Differences in the coking and non-coking coals from the standpoint of carbon structure

Abstract

The purpose of the present study is to clarify the differences in the carbon structure of cokes derived from coking coals and non-coking coals. The structures of the carbonized coals at 1000°C were estimated from the X-ray diffraction and Raman spectroscopy measurements of the carbons heat-treated at 3000°C. This was based on the conventional recognition in carbon science such that the structures of carbons become obvious after heat-treatments at graphitization temperature, 3000°C. Three polymers and five coals confirmed the above recognition from the analyses of the carbons prepared at different temperatures. Essentially, coking coals and non-coking coals could be classified to graphitizing and non-graphitizing carbons, respectively. By close inspections of carbon (002) X-ray diffractions of 3000°C treated coals, it was found that the degrees of graphitizing and non-graphitizing abilities of coals were not as complete as the typical polymer-derived carbons. The Raman spectra of the carbons from non-coking coals prepared at 3000°C revealed the inhomogeneous structures of the carbons, because they gave position-dependent Raman spectra. Structural models of the cokes from coking and non-coking coals by taking account of continuous self-dissolving model were proposed. The important point of the model is that cokes consist of ordered matrix and disordered 'islands' in the matrix. The differences between the coking coal-derived ones and the non-coking coal-derived ones are found in the size and the distribution of the disordered islands.