Kaolinite Modified By Compound Organic Acids And Its Application In Ceramic Industry

Kaolinite is an important raw material of traditional ceramic. Because of large bondenergy of Si-O bonds and Al-O bonds in the kaolinite crystal structure, the temperature ofbond break and crystal lattice restructuring is very high, which results in a high sinteringtemperature and consuming a great deal of energy. In this work, kaolinite is activated by thelow molecular weight organic acids, and is added to the ceramic body, in order to reducingthe sintering temperature.Oxalic acid, citric acid and oxalic acid/citric acid (1:4) compound acids were applied toactivate the kaolinite in the experiment. The kaolinite and ceramic body treated with acids arecharacterized by DSC, XRD, SEM and FTIR techniques, and phase constitution andmicrostructure changes in the sintering process are studied in order to explore the bestscheme of modifying the kaolinite and the feasibility of decreasing sintering temperature bythe activation of low molecular weight organic acid.The results indicate that Al and Si of kaolinite can be dissolved after being treated withorganic acids and forming complexes with anionic ligand and both the SiO2content andAl2O3content in the treated kaolinite decrease. Under certain condition, oxalic/citric acid (1:4)compound acids is the most effective to activate kaolinite in the experiment. The particlediameter and crystallinity of activated kaolinite which is treated by compound acids decreaseand specific surface area increases. Moreover, mullite phase can be formed at a lowtemperature of1050℃in the kaolinite treated by compound acids.In addition, the ceramic body containing a different ratio of kaolinite treated with1Mcitric acid,0.3M oxalic acid and oxalic/citric acid (1:4) compound acid is sintered at differenttemperature. The result is that the crystal phase structure, microstructure and mechanicalproperties in the ceramic body added3%content of kaolinite activated by compound acidsintered at1250℃are very well, and even better than that of blank ceramic body at1320℃,which indicates that the sintering temperature can be reduced by70℃. On the whole, thesintering temperature of the ceramic body is obviously reduced after added3%kaolinitetreated with compound acids.