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...
Previously [i] investigators showed that it is possible to regulate the chemical and adhesive reactions at the contact point of metallic melt and refractory oxide in a systematic way by alloying the latter with various additives.In particular, additions made to the corundum transition metals, and also zircon and titanium, leadto a reduction in the energy of adhesion in a certain range of concentration, and correspondingly produce a reduction in the mass exchange between the lining and the metal.And, on the other hand, dilution of corundum batch with powdered oxides of the alkaline-earth metals increases the chemical and adhesive reaction, which may find extensive use in cermet production.Theoretical predictions of the possibility of regulating the catalytic activity of oxides were based on an approach to the physical nature of this interaction from the viewpoint of the electron--ionic energy structure of the refractory and its dependence on the extraneous additives, the perfection of the structure, and the material's previous history.The electron structure of the material governs its electrophysical, optical, and other properties. The correlation obtained later between the experimental data for electric conductivity and setting edge angle of the substratum of droplets of steel [2] stimulated further investigation toward the detailed development of an electron--ionic model of interaction on the boundary of oxide with melt (adhesion, mass exchange, diffusion, reaction capacity, phase inversion, etc.) the full picture of which remains unclear.The present authors studied the volume electric conductivity of single-crystal substrate of sapphire (pure corundum), ruby (corundum with an addition of chromium in amounts of about 1%),* and pure magnesium oxide, and also ceramic substrata of the same composition, using the triple-electrode method (with a guard ring for the dc current). The results were obtained for the range 900-1800~ in vacuum (0.0133 Pa). After repeated measurements of the electric conductivity without breaking the vacuum on the specimens during heating and cooling (until stable results were obtained) the substrata with the metallic tablets were placed in equipment for measuring the wetting angle, in which they were held under the droplet of melt for up to 8 min.In this case we noted intense deoxidation of the metal stimulated by the substratum, masked sticking of the tablet to some specimens, and a change in the color of the contact site. Then the remaining, undamaged, substratum was again subjected to careful testing for electric conductivity.The results of y before and after the action of the droplet of melt 80N are shown in the form of graphs log y = f(lO4/T) in Fig. i. The concept accepted in semiconductor physics of a temperature relationships for electric conductivity in the form log y = f(104/T) enables us to calculate the value of the energy of formation of free discharges (energy of activation of the current carrier), ensuring electric conductivity.Bearing in mind the zone theory of activation Ea,...
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