Nonaqueous Suspension Properties of Al 2 O 3 and Silicate Glass Powders
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NONAQUEOUS SUSPENSION PROPERTIES OF A12 0 3 AND SILICATE GLASS POWDERS M.D. SACKS AND M.I. ALAM Department of Materials Science and Engineering University of Florida Gainesville, Florida 32611
INTRODUCTION Colloidal suspensions prepared with nonaqueous liquids are important in ceramic processing operations such as tape casting, slip casting, etc. However, investigations of the properties of such suspensions are [1,21. limited. In the present work, the suspension behavior of Al 2 0 3 and silicate glass powders was studied using two nonaqueous liquids - methanol (MEOH) and Rheological, sedimentation, and methyl isobutyl ketone (MIBK). electrokinetic properties were determined for various mixed liquid ratios. The effect of polyvinyl butyral resin, a polymeric binder, on silicate glass suspension properties was also investigated.
EXPERIMENTAL Experiments were carried out with a-AI 2 0 3 (C-75, Alcan Aluminum Co.) and glass (Si0 2 -A1 2 0 3 -MqO-CaO, Pemco Products) powders. The AI 2 0 3 had a median equivalent Stokes diameter of -2pm and a specific surface area of -2 m2/q, while the corresponding values for the silicate glass were -31m and 2 -2.5 m /g, respectively. Additional information on these powders is provided elsewhere [3,4]. Suspension liquids were methanol (MEOH, duPont Co.) and methyl isobutyl ketone (MIBK, Ashland Chemical Co.). The polymer used in this study was a polyvinyl butyral resin (B-98, Monsanto Co.). All suspensions were prepared with 30 vol% solids, 65-70 vol% liquid, and 0-5 vol% polymer. Suspension rheological flow curves (shear stress, T, vs. shear rate, behavior) were determined using a narrow-gap, concentric cylinder viscometer (Haake, Inc.). Viscosity values, n, were obtained from the flow curves using the relationship:
n = T/ Sedimentation density was determined by pouring the suspension (of known weight) into a 50 mL graduated cylinder, covering the cylinder to prevent liquid evaporation, and allowing particles to settle until the sediment height no longer changed with time. The measured bulk density was divided by the powder true density in order to obtain the relative density. Electrical conductivity measurements were made on the "pure" liquids (various MEOH/MIBK ratios) and on the supernatant liquids of extremely wellcentrifuged suspensions. A microelectrophoresis apparatus (Rank Brothers Co.) was used to measure the electrokinetic mobility of particles. Zeta potentials were determined from the electrophoretic mobilities using the Helmholtz-Smoluchowski equation [5]. Polymer adsorption isotherms were determined qravimetrically.
RESULTS AND DISCUSSION Effect of MIBK/MEOH Ratio on Suspension Properties The effect of liquid ratio (MIBK/MEOH)
on suspension properties was
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investigated for A1 2 03 /liquid and glass/liquid suspensions. Plots of viscosity (at shear rates of 3, 30, and 300 s-1) vs. vol% MIBK (in the liquid phase) are shown in Fig. 1. Several observations are noted: (1)
All suspensions sh
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