Microporosity and surface-area study of pine wood charcoal by SAXS and CO₂ absorption techniques

Pine wood samples (Pinus elliottii) were heat treated at temperatures from 873 to 2873 K. Small-angle X-ray scattering (SAXS) and carbon dioxide adsorption techniques were used to characterize micropore number, diameter and corresponding internal surface area (ISA) for all samples. The adsorption data showed a maximum at about 1273 K, whereas SAXS data indicated a significant decrease of ISA at those heat-treatment temperatures (HTT). At higher HTT both techniques showed similar trends. To investigate these findings further, the evolution of the turbostratic structure of all samples was studied from X-ray powder diffraction spectra. It was then concluded that the dynamics of microcrystallite growth affect the microporosity by decreasing the number of micropores and associated surface area. The increase in ISA observed by adsorption techniques is due to the creation of a large number of channels by the expulsion of volatile matter.