmosphere at 500 and 750~ the strength of the materials decreases significantly (2-3 times) and their open porosity increases because of the changes occurring in the binders ~uring the heating process.Based on the data concerning the c...

Service conditions for refractories and physicochemical processes at their contact with molten aluminum are provided. Thermodynamic calculations establish the relative wear resistance of a number of oxides, silicates, and oxygen-free compounds towards aluminum in the range 700 -1200°C (937 -1473 K). The role is revealed of contact physicochemical processes at the boundary of a refractory with molten aluminum. The high resistance towards aluminum is demonstrated for high-alumina calcium aluminates, particularly bonite CaO · 6Al 2 O 3 and spinel MgO · Al 2 O 3 . The most practicable wear-resistant fuzed materials for preparing lining of melting furnaces are lime-aluminate slags of OAO Klyuchevsk Ferroalloy Plant.The practice of lining metallurgical units for preparing primary, secondary aluminum and alloys based on them has established the increased corrosiveness of the metal towards the majority of traditional refractories [1 -4]. In spite of the relatively low temperature level in the pyrometallurgy of these metals (800 -1200°C), there is intense wear of even some highly refractory materials with a melting temperature (or refractoriness) exceeding by a factor of two to three the operating temperatures in melting and other units. Use of highly refractory materials and components that exhibit resistance at service temperatures of 1550 -1700°C in ferrous metallurgy units in furnaces for the production and processing of nonferrous metals is often economically and technically undesirable since here sufficient lining durability is not achieved, and the refractory resource is not entirely used.It is generally assumed that the main reason for the intense wear of the lining of aluminum thermal units and different devices is chemical reaction of the metal with minerals of the refractory components. At the boundary of oxide compounds with molten aluminum there is an oxidation-reduction reaction causing transformation of refractory minerals into a metal phase and oxidation of aluminum to oxide (corundum or g-Al 2 O 3 ). The general scheme for chemical reaction of oxide materials with aluminum is:where Me m O n is refractory oxide compound; Me is reducing metal (element).The resistance of refractories to corrosive slag and molten metal is determined by a collection of thermodynamic and kinetic factors that specify correspondingly the fundamental possibility of chemical reactions in a refractory compound-melt system and the rate of its occurrence. The probability of reaction of aluminum with refractory compounds may be calculated by classical chemical thermodynamic methods. Given in Table 1 as an example are calculations of isobaric-isothermal potential G T 0 (Gibbs energy) for the interaction of some oxygen-containing compounds with aluminum in the range 800 -1000°C (1073 -1273 K). It is established that the thermodynamically stable oxides CaO, MgO and ZrO 2 do not react with aluminum under these conditions. All of the rest of the compounds, including mullite and silicon minerals, are subject to aluminothermaic reduction whos...

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The development of electrometallurgical processes, the construction and introduction into service of large tonnage arc electric furnaces, the hardening of service conditions for the refractories in these units, especially with the introduction of furnaces of superhigh capacity, require use to be made of high-grade refractory materials. Besides the increased resistance of the walls, one of the most urgent problems is to get an increase in the life of the roof linings in electric furnaces.Foreign practice and Soviet experience show that in the linings of the roofs of steelsmelting furnaces it is possible successfully to use high-alumina refractories with a mass percentage of 75-85% A1203. The essential property of such articles in addition to spalling resistance should be the high deformation resistance during high service temperatures [1][2][3].The essential condition in making such products is the use of high-purity raw materials. The traditional methods of making mullite and mullite-corundum articles in our country are usually based on using mixtures of natural aluminosilicate raw materials (clays, kaolins, bauxites) with alumina.Abroad, as a rule, high alumina refractories are made on the basis of high purity bauxites, for example, Guyana, containing 60% A1203, 1.4% Fe203, 2.8% Ti02, 4-6% Si02, 31% Amcalc [4].The impurity oxides contained in the natural raw materials contribute to the formation of glass phase which, in the refractory, has a continuous distribution nature, and in most cases fills the role of bond (intercrystalline layer) betweenthe aggregates of grains of corundum and mullite [5, 6]. The presence of such a bond reduces the refractoriness, and the resistance to deformation at elevated temperatures, and limits the possibility of high-temperature use of the refractories, despite their adequately high concentration of A1203.The production technology for articles based on aluminosilicate raw materials or mixtures with alumina is complicated by the need to carry out double firing (pellets and articles) and double milling (alumina and chamotte).The East Institute of Refractories has developed a method for producing synthetic mullite--corundum articles intended, among others, for lining the roofs of electric steel-smelting furnaces. The technological developments for roof refractories involved the use of the results of previous work [7][8][9][10][11]. The production of such goods is based on the use of granular electrofused corundum and a combination of polydispersed mixtures of alumina (corundum) and silica (coarse crystalline quartzite). The granular electrocorundum acts as an inert filler, and the dispersed corundum and the coarsely crystalline quartzite are synthesized into mullite.The firing cycle of the products, isothermal soaking in the region of the chemical reaction of mullite formation, and polymorphic inversions of the silica, accelerating the solid phase mullitization, enabled us to obtain up to 35-45% mullite phase in the products. The starting components during sintering of the articles a...