This is the third report on a project whose aim is to explore in a fundamental manner the factors that influence the development of porosity in coal chars during the process of activation. It is known that choices of starting coal, activating agent and conditions can strongly influence the nature of an activated carbon produced from a coal. Interest in this phase of the project turned to characterization of one particular char. Results have been published on Pittsburgh No. 8 char using an entirely different porosity characterization method. The interpretation of the results in that other study is not entirely consistent with what has been observed in this study. In particular, the results of the present study seemed to indicate the opening up of existing porosity, as opposed to creation of new porosity. It is difficult to infer much, based upon the porosity characterizations alone. Instead, attention was turned to the correlation of porosity with reactivity, which can provide a clue as to whether there was actually full accessibility of all of the observed porosity. The conclusion is that the pores are not all fully accessible, and that different oxidizing gases behave differently. The suggestion is that measured porosity is not all accessible to reactants. Also, attempts to correlate reactivity of chars with surface area are likely to be problematic, if different gases behave differently in this regard.
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