Effect Of Adding La₂O₃,Y₂O₃,CeO₂ On The Structures And Properties Of Alumina Ceramics

Due to high mechanical strength and rigidity,resistance to wearing,corrosion and high temperature,as well light weight and good insulation performance,alumina ceramics,as a low cost and multipurpose ceramic material,is widely used in industries such as textile,coal,petroleum,chemicals,electronics and construction.However,pure alumina ceramics has poor tenacity performance and insuffic ient strength and abrasive res istance performance,thus its application is limited.Multi-phase synergistic modification is a research direction for improving the mechanical performance and wearing resistance of alumina ceramics.Rare earth oxide,as a kind of stabilizer and additive during sintering,can effectively improve the strength,tenacity,dens ity and microstructure of the ceramics,thus to obviously improve the mechanical and electric performance of ceramics.In consideration of the varying modification effect of REOs in different sintering powder formulas,in this research,alumina ceramics samples were made in batch-type furnace,where normal atmospheric pressure and temperature of 1550?was applied and there was no special gas,with main material of extremely fine?-Al₂O₃ powder of average diameter 0.3um,and basic sintering additives formula for industrial production of high-rigidity alumina ceramics.The samples were made into sheets with compression molding.Different quantities of La₂O₃,Y₂O₃ and CeO₂ were added in the process.Various testing methods such as SEM,EDS,XRD,relative density,nanoindentation,frictional wear,dielectric constant and loss are adopted to study the influence of addition of La₂O₃?Y₂O₃ and CeO₂ on the microsctructure,mechanical performance and electric performance of alumina ceramics.The law of varying of material performance of alumina ceramics according to the species and quantity of addition of REO is studied,and the microstructure and phase composition of alumina ceramics,as well as the mechanism of action of rare-earth cations during the sintering process are analyzed.Following conclusions can be made from the experiments:the princ ipal crystalline phase of alumina ceramics is corundum??-Al₂O₃?;large and small crystalline grains closely contact to each other;boron-rich glass phase exists in the gaps between the grains;along with the increase of addition of Y₂O₃ and CeO₂,related sub-phase of composite oxides are formed gradually.Addition of proper quantity of REO can improve the microstructure of alumina ceramics.The finest grains can be obtained when the addition percentage of three REOs respectively is 0.5%;the maximum relative density can be reached when the addition percentage of Y₂O₃ or CeO₂ is 0.5%,or the addition percentage of La₂O₃ is 1.5%.The mechanism of action of REO is that the diameter of rare earth cations are much larger than aluminum ions,so they can't solve into each other.Rare earth elements exist at the crystal boundary of Al₂O₃,and the volume of rare earth oxide with glass mesh structure is too large to move,which hinders the immigration of other ions,and consequently,reduces the crystal boundary migration rate and inhibits the formation of extremely large grains.For mechanical performance,addition of REO can improve the rigidity and elastic ity modulus of alumina ceramics.Maximum rigidity can be reached when the addition percentage of Y₂O₃ or CeO₂ is 1.5%,or the addition percentage of La₂O₃ is 0.5%.The law of varying of elastic ity is similar to that of rigidity.For wearing resistance,addition of appropriate quantity of REO can improve the anti-abrasion performance of ceramics.Ceramics with 0.5%of three REOs respectively show good anti-abrasion performance.For dielectric property,addition of REO can increase the dielectric constant but also the dielectric loss of alumina ceramics.Maximum dielectric constant and loss can be reached when the addition percentage of La₂O₃ or Y₂O₃ is 2.5%,or the addition percentage of CeO₂ is 0.5%.Within the frequency range from 104-106Hz,the addition of REO will increase the dielectric constant of alumina ceramics,but not increase the dielectric loss.