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Accurately acquiring crucial data on tube furnaces and real-time temperature monitoring of different temperature zones is vital for material synthesis technology in production. However, it is difficult to achieve real-time monitoring of the temperature field of tube furnaces with existing technology. Here, we proposed a method to fabricate silver (Ag) resistance temperature detectors (RTDs) based on a blade-coating process directly on the surface of a quartz ring, which enables precise positioning and real-time temperature monitoring of tube furnaces within 100–600 °C range. The Ag RTDs exhibited outstanding electrical properties, featuring a temperature coefficient of resistance (TCR) of 2854 ppm/°C, an accuracy of 1.8% FS (full scale), and a resistance drift rate of 0.05%/h over 6 h at 600 °C. These features ensured accurate and stable temperature measurement at high temperatures. For demonstration purposes, an array comprising four Ag RTDs was installed in a tube furnace. The measured average temperature gradient in the central region of the tube furnace was 5.7 °C/mm. Furthermore, successful real-time monitoring of temperature during the alloy sintering process revealed approximately a 20-fold difference in resistivity for silver-palladium alloys sintered at various positions within the tubular furnace. The proposed strategy offers a promising approach for real-time temperature monitoring of tube furnaces. [ABSTRACT FROM AUTHOR]

Selected results of investigations focused on the changes to some mechanical properties of palladium and several palladium-based alloys caused by exposure to hydrogen have been collected and presented. The findings indicate that the mechanical properties of pure palladium are highly susceptible to alteration upon exposure to hydrogen. In the cases of alloying palladium with silver and copper, the alloys, as compared to palladium, appear to resist changes to mechanical properties. In the case of alloying palladium with manganese, the interesting order–disorder phenomenon plays an important role on the effects of hydrogen exposure on their mechanical properties. [ABSTRACT FROM AUTHOR]

Atomically precise thiolate-protected coinage metal nanoclusters and their alloys are far more numerous than their selenium congeners, the synthesis of which remains extremely challenging. Herein, we report the synthesis of a series of atomically defined dithiophosph(in)ate protected eight-electron superatomic palladium silver nanoalloys [PdAg20{S2PR2}12], 2a–c (where R = OiPr, a; OiBu, b; Ph, c) via ligand exchange and/or co-reduction methods. The ligand exchange reaction on [PdAg20{S2P(OnPr)2}12], 1, with [NH4{Se2PR2}12] (where R = OiPr, or OnPr) leads to the formation of [PdAg20{Se2P(OiPr)2}12] (3) and [PdAg20{Se2P(OnPr)2}12] (4), respectively. Solid state structures of 2a, 2b, 3 and 4 unravel different PdAg20 metal frameworks from their parent cluster, originating from the different distributions of the eight-capping silver(I) atoms around a Pd@Ag12 centered icosahedron with C2,D3,Th and Th symmetries, respectively. Surprisingly ambient temperature crystallization of the reaction product 3 obtained by the ligand exchange reaction on 1 has resulted in the co-crystallization of two isomers in the unit cell with overall T (3a) and C3 (3b) symmetries, respectively. To our knowledge, this is the first ever characterized isomeric pair among the selenolate-protected NCs. Density functional theory (DFT) studies further rationalize the preferred geometrical isomerism of the PdAg20 core. Atomically and structurally precise silver nanoclusters hold great potential for catalytic and optoelectronic applications. Here, the authors synthesize and characterize a series of atomically defined dithio- and diselenophosphate-protected eight-electron superatomic palladium-doped silver nanoclusters, including an unprecedented pair of selenolate-protected isomers. [ABSTRACT FROM AUTHOR]

[Display omitted] The highly selective oxidation of cyclohexane to cyclohexanone and cyclohexanol (KA oil) is one of the most challenging issues in the chemical industry. However, the difficulty in attaining high selectivity and high conversion rate in parallel for the existing catalysts limits its practical application. In this paper, a novel photo-thermo synergistic catalyst was reported for the aerobic oxidation of cyclohexane. The uniform blue MoO 3-x nanowires with small diameter stabilized by polyvinyl pyrrolidone (PVP) were synthesized by a hydrothermal method, and a series of MoO 3-x -AgPd composite materials of different proportions were prepared by an in-situ reduction process. The morphology, crystalline structure, surface chemical bonding, photoelectrochemical properties of MoO 3-x -AgPd composites are thoroughly characterized. The MoO 3-x -AgPd composites present significantly increased catalytic performance than MoO 3-x nanowires in the photo-thermo synergistic catalytic oxidation of cyclohexane under dry air. The high conversion rate of 11.3% with the KA oil selectivity of 99.0% was achieved by the MoO 3-x -Ag 20 Pd 20 composites under photo-thermo catalytic process at 120 ℃, which is 1.5 times of that by MoO 3-x nanowires. Under photo-thermo catalytic process, a high cyclohexane conversion rate similar to that of higher temperature thermal catalysis can be obtained at lower reaction temperature, and more cyclohexanol can be produced with a ketone to alcohol (K/A) ratio of 0.254. The significantly enhanced catalytic activity can be attributed to the effective charge transfer in the AgPd alloy nanoparticles, the optimized band gap structure, the suppressed charge recombination, and the promoted photo-thermo synergetic catalytic effect. This work provides a new reference scheme for the design and preparation of high-efficiency photo-thermo catalysts for the selective oxidation of cyclohexane. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Ozone-assisted catalysis was able to remove CO efficiently at room temperature. • Bimetallic Ag-Pd catalyst exhibited a cooperative effect. • In situ FTIR measurement provided useful insights into the mechanism of the catalytic reaction. Abstract The room-temperature oxidation of CO using ozone-assisted catalysis (OAC) over monometallic or bimetallic catalysts supported on γ-Al 2 O 3 is presented. Within the tested particle size range, ozone decomposition was insensitive to the size of the Ag particles (6.6–11.9 nm) at weight hourly space velocities of up to 360 L·g−1·h−1. Among the tested monometallic catalysts (Ag Pd, Fe, Mn, and Cu), Ag showed the highest activity for CO oxidation. Bimetallic catalysts (Ag-M or Pd-M where M = Cu, La, Ru, and Fe) were also considered by adding a second metal or perovskite oxide (LaFeO 3) to Ag. A cooperative effect was observed with the bimetallic Ag-Pd catalyst for the OAC of CO oxidation at room temperature, whereas the other bimetallic catalysts showed slightly lower performance compared to the monometallic catalyst. A high ozone utilization efficiency of 0.94 was achieved with the bimetallic Ag-Pd/γ-Al 2 O 3 catalyst. High-angle annular dark-field scanning tunneling electron microscopy (HAADF) and energy dispersive X-ray (EDX) spectroscopy measurements confirmed the proximity of the two components, which is essential for their interaction. The in situ FTIR measurements revealed that the cooperative effect in the bimetallic Ag-Pd catalyst involved modification of CO adsorption and the suppression of product accumulation. Two typical IR absorption bands of linear- (2090 cm−1) and bridge-CO (1918 cm−1) on Pd disappeared in the presence of Ag nanoparticles. Thus, the presence of Ag in contact with Pd inhibited the accumulation of carbonates, which led to enhanced catalytic performance. Adsorption site-dependent CO oxidation on Pd was also confirmed by the in situ Fourier transform IR measurement. [ABSTRACT FROM AUTHOR]

The AgPd alloys were electrodeposited onto Au and glassy carbon disc electrodes from the solution containing 0.001 mol dm-3 PdCl2 + 0.04 mol dm-3 AgCl + 0.1 mol dm-3 HCl + 12 mol dm-3 LiCl under the non-stationary diffusion (quiescent electrolyte) and convective diffusion (ω = 1000 rpm) to the different amounts of charge and at different current densities. Electrodeposited alloy layers were characterized by the anodic linear sweep voltammetry (ALSV), scanning electron microscopy, energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The compositions of the AgPd alloys determined by the EDS were almost identical to the theoretically predicted ones, while the compositions obtained by XPS and ALSV analysis were similar to each other, but different from those obtained by EDS. Deviation from the theoretically predicted values (determined by the ratio jL(Pd)/j(Ag)) was more pronounced at lower current densities and lower charges of AgPd alloys electrodeposition, due to the lower current efficiencies for alloys electrodeposition. The ALSV analysis indicated the presence of Ag and Pd, expressed by two ALSV peaks, and in some cases the presence of the additional peak, which was found to correspond to the dissolution of large AgPd crystals, formed at thicker electrodeposits (higher electrodeposition charge), indicating, for the first time, that besides the phase structure, the morphology of alloy electrodeposit could also influence the shape of the ALSV response. In addition to Ag and Pd, the XPS analysis confirmed the presence of AgCl at the surface of samples electrodeposited to low thicknesses (amounts of charge). [ABSTRACT FROM AUTHOR]

In this study, we report the direct synthesis of amides and ureas via the catalytic dehydrogenation of volatile alcohols and amines using the Milstein catalyst in a Pd-Ag/ceramic membrane reactor. A series of amides and ureas, which could not be synthesized in an open system by catalytic dehydrogenation coupling, were obtained in moderate to high yields via catalytic dehydrogenation of volatile alcohols and amines. This process could be monitored by the hydrogen produced. Compared to the traditional method of condensation, this catalytic system avoids the stoichiometric pre-activation or in situ activation of reagents, and is a much cleaner process with high atom economy. This methodology, only possible by employing the Pd-Ag/ceramic membrane reactor, not only provides a new environmentally benign synthetic approach of amides and ureas, but is also a potential method for hydrogen storage. [ABSTRACT FROM AUTHOR]

Intermetallic diffusion between the Pd layer and the porous metal support can limit the hydrogen permeability, and ultimately give rise to serious problems in the long-term stability of Pd alloy hydrogen separation membranes. In this study, we developed a multi-layered Pd–Ag membrane having a uniform-microstructure and thermally stable alloy composition by DC magnetron sputtering and Ag up-filling heat treatment. This multi-layered Pd–Ag alloy membrane was introduced in order to prevent Ag segregation, to block the intermetallic diffusion from the porous stainless steel (PSS), and to improve the stability of the membrane. Experimental results showed that the homogeneous Pd–Ag alloy membranes acted as an extremely effective diffusion barrier and provided significant improvement on the thermal stability over a period of 2000 h. [ABSTRACT FROM AUTHOR]

Highly dispersed bimetallic AgPd nanoparticles with different composition have been successfully deposited on the metal-organic frameworks (ZIF-8) by using a simple liquid impregnation method. The resultant catalysts are composition dependent toward dehydrogenation of formic acid, while Ag 18 Pd 82 @ZIF-8 exhibits exceedingly high catalytic activity, with the turnover frequency (TOF) value of 580 h −1 , and 100% hydrogen selectivity at 80 °C. [ABSTRACT FROM AUTHOR]

Palladium–silver (PdAg) alloy nanospheres with unique structure were prepared using a one-pot procedure based on the galvanic replacement reaction. Their electrocatalytic activity for ethanol oxidation in alkaline media was evaluated. The morphology and crystal structure of the samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Electrochemical characterization techniques, including cyclic voltammetry (CV) and chronoamperometry (CA) measurements were used to analyze the electrochemical performance of the PdAg alloy nanospheres. The SEM and TEM images showed that the PdAg alloy nanospheres exhibit a hierarchical nanostructure with hollow interiors and porous walls. Compared to the commercial Pd/C catalyst, the as-prepared PdAg alloy nanospheres exhibit superior electrocatalytic activity and stability towards ethanol electro-oxidation in alkaline media, showing its potential as a new non-Pt electro-catalyst for direct alcohol fuel cells (DAFCs). [ABSTRACT FROM AUTHOR]

In this study, the local order and the structural evolution of the PdAg binary alloy system during the crystallization process from the amorphous phase under different pressures was investigated using the molecular dynamics simulation method. The structural development and phase transformation of the model alloy system for pressures of 0, 1, and 5 GPa are analysed based on variations of the radial distribution function, the bond orientational order parameters, and Honeycutt-Andersen bond-type index method. The simulation results showed that higher pressures favoured amorphous-type atomic clusters and had an important effect on the bond orientational order parameters of the model system of the transformation from amorphous state to stable crystal phase during the isothermal annealing. [ABSTRACT FROM AUTHOR]

Short-range correlations in Ag-Au and Ag-Pd alloys are investigated by analyzing the ab initio total energy of face centered cubic (fcc) based random AgcAu1-c and AgcPd1-c. Since the information on the atomic interactions is incorporated in the energetics of alloys it is possible with a suitable model, Bethe-Peierls-Weiss model is used in the present work, to invert the problem, i.e. to obtain information on the short-range correlation from the total energy of a random system. As an example we demonstrate how site correlations can be extracted from random alloy data. Bethe-Peierls-Weiss model predicts negative (positive) first neighbor correlator for substitutional fcc Ag-Au and (Ag-Pd) alloys at low temperature which can be related to the optimal structures of Ag0.5Au0.5 (and Ag0.5Pd0.5). [ABSTRACT FROM AUTHOR]

Silver-palladium alloys have various industrial applications, such as in hydrogen permeation and hydrogen storage materials. The objective of the present study is to determine experimentally the thermodynamic properties of solid state silver-palladium alloys in low temperatures. Thermodynamic measurements of silver-palladium alloys have been performed over a temperature range of 450-750 K by the electromotive force method with superionic conductor AgI as the solid electrolyte. The activity and partial molar Gibbs energy of silver were obtained for Ag-Pd alloys over the whole composition range, and the thermodynamic properties of palladium were calculated using the Gibbs-Duhem equation. The results show that activities of silver exhibit fairly large negative deviations over most of the composition range, and the activities of palladium are characterized by both negative and positive deviations from the ideal Raoultian behavior. The results also show the minimum integral enthalpy of mixing of Ag-Pd alloys to locate at around 60 at.% Ag. [ABSTRACT FROM AUTHOR]

Monodispersed bimetallic PdAg nanoparticles can be fabricated through the emulsion-assisted ethylene glycol (EG) ternary system. Different compositions of bimetallic PdAg nanoparticles, Pd80Ag20, Pd65Ag35 and Pd46Ag54 can be obtained via adjusting the reaction parameters. For the formation process of the bimetallic PdAg nanoparticles, there have two-stage growth processes: firstly, nucleation and growth of the primary nanoclusters; secondly, formation of the secondary nanoparticles with the size-selection and relax process via the coalescence or aggregation of the primary nanoclusters. The as-prepared PdAg can be supported on the carbon black without any post-treatment, which exhibited high electro-oxidation activity towards methanol oxidation under alkaline media. More importantly, carbon-supported Pd80Ag20 nanoparticles reveal distinctly superior activities for the methanol oxidation, even if compared with commercial Pt/C electro-catalyst. It is concluded that the enhanced activity is dependant on the unique twinning structure with heterogeneous phase due to the dominating coalescence growth in EG ternary system. [ABSTRACT FROM AUTHOR]

Abstract: A multiplexed electrochemical biosensor has been developed for fast and sensitive detection of ractopamine (RAC), salbutamol (SAL) and clenbuterol (CLB) based on reduced graphene oxide (rGO) and silver–palladium alloy nanoparticles (AgPd NPs). In this paper, rGO with high conductivity was used as an electrode material to immobilize artificial antigens and amplify electrochemical signal. AgPd NPs are used to label antibodies and generate a strong electrochemical signal in phosphate buffered saline (PBS) without any other substrates. Screen-printed carbon electrode (SPCE) and competition strategy were adopted to achieve simultaneous detection of RAC, SAL and CLB without cross-talk between adjacent electrodes. This method can simultaneously detect RAC, SAL and CLB ranging from 0.01 to 100ngmL−1 with detection limits of 1.52pgmL−1, 1.44pgmL−1 and 1.38pgmL−1, respectively. Satisfactory results are achieved in pork sample analysis. The designed strategy provides a promising potential in determination of other biological samples. [Copyright &y& Elsevier]

Abstract: The mechanism of the oxidation of glycerol to dihydroxyacetone over Pd–Ag catalysts was discussed. Characterization results suggest that the metal composition of the surface of the crystalline Pd–Ag alloy particles is almost the same as the bulk composition. The synergetic effects of Pd and Ag appear on the oxidation of the secondary OH group of vic-diols. The reaction order with respect to glycerol concentration over Pd–Ag/C was zero, suggesting the strong interaction between glycerol and the catalyst surface. The reaction order with respect to O2 pressure was 0.4, suggesting that the rate-determining step is the reaction involving oxygen species. These reaction trends and characterization results support the mechanism where the terminal OH group of glycerol is adsorbed on the Ag site and the neighboring secondary OH group (CH–OH) is attacked by the oxygen species dissociatively adsorbed on the Pd site. [Copyright &y& Elsevier]

Abstract: Thin PdAg alloy membranes with 20–25% Ag are being developed for hydrogen separation technology. Despite many investigations on such membranes as well as representative experimental and theoretical model systems, unresolved issues remain concerning the effect of the alloy surface structure and composition on adsorption and vice versa. Therefore, the interaction between hydrogen, carbon monoxide or oxygen with the surface of a PdAg model alloy was studied using periodic self-consistent density functional theory (DFT-GGA) calculations. In particular, the adsorption structure, coverage dependence and possible adsorption-induced segregation phenomena were addressed using Pd3Ag(111) model surfaces with varying degrees of surface segregation. In agreement with previous experimental and theoretical investigations, we predict Ag surface termination to be energetically favorable in vacuum. The segregation of Ag is then reversed upon adsorption of H, CO or O. For these adsorbates, the binding is strongest on Pd three-fold hollow sites, and hence complete Pd termination is favored at high coverage of H or CO, while 25% Ag may remain under oxygen because of the lower O-saturation coverage. CO adsorption provides a somewhat stronger driving force for Pd segregation when compared to H, and this may have implications with respect to permeation properties of PdAg alloy surfaces. Our predictions for high coverage are particularly relevant in underlining the importance of segregation phenomena to the hydrogen transport properties of thin PdAg alloy membranes. [Copyright &y& Elsevier]

Abstract: Using ab initio alloy theory in combination with the Chen-Möbius inversion method, we obtain the interaction potentials between layers of the face centered cubic (fcc) (111) plane family for elemental Pd and Ag metals and for Pd0.5Ag0.5 random alloy. Based on the interlayer potentials, we investigate properties related to the fcc (111) planes, such as the stacking fault energy, shear elastic constant, surface energy, surface relaxations, and phonon dispersion along the fcc [111] direction. The results agree well with those obtained by fully self-consistent ab initio calculations and also with the available experimental data, indicating that the properties related to the close-packed planes are well described by the interlayer potentials. [Copyright &y& Elsevier]

Abstract: Dispersed silver/palladium (Ag/Pd) nanoplatelets were prepared by delivering in parallel solutions of mixed metal nitrates and L-ascorbic acid into a nitric acid solution containing Arabic gum. The shape and size of bimetallic nanoparticles varied with the silver/palladium weight ratio and the concentration of nitric acid. The optimum conditions for platelets formation were a palladium content of ∼2.0wt.% and nitric acid concentrations above 1.0moldm−3. The data presented show that both parameters play a critical role in the nucleation and growth of AgPd particles. A mechanism explaining the formation of the bimetallic nanoplatelets is proposed. [Copyright &y& Elsevier]

Abstract: Various mesoporous Nb-doped titania materials were synthesized by a hydrothermal method and examined as catalyst support for PdAg alloy particles for alkaline direct ethanol fuel cell (ADEFC). X-ray diffraction, nitrogen adsorption/desorption, transmission electron microscopy (TEM), cyclic voltammetry (CV) and chronoamperometry (CA) were used to investigate the properties of the supports and catalysts. 700°C was found as the optimal activation temperature for Nb-doped TiO2 due to the high electronic conductivity achievement and mesoporosity conservation. X-ray diffraction (XRD) revealed that Nb x Ti1−x O2 had a structure of mixed anatase and rutile phases. PdAg/Nb x Ti1−x O2 exhibited excellent performance for the electrooxidation of ethanol and higher durability in alkaline solution compared with PdAg/C and PdAg/commercial TiO2. The results open a new way to develop durable and effective electrocatalysts for ADEFC. [Copyright &y& Elsevier]

Abstract: Pd–Ag alloys containing different amounts of Ag (8, 21 and 34at.%) were prepared in order to evaluate their catalytic activity towards the ethanol oxidation (EOR) and oxygen reduction (ORR) reactions. A sequential electroless deposition of Ag and Pd on a stainless steel disc, followed by annealing at 650°C under Ar stream, was used as the alloy electrode deposition process. From half-cell measurements in a 1.0M NaOH electrolyte at ≅20°C, it was found that alloying Pd with Ag leads to an increases of the ORR and EOR kinetics, relative to Pd. Among the alloys under study, the 21at.% Ag content alloy presents the highest catalytic activity for the EOR and the lowest Ag content alloy (8at.% Ag) shows the highest ORR activity. Moreover, it was found that the selectivity of Pd–Ag alloys towards ORR is sustained when ethanol is present in the electrolyte. [Copyright &y& Elsevier]

Abstract: This paper reports the results obtained with different composite membranes used on a membrane reactor for the production of high purity hydrogen. The dry reforming of methane was carried out over a Rh/La2O3 catalyst. Two types of composite membranes were synthesized, Pd and a Pd–Ag alloy. The metal films were deposited by electroless plating on modified porous stainless steel. The support surface was previously modified with a NaA zeolite by dip coating and hydrothermal synthesis. The composition and crystalline structures of the alloy films were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The membrane reactor was designed and built to use either the Pd or the Pd–Ag composite membrane whose crystalline structure and typical morphology were not affected after different reaction conditions. The Pd membrane showed the best behavior in the membrane reactor with the highest methane conversion, H2/CH4 selectivity and permeation flux. After operation of the membranes at 450–500°C on stream for up to 570h no modification of the permeation parameters was observed. [ABSTRACT FROM AUTHOR]

Abstract: A theoretical model is proposed to describe hydrogen permeation in palladium and silver–palladium membranes in presence of a non-inert gas as CO; it is known indeed that hydrogen flux through palladium-based membranes drastically decreases when H2 is fed in mixtures containing carbon monoxide due to the interaction of the latter gas with the membrane surface. To model this process, the adsorption step of the well-known approach suggested by Ward and Dao has been suitably modified, since it must be considered as a competitive adsorption of the different non-inert molecules on the metal interface. In particular, the competitive adsorption of CO and H2 has been examined accounting for the spectrum of information available for CO adsorption on palladium, as well as for hydrogen in palladium and palladium–silver alloys. A validation of the model proposed has been performed through a comparison between several literature data and model calculations, over a rather broad range of operating conditions. A quite good agreement was obtained in the different cases; the model, thus, can be profitably used for predictive purposes. [ABSTRACT FROM AUTHOR]

Abstract: The effect of the alloying elements on the distribution of deuterium in Pd–Au has been investigated by total neutron scattering. The data are analyzed by Reverse Monte Carlo modeling in order to assess the type of interstitial sites occupied with deuterium and how this is correlated with the distribution of the Pd and Au atoms on the host metal lattice. The results show that in Pd–Au alloys deuterium occupies both octahedral and tetrahedral interstitial sites: the overall occupancy of tetrahedral sites increases with increasing Au content and decreasing overall D content. Short-range ordering (SRO) is identified in the D occupancy of interstitial sites in the sample with higher Au content. Indications of SRO and D-induced reorganization in the metal lattice are discussed. [ABSTRACT FROM AUTHOR]

Abstract: The existing assessment of thermodynamic and phase equilibrium data in the Ag–Pd system was revised on the basis of calorimetric data for liquid Ag–Pd alloys published recently in the literature and on new determination of liquidus and solidus temperatures and activity data for Ag in liquid phase, using differential scanning calorimetry (DSC) coupled with Knudsen cell mass spectrometry (KC/MS). A substantially narrower liquid/fcc two-phase field in phase diagram as well as new non-ideal activity data were revealed. [ABSTRACT FROM AUTHOR]

Multilayer technology relies heavily on the chemical compatibility of metal and ceramic. This work focuses on the ceramic–electrode interaction between 92Bi0.5Na0.5TiO3–6 BaTiO3–2K0.5Na0.5NbO3 [(Bi0.46Na0.47Ba0.06K0.01)(Nb0.02Ti0.98)O3], a promising actuator material and forerunner to an emerging class of lead-free actuator materials, and a silver–palladium alloy for inner electrodes, the only currently viable material for the firing temperatures necessary (1100°C). Of special concern was the high content of bismuth in the ceramic since prior investigations suggest that Bi2O3 (as well as various bismuth titanates) used as a fluxor in electroceramics are prone to forming the intermediate-phase bismuth palladate (Bi2PdO4), which can lead to poor contacting and delamination of multilayer stacks. Remarkably, no evidence of bismuth palladate formation could be found. However, the phase relations of the bulk ceramic have proven to be quite complex. Potassium was being drained out of the bulk ceramic either constituting the secondary phase K4Na2(TiO3)3 in unmodified experiments or evaporating and being replaced by silver in samples in contact with Ag. Mechanisms for the formation of these phases or the lack thereof are proposed. These findings were obtained by XRD, TG-DSC, and SEM with EDX, and LA-ICPMS. [ABSTRACT FROM AUTHOR]

Abstract: An in situ tensile test with grey scale correlation has been performed to study the deformation process in ultrafine grained (UFG) Pd and Pd–x at.% Ag (x =5 or 20) alloys produced by high-pressure torsion. Shear band nucleation and propagation was found to be an important deformation mechanism after strain localization during the tensile test. The underlying microscopic mechanism is related to cooperative grain boundary sliding. Moreover, the additional influence of stacking fault energy was found to change the nature of the deformation mechanism from localized strain in Pd to more homogeneous deformation in Pd–20% Ag. In situ analysis and the findings are new and give innovative insight into the basics of deformation in UFG face-centred cubic metals. [Copyright &y& Elsevier]

Abstract: Porous triangular Ag–Pd nanoplates of various bimetallic ratios were prepared by a galvanic displacement reaction in which Pd(OAc)2 reacted with Ag nanoplates. In order to reduce the interaction of free hexadecyltrimethylammonium bromide (CTAB) with the synthesized Ag–Pd nanoplates during this reaction, Ag nanoplate/CTAB solution was precipitated by high-speed centrifugation before synthesizing the porous bimetallic nanotemplates. The kinetics of electroless copper deposition (ECD) catalyzed by these bimetallic nanoplates are analyzed by using a quartz crystal microbalance (QCM). The results reveal that Ag18Pd1 nanoplates show better catalytic activity than Ag18Pd1.5 and Ag18Pd2 nanoplates. Further, the catalytic activity of the porous nanoplates in the ECD bath can be controlled by varying their alloy ratios. [Copyright &y& Elsevier]

Abstract: In this work a novel modelling approach based on Computational Fluid Dynamics (CFD) for the prediction of the gas separation process in a Pd–Ag membrane module for H2 purification is presented. With this approach, the pressure and velocity flow fields of the gas mixture and the species concentration distribution in the selected three-dimensional domain are simultaneously and numerically computed by solving the continuity, momentum and species transport equations, including a gas-through-gas diffusion term derived from the Stefan–Maxwell formulation. As a result, the H2 permeation calculations depend on the local determination of the mass transfer resistances offered by the gas phase and by the membrane, which is modelled as a permeable surface of known characteristics. The applicability of the model to properly predict the separation process under a wide range of pressure, feed flow rate, temperature and gas mixtures composition is assessed through a strict comparison with experimental data. The influence of inhibitor species on the module performance, that is obtained by implementing in the CFD model a suitable literature correlation, is also discussed. [Copyright &y& Elsevier]

Abstract: For many years enhancement of the hydrogen permeation rate through Pd and Pd-alloy membranes has been accomplished by decreasing the membrane thickness. This approach is based on the idea that the permeation rate is limited by the diffusion process through the membrane bulk material. Theoretical modeling suggests that as membrane thickness is reduced into the micrometer range the rate-limiting permeation mechanism may shift to desorption from the permeate surface. In order to test the model predictions, free-standing Pd–Ag alloy membranes (23wt% Ag) with a thickness on the order of 1μm have been microfabricated and their hydrogen permeation behavior has been experimentally determined. At temperatures between 523 and 723K, hydrogen permeation is limited by the diffusion process and is characterized by a membrane permeability pre-exponential factor of 5.51E−8±1.34E−8mol/m/s/Pa0.5 and an activation energy of 10.8±1.25kJ/mol. At temperatures below 500K, the activation energy increases appreciably. This transition is consistent with diffusion-limited permeation in the presence of non-ideal absorption behavior of hydrogen in the Pd–Ag alloy. A transition into a desorption-limited permeation regime is not observed under the operating conditions in this study. Additionally, two distinct failure modes have been observed for these microfabricated devices. The operating conditions leading to failure and cause of each failure mode are discussed. [Copyright &y& Elsevier]

Abstract: Current theoretical models for the permeation behavior of hydrogen through palladium and palladium alloys predict that low temperature operation of thin membranes will result in permeation which is no longer controlled by the diffusion of hydrogen through the metal lattice. Specifically, the process of desorption from the downstream surface is predicted to become the dominant resistance to mass transfer. However, these models neglect the non-ideal absorption behavior of hydrogen in palladium which typically occurs at temperatures below 300°C. In this work a model is developed which accounts for the non-ideal behavior of hydrogen in palladium–silver alloys (25% silver by weight) which are typically used for hydrogen purification. This model predicts that the diffusion-limited regime should be characterized by an increase in the activation energy to ∼32kJ/mol at temperatures below 200°C. This prediction is supported by data available in the literature for thick (>125μm) palladium–silver alloy membranes. [Copyright &y& Elsevier]

Abstract: Pure and mixed gas permeation tests were performed on Pd-based hydrogen selective membranes at different experimental conditions. In particular the permeance of pure hydrogen as well as of binary and ternary mixtures containing hydrogen, nitrogen and methane was measured, at temperatures ranging from 673 to 773K and at pressure differences up to 6bar. The membranes, supplied by NGK Insulators Ltd., Japan, were formed by a selective Pd–Ag layer (20wt% Ag) deposited on a tubular ceramic support, and showed very high hydrogen permeance and a practically infinite selectivity toward hydrogen. Interestingly, the permeance values measured in pure gas experiments resulted always higher than those obtained in permeation tests with gas mixtures; in the latter case, moreover, the permeate flux significantly deviates from Sieverts’ law based on the hydrogen partial pressure in the bulk gas phase. Both facts suggest the existence of non-negligible resistances to hydrogen transport in the gas phase itself, in addition to that offered by the metallic membrane. Experiments performed with increasing feed flow rates, showed also an increase in hydrogen permeance thus revealing the importance of the concentration polarization effects inside the module. Gas phase mass transport coefficients were calculated and used to determine the role of such a resistance in the overall mass transport process. The Sherwood number was also evaluated and was found to follow a boundary layer type of correlation. A general sensitivity analysis was performed in order to compare the effects on the transmembrane hydrogen flux of the two resistances, with different physical dimensions, offered by the gas phase and the metallic membrane. The concentration polarization number thus introduced allows for an a priori identification of the leading resistance at any operating conditions and gives clear indications on the actions required to improve the module performance. [Copyright &y& Elsevier]

Abstract: The performances and long-term stability in the 350°–450°C temperature range of a Pd–Ag alloy thin film membrane are reported. The membrane was prepared by electroless plating deposition (EPD) on the inner walls of a tubular alumina asymmetric support using a novel seeding procedure based on Pd-only complexes. A defect-free film with thickness around 12 microns is obtained. Scanning electron microscopy (SEM) images evidence the presence of aggregates of small crystallites of few hundred nanometers. The membrane shows a stable behaviour for at least 260h of time-on-stream in pure H2 and permeability tests indicate a high hydrogen flux with an activation energy of about 14kJ/mol. The permeability follows Sievert''s law with an exponent of 0.5, indicating a bulk diffusion of hydrogen as the rate-controlling step. There is an initial increase in the transmembrane H2 flux during the time-on-stream tests, due to hydrogen absorption in the Pd–Ag alloy which increases the permeation rate. The presence of two mechanisms of transport, within Pd–Ag alloy crystallites and in the intergrain boundary region, is discussed. The permeability behaviour using H2:N2 mixtures as the feed is also shown. The presence of N2 induces a large decrease in the H2 permeation rate, greater than that expected by dilution effect. The membrane is stable in the 350°–400°C temperature range with a high separation factor between H2 and N2, but at 450°C shows an initial fast decrease of the selectivity with time-on-stream up to reach a nearly constant value. The effect is interpreted in terms of formation of NH x species which inhibit hydrogen diffusion in the intergrain boundary region, as suggested also from literature data. [Copyright &y& Elsevier]

Abstract: In order to examine the influence of Ag on the growth behavior of compounds at the interconnection between the Sn-base solder and the multilayer Pd/Ni/Cu conductor during energization heating, the kinetics of the reactive diffusion in the (Pd–Ag)/Sn system was experimentally studied at solid-state temperatures. Diffusion couples consisting of pure Sn and binary Pd–Ag alloys with concentrations of 25 and 50at.% Ag were prepared by a diffusion bonding technique, and then isothermally annealed in the temperature range between T =433 and 473K for various times up to 312h. During annealing, a PdSn4 compound layer dispersed with fine particles of Ag3Sn is formed at the (Pd–Ag)/Sn interface in the diffusion couple. The square of the mean thickness l of the compound layer is proportional to the annealing time t as follows: l 2 = Kt, where K is the parabolic coefficient. Since the grain size of PdSn4 monotonically increases with increasing annealing time, the growth of the compound layer is controlled by volume diffusion in each phase. The value of K becomes less than half due to addition of Ag with 50at.% into Pd. Hence, the addition of Ag into the Pd layer inhibits the deterioration of the electrical and mechanical properties at the interconnection between the Sn-base solder and the multilayer Pd/Ni/Cu conductor during energization heating. [Copyright &y& Elsevier]

Abstract: The long-term stability of Pd–23%Ag/stainless steel composite membranes has been examined in H2/N2 mixtures as a function of both temperature and feed pressure. During continuous operation, the membrane shows a good stability at 400°C while the N2 leakage increases very slowly at a temperature of 450°C (P feed =10bar). After 100 days of operation (P feed =5–20bar, T =350–450°C), the N2 permeance equals 7.0×10−9 molm−2 s−1 Pa−1, which indicates that the H2/N2 permselectivity still lies around 500, based on a H2 permeance equal to 3.0×10−6 molm−2 s−1 Pa−1. Despite the generation of small pinholes, a membrane life-time of several (2–3) years (T ≤425°C) is estimated for the experimental conditions employed based on long-term stability tests over 100 days. Post-process characterisation shows a considerable grain growth and micro-strain relaxation in the Pd–23%Ag membrane after the prolonged permeation experiment. Changes in surface area are relatively small. In addition, segregation of Ag to the membrane surfaces is observed. The formation of pinholes is identified as the main source for the increased N2 leakage during testing at higher temperature. [Copyright &y& Elsevier]

Abstract: With the miniaturization trend of modern electronic devices and increasing demand for multilayer ceramic chip components, a full understanding of the role of the co-fired ceramic/electrode interface in the performance and long-term reliability of the components becomes very important. In the present work, the inter-diffusion and structure of the co-fired interface of Pb-based relaxor ferroelectrics and Ag–Pd metal electrode were investigated by scanning electron microscopy (SEM) and transmission electron microscopy–energy dispersive analysis of X-rays (TEM–EDAX). No strong structural distortions were observed at the co-fired ceramic/electrode interface except for a thin interfacial layer of 1.5nm thick on each side of the interface. The ceramic near the interface retains the perovskite lattice structure. It is suggested that the diffused electrode compositions could be incorporated into the perovskite lattice. [Copyright &y& Elsevier]

We have used IR spectroscopy of adsorbed CO to study the effect of the method for preparation of silver-palladium catalysts on a TiO2 substrate and exposure to an oxidizing or reducing gaseous atmosphere on the state of Ag and Pd centers. We have shown that as a result of the metal-support interaction, the reducibility of the Ag and Pd particles is increased, which leads to a change in their adsorption and catalytic properties. [ABSTRACT FROM AUTHOR]

The present work deals with the study of palladium-silver (PdAg) and palladium-gold (PdAu) binary alloys over a broad range of temperatures and alloy compositions using density functional theory (DFT) to find possible conditions where the solubility of hydrogen (H) is significantly higher than that of pure palladium (Pd). Several alloy structures, such as Pd100-xAgxwith x 14.81, 25.93, 37.04, and 48.51, Pd100-xAuxwith x 14.81, 25.93, and 37.04, and Pd100-xCuxwith x 25.93 and 48.51 were considered. The lattice constants of these structures were optimized using DFT, and relaxed structures were used for the estimation of binding energy. It was found that the solubility of H in PdAg is higher than pure Pd with a maximum at approximately 30% Ag at 456 K. Also, the solubility of PdAu alloys was higher than pure Pd with a maximum at about 20% Au with a solubility 12 times higher than that of pure Pd. It was found that for a 3.7% H concentration in a PdAg alloy, a cell expansion of 0.15-0.2% occurs, which if ignored may affect the individual binding energy of the O-site by approximately 3.56% and may affect the predicted solubility by approximately 11.8%. [ABSTRACT FROM AUTHOR]

Palladium dental casting alloys are alternatives to gold alloys. The aim of this study was to determine the electrochemical behaviour and the corrosion mechanism of binary silver–palladium alloys. Seven binary silver–palladium alloys and pure palladium and silver were tested in a model saliva solution. Electrochemical tests included corrosion potential, polarization resistance, and potentiodynamic polarization measurements. The corrosion products, which may be theoretically formed, were determined by thermodynamic calculation.The behaviour of silver and silver-rich alloys was dominated by the preferential formation of a thiocyanate surface layer, which controlled the free corrosion potential. Palladium dissolved in the form of a thiocyanate complex, but the surface became passivated by either palladium oxide or solid palladium thiocyanate layer, the thermodynamic calculations indicating preference for the oxide. Palladium-rich alloys showed evidence of silver depletion of the surface, resulting in behaviour similar to palladium.Examination of binary silver–palladium alloys has made possible determination of the role of the components of the alloys and model saliva in the corrosion behaviour. The findings are applicable to the more complex commercial dental alloys containing silver and palladium as major components. [Copyright &y& Elsevier]

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 〈110〉-oriented silicon wafer in which deep grooves were etched in a concentrated KOH solution, leaving silicon membranes with a thickness of ca. 50 µm. 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]/m² · 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. [ABSTRACT FROM AUTHOR]

Pd–Ag alloy coated V-15Ni composite membranes were prepared by co-sputtering of separate pure Pd and Ag targets using a DC multi-target sputtering system where voltage for each target can be controlled independently. The film composition was controlled by changing the target voltage. Hydrogen permeation characteristics of as-prepared composite membranes were investigated using the gas permeation technique in the temperature range of 423–673 K. The hydrogen permeation of the composite membranes was mainly bulk-diffusion limited at a temperature higher than 473 K. At 473 K or lower, the hydrogen permeability of the composite membranes increased with the Ag content until 30 at%. [Copyright &y& Elsevier]

The purpose of this systematic review was to investigate the clinical outcomes of frameworks made of different materials in patients with implant-supported full-arch prostheses. A literature search was conducted on MEDLINE, Scopus and Cochrane Library, until the 1st of March 2021, with the following search terms: framework or substructure combined with "dental implants". The outcomes evaluated were: implant and prosthesis survival, bone resorption, biological and technical complications. The Cochrane Handbook for Systematic Reviews of Interventions was employed to assess the risk of bias in randomized clinical trials. The Newcastle–Ottawa quality assessment scale was used for non-randomized studies. In total, 924 records were evaluated for title and abstract, and 11 studies were included in the review: 4 clinical randomized trials and 7 cohort studies. The framework materials investigated were: gold alloy, titanium, silver-palladium alloy, zirconia and polymers including acrylic resin and carbon-fiber-reinforced composites. High implant and prosthetic cumulative survival rates were recorded by all included studies. Various materials and different fabrication techniques are now available as alternatives to traditional cast metal frameworks, for full-arch implant-supported rehabilitations. Further long-term studies are needed to validate the use of these materials and clarify their specific clinical indications and manufacturing protocols to optimize their clinical outcomes. [ABSTRACT FROM AUTHOR]

An efficient process for the recovery of palladium from waste printed circuits boards (PCBs) is detailed. Palladium is employed as an electrode material in multi-layer ceramic capacitors (MLCCs). These components can be easily removed from PCBs by de-soldering. As palladium is alloyed with silver, its dissolution is readily achieved using dilute nitric acid. As a result, a solution containing palladium along with base metals, mostly copper and iron, is obtained. This solution is then processed through solvent extraction (SX) with a solvent based on N , N ′-dimethyl, N , N ′-dibutyltetradecylmalonamide (BDMA), a robust extracting molecule previously developed in the frame of the reprocessing of waste nuclear fuel. The volume of effluents generated during the SX sequence is limited: iron scrubbing is operated with a very low aqueous to organic phase volume ratio, no specific metal chelator is required for palladium stripping, and no shift from acidic to basic media is required. Finally, a ca 1 g/L Pd(II) aqueous solution with 99,4% purity is obtained, from which palladium is directly isolated as dichlorodiammine palladium(II) salt (Pd(NH 3) 2 Cl 2) after precipitation with ammonia. Overall, palladium is quantitatively recovered from the leaching solution, and no palladium was detected in the remaining solid residue. Purity is high, as no contaminating metal could be detected in the final palladium salt. The proposed approach is simple and complementary to existing hydrometallurgical processes dedicated to gold and copper recovery. • A palladium recovery process from waste PCBs was developed at laboratory scale. • This hydrometallurgical process is a block complementary to existing processes. • Palladium containing components are separated from the board by de-soldering. • Leaching with 3 M nitric acid and solvent extraction enable pure palladium isolation. • Effluents are well controlled during palladium purification with solvent extraction. [ABSTRACT FROM AUTHOR]

Polyhedral noble-metal nanocrystals have received much attention and wide applications as electrical and optical devices as well as catalysts. In this work, a straightforward and effective hydrothermal route for the controllable synthesis of the high-quality Pd-Ag alloy polyhedrons with uniform size is presented. The morphology, composition and structure of the Pd-Ag alloy polyhedrons are fully characterized by the various physical techniques, demonstrating the Pd-Ag alloy polyhedrons are highly alloying. The formation/growth mechanisms of the Pd-Ag alloy polyhedrons are explored and discussed based on the experimental observations and discussions. As a preliminary electrochemical application, the Pd-Ag alloy polyhedrons are applied in the formic acid oxidation reaction, which shows higher electrocatalytic activity and stability than commercially available Pd black due to the 'synergistic effects' between Pd and Ag atoms. [ABSTRACT FROM AUTHOR]