Effect of Natural Mineral Inclusions on the Graphitizability of a Pennsylvania Anthracite

Abstract

A Pennsylvania anthracite was heat-treated to temperatures in excess of 2000 °C. Carbides formed at ∼2200 °C and then decomposed at ∼2500 °C. This process aided in the graphitization of the anthracite. The carbide formation−decomposition reactions were the sole graphitization mechanism for this anthracite. This was shown by demineralizing (to remove the natural mineral inclusions) and then heat-treating the sample to 2600 °C. X-ray diffraction (XRD) of the heat-treated demineralized sample showed that the (112) peak, which is indicative of three-dimensional ordering and was previously observed in the native heat-treated anthracite, was no longer present. The demineralized anthracite was remineralized by individually adding four types of minerals (rutile, quartz, calcite, and hematite) to demineralized samples. Each of the remineralized samples was heat-treated and found to exhibit the (112) peak again. The absence of the (112) XRD peak after removal of minerals and heat treatment followed by its reappearance after remineralization and heat treatment strongly suggests that the anthracite was only graphitizable if mineral matter was present.