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Rigid demands are placed on refractories intended for design elements in steel ladles, especially in terms of density, strength, slag and metal resistance, and thermal-shock resistance.Periclase refractories are distinguished by a high resistance to the chemical action of molten steel and slag, but they have low thermal-shock resistance and mechanical strength and a high porosity. This paper gives the results of a study into the influence of compositional additions of Cr20a and Ti02 on the physical-ceramic and thermomechanical properties of specimens based on electrofused periclase with the aim of using the newly developed material in plant working at high temperatures and under melt conditions and thermal stress.The starting materials consisted of electrofused periclase of the following chemical composition, %:~ MgO 94.66, SiO2 1.88, AI20a 0.60, Fe20a 0.39, CaO 2.44, Am 0.44; chromium oxide OKhM grade as specified by GOST 2912-79; and titanium dioxide of chemical purity grade as specified by TU 6-09-2166-77.Specimens were pressed at 150 MPa from batches of the following grain-size composition: 45% electrofused periclase fractions 2-0.5 mm, 20% fractions 0.5-0.063 mm, and 35% fractions minus 0.063 mm. The compositional additives were incorporated in the finely milled form (minus 0.063 mm) as a result of reducing the amount of finely grained constituent of the batch.The bond consisted of an aqueous solution of sulfite lye with a density of 1.16 g/cm 3. The firing temperature of the perlclase specimens containing the additives was 1780~ with a soak at this temperature of 6 h.The results of the study of the effect of the additives on the main properties of the specimens are shown in Table i.The introduction of the compositional mixtures contributed to an increase in the apparent density of the fired specimens from 3.05 to 3.13-3.29 g/cm 3. A marked reduction in the open porosity (by about 4%) is noted only in specimens containing 5-10% Cr=Om and about 6.5% Ti02.Specimens containing more than 13.0% Cr2Oa, regardless of the content of TiO2, are badly sintered in practice.An increase in the open porosity in this case is possibly connected with the separation of chromium oxide from the system as a result of the oxidation of the chrome-spinel in the firing process according to the equation [i]:MgCr20~+l~502-~MgO+2Cr03.gas s~ g~ Uniformly with a reduction in the open porosity there is an increase in the mechanical strength to maximum values of 106 and 100.7 MPa, which correspond to specimens prepared from batches Nos. 8 and i0 (see Table i).The specimens' resistance to the thermal loading is in reverse relationship to the mechanical strength of the refractories.The highest thermal-shock values (3-4 heat cycles) are noted in specimens whose compressive strength is 28.2-66.3 MPa, which agrees with [2].The refractoriness under load of 0.2 MPa is reduced with increase in the content of titania, especially with a reduction in the amount of chromium oxide (batches Nos. 4, 5, and 7).The resistance of periclase specimens with the...

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Refractory materials of the AI203--Zr02--Si02 system obtained using normal ceramic technology have currently become widely used in the lining of various design elements in glassmelting furnaces.It was established in []] that it is possible to obtain corundum zircon refractories based on grainy mixtures of corundum and zircon which have a thermal-shock resistance up to 30 cycles of 1300~ into water.* Such refractories have been successfully used in equipment for the production of glass fibers by the one-stage method from aggressive alkali-free borosilicate glass.The corundum-zircon port blocks and the mantle blocks of the curtain wall were found to be in good condition after 36 months of service.The results of a study of the microstructure of the composite material based on corundum and zircon showed that the zircon decomposes during the firing of the specimens, forming a multiphase system which consists of corundum (basic material) and new formations in the form of mullite, monoclinic ZrO2, and a glassy substance [2]. It therefore seemed of interest to study the properties of specimens based on corundum with the separate addition of the components formed on the decomposition of zircon (ZrO2 and SiO2); these were added in a stoichiometric ratio.We would thus hope to find the extent of the effect of each of these components on the thermal-shock resistance of the specimens and establish whether it would be possible to replace zircon by baddeleyite and (or) a silicaceous component, e.g., quartz sand. The latter would be particularly effective because of the scarcity of zircon.The additions of baddeleyite and quartz sand were added as unmilled (original graininess) and vibromilled components in amounts of 5.0-13.5 and 2.5-6.6%,# respectively, to masses based on electrocorundum.Such quantities of Zr02 and SiO2 are actually precipitated in masses containing 7.5-20% zircon (after decomposition).Specimens based on corundum plus baddeleyite, quartz sand, or a mixture of these were pressed at I00 MPa; the corundum--zircon specimens plus Novoselitsk kaolin were pressed at 60 MPa because of the development of overpressing cracks.The specimens were fired in a batch furnace at 1580~ with a dwell of 6 h.It follows from Fig. I that the most intense loosening of the specimens based on corundum by comparison with the corundum-zircon specimens is effected by the addition of baddeleyite of original graininess and a fine-milled mixture of baddeleyite and quartz sand. The mixture of baddeleyite and quartz sand added as components of original graininess (fractions <0. I mm) in an amount corresponding to 15-20% zircon increases the Pop of the specimens by not more than I-2%.A change of the same order was observed for the strength properties.The thermal-shock resistance (1300~ --water) of specimens to which the baddeleyite and quartz sand had been added individually in a ratio corresponding to 7.5% of zircon was similar to the thermal-shock resistance of corundum-zircon specimens; when the mixture of components added to the composition of...