Solid electrolytes of zirconium dioxide completely or partly stabilized with yttrium oxide (ChSTs) are finding increasing use for making electrochemical sensors. We are aware [i] of a solid electrolyte made of ZrO 2 with molar parts of Y203 equal to 4%, working in oxygen sensors at temperatures of from 300 to 1700~A number of patents exist [2]* for compositions of solid electrolytes of the ChSTs type. Moreover, ceramics have been patented* for zirconia partly stabilized with Y203 (molar parts 0.5-5.0%) and/or other oxides (rare-earth elements, potassium, magnesium) consisting of 30-100% tetragonal modifications, and containing in the surface layer of the stabilizing oxide 1-20% more than in the average volume. The ceramic is coated with a layer of powder suspension with 12% Y203 and/or other stabilizing oxides, followed by sintering at 1000-1600 ~ as a result of which a surface layer is formed with the cubic modification, 0.1-200 ~m thick.The tetragonal monoclinic inversion of zirconia is used in order to increase the thermal-shock resistance and mechanical strength of the zirconia ceramics. To preserve the stability of the tetragonal phase at room temperatures, the grain size of the ceramic should be in the range 0.03-1.50 Dm. The presence in the ceramic of a second (cubic) phase limits the growth of the tetragonal grains [3].Oxygen conductivity of tetragonal ZrO 2 is noted in the same temperature and oxygenpressure region as in the cubic, but the electrical resistance of the tetragonal zirconia is 1.5-2.0 times greater than in the cubic. It is known [4] that high-temperature aging reduces the strength of ChSTs ceramics, but in ceramics stabilized with Y203 this reduction is slight and does not exceed 10%.We studied the possibility of obtaining ceramics from ChSTs for solid electrolytes with the simultaneous application of an electrode layer, which enables us to form a cubic structure in it, preventing the spreading of a monoclinic phase deep down, and which will increase the density and reduce the electric resistance of the solid electrolyte. The electrode layer was applied by using additions of materials with an electron conductivity used in the compositions of current-conducting materials for electric heaters [5,6]. The task was complicated by the fact that the penetration of the stabilizing additives (rareearth oxides and materials with electron conductivity) in the base material should be minimal, so as not to create a support layer (with a high electrical resistance) on the surface of the solid electrolyte.The investigations were done on specimens prepared from ZrO 2 partly stabilized with Y203 (mass 6.2%). Specimen tablets of diameter and height i0 nun and rods measuring 5 • 5 x 55 mm were extruded or cast under pressure using thermoplasticized bodies; firing was done in a tempering cycle and subsequent annealing in air.The coating was applied by using a slip containing both a solution of polyvinyl alcohol and powdered zirconia with additions (see Table i , 18), and also a mixture of a solution of chlori...

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For blowing-through from below of Soviet-produced steel~ e~go~ low-carbon steel with vacuum treatment for decarbonizing, porous periclase tuyeres are used [ii 2]. These are made from high-quality fused periclase with a concentration of ~ 95% MgO "~ and a grain composition close to single-fraction [3].We have now studied the possibility of using the skin of a periclase block formed during smelting electrotechnical periclase in arc furnaces in order to obtain dense materials, e.g., for blowing-through a mass-produced metal whose temperature in the steel bucket during the gas treatment is ~ 1570-1600~we also hoped to obtain porous masses for the blowing-through of the metal via a gas-permeable floor [4].The justification for using a periclase skin in the manufacture of porous articles after milling is, apart from the chemical composition (Table i), the grain composition which is characterized by very narrow limits of grain size and a small quantity of fine fractions (Table 2). We used a periclase skin with calcination loss of < 1%o The use of periclase skin with > 1% calcination loss in the manufacture of the gas-permeable, dense refractories would cause a loss of strength as a result of the degree of hydration of thepericlasematerial.The crushed periclase was mixed with finely milled bonding. Ten mass compositions (Nos. I-i0) were prepared.For the finely milled bonding we used refractory clay (masses 1-8); a mixture of simultaneously milled alumina and clay in the ratio of 60-70:30-40 (mass No. 9); and a chromium magnesite mixture (TU 14-8-60-72) containing 70% MgO and 26% Cr203 (mass No. i0).In selecting the finely milled bondings, we took into account current industrial experience of their addition to increase plasticity and improve the sintering of masses of a periclase composition (clay); to improve the firing properties (chrome magnesite); and to strengthen the products while simultaneously retaining good gas permeability (the mixture) of simultaneously milled clay and alumina).The mass composition Nos. 1-8 with the addition of clay are given in Table 3. Masses 9 and i0 contained 90% of i-0 mm periclase fractions and 10% of a mixture of simultaneously milled alumina and clay (mass No. 9) or a chrome-magnesite mixture (mass No. i0). Specimens were pressed from the masses.In the preparation of specimens from masses 2, 3, 5, 7, 9, and i0, we used sulfite distillery waste (sdw) with a density of 1.20 g/cm ~ as the temporary production bonding and for the specimens from masses Nos. i, 4, 6, and 8, we used a magnesium phosphate bonding (MPB) with a density of 1.42 g/cm 3.The analysis of the specimens fired at various temperatures showed (Table 4) that the addition of finely milled refractory clay (5-10%) and sdw as the production bonding to a periclase grain composition close to monofractional makes it possible to obtain articles with excellent gas permeability (> 40 ~m 2) as well as sufficiently good strength (masses Nos. 3, 5, and 7).The change in the grain composition of the periclase from 2-0 or 2-0.5 to 1-0.5 m...

At the Nizhnetagil ~ Metallurgical Combine (NTMC), in pouring 160-ton melts of killed steel St3sp in a curvilinear MNLZ, 2-3 chamotte-graphite deep-bottomed nozzles, 360 mm high, are consumed.With the aim of assessing the feasibility of replacing the chamotte-graphite nozzles with more stable ones, at the NTMC we have tested deep-bottomed corundum-graphite nozzles made at the Novomoskovsk Refractories Works.The corundum-graphite nozzles, 600 mm high with a wall thickness of 40 mm and an outlet channel hole diameter of 60 or 75 mm, were made by hydrostatic pressing in a machine built at the All-Union ScientificResearch and Design Institute of Metallurgical Machine Construction (VNIImetmash). The graphite-containing aluminum-silicate mass included 55% of white synthetic corundum {with 96-98% A1203) , 20% ZT graphite, 70/0 silicon carbide, 15% of Druzhkovka clay DN-1, and 370 of crystalline silicon [1, 2], The open porosity was 15-18%, and the apparent density was 2.60-2.63 g/cm 3, while the compressive strength was 28-32 MPa and the tensile strength was 3.0-3~ MPa.In contrast with the chamotte-graphite nozzles 360 mm high, the corundum-graphite ones can pour steel in a totally enclosed stream, reducing oxidation of the steel on the way from the intermediate ladle to the crystallizer. The corundum-graphite nozzles were tested on a one-armed curvilinear MNLZ for pouring steels St3sp, M16s, and low-alloy steel 14G2 {Table 1).In all we tested 30 nozzles. The results of tests on six nozzles are listed in Table 2. One melt was also poured through each of the remaining 24 nozzles. The nozzles were warmed up by a gas flame to about 1000~ for 2-4 h. Nozzle No. 6 was fitted when insufficiently warmed up. The temperature of the steel in the intermediate ladle was 1540-1560~ the rate of pouring was 0.5-0.6 m/rain, the duration of pouring was 100-110 min, the length of the cast slab was 55-58 m, and the cross section of the slab was 1500 • 250 ram. The steel was deoxidized with aluminum. The composition of the fluoride mix added to the crystallizer was as follows: 46% portland cement; 24% nepheline; 67o graphite; 670 silicate clods; 18~0 fluorspar. The chemical composition of the fluoride mixture was as follows: 34-3~0 CaO; 26-31% SIO2; 7-1270 A1203; 6-8% CaF2; 5.9-7.3% Na20 + K20.The changes in the holes in the outlet channels of the nozzle were characterized by the relative overgrowth or erosion K on a side per meter of cast slab per unit time: