Microporosity Development in Coal-Based Carbon Foams

This paper presents a novel method of manufacturing carbon foams from coals with a bimodal porosity structure (macro- and microporosity), by means of a carbonization process at 450 or 475 degrees C that produces the carbon foam, followed by chemical activation with zinc chloride at 500 degrees C. The activation agent influences the development of macroporosity during the foaming step and gives rise to microporosity (major pore sizes in the 0.6-1.1 nm range) and a specific surface area (up to 762 m(2) g(-1)) in the activation step. A coal with a lower volatile matter content and less fluidity gives rise to carbon foams with a higher macropore volume but a lower macropore size. A higher gas flow and a longer soaking time in the activation step lead to a larger micropore volume and a higher surface area. Foams with a still significant micropore network can be obtained by performing simultaneous chemical (with ZnCl2) and physical (with CO2) activations at 800 degrees C. Presumably, such foams would display higher mechanical strength and electrical conductivity.