The consolidation behavior of flocculated alumina suspensions has been analyzed as a function of the interparticle energy. Consolidation was performed by a centrifugal force field or by gravity, and both the time-dependent and equilibrium density profiles were measured by a gamma-ray absorption technique. The interparticle energy at contact was controlled by adsorbing fatty acids of varying molecular weight at the alumina/decalin interface. We found that strongly attractive interactions result in a particle network which resists consolidation and shows compressible behavior over a large stress range. The most weakly flocculated suspension showed an essentially incompressible, homogeneous density profile after consolidation at different centrifugal speeds. We also found a significant variation in the maximum volume fraction, phi(m), obtained, with phi(m) almost-equal-to 0.54 for the most strongly flocculated suspension to phi(m) almost-equal-to 0.63 for the most weakly flocculated suspension. The compressive yield stresses show a behavior which can be fitted to a modified power law. In this paper, we discuss possible correlations between the fitting parameters and physical properties of the flocculated suspensions.
The high surface charge of small ceramic particles such as alumina particles prevents them from dispersing evenly in aqueous suspensions and forming high-density compacts. However, suspensions of 400-nm-diameter alumina particles treated with alginate from the bacterium Azotobacter vinelandii were well dispersed. The alginate bound firmly to the particle surface and could not be removed by repeated washing with distilled water (2.82 mg of the bacterial alginate adsorbed to 1 g of the alumina particles). Furthermore, A. vinelandii grew and produced alginate in the presence of up to 15% (vol/vol) alumina particles. These results suggest that an in situ process using this bacterium to coat ceramic particles with alginate might be developed. In in situ processing experiments, the particle-packing densities were significantly increased and the viscosities of 5 and 10% (vol/vol) suspensions were reduced 4- and 60-fold, respectively, over those of controls. The bacteria were readily removed from the alumina particles by washing.
The process comprises forming a consolidated ceramic, e.g., green compact of Al2O3 powder, impregnating the greenware with an inorg. polymer, e.g., polyaluminoxane having general formula [-M(R)n-X(R1)p-]m, (M = trivalent or tetravalent inorg. ion; when M = trivalent, n = 1, when M = tetravalent, n = 2; X is O-2, S-2, or N-3; when X = O-2 or S-2, p = 0; when X is N-3, p = 1; R, R1 = alkyl, alkoxy, acyloxy, Ph, or phenoxy group contg. a chain of ≥3 C atoms; and m = 5-1000) and sintering the greenware, preferably at 1000-1400°. The ceramics are useful for the electronics industry. [on SciFinder(R)]