(362d) Evaluation And Characterization Of Pd-Based Membrane Fabricated By Surfactant Induced Electroless Plating
Deposition of Pd/Pd-alloy thin film on microporous ceramic and stainless steel substrates by electroless plating for fabricating H2-selective membrane for high temperature gas separations and membrane reactors have been studied extensively over the past two decades and continue to be studied in a laboratory scale. Initially, electroless plating route for thin film deposition promised significant advantages over other methods (e.g. Chemical Vapor Deposition, Physical Vapor Deposition, Radio Frequency Cathodic Sputtering, etc.), but there are technological issues that still need to be resolved. In the conventional electroless plating, oxidation-reduction reactions between Pd-complex and hydrazine (reducing agent) result in evolution of ammonia and nitrogen gas bubbles. When adhered to the substrate surface and in the pores, these gas bubbles hinder uniform Pd-film deposition. This is a major weakness of the conventional electroless plating bath recipe. Stirring or rotation of substrate during plating may lessen the problem but can not provide satisfactory resolution of the Pd-grains and subsequent agglomeration. To address the problem associated with the growing gas bubbles within the plating substrate vicinity, we explored the role of surface active agents with favorable structures in the electroless plating process. The surface morphology and compositional microstructures were examined using SEM (Scanning Electron Microscopy) coupled with in-situ EDS (Energy Dispersive Spectroscopy). Palladium deposition rate was measured by the weight gain as a function of time. The surfactants studied included Triton X-100 (non-ionic surfactant), dodecyltrimethyl-ammonium chloride (cationic surfactant) and sodium dodecyl-benzenesulfonate (anionic surfactant). The surfactant molecules play an important role in the plating process by removing tiny gas bubbles through adsorption at the gas-liquid interface. The water-soluble surfactants which have almost neutral HLB (hydrophilic-lipophilic balance) value are believed to have stronger capability of removing gas bubbles from the substrate surface. It was observed that addition of non-ionic surfactant increased the palladium deposition rate by about 20% with improved surface morphology and microstructures. These membranes were tested for H2-perm-selectivity using pure and mixed gases at elevated temperature. Some of these results will be presented in this paper.