Refractories containing in their composition carbon and oxygen-free compounds such as carbides, nitrides, borides, etc. are acquiring increasing practical value [i].Present and future areas of their use include the linings of converters and electric arc furnaces, refractories for ladle gate valves and teeming of steel in continuous billet casting machines, etc.In their interaction with molten metals these refractories exhibit specific features, some of which are discussed in this article.As a first approximation as the result of the high surface activity of oxygen and sulfur in it (their surface activity may exceed the content by tens of times) the surface of molten steel may be represented in the form of the highly electronegative anions 0 =-and S =-in coordination with the cations Fe 2+, Mn =+, etc.In interaction with the oxidizable elements of the refractories the anions form intermediate products all the way to oxides, including gaseous ones.The corrosion of carbon-containing refractories under the action of steel under equilibrium conditions may be represented in three stages [2]:at the steel--refractory contact under the action of surface-active oxygen, oxidation of the carbon occurs and a decarburized zone is formed; the decarburized zone with increased porosity rapidly forms a slag and the products of the interaction have decreased refractoriness, mechanical strength, and thermal coefficient of volumetric expansion differing from the original material; for these reasons the slagged layer of the refractory is rapidly washed away by the steel.The increase in metal resistance of a refractory with the addition of oxygen-free additions, particularly carbon, is the result of the following facts: frequently, the carbon addition is made by impregnation or precipitation from the gaseous or liquid phase into the finished refractory and the carbon partially replaces the porous spaces, mechanically preventing penetration of the molten metal; the products of gasification of the carbon pneumatically prevent penetration of the molten metal into the voids; in the microvolumes carbon deoxidizes the molten metal in contact with it and the highly active oxide forms of iron are converted into less active lower oxides all the way to the metallic state, a confirmation of which is the presence of beads of pure iron in the reaction zones of carbon-containing refractories after their wetting even by slag.To the products of gasification of carbon are added the gases entrapped in the void space and the gaseous products of reduction by carbon of the oxides of the refractory occurring according to reactions of the type:(SiO2, AI2Oa, ZrO~, ZrO=.SiO,, MgO era. )ml+Cso~C0g~+SiOg ~ AIOg~ era.These reactions occur both in the contact zone and in the thickness of the refractory with diffusion of CO and gaseous suboxides into the contact zone. In addition, the decomposition of oxygen-free compounds is possible according to reactions of the form SiaN4--+2N2+3Si.All-Union Refractory Institute.

The addition of peptlzers and surfactants in optimal amounts makes it possible to reduce the moisture content of the suspensions by 10-15% and thereby to increase the efficiency of the technological process.One of the most important properties of the refractories used in the lining of metallurgical plants is wettability by molten metals and slags. Wetting in equilibrium conditions is characterized by an equilibrium wetting angle 8o [i, 2].The equilibrium wetting angles in the system of refractory--slag melt establish themselves slowly because of the multiformity of the processes involved (spreading, permeation, reciprocal diffusion, solution, etc.) and are near zero. A study of wetting in these systems therefore presents difficulties.

The widely used method of making linings for induction furnaces by means of pneumatic rams is unproductive and laborious. The resulting crucibles have low density and strength and their density varies with height. The process of bringing these crucibles into operation after manufacture, including drying and firing during the first ungraded melt, is very laborious, requires large amounts of eleetrical power and metal burden, and constitutes an unproductive use of costly electrical equipment. The output of the furnace and the purity of the smelted metal depend on the stability of the refractory lining during vacuum induction melting [i-3].

The refractory lining in which a metal is smelted has a significant effect on the properties of the metal.An equilibrium concentration of oxygen, which depends on the chemical nature of the crucible material, is established in the molten metal when subjected to a long dwell in the crucible [i]. Under actualconditions, the induction crucible furnace with intense electromagnetic perturbation and a relatively large specific interface surface between the metal and lining, which helps to bring the system (metal-lining) rapidly to the thermodynamic equilibrium, is close to this laboratory situation.It was shown [2] that a metal with a small concentration of vanadium, which is active towards oxygen, more quickly establishes equilibrium with the lining and the concentration of oxygen in it on melting than the same metal without vanadium.The concentration of nitrogen is related to the concentration of oxygen in the metal on melting and this is explained by the difference in surface activity of oxygen and nitrogen at the metal-atmosphere and metal-lining interfaces.Oxygen being the more surface-active element is absorbed in the surface layer of metal and occupies the adsorption centers, thus preventing the removal of nitrogen [2].It was shown in [3] that the role of the metal-lining surface is also active in the deoxygenation and doping of the metal.Thus the existing facts indicate that refractory oxides can be used as sorbents for the removal of oxygen from a liquid metal.There is virtually no data in the literature relating to the sorption tendency of refractories.Therefore the aim of the present study was to investigate the oxygen-sorption behavior of periclase and corundum.The specimens of refractory were prepared in the form of substrates 18 mm in diameter and 5 mm thick and as crucibles to contain 0.25 kg of metal.Refractories of different porosity were obtained by selecting the grainy composition of the original refractory powders and by the use of different pressing pressures and firing temperatures.As the original materials we used fused periclase with a 92.50%* concentration of MgO and corundum with an AI20~ concentration of 96.84%; to the masses we added 1.5% of boric acid.In the experiments we also used corundum and periclase single crystals.The open porosity of the periclase refractories was P~ ~ 27%, P2 ~ 23%, and P3 ~ 21%; of the corundum specimens, P~ ~ 26%, P~ ~ 24%, and P~ ~ 20%.The metal for the experiments (the 80N alloy) was melted in an open induction furnace with a 15-kg capacity magnesite crucible by alloying carbonyl iron with electrolytic nickel, grade NI.Forged and turned metal was remelted in a vacuum induction furnace in a corundum crucible.The characteristics of the metal used a=e given in Table i.The turned metal specimens were stored before the experiment in weighing bottles contain ~ ing carbon tetrachloride.The wetting experiments were carried out on the apparatus described in [4] at 1490~ in an argon medium with a 99.997% concentration of the main metal and 0.0003% of oxygen.The argon w...