Fabrication Of Nanosized Cr₂O₃/MgCr₂O₄ And Their Effects On The Structures And Properties Of Magnesia Based Refractories

Cr₂O₃ is possessed of outstanding, eminent slag corrosion resistance. So, the chrome-bearing refractories are all the same used in key part of RH finery, copper or nickel refining furnaces and coal gasifiers for use as important refractories. It would be a fire-new route that the the properties of exsiting chrome-bearing refractories had been improved or ameliorated by utilizing nano-tech. The very important industrial significance would be evident that the nanosized chrome-bearing oxide powders, sol or gel can be applied in magnesia-based refractories.The method and technique of fabrication of nanometer Cr₂O₃ and MgCr₂O₄ powders or sol have been investigated. The sintering mechanism of nanometer powder has been studied firstly. The prepared nanosized Cr₂O₃ and MgCr₂O₄ were applied in magnesia-based castables to research effects of nanosized sol or powders on the properties of castables. And chrome-bearing sols were applied in impregnating on magnesia-chromite refractory bricks for copper furnace and RH furnace to research the effects of chrome-bearing sol on properties of magnesia-chromite bricks. The main conclusions are listed as following:1. The effects of chemical precipitation on preparation of Cr₂O₃ and magnesia-chrome oxide spinel powders, sol or gel were studied: ones of temperature, precipitator and value of pH on growth and size of crystal have been investigated and analyzed. Different sorts of sol were dried by using different drying methods, The particles sizes of nanometer oxides which were fabricated by using supercritical flowing drying (SCFD) were less and more uniform than one of powders by common drying method. The particle size of precursor powder was showed with un-regular shape, and rather more aggregations were found in powders. At the same time, it was found that most of aggregations in powder can be eliminated through calcined at a certain temperature. Probability of nanophase Cr₂O₃ powder fabricated by instantaneous combustion method has been researched. The result shows that nanosized Cr₂O₃ powder can be prepared by using this method.2. The results, applying nanosized oxides powder or sol in magnesia-based castables, show that the properties of castables added with nanosized Cr₂O₃ powders prepared by instantaneous combustion method were inferior to ones of castables added with nanosized Cr₂O₃ powder fabricated by conventional drying method. Though the bulk density and apparent porosity of castables added with sols were not be improved obviously, but the results of porosimetric analysis show that the pore sizes have been minimized which indicates the slag-resistance and thermal shock-resistance of castables would be improved if the concentration and pH value of sol were controlled strictly.3. Chrome-bearing sols were prepared by direct precipitation and symmetrical precipitation method, which were applied in vacuum impregnation of magnesia-chromite bricks. The phenomena of salt out, is similar to impregnate by MgSO₄ solutions, would be never appeared if the impregnated liquid were chrome-bearing sols.The results show:â‘  The apparent porosity and pore sizes distribution of bricks impregnated after were improved at a certain degree because the sol particles size, fabricated by direct precipitation method, are in the nanometer scale range.