Abstract
The palladium-silver alloy membrane has been extensively studied in recent years due to the of absence α→β phase transition and embrittlement associated with hydrogen permeation. In addition to the application for ultra high purity hydrogen separation, it is also widely utilized in recovery or purification of hydrogen in petroleum industry, hydrogen reactor in fuel cells, and methane stream reforming. In the present work, a porous stainless steel Mott-0.2 with 10∼30um surface pores was chosen as the substrate material. A palladium-silver alloy film was sputter deposited on the substrate as a separation membrane. Prior to deposition, the surface was filled with 1um Ag or Pd70Ag30 particles and then with nanocrystalline Pd70Ag30 particles to reduce the pore size, followed by deposition with a Pd70Ag30 alloy film. The crystal structure and chemical composition of the membrane was analyzed by X-ray diffraction (XRD).The morphologies of the modified surace and coated membrane were examined by scanning electron microscop (SEM). Besides, the permeation rate and separation factor of nitrogen and hydrogen were measured by a gas permeation apparatus. It is found from the SEM observation that without modification a dense and continuous film can not be obtained, but it can be achieved on the modified substrate with a thickness as low as 5um. The membrane is gas-tight in nitrogen gas under a pressure of 5kg/cm2. The hydrogen permeation flux through the membrane increases monotonically with pressure but deviates from the Sievert's law. With different thicknesses of membrane, it is found that hydrogen permeation through the membrane is controlled by an interface process.