Optimization Of Process And Performance Of Corundum Abrasives Prepared By Sol-gel Route

Corundum abrasive is superior to traditional corundum abrasives in strength,toughness,self sharpening and other aspects,and the price is far lower than that of diamond,cubic boron nitride and other ultrahard abrasives,So it has always been popular in the field of machining.In this paper,alkaline sol-gel route and acidic sol-gel route were systematically studied.The effects of seeds,additives,sintering schedule and precursor preparation process on the structure and properties of corundum abrasives were discussed.The results of seed research indicated that the larger the specific surface area of seed is,the more obvious the promotion on the phase transformation ofθ-Al₂O₃ toα-Al₂O₃ is.The average grain size ofα-Al₂O₃ seed sintered at 1100°C is below 150nm,and the phase transformation temperature can be reduced to 1117°C when the content of seed was 3 wt%.When corundum abrasives are prepared by alkaline sol-gel route with different additives,the optimum process parameters are different.In the system of（NH₄）₃AlF₆-TiO₂-La₂O₃ternaryadditives,theabrasivesamplewithfine microstructure and high density was developed when the molar ratio of additives was6:10:5 with 3 wt%adding content and sintered at 1400°C for 1 h.Most of the grains were equiaxed,and some of them were plate-like.The average size of grains was less than 450 nm,and the single particle compressive strength of the abrasive simple was as high as 44 N.In the additive system of La₂O₃-TiO₂-SiO₂,La₂O₃ can form phases of LaAl₁₁O₁₈8 and La₄Ti₃O₁₂2 by reacting with TiO₂ and Al₂O₃,which inhibited the grain boundary migration to obtain fine grain and improve the single particle compressive strength.When simple sintered at 1400°C for 1 h when the amount of additive components was 2.5 wt%with La₂O₃:TiO₂:SiO₂ molar ratio 3:6:5,the relative density of the abrasive sample reached 96.5%and the average grain size was about 400 nm.The single particle compressive strength of sample has a maximum value of 50.3 N.Stable t-ZrO₂ andα-Al₂O₃ composite ceramic abrasives can be obtained by alkaline sol-gel process,in which ZrO₂ existed in the matrix as ZrO₂/Al₂O₃ composite phase.The single particle compressive strength of all simples were higher than 35 N which profited from the ZrO₂/Al₂O₃ composite structure.When the content of ZrO₂was 20 wt%and TiO₂/SiO₂（molar ratio 6:5）content was 3 wt%,the second phase grains uniformly dispersed and grain size distribution was very narrow.Corundum abrasives can also be obtained by more effcient process which used pseudo boehmite and HNO₃ as raw material.In this part,the effect of additives on the microstructure and properties were also studied.Abrasive simples with plate-like grain can be prepared by acid sol-gel route when SiO₂ unitary additive or La₂O₃/SiO₂binary additives were added.In the binary additive system of MgO/SiO₂,the grains maintained equiaxed while the content of MgO additive is increased.When the molar ratio of La₂O₃-TiO₂-SiO₂ was 3:6:5 and the additive content was 2 wt%,the grains were equiaxed and the single particle compressive strength of the sample obtained the maximum value of 48.9 N due to the fine microstructure and narrow grain size distribution.The preparation process is more efficient when using acid sol gel route,and the samples still maintain excellent performance,and this shows that we have achieved process optimization.