Study On The Evolution Of Mineral Matter During The Carbothermal Reduction-nitridation Reaction From Coal Gangue

The preparation of Sialon materials and the multiphase materials such as?-Sialon-Al₂O₃ and?-Sialon-SiC by carbothermal reduction-nitridation reaction from coal gangue is one of the effective ways to realize the high-value utilization of coal gangue.In the process of carbothermal reduction-nitridation reaction,minerals in coal gangue,minerals and additives,minerals and carbon in coal gangue react with each other to form new phase,which is the theoretical basis for using coal gangue to prepare sialon and other refractory materials.Due to the complex chemical composition of coal gangue,the chemical composition of coal gangue,the choice of suitable reducing agent and the control of reaction temperature,atmosphere,residence time and other conditions are the main difficulties for the control of coal gangue to prepare high-quality Sialon materials.Therefore,its very important to study on the evolution of mineral matter during the carbothermal reduction-nitridation reaction process of Sialon material from coal gangue.In this thesis,X-ray diffraction and scanning electron microscopy?with electron spectroscopy?were used to study the evolution behavior of minerals in coal gangue under different high temperature atmospheres.Firstly,the carbothermal reduction and nitriding reaction of minerals in different kinds of coal gangue under nitrogen atmosphere,and the influence of atmosphere on the reaction of minerals in gangue was investigated.On this basis,the reactions between minerals in coal gangue and interaction mechanism of minerals,organic matter and inorganic components were further explored.The following main conclusions are about the influence of carbon content,carbon microcrystalline structure and some inorganic components on the carbothermal reduction nitridation reaction of minerals.?1?In the high-temperature nitrogen atmosphere,among four kinds of coal gangue whose main mineral compositions are kaolinite and quartz,carbothermal reduction-nitridation reaction in minerals of PingShou coal gangue and Liulin coal gangue can occur above 1300?,because of their higher carbon content,while carbothermal reduction nitridation reaction of Zhongyang coal gangue is difficult to carry out because of its low carbon content;and Lingshi coal gangue with high fusible oxide content?Fe₂O₃ and CaO?are also difficult to occur carbothermal nitridation reaction.?2?At high temperatures and in different atmospheres,when only Ar is introduced,mullite in high-temperature samples begins to undergo carbonothermic reduction reaction at 1300?,and form carbon silica?SiC?;when only N₂ is introduced,mullite is at 1300?.The carbothermal reduction and nitridation reaction takes place to produce?-Sialon phase?Si₅AlON₇?and corundum phase?Al₂O₃?.The carbon silica formed in the sample was transformed into?-Sialon after entering the N₂ for 2h at first Ar and stopped for 1h,and the formation of the intermediate carbon silica could obviously promote the conversion of mullite to the?-Sialon.When the carbon content in coal gangue is low,it is difficult to generate SiC phase and Sialon phase simultaneously during heat treatment.?3?The addition of carbon-containing substances can promote the carbothermal reduction and nitridation reaction of minerals in Zhongyang coal gangue,and the content of?-Sialon phase increases with the increase of carbon content,At the same time,the degree of promotion of carbothermal reduction and nitridation of five different carbonaceous materials were different.The amount of?-Sialon phase is proportional to the distance between layers.The larger the spacing of the carbon microcrystalline structure,the higher the reactivity,and the more favorable it is to promote the carbothermal reduction and nitriding of minerals in coal gangue.?4?The contents of CaO,Fe₂O₃ and MgO in coal gangue have important influence on the carbothermal reduction and nitridation of minerals at high temperature.With the increase of CaO content in coal gangue,the content of?-Sialon and mullite gradually decreased,whereas the content of anorthite?CaO·Al₂O₃·2SiO₂?gradually increased,indicating that the content of CaO increased with 1400?atmosphere,the mullite and CaO tend to transform to the feldspar.With the increase of the MgO content,the melting temperature of the sample decreased,sintering occured,and the carbon-nitriding reduction reaction was hindered.When the content of Fe₂O₃ in coal gangue is lower than 5%,the presence of Fe₂O₃ has little effect on the carbothermal reduction and nitridation of minerals.However,when the Fe₂O₃ content is more than 5%,the samples tend to sinter and inhibit the nitridation reaction.