Research On The Preparation Of Carbon Alumina By Carbothermal Reduction Method

Alumium oxycarbides has a series of excellent properties such as strong hydration resistance,good chemical stability,good oxidation resistance and high temperature resistance,so it is considered to have potential applications in the fields of refractory materials.There are two types of alumium oxycarbides,Al₄O₄C and Al₂OC,whose preparations are still under laboratory research.The carbothermal reduction in inert atmosphere is the main method for preparing alumium oxycarbides.This method has the advantages of sim ple operation and easy access to raw materials.However,this method requires high reaction temperature and long reaction time,and it is difficult to synthesize pure phase.The formation mechanism of the alumium oxycarbides has not been explained uniformly so far,and its formation path is not clear,which directly restricts the preparation of the alumium oxycarbides.In this paper,the preparations of alumium oxycarbides by carbothermal reduction under argon atmosphere and vacuum condition were studied through experiment and thermodynamic analysis.The phase constitutes were analyzed by X-ray powder diffraction(XRD),and the microstructures of the products were observed by scanning electron microscopy(SEM).The changes of the phase and microstructure of the materials with raw material ratios,reaction temperatures and holding times were obtained.According to thermodynamic analysis and experimental results,the formation mechanism of Al₄O₄C was obtained.The formation of Al₄O₄C is divided into two steps:firstly,?-alumina and graphite(or?-alumina,aluminum and graphite)are reacted with each other to form aluminum-containing gases Al₂O(g),Al(g)and CO(g),and high temperature and low pressure are favorable to the formation of gaseous products,and then Al₄O₄C is produced by the reaction of Al containing gas with CO(g),and low temperature and high pressure are favorable to the formation of Al₄O₄C.The results indicated that only Al₄O₄C fromed in this work,and no trace of Al₂OC could be found at any raw material ratios.Al₄O₄C was formed at 1400?when?-alumina and graphite were used as raw materials in flowing argon,and decomposed at the high enough temperatures.After adding aluminum powder to the mixtures of alumina and graphite,Al₄O₄C was formed at 1300?,demonstrating that the addition of aluminum significantly decreased the onset temperature for the formation of Al₄O₄C.The addition of excessive Al powder did not significantly promote the formation of Al₄O₄C.When the raw materials of?-alumina,aluminum and graphite with a ratio of 1:4:3 were heated at 1500°C for 60 min,Al₄C₃ was primarily product,and Al₄O₄C was not found.The optimum conditions were as follows:after heating at 1500°C for 90 min,the raw materials of?-alumina,aluminum and graphite with a molar ratio of 4:4:3 were completely transformed into the Al₄O₄C products with a little Al₂O₃.When?-alumina and graphite were used as raw materials in vacuum to prepare Al₄O₄C,the temperature required was lower,the time required was shorter,and the content of Al₄O₄C in the product was higher than in argon.The?-Al₂O₃ was used up after heating at 1400°C for 10 min using the same raw materials as the experiments in argon.With the increasing of Al powder contents,reaction temperatures and holding times,the content of Al₄O₄C decreased and the impurity phase increased.The optimum conditions were as follows:after heating at 1400°C for 10 min,the raw materials of?-alumina and graphite with a molar ratio of 1:1.5 were completely transformed into the Al₄O₄C products with a little Al₂O₃.