Thermodynamic Research and Application of Synthetic Cordierite with Fly Ash of High Alumina

Author:Ma Li Jian

Supervisor:xu de long


Degree Year:2017





This dissertation is part of an applied basic research project for the purpose of comprehensive utilization of industrial solid wastes,on the basis of cordierite synthesized thermodynamics calculation.When the content of the fly ash of alumina is above 75%,the content of the synthetic cordierite is above 96%.Therefore,it is very suitable for the preparation of high temperature structural materials and ceramic foam carrier.According to the stoichiometric ratio of cordierite(MgO 13.8wt%,Al2O3 34.9wt%,SiO251.3wt%),prepared samples were synthesized respectively in different temperatures in order to find out the optimal synthesis temperature of the theoretical formula.On this basis,the compositions of the synthetic products of magnesium-rich,magnesium-poor,alumina-rich and alumina-poor formulas were studied;both XRD analyses of K value method and SEM microstructure analyses results were used to calculate the content of cordierite phase through basic properties analyses.The best ratio of alumina powder fly ash synthetic cordierite was determined and optimized accordingly.It was found that a moderate amount of additives can not only improve the generation of synthetic cordierite,but also reduce the overall thermal expansion coefficient of cordierite ceramics.Different additives were added to the raw material to synthesize cordierite with its basic properties,mineral compositions and micro-structure measured so as to find out different effects caused by different addictives in the process of synthesizing cordierite.The experiments combined gel-casting and foaming to mold cordierite honeycomb ceramics prepared by the carrier,to optimize the preparation process,and to improve the mechanism of the preparation.The results show that:(1)Through process optimization,theoretical formula is the best synthetic formula.The best temperature range of synthesis cordierite under the theory formula is1290℃1310℃.With the increase of the synthesis temperature,volume shrinkage,porosity and water absorption of samples go downward,while the volume density and the compressive strength increase accordingly.With the increase of sintering temperature,the thermal expansion coefficient falls.When the synthesis temperature is1310℃,the average thermal expansion coefficient of specimen is 2.18×10-6℃-1,(from room temperature to 1000℃),and the content of cordierite phase is calculated as 96%by using XRD analyses of K value method.(2)Through process optimization,theoretical formula is the best synthetic formula.Compared with the pure raw material to synthesize cordierite,magnesium-rich formula,magnesium-poor formula,alumina-rich formula and alumina-poor formula can neither improve the strength and density of the composite sample nor reduce the thermal expansion coefficient of the sample.(3)ZrO2 can improve the density of the sample.When the addition is 1wt%,the sample has smooth surface without cracks;part of the beta cordierite shifts to alpha cordierite,and the amount of cordierite increases.When the amount of ZrO2 is 2wt%with the sintering temperature of 1310℃,there is micro expansion on volume,and some micro cracks on body surface.The generated cordierite is decomposed into mullite and glass phase,leading to the content of cordierite reduced and the content of mullite increased.Mixed with 1wt%Li2CO3,when the synthesis temperature is 1310℃,the average thermal expansion coefficient is 1.96×10-6℃-1(from room temperature to1000℃),and the content of cordierite phase is calculated as 98%by using XRD analyses of K value method.Meanwhile,the main mineral phase is beta cordierite,and the increasing number of beta cordierite is helpful to reduce the thermal expansion coefficient of sintered products.(4)Cordierite ceramic powders are prepared by sol-gel method as the raw materials,with ZrO2 nanometer powder as additive,and then cordierite honeycomb ceramics are prepared by the carrier through gel-casting and foaming.The experiments show the optimum parameters of cordierite slurry as follows:the content of solid is60wt%,the content of monomer 15wt%,the ratio of monomer and crosslinking agent12:1;When the sintering temperature is 1250℃,the addition of ZrO2 nanometer powder content is 1wt%,which can promote the synthesis of cordierite,and reduce the thermal expansion coefficient of cordierite honeycomb ceramics carrier;CTAB foaming agent is better than foaming agent of SDBS in foaming ability and stability of bubbles;porosity in the sample with CTAB is larger than that in the sample with SDBS.