At the present time, the electrolytic cells used for theproduction of aluminum are lined With the chamotte refractories of the ShB and ShV grades. Their effectiveness (operational efficiency) depends to a large extent on the thermal stability (shock resistance) of the refractory lining. The aim of our study is to obtain a gunite-coating having superior service characteristics than the chamotte lining of the electrolytic cells.When developing the composition of the coating, minimizing the contamination of the melt with harmful components such as Cr, Fe, Si, and P and increasing the resistance of the coating to the cryolite-alumina melt formed the main criteria [i]. Based on this, we developed bodies of the lining-slag type whose composition is close to that of the aggressive medium (Table i).

In recent years, extensive studies have been carried out on the synthesis of amorphous metals and alloys having improved physicochemical properties. Centrifugal-casting units are used for maintaining the melt in its amorphous state during the course of its solidifcation. Their operation is based on rotating a bowl at a speed of approximately i0,000 rpm and continuously feeding a thin jet of the molten material having a temperature of 1500-1600~ onto its bottom portion.The melt comes into contact with the bottom of the bowl and forms a film having a thickness up to 200 ~m under the action of the centrifugal force. This film is driven upwards to the edge of the bowl and is separated from it to form granules having a size of approximately 200 zm. The bowl is cooled using liquid nitrogen (T = 173 K) so as to ensure retention of the amorphous state of the granules during their fall and to avoid ~heir crystallization.Until recently, graphite bowls or water-cooled copper bowls have been used for carryin g out atomization of the melts. However, the extent of their corrosion under the action of the melt is so significant that they can not be reused after the very first melting. Furthermore, the molten metal is contaminated with the material of the bowl. Bowls made from fused quartz are also not being used widely because of cristobalitization and cracking during the course of cooling.This paper deals with a study of the possibility of replacing such bowls and other products used under the conditions involving the action of aggressive chemical media and temperature gradients with ceramic components. When developing the components, it was borne in mind that they must possess the following set of properties simultaneously: a high thermal shock resistance (heating internally up to 1550-1600~ and cooling from the outside up to 100~ nonwettability with the melts; ability to retain mechanical strength under the conditions involving prolonged action of temperature gradients along (across) the wall of the bowl; and sufficient mechanical strength for withstanding the stresses develped in the edge of the bowl under the action of significant centrifugal loads and the shear stresses developed during the operation.The accumulated experimental and the theoretical data show that some of the properties (for example, refractoriness and the limits of temperature compatibility of the products) are controlled by the physicochemical nature of the compact ceramic materials. However, their mechanical strength and corrosion resistance can be improved using different technological routes and new heterophase materials having a specific structure [i].In view of the fact that the structure consists of an aggregate of pores and a solid region containing crystals, a glass, and an amorphous phase, one can develop materials having the required service characteristics by changing the quantitative and the qualitative ratios of the structural elements and establishing the structure--property relationships.It is known that the nature of the pore structure of ...

The interaction of refractories of various grades with liquid slags whose samples were taken in different stages of melting from an electric furnace are investigated by wetting for temperatures ranging from 20 to 1550°C. The compositions of the slags differed in the CaO/SiO2 proportion and the content of chromium oxide. It has been established that the olivinite refractory has advantages under the conditions of eleclzic melting, which seems to be explainable by its chemical composition and specific pore structure. The results of the investigation were used to develop compositions of gunite powders for torch guniting of linings of the slag belt of an arc steel melting furnace.One of the main factors decreasing the output of arc steel melting furnaces (ASMF) is the short lifetime of their linings due to the severe operating conditions of the refractories. Specifically, the lining of the slag belts of such furnaces wears out by 70 mm in each heat. The re&actoties are subjected to a strong effect of overheated slag with a low viscosity and a high convection rate that reaches a few meters per second. The lower part of the lining also experiences the corrosion effect of slags with different chemical compositions and basicity.The damage to lining refractories of ASMF has been investigated quite well [I -I0]. The present work is devoted to a detailed investigation of the interaction between slags in ASMF of the "Severstar' Joint Stock Company and refi'actories of various chemical compositions.It is known that the dominant role in wear of the lining of the slag belt of such a furnace is played by the physicochemical processes occurring in the process of penetration of iron I St. Petersburg Institute of Refractories, St. Petersburg, Russia.silicate and slag melts into the pores and cracks in ref~acto-ties. The formation of a contact zone is caused by wetting of the surface of the refractories by corroding agents.The compatibility of materials is qualitatively characterized by the chemical nature of the refractory and the specific features of its binder, in particular, their basicity with respect to the silicate module of the slag.Since the thermomechanical, thermophysical, and physicochemical processes occurring under the operating conditions of the refractory in ASMF are very complicated, the interaction between the refractory and the slags is estimated by wetting the surface of the refractory with liquid slags. For this purpose we took slag samples in different stages of the melting process in furnace No. 3 of Severstal and determined their chemical composition and the duration of the action on the lining (Table I). In the experiments we used slags Nos. 2, 5, and 6 with compositions differing in the CaO/SiO2 proportion and the content of chromium oxide.

666.762.62;[669o!84o In view of the high cost of the refractories and expenses of relining of the converters, it is necessary to carry out studies for improving the service life of the linings of the metallurgical units according to the method of torch (flame) guniting. In the absence of abundant resources of magnesite, lime gains in importance as a refractory component of the gunite powders [I].In order to improve the coating technology and to optimize the properties, we studied the structure of the calcareous gunite coatings in the original condition and after their exposure to a lime-fayalite melt during the converter steelmaking process.The experimental specimens included fragments of an already used gunite-coated lining of a converter belonging to the Zapadno-Sibirsk Steel Plant (ZS~) after completing the industrial cm~ipaign using torch guniting and, also, blocks (bars) that were specially obtained by guniting the periclase-carbon bricks located in the taphole of the converter.A mixture of blast furnace slag (7-12%*), coke (28-30%), and lime (remainder) was used as a gunite powder. T he as-received granular materials having a moisture content of not more than 1% were milled in a ball mill until the content of the minus 0.088 nm~ fraction amounted to not less than 90%; mixing with predetermined quantities of the finely dispersed additives (that were obtained in advance) was carried out simultaneously. Guniting was carried out maintaining the following parameters: temperature of the flame approximately 1600~ consumption of oxygen 350-500 m3/min, and consumption of the powder 1000-1300 kg/min. The duration of guniting did not exceed 20 min. The thickness of the coating amounted to 20-30 nm~.

The wastes from this treatment (trapped dust and fine fractions) were found by test to be a valuable material for agricultural use, as is evident also from foreign experience [3], so the method can be operated without any waste at all.Material purified to a residual calcium oxide content of below 1.7% with either oven has been used in producing electrotechnical periclase at the Ogneupory Cooperative with the existing techniques to make only the first class of electrotechnical periclase.Material treated in the rotating oven without leaching and having a residual calcium oxide content less than 2.1% has given electrotechnical periclase of classes 2 and 3 with yields correspondingly of 80 and 20%.At the Eastern Refractories Institute, we have developed a technology for making dense sintered periclase clinker from thermochemically treated brucite for making high-grade refractories containing over 96% of the main substance.