Babak Raissi

Electrophoretic Deposition of YSZ Electrolyte on Porous NiO-YSZ Substrate for Solid Oxide Fuel Cells

: In this study a thin dense YSZ film has been fabricated from stable non-aqueous suspensions by Electrophoretic Deposition (EPD) method on a porous pre-sintered NiO-YSZ substrate. Thin film of YSZ and NiO-YSZ composite were used as electrolyte and anode, respectively, in SOFCs that should have certain characteristics. Process parameters like porosity, pre-sintering temperature, voltage and time of deposition have been considered and optimized for obtaining a controlled thickness. After depositing a conductive layer, EPD has been performed on NiO-YSZ composites. These layers were sintered and a crack-free dense thin film of 8 mol % YSZ was obtained on porous NiO-YSZ anode. The interface and adhesion between the two layers was investigated by Scanning Electron Microscope and microstructural observations.

Deposition of Multiwall Carbon Nanotubes Using Low Frequency Alternating Electrophoretic Deposition

In this paper, electrophoretic deposition of multiwall carbon nanotubes (MWNTs) using low frequency (0.01-1000 Hz) AC electric fields, is reported. The effect of depositing parameters such as frequency and waveform on deposit yield is investigated. Results show that the deposit yield decreases with frequency. The rectangular waveform yields more deposit yield than sinusoidal and triangular waveforms. The deposition pattern is also different in AC and DC electric fields. This technique may be used for deposition of MWNTs thick films.

Aging Behavior of Yttria Stabilized Zirconia (YSZ) in Non Aqueous Suspensions for Electrophoretic Deposition Application

In this research aging behaviors of yttria stabilized zirconia (YSZ) in non aqueous suspensions, namely ethanol, isopropanol, n-propanol, acetylacetone and the mixture of ethanol-acetylacetone were investigated. For this purpose, electrical conductivity, electrophoretic mobility and suspension stability during aging time (6 to 7 days) were evaluated. Except for the ethanol-acetyl acetone mixture, each suspension contained 0 to 0.8 g/L iodine. It was revealed that, the alcoholic suspensions indicated lower conductivity in comparison with acetylacetone suspensions. However, acetylacetone suspension showed lower conductivity variation with time. Although iodine could improve the electrophoretic mobility of ethanol and acetylacetone suspensions, it had little effect on electrophoretic mobility of isopropanol and n-propanol suspensions. Also, it was indicated that iodine as a dispersant was not helpful for alcoholic suspensions stability. It was concluded that the mixture of acetylacetone-ethanol suspension was the best candidate in this study for electrophoretic deposition of YSZ, owing to its little behavior variation with the aging time, low conductivity and high electrophoretic mobility. High quality crack-free layers were electrophoretically deposited from this suspension on the substrate by applying 50 V/cm electrical field.

Fabrication of Solid Oxide Fuel Cells (SOFCs) Electrolytes by Electrophoretic Deposition (EPD) and Optimizing the Process

Fabrication of Solid Oxide Fuel Cells (SOFCs) electrolytes by Electrophoretic Deposition (EPD) was the target of our study. For such purpose, thin layers of Yttria Stabilized Zirconia (YSZ) were electrophoritically deposited on pre-sintered NiO-YSZ pellets. A thin graphite film on each pellet was painted to make it conductive and can act as a working electrode for EPD. In this research acetylacetone-ethanol mixture (1:1 by vol.) was selected as the solvent and by applying different electrical fields (25, 50, 75, 100V/cm) in different deposition times (6, 3, 2, 1.5 min respectively), the obtained layers were examined. It was revealed that although electrical field multiplied deposition time remained constant in our experiments, the thicknesses of the deposited films were increased with increasing the applied electrical field which could not be explained easily by the Hamaker equation. For the next step, sintering of the deposited layers which prepared by applying 75 V/cm electrical field during 2 minutes was investigated. It was found that although the sintering processes were activated at 1250oC, 2 hours soaking time was not enough to produce a non-permeable layer. On the contrary, the layer which sintered at 1400oC for 2 hours was dense and crack-free. The thickness of the obtained layer was about 7μm and this layer seemed to be suitable for electrolyte of SOFCs.

Comparison of wetting models and geometrical analysis in describing the effect of cavity number, size, and position on apparent contact angle

Abstract A critical subject of surface science is whether contact area or the triple-phase contact line (TPCL) directly affects the apparent contact angle (APCA). On this premise, effect of cavity size and position on APCA is studied. Cavities were created using a laser machining process. Optimal conditions for laser patterning were obtained via trial and error. It was impossible to deposit a droplet that could rest on all of the cavities for about 0.16 mm distance between the edge of the patterns and the drop’s perimeter. Neither Wenzel nor Cassie–Baxter models can fully explain the acquired data from static contact angle measurements. Revised Cassie–Baxter equation also fails, while a simple geometrical analysis based on Spherical Cap assumption shows a better agreement with the data as long as the cavities are sufficiently far from TPCL. Based on our results, we believe that theoretical analyses regarding wetting models are not in line with engineering aspects of wetting which should be focused on TPCL.

AC Electrophoresis, a New Technique for Deposition of Ceramic Nanoparticles; Introduction, Application and Mechanism

Deposition of ceramic nanoparticles (dispersed in non-aqueous suspension) on in-plane electrodes and under the influence of AC electric fields in the frequency range of 0.01 Hz - 10 kHz is investigated. Analysis of the particle response to the applied field is a difficult task due to the mutual effect of electric and hydrodynamic forces which are present in the system. In this work, however, we show the possibility of dividing the frequency range into four domains with four distinct governing mechanisms. Possible mechanisms are suggested and dominant forces are determined for each domain. In situ optical microscopy observations are used for visualization of nanoparticles´ movement dispersed in liquid medium. These observations show that applying AC electrophoresis at frequencies below 10 kHz is an effective way for manipulating ceramic nanoparticles and device fabrication.

DC-EPD of nanoceramic particles accelerated via anodic dissolution in organic media

Abstract This paper presents the fabrication of nanoceramic layers by electrophoretic deposition. Suspensions containing TiO2 nanoparticles were prepared in different organic solvents, such as ethanol, methanol, acetone, and acetylacetone. During electrophoretic deposition, the color of organic media at around 200 V cm−1 began to change. This phenomenon is related to the anodic dissolution, which may assist deposition processes in some cases. Deviation from Hamakers equation was observed upon measuring the deposited mass using different anode electrodes. Atomic absorption spectroscopy was used to measure concentrations of chemical elements liberated in the suspension due to the dissolution of anodes. These results show that anodic dissolution directly affects deposition rate. We observed this event even in the absence of powder and additives. Therefore, this is advantageous if anodic contaminants are not effective or influential.

MODELING OF THE SURFACE TENSION OF COLLOIDAL SUSPENSIONS

Surface tension is one of the fundamental properties of the colloids, which can be altered by concentration and size of colloidal particles. In the current work, modeling of the surface tension of suspension as it would be analyzed by maximum bubble pressure method has been performed. A new modified equation to correlate the surface tension with the bubble pressure is derived by applying fundamental thermodynamic relation considering the presence of particles in suspension and curvature of the interface between the particles and bubbles inside liquid. Moreover, the change of particles concentration in air–water interface due to capillary force is also considered. The predicted surface tension using the developed model has been verified by numerous experimental data with deviation less than 5% in most of cases. It was found that the calculated surface tension is altered by contact angle and particle radius as well as particle concentration. The obtained model may have potential application to predict the surface tension of colloidal suspension.