Abstract
The present study aimed at investigating the influence of the concentration of sodium silicate and sodium hexametaphosphate on the dispersion of an aqueous kaolinitic clay slurry regarding further use for the tape casting process. The zeta potential of the kaolinitic clay slurry matched the requirements for tape casting. The addition of magnesite in the kaolinitic slurries tended to increase the zeta potential towards the required limit values. Despite this, the further addition of surfactants allowed improving the zeta potential in agreement with the tape casting conditions. Accordingly, the rheological behavior, under continuous and oscillatory flow conditions, of various mixtures of magnesite and a kaolinitic clay was studied. Regarding the pH and the zeta potential measurements, the E–F attraction prevailed at low pH value, and F–F or E–E attraction was predominant at high pH value. All slurries exhibited a shear thinning behavior, which was well-correlated by the Herschel–Bulkley model. It appeared that the best stability for the kaolinitic clay slurries was obtained while using 0.4 mass% and 1.2 mass% of sodium hexametaphosphate and sodium silicate, respectively. An increase in the magnesite concentration above 6 mass% led to a complex behavior with low cohesion energy due to the occurrence of soluble complexes.
Highlights
Ceramic slurries contain inorganic components, water or organic solvents, and most frequently, organic or inorganic additives
The effect of magnesite to the aqueous kaolinitic clay dispersion may cause a decrease or increase in the repulsive force interactions between the solid particles in the slurry, which directly affect the rheological parameters of the medium, as well as its pH
Prior to the tape casting, the slurries were de-aired on rollers during 22 h and sieved at 100 μm to ensure the elimination of the non-dissolved binder or impurities
Summary
Ceramic slurries contain inorganic components (clay minerals, quartz, feldspar, and oxide), water or organic solvents, and most frequently, organic or inorganic additives (dispersants, plasticizers, fluidizers, antifoams, lubricants, etc.). Among the dispersants that have been introduced to disperse clay particles by electrostatic interactions, sodium silicate (Na2 SiO3 ) and sodium hexametaphosphate (NaPO3 ) appeared to provide an efficient dispersion effect [1,7,11,12,13,14,15,16,17] Both dispersants adsorbed onto the surface charge of particles by the Van Der Waals interactions and hydrogen bondings, which induce repulsion/attraction interactions [14,18,19]. The effect of magnesite to the aqueous kaolinitic clay dispersion may cause a decrease or increase in the repulsive force interactions between the solid particles in the slurry, which directly affect the rheological parameters of the medium, as well as its pH. The optimized slurries were tested for the tape casting process
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