Effect Of Rare Earth Oxides On The Wear Reaiatance And Acid Resistance Of High-Alumina Ceramic

Alumina ceramic has been applied in many fields because of its excellent performance.Now,with the development of industrial technology,materials should get higher performance.How to break through the manufacturing techniques of high-alumina ceramic with good acid resistance or wear resistance to meet market demand,which is an important chanllenge for researchers all over the world.In this thesis,we researched the effect of rare earth on the wear resistance and acid resistanc of alumina ceramic in a CaO-MgO-Al₂O₃-SiO₂ system and revealed their mechanisms with the entry points of grind media and fracturing proppant.This research filled the gap of mechanism study that is the effect of rare earth on the wear resistance and acid resistance of alumina ceramic.It lays the theoretical foundation for exploring and developing alumina ceramics with more excellent characteristics.The main research achievements are as following.1.Adding rare earth oxides?Sc?Gd?Yb?Lu?can inhibit grain growth and improve density.On the other hand,it can change phase composition of ceraimc.Rare earth ions can promote the formation of CaAl₁₂O₁₉ by solid solution or the impurity ions on the grain boundary solubilize in the Lanthanon aluminates,which play an important role in purifying grain boundary and optimizing the grain boundary cohesion.Besides,rare earth oxides can reduce the thermal expansion coefficient and softening temperature of glass phase to change the residual stresses and enhance the liquide phase absorption effect of residual stresses by viscous flow at the grain boundary.The synergy among several factors improve the wear reaiatance of alumina ceramic.Those rare earth oxides also include Y,La,Ce,Nd,Sm,Gd,Tb,Dy,Er.But,Tm₂O₃lead to generation of Lanthanon aluminates or glass phase whose thermal expansion coefficient considerably is larger than that of alumina.In the cooling process,intergranular crack appeared because of big volume shrinkage.Meanwhile,the tensile stress would increase at the grain boundary.It destroys the structure of materials and weakens the bonding strength between grains,causing bad wear resistance.Those rare earth oxides also include Pr,Eu,Ho.2.Generation of acid-resistant phase is the key to improve the acid resistance of alumina ceramic.Acid-resistant mechanisms mainly include crust mechanism and segregation mechanism of corrosion products.Adding rare earth oxides?Sc,La?make it to generate acid-resistant phase in ceramic.Dissolve non-corrosive substance,the remaining phases whose acid resistance are good formed a porous and strong crust.Porous structure makes corrosive path very complex,so the corrosion rate slows down and the concentrations of acid solution decrease gradually during outside-in diffusion.Protection effect of inside the sample are ery notable.La₂O₃ can react with acid solution,resulting in generation of fluoride containing rare earth with steady chemical property.The fluoride can isolate the sample from acid solution.Besides,dense structure reduces the contact area of sample with acid solution,which is another reason for improving acid resistance of alumina ceramic.3.Lanthanon aluminates can form solid solution with Si,Ca,and Mg at grain boundary,which reduces the content and change the chemical composition of glass phase.It plays an important role in puritying and narrowing grain boundary.This opens a way to regulate wear resistance and acid resistance of alumina ceramic by using grain boundary engineering?GBE?.The thesis puts forward a thought that the wear resistance and acid resistance of alumina ceramic can be improved by adding rare earth oxides.The bottleneck that is improving the wear resistance of 99 alumina ceramic was been broken.The wear rate of sample is only 0.000238‰.In addition,the acid solubility of sample containing rare earth oxides reduces to 0.18%.It develops a new area of research on acid-resistant alumina ceramic and has a reference meaning.