The Preparation And Structural Properties Of Magnesia With Rare Earth Oxides

Magnesia is one of the foundational raw materials for basic refractories as the result ofcharacteristics with high melting point and excellent resistance to slag. Properties of basicrefractories was decision of the density grain size, grain boundary cohesion distribution ofmagnesia.The effect of rare earth oxides on the sintering properties and microstructure ofmagnesium and magnesia powder containing rare earth oxides on the properties of magnesiarefractories had been investigated in this work.Magnesium oxide specimens were prepared by MgCO3, Mg（OH）2and3.0wt.%rare earthoxides （Y₂O₃, La₂O₃, Nd₂O₃, CeO₂, Sm₂O₃） as additives sintered at1600℃,1650℃,1700℃for3h. The effect of rare earth oxides on sintering and microstructure was studied and the phasecomposition and microstructure were analyzed and characterized by XRD, SEM and EDS. Theresults indicated that the addition of rare earth oxides can improve the crystalition of magnesiumoxide and are beneficial for sintering densification of magnesium oxide. The highest density isobtained for the Mg（OH）2specimen containing3.0wt.%Y₂O₃,the bulk density is3.50g.cm-3andits crystal grain grows well.The grain size of magnesia made by Mg（OH）2is larger thanmagnesia made by MgCO3and grains combination was more closely.Magnesia specimens were prepared by two different C/S ratio magnesite adding five rareearth oxides （Y₂O₃, La₂O₃, Nd₂O₃, CeO₂,Sm₂O₃） sintered at1600℃,1650℃,1700℃for3h.Theeffect of the type and amount of rare earth oxides, rare earth oxides composite with Y₂O₃,sintering temperature and different C/S ratio of raw material on reaction sintered andmicrostructure of magnesia was studied. The results indicated that the addition of rare earthoxides can improve the density and the crystalition of specimens，the bulk density is anincreasing trend as the increase of rare earth oxide added.The rare earth silicate compounds withhigh melting point are distributed between the grains of MgO in the specimens adding Y₂O₃,La₂O₃, Nd₂O₃and Sm₂O₃. In the specimens of different C/S ratio, The bulk density of specimenswith C/S ratio of5.90is higher than the specimens with C/S ratio of1.17.In the specimensadding CeO₂, CeO₂distribution in the grains as the free state and solution to the MgO grains,resulting in lattice distortion to promote sintering densification. Y₂O₃, CeO₂can significantlyimprove the anti-hydration performance of specimens respectively and1.0wt%Y₂O₃,3.0wt%CeO₂is best.As the sintering temperature higher，the performance specimens with Y₂O₃is betterbut the performance specimens with CeO₂is almost unchanged. rare earth oxides compositeswith Y₂O₃can improve the density of specimens and the highest density is obtained for magnesiaspecimens is specimens with1.5wt%Y₂O₃+1.5wt%La₂O₃。In the specimens with three differentpreparation methods，the bulk density of samples calcined one step was highest.The effect of magnesia powder containing Y₂O₃on the sinterability, mechanical propertiesand high-temperature working properties of magnesia refractories were investigated with fusedmagnesite and magnesia powder containing Y₂O₃. The results indicated that the sinteringdensification and mechanical properties at room temperature of magnesia refractories are widely promoted by adding magnesia powder containing Y₂O₃. The highest bulk density and hotbending strength （1400℃） is obtained for the samples added10.0wt.%magnesia powdercontaining Y₂O₃，they are3.01g.cm-3and7.81MPa.