Surface interactions between fayalite slags and synthetic spinels and solid solutions
- PDF / 2,244,756 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 92 Downloads / 144 Views
I.
INTRODUCTION
CURRENTLY, the refractory bricks employed by copper and nickel producers contain a mixture of magnesia in the form of periclase and chromite ore in varying ratios. Overall, the general composition of the refractory bricks involves MgO, Cr2O3, Al2O3, FeO, and Fe2O3. Figure 1 illustrates the quaternary system of interest and indicates the average compositions of some commercially available refractory bricks. The compositions are situated in a region enclosed by MgO and the magnesia based spinels, namely, spinel (MgAl2O4), picochromite (MgCr2O4), and magnesium ferrite (MgFe2O4). The mineralogy of the bricks is such that magnesia exists in its pure state, but the other oxides and spinels exist in solid solution with each other and with the magnesia.[1] Periclase has a relatively high thermal expansion coefficient (a), which, in a high-temperature furnace environment, makes the material very susceptible to thermal shock. Spinels, in the form of chromite ore, are mixed with the periclase to reduce the thermal expansion coefficient and to ‘‘prestress’’ the structure by adding cracks that, during operation, will assist in the prevention of large crack propagation. However, there are several problems associated with the use of chromite ore in refractory bricks. First, it is very expensive and must be imported, since the major copper producing regions have no chromite ore reserves. Second, although the chromium in the bricks is associated with stable, complex solid solutions, increasingly stringent environmental dumping legislation could soon target disposed refractory bricks. Possible alternatives for the addition of chromite ore to the refractory include MgAl2O4 and Fe3O4, both of which are economically available. These spinel adJ.R. DONALD, formerly Graduate Student with the Department of Metallurgy and Materials Science, University of Toronto, is Refractory Engineer, Hatch Associates, Mississauga, ON, Canada L5K 2R7. J.M. TOGURI, INCO/NSERC Professor, is with the Department of Metallurgy and Materials Science, University of Toronto, Toronto, ON, Canada M5S 3E4. C. DOYLE, Group Leader, is with the J. Roy Gordon Research Laboratory, INCO Technical Services Ltd., Mississauga, ON, Canada L5K 1Z9. Manuscript submitted December 2, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS B
ditives may provide significant cost savings if the performance of these bricks is comparable to the chromite additives. The erosion mechanism of refractory bricks in nonferrous operations is becoming increasingly important due to globalized competition and the need to minimize all operational expenditures. Refractories are eroded by both mechanical and chemical means. Mechanical erosion includes spalling, when the inherent turbulence of the melt causes small pieces of the brick to break off. Other causes of mechanical erosion include internal cycles due to furnace rotation, charging, and pouring. Chemical corrosion involves the dissolution of the solid refractory into the melt. In addition, the reaction product between the melt and
Data Loading...
