Pd Thickness Research Articles

A highly permeable hollow fibre substrate for Pd/Al2O3 composite membranes in hydrogen permeation

In this study, a highly permeable ceramic hollow fibre substrate has been fabricated for developing Pd composite membranes. The substrate consists of one thin outer sponge-like layer for depositing Pd membranes by electroless plating and a plurality of self-organized micro-channels for reducing gas permeation resistance. A dense defect-free Pd membrane with approximately 1 μm was formed on the outer surface of the sponge-like layer, which suggests a great uniformity of the substrate. As a result, a hydrogen permeation flux of 0.87 mol s−1 m−2 can be achieved at 450 °C and 165 KPa. Hydrogen permeation of the several composite membranes with different Pd thicknesses (1.0 and 3.3 μm) and different substrates sintered at different temperatures (1300 and 1400 °C) was also investigated. It was found that an intermediate layer, which is normally formed due to the Pd penetration during the electroless plating, shows an adverse effect in hydrogen permeation, especially when the Pd membrane is very thin.

Hydrogen production in a Pore-Plated Pd-membrane reactor: Experimental analysis and model validation for the Water Gas Shift reaction

A laboratory reactor equipped with a Pd-composite membrane prepared by ELP “pore-plating” method (Pd thickness of 10.2 μm) has been used for performing the water gas shift reaction (WGSR). Reaction experiments were carried out with and without the membrane at different operating conditions: H2O/CO ratio (1–3), temperature (350–400 °C) and GHSV (4000–5500 h−1). In all cases, CO conversion was found to be higher when using the membrane to separate hydrogen. The membrane maintained the integrity with complete selectivity to H2. The membrane reactor has been modelled using a 2D mathematical model, capable of modelling the non-ideal flow pattern formed in this type of reactors. The model predicts the experimental CO conversion with an accuracy of ±10%. The proposed model was used as a tool in the scale-up of a membrane reactor for the water–gas-shift reaction (feed: 100 m3/h synthesis gas), designed to achieve high CO conversion (>99%) and hydrogen recovery (>99.5%). The permeation of hydrogen through the membrane was found to be ruled by mass transfer in the membrane support and palladium layer.

Evaluation of Pd composite membrane for pre-combustion CO2 capture

Carbon capture with hydrogen-selective Pd membranes can be realized as highly integrated process and CO2 can be separated at high pressure without employing environmentally harmful sorption agents. This study investigates the technical viability of using ultrathin Pd/ceramic composite membranes with innovative ceramic-to-metal connections under conditions that are practically interesting for natural gas-fired power stations, i.e. high feed and permeate pressures and high H2 recovery at elevated temperature. The 90% CO2 capture target was well exceeded during a 150 day test in water gas-shifted reformate at 673K. After system stabilization 98% carbon were held back by the membrane while 98% H2 were separated at nominally 99.5% H2 purity. Special attention has been paid to long-term operation effects on the 2–4μm thick Pd layer. These include the development of a striking, cavernous Pd morphology which increases mechanical stability of the composite membrane, a somewhat reduced but steady H2 permeability, and the disappearance of most membrane defects. The latter is attributed to carbon deposits as exit flow analyses point to CO2 reduction preserving effectively membrane selectivity. Altogether, carbon capture with supported Pd membranes projects as feasible from a technological vantage point.

Effect of Pd(P) thickness on the soldering reaction between Sn–3Ag–0.5Cu alloy and ultrathin-Ni(P)-type Au/Pd(P)/Ni(P)/Cu metallization pad

The strong effect of the Pd(P) thickness (δPd(P)) on the interfacial reaction between Sn–3Ag–0.5Cu solder and ultrathin-Ni(P)-type Au/Pd(P)/Ni(P)/Cu pad was revealed. We observed that the P of the Pd(P) film would redeposit over the Ni(P) platings and formed layered Ni2SnP in the early stage of soldering reaction. An excessive growth of Ni2SnP inhibited the formation of layered (Cu,Ni)6Sn5, which is argued to be an effective diffusion barrier of Ni. Thus, an extremely fast depletion of the Ni(P) film accompanied by a substantial dissolution of the Cu pad might be induced for large δPd(P). These observations demonstrated that δPd(P) plays a dominant role in determining the interfacial microstructure of solder joints and that a precise control on the δPd(P) value is required for microelectronic packaging reliability.

Interfacial Reaction and Mechanical Characterization of Sn–Ag–Cu/Au/Pd(P)/Cu Solder Joints: Thick Pd(P) Deposition

The solderability of an Au/Pd(P)/Cu trilayer structure (thickness 0.15 μm/0.6–1.0 μm/20 μm) was investigated by use of a scanning electron microscope equipped with an electron backscatter diffraction system, electron probe microanalysis, and high-speed ball shear (HSBS) testing. Thick Pd(P) deposition, particularly the structure with a Pd(P) thickness of 1.0 μm, resulted in a substantial amount of (Pd,Cu)Sn4 intermetallic compound in the solder matrix after reflow. This phase gradually resettled at the interface and formed a dense layer of (Pd,Cu)Sn4 over (Cu,Pd)6Sn5 during solid-state reaction. A Cu–Pd–Sn isotherm was examined to explain the formation and resettlement of (Pd,Cu)Sn4. The (Pd,Cu)Sn4/(Cu,Pd)6Sn5 dual layer at the interface was a crack initiation site in HSBS testing, and led to substantial degradation of the mechanical strength of solder joints, indicating that thick Pd(P) deposition should be avoided to prevent the Pd-induced embrittlement.

Dependence of the large coercivity on Pd thickness in CoSiB/Pd multilayer films

The magnetic properties of CoSiB/Pd multilayers were prepared by a DC sputtering system have been investigated using a vibrating sample magnetometer. We investigated the magnetic properties of CoSiB/Pd multilayers for various CoSiB thicknesses in a previous article. Based on those data, the CoSiB thickness was kept constant at 7 A while the Pd thickness was varied from 11 to 24 A. The largest value of the coercivity obtained as ~237 Oe for tPd = 13 A, and the smallest value of the saturation magnetization obtained was ~594 emu/cc for tPd = 24 A. With increasing Pd thickness, the coercivity increased and the saturation magnetization decreased. When tPd = 24 A, the hysteresis loop showed a step-shape.

Oxidation of palladium on Au(111) and ZnO(0001) supports.

The oxidation behavior of supported Pd-deposits on Au(111) and ZnO(0001) single crystals has been studied by x-ray photoemission spectroscopy (XPS). Oxidation has been carried out ex situ in a high-pressure cell and subsequent vacuum-transfer and characterization by ultra-high vacuum XPS, as well as in situ characterization by synchrotron based near ambient pressure XPS. On Au(111) alloying of Pd with the substrate competes with oxidation and only for sufficiently thick Pd films oxidation is obtained. For Pd deposits on ZnO the oxidation condition depends on the amount of deposited Pd. Thicker Pd-deposits behave similar to bulk Pd-samples, while for thinner films the oxidation temperatures may be lowered. Interestingly, for very small amounts of Pd, in situ XPS shows full oxidation at room temperature and at less than 0.6 mbar O2 pressure. This indicates lowering of the kinetic barriers for oxidation of very small supported Pd-clusters. The formed oxide is, however, not stable in ultra high vacuum and a slow reduction is observed. The instability of this oxide in UHV indicates that the formed Pd-oxide at the interface to ZnO may have different chemical properties compared to bulk PdO or surface oxides on Pd.

Effect of Au and Ru in Au@Pd and Ru@Pd Core@Shell Nanoparticles for Direct Formic Acid Fuel Cells

The study of Pd-based core@shell bimetallic catalysts with Pd as the shell and another transition metal as the core has generated great interest in the field of PEM fuel cells because their electronic and chemical properties are completely different from pure Pd. As the anode catalyst in direct formic acid fuel cells (DFAFCs), an enhanced activity has been obtained for these Pd-based core@shell nanoparticles compare to pure Pd for formic acid oxidation [1,2]. However, there is a lack of understanding of how these added transition metals interact with Pd, namely by influencing their electronic structure and chemical property toward electrochemical oxidation of formic acid. It is important to fill this knowledge gap and find out a trend between the effect of the transition metals and the activity. This will help developing more efficient and less cost DFAFCs.In this study, Au@Pd and Ru@Pd core@shell nanoparticles with same thickness of Pd are synthesized via a two-step process. Non-supported nanoparticles are used for TEM and X-ray photoelectron spectroscopy (XPS) analysis. TEM is used to characterize the structure and morphology of the nanoparticles. XPS is used to differentiate the chemical shifts due to charge transfer between Pd and Au (or Ru). XPS analysis shows a different binding energy shift for Pd peak of Au@Pd and Ru@Pd compare to that of pure Pd nanoparticles. In addition, a change of the XPS valence band shape and down-shift of the d-band center are also observed. This different binding energy shift indicates that Au and Ru core interact with Pd shell and significantly influence the electronic structure of Pd. Electrochemical measurements (cyclic voltammetry and chronoamperometry) are used to investigate the electrochemical activity of carbon supported Au@Pd and Ru@Pd core@shell nanoparticles toward formic acid oxidation. The Pd loading of the carbon supported samples is 40wt%. Based on CV results shown in Figure 1, Au@Pd shows the best activity toward formic acid oxidation, which is about twice higher than that of Pd/C. The relationship between the electronic perturbation and electrochemical activity will be elucidated in this paper. Furthermore, a real direct formic acid fuel cell test will be also operated with these Au@Pd and Ru@Pd core@shell nanoparticles under the various fuel cell operating conditions.

Perspectives of suspension plasma spraying of palladium nanoparticles for preparation of thin palladium composite membranes

Suspension plasma spraying (SPS) of Pd nanoparticles was evaluated as a new method for coating of dense Pd films for H2 separation on porous substrates. The substrates were prepared by coating porous sinter metal disks with a porous yttria stabilized zirconia (YSZ) layer acting as a barrier against intermetallic diffusion between the sinter metal and the Pd membrane (diffusion barrier layer, DBL). Before applying the Pd coating, the sinter metal substrates were characterized by N2 permeance measurements. The maximum pore sizes before and after coating of the DBL were determined. For SPS of Pd, particles with diameters in the range between 250nm and 550nm were suspended in ethyl cellulose containing diethylene glycol monobutyl ether solution. A wide process parameter field was tested in the SPS. After Pd coating, the membrane morphology was characterized with scanning electron microscopy (SEM) and electron probe microanalysis (EPMA), and the membrane performance was evaluated with N2 and H2 permeation measurements. The thickest Pd layer (9.5µm) showed an ideal H2/N2 permselectivity of 60 at 350°C and a H2 permeability of 1.2×10−7exp(−1392/T) molm−1s−1Pa−0.5. Yet rather thick Pd layers of around 10µm were required to close the pores of the rough YSZ layers, but with further optimizations, SPS appears to be a promising new way for the fabrication of robust Pd coatings on porous substrates. A particular advantage is seen in the very quick deposition.

Influence on optical properties and switching durability by introducing Ta intermediate layer in Mg–Y switchable mirrors

Magnesium–yttrium alloy switchable mirrors capped with a Pd layer with a thickness of 7.5nm have been shown to have a high switching durability of over 10,000 cycles between reflective and transparent states. However, the durability decreased considerably when the Pd thickness was decreased to improve the transmittance in the transparent state. Switchable mirrors with a thin Ta intermediate layer inserted between Mg–Y alloy layer and thinner Pd layers were then prepared by a direct-current magnetron sputtering method, and the optical switching durability was studied. Such a mirror capped by a Pd layer with a thickness of 3nm had a high switching durability of over 10,000 cycles, although a mirror without the Ta intermediate layer capped by a Pd layer with the same thickness never changed from the reflective to the transparent state. Owing to the decrease of the Pd thickness from 7.5 to 3nm, the visible transmittance in the transparent state increased, respectively, from 32% to 44% with high switching durability. The results of X-ray photoemission spectroscopy and transmission electron microscopy showed that the inserted Ta layer fully inhibits alloying between the Pd and Mg–Y layers, and that the Pd existed at the surface region and scarcely diffused into the Ta and Mg–Y layers even after switching of 10,000 cycles. Because alloying is one of the main reasons for the reduction in durability with decreasing Pd thickness, the prevention of alloying is expected to cause high switching durability.

H2 production via water gas shift in a composite Pd membrane reactor prepared by the pore-plating method

In this work, H2 production via catalytic water gas shift reaction in a composite Pd membrane reactor prepared by the ELP “pore-plating” method has been carried out. A completely dense membrane with a Pd thickness of about 10.2 μm over oxidized porous stainless steel support has been prepared. Firstly, permeation measurements with pure gases (H2 and N2) and mixtures (H2 with N2, CO or CO2) at four different temperatures (ranging from 350 to 450 °C) and trans-membrane pressure differences up to 2.5 bar have been carried out. The hydrogen permeance when feeding pure hydrogen is within the range 2.68–3.96·10−4 mol m−2 s−1 Pa−0.5, while it decreases until 0.66–1.35·10−4 mol m−2 s−1 Pa−0.5 for gas mixtures. Furthermore, the membrane has been also tested in a WGS membrane reactor packed with a commercial oxide Fe–Cr catalyst by using a typical methane reformer outlet (dry basis: 70%H2–18%CO–12%CO2) and a stoichiometric H2O/CO ratio. The performance of the reactor was evaluated in terms of CO conversion at different temperatures (ranging from 350 °C to 400 °C) and trans-membrane pressures (from 2.0 to 3.0 bar), at fixed gas hourly space velocity (GHSV) of 5000 h−1. At these conditions, the membrane maintained its integrity and the membrane reactor was able to achieve up to the 59% of CO conversion as compared with 32% of CO conversion reached with conventional packed-bed reactor at the same operating conditions.

The spin Hall angle and spin diffusion length of Pd measured by spin pumping and microwave photoresistance

We present the experimental study of the spin Hall angle (SHA) and spin diffusion length of Pd with the spin pumping and microwave photoresistance effects. The Py/Pd bilayer stripes are excited with an out-of-plane microwave magnetic field. The pure spin current is thus pumped and transforms into charge current via the inverse spin Hall effect (ISHE) in Pd layer, yielding an ISHE voltage. The ISHE voltage can be distinguished from the unwanted signal caused by the anisotropic magnetoresistance according to their different symmetries. Together with Pd thickness dependent measurements of in and out-of-plane precessing angles and effective spin mixing conductance, the SHA and spin-diffusion length of Pd are quantified as 0.0056 ± 0.0007 and 7.3 ± 0.7 nm, respectively.

Sol–gel synthesis of thin alumina layers on porous stainless steel supports for high temperature palladium membranes

The synthesis of thin, defect-free and long lifetime Pd-based membranes for H2 separation is still a challenging task. A porous support is necessary in order to give mechanical stability to very thin layers. Sintered porous metal supports are very promising candidates having numerous advantages over the widely studied ceramic supports. The deposition of a non-metallic barrier between the stainless steel support and the Pd dense layer can prevent the intermetallic diffusion of elements from the support to the Pd-based layer and improve the characteristics (e.g. pore size, topography) of the support surface which actually limits the minimum Pd thickness required in order to obtain high selectivity membranes.In the present paper, the deposition of intermetallic barrier layers made of alumina obtained via sol gel technique was investigated using commercial porous stainless steel supports, both with their original roughness and after a mechanical smoothing treatment. The quality of the deposited alumina layer was related to the surface characteristics of the supports, sol composition (aluminium and additive content) and viscosity. Pd dense layers were grown via electroless plating technique on the alumina barrier by activation with an additional Pd doped thin alumina layer.

Evaluation of mechanical properties of low-Ag ball grid array solder joints using a high-speed ball shear test

Solder joints of Sn–1.0Ag and Sn–1.0Ag–0.1Ce on electroless nickel/electroless palladium/immersion gold (ENEPIG) were studied and mechanically evaluated using a high-speed shear test. The effect of Pd thickness in ENEPIG on the reliability of solder joints was evaluated after multiple reflows. Microstructural observations of the solder joint interfaces and fractures after shear tests are shown. For comparison, conventional SAC305 Pb-free solder was also mechanically evaluated under the same conditions. By adding a thin Pd layer in ENEPIG surface finish, the intermetallic compound (IMC) layer’s morphology of SAC305 change from needle type (as Pd thickness=0μm) to scallop type (as Pd thickness=0.1μm). While the intermetallic compounds (IMCs) layer’s morphology of 1.0Ag solders change from facet type (as Pd thickness=0μm) to needle type (as Pd thickness=0.1μm). ENEPIG with thicker Pd layers was suitable for 1.0Ag solders during high speed shear test whereas conventional SAC305 showed the highest shear strength with an ENIG surface finish.

Thermal stability and effect of typical water gas shift reactant composition on H2 permeability through a Pd-YSZ-PSS composite membrane

This work comprises a study of hydrogen separation with a composite Pd-YSZ-PSS membrane from mixtures of H2, N2, CO and CO2, typical of a water gas shift reactor. The Pd layer is extended over a tubular porous stainless steel support (PSS) with an intermediate layer of yttria-stabilized-zirconia (YSZ). YSZ and Pd layers were incorporated over the PSS using Atmospheric Plasma Spraying and Electroless Plating techniques, respectively. The Pd and YSZ thickness values are 13.8 and 100 μm, respectively, and the Pd layer is fully dense. Permeation measurements with pure, binary and ternary gases at different temperatures (350–450 °C), trans-membrane pressures (0–2.5 bar) and gas composition have been carried out. Moreover, thermal stability of the membrane was also checked by repeating permeation measurements after several cycles of heating and cooling the system. Membrane hydrogen permeances were calculated using Sieverts' law, obtaining values in the range of 4·10−5–4·10−4 mol m−2 s−1 Pa−0.5. The activation energy of the permeance was also calculated using Arrhenius' equation, obtaining a value of 16.4 kJ/mol. In spite of hydrogen selectivity being 100% for all experiments, the hydrogen permeability was affected by the composition of feed gas. Thus, a significant depletion in H2 permeate flux was observed when other gases were in the mixture, especially CO, being also more or less significant depending on gas composition.

Effect of Pd thickness on wettability and interfacial reaction of Sn-1.0Ag-Ce solders on ENEPIG surface finish

The wetting balance test was used to study the wettability of Sn-1.0Ag-Ce (Ce content = 0, 0.1, 0.3, and 0.5 wt%) solder alloys on electroless nickel/electroless palladium/immersion gold (ENEPIG) surface finishes with Pd thicknesses of 0, 0.05, 0.1, and 0.15 μm. Scanning electron microscopy was used to evaluate the interfacial reaction between the molten solders and surface finish materials during the wetting test. The Ni3Sn4 intermetallic compound (IMC) plays an important role in promoting wetting properties. The Pd layer retards formation of the Ni3Sn4 IMC and changes its morphology, thereby affecting the wettability of the surface finish/solder systems. ENEPIG surface finishes seem to be suitable for use with cerium-containing solders.

Pd distribution of switchable mirrors based on Mg–Y alloy thin films

Pd-capped magnesium–yttrium alloy switchable mirrors were found to have high switching durability of over 10,000 cycles between reflective and transparent states. However, the durability decreased with the decreasing Pd thickness. Switchable mirrors with various Pd thicknesses were then prepared by a direct-current magnetron sputtering method, and the degradation in durability was studied by observing the distribution of each element of the switchable mirrors from the film surface to the substrate. X-ray photoemission spectroscopy and transmission electron microscopy showed that Pd with a short sputtering time (corresponding to layer thickness of 3nm) resulted in surface oxidation of Mg and Y, and no Pd was present at the surface. The deposited Pd was alloyed with the Mg–Y layer and after taking the sample out from the vacuum chamber a Pd-rich layer appeared between the surface oxides and the Mg–Y layers. With increasing deposition time, a Pd layer was formed on the oxide layer and the Pd layer thickness increased. The mirror with switching durability of over 10,000 cycles had a sufficiently thick Pd top layer of ~7nm and a very thin oxide layer. This thick Pd layer is believed to be the reason for the high switching durability.

Ultra-thin (

Ultrathin (<1μm) Pd–Ag alloy membranes have been successfully coated on the internal surface of YSZ-mixed Al2O3 hollow fibers by sequential electroless plating. The H2 permeance and selectivity of internally-coated (0.8μm thick) Pd–Ag alloy membrane is more than 5μmolm−2s−1Pa−1 and well over 1200, respectively, at 450°C and the pressure difference of 100kPa. The internally-coated Pd–Ag alloy membranes exhibit the significantly improved thermal stability and durability of membranes. This is due to the support layer constrains the thermal expansion of Pd–Ag alloy during the annealing as well as the permeation tests, preventing the delaminating of Pd–Ag alloy membrane, and hence allowing the membranes to tolerate the repeated cyclic permeation tests over at least 5 cycles (10h/cycle) without the significant loss of H2 selectivity. Moreover, mechanical damages (e.g., scratching) of Pd–Ag membrane can also be prevented as the Pd–Ag membrane is not exposed directly to the external surface.

Induced magneto-transport properties at palladium/yttrium iron garnet interface

As a thin layer of palladium (Pd) is directly deposited on an yttrium iron garnet or YIG (Y3Fe5O12) magnetic insulator film, Pd develops both low- and high-field magneto-transport effects that are absent in standalone Pd or thick Pd on YIG. While the low-field magnetoresistance peak of Pd tracks the coercive field of the YIG film, the much larger high-field magnetoresistance and the Hall effect do not show any obvious relationship with the bulk YIG magnetization. The distinct high-field magneto-transport effects in Pd are shown to be caused by interfacial local moments in Pd.

Interfacial tuning of perpendicular magnetic anisotropy and spin magnetic moment in CoFe/Pd multilayers

We report on a strong perpendicular magnetic anisotropy in [CoFe 0.4nm/Pd t]6 (t=1.0–2.0nm) multilayers fabricated by DC sputtering in an ultrahigh vacuum chamber. Saturation magnetization, Ms, and uniaxial anisotropy, Ku, of the multilayers decrease with increasing the spacing thickness; with a Ms of 155emu/cc and a Ku of 1.14×105J/m3 at a spacing thickness of t=2nm. X-ray absorption spectroscopy and X-ray magnetic circular dichroism measurements reveal that spin and orbital magnetic moments of Co and Fe in CoFe film decrease as a function of Pd thickness, indicating the major contribution of surface/interfacial magnetism to the magnetic properties of the film.