Effect of kind of acid and the solid fraction on the viscosity by the gamma-Al2O3 nanofiber in the form of precursor slurry for the final ceramic

摘要

Nanofibers of gamma alumina were dispersed in acid aqueous media and the effect of hydrochloric and nitric acid on viscosity was investigated. The viscosities of the aqueous suspensions were determined under controlled shear rate conditions, varying the pH and solid concentration. A lower viscosity is observed with nitric acid because the nitrate ion produces stronger double layer repulsion, in comparison with that obtained with the chloride ion. It was found that the maximum solid loading in the suspension at pH 4.5 adjusted with HNO3 and HCl was 42 and 35 wt%, respectively. The isoelectric point (IEP) of the alumina powder in the suspension occurs at pH 8.5. High solid concentrations and a pH close to the IEP produced high viscosity and shear thinning at the low shear rates due to slurry agglomeration. This increases the viscosity of the suspension and diminishes the final relative density of the slip casting body.