| Tape Casting is a low cost process for making large-area, thin, flat ceramics, which traditionally utilizes organic solvents to allow fast drying.;Although water is of low cost, nonflammable and safe to the environment, its heat of vaporization is high, 540 kca/g, compared to that of toluene, 74 kca/g.;A high solids loading of above 50 vol% is an alternative approach to obtain sufficiently rapid drying for a thicker tape (up to 0.8 mm) since the water content is originally minimized. In order to obtain a high solids loading, the dispersants and binder systems were carefully tailored during the present research project. Low molecular weight polyelectrolytes, such as polyacrylic acid PAA (M.W. 1800) and citric acid, were found to be effective for high solids loading of Al;For the coarser powder, A-152SG, the dilatancy was a major problem that obstructed a further rise in solids loading. The dilatancy could be minimized by modifying the size distribution with A-152SG plus A-16SG and using a proper pH and amount of dispersants. An extremely high solids loading of 71-73 vol% could be reached in an aqueous system for the size-modified powder, before binder addition.;An emulsion binder ;Water-based tape casting of A1N was possible in a buffer solution. Polyacrylic acid, PAA (M.W. 1800), aided dispersion and also minimized hydrolysis of A1N in water. Poly(vinyl pyrrolidone), PVP (M.W. 160,000), gave a lower viscosity to suspension compared to poly(vinyl alcohol) and cellulose ether, and had less bubble formation. The suspension could be processed for more than 72 h without degradation. With optimization of dispersant and binder, a high solids loading formulation of 52 vol% could be obtained. When the organic components were burned out in the air, AlN with 3wt% Y... |
