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Al2O3 coatings on stainless steel porous supports as intermetallic diffusion barrier for H2 separative membranes

pubblicazioni - Articolo

Al2O3 coatings on stainless steel porous supports as intermetallic diffusion barrier for H2 separative membranes

The synthesis of thin, defect free, stable and with sufficient lifetime Pd-based membranes is still a challenging task. Thin layers of Pd having a thickness below 20 µm can be grown on a porous support using different techniques (e.g. electrochemical or electroless deposition).

Ceramic supports are commercially available in a variety of materials, pore structure and quality but unfortunately the assembly of the Pd-based ceramic membranes into modules is still a not solved problem due to their brittle nature and to the significant leakages from the seals, which lower the H 2 separation selectivity. Therefore a large attention is also devoted to porous metal supports (e.g. sintered porous stainless steel) which can be easily assembled into modules by welding. Although Pd-based layers can be grown directly on porous stainless steel (PSS) supports, at the high working temperatures the migration of elements from the support to the Pd-based layer (known as intermetallic diffusion) can take place decreasing H 2 permeability and membrane lifetime [1]. Moreover commercial PSS supports have still large nominal pore size and a high average rugosity which does not consent to deposit very thin (less than 10 µm) and defect-free Pd-based layers. The deposition of a non-metallic barrier between the support and the Pd layer would prevent the intermetallic diffusion phenomena and improve the support characteristics [2]. In this work the deposition of Al 2 O 3 coatings on PSS supports was carried out using the sol gel technique. The PSS supports were used as received from the manufacturer and after a mechanical treatment to reduce their average rugosity. PSS supports were dip-coated using boehmite sols containing organic additives (namely polyvinyl alcohol and glycerin). The composition and viscosity of the sols were investigated in order to obtain homogeneous and defect-free Al 2 O 3 layers. A further coating of Pd/Al 2 O 3 was deposited on the Al 2 O 3 coated PSS supports to create an activated layer where to grow the Pd layer through the electroless plating technique. The morphology and thickness of the deposited layers was investigated by SEM and the gas permeance at various stages of membrane synthesis was measured at both room (using He and N 2 ) and high temperature (with He and H 2 ).

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