Particle size effects on colloidal processing of oxide powders

Abstract

Rheological behavior, properties of colloidal solids consolidated by filtration, and their structure change during drying were studied with aqueous suspensions of a mullite powder of nanometer size and two kinds of alumina powders of submicrometer sizes. The rheological properties of non-Newtonian flow suspensions were analyzed by a power law equation of S = Ky n , where S is the shear stress, y the shear rate, and K and n (0 ^ n ^ 1) constants. The critical solids content (V c ) at n = 0 (indicating colloidal solids) depended greatly on the zeta potential of particles in suspensions, and dominated the densities of dried green compacts (V s ) of submicrometer sized powders. In a nanometer sized powder, the densities of dried green compacts were dependent on both V c value and the solid contents of suspensions. Phase diagrams of one-component colloidal systems were constructed by plotting the V c and V g values against the zeta potential of particles. These phase diagrams indicate that the colloidal solids range (surrounded by V c and a minimum V g lines) is narrow for nanometer sized powder and wide for submicrometer sized powder. The solids content range of dried green compacts was very narrow for submicrometer sized powder but relatively wide for nanometer sized powder due to the low flexibility of colloidal structure during drying.

Textured Development of Feeble Magnetic Ceramics by Colloidal Processing Under High Magnetic Field

“…21(a). Such a weak alignment of the whisker is usually observed 57) because the energy of gravity is predominant in the dispersed system when the particle size exceeds 0.1 mm 58) as is the case of the present experiment. It is also seen that the in tensities of both the top and the side of the samples consolidat ed as B // the fluid flow, is similar to those without a magnetic field (Fig.…”

ζ Potential of Nanoparticle Suspensions: Effect of Electrolyte Concentration, Particle Size, and Volume Fraction

“…For these small particles, the influence of electrolyte content is significant because of the much higher particle concentration in the suspensions for the Acoustosizer than for the Zetasizer. The ζ potential results and IEP values of AKP‐50 α‐alumina are consistent with data previously reported using the Acoustosizer 4,13,15,16,26 and using electrophoresis instruments 27,28 …”

“…The z potential results and IEP values of AKP-50 a-alumina are consistent with data previously reported using the Acoustosizer 4,13,15,16,26 and using electrophoresis instruments. 27,28 The difference in the magnitude of the z potentials as determined by the electroacoustic and electrophoresis techniques for the larger particles, where the electrolyte concentration in suspensions for both ESA and LDE are fairly low arises from the methods of determining the z potentials from the mobilities. The LDE mobility was converted into z potentials using Henry's approximation, while the ESA mobility data were converted into z potential using the relation developed by O'Brien.…”

Fabrication of Highly Microstructure Controlled Ceramics by Novel Colloidal Processing

“…I then introduce the fabrication of dense nano-sized zirconia by the following methods without pressure sintering; 1 direct pressure filtration of zirconia sols without the powdering step and low-temperature sintering, 5 2 pressure filtration of Cu modified zirconia suspension and liquid-phase sintering 6,7 3 slip casting using nano-sized zirconia particles and their composites, and lowtemperature sintering. [8][9][10] Next, I demonstrate the fabrication of porous ceramics with a controlled pore size by the hetero-coagulated suspension of ceramics and polymer.…”