Preparation and properties of corundum HCBS and ceramic concretes. Part 1. Mixed HCBS in the system electrocorundum — very fine quartz glass

Abstract

A mixed highly concentrated suspension with improved rheological properties in the system corundum (89%) -quartz glass (11%) is prepared by combined wet grinding. A semifinished product with a porosity up to 17.5% with an ultimate strength in bending up to 5 MPa is prepared on the basis of it. The effect of heat treatment temperature on material properties is studied. The HCBS composition obtained as a matrix system combined with corundum or high-alumina fillers is promising for the preparation of ceramic concretes.The majority of molded and unmolded ceramic concretes developed or produced within Russia relate to a group of aluminosilicate of high-alumina materials [1 -11]. Most in demand and used extensively in many enterprises are refractories based on fired Chinese bauxite with an Al 2 O 3 content within the limits 87 -90% [1 -5]. The basis of their technology is preparation of a HCBS of mixed composition within a bauxite -very fine quartz glass (VFQG) system. The VFQG content is 10 -12%. The HCBS prepared by wet combined grinding is a matrix (binder) system for producing numerous molded and unmolded refractories using a granular filler of bauxite, corundum, silicon carbide, or mixtures of them. The following fact demonstrates the importance and promising nature of producing these refractories. Whereas output of refractories in Russia in 2009 compared with 2008 decreased by not less than a factor of 1.5, the production of high-alumina ceramic concretes in OAO Pervoural Dinas Plant, manufactured from a license of the Kerambet Ogneupor firm, increased by 30% in the third quarter of 2009 compared with the similar pre-crisis quarter of 2008.Recently the possibility has been considered of preparing HCBS with similar production and binder properties using electromelted corundum as the basic material. The second component, VFQG, is introduced in an amount of 10 -15%. It has been assumed that use of HCBS of this mixed composition, with an increased Al 2 O 3 content and a reduced amount of admixtures typical for bauxite, will make it possible to prepare materials with improved thermomechanical property indices, compared with those of numerous molded and unmolded refractories produced on a basis of bauxite HCBS [1 -5].In previous studies [9, p. 250 -254, 12, 13] the problem was posed of preparing a binder suspension based on both fired alumina and corundum, containing a glass phase (SrO, TiO 2 , MgO, BaO). In these works, although significant binder properties were achieved for suspensions (ultimate strength in bending of a casting after drying 5 -10 MPa), their volume concentration C V was relatively low (0.40 -0.52), and castings prepared based on them had a porosity of 30 -40%.In [14] by means of wet grinding in ball mils a suspension was obtained on the basis of electrocorundum. Taking account of the data provided for the density of fired material (3.30 -3.55 g/cm 3 ) with shrinkage up to 5%, it was possible to suggest that in this case the parameters of suspensions