The carbonization of wood has been studied by means of thermoanalytical methods, in particular, thermogravimetry (TG). This method subjects the sample to a temperature program in a defined atmosphere. The samples were first treated to give a certain degree of charcoal, which could then be analyzed immediately in a second step.
As shown by means of the individual decomposition step of cellulose and lignin, time aging affected the degradation of lignin, whereas thermal aging (the charring process) decomposed the cellulose and turns lignin into charcoal. X-ray analysis showed that because of its chemical structure, lignin turned into paracrystalline coal, a precursor graphite.
In the natural process of carbonization, different kinds of coals such as lignite, bituminous coal, anthracite, or even graphite are formed. TG proved suitable for characterizing these coals by proximate analysis and studying the burning profiles.
Comparable measurements with graphites showed that the combustion rate depended strongly on the composition and structure of the coal.