Papers by Author: Babak Raissi

Abstract: 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.

Abstract: 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.

Abstract: : 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.

Abstract: 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.