Effects of foaming temperature on structure and mechanical strength of coalbasedcarbon foam prepared by selffoaming technique under ambient pressure

The materialization of coal is one of the important ways to realize its lowcarbon and high valueadded utilization. Coalbased carbon foam has good application prospects due to the unique physical and chemical properties. Herein,the coking coal as the precursor was adopted to prepare the amorphous coalbased carbon foam with an opencell structure through the selffoaming technique under ambient pressure by selecting different foaming temperature in the plastic interval. The microscopic morphology,cell structure and crystal structure of carbon foams were characterized by SEM,XRD,a mercury porosimeter and a helium gas displacement pycnometry system；the mechanical strength of the carbon foam was measured by electronic universal testing machine,and by analyzing the effects of foaming temperature on the structure and the performance of the final products was deeply investigated. The results showed that the changes in the thermal decomposition of raw coal and the fluidity behavior of the metaplast caused by the different foaming temperature,resulted in different degrees of foaming of coal samples during the preparation process,which would affect the cell and carbon skeleton structures of the green carbon foam(NCF). Combined with these changes,when the foam temperature at 480 ℃ corresponding to the maximum fluidity was selected and then the obtained NCF-480 had the highest open porosity(70.89%),the smallest bulk density(0.460 g/cm3)but the relatively dense carbon framework structure,which jointly lead to its better mechanical strength. Its compressive strength and flexural strength reached 1.63 MPa and 1.11 MPa,respectively. After hightemperature carbonization,the pore size of the obtained carbonized carbon forms(CCF)reduced,while their open porosity and bulk density increased. Meanwhile,their carbon skeletons became more compact under the polycondensation reaction. These changes resulted in a significant increase in its mechanical strength compared with NCF samples. Among them,the CCF-490 sample had a benign structural balance with the middle value of average pore diameter,open porosity and bulk density,and small differences of its pore size,which made its mechanical performance best with compressive strength of 8.52 MPa and flexural strength of 5.14 MPa,respectively. This study not only synthesizes coalbased carbon foam materials with good structural properties,showing excellent application prospects,but also provides a new idea for the materialization and high valueadded utilization of coal.