Microstructural characterization of white charcoal

Abstract

There has been an upsurge of interest in using high density and low volatile matter charcoal to replace coke and coal in the manufacture of aluminium and steel due to its potential to reduce net greenhouse gas emissions from the production process. ‘White’ charcoal is envisaged as a potential candidate for this application. It is synthesized by pyrolysing wood at low temperature (∼240°C) for 120h, and then raising the kiln temperature to ∼1000°C towards the end of the carbonization process. The charcoal is then withdrawn and smothered with a moistened mixture of earth, sand and ash. However, to date, little is known about the structure of this form of charcoal, which is essential before this material can be widely applied in extractive metallurgy. Characterization of white charcoal with nuclear magnetic resonance and X-ray photoelectron spectroscopy revealed a high fixed carbon content (>95wt%) with ∼82at.% of the carbon present in the form of condensed aromatic rings. Scanning electron microscope analysis depicts a porous microstructure with pores ∼100μm in diameter aligned across the surface and a high density of macropores <10μm in diameter scattered across the surface. Transmission electron microscope and X-ray diffraction analysis of white charcoal showed a mainly amorphous carbon structure with localized regions of crystalline graphite and calcites. The suitability of white charcoal as a replacement for coke is also discussed.