The effects have been examined from the form and amount of dispersant on the flow of suspensions based on microgranular periclase, and also the fluidity in the vibration of granular periclase-spinel materials. The best form and amount have been established for dispersants that provide the required flow at various environmental temperatures in the vibration of the granular periclase-spinel materials of water content 5.0–6.5% and working time not less than 3 h.

Data on some novel kinds of refractory articles and materials developed and produced by the Berezhnoy Ukrainian Research Institute for Refractories (Berezhnoy UkrNIIO) are presented. Corundum articles with Sialon binder and unshaped materials of various kinds (ramming mixtures, dry mixtures, traditional and low-cement refractory concretes) containing normal electrocorundum or refractory scrap instead of the costly white electrocorundum are described.

Creep behavior of an MK-73 strain-resistant mullite-corundum refractory under high temperature and loading conditions is analyzed and its service life predicted.

A material consisting mainly of α-Al2O3 and Al4O4C has been prepared by fusion of a mixture of alumina and thermoanthracite. The crystal-optical constants of Al4O4C have been determined: biaxial, negative, oblique attenuation, rhombic system,N g = 1.809,N m = 1.802,N p = 1.779,N g -N p = 0.030,z-,2V = 123°. The analytical refraction index has been found to beN av = 1.796. The phase composition and the structure of various portions of fused blocks and of granules of the fused material based on Al2O3 and C have been investigated. The interval of the ultimate temperatures of stability of the material (1400 – 1500°C) and the nature of phase and structural transformations in a reducing medium at 1500°C have been established. Articles were manufactured from the fused material 2nd tested in steel pouring with the use of gate valves. The nature of the phase and structural transformations of the articles in operation has also been investigated.

A material consisting mainly of α-Al2O3 and Al4O4C has been prepared by fusion of a mixture of alumina and thermoanthracite. The crystal-optical constants of Al4O4C have been determined: biaxial, negative, oblique attenuation, rhombic system,N g = 1.809,N m = 1.802,N p = 1.779,N g -N p = 0.030,z-,2V = 123°. The analytical refraction index has been found to beNav = 1.796. The phase composition and the structure of various portions of fused blocks and of granules of the fused material based on Al2O3 and C have been investigated. The interval of the ultimate temperatures of stability of the material (1400 – 1500°C) and the nature of phase and structural transformations in a reducing medium at 1500°C have been established. Articles were manufactured from the fused material 2nd tested in steel pouring with the use of gate valves. The nature of the phase and structural transformations of the articles in operation has also been investigated.

The use of foamed polystyrene inserts in making especially complex articles with internal cavities can greatly simplify the technology and give clear nondeformed internal cavities, ensure an increase in the yield of sound products, improve the quality, reduce the amount of manual work, increase productivity, and improve the ecology of production.

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.

Superior as-sintered properties are achieved when using the fused mullite powders obtained after carrying out vibrational milling. Vibromilled mullite is characterized by a larger specific surface area and a higher content of the minus 10 μm particles as compared to the powders subjected to pulverization in the air-swept grinding mill.

It is shown that, depending on the composition of the original body, with the same cooling conditions for the melt, crystallization of mullite develops in three different types distinguished by structure, chemical, and phase composition.

It is shown that the temperature of initial crystallization of glass spheres of mullite composition with diameters of less than 0.1 mm, in the metastable state, equals 935°C. The phase composition of the spheres of diameters from 0.1 to 0.5 mm varies. With an increase in the diameter of the spheres from 0.5 to 1–1.7 mm their properties vary slightly.

The production technology of large and intricate mullite and mullite-corundum products was developed using the vibrocasting method (based on fused mullite).

Mullite-corundum refractories based on 63 – 90% fused mullite have been produced and tested in the roof of a 50-ton electric arc furnace. It has been established that their wear resistance is no worse than that of heat-resistant mullite-corundum bricks of grade MK-80 produced according to TU 14-80405-82. The tested refractories were worn due to their saturation with oxides from the molten products and the interaction of the latter with the structural components of the refractory. This promoted the decomposition of mullite into corundum and a glass phase with aftercompaction ands spalling of the refractory.

Thus, the life of roofs in the arch-suspension design of powerful 100-ton furnaces with a roof rise of from 0.13 to 0.14 of its diameter (to provide adequate constructionstrength) is on average 80-90 heats [i]; and in this case the chief causes of destruction of the refractories in the peripheral zones are cracking and spalling under the action of stresses developing during regeneration and volume changes in the refractory, saturated with slag, and also the influence of thermal impacts, gravity forces, etc; and in the central part spalling and melting as a result of the formation of relatively low-melting compounds due to the saturation of the working zone of the refractory with iron oxides, silica and other elements from the furnace dust and the action of high temperatures. Investigations show that the life of the roofs made from periclase--chromite refractories can be increased by 15-20% as a result of design changes in the structure (for example, annular construction instead of sector-arch, etc.) [2, 3]. In foreign plants, for electric furnace roofs extensive use is being made of high-alumina refractories and materials containing from 65 to 97% A1203. However, working experience shows that only refractories containing 85% or more A1203 will provide adequate roof life. It is noted that the successful use in these roofs of refractories made of alumina materials should possess, in addition to good slag resistance, an enhanced mechanical strength at elevated temperatures, and also significant spalling resistance [4]. In this article we shall present results from the use of mullite corundum refractories in the roofs of electric furnaces of average specific capacity (250 kVA/ton), melting stainless and ball-bearing steels. The Institute together with the Semiluksk refractories factory has developed grade MK-80 refractories (TU 14-8-405-82) of mullite corundum composition with structural reinforcement using nonisometric grains of fused mullite [5]; the production of these refractories was mastered at the Semiluksk plant. Testing of the mullite corundum articles MK-80 possessing high spalling resistance (Table i) was done in stages in the roofs of 50-ton (actual capacity 65 tons) electric furnaces at the Dneprospetsstal' factory; in the first stage for melting stainless, and in the second ballbearing steels. The roofs had a sector-arch structure with a rise of from 0.08 to 0.09 of their diameters. In the first stage the roof was laid dry; one roof was almost completely made up of experimental products, in the second -- the experimental refractories were used to make only the central part and the zone around the fourth aperture (gas duct), while the peripheral part was made from periclase-chromlte refractories grade PKhSUT, according to GOST 10888-76 (see Table I). Tests were done without changing the energy and technological regimes typical of the stated electric furnace: the specific consumption of electric power was 650-660 kW'h per ton of liquid metal; the consumption of oxygen was 28-30 m 3 per ton of melt, and the melting time was 5.5-6 h.

Refractories based on fused mullite are promising materials for industrial application~ Mullite blocks (weighing 3.0-3.5 ton) obtained by cooling the melt in ingot molds consist of 91-96%* mullite and 4-9% glass phase. Mullite is present in the form of long prismatic crystals (measuring up to 10~mm in length and from 0.3 up to 1.15 mm in thickness) surrounded by thin layers of glass phase. Mullite crystals are dispositioned perpendicular to the cooling surface. Free corundum is absent in the material when accurate dosing of alumina and quartz sand is made and optimal melting regimes are followed [1-3].

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.