Low Temperature Sintering Of Alumina Ceramics And Crack Healing Reaserch

Low temperature sintering of alumina ceramics is one of the very important research work in ceramic area,introducing additives to ceramics is very useful method.Cracks were appeared frequently during the process of manufacture and application of ceramics;crack-induced decreasing of the strength and reliability greatly reduced the application of the material.In this paper,the alumina ceramics were made by slip casting method and MgO-MnO₂-TiO₂-SiO₂ composite additives was introduced into alumina ceramics as sintering agent,then sintered at 1400℃and 1450℃respectively in air for 1h.The effects of the amount and particle size of the SiO₂ additive on the properties of the alumina ceramics were studied.In this research work,Vickers indentation was introduced in alumina ceramic materials with different amount of nano-SiO₂ additive after sintered at 1450℃,then heat treated at 1000℃,1100℃1200℃for 1h.The density,shrinkage and hardness of sintered specimens were tested.Three-point bending strength of sintered,before and after crack healing specimens were tested,Phases of specimens were analyzed by XRD,surface and fracture morphology of the specimens were observed by SEM. The mechanism of sintering and crack healing were also discussed.The results show that SiO₂ additive is beneficial to the sintering process of material significantly.When added 0.5wt%SiO₂,material has the maximum three-point bending strength of 299MPa;but with the increasing amount of SiO₂, the three-point bending strength of alumina ceramics are decreased.The particle size of additive also affect the properties of material greatly.When 0.5wt% nano-SiO₂ was used,three-point bending strength of the specimen is 306.21MPa and the relative density is 98.12%.Samples with additive of nano-SiO₂ were indented and then heat treated at 1000℃,1100℃,1200℃for 1h.Then the surface indentation cracks were found to self-healed to some extent.The indentation strength of materials after healing were increased,but the increased range was different.Samples with1wt%nano-SiO₂ additive had the highest bending strength after heat treated at 1200℃for 1 hour, reaching 300.27MPa(Recovery rate:61.84%),similar with the original material;the samples with 3wt%nano-SiO₂ additive showed the best healing effect(Recovery rate:112.2%),three-point bending strength reached 296.7MPa,even higher than the strength of the sintering material without indentation.Therefore,SiO₂ additive showed obvious effect on the low temperature sintering and crack healing of alumina ceramics,but the optimum amount is different,for the sintering process,0.5wt%SiO₂ is the best,too much addition can lead to the decreasing of the strength,but for the crack healing process,the material with more additive showed better crack healing effect.