Characterization of Al2O3 suspensions stabilized with polyelectrolyte dispersant

U ovom radu opisuje se postupak pripravljanja Al2O3 suspenzija za oblikovanje keramike postupkom lijevanja. Da bi suspenzija bila stabilna, u nju je potrebno dodati neku vrstu aditiva. Disperzanti su jedna od vrsta aditiva koji se dodaju kako bi se postigla stabilnost, a u suspenziju se moraju dodati u optimalnoj koncentraciji, kako bi se postigla optimalna viskoznost. Istraţivanje je usmjereno na nalaţenje optimalne koncentracije disperzanta Darvan C-N (amonijeva sol polimetakrilne kiseline). Prilikom ispitivanja pripravljeno je pet 70%-tnih suspenzija s različitim udjelima disperzanta: 0,4 – 1,2%. Priprava suspenzija sastoji se od homogenizacije Al2O3 praha s disperzantom i vodom u planetarnom kugliĉnom mlinu, uklanjanja mjehurića zraka u ultrazvučnoj kupki, potom mjerenja pH vrijednosti pomoću pH metra te reoloških svojstava na rotacijskom viskozimetru. Pomoću viskozimetra snimaju se krivulje tečenja (ovisnost viskoznosti o brzini smicanja i ovisnost smičnog naprezanja o brzini smicanja). Dobiveni se rezultati potom usporeĊuju s Power-law (potencijskim) modelom,Herschel-Bulkleyjevim modelom te Binghamovim modelom. Iz rezultata reoloških mjerenja utvrđeno je da suspenzija Al2O3 s 0,6% Darvan C-N disperzanta ima najpovoljnija svojstva za oblikovanje keramike postupkom lijevanja.In this paper the procedure of preparing Al2O3 suspension for ceramic molding by slip casting is described. To achieve suspension stability, it is necessary to add some kind of an additive. Dispersants are one of the types of additives added to a suspension to achieve stability, but they must be added at an optimum amount to achieve optimal viscosity. The research is focused on finding the optimal concentration of Darvan C-N (ammonium polymethacrylate) dispersant. During the assay, five 70% suspensions with different concentrations of dispersant were prepared: 0.4 to 1.2%. Preparation of the suspension consists of the homogenization ofAl2O3 powder with dispersant and water in the planetary ball mill, removal of the air bubbles in the ultrasonic bath, then measuring the pH value with pH meter and the rheological properties on the rotational viscosimeter. Viscosimeters record flow curves (viscosity vs. shear rate and shear stress vs. shear rate). The results are then compared to the Power-law (potential) model, the Herschel-Bulkley model and the Bingham model. From the results of rheological measurements, it was found that the Al2O3 suspension with 0.6% Darvan C-N dispersant has the most favorable properties for ceramic molding by slip casting