Deep Electrophoretic Penetration and Deposition of Ceramic Particles inside Porous Substrates: I . Analytical Model

Abstract

The electrophoretic penetration of colloidal silica particles into a carbon-carbon porous substrate is investigated. The carbon substrate is immersed in a solution containing the particles and positioned between two electrodes. An electric potential gradient between the electrodes is used to drive the solute (silica particles) into the pores. Three driving mechanisms are identified: the hydrodynamic drag force exerted on the particles due to the electroosmotic flow of the solvent inside the pores, the electrophoretic force exerted on the particles, and the stochastic Brownian force due to thermal fluctuations of the solvent molecules. While subjected to these forces, the particles may reach the walls of the pore and the short range van der Waals forces may cause their capturing and deposition onto the walls. The objectives of this paper are to predict the penetration depth of a single ceramic particle moving inside a porous substrate under the effect of an electric potential gradient, to derive the nondimensional parameters characterizing the motion of the ceramic particles, and to gain a physical insight on the various mechanisms governing penetration. Qualitatively, the results are that penetration depths are governed by a favorable (if large) Peclet number and unfavorable (if large) Damk6hler number. Quantitative results are also provided.

Electrophoresis of a colloidal sphere in a circular cylindrical pore

“…In capillary electrophoresis, gels in the capillary column can minimize the particle diffusion, prevent the particle adsorption to the capillary walls, and eliminate electroosmosis, while serving as the anticonvective media (Ewing et al, 1989). Deep electrophoretic penetration and deposition of inert colloidal particles over the interstitial surfaces of porous composites has been suggested in the aerospace industry to protect the composites from burning or deterioration (Haber and Gal-Or, 1992). Other examples of electrophoresis with a bounded environment were given by Keh and Anderson (1985) and Zydney (1995).…”

Electrophoretic Deposition in Production of Ceramic Matrix Composites

“…Theoretical analysis of the influence of liquid media on penetration of particles into porous substrate (valid also for the voids between the fibres) was performed by Haber and Gal-Or [29]. They found that the penetration is enhanced at large values of Peclet number, Pe, which is a dimensionless parameter that in fluid dynamics determines the relative significance of the convective process vis-à-vis the diffusive process:…”

“…According to Haber and Gal-Or [29], electric field has a dual effect on the extent of particle penetration into fibre-preform. Due to increase of the particle velocity and Peclet number with field strength, penetration is enhanced.…”

Conformado de materiales cerámicos por electroforesis en medios acuosos

“…Tanto las suspensiones como las disoluciones de estos materiales se preparan por lo general en medio org ‡nico para no da-ar las propiedades intr'nsecas del material final. No obstante, ya fuera del campo de los supercondutores, Gal-Or y col. [70][71][72][73][74] han abierto una prometedora l'nea de investigaci-n sobre la deposici-n de Al 2 O 3 , ZrO 2 , ZrTiO 4 a partir de las disoluciones de los cationes correspondientes.…”