Surface Characterization of High Temperature Heat-Treated White Charcoals

Lee JH, Kwac LK, Ryu SK and Kim HG

Published on: 2023-04-04

Abstract

Oak tree-based white charcoals prepared from a South Korean traditional furnace were ground finely and treated with high temperature to analyze the surface morphology and changes in microporosity. When the charcoal was heat-treated at 1,500°C for 60 min in an N2 atmosphere, the fixed carbon content (C) increased to 97.25 wt%. Heat treatment at 1,800°C for 60 min, 2,000°C for 30 min, and 2,400°C for 10 min in an Ar environment increased the C to 99.88, 99.96, and 100 wt%, respectively. Heat treatment over 1,800°C caused most micropores to shrink and disappear. However, some micropores coalesced to large pores, increasing the average pore size. During the time, the surface structure changed to a tight lattice layer. Following heat treatment at 2,000°C, all pores had decomposed and presented an irregular surface. The nitrogen adsorption isotherm of charcoal flake was peculiar, showing a mixed Type I and IV curve due to low-pressure hysteresis as a result of nitrogen molecules embedded in the entrance of micropores. This low-pressure hysteresis was lost following fine grinding or high-temperature treatment of charcoals presenting a Type IV curve, since most micropores were lost or coalesced to large pores, with few remaining mesopores. Following heat treatment at 2,400°C, the charcoal surface presented a graphite-like structure, showing a non-porous Type II curve and the specific surface area was 8.10 m²/g, similar to that of artificial graphite.