F.C. Gielens

Fabrication and characterization of dual sputtered Pd-Cu alloy films for hydrogen separation membranes

this paper, submicron thin Pd–Cu alloy films are deposited using a dual sputtering technique, which allows a high composition control of the layer. The composition, surface morphology and phase structure of the sputtered layers are investigated by energy-dispersive spectrometry (EDS), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffractiometry (XRD). For example, the XRD data prove that the Pd–Cu layers are an alloy of Pd and Cu. Subsequently, the characterized Pd–Cu alloy layers are deposited on a silicon support structure to create a 750-nm thin Pd–Cu membrane for hydrogen separation. The reported membrane obtained a high flux of 1.6 mol H2/m2 s at a temperature of 725 K, while the selectivity is at least 500 for H2/He.

Microfabrication of palladium-silver alloy membranes for hydrogen separation

In this paper, a process for the microfabrication of a wafer-scale palladium-silver alloy membrane (Pd-Ag) is presented. Pd-Ag alloy films containing 23 wt% Ag were prepared by co-sputtering from pure Pd and Ag targets. The films were deposited on the unetched side of a -oriented silicon wafer in which deep grooves were etched in a concentrated KOH solution, leaving silicon membranes with a thickness of ca. 50 /spl mu/m. After alloy deposition, the silicon membranes were removed by etching, leaving Pd-Ag membranes. Anodic bonding of thick glass plates (containing powder blasted flow channels) to both sides of the silicon substrate was used to package the membranes and create a robust module. The hydrogen permeability of the Pd-Ag membranes was determined to be typically 0.5 mol H/sub 2//m/sup 2//spl middot/s with a minimal selectivity of 550 for H/sub 2/ with respect to He. The mechanical strength of the membrane was found to be adequate, pressures of up to 4 bars at room temperature did not break the membrane. The results indicate that the membranes are suitable for application in hydrogen purification or in dehydrogenation reactors. The presented fabrication method allows the development of a module for industrial applications that consists of a stack of a large number of glass/membrane plates.

Microsieve supporting palladium-silver alloy membrane and application to hydrogen separation

A submicron thick and defect-free palladium-silver (Pd-Ag) alloy membrane is fabricated on a supporting microsieve by using microfabrication techniques. The microfabrication process also creates a robust wafer-scale membrane module, which can easily be inserted into a membrane holder to have gas-tight connections to the outer world. The microfabricated membrane demonstrated high separation fluxes of up to 4 mol H/sub 2//m/sup 2//spl middot/s with a minimal selectivity of 1500 for hydrogen over helium (H/sub 2//He) at 450/spl deg/C and 83 kPa H/sub 2/ retentate pressure. The present membrane has great potential for hydrogen purification and in applications like dehydrogenation chemistry. In addition, the presented technology can be used to fabricate other kinds of ultrathin but strong and defect-free membranes to set up new applications.

High-flux palladium-silver alloy membranes fabricated by microsystem technology

In this study, hydrogen selective membranes have been fabricated using microsystem technology. A 750 nm dense layer of Pd (77 wt%) and Ag (23 wt%) is deposited on a non-porous 1 mm thick silicon nitride layer by cosputtering of a Pd and a Ag target. After sputtering, openings of 5 μm are made in the silicon nitride layer to create a clear passage to the Pd/Ag surface. As a result of the production method, these membranes are pinhole free and have a low resistance to mass transfer in the gas phase, as virtually no support layer is present. The membranes have been tested in a gas permeation system to determine the hydrogen permeability as a function of temperature, gas flow rate, and feed composition. In addition, the hydrogen selectivity over helium has been determined, which appears to be above 1500. At 0.2 bar partial hydrogen pressure in the feed, the hydrogen permeability of the membranes has been found to range from 0.02 to 0.95 mol.H2/m2×s at 350 and 450°C, respectively. It is expected that by improving the hydrodynamics and increasing the operation temperature, substantially higher fluxes will be attainable.

A hydrogen separation module based on wafer-scale micromachined palladium-silver alloy membranes

A thin but strong and defect free palladium-silver (Pd-Ag) alloy membrane is fabricated with a sequence of well-known thin film and micromachining techniques. A microfabrication process also creates a robust wafer-scale membrane module, which is easy to be integrated into a membrane holder to have gastight connections to the outer world. The microfabricated membranes have been tested to determine the mechanical strength, hydrogen permeability and hydrogen selectivity. The membranes have high mechanical strength and can withstand pressures up to 3 bars at room temperature. High flow rates of up to 3.6 mol H/sub 2//m/sup 2/.s have been measured with a minimal selectivity of 1500 for H/sub 2//He. The membranes survived operation at 450/spl deg/C, which is a temperature relevant for practical application in industry, for more than 1000 hours.

Fabrication and characterization of MEMS based wafer-scale palladium-silver alloy membranes for hydrogen separation and hydrogenation/dehydrogenation reactions

In this paper, a MEMS based wafer-scale palladium-silver alloy membrane (MWSPdAgM) is presented. This membrane has the potential to be used for hydrogen purification and other applications. A palladium-silver alloy layer (Pd-Ag) was prepared by co-sputtering. The thin Pd-Ag alloy has high hydrogen selectivity, high permeation rate as well as high mechanical and chemical stability. Typical flow rates of 0.5 mol H/sub 2//m/sup 2/.s have been measured with a minimal selectivity of 550 for H/sub 2//N/sub 2/. Anodic bonding of thick glass to silicon was used to package the membrane and create a very robust module. The membrane has high mechanical strength and can withstand pressures up to 4 bars at room temperature. The presented fabrication method allows the development of a module for industrial applications that consists of a stack with a large number of glass/membrane plates.