Cast corundum components

Abstract

Aqueous and thermoplastic slips have been used in casting corundum components for use in the refractories and metallurgical industries. The characteristics of these components are given. This company has researched making ceramic materials and developing technologies based on them for various areas in industry, including metallurgy. Developments that have found practical use include the technology for making corundum components by casting, and those components have been successfully used. Corundum ceramics are fairly familiar and are widely used for their properties: resistance to corrosive media and viability at high temperatures (melting point of corundum 2050°C). Table 1 [1] gives the compositions and properties of electromelted refractories.A corundum-mullite material developed by this company has been used in crucibles for melting nickel alloys. The material of such crucibles should not interact with the metal and should not contaminate the alloy and should work at temperatures above 1600°C. The materials from which such crucibles are traditionally made are as follows: periclase (magnesite), magnesian spinel, corundum, mullite, and combinations of them. At many metallurgical organizations, nickel alloys are melted in crucibles made of periclase with the addition of corundum and a binding agent. Recently, more frequent use has been made of cast crucibles from corundum, corundum-mullite, corundum-spinel, and periclasespinel materials [2].The corundum-mullite material of grade OTM-959 is made by slip casting from a highly concentrated suspension (slip) with granular filler. The slip is made in ball mills by wet grinding of the initial material and with the addition of an electrolyte to accelerate the grinding. This has given mullite and corundum slips. Figure 1 shows the effects of firing temperature on the strength and shrinkage of slip castings from fused mullite and electrocorundum. The strength of the electrocorundum castings increases with firing temperature up to 1750°C, while that for castings of mullite after firing at 1580°C is reduced, so electrocorundum was chosen as the basis for high-temperature components, while mullite was added to the corundum slip along with other additives as a filler. The shrinkage of the slip castings at a firing temperature of 1750°C was up to 5%, while when a filler was added, it did not exceed 1%.Adding large mullite grains to finely divided slip corundum basis provides a microcrack structure in a material and raises considerably the thermal resistance. The basic

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

“…By analogy with bauxite suspensions [1,2,16] features of the change in rheotechnological properties during preparation and stabilization of HCBS of the test composition may be explained to a considerable extent from the point of a view of a change in their acid-base properties, specifying not only the ion potential index, calculated proceeding from the volume ratio of the components (in this case IP = 65), but also their dispersion. By analogy with data provided in [2,14], a considerably higher degree of HCBS dispersion compared with corundum of basic composition, changes the acid-base properties of the mixed suspension. This is due to the fact that action of colloid chemical interaction between the solid and liquid phases occurs at their interface, and therefore not only the volume ratio of the components, but also the amount of interphase surface, govern this process.…”

“…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 were comparable with those of the cited works [12,13].…”