Adsorption of poly(vinyl butyral) in nonaqueous ferrite suspensions
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Adsorption of poly(vinyl butyral) in nonaqueous ferrite suspensions Jau-Ho Jean and Shun-Fen Yeh Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan, Republic of China
Chi-Jen Chen Materials Research Laboratories, Industrial Technology Research Institute, Hsinchu, Taiwan, Republic of China (Received 31 May 1996; accepted 13 September 1996)
The adsorption of poly(vinyl butyral) (PVB) on NiCuZn ferrite powder in binary solvent systems of 1-butanol and toluene has been investigated. The adsorption isotherms of different PVB’s on ferrite powder from various solvent mixtures follow closely the Langmuir monolayer types and can be explained by adsorption competition between solvents and PVB. A relatively poor solvent for PVB increases its adsorption on ferrite powder and thus improves the dispersion of the powder in the nonaqueous suspension. The adsorbance of PVB increases with increasing hydroxyl content in PVB suggesting that PVB is bonding strongly to the protruding surface hydroxyl groups on ferrite powder.
I. INTRODUCTION
Dispersion of ceramic powders in organic media is important in preparing green sheets with high packing density and uniform microstructure by tape casting. Polymeric dispersant is always used to achieve colloidal stabilization in organic liquids. Addition of polymeric binder and plasticizer into the casting slurry is done to provide the required strength, flexibility, and laminability of the green sheet prior to sintering. To minimize the amount of organic additives used in the slurry, there might be some advantage in choosing a polymer to function not only as a binder, but also as a dispersant. This requires the adsorption of polymeric binder onto the particle surface to give steric stabilization.1,2 Therefore, fundamental understanding of the adsorption behavior of polymeric binder in different solvents is imperative to design organic compositions to obtain well-dispersed suspensions. The purpose of the present study is to investigate the adsorption of poly(vinyl butyral) (PVB) onto NiCuZn ferrite powder in nonaqueous solvents of 1-butanol and toluene. PVB was chosen because it had been often used as an organic binder in tape casting.3,4 Rheological and sedimentation behaviors were used to assess the degree of dispersion and its relation to the adsorption of PVB. The bonding mechanism between ferrite powder and PVB was examined by diffuse reflectance Fourier transform infrared (FTIR) spectroscopy. II. EXPERIMENTAL PROCEDURE
The composition of the low-temperature fired ferrite powder was similar to that published in the literature.5 1062
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J. Mater. Res., Vol. 12, No. 4, Apr 1997
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Powders of NiO, CuO, ZnO, and Fe2 O3 were mixed, dried, and then calcined at 800 ±C for 16 h. The calcined powders were ground by aqueous ball milling for 24 h and dried at 100 ±C for 24 h. Particle size distribution and specific surface area of the as-ground powders were de
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