James S. Reed

The packing density of binary powder mixtures

Abstract The maximum particle packing density in a binary powder system can be predicted by the Furnas model. The packing density is lower when the size ratio of coarse particles to fine particles decreases, and is also governed by the volume fraction of coarse or fine particles. Here an empirical equation is derived which describes the packing density as a function of the initial packing efficiencies of particles, the particle size ratio, and the volume fraction variations of the system.

Infrared spectral investigation of polyacrylate adsorption on alumina

Diffuse reflectance infrared Fourier transform spectroscopy was used to investigate the structural nature of polyacrylates adsorbed on alumina from aqueous solution. The presence of sodium bicarbonate or sodium ions on the alumina surface could inhibit the carboxylate groups on the polymer chains from forming covalent bonds with aluminium ions on the surface. More carboxylate groups of the chains were adsorbed on surface sites at lower polymer concentration and higher pH. Also, an increased loop formation of the polyacrylate chains occurred with a decrease in treatment of pH and an increase in polymer concentration. When the pH changed from higher to lower values in steps, the adsorbed polymer did not increase as much from the stretched-out form to the coiled form as was noted if one initially only treated the aqueous polyacrylate/alumina slurry at the lower pH. The adsorption of water on the polyacrylate-treated surface changed the ratio between covalently and ionically bonded carboxylate groups, causing more ionically bonded species.

Affect of grinding and polishing on near-surface phase transformations in zirconia

Abstract The transformation of near-surface material on grinding and polishing has been investigated in sintered zirconia of 1 μm grain size and 99 % density containing 4.5 and 7.0 mol % Y 2 O 3 . Rough wet and dry grinding transformed ca 20 % cubic phase into 18 % tetragonal and 2 % monoclinic in material initially 47 % cubic and 53 % tetragonal (4.5 mol % Y 2 O 3 ) but no change of phase in material that was fully cubic (7.0 mol % Y 2 O 3 ). Annealing and polishing reduced lattice strain but only polishing reduced the concentration of monoclinic and tetragonal phases. Microhardness studies indicated that lattice strain and the phase transformations increased the penetration hardness to a depth of ca 4 μm.

Binder coagulation casting of ferroelectric components

Abstract Binder coagulation casting (BCC) is a novel method for near-net shape forming of ferroelectric components with complex geometry or intricate surface features. The process uses low concentrations of nontoxic polymeric binders in an aqueous system to form a low-viscosity slurry, which can be cast in a nonporous mold and coagulated under controlled conditions. This paper highlights an application of BCC technique in prototype manufacturing of a PZT piezoelectric actuator.

Incipient flocculation molding: A new ceramic forming technique

Abstract Incipient Flocculation Molding (IFM) is a new and low-cost net-shape forming technique for ceramic components. Unlike other ceramic forming processes, the slurry has a very low viscosity, which facilitates molding very intricate features. IFM utilizes a concentrated, non-aqueous, sterically stabilized ceramic colloidal suspension that is injected into a nonporous mold at a very low pressure. As the temperature of the suspension is lowered below the theta-point of the stabilizer-solvent system, it is destabilized, resulting in flocculation of the slurry to a solid mass. The flocculation process is both rapid and reversible. IFM operates essentially as a temperature-dependent deflocculant. IFM is ideal for molding ferroelectric ceramics, particularly PZT powders, for manufacturing actuators having complex and intricate features. This is accomplished by dispersing the powders in a solvent, stabilized by grafted polyethylene glycol (PEG), and injecting into a mold. The solvent is removed by vacuum ev...