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Research On The Preparation Of Carbon Alumina By Carbothermal Reduction Method

Posted on:2022-03-08Degree:MasterType:Thesis
Country:ChinaCandidate:M Y ZhangFull Text:PDF
GTID:2511306554973859Subject:Applied Chemical Physics
Abstract/Summary:PDF Full Text Request
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 1500C for 60 min,Al4C3 was primarily product,and Al4O4C was not found.The optimum conditions were as follows:after heating at 1500C 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 1400C 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 1400C 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.
Keywords/Search Tags:carbothermal reduction, alumium oxycarbides, Al-contatining gases, flowing argon, vacuum
PDF Full Text Request
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