Effect Of The Rare Earth Oxides On Properties Of Fired MgO-CaO Refractories

MgO-CaO refractories,due to their excellent stability and basic slag corrosion resistance atthe high temperatures,and particularly unique function of purifying the molten steels,have beenused widely in clean steels and stainless steels.In the present work, the characteristics,preparingmethods, applications,current problems and measures for improving the hydration resistance ofMgO-CaO refractories were reviewed.Also,the effect of rare earth oxides addition on theproperties of MgO-CaO refractories was investigated to optimize and enhance their performance.MgO-CaO samples were prepared using synthetized dolomite of different particlesize,magnesia powders and rare earth oxides（Y₂O₃,La₂O₃,Nd₂O₃,CeO₂and Sm₂O₃） with differentaddition amount（0.5%,1.0%and1.5%） as raw materials and paraffins as binder. The effects ofrare earth oxides and complex rare earth oxides addition on physical properties,hot modulus ofrupture（HMOR） and microscopic structure of MgO-CaO material were studied. The resultsindicated that firstly,different addition amount of rare earth oxides can promote the sintering ofMgO-CaO material,and improve their physical properties,and MgO-CaO samples containing1.0wt%of rare earth oxides has the best properties;Secondly,Rare earth oxides can promoteMgO and CaO grains grew up and increase the solid solution between MgO and CaO,improvethe sintering of MgO-CaO materials and the densification,and the optimized properties for Y₂O₃and Nd₂O₃added MgO-CaO samples;Thirdly,The HMOR of the samples is also improved by theaddition of rare earth oxides,in which the samples with1wt%Nd₂O₃has the highest HMOR of12.9MPa,the following for the samples containing Y₂O₃or CeO₂;Finally the effect of complexrare earth oxides addition on the properties of MgO-CaO refractories is slightly.MgO-CaO samples are prepared using synthetized dolomite of different particle size,magnesia powders,raw dolomite powders and rare earth oxides as raw materials and paraffins asbinder. The effects of rare earth oxides addition and different addition amount of raw dolomiteon physical properties,HMOR and microscopic structure of MgO-CaO materials are studied. Theresults indicated that firstly, the apparent porosity（AP） of MgO-CaO samples increased,whiletheir bulk density（BD）,cold crushing strength（CCS）,cold modulus of rupture（CMOR）,HMORand the slag corrosion resistance decreased with the increasing of raw dolomite; Secondly,theproperties of MgO-CaO samples with rare earth oxides is similar to that of no rare earth oxidessamples,but containing Sm₂O₃and CeO₂has the better properties; Thirdly the rare earth oxidescan improve the HMOR of MgO-CaO samples and the samples with Nd₂O₃and Sm₂O₃has thehighest HMOR of4.59MPa and4.39MPa respectively.MgO-CaO samples are prepared using synthetized dolomite of different particle size,magnesia powders and rare earth oxides（Y₂O₃,La₂O₃,Nd₂O₃,CeO₂and Sm₂O₃） as raw materials and resin without water as binder. The effects of rare earth oxides on physical properties,HMORand microstructure of MgO-CaO materials are studied. The results indicated that firstly rare earthoxides can promote the sintering of MgO-CaO material, improve their densification increase theBD and decrease the AP. Secondly, the mechanical properties of MgO-CaO refractories can beimproved by adding rare earth oxides,in which the samples with Sm₂O₃has the highest CCS of183.7MPa; Thirdly,compared with no rare earth oxides samples,the HMOR change of MgO-CaOsamples with rare earth oxides was not obvious,and the samples with Y₂O₃had the highestHMOR of5.93MPa,which might be attributed to the formation of the liquid phase fromSiO₂,Fe₂O₃impurities in synthetized dolomite raw materials.