The Study On Sintering And Properties Of Cordierite Porous Ceramic Prepared With Coal Gangue

Coal gangue is a kind of industrial solid waste that has brought serious resource waste and environmental pollution problems. Cordierite porous ceramics have been wildly applied in the porous catalyst carrier, solar heat storage materials. Because it has low thermal expansion coefficient and low dielectric constant, besides it has also high specific and pore structure of porous ceramics. So it has important practical significance and value if cordierite porous ceramic is prepared with the low cost of raw materials, such as coal gangue. In the thesis, porous cordierite ceramics were successfully fabricated via recycling coal gangue, 4MgCO3·Mg(OH)2·5H2O and bauxite by polymeric sponge infiltration method. The influence of processing parameters on the property and structure of the porous ceramics, including slurry solid content, sintering temperature, sintering time, acid leaching, acid-gangue ratio, acid leaching temperature, etc. have been investigated. The characterization was focused on phase evolution, sintering behavior and microstructure evolution by using XRD and SEM. Meanwhile, the porous ceramic properties of porosity and compressive strength were investigated.(1) The influence of sintering temperature and duration on cordierite ceramic phase formation. Cordierite phase begin to form at 1150℃. Cordierite content increases gradually with the sintering temperature rising, and the ratio of cordierite and spinel also improves. Compressive strength of the sample increases and the porosity decreases as cordierite content improved. However, the abnormal phenomenon occurs at 1200℃, that is due to the impurity of coal gangue promoting a large number of liquid at high sintering temperature. The liquid cause huge bubbles appeared on the surface of samples to increase porosity. The property will not change significantly as the sintering duration prolonged(2) The influence of slurry solid content. The porosity and compressive strength of porous ceramics improves as the slurry solid content increases from 45 wt.% to 60 wt.%. As the content of slurry solid increases, the sponge template adsorbed so much slurry, so that low shrinkage of sponge skeleton results in the porosity and compressive of samples increase during sintering process. The results reveal that the cordierite porous ceramics with slurry solid content of 60 wt.% sintered at 1200℃ with high porosity of 73.69% exhibits an average compressive strength of 2.23 MPa.(3) The influence of the impurity content in the coal gangue on sintering characteristic and properties of porous ceramic. The large amount of liquid phase has effect on the properties of ceramics due to the impurity exist. The impurity removal rate of coal gangue is controlled by different acid leaching conditions, such as acid leaching time, acid-gangue ratio and acid leaching temperature. The research shows that the extension of the acid leaching time, acid-gangue ratio and acid leaching temperature can improve the porosity and compressive strength of porous ceramic, that because the impurity removal rate was controlled. As the impurity removal rate increased from 40.11% to 53.73%, the sample shows porosity decreased from 83.55% to 76.40%, while the compressive strength increases. Acid of gangue ratio has the most influence on the rate of removing impurity, followed by acid leaching time, finally the acid leaching temperature. When the impurity removal rate is 40.11%, the porosity of sample reaches the maximum(83.55%), and the compressive strength is kept at 2.31 MPa. When the impurity removal rate is 47.21%, the compressive strength of sample reaches the maximum 3.68 MPa and the porosity is maintained 79.31%.(4) The mechanism of using coal gangue as raw material to sinter cordierite porous ceramics. Cordierite ceramics formation temperature is usually 1300 ℃, however, in the thesis the formation of cordierite phase is 1150℃. The main reason is the impurities play the role of sintering aids in the coal gangue, which forms the liquid phase make them closer to participate in reaction of solid particles during the sintering process of ceramic. Besides to transfer media for cordierite is benefit to prompt cordierite crystal nucleus emerge and grow up, so that the cordierite formation temperature is decreased. Meantime the impurities also promote the activity of MgO and Al2O3 to format the spinel that reacts with the amorphous SiO2 to form cordierite at low temperature.