Precipitation behavior of Ag–Pd–In dental alloys

Age-hardening characteristics and precipitation behavior of Ag–25%Pd–3%In–1%Zn–0.5%Ir alloy were investigated in detail by means of hardness testing, X-ray diffraction, electron microscopy and resistivity measurement. The solution treating could be accomplished at 980 °C and the aging in the temperature range from 950 to 850 °C occurred by continuous precipitation. The aging in the temperature range from 850 to 450 °C occurred first, forming GP-zones with a hardness increase and then in overaging stage by forming discontinuous precipitation, which consisted of lamellae of solute (Pd, In, Zn) depleted Ag-rich phase and (Pd,Ag)₃(In,Zn) intermetallic phase. The hardness increased very fast to its peak in 10 min during aging at temperatures between 450 and 550 °C.     

High–temperature phase chemistry of the system Gd–Pd–O

Anisothermal sectionof the phase diagram for the system Gd–Pd–O at 1223 K has been established by equilibrationof samples and phase identification after quenching by optical and scanning electron microscopy, X–ray powder diffraction, and energy dispersive spectroscopy. Three ternary oxides Gd₄PdO₇,Gd₂PdO₄ and Gd₂Pd₂O₅ were identified. Liquid alloys, the four inter–metallic compounds and Pd–rich solid solutionwere found to be inequilibrium with Gd₂O₃.

Based on the phase relations, four solid–state cells were designed to measure the Gibbs energies of formation of the three ternary oxides in the temperature range from 920 to 1320 K. Although three cells are sufficient to obtain the properties of the three compounds, the fourth cell was deployed to cross check the data. An advanced version of the solid–state cell incorporating a buffer electrode with yttria–stabilized zirconia solid electrolyte and pure oxygen gas at a pressure of 0.1 MPa as the reference electrode was used for high–temperature thermodynamic measurements. The standard Gibbs energy of formation of the inter–oxide compounds from their component binary oxides can be represented by the following equations:

Gd₄PdO₇(s) : Δ_f(ox)G⁰/J mol^–1 = –25,030 + 0.33T (±140), Gd₂PdO₄(s) : Δf(ox)_f(ox)G⁰/J mol^–1 = –25,350 + 0.84T (±135), Gd₂Pd₂O₅(s) : Δf(ox)_f(ox)G⁰/J mol^–1 = –48,700 + 0.38T (±270)

Based on the thermodynamic information, isothermal chemical potential diagrams and isobaric phase diagrams for the system Gd–Pd–O are developed.     

Microstructure and Property of AlN Joint Brazed with Au–Pd–Co–Ni–V Brazing Filler

An Au–Pd–Co–Ni–V brazing alloy was designed for Al N ceramic joining. Its wettability on Al N was studied with the sessile drop method. The results showed that the contact angle was decreased gradually with increasing temperature and the prolonging of holding time. Sound Al N/Al N joints were achieved with the brazing alloy at 1170 °C for 10 min. The microstructure of the Al N/Al N joints was examined by scanning electron microscopy(SEM). It was found that element V played the active role in the interfacial reaction between the ceramic and the brazing alloy. V reacted with N decomposed from Al N, resulted in the formation of V–N compound. Based on the energy-dispersive spectroscopy(EDS)and X-ray diffraction(XRD) analysis results, the V–N reaction product was verified as V2 N. The overall reaction during the brazing process can be described by the following equation: 2V + AlN + 2Pd = V2 N + Pd2 Al.The Al N/Al N joints brazed with the Au–Pd–Co–Ni–V brazing alloy exhibited three-point bend strength of 162.7 MPa at room temperature, and under the bend test the fracture of the joint occurred at the Al N ceramic substrate.     

A theoretical study of H absorption at a Fe(110)–Pd(100) interface and Fe–Pd alloys

The electronic structure and bonding at a Fe(110)–Pd(100) interface was theoretically analyzed in the framework of semi-empirical quantum chemical calculations. The Fe–Pd interface was modeled by a Fe₇₄Pd₇₄ cluster and a Fe–Pd six layer slab.The extended Hückel tight binding (EHTB) method and its modifications, including repulsive interactions, were used to calculate the interfacial adhesion and the H-absorption energy.The energetic minimum position for H is found at the Fe–Pd interface closer to the Pd layer.The interfacial Fe–Pd distance result to be 1.73 Å where Fe–Pd develops a strong bonding interaction. An important metal–metal adhesion was also found.The changes in the Density of States (DOS) and the Crystal Orbital Overlap Population (COOP) were compared in different structures: clusters, slab and two types of Fe–Pd alloys.The H as an impurity is responsible for a Fe–Fe and Pd–Pd bond weakening.However, the H effect is much less detrimental for the Fe–Pd bonds at the interface.When H is located at interstitial sites in bulk Fe–Pd alloys, the Pd–Pd overlap population shows a notorious decrease in the case of fcc structures while for fct structures the change is only 12%. The intermetallic bonding was also weakened as compared with the pure alloys. The objective of this work is to bring a plausible explanation to the null permeability to hydrogen in Pd-coated Fe films.     

ZIF-67负载Pd/Pd–Cu复合纳米催化剂的制备及其加氢催化性能

1,3-丁二烯选择性加氢是石油化工中有效脱除1,3-丁二烯的方法。选用金属有机骨架ZIF-67作为载体,通过浸渍和H₂还原法控制合成了Pd/ZIF-67和PdCu/ZIF-67复合纳米催化剂。采用XRD、氮气低温物理吸附、TEM、EDS、XPS等方法对Pd/ZIF-67和PdCu/ZIF-67进行了系统的物理化学性质表征,并在石英微型固定床上探索了其在1,3-丁二烯加氢反应中的催化活性、选择性和稳定性。结果表明,Pd/ZIF-67和PdCu/ZIF-67(1∶1)中Pd和Cu分别以Pd²⁺和Cu²⁺存在,Pd纳米粒子和Pd–Cu纳米粒子高度分散在ZIF-67上。由于金属Pd–Cu和载体ZIF-67之间的相互作用以及Pd和Cu双金属间的几何效应,PdCu/ZIF-67(1∶1)的催化活性低于Pd/ZIF-67。Pd/ZIF-67在50℃催化1, 3-丁二烯加氢时,1,3-丁二烯的转化率和总丁烯的选择性分别为99.9%和79.6%。PdCu/ZIF-67(1∶1)在130℃催化反应7 h后1,3-丁二烯的转化率和总丁烯的选择...     

Grain interior precipitation and related lamellar forming grain boundary reaction in Ag–Pd–Cu–Au–Zn alloy

Abstract

Grain interior precipitation and related lamellar forming grain boundary reaction in an Ag–Pd–Cu–Au–Zn alloy were examined by characterising the hardening behaviour, phase transformations, changes in microstructure and changes in element distribution during aging. The solution treated specimen was composed of the Ag–Au rich α₁ matrix and the CuPd β₁ particle-like structures of various sizes containing Zn. The α₁ phase decomposition into α₂ and α₃ in the grain interior accompanied the microstructural changes into fine tweed-like structure containing lattice strains in the interphase boundaries, resulting in hardening in the early stage of aging process. The increased lattice strains in the grain interior induced the grain boundary reaction, stimulating the development of coarse lamellar structure composed of the α₂ and α₃ phases. The increase in volume fraction of the lamellar structure accompanied the decrease in hardness by consuming the dense interphase boundaries of the fine tweed-like structure.     

Microstructure control for developing Fe–Pd ferromagnetic shape memory alloys

The effect of microstructure on the ferromagnetic shape memory effect in Fe–Pd alloys was examined focusing on the orientation distribution, the grain boundary character and the grain size. Fe–29.7–31.0 at.%Pd polycrystals composed of columnar or equiaxed grains were prepared and their magnetostriction was measured under a magnetic field up to 10 kOe. The magnetostriction of the columnar crystals was much larger than that of the equiaxed ones due to the development of 〈100〉 fibre texture and 〈100〉 tilt grain boundary. In particular, a large magnetostriction of 4.5×10⁻⁴ was obtained even in the polycrystals. The grain boundaries of the columnar crystals also influenced the variant selection of martensites, resulting in strong dependence of the magnetostriction on the direction of magnetic field. Larger grain size did not always result in larger magnetostriction in Fe–Pd alloys. An increase in the grain size of the alloys was sometimes accompanied by the development of several sets of twin variants within a grain, resulting in a decrease in the magnetostriction.     

Co–C and Pd–C Eutectic Fixed Points for Radiation Thermometry and Thermocouple Thermometry

Two Co–C and Pd–C eutectic fixed point cells for both radiation thermometry and thermocouple thermometry were constructed at NMC. This paper describes details of the cell design, materials used, and fabrication of the cells. The melting curves of the Co–C and Pd–C cells were measured with a reference radiation thermometer realized in both a single-zone furnace and a three-zone furnace in order to investigate furnace effect. The transition temperatures in terms of ITS-90 were determined to be \(1324.18\,{^{\circ }}\hbox {C}\) and \(1491.61\,{^{\circ }}\hbox {C}\) with the corresponding combined standard uncertainty of \(0.44\,{^{\circ }}\hbox {C}\) and \(0.31\,{^{\circ }}\hbox {C}\) for Co–C and Pd–C, respectively, taking into account of the differences of two different types of furnaces used. The determined ITS-90 temperatures are also compared with that of INRIM cells obtained using the same reference radiation thermometer and the same furnaces with the same settings during a previous bilateral comparison exercise (Battuello et al. in Int J Thermophys 35:535–546, 2014). The agreements are within \(k=1\) uncertainty for Co–C cell and \(k = 2\) uncertainty for Pd–C cell. Shapes of the plateaus of NMC cells and INRIM cells are compared too and furnace effects are analyzed as well. The melting curves of the Co–C and Pd–C cells realized in the single-zone furnace are also measured by a Pt/Pd thermocouple, and the preliminary results are presented as well.     

Combinatorial Electroless Plating Characteristics for Dense Pd–PSS Composite Membrane Fabrication

Emphasizing upon a process–product combinatorial perspective, this article addresses the role of rate enhanced electroless plating baths for the fabrication of dense Pd/porous stainless steel composite membranes. Adopting phasewise contacting pattern of the reducing agent, plating experiments have been carried out with variegated Pd electroless plating baths at a palladium solution concentration of 0.005 M with a loading ratio of 203 cm²/L for the plating time of 2–6 h. Amongst all processes, surfactant and sonication coupled electroless plating baths provided optimal combinations of combinatorial plating process characteristics for dense Pd composite membrane fabrication.     

Recent progress in the structure control of Pd–Ru bimetallic nanomaterials

Pd and Ru are two key elements of the platinum-group metals that are invaluable to areas such as catalysis and energy storage/transfer. To maximize the potential of the Pd and Ru elements, significant effort has been devoted to synthesizing Pd–Ru bimetallic materials. However, most of the reports dealing with this subject describe phase-separated structures such as near-surface alloys and physical mixtures of monometallic nanoparticles (NPs). Pd–Ru alloys with homogenous structure and arbitrary metallic ratio are highly desired for basic scientific research and commercial material design. In the past several years, with the development of nanoscience, Pd–Ru bimetallic alloys with different architectures including heterostructure, core-shell structure and solid-solution alloy were successfully synthesized. In particular, we have now reached the stage of being able to obtain Pd–Ru solid-solution alloy NPs over the whole composition range. These Pd–Ru bimetallic alloys are better catalysts than their parent metal NPs in many catalytic reactions, because the electronic structures of Pd and Ru are modified by alloying. In this review, we describe the recent development in the structure control of Pd–Ru bimetallic nanomaterials. Aiming for a better understanding of the synthesis strategies, some fundamental details including fabrication methods and formation mechanisms are discussed. We stress that the modification of electronic structure, originating from different nanoscale geometry and chemical composition, profoundly affects material properties. Finally, we discuss open issues in this field.     

Age-hardening associated with precipitation reaction and spinodal decomposition in a commercial dental low-carat Au–Ag–Cu–Pd alloy

Two distinguishable hardening mechanisms, depending on the temperature, were found by isothermal ageing in a commercial dental low-carat Au–Ag–Cu–Pd alloy. Age-hardening was attributed to the precipitation of the metastable AuCu I and equilibrium AuCu I ordered phases and spinodal decomposition depending on the ageing temperature. It was clearly visible, by using the direct-ageing method, that the XRD peaks of the parent phases showed a shift during transformation.     

The influence of Pd on growth behavior of a quaternary (Cu,Ni,Pd)6Sn5 compound in Sn–3.0Ag–0.5Cu/Au/Pd/Ni–P solder joint during a liquid state reaction

This study investigated the liquid state reaction of a Sn–3.0Ag–0.5Cu solder jointed with electroless Ni–P/immersion Au (ENIG) and electroless Ni–P/electroless Pd/immersion Au (ENEPIG) surface finishes. Treatments with various soldering temperatures (240, 250, and 260 °C) and times (60, 180, 300, and 600 s) were performed to study the microstructure evolution. Detailed interfacial images revealed that the morphology of (Cu,Ni)₆Sn₅ affects the formation of Ni₃P and the curvature of the interface between them. In addition, the growth kinetics of (Cu,Ni)₆Sn₅ and (Cu,Ni,Pd)₆Sn₅ were studied and compared. The effect of grain coarsening during extended reflow modified the diffusion transport mechanism. However, because of the refinement of Pd on the grain structure, reduced IMC growth and a lower degree of transition from grain boundary diffusion to volume diffusion could be observed in the growth kinetics of (Cu,Ni,Pd)₆Sn₅. Moreover, the activation energy of IMC growth was evaluated using the Arrhenius equation. Pd may act as heterogeneous nucleation sites in the initial stage of soldering and lower the activation energy of (Cu,Ni,Pd)₆Sn₅, compared to (Cu,Ni)₆Sn₅. The lower activation energy of (Cu,Ni,Pd)₆Sn₅ growth ensured that no phase transformation occurred in the SAC305/ENEPIG joints, which may benefit the solder joint reliability. Finally, the detailed influence of Pd on the growth kinetics of IMC formation was investigated and discussed.     

Comparisons of Co–C and Pd–C Eutectic-Point Cells for Thermocouple Calibration Between NMIA and NMIJ

Comparisons between NMIA and NMIJ on the melting temperatures of the Co–C eutectic point and the Pd–C eutectic point were performed using an NMIJ high-temperature furnace. The eutectic-point cells were constructed by NMIA and NMIJ following two different specifications. NMIA designed two miniature crucibles, one for Co–C and one for Pd–C eutectic-point cells. NMIJ designed larger eutectic-point cells, one for Co–C and one for Pd–C eutectic-point cells. Prior to performing the comparisons, the effect of conductive heat flow through the thermocouple stem was evaluated during the melting. The comparisons of the Co–C eutectic-point cells and of the Pd–C eutectic-point cells were performed using types R, B and Pt/Pd thermocouples. Despite the different cell designs and different material sources, the melting temperatures of the Co–C and Pd–C eutectic-point cells under investigation agreed within 0.1 \(\,{^{\circ }}\hbox {C}\).     

Microstructure and anodic polarization behavior of experimental Ag–18Cu–15Pd–12Au alloy in aqueous sulfide solution

The anodic corrosion behavior of an experimental Ag–15Pd–18Cu–12Au alloy in 0.1% Na₂S solution in relation to its microstructure was investigated using potentiodynamic and potentiostatic polarization techniques with analyses of corrosion products by X-ray diffractometry, Auger electron spectroscopy, and X-ray photoelectron spectroscopy. The role of Pd in improvement of the corrosion resistance was also investigated. In the potential/current density curve, three distinct current peaks, at –520 mV (peak I), –425 mV (peak II) and –175 mV (peak III), were observed. The Ag-rich ₂ matrix with coarse Cu and Pd-rich lamellae was the most corrosion-susceptible region, and this region was preferentially corroded at peak I with the formation of granular deposits of Ag₂S. A small amount of Ag–Cu mixed sulfide deposited on the Cu and Pd-rich coarse particles and dissolution of Ag as AgO^– might have occurred in parallel with Ag₂S formation at peak II. Enrichment of Pd on the alloy surface occurred at peak III due to preferential dissolution of Ag and Cu. A high level of corrosion resistance was attained with the formation of a thin Pd-rich sulfide film, which enhanced the passivity of the alloy in an alkaline sulfide solution. It was found that passivity is an important phenomenon not only for base metal alloys but also for noble metal alloys to maintain high levels of resistance to corrosion and tarnishing in sulfide environments.     

Comparative Study of Pt/Pd and Pt–Rh/Pt Thermocouples

The Pt/Pd thermocouple has demonstrated superior thermoelectric drift and homogeneity performance over conventional Pt–Rh/Pt thermocouples. Here, we present a systematic comparison of the drift and homogeneity performance of Pt/Pd and Type R thermocouples by ageing the thermocouples at 1350 °C for a total of 500 h and measuring the performance at regular intervals during this time. The thermocouples studied were one Pt/Pd thermocouple, one Type R thermocouple and one ‘special’ Type R thermocouple which was given the same preparatory annealing treatment as the Pt/Pd thermocouple prior to use. The thermoelectric stability of each thermocouple was measured at the freezing point of Ag (961.78 °C) and the melting point of Co–C eutectic (1324.29 °C). The thermoelectric homogeneity of the thermocouples was also measured. Two difference methods were used by withdrawing the thermocouple from the Ag cell and by moving a localized heat source along the thermocouple. The long-term drift of the Pt/Pd thermocouple was around 50 mK (Ag) and 65 mK (Co–C) after the first 100 h ageing at 1350 °C, followed by a further 25 mK (Ag) and 35 mK (Co–C) over the subsequent 400 h ageing. This drift performance and inhomogeneity were an order of magnitude lower than for the two Type R thermocouples. The Type R thermocouple which was given the ‘special’ preparatory treatment was about 50 % more stable than the conventional Type R thermocouple.     

INRIM–NMC Comparison of Pt/Pd Calibration Above the Ag Point

A comparison of a Pt/Pd calibration above the Ag point between the INRIM and NMC was arranged with the aims of evaluating measurement systems and exploiting the potential of the Pt/Pd thermocouples. Two commercial Pt/Pd thermocouples were used as transfer thermometers. A calibration method using a blackbody cavity as a transfer source and a radiation thermometer as a reference thermometer was adopted in both institutes. The T ₉₀ carried by the radiation thermometers is established by an extrapolation technique for INRIM and by scale realization according to ITS-90 definition for NMC and, therefore, this exercise is also a useful comparison of different approaches to disseminate T ₉₀ above the Ag point. The comparison results are presented and analyzed.     

The characteristics of a Pd–Ni/Pd–Cu double coating on 316L stainless steel and the corrosion resistance in stirred boiling acetic and formic acids mixture

A Pd–Ni/Pd–Cu double coating was deposited on stainless steel surface by electroplating. The microstructure and corrosion resistance of the double coating in strong reducing corrosive media were studied. In boiling 90 wt% acetic acid +10 wt% formic acid mixture containing 0.005 mol L⁻¹ NaCl with 900 r min⁻¹ stir, the corrosion rate of the double coating coated 316L stainless steel is one order of magnitude lower than that of Pd–Cu coated samples. The double coating shows lower porosity, higher hardness and elasticity modulus as well as higher adhesive strength, which may explain the better corrosion resistance in the testing environments.     

CoFe2O4–Pd (0) Nanocomposite: Magnetically Recyclable Catalyst

This study reports on the fabrication and characterization of magnetically recyclable catalysts of CoFe₂O₄–Pd (0) nanocomposite as highly effective catalysts for reduction reactions (hydrogenation reactions) in liquid phase. The CoFe₂O₄ nanoparticles were prepared by a sonochemical method, and the reduction of Pd²⁺ was accomplished with polyethylene glycol 400 (PEG-400). The formation of CoFe₂O₄–Pd (0) magnetically recyclable catalysts (MRCs) was confirmed by X-ray diffraction, Fourier transform infrared spectroscopy, and inductively coupled plasma. Vibrating sample magnetometer showed the ferromagnetic property of the product. The crystallite size (16 ± 4 nm) obtained from XRD was consistent with the particle size (15 ± 5 nm) from TEM. Thus, formed CoFe₂O₄–Pd (0) MRCs showed a very high activity in reduction reactions of 4-nitroaniline and 1,3-dinitrobenzene in liquid phase. Magnetic character of this system allowed recovery and multiple uses without significant loss of its catalytic activity. Graphical Abstract

?Preparation steps for fabricating CoFe₂O₄–Pd (0) MRCs     

Information on deformation mechanisms in nanocrystalline Pd–10% Au inferred from texture analysis

There is still a lack of understanding of deformation mechanisms in nanocrystalline (nc) materials. Studies on microstructures formed in nc Pd–10% Au (grain size about 15 nm) after high pressure torsion revealed signatures of various deformation processes as cooperative grain boundary sliding (GBS), shear banding, dislocation slip and twinning. In order to estimate contributions of these processes to total strain, a comparison was made between torsion textures formed in nc and coarse grained (cg) samples after identical shear strain. The textures were measured with synchrotron radiation. Intensities of characteristic components of the shear texture are two times stronger in the cg sample than in the nc one, indicating that dislocation slip is less significant in the nc sample. It is proposed that numerous planes of cooperative GBS revealed by TEM contribute to plasticity of nc alloy.