Settling Behavior of Alumina Dispersions and Resultant Green Body Characteristics: Solvent, Binder, and Dispersant Compe
- PDF / 482,001 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 102 Downloads / 200 Views
SETTLING BEHAVIOR OF ALUMINA DISPERSIONS AND RESULTANT GREEN BODY CHARACTERISTICS: SOLVENT, BINDER, AND DISPERSANT COMPETITION IN MODEL SYSTEMS Anthony A. Parker, Mei-Yuan Tsai, Girma Biresaw, Todd T. Stanzione, George H. Armstrong, Aluminum Company of America, Alcoa Center, PA 15069 Joseph J. Marcinko, University of Akron, Akron. Ohio 44325
ABSTRACT The chemical functionality of binders, dispersants, and solvents will influence competitive adsorption/desorption behavior on alumina powder, and hence will affect both slurry and ultimate green tape properties. Given that multiple competitive interactions are common to most dispersions, it is usually difficult to ascertain mechanisms from simple settling density experiments. However, this problem can be partially overcome with the choice of model systems that minimize the number of competitive processes. This criterion is met to a first approximation with a model system of toluene solvent, polystyrene binder, and a C8 aliphatic dispersant with an anchor group of variable functionality. Plateau adsorption concentrations from settling experiments in toluene 2 show that surface coverage for efficient dispersants is typically achieved at about 6l1moles/m . Less efficient dispersants adsorb at higher plateau concentrations, and are eventually displaced after repeated washing steps in toluene. The settling densities of dispersions prepared with C8 dispersants are consistently higher than densities achieved in toluene alone, and as seen in a case study with n-octylsilane, the settling densities are independent of the presence of polystyrene. Green bodies cast from a polystyrene/Al203 slurry also show increased densities in the presence of n-octylsilane dispersant. However, despite the apparent low levels of interaction between polystyrene and n-octylsilane in the dispersion state, solid state NMR and dynamic mechanical results show that the solid state molecular motional behavior of polystyrene is strongly affected by the presence of n-octylsilane dispersant. INTRODUCTION The settling behavior of ceramic slurries has often been used to provide some indication of dispersion stability (1). These experiments have also been used to give a relative measure of solvent affinity for inorganic powder surfaces through attempts to correlate sedimentation behavior with solvent dielectric and wetting properties (2). Slurries with well dispersed particles will produce well packed sediment and higher sediment densities. Thus, the existence of floc structures in the dispersion state will lead to a loosely packed sediment of low density (1). Because the packing of sediment is also influenced by particle density, shape, and size distribution (3), it is difficult to establish trends by comparing the settling behavior of different powders. Caution must also be used when comparing results with those in the literature since observed settling densities are sensitive to experimental details such as powder loading, and the aspect ratio of the container. Moreover, even when the powder type is kept c
Data Loading...
