Papers by Keyword: Hamaker

Abstract: 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.

Abstract: This study was triggered by our experience on electrophoretic deposition (EPD) with different suspension systems showing evidence of a particle concentration threshold, below which no deposit was formed. In this study, the role of particle concentration in the mechanism of EPD was investigated with a model system, consisting of isopropanol suspensions with TiO2 nanosized particles (d50 = 130 nm). The investigated concentration range was 0.01 - 0.4 vol% TiO2. Constant voltage EPD tests with variable particle concentration were performed for 1 min under different applied voltages (25 - 300 V corresponding to 62.5 - 750 V/cm). A longer deposition time (30 min) was tested for a lower concentration value (0.003 vol% TiO2). The deposition process was evaluated in situ by means of the current measured during EPD. The deposits obtained were characterized by weight and profile measurements and scanning electron microscope (SEM). The results confirmed the finding of a lower limit value of particle concentration, determining a threshold in the formation of an EPD coating. Above this threshold, proportionality between deposited mass and particle concentration was observed, in agreement with the equation of Hamaker. Below this threshold, the proportionality was lost with evidence of a lack of coating formation. A possible interpretation for this experimental finding was provided.