Vibro-cast periclase refractories of a grainy structure and some of their properties

Abstract

Magnesial refractories whose basic mineral component is periclase occupy a dominating position among the main refractories [I, 2]. The magnesial products are fired or unfired and are produced in the form of molded refractories and concretes [3][4][5]. It is well known that periclase refractories have excellent refractoriness, slag-and metal-resistance, but a low thermal-shock resistance as a result of the s%gniflcant thermal-expansion of MgO. However, under special conditions [20], it is possible to obtain adequately thermal-shock resistant, pressed periclase refractories in which cracks first appear after 9-12 heat cycles from 1300~ to running water and which will withstand more than 20 thermal shocks under plasma heating to 2100~The special features of such refractories are the significant (up to 40%) concentration of coarse (5-10 mm) fractions and a fragmentary structure formed after sintering at 1700~The grain composition of the pressed and fired refractories is close to that of the unfired periclase concrete obtained by vibro-molding Or casting [3,4]. Normally their composition includes 75% of fused periclase or cullet in fractions of 0-15 mm; periclase cement (finely milled periclase with a predominant particle size of 0.06 mm); and 7-18% of binder (normally a solution of sodium polyphosphate, density 0 = 1.35-1.45 g/cm S or water glass, p = 1.30-1.35 g/cmS). The periclase refractories are often used in furnaces for smelting high-quality heat-resistant alloys [3, p. 188] and therefore an important requirement is that they contain no low-melting oxides, for example Na20, in the added binder.In the present paper we report some results of a study of the process for obtaining vibro-cast periclase refractories based on the fine-and coarse-grained molded systems using as the binder a low-concentration (5%) HCI solution. Such materials have a high mechanical strength in the initial (unfired) state and can be considered as concretes. We also studied the process of sintering the obtained vibro-cast materials and show that their properties are comparable with those of the normal fired periclase refractories. The production of such materials was based on the tendency of the finely milled periclase in conjunction with the HCI solution to form an air-hardening bonding with a fairly high mechanical strength and limited hydration [6].As in the previous studies [6,7] we used perlclase with a higher concentration of MgO (98.02%). The studies were carried out on two grain compositions selected from the results of previous studies: a fine-grained composition (the filler was periclase with a particle diameter Df = 0.1-3 mm) and a coarse-grained (filler was periclase with Df = 0.i-i0 mm). In the first case (Fig. i, curve i), the mass fraction of the finely dispersed perlclase (cement) was 30% and in the second, 20%. This was made necessary because of the need to reach a maximum density of the mixture on molding. In the case of the fine-grained composition the disperseness of the cement was characterized by a specific surface o...

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