Effect of surface-active agents on the structural and mechanical properties of semidry chromium oxide masses

Abstract

Chromium oxide refractory products are irreplaceable for lining glass-melting tank furnaces for producing alkali-free borosilicate glass at 1550-1600~In mastering the production of chromium oxide blocks (measuring 710 x 360 • 90 mm in the raw state) from finely milled masses, a significant quantity of reject crock was obtained because of the prevalence of overpressing cracks. It therefore seemed of interest to study the structure--mechanical characteristics of finely dispersed chromium oxide masses.The present paper deals with a study of the effect of some surface-active materials on the structuremechanical properties of finely milled chromium oxide masses. It is well known [1][2][3][4][5] that the surface-active material forms a shell on the surface of the mineral particles and helps to increase the plasticity of the powdered masses thus ensuring that a dense and strong system is achieved after pressing.As the starting materials we used industrial chromium oxide, grade OkhM (GOST 2912-73) with a concentration of CrO 2 of > 99%; the material consisted of tablet-shaped crystals predominantly 2-20 ~m in size. The maximum size of the crystals was from 40 to 150 #m. The chromium oxide was milled in a ball mill for 18 h using the dry method (material : ball ratio = 1 : 1) to a grain size of ~-10 ~m. Two hours before the end of the milling, a sintering additive of TiO z [6,7] was added to the mill. The mixture thus obtained was moistened with water, an aqueous solution of sulfite alcohol distillery waste (SAD), or methyl cellulose in various concentrations up to a moisture content of 6%. The specimens were pressed under a pressure of 300 kgf/cm2.The structure--mechanical constants of fine-grain, semidry CrO 2 masses were determined in the apparatus designed by D. M. Tolstoi using the method described in [3,9]. The values of the rapid era p and slow esl elastic deformations; the plastic deformation epl; and the rate of deformation d~/d~ after the flow had been established were determined from the deformation curve of the dependence ~ = fff), where e is the deformation of pure shear and ~-is the time. We then calculated the rapid E 1 and slow E 2 elastic deformations, the greatest plastic viscosity ~ 1, the nominal static ultimate limit of flow Pk,, the elasticityk, the Volarovich plasticity Pkl/~i, and the relaxation time el.The characteristics of the structure--mechanical properties of chromium oxide masses as a function of the SAD concentration are given in Table 1.The masses moistened with water alone have very good structure--mechanical properties. It is clear that with this particular ratio of ~i, El, and E2, the deformation is associated mainly with the rotation at the contacts of the particles without any slip. When the mass is moistened with a 12.5% ~ iution of SAD, the

Structural-mechanical properties of corundum bodies containing a porous filler

“…These data show that the static yield point, the maximum plastic strength, and the elasticity following the incorporation of corundum porous filler, without any plasticizing additives, are considerably lower than for corundum, finely grained bodies without the porous fillers [15], and chromium oxide granular bodies [16]. However, with the addition of porous filler in the form of corundum briquet these values are higher than with the incorporation of spherical corundum, which is connected with the sharply different shape and roughness of the surface of the filler.…”

Influence of additives and compound preparation on the granulation and properties of corundum and zirconia pellets

“…One of the advantages [7] is that we can obtain both laminated granules~ which is important for preparing briquet for subsequent milling and ensuring the best shellshaped grain form [2], and also homogeneous dense granules from highly refractory oxides used as finished goods [3, 4].…”

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666.762.11+666o762.5]:66~099~2In recent years great interest has been shown in the granulation (pelletization) of refractories in order to produce high-density briquet [i, 2], and also in the use of granules as a finished product for various applications* [3][4][5].To obtain spherical bodies in the pellet form it is best to use a pan granulator with a high output [5][6][7].One of the advantages [7] is that we can obtain both laminated granules~ which is important for preparing briquet for subsequent milling and ensuring the best shellshaped grain form [2], and also homogeneous dense granules from highly refractory oxides used as finished goods [3, 4].One of the drawbacks of spherical articles obtained by granulation on a pan granulator is the ellipticity, numerically expressing the magnitude of the deviation from the sphere over three mutually perpendicular diameters.Furthermore, according to [5] the mechanical strength of freshly shaped granules is low, which causes loss both in the granulation process and during discharge from the granulator.Separation of the fragments (broken spheres) from the finished product is a laborious job.The present authors studied the effect of binders and body preparation on granulation and the properties of corundum and zirconia granules.The starting materials consisted of alumina GK and G-00 as specified by GOST 6912-74 containing more than 99.59 and 99.70% A1203, respectively, t The GK alumina contained 0.25% Na20, 0.19% alumina G-00.The concentration of other impurities was slight. We used zirconia grade Tsr0-1 (TsMTU 05-190-69), containing 99.4% Zr02, 0.2% SiO2, 0.1% A1203, 0.07% Fe203, 0.12% CaO, 0".11% Ti02.

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