Carbonized wood and sunflower seed hull pellets as a substitution for carbon black for the production of MgO-C refractories

Refractories based on MgO with up to 20 wt% carbon are the dominating lining materials for vessels in steelmaking and refining plants, where they have to withstand high temperatures, thermal shock, and aggressive steel/slag systems. To preserve limited resources and establish regional raw material supply chains, alternative resources for graphite as a carbon source are required. In this study, pellets from sunflower seed hull and wood were converted into carbon by a carbonization process and added to a MgO-C batch (3 % C) to replace up to 1.1 wt.-% of carbon black. After hardening and carbonizing the MgO-C samples at 1000 C, their phase composition, microstructure, porosity, density, cold crushing strength (CCS), refractoriness under load (RuL), and oxidation resistance were investigated. The addition of carbonized wood and sunflower seed hull pellets reduced the CCS by more than 25 % due to an inhomogeneous microstructure with poor grain bonding to the matrix, but the porosity was not affected negatively. The RuL is at the same level as the reference samples, even if the carbonized pellets contain ashes with a high amount of K2O (50 %). The addition of carbonized biomass pellets has in particular a positive effect on the oxidation resistance, resulting in 30 % less carbon oxidation of wood pellet coke compared to carbon black at 1600 degrees C. Hence, sunflower seed hull and wood pellets were found to be prospective carbon sources for MgO-C refractories to support their evolution into a carbon-neutral material.