Sintering Preparation And Microstructure And Properties Of Al₂O₃ Ceramics

Al₂O₃ ceramic materials have the characteristics of corrosion resistance,high temperature resistance and high hardness and so on.But they have a very high melting point and strong covalent bonds,and their atoms diffuse very slowly,so even under high temperature,it is difficult to sintering.In order to promote the sintering of Al₂O₃ceramic materials and improve the density and the mechanical properties of Al₂O₃ceramic,liquid phase sintering which uses MgO-Al₂O₃-SiO₂ powder as sintering assistant has become a research hotspot at present.The MgO-Al₂O₃-SiO₂ composite powder with a low melting point can form liquid phase at low temperature.However,the premise condition is that the above three powders must be uniformly mixed.Up to now,there are many preparation methods of sintering assistant?MgO-Al₂O₃-SiO₂?,and the most common method is ball milling.But the powder's uniformity prepared by this method is not enough,and the aggregate is obvious.Therefore,an uniform mixed MgO-Al₂O₃-SiO₂ is prepared by polymer network and used as sintering aids to prepare Al₂O₃ ceramic materials under atmospheric pressure in this study.This is also the main characteristic and innovation of this study.The main research contents of the composite powders for sintering additives prepared by polymer network method are the effects of water volume,crosslinker content,particle dispersant and calcining temperature on the particle size and uniformity of sintering aids powder,and the effects of sintering temperature,time and aids contents on densification and mechanical properties.In addition,the sintering aids powders prepared by polymer network method and ball milling mixing method were compared.During the exploration process of preparing MgO-Al₂O₃-Si O₂ powder by polymer network method,using aluminum nitrate as the aluminum source,four ethyl orthosilicate as silicon source,magnesium nitrate as source of magnesium.The study range of water is from 60ml to 100ml,the optimal content is 80ml,and the study range of cross-linking agent is from 0.5g to 0.9g,the optimal content is 0.6g.As studying the types and contents of dispersing agents,the best dispersion agent is PAA and the best content is 0.3%.According to the comprehensive thermal analysis of TG-DTA,the best calcination temperature is 600?.Results show that the element distribution in MgO-Al₂O₃-SiO₂ powder is uniformly,and its grain size is approximately 850nm.In the study of Al₂O₃ ceramics prepared by pressureless sintering,molding by pressure after mixing purchase of Al₂O₃ powder with the self-made MgO-Al₂O₃-SiO₂powder,then the samples are sintered within the sintering temperature range of 1400?-1600?,and the optimum sintering temperature is 1550?.Studying holding time at this sintering temperature from 2h⁴h,the best holding time is 3h.The contents of sintering additives are 3%,5%,6%,7%,8%and 9%respectively at the optimum sintering temperature and holding time,and the best sintering additives content is 8%.Results show that Al₂O₃ ceramic samples obtained under the best process the highest mechanical properties,bending strength and hardness are 430.2MPa and 1416.6MPa respectively.In addition,it is also studied the influences of two preparation methods of sintering additives?network method and ball milling method?on microstructure and mechanical properties of Al₂O₃ ceramics.The results show that at the same sintering temperature?1550??and holding time?3h?,the sintering additive range of 5%⁹%,the mechanical properties of Al₂O₃ ceramics correspond to two kinds of methods change basically consistently with the addition of sinterning additives.But the mechanical property of Al₂O₃ ceramics prepared by polymer network has been higher than the ball milling method all the time.Because the activity of the powder prepared by the polymer network method is far greater than the ball milling method,the components with uniform distribution and grain size with narrow distribution are presented.While the agglomeration of the MgO-Al₂O₃-SiO₂ powder prepared by ball milling is obvious,The sintering property is low and the mechanical properties are low.