Rheology of alumina slips

The aim of the present work is to study the rheological behaviour of concentrated aqueous alumina suspensions. Aqueous alumina suspensions were prepared at various solid contents (65 to 77.5 wt%). Rheological tests were carried out at 25±0.1°C by using the rate controlled coaxial cylinder viscometer Rotovisko-Haake 20, system M5-osc., measuring device SV2P with serrated surfaces. The tests were performed under both continuous and oscillatory flow conditions. All the suspensions studied show a theological behaviour of the shear-thinning type; in addition, the presence of a yield stress is noticed. Some theological equations of both τ=f(γ) and ηr=f(φ, γ) type have been taken into consideration for describing the flow behaviour of the alumina slips investigated. A master-curve procedure was applied in order to give a compact representation of the flow curves drawn for the alumina suspensions examined. Finally, the effect of the addition of a dispersing agent (sodium polyphosphate) on the rheology of alumina slips was investigated and its optimum dosage was determined as well.