Cd Alloy Research Articles

Opportunities and challenges in the electrocatalysis of CO2 and CO reduction using bifunctional surfaces: A theoretical and experimental study of Au–Cd alloys

Electrolysis could enable the large-scale conversion of CO2 to fuels and small molecules. This perspective discusses the state-of-the-art understanding of CO2 and CO reduction electrocatalysis and provides an overview of the most promising approaches undertaken thus far. We set to explore “bifunctional” catalysts using Au–Cd based alloys inspired by theoretical modelling. Density functional theory calculations suggest more favourable thermodynamics for CO2 reduction to CO and methanol on mixed Au–Cd sites on Au3Cd relative to similar values on Au. We use various tools to test the bulk and surface alloys experimentally. We find that Au3Cd in neutral media exhibits lower CO evolution activity than Au, and Au–Cd alloys also show negligible activity for CO reduction in alkaline media. This indicates that the mixed Cd–Au sites predicted to be catalytically active are not present in the sample. The catalytic performance is most consistent with Au-terminated step surface on a bulk alloy, possibly formed through adsorbate-induced restructuring. We highlight that future bimetallic catalysts must consider potential-dependent surface restructuring effects caused by reaction intermediates.

Complex structures in the Au – Cd alloy system: Hume-Rothery mechanism as origin

The binary (simple metal) phase diagram Au–Cd contains a number of intermetallic compounds with various distortions, superlattices and vacancies. To understand the reasons of these structural complexities and their phase stability, we analyze these crystal structures within the nearly free-electron model in the frame of Fermi sphere – Brillouin zone interactions. Examination of the Brillouin-Jones configuration in relation to the nearly-free electron Fermi sphere provides insights for significance of the valence electron energy contribution to the phase stability. Representation of these complex structures in the reciprocal space clarifies their relationship to simple basic cells. This approach shows the importance of the additional planes for the stability of superlattices. The AuCd-hP18, AuCd3-hP24 and AuCd4-hP273 structures are shown to be related to the AuCd-cP2 via rhombohedral distortion with superlattices and vacancies.

Determination of density of defect states in glassy Se98M2 (M = Ag, Cd and Sn) alloys using a.c. conductivity measurements

In the present work, we have used a.c. conductivity measurements as a powerful tool to estimate density of defect states in some glassy alloys. For this, we have studied the temperature and frequency dependence of a.c. conductivity of binary glasses of Se98M2 (M=Ag, Cd and Sn) system. The a.c. conductivity, σac (T, ω) is found to obey the universal law σac (T, ω)∝ωs. The agreement between experimental and theoretical results of a.c. conductivity suggests that the thermally activated a.c. conduction in binary glassy Se98M2 (Ag, Cd and Sn) system can be successfully explained using correlated barrier hopping (CBH) model. The optimum values of different electrical parameters are obtained in case of glassy Se98Sn2 alloy. The results confirm the dominance of bi-polaron hopping over single-polaron hopping in present glassy alloys.

Surface segregation of cadmium atoms at the interface of mechanically renewable Ag–Cd alloy electrode with surface-inactive electrolyte solution

The surface segregation of cadmium atoms at the interface of mechanically renewed electrodes of the Ag–Cd alloy (containing 1 at % Cd; the region of cadmium solid solutions in silver) with a surface-inactive electrolyte solution is studied in the potential range of ideal polarizability by means of impedance spectroscopy and cyclic voltammetry. It is shown that method of mechanic renewal makes it possible to obtain well reproducible data on the kinetics of electrode surface enrichment with atoms of cadmium which is the surface-active component of this alloy. As follows from the analysis of dependences of the electric double layer (EDL) capacitance on the potential (C vs. E curves) pertaining to different times after the electrode renewal, these dependences can be well described in terms of the model of capacitors connected in series (“the common dense layer”). Using this model, the dependences of the alloy surface coverage with cadmium atoms on the time of exposure of the freshly renewed electrode surface to the electrolyte solution are calculated. The mechanism of surface segregation of cadmium atoms is proposed. It allows the kinetics of relaxation processes that occur in the alloy surface layer to be consistently interpreted. The electrochemical data are supplemented and compared with the results of analysis of the surface composition and the data of the profile analysis over the depth of the same alloy at its interface with vacuum, performed by means of Auger electron spectroscopy.

Formation of porous α tantalum in films

Ta—Cd alloys in the form of coatings with up to 66.2 at % Cd are fabricated for the first time by ion-plasma sputtering and the subsequent codeposition of ultradispersed Ta and Cd particles. At a concentration higher than 44.0 at % Cd, tetragonal β-Ta transforms into bcc α-Ta. Beginning from 74.4 at %, cadmium forms its hexagonal lattice and tantalum in the coatings is represented by an amorphous phase. During vacuum heat treatment at 700–750°C, cadmium evaporates from the binary tantalum—cadmium system containing more than 74.4 at % Cd, and a porous tantalum coating with a well-developed surface forms. Tantalum in the coating is represented by various flakelike crystallites, and tantalum in the near-surface layer mainly has a globular shape. A comparison of the specific surface areas of a tantalum film and the porous tantalum coating, which is performed by the BET method, demonstrates that the specific surface area increases by 277.5 m2/g Ta. Our results can be applied to other binary systems having similar properties.

Features of the percolation scheme of transformation of the vibrational spectrum with varying alloy composition for Cd(TeSe) and (CdZn)Te alloys with soft bonds

An interpretation of the lattice vibration spectra of mixed II–VI crystals Cd(Te,Se) and (Cd,Zn)Te within the percolation scheme (1-bond→2-modes) of transformation of the vibrational spectrum with varying alloy composition is presented. For two-mode alloy systems, the higher-frequency mode is split into two. For Cd(Te,Se) and (Cd,Zn)Te alloys, CdSe- and ZnTe-like vibrations are characterized by percolation doublets with a split of δ ≈ 8 and 4 cm–1, respectively. For these II–VI alloys with soft bonds, the distributions of oscillator strengths between percolation doublet modes differ from the model representation originally proposed for chalcogenides (Zn,Be)VI with high contrast in the bond stiffness of binary alloy components.

Contribution to the description of the absorber rod behavior in severe accident conditions: An experimental investigation of the Ag–Zr phase diagram

Most pressurized water reactor (PWR) absorber rods are composed of an Ag–In–Cd (SIC) alloy inside a stainless steel (SS) cladding, themselves inserted into a Zircaloy tube. During a severe accident, the SIC alloy which melts at 800 °C does not practically interact with SS. However, the cladding failure results from its internal pressurization and its eutectic interaction with Zircaloy and occurs at temperatures greater than 1200 °C. The subsequent interaction between the SIC melt and the Zircaloy has a strong impact on the quantities of aerosols released into the primary circuit and finally on the iodine chemistry. Accurate knowledge of the Ag–Zr system is a prerequisite to address this issue. Within this concern, our experimental work is focused both on the investigation of the Ag–Zr phase diagram and on the determination of the thermodynamic properties of the intermetallic compounds in the system. Two intermetallic compounds (AgZr and AgZr2) were identified. Ag–Zr cast alloys with a Ag/Zr ratio of 1:1 elaborated using an arc-melting furnace, once annealed, contained only a single phase AgZr. From metallographic observations, it appears that AgZr2 likely forms by the peritectic reaction from liquid and the bcc (βZr) phase. The partial enthalpies of solution of silver and zirconium in aluminum were experimentally determined at 723 °C in order to determine the enthalpies of formation of the intermetallic compounds. For silver solution calorimetry in aluminum bath, our measurements were successful and in agreement with the previous data. Yet, this study shows that liquid aluminum should not be used as a solvent for zirconium below 1000 °C.

Structural Origin of the Band Gap Anomaly of Quaternary Alloy Cd(x)Zn(1-x)S(y)Se(1-y) Nanowires, Nanobelts, and Nanosheets in the Visible Spectrum.

Single-crystalline alloy II-VI semiconductor nanostructures have been used as functional materials to propel photonic and optoelectronic device performance in a broad range of the visible spectrum. Their functionality depends on the stable modulation of the direct band gap (Eg), which can be finely tuned by controlling the properties of alloy composition, crystallinity, and morphology. We report on the structural correlation of the optical band gap anomaly of quaternary alloy CdxZn1-xSySe1-y single-crystalline nanostructures that exhibit different morphologies, such as nanowires (NWs), nanobelts (NBs), and nanosheets (NSs), and cover a wide range of the visible spectrum (Eg = 1.96-2.88 eV). Using pulsed laser deposition, the nanostructures evolve from NWs via NBs to NSs with decreasing growth temperature. The effects of the growth temperature are also reflected in the systematic variation of the composition. The alloy nanostructures firmly maintain single crystallinity of the hexagonal wurtzite and the nanoscale morphology, with no distortion of lattice parameters, satisfying the virtual crystal model. For the optical properties, however, we observed distinct structure-dependent band gap anomalies: the disappearance of bowing for NWs and maximum and slightly reduced bowing for NBs and NSs, respectively. We tried to uncover the underlying mechanism that bridges the structural properties and the optical anomaly using an empirical pseudopotential model calculation of electronic band structures. From the calculations, we found that the optical bowings in NBs and NSs were due to residual strain, by which they are also distinguishable from each other: large for NBs and small for NSs. To explain the origin of the residual strain, we suggest a semiempirical model that considers intrinsic atomic disorder, resulting from the bond length mismatch, combined with the strain relaxation factor as a function of the width-to-thickness ratio of the NBs or NSs. The model agreed well with the observed optical bowing of the alloy nanostructures in which a mechanism for the maximum bowing for NBs is explained. The present systematic study on the structural-optical properties correlation opens a new perspective to understand the morphology- and composition-dependent unique optical properties of II-VI alloy nanostructures as well as a comprehensive strategy to design a facile band gap modulation method of preparing photoconverting and photodetecting materials.

EC-STM study of the initial stages of the electrochemical Au(1 1 1)–Cd alloy formation

We have studied the formation of an Au(1 1 1)–Cd alloy in a H2SO4 electrolyte by means of electrochemical STM (EC-STM). To this end, we first characterized the underpotential deposited (upd) Cd overlayers on Au(1 1 1) electrodes. We confirmed the existence of two upd phases on the reconstructed Au(1 1 1) surface, of which the first can be described with a 4×3 unit cell and the second one with a 3×3 unit cell in coexistence with a 2×3 unit cell. At more negative potentials, an alloy with the Au(1 1 1) substrate is formed. In order to obtain a deeper insight into the alloying process, we had to avoid further Cd deposition at these potentials. This was achieved by exchanging the electrolyte after Cd deposition for a Cd-free solution under potential control. We found that the Au–Cd alloy exhibits an atomic structure with a close to square unit cell and locally interferes with the pattern of the Au(1 1 1) “herringbone” reconstruction. This Au–Cd alloy increases the overpotential for the hydrogen evolution reaction (HER) by about 130mV.

Microstructure and creep mechanism of the Ag–In–Cd alloy under compressive load at 300–400 °C

Microstructure and compressive creep mechanism of the Ag–In–Cd alloys were investigated at 300–400°C. Deformation twins are formed in the crept Ag–In–Cd alloys due to the lower stacking fault energy. Abundant dislocations are piled up on the twin boundaries and the creep process is primarily controlled by dislocation slip at 300°C. With temperature increasing to 400°C, dislocation density dramatically decreases as a result of the dislocation climbing and reaction of dislocations with twin boundaries. The dominant creep mechanism presumably turns into dislocation climbing.

Fundamental study on heavy metal freezing behavior for stop of water leakage from LWR containment vessel

For the application of heavy metal technology to the stop of water leakage from LWR containment vessel, the freezing behavior of molten heavy metal on a metal plate in water and air environments was investigated. Wood's metal (Pb–Bi–Sn–Cd alloy) and gallium were used as a candidate sealing metal and simulant one, respectively, while brass and stainless steel plates were used as a water-leaking structure. The freezing feature is better in cases of the heavy metal discharged to a water-cooled metal plate with higher thermal conductivity at lower heavy metal temperature in a water atmosphere rather than an air atmosphere. An one-dimensional unsteady heat conduction and freezing model could predict the freezing temperature well, which suggested the capability of simulation of practical freezing phenomena of liquid metal for stop of water leakage with the extention of this model. The present result is useful to develop an equipment for stopping the water leakage in a water environment using heavy metal freezing.

Electrochemical synthesis of Cd–Ag bimetallic particles and the involved alloy formation

The formation of bimetallic Cd–Ag nanoparticles on vitreous carbon (VC) and the involved alloy formation have been studied by conventional electrochemical techniques and ex-situ atomic force microscopy (AFM). Both metals were deposited by sequential electrodeposition using single potentiostatic pulses. The AFM images of Ag deposits showed small differently sized Ag nanocrystallites uniformly distributed over the VC-substrate. This modified substrate was immersed in an electrolyte solution containing Cd2+ ions and bimetallic Cd–Ag particles were prepared by underpotential deposition (UPD) of Cd. The alloy formation phenomena observed previously during Cd UPD on massive Ag electrodes were found also in the case of Cd UPD on Ag nanoparticles. The desorption spectra in the system Cd/Ag (nanoparticles)/VC employing different polarization times, showed three desorption peaks associated with the dissolution of the Cd OPD and UPD deposits and an Ag–Cd alloy formed at low underpotentials, respectively. The electrochemical behavior of the bimetallic system was also studied applying other polarization routine designed for this purpose.

Multiple exciton generation in cluster-free alloy Cd(x)Hg(1-x)Te colloidal quantum dots synthesized in water.

A number of different composition CdxHg1-xTe alloy quantum dots have been synthesized using a modified aqueous synthesis and ion exchange method. The benefits of good stoichiometric control and high emission quantum yield were retained whilst also ensuring that the tendency to form gel-like clusters and adsorb excess cations in the stabilizing ligand shells was mitigated using a sequestering method to remove excess ionic material during and after the synthesis. This was highly desirable for ultrafast carrier dynamics measurements, avoiding strong photocharging effects which may mask fundamental carrier signals. Transient grating measurements revealed a composition dependent carrier multiplication process which competes with phonon mediated carrier cooling to deplete the initial hot carrier population. The interplay between these two mechanisms is strongly dependent on the electron effective mass which in these alloys has a marked composition dependence and may be considerably lower than the hole effective mass. For a composition x = 0.52 we measured a maximum carrier multiplication quantum yield of 199 ± 19% with pump photon energy 3 times the bandgap energy, Eg, whilst the threshold energy is calculated to be just 2.15Eg. There is some evidence to suggest an impact ionization process analogous to the inverse Auger S mechanism seen in bulk CdxHg1-xTe.

Evaluation of Gibbs free energies of formation of Ce–Cd intermetallic compounds using electrochemical techniques

Gibbs free energies of formation of six Ce–Cd intermetallic compounds, CeCd, CeCd2, CeCd3, CeCd58/13, CeCd6 and CeCd11, were evaluated systematically using electrochemical techniques in the temperature range of 673–923K in the LiCl–KCl–CeCl3–CdCl2 molten salt bath. The linear dependence of the Gibbs free energies of formation on temperature yields to the enthalpies and entropies of formation of these intermetallic compounds. By extrapolating the Gibbs free energy of Ce–Cd intermetallic compounds to the Cd distillation temperature, it was clear that the Gibbs free energy of Ce–Cd intermetallic compounds decreases gradually from CeCd6 to CeCd2 and attains minimum value at CeCd2. This suggests on the Cd distillation from the U–Pu–Ce–Cd alloy that the dissolution of U or Pu into CeCd2 should be mostly taken into consideration.

Magnetically Induced Codeposition of Ni–Cd Alloy Coatings for Better Corrosion Protection

The effects of applied magnetic field, B (both parallel and perpendicular) during process of electrodeposition of Ni–Cd alloy coating on mild steel from a newly proposed electrolytic bath have been studied by using X-ray diffraction (XRD), energy-dispersive X-ray (EDX), and scanning electron microscopy (SEM) analysis. Both parallel and perpendicular B reduced the corrosion rates (CRs); however, the effect is more pronounced in case of perpendicular B. Progressive decrease of CR with increase in the intensity of B showed that corrosion protection efficacy bears close relation with changed composition and crystallographic orientation of the coatings. Under optimal condition, Ni–Cd coating deposited at 0.8 T (perpendicular) was found to be 35 times less corrosive than the conventional Ni–Cd coating (B = 0 T) deposited from the same bath for same time. The effect of B on thickness, microhardness, surface morphology, composition, and crystallographic orientation, and hence, the corrosion resistance of the coatings were analyzed in the light of magnetohydrodynamic (MHD) effect.

First-principles study of the properties of Li, Al and Cd doped Mg alloys

The major mechanical and electronic properties of the Li, Al and Cd doped Mg solid solutions were investigated by employing the first principles density functional theory methods. The solute atoms were chosen since they have a larger range of solubility. Each of the alloy models consists of fifteen Mg atoms and one solute atom. The elastic parameters Cij were evaluated, and the bulk modulus (B), shear modulus (G), Young’s modulus (E) and Poisson’s ratio (ν) were further derived. The results show that the B/G ratio (an estimation of the metal ductility) of Mg, Mg–Al, Mg–Li and Mg–Cd are 1.92, 1.80, 1.47 and 2.17, respectively, which indicates that the Mg–Al and Mg–Cd alloys are ductile and the Mg–Li alloy is slightly brittle. For the Mg–Cd alloy, its plasticity might be better than that of the others due to a larger Poisson’s ratio and lower values of C11−C12 and E. The tensile test simulation of the Mg metal and Mg–Al, Mg–Li and Mg–Cd alloys reaches the strengths of 5.05, 5.32, 5.28 and 4.89GPa, respectively.

Development of Au–In–Cd decoupler by a hot isostatic pressing (HIP) technique for short pulsed spallation neutron source

In order to utilize the Au–In–Cd alloy as a decoupler for the MW-class spallation neutron sources, it is required to bond Au–In–Cd alloy to an aluminum alloy (A5083), which from the structural material of the moderator in the Japan Spallation Neutron Source. The hot isostatic pressing (HIP) technique is adopted to bond the Au–In–Cd alloy to the A5083 alloy in the form of the curved shape of the moderator vessel. We obtained an adequate bonding strength of 95.2MPa, which was three times larger than the required design strength (30MPa) under the conditions of a temperature of 535°C, pressure of 100MPa and a holding time of 1h.

Synthesis and Electrochemical Study of Pd-Based Trimetallic Nanoparticles for Enhanced Hydrogen Storage

The success of acceptable hydrogen storage capacities on high surface area carbon materials at ambient temperature requires the combination of both physisorption and chemisorption. Despite the sole reliance on physisorption for hydrogen uptake in carbon, the dispersal of transition metal catalysts on carbon materials significantly enhances hydrogen uptake at ambient temperatures, via the process of hydrogen spillover. In the present study, hydrogen electrosorption onto activated carbon materials modified with different trimetallic dissociation catalysts (Pd–Ag–Cd) was investigated in an acidic medium using cyclic voltammetry and chronoamperometry. A significant synergistic effect on hydrogen storage was observed, which could be attributed to the electrochemical reduction of hydrogen ions initially at the Pd-based nanoparticles and the hydrogen surface diffusion subsequently to the activated carbon. Utilizing electrochemical methods, the optimized composition of the Pd–Ag–Cd alloys was determined to be Pd80Ag10Cd10, with the highest hydrogen sorption capacity at a hydrogen desorption charge of 18.49 C/cm2·mg. With increased kinetics and a decrease in the phase transition, the significant enhancement of hydrogen sorption, in comparison to the Pd–Ag and Pd–Cd bimetallic alloys, was further demonstrated, making Pd–Ag–Cd catalysts attractive for use as hydrogen dissociation catalysts for applications in both hydrogen purification and storage.

Thermal Conductivity of Solid and Liquid Phases for Pb-Cd Alloys

Thermal conductivities of solid phases for pure Pb and Pb-x weight% Cd (5, 12, 17.4, 50, and 95) binary alloys were measured with a radial heat flow apparatus. Thermal conductivity depending on temperature and composition for pure Pb and Pb-x weight% Cd (5, 12, 17.4, 50, and 95) binary alloys were obtained to be , , , , , and . The thermal conductivity ratio of liquid phase to solid phase for the eutectic Pb-17.4 weight% Cd alloy at its melting temperature is found to be 1.31 with a Bridgman-type directional solidification apparatus. Thus, the thermal conductivity of the liquid phase for the eutectic alloy at its melting temperature was found to be by using the values of solid phase thermal conductivity and the thermal conductivity ratio of liquid phase to solid phase.

Effect of travelling magnetic field on interface morphology in directionally solidified Sn–Cd alloy

The diversity of interface morphologies is observed for directionally solidified Sn–0.65%Cd alloy under a travelling magnetic field (TMF) in the 4 mm-diameter sample. Under an upward TMF, planar and cellular interface morphologies transform alternately with increasing magnetic flux density (B≤10.3 mT). The interface morphology transforms from shallow cellular to deep cellular morphology under a weak downward TMF (B=3.2 mT). When the magnetic flux density increases further, both sides of the interface morphology appear to be slightly inconsistent, but they roughly tend to be planar under a strong downward TMF (B≤10.3 mT). The interface instability may be attributed to the flow driven by the TMF. Moreover, the shape of interface appears to be almost flat under an upward TMF, but deflective under a downward TMF.