Studying carbonisation with raman spectroscopy

Abstract

Raman spectroscopy can provide fast and non-destructive analysis of carbonaceous materials. As it is able to detect nanometre-sized structural features, Raman spectroscopy is widely used in the study of carbon nanotubes, fullerenes, graphenes, and many other carbon-rich materials. Raman analysis has previously shown potential for estimating the heat treatment temperatures (HTT) employed in the preparation of Japanese cedar charcoals which suggested future usefulness in quality control . In the current work, Raman spectroscopy was used to investigate the nanostructural development which had occurred within various chars prepared and carbonised at a range of heat treatment temperatures between ≈ 340°C and 1000°C. Chars were produced from sucrose sugar as standard precursor of high purity and two sources of biomass common in New Zealand (Radiata pine wood and Harakeke leaf fibres). In chars produced at lower HTTs, signals could be detected which were interpreted as representing hydrogen-rich amorphous carbon structures. In contrast, the Raman spectra of well-carbonised chars produced at higher HTTs featured signals consistent with graphene-like structures with coherent domains limited in size to below a few nanometres across. Measurement of such signals provides the ability to evaluate the extent of nanostructural development, identify char samples which are ‘undercooked’ when compared to other char samples, and estimate effective HTTs used in the production of a given char sample. More detailed Raman analysis of Radiata-derived chars was carried out, including analysis of chars produced from carbonising pyrolysis tars. Results of Raman analysis were correlated to H/C atom ratios obtained through elemental analysis for these chars produced from Radiata pine.