Influence Of MgO Content And Spinel Composition On Thermal Expansion And Slag Resistance Of Al₂O₃-MgO Based Castables

In this paper，the Al₂O₃-MgO based castables with different magnesia powder addition （4%,6%,8%,10%respectively） and different composition spinel （as Al₂O₃-rich，theoretical andMgO-rich spinel fine powder, keeping MgO content constant） addition were studied. The typicalphysical properties of castable samples such as apparent porosity, bulk density, permanent linearchange, cold modulus of rupture （CMOR） and cold crushing strength （CCS） were examined afterdifferent heating treatment at110℃×24h,1100℃×3h,1500℃×3hand1600℃×3hrespectively. After heating treatment at110℃×24h, the linear expansion coefficient at therange of200℃～1500℃were tested. Based on two different kinds of basicities slag, the slagresistances after1600℃×3h slag attack test werestudied. The influence of MgO content andspinel composition on the linear expansion coefficient and wear resistance of Al₂O₃-MgO basedcastables was investigated. With the techniques of XRD, SEM, EDS and mass spectrometeranalysis, the phase transformation for samples after heating treatment, microstructurecharacteristics and chemical composition change for those after slag corrosion resistance testswere carefully studied.For the influences of MgO content and spinel composition on typical physical properties ofalumina-magnesia castables, they were found that：with the MgO content increasing, theapparent porosity rose, bulk density reduced and permanent linear change increased. When thetemperature rose above1500℃, the changes of apparent porosity, bulk density and permanentlinear change became more significantly. After heating treatment at110℃×24h, the changes ofthe CMOR for all samples were very small, with the heating treatment temperature rising, theCMOR and CCS were decreased. The sample with MgO-rich spinel addition had the smallestapparent porosity and largest bulk density at110℃; the sample with theoretical spinel additionhad the lowest apparent porosity，maximal bulk density and smallest permanent linear changeafter heat treated at1500℃×3h; the sample with Al₂O₃-rich spinel addition had the lowestCMOR and CCS after heating treatment at1500℃×3h.For the influences of MgO content and spinel composition on linear expansion coefficient,the research results indicated that:（a） for samples with different magnesia powder addition, thelinear expansion coefficients were increased with temperature rising at the range of200℃～1100℃; as the temperature rose further, the linear expansion coefficients of samples with4%and6%magnesia powder addition were raised steadily, however, for the samples with8%and10%magnesia powder addition, the linear expansion coefficients were raised rapidly, and wouldbe reduced sharply at about1350℃.（b） for castables with different composition spinels addition,the linear expansion coefficients of all samples were the smallest at about300℃, after thistemperature, the linear expansion coefficients of all samples were increased until at thetemperature of1250℃, soon afterwards, the linear expansion coefficients were reduced rapidly. It was also found that the sample with MgO-rich spinel addition，the linear expansion coefficientis smaller than those with theoretical spinel and Al₂O₃-rich spinel addition.The results of slag resistance tests （with different basicity slag） indicated that:（a） in thecase of Al₂O₃-MgO based castables with different MgO content, with the MgO contentincreasing, the slag erosion resistance could be increased, however, the slag penetrationresistance would be decreased. The slag resistance performance was best with the sample of6%MgO content.（b） for the slag resistance of Al₂O₃-MgO based castables with differentcomposition spinel addition （the slag basicities C/S are3.4and1.16respectively）, the slagerosion resistance of the specimens with Al₂O₃-rich spinel and MgO-rich spinel addition wassuperior to the one with theoretical spinel addition; the slag penetration resistance for thespecimens with Al₂O₃-rich spinel and theoretical spinel addition was better than the one withMgO-rich spinel addition. For comprehensive，the specimen with Al₂O₃-rich spinel addition hadthe best slag resistance ability. The results also showed that for alumina-magnesia castables, theability to resist high basicity slag was better than to the low basicity slag.