Effect of heat treatment on properties of carbonaceous materials

Abstract

Submerged electric arc furnace (SAF) is the major process in industrial production of ferroalloys, in which metal oxides are reduced by carbon. To decrease the production cost, a variety of carbonaceous materials is used including metallurgical cokes, chars and coals. Properties of these carbonaceous materials are strongly affected by the heating in the furnace. The project studied effect of heat treatment on properties of cokes, chars and coals (laboratory chars), including microstructure (XRD and Raman spectroscopy of inert and reactive maceral-derived components IMDC and RMDC), micro-strength (micro-indentation of IMDC and RMDC) and macro-strength (tumbling strength and tensile strength), pyrolysis and porosity. The project s aim was to develop further understanding of factors affecting integrity of carbonaceous materials under conditions of SAF in production of manganese alloys. Upon the heating, strength of chars and laboratory chars was strongly enhanced by the heat treatment at temperature below 1100 °C; strength of cokes was slightly degraded after heat treatment at 1500 °C. Mechanical strength of carbonaceous materials was demonstrated to be significantly affected by micro strength and porosity. Micro strength of chars and coals was significantly enhanced by heat treatment, whereas micro strength of cokes was only marginally increased by heat treatment. The major growth in the micro strength of chars and coals took place at annealing temperature below 1100 °C as a result of pyrolysis. Porosity of chars and coals significantly increased in the annealing at temperature below 1100 °C due to volatile matter release. Further increasing annealing temperature from 1100 ‒ 1500 °C caused marginal porosity evolution in coals and chars by the reduction of oxides of a mineral phase. Porosity of cokes increased slightly in the temperature range of 1300 ‒ 1500 °C as result of reactions with the mineral phase. Heat annealing of carbonaceous materials above 1100 ºC significantly increased the degree of graphitization. Graphitisation degree of RMDC was higher than that of IMDC, and annealing had a stronger effect on the graphitisation of RMDC than on IMDC. It was concluded that among carbonaceous materials studied in this project, Char 1 and Coal 1 are most suitable to replace coke.