A comparison between the adhesion and electrophysical characteristics of oxides may be useful in predicting the interaction between the latter and a metal.The experimental and calculated data for these characteristices taken both from our own studies and from the published literature [i] are given in Table i. The values of the limiting wetting angle and the electrical conductivity of oxides are given for temperatures of 1700-1800~ at which the region of intrinsic conductivity is reached.The published data which is lacking for the electrical conductivity of oxides at this temperature were obtained by extrapolation using the activation energy [I]. Table 1 also gives the calculated values of log electrical conductivity; the experimental values [I] and the values we calculated using the method in [2] involving the band gap and assuming that the oxides have a semiconducting conduction mechanism.The limiting wetting angle between specimens of several oxides and a liquid metal was measured at 1823~ by the resting drop method developed at the M. I. Kalinin Polytechnic Institute.From the results of the measurements we calculated the adhesion energy.As the liquid metal we used OZZhR-grade iron whose chemical compositions in the initial state and after fining in an ISB-001-PI vacuum furnace are given in Table 2. A comparison of the parameters indicates the absence of any correlation between the adhesion energy and the band gap but the existence of a correlation between the former and the log electrical conductivity. Figure 1 shows the dependence of the adhesion energy on the log conductivity of the oxide.Disregarding the data for oxides of rare-earth elements, we can see that there is a linear relationship with an acceptable spread.The dependence of the electrical conductivity on the reciprocal temperature has the same form; there is an exponential dependence in the activation model for the formation of current carriers, i.e., a ~ aoe~Ea/kT or c = enH, where o 0 is the electrical conductivity extrapolated to I/T = 0; e, charge on an electron; k, Boltzmann's constant; T, absolute temperature; n, concentration of current carriers; n--Noe-Ea/kT; No, concentration of electrically active centers; and H, their mobility. T(O~ / ZOO0
Impurities intensify the structural changes in the articles being tested and change theirproper~ies. A concentration of SiO 2 and Fe203 in amounts of 0.5-1.0% increases the extent of the chemical reaction betnveen the refractory and the alkalis and lowers the electrical resistivity by an order of magnitude.The erosion of the periclase articles made from sintered and electrosmelf~d material is approximately the same at high temperatures and in a medium with a higher concentration of oxygen (23%)o The conditions under which the bushing is used in plasma-chemical apparatus with an are-column temperature of 4500--6000~ are somewhat complex and therefore it is necessary to develop an optimum design of the plasmatron unit and better methods of protecting the articles in use. LITERATURECITED
Smelting steel in industrial furnaces has several technical, economic, health and hygiene, and ecological advantages over other steel-smelting methods. The widespread use of induction smelting of steel, particularly of alloyed steel, is hindered by the low resistance of the main lining, which is the result of ignoring the special features of the manufacture of the lining, its bringing on line, and operation. The consumption of refractories in induction smelting sometimes reaches 40 kg per ton of liquid steel.An important feature of induction furnaces is the presence of a large (up to 20-30=C/mm) temperature gradient between the working surface and the water-cooled inductor, which leads to the emergence of significant thermal and mechanical stresses in the lining as well as to intermittent working.The high working temperature of smelting and the intense electromagnetic perturbation of melts cause significant interaction to occur with the lining.The material of the lining should not be wetted by the molten metal and slag if one is to avoid migration of the melts into the depth of the lining. Corundum, fused magnesite, and composites of these in various compositions are most frequently used as the lining materials for induction furnaces, particularly vacuum furnaces; mineralizing and building components are added to the main refractory material in the batch for the manufacture of the lining.All the operations of preparing the crucible for the first standard smelting are directed to obtaining a crucible with the optimum material compositions and the optimum porosity of the structure. In order to reduce the wetting it is necessary to strive for a reduction in .•130
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