Role of catalytic agents and processing parameters in the graphitization process of a carbon-based refractory binder

The chemical resistance and thermo-mechanical properties of carbon-containing refractories are highly dependent on the presence of carbonaceous phases with structures similar to graphite ones. However, most of the thermosetting resins (used as binders) are classified as non-graphitizing carbon sources. Consequently, there is a high degree interest in finding alternative routes to induce an effective graphitization of such polymeric components at temperatures and conditions similar to the ones that refractories are submitted to in service. This research evaluates the effect of different catalytic agents (ferrocene, hematite and nano-Fe2O3 powder) and some processing parameters (i.e., temperature, dwell time, heating rate, amount of cross-linking additive) on the graphitization process of a novolak resin. X-ray diffraction, SEM/EDS and thermogravimetric analyses were carried out to identify the phase and microstructural evolution of the prepared compositions. According to the attained results, carbon graphitization was observed after firing the samples at 1000 °C and 1400 °C for 5 h under a reducing atmosphere. The addition of ferrocene (>2 wt%) favored the generation of a higher amount of iron oxide particles in the microstructure at 1400 °C and led to a more effective graphitization, whereas the greater tendency for nano-Fe2O3 powder to agglomerate during the initial samples' mixing step inhibited carbon crystallization. Regarding the effect of the processing parameters, the use of a heating rate of 3 °C/min and dwell time of 5 h at the maximum temperature of 1400 °C, led to the generation of a maximum amount of graphitic carbon, 33.1%, in the composition with novolak resin +3 wt% ferrocene.