Study On Low-temperature Sintering Of Alumina Ceramics

The main raw material of alumina ceramics is ?-Al₂O₃,and its crystalline phase is corundum.Because of its high mechanical strength,wear resistance,corrosion resistance,heat resistance,low loss tangent,high power resistance and other excellent performance,alumina ceramics have been widely applied in machinery,automotive,chemical,building materials,coatings,electronics and other industries.However,because of strong Al-O ionic bonding,previous pressureless sintering of alumina ceramics has required high temperatures,which consumes a lot of energy.In this study,a solid-state sintering process was used to reduce the sintering temperature of alumina ceramics by adding sintering additives.The effects of four additives?TiO₂?CuO?MnO₂ and Fe₂O₃?on the sintering properties of alumina ceramics were studied in detail.The experimental results show that these four additives can reduce the sintering temperature of alumina ceramics.The solid-state reaction of TiO₂ and Al₂O₃ at 1280? has the most significant effect on the sintering of alumina ceramics.The liquid phase from CuO appeared at 1200?,and the liquid-state reaction has a significant effect on the sintering of alumina ceramics.The temperature of MnO₂ and Fe₂O₃ reacted with Al₂O₃ was high,so MnO₂ and Fe₂O₃ has no significant effect on the sintering of alumina ceramics.On this basis,the mechanism of binary additive in reducing the sintering temperature of alumina ceramics was studied innovatively.Choosing TiO₂ and CuO as binary additive through a large number of exploratory experiments.And the basic formulation for preparation of alumina ceramics material was determined as following: Al₂O₃ 95 wt%?TiO₂ 4 wt%?CuO 1 wt%.Effect of Ti O₂-CuO additive on the sintering of alumina ceramics was examined in detail.The experimental results shown that the liquid phase from CuO appeared at approximately 1200?,so the solid-state reaction between Al₂O₃ and TiO₂ took place at a lower temperature.Such solid-state reaction sintering had a strong impact on the grain growth and greatly promoted the densification of alumina ceramics.In the process of grain growth,the liquid phase penetrated along the Al₂O₃ particles and then inhibited the abnormal grain growth and microcraking.Effects of the raw material formula and temperature on the relative density,flexure strength,microstructure etc.were examined in detail.The processing parameters were optimized with the orthogonal experiments,and the optimized condition was the ball milling time 1 hour,sintering temperature 1450?,holding time 2 hours.High density and strength of alumina ceramics was prepared in these optimized conditions,the relative density reached 98.2% and the flexure strength reached 342 ± 21 MPa.Under the same conditions,the relative density and flexure strength of pure alumina ceramics were 57.3% and 198 ± 12 MPa,respectively.In this study,the environment-friendly alumina ceramics was prepared from coarse alumina powder.It is believed that this work will have a significant contribution to reduce manufacturing cost,and it also has a very important social-economic significance and scientific value for energy saving in the alumina ceramics industry.