Preparation And Mechanism Of High-Strength Foam Ceramics From Shale And Solid Wastes

In this paper,foam ceramics were prepared from sand shale and solid wastes using silicon carbide as foaming agent.The effects of formula composition and firing schedule on the properties of foam ceramics were investigated.The foam ceramics were characterized via XRF,DTA-TG,XRD,SEM,EDS and Micro-CT.The porosity,bulk density,flexural strength and thermal conductivity of the samples were tested.Fractal dimension and grey system theory were used to study the effects of pore structure parameters and properties（flexural strength and thermal conductivity）of foam ceramics.Foam ceramic was prepared from sand shale,coal fly ash and steel slag as the main raw materials and silicon carbide as foaming agent.The introduction of magnesite promoted the formation of diopside crystal phase in the sample and effectively improved the flexural strength of the sample.The correlation between the pore structure parameters and flexural strength of foam ceramics with different magnesite contents was studied by using grey system theory.The results show that the comprehensive properties of the samples are the best when 83.33 wt.%of sand shale,8.33 wt.%of coal fly ash,8.33 wt.%of steel slag,5 wt.%of magnesite and 0.2 wt.%of silicon carbide are added.Its total porosity is 64.11%,the closed porosity is 60.55%,the bulk density is 0.918 g/cm~3,the flexural strength is 10.02 MPa,and the thermal conductivity is 0.133 W/（m·K）.The order of correlation between pore structure parameters and flexural strength of samples with different magnesite contents is as follows:total porosity,fractal dimension,closed porosity,average pore size,pore size distribution ratio greater than 0.8 mm,pore size distribution ratio less than 0.4 mm,pore size distribution ratio of 0.4～0.8 mm.In order to further reduce the thermal conductivity of foam ceramics,the pore structure of foam ceramics was effectively improved by adjusting the amount of foaming agent and heat treatment schedule.The foam ceramics with thermal conductivity of 0.081W/（m·K）were prepared.The correlation between the pore structure parameters and thermal conductivity of foam ceramics at different holding time was studied by using the grey system theory.The results show that the comprehensive properties of the samples are the best when the content of silicon carbide is 0.3 wt.%,the sintering temperature is1160℃and the holding time is 50 min.The total porosity is 75.07%,the closed porosity is 54.16%,the bulk density is 0.651 g/cm~3,the flexural strength is 4.75 MPa,and the thermal conductivity is 0.081 W/（m·K）.The order of correlation between pore structure parameters and thermal conductivity of samples with different holding time is as follows:fractal dimension,total porosity,closed porosity,pore size distribution ratio of 0.8～1.6mm,average pore size,pore size distribution ratio of less than 0.8 mm,pore size distribution ratio of more than 1.6 mm.In order to prepare foam ceramics with high strength and low thermal conductivity,this paper introduced the influence of high alumina raw materials on the properties of foam ceramics by introducing high alumina raw materials,using andalusite instead of coal fly ash and introducing spodumene as flux.The results show that the comprehensive properties of the samples are the best when 69.24 wt.%of sand shale,16.92 wt.%of andalusite,8.46 wt.%of steel slag,5.38 wt.%of magnesite,2 wt.%of spodumene and0.3 wt.%of silicon carbide are added.The total porosity is 61.02%,the closed porosity is55.30%,the bulk density is 0.944 g/cm~3,the flexural strength is 11.15 MPa,and the thermal conductivity is 0.091 W/（m·K）.The main crystalline phases are anorthite,andalusite,diopside and quartz.