Papers by Author: G. Falk

Abstract: Local electrophoretic deposition of alumina nanoparticles under external DC electric field conditions with submerged impinging jet type capillaries arranged at ion exchange membrane substrates is presented. In order to evaluate particle deposition mechanisms a mathematical model is derived describing electroosmotic pumping of electrolyte through a micrometre scaled channel. The system is governed by surficial charge discontinuities and modeled by coupled mass balances, Ohmic law, Navier Stokes, and Nernst-Planck equations. Based on the boundary conditions of bulk convective electrodiffusion the effect of the imposed surface potential on the fluid flow behaviour and on particle tracing characteristics is studied by means of numerical analysis. The following findings have been obtained. At the corner edges of the charged surficial boundaries micro-vortices are generated to build up local stagnation points onto the modeled membrane surface. Particle tracing analysis reveal that the particle movement is caused by mass transport within the membrane directed velocity field to the stagnation point. The complex electrokinetics and electrohydro-dynamics suggest further investigations at membrane pore sizes in the range of the Debye-length to model the non-linear current-voltage characteristic that has already been experimentally proven for these kind of membrane EPD systems.

Abstract: Processing of colloidal gels with electrified interfaces to form ceramic bulk and composite materials as well as coatings of complex shapes with well definded structures in the nanoscale requires the understanding of fundamental role of the coupling between hydrodynamic and electric interactions in colloidal deposition and colloidal arrangement. In this article, fundamental equations of electrohydrodynamics of membrane supported electrophoretic deposition (EPD) as well as exemplary numerical FEM-simulations of electrophoretically deposited colloidal gels are presented. Based on microfluidic physics a model is then used to study electrohydrodynamic EPD phenomena, especially electroosmotic flow incorporated with modulated surface potentials, particle interactions and electrostatic potentials. Some practical applications of EPD as well as visions of general purpose of the computational modelling results were given.

Abstract: In this paper results of electrophoretically activated processes for domestic wastewater treatment in lab and field scale experiments are presented. The principal mechanisms of non-membrane and membrane based electrokinetic solid liquid separation by electrophoresis are described. In the case of non-membrane based electrokinetic wastewater treatment a modular processing scheme is suggested in order to achieve economically and ecologically suitable processing conditions based on colloidal wastewater characteristics. In the case of membrane based electrokinetic waste water treatment an effective anti-membrane fouling process is designed controlled by colloidal characteristics of the wastewater, especially zetapotential, as well as external field parameters and microfiltration module geometries. The specific energy input of the membrane based and non-membrane based electrophoretic waste water treatment methodologies are compared and future perspectives of electrokinetic activated waste water purification processes are proposed.

Abstract: Sub-micrometer scaled CGO (Ce0,9Gd0,1O1,95) powder is used in order to manufacture Ni/CGO functionally graded green bodies with high green densities. Thereby the near-shape manufacturing of Ni/CGO cermets by gel casting of CGO and Ni powder mixtures and electrophoretic impregnation of sub-micro scaled ceria doped particles into a Ni/CGO mesoporous matrix is described. Solids content of dispersed suspensions is varied as well as the mixing ratio of sub-micro sized and micro sized particles. The influence on green density and sintering behavior is investigated in order to achieve maximum CGO densities in combination with maximum ionic conductivity for potential use in SOFC. Shrinkage rates from sintering experiments with constant rates of heating (CRH) are analyzed to determine most suitable co-sintering conditions of Ni-Ni/CGO composite anode materials.