Fused refractory materials based on magnesia slags

Abstract

One way of extending the raw materials base of the refractories industry is to use certain slags from the iron and steel industry [i]. Of great practical interest for the mass production of fused refractories based on forsterite-spinel composition are magnesia--silicate slags formed during the smelting of ferrochromium in ore-thermic furnaces in a number of ferroalloy factories. The output of slags is about 400,000 tons a year, and there is a tendency to increase this output [2].These slags are formed as a result of carbon-thermic reduction of chromium ores; therefore, in contrast to other metallurgical slags containing calcium oxides, the slags of carbon and cast iron ferrochromium-magnesia slags have their CaO in the form of impurity. Slags contain* 28--36% Si02, 35--50% MgO, 15--25% AI2Os, 2--8% Cr2Os. Impurities of CaO and FeO are present, as a rule, in amounts of not more than 2 and 1%, respectively. The total of three components (MgO, Si02, and AI2Oa) in the slags is 90-95%. On the phase diagram for the system MgO--AI2Oa--Si02 the slag compositions lie in the field of crystallization for forsterite and spinel (Fig. i).Slag melt after discharge from the furnace crystallizes, and is cooled in the slaggers; after cooling it consists of a stony mass with coarsely crystalline structure. The phase composition of the slags from the cast iron and carbon meltings consists of forsterite, spinel, and siliceous glass enriched with oxides of calcium, aluminum, chromium, and iron. Depending on the chemical composition and cooling rate (central or peripheral part of the ingot) the amount of glass may vary from 10-15 to 30-40%. With a reduction in the melt in the MgO/Si02 ratio, enstatite in addition to glass is formed. The chromium oxide is present as aluminochrome spinel. Magnesium and calcium aluminosilicates crystallize in small amounts in the intermediate substance; these are cordierite, augite, and montichellite, for example. The slags contain buttons of ferrochromium. Figure 2 shows the typical microstructure of the original slag for cast ferrochromium melting.The melting temperature of the slags is 1630-1670aC. The siliceous glass phase markedly reduces their refractory properties. Anegative influence on the refractory is also exerted by the metal remaining in the slag. In the German Democratic Republic it is proposed to use slag as the fused "grain" with finely milled magnesite bond to obtain sintered forsterite refractories [3]. Research has been carried out with the use of dump slag as fillers for heat-resistant concretes, but the refractory properties of the resulting concretes were poor [4]. At present slags from cast iron and carbon ferrochromium smelting are hardly used, and are taken to dump in the form of ingots. A marked improvement and stabilization in their compositions and refractory properties are necessary for their use.An improvement in the refractory properties of these slags, as follows from the phase diagrams, should occur by increasing their concentrations of MgO, Al2Oa, and Cr20a (separately or...

Estudo \"Post Mortem\" em revestimentos refratários em panela de aciaria elétrica

“…A magnetita, comumente encontrada na maioria das escórias de aciaria, foi identificada nas composições A25 e A50 (exceto para a temperatura de 1500ºC Sabendo que a escória é rica em Fe2O3, é possível que a enstatita -(Mg, Fe)SiO3 contenha óxido de ferro em solução solida, conforme proposto por alguns autores (OZDEMIR et al, 2007;BEALL, 1987;MOLIN et al, 2005;ZALDAT et al, 1984 Na temperatura de 116 ºC houve uma perda na ordem de 0,17%, atribuída à perda de água livre para todas as amostras.…”