Structural-mechanical properties of corundum bodies containing a porous filler

Abstract

Corundum heat-insulating articles containing more than 98%* A1203 are irreplaceable materials for service at temperatures of 1750-1800~ in furnaces using protective atmospheres [i, 2]. The production and use in the USSR of corundum heat-insulating articles is slight and is limited to the preparation of articles containing 95% A1203 and an application temperature of not more than 1550~ [3,5]. Furthermore, in recent years it has become necessary to use corundum heat-insulating articles, including large complex shapes, at service temperatures of 1750-1800~Insulating materials developed from finely dispersed bodies containing combustible additives [6-8] possess a high green shrinkage during firing, which hinders the production of large items of complex shape, the production of which is essential for the industrialization of building and repairs to heating plant [9, i0].One of the methods of obtaining lowshrinkage bodies is to usevibrocompacted materials and porous fillers --spherical corundum (hollow corundum) o~ porous corundum briquet [ii]. However, the development of the vibrocompaction technique requires data about the structural-mechanical properties of the bodies. This article presents the results of research into the influence of certain surface-active substances on the structural-mechanical properties of granular corundum bodies with the aim of developing compositions and a technology for the manufacture of heat-insulating goods of complex shape and with concentrations of 98-99% A1203, and an application temperature of not less than 1750~The starting materials for the investigation consisted of spherical corundum obtained by blowing molten alumina [12], or porous brique t prepared by crushing porous corundum blanks [13], followed by screening into fractions of the prescribed sizes.The bulk density of the spherical corundum was 1.16-1.20 g/cm ~, the size of the spheres 2-1 mm; and the same factors for the briquet were respectively 1.28-1.32 g/cm 3 and 2-1 mm (the porosity of the briquet was 65-68% 3 .The body was prepared by mixing the grains of filler (porous briquet or spherical corundum) with the finely dispersed bond component --by vibromilling to the grain size of less than 8 ~m (content of grains less than 3 ~m was 85%) using GK alumina, with subsequent moistening of the body with water or a solution of technical lignosulfonate (LST) or silicone GKZh-II liquid to a moisture content of 5.6-7.5%.The structural-mechanical properties of the granular bodies were determined on the apparatus designed by D. M. Tolstoi, using the method described in [14]. Using the deformation curves for the relationship e = f(~), where s is the deformation of pure shear, r is the time, equal to 900 sec, we determined the magnitude of the rapid G o and slow ~2 elastic deformations, the plastic deformation with fixed flow dE'/dT, and then we calculated the modulus of rapid El and slow E2 elastic deformations, the maximum plastic strength ~i, the tens static yield point Pk~, the elasticity %, the Volarovich plasticity Pkl/~, and ...

Heat-Insulating Refractory Material Based on Hollow Corundum Microspheres

“…After being fired at 1750°C, the apparent density of the material was no greater than 2.0 g/cm 3 and its ultimate compressive strength was 14 MPa. The authors of [3,4] proposed the use of a method which involves vibrational compaction in wooden or gypsum molds to obtain large products and products of complex shape from mixes based on hollow granules. Surface-active additives are used in the process.…”