Electroacoustic investigation of aqueous suspensions of raw materials for AL2O3-C refractories

The influence of the pH value and of an anionic polyelectrolyte on the zeta potential of different raw materials that are used for producing carbon-bonded alumina refractories was studied by measurements of the electrokinetic sonic amplitude (ESA). The following raw materials were investigated: alumina CT 3000 SG, tabular alumina T60/T64, modified coal tar pitch Carbores (R) P, graphite AF 96/97, carbon black LUVOMAXX (R) MT N-991 and RW micro-silica. The isoelectric points of these materials were identified, except for the graphite and the micro-silica, which exhibited a negative surface potential over the entire pH range investigated (pH 3-11). An anionic polyelectrolyte (Dolapix CA) was found to increase not only the value of the zeta potential of the oxides at the inherent suspension pH but also that of the graphite and the carbon black. Its addition to concentrated slurries containing a mixture of the investigated raw materials reduced the viscosity and resulted in a decrease in the apparent porosity of carbon-bonded alumina samples produced by pressure filtration. The suitability of the suspension composition for shaping large-sized samples by pressure slip casting and the high thermal shock resistance of the fabricated alumina-carbon refractory have been demonstrated.