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Microporosity Development in Coal-Based Carbon Foams

Rodríguez, Elena, García, Roberto
Energy & Fuels 2012 v.26 no.6 pp. 3703-3710
carbon, carbon dioxide, carbonization, chlorides, coal, electrical conductivity, foaming, manufacturing, porosity, soaking, strength (mechanics), surface area, zinc
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 and electrical conductivity.