Preparation And Properties Of Glass-ceramics From Gasification Slag

With the development of China’s coal chemical industry,the installed capacity of coal gasifier is increasing,and a large number of accumulated gasification slag has become a problem threatening the safety of human environment.In this thesis,the preparation of glass ceramics from gasification slag is studied.The purpose is to broaden the way of resource utilization of gasification slag and solve the environmental problems caused by gasification slag.By analyzing the composition of gasification slag and the demand of glass ceramics,red mud was selected as the main raw material to prepare gasification slag glass ceramics.The total content of gasification slag and red mud is fixed at 95%,the additive content is fixed to 5%,and the addition of gasification slag is 70%,65%,60%,55%and 50%respectively.Glass ceramics were prepared by melting method.According to the DSC curve of the basic glass,the heat treatment plan was made;XRD and SEM were used to test the phase and microstructure of the samples;the influence of the addition of raw materials and the change of heat treatment system on the glass ceramics of gasifier slag is analyzed by combining the data of flexural strength,density and chemical stability.The experimental results show that the main crystalline phase of the gasification slag glass ceramics is pyroxene（CaFe[Si₂O₆]）,the secondary phase is rankinite（3CaO·2SiO₂）and gehlenite（Ca₂Al₂SiO₇）.When the content of raw material is changed,the type of precipitates and the change of primary and secondary phases will not be affected.With the decrease of gasification slag content and the increase of red mud content,the crystallinity of the sample increases,the grain arrangement becomes more compact,the degree of uniformity increases,and the flexural strength and acid alkali resistance gradually increase;however,when the reduction of gasification slag and the increase of red mud are too large,the Fe₂O₃ in the system increases,which leads to excessive crystallization of the basic glass,the reduction of SiO₂ and Al₂O₃ content forming network structure,the reduction of flexural strength,the weakening of acid corrosion resistance and the enhancement of alkali corrosion resistance.Therefore,the optimum ratio of raw material is 3#formula:gasification slag 60%,red mud 35%,additive 5%.The sample prepared by this ratio has outstanding performance,and its flexural strength can reach 162.5 MPa.Based on the basic glass prepared with 3#formula,the influence of heat treatment system on the gasification slag glass ceramics was analyzed.The results show that the change of heat treatment system will not change the type of crystalline phase and the primary and secondary phases.The results show that the crystallization degree of the basic glass increases with the increase of heat treatment temperature,and the grain arrangement is gradually compact and uniform,however,the defects such as voids and cracks will appear in the sample when the temperature is too high;the heat treatment time is the decisive factor affecting the grain growth process.Appropriate heat treatment time can promote the grain growth to complete,but too long time can also make the grain abnormal development and accumulate into blocks,resulting in the degradation of glass ceramics properties.Therefore,the optimal heat treatment system of 3#basic glass is determined as follows:heat treatment temperature 950℃,heat treatment time120min.The results show that the flexural strength of the base glass with the best ratio can reach163.5 MPa after the best heat treatment system,and the minimum mass loss in acid-base solution is 0.33%and 0.17%respectively,which meets the building use standard.