Microporosity Development in Coal-Based Carbon Foams

Abstract

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 °C that produces the carbon foam, followed by chemical activation with zinc chloride at 500 °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 m2 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 °C. Presumably, such foams would display higher mechanical strength ...