Effect Of Rare Earth Oxides On The Compactness Of Magnesia

Magnesia is widely used in high-temperature industries such as steel,metallurgy,and cement due to its outstanding heat resistance and erosion resistance.Currently,the production of magnesia is moving towards high purity and high density.The combination and distribution of binding phases in magnesia directly affect its high-temperature performance,making it necessary to optimize the binding phases and microstructure of magnesia.This study used lightly calcined Mg O powder obtained at 900℃as raw material and employed various methods such as phase analysis,physical property testing,and microstructure examination to investigate the influence of rare earth oxides（Sc₂O₃,Y₂O₃,La₂O₃and Hf O₂）on the densification of sintered magnesia prepared from magnesite.Furthermore,the optimal conditions for magnesia containing these four rare earth oxides were determined through electromagnetic field sintering.The research findings are as follows:（1）When adding Sc₂O₃,Y₂O₃,or Hf O₂,they all undergo solid solution with Mg O,entering the Mg O lattice,causing distortion,activating the lattice,promoting ion diffusion and sintering,and stimulating grain growth.Simultaneously,they react with impurities Ca O or Si O₂in magnesia to generate high-melting-point phases such as Y₂Si₂O₇,Ca Hf O₃,and Ca Hf O₃,which fill the gaps between Mg O grains,reduce porosity,and enhance density.The addition of La₂O₃generates the phase Ca La₄Si₃O₁₃by reacting with Ca O and Si O₂,altering the bonding phases between Mg O grains and enhancing the bonding energy between Mg O grains.（2）In the magnesia sample with added Sc₂O₃,electromagnetic field sintering significantly enhances the solid solubility of Sc³⁺,alters the dendritic formation process,refines the structure,and thus improves the density of the magnesia sample with Sc₂O₃.At an electromagnetic field intensity of 16 Kw,the magnesia sample containing 3 wt%Sc₂O₃exhibits optimal performance.（3）The electromagnetic field provides a driving force for ion diffusion,enhancing ion migration,and influencing the formation and properties of intergranular bonding phases.In the magnesia sample with added Y₂O₃,new phases such as Mg Y₄Si₃O₁₃and Ca₃Y₂Si₆O₁₈,in addition to Y₂Si₂O₇,are generated,enhancing the density of the sample.At an electromagnetic field intensity of 16 Kw,the magnesia sample containing 2 wt%Y₂O₃demonstrates optimal performance.In the magnesia sample with added La₂O₃,the generation of La₂Si₂O₇,in addition to Ca La4Si₃O₁₃,fills the pores as intergranular bonding phases,enhancing the density of the sample.At an electromagnetic field intensity of 18 Kw,the magnesia sample containing 1.5 wt%La₂O₃exhibits optimal performance.In the magnesia sample with added Hf O₂,the bonding phases Ca Hf O₃and Mg₂Hf₂O₁₂improve the sintering ability of magnesia.At an electromagnetic field intensity of 16 Kw,the magnesia sample containing 2 wt%Hf O₂demonstrates optimal performance.（4）Considering comprehensive physical performance indicators,the optimal formula for preparing magnesia is to add 3 wt%Sc₂O₃with an electromagnetic field intensity of 16 Kw.