Studies on Refractories from Open-Hearth Furnace, (V)

Abstract

A sample of brick was taken from a zebra roof of a 40-tons open-hearth furnace after 402 heat services. The mineralogical constitution of five coloured layer zones in this brick was studied by the aid of microscope and integration stage. The chemical composition, specific gravity, and weight percentage of matrix in this brick were determined by the following two methods. 1) From the microscopic observation the volume percentages of quartz, cristobalite, tridymite and matrix were first determined in each zone, and then the chemical composition and specific gravity of each matrix were calculated from the results of chemical analysis and specific gravity of each zone. 2) The matrix in each zone was separatedfrom the SiO2 modifications by heavy liquid method, and the chemical composition and the amount of matrix were determined directly. As compared with the former method, the latter method gave a higher value of silica of matrix because of imperfect separation.The results obtained may be enumerated as follows;1) As for the changes in composition with distance from the hot face, the high concentrations of Fe2O3, CaO, Al2O3 and MgO in zones II and III are caused by migration of the original matrix in the brick from the hotter face. On the other hand, the decrease of Al2O3, MgO and CaO contents in the working face (zone I) may be due to washing out by splash of the slag, and the increase of iron oxide content may be due to formation of magnetite by the decomposition of ferrous silicate under oxidizing conditions.2) The content ratio of silica to total amount of other oxides in the matrix was 3.5:1 in the hot face and 2:1 in the middle area.3) In the low temperature area this ratio was 4:1 by the imperfect separation of microcrystalline tridymite.4) On the hotter area of the silica brick adjoined to a chrome-magnesite brick, iron oxide and magnesia migrated into the matrix of silica brick from chrome-magnesite brick.