Abstract:
This report investigates the cause of the reduction in workability and increased ageing of a blast furnace taphole clay. The taphole clay contains 60 mass% alumina, with a phenol-formaldehyde resole resin (PFR) and liquid pitch as a binder system. The clay aggregates as well as powder matrix raw materials were analysed using XRF, XRD and SEM-EDS for characterisation and impurity detection such as sulphur and free lime. The presence of free lime can cause premature cross-linking of the resin in the binder while the presence of sulphur can reduce the curing time of the resin. The wettability as well as particle size distribution (PSD) of all the raw materials were investigated to confirm a uniform particle size distribution of the dry aggregate of the taphole clay and wettability compatibility between the dry raw material and both resin and liquid pitch. The resin and liquid pitch characterisation, as well as interaction between resole resin and liquid pitch, were evaluated using viscosity measurements, Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The analyses confirmed a chemical interaction between the resole resin and liquid pitch, where the chemical structure of the resole resin was broken down when the two liquids were mixed. This prevented curing of the resin to occur. After ageing of the resin and liquid pitch mixtures, premature cross-linking of the resin occurred, causing the curing process to move to lower temperatures, i.e. earlier onset of curing. This reduction in curing temperature, after ageing, was confirmed by an increase in binder viscosity at lower temperatures (starting at 60°C) than the curing temperature (121-126°C) of the virgin resole resin in the binder. This increase in viscosity of the binder mixture is the primary cause of the reduced workability, increased ageing and increasing Marshall extrusion pressure (MEP) of the taphole clay.
