Technogenic mineral formation in refractory materials in the open-hearth process

Abstract

Zonal changes have been studied for a refractory mix of OAO Kombinat Magnezit (Satka) on reaction with melt in the open-hearth process. Four zones of change are isolated. In successive zones there is a reduction in MgO content in the material and a relative increase in the amount of CaO, TiO 2 , Al 2 O 3 , SiO 2 , and Fe. In this direction there is an increase in feruginosity of periclase and an increase mix porosity, melt and substitution solid phases appear. These changes reduce refractory mix resistance and promote its breakdown.A study has been made in a series of researches by authors of the present article of features of the change in phase and chemical composition of magnesia refractory mixes, used in the hearths of open-hearth furnaces and subject to chemical corrosion during their reaction with metallurgical melts. During performance of this work the hearth wear mechanism was studied during service using for ramming magnesia powder grade PPM-85 (GOST 24862) of domestic production (OAO Kombinat Magnezit). Previously magnesia dolomite mixes grade Ankerhearth [1] and Jehearth grade [2], obtained from overseas enterprises, were studied for this purpose.In studying material the methods used were microprobe, silicate and x-ray phase analysis, optical and electron microscopy. In particular microprobe analysis complex of the petrology faculty of MGU was used on the basis of a Jeol JSM 6480DMÉ microscope with a combined system for x-ray spectral scanning microanalysis combining energy dispersion INCA-Energy 350 and wave diffraction four-crystal INCA-wave 500 spectrometers. Photographs provided in the article were taken in reverse scattered electrons. The original refractory powder grade PPM-85 (fired magnesite of the Satka deposit) represents the material with a predominant grain size comprising tenths of a millimeter. Within 20 -30 vol.% of the powder fragments of various sizes are present (from several millimeters to 3 mm) sintered into a dense mass. Periclase in the from of aggregates of polygonal grains with a size of 0.5 -2.0 mm have a stable feruginosity factor of 0.3. The binder mix consists of skeletal crystals of bicalcium silicate and calcium titanate (perovskite) cementing them. Within the composition of bicalcium silicate 10 -12% Ca is replaced by Mg; in addition, within it there is a permanent presence of impurities, Ti, Al, and Fe. Within the composition of the perovskite phase 10% of the titanium is replaced by Al; in addition it contains impurities of Si, Mg, and Fe. From the position in the material microstructure and according to phase composition diagrams these two phases separated from the melt.In specimens of refractory material that are within the region of metallurgical melt reaction on the refractory mix, there is clear zonality, expressed as a change in color, texture and chemical composition (Table 1). Removal from contact with the melt zone 1 is characterized by a dense deposit of small to medium grain size. Zone 2, with a thickness of 5 -14 mm of gray color has a brecciated structure d...