Stabilization of Al2O3 suspensions with citric acid

U ovom radu pripravljene su 70%-tne Al2O3 vodene suspenzije uz različiti udio limunske kiseline kao disperzanta. Suspenzije su homogenizirane u planetarnom mlinu, potom im je izmjerena pH vrijednost te uklonjeni mjehurići zraka u ultrazvučnoj kupelji. Rotacijskim viskozimetrom izmjerena je viskoznost suspenzija te snimljeni dijagrami tečenja (ovisnost smičnog naprezanja o smičnoj brzini te ovisnost viskoznosti o smičnoj brzini). Iz dobivenih rezultata određen je i optimalni udio disperzanta tj. limunske kiseline, koji iznosi 0.1 %. Stabilnost suspenzija pri različitim pH vrijednostima ispitana je sedimentacijskim testovima na 20 %-tnim suspenzijama aluminijevog oksida uz dodatak optimalne količine disperzanta. Dobiveni rezultati pokazuju da su 20 %-tne suspenzije aluminijevog oksida stabilne do 96 sati pri pH vrijednosti oko 2 i između 8 i 11 , a nakon sedam dana sedimentiraju u potpunosti.In this paper 70 wt.% aqueous Al2O3 suspension were prepared with different amounts of citric acid as a dispersant. Suspensions were homogenized using a planetary ball mill, after which pH values were measured and air bubbles removed using an ultrasonic bath. The rotational viscosimeter was used to measure the viscosity of prepared suspensions and to record flow curves (dependence of shear stress on shear rate and dependence of viscosity on shear rate). From the obtained results, the optimal amount of dispersant i.e. citric acid was determined and amounts to 0.1 wt.%. Stability of the prepared suspensions at different pH values was evaluated by sedimentation tests on 20 wt.% aluminum oxide suspensions, with the addition of an optimum amount of dispersant. The obtained results show that 20 wt.% aluminum oxide suspensions are stable for 96 h at pH values 2 and from 8 to 12, while after 7 days they completely settled as sediment