Ag-Ni Research Articles

Controlling and probing heat generation in an optical heater system

Abstract Understanding how plasmonic nanostructures generate heat upon exposure to light, and thus increase the local temperature of the surrounding medium is important for many applications. Reliable temperature manipulation requires analyzing the local temperature distribution as a function of laser density. In this work, an optical heating system containing silver nano-islands (Ag NIs) is designed to enable heat generation at the micro/nanometer scale and the local temperature can reach 1458 K. The heat generation by Ag NIs exposed to near-IR laser light, and the temperature distribution, are detected in situ via the fluorescence intensity ratio technique. It was found that the temperature of the system can be controlled by changing the excitation power. Furthermore, the temperature-dependent UCL of a single Y2O3:Yb3+/Er3+ microrod is studied by taking advantage of the controllable local temperature in the optical heating system. It was found that the color of the upconversion luminescence can be tuned by managing the local temperature, and conversely, the local temperature at the optical heater can be monitored by observing the color change of the rare-earth microrod. The real-time manipulation of plasmonic heating offers an opportunity to control outcomes of thermo-plasmonic effects, which then enables a myriad of practical applications.

Raman enhancement properties of Ag nano-islands with SiO2 microsphere arrays prepared by self-assembly technology and the thin-film annealing method

Combining self-assembly technology and the thin-film annealing method, annealed Ag nano-islands (Ag NIs) with SiO2 microsphere (MS) arrays were prepared as surface-enhanced Raman scattering (SERS) substrate in this paper. A “top-binding” model was established to analyze the effect of SiO2 MS at different annealing temperatures and different Ag film thickness. The corresponding comparative analysis with and without MS templates have been carried on. We simulated the electric field enhancement, coupling enhancement spectrum and the optical focus function of SiO2 MS. Characterization and experiments showed that the use of a SiO2 MS array as a dewetting template can well regulate the size and morphology of Ag NIs. Among them, SiO2 MS-Ag-20 can achieve the most uniform particle size at an annealing temperature of 873.15 K. According to the UV-Vis absorption spectrum, it had an active SERS analytical enhancement factor (AEF) of ∼3.91×105 and good SERS reproducibility (relative standard deviation, RSD = 0.113) for R6G when the wavelength was 532 nm.

Surface and segregation energies of Ag based alloys with Ni, Co and Fe: Direct experimental measurement and DFT study

A direct measurement of the surface energy polytherm in Ag + 0.5 at.% Fe alloy and first-principles calculations of segregation energy in silver-based systems with iron, cobalt and nickel were performed. The surface energy was measured in situ on silver foils with 16 μm thickness in the temperature range (0.8 - 0.95) TmAg in Ar+10% H2 atmosphere. Iron was introduced by electrolytic deposition and annealing. The segregation energy calculations were performed using density functional theory (DFT). DFT calculations were used to obtain the segregation energies of Fe, Co and Ni on the (100), (110), and (111) surfaces of Ag. It was shown that alloying of silver with Ni, Co and Fe (~ 0.5 at.%) leads to a significant increase in the surface energy and this effect increased with decreasing temperature. The alloys behaved in a similar way with decreasing temperature: the surface energy of the alloys increased to values close to the surface energy values of the second components in their standard reference states. DFT calculations of the segregation energy showed a strong “anti-segregation” behavior of Ni, Co and Fe in Ag; the segregation energy took positive values of about 0.4 eV/atom for all solute atoms. Surface studies by AFM and AES methods showed that the surface was two-phase, a silver phase and a small fraction of the second bcc-Fe phase particles coated with a thin silver layer. These observations indicated a quite pronounced desorption of iron on silver on one hand and the adsorption of silver on iron on the other hand. The positive segregation energies of Ni, Co and Fe to Ag surfaces, experimentally observed desorption behavior of these solutes as well as an increase of the surface energy with the increasing concentration of the second component, point at the fundamental reversibility of the Gibbs adsorption equation.

Pyrite Textures and Trace Element Compositions from the Granodiorite-Hosted Gold Deposit at Jonnagiri, Eastern Dharwar Craton, India: Implications for Gold Mineralization Processes

Abstract The lone granodiorite-hosted gold deposit at Dona sector of Jonnagiri, eastern Dharwar craton, India, contains typical shear-hosted and vein-hosted alteration zones. Pyrite is the dominant sulfide mineral in these alteration zones. Texturally three varieties of pyrites were identified in these alteration zones: (1) early pyrite-I is coarse to medium grained and subhedral shaped and contains near margin-parallel silicate inclusions, (2) main (ore)-stage pyrite-II overgrows early pyrite-I and also occurs as discrete grains invariably associated with visible gold, and (3) late-stage pyrite-III is anhedral and coarse grained and contains randomly oriented inclusions of silicates, sulfides, and native gold grains. Electron microprobe analysis, coupled with X-ray element mapping and laser ablation-inductively coupled plasma-mass spectrometry, reveals that most early pyrites (pyrite-I) have higher concentrations of As and Au in both the zones. The shear-hosted main-stage pyrite-II can be divided into Ni-rich (median 211 ppm) pyrite-IIa and Co-rich (median 274 ppm) pyrite-IIb, respectively. While invisible gold content is higher in vein-hosted late-stage pyrite (pyrite-IIIa; ≤287 ppm) when compared to shear-hosted pyrites, native visible gold is associated with only vein-hosted main- and late-stage pyrites (pyrite-II and IIIa). Arsenic, Ni, Au, Se, Mo, and Te concentrations decrease from pyrite-I to pyrite-III, reflecting remobilization of trace elements during subsequent dissolution-reprecipitation of early formed pyrites. The oscillatory zoning of As, Co, and Ni and slight increase in Bi, Te, Se, Au, and Ag in pyrite-II and pyrite-IIIa represent pressure fluctuations and repeated local fluid phase separation in the ore-forming environment. A positive correlation of Au with Pb, Sb, Bi, and Te confirms the presence of nanoinclusions of mineral phases such as nagyagite, Pb-Sb-Bi tellurides, Au-Ag tellurides, tellurosulfides, and sulfosalts within pyrites, particularly in the vein-hosted zone. Based on several lines of evidence, the following paragenetic sequence is proposed for pyrite formation at Dona, Jonnagiri. Rapid crystallization of early (porous) pyrite-I was followed by its dissolution during ~E-W–trending Sh1 shearing. Crystallization of main-stage pyrite-II and the late-stage pyrite-IIIa is the product of dissolution-reprecipitation of early pyrite during ~N-S–trending Sh2 shearing. Changing fluid compositions caused by episodic fault-valve actions and associated boiling resulted in dissolution-reprecipitation of early formed pyrites and remobilization of trace elements. This further resulted in precipitation of the bulk of gold within the inner vein-hosted zone during the later Sh2 shearing event. At the culmination of shearing, late-stage pyrite-IIIb precipitation occurs with very low concentrations of all trace elements, including gold.

Is electronic stopping of ions velocity-proportional in the velocity-proportional regime?

We have studied systematic deviations of reported electronic stopping cross sections from velocity proportionality predicted by Lindhard and Scharff. Most pronounced is an apparent drop-off at beam energies below ∼0.01 MeV/u. In the frequently-used transmission technique, only a narrow cone of the beam is analysed in order to minimize the contribution from nuclear stopping. This has the consequence that a reduced instead of the full electronic energy loss is recorded. The magnitude of this effect has been computed on the basis of a recently developed extension of the scheme of Fastrup et al. to correct for nuclear stopping. In a detailed study of the C-Ar system based on our PASS code we find close agreement between the derived reduced electronic stopping cross section and the experimental result reported by Ormrod. Results are reported for eight ions on argon, for O in C and Cl in C and for Ni in Ag. For Ni in Ag as well as for one set of reported stopping cross sections for N in Ar a particularly sharp drop-off is shown to be caused by an inadequate nuclear-stopping correction. Our findings do not support Paul’s assertion of a gas-solid difference in electronic stopping of low-energy heavy ions.

New approach in Auger elemental relative sensitive factor calculation by using TEM-EDS analysis based on bi-layers of pure elements

In fabrication of microelectronic devices two important steps are often recognized: i) all the processes performed on the wafer in order to build the active part of the devices and, ii) the assembly and packaging processes, typically performed on a chip, in order to fabricate interconnections between active part and exterior. The wafer back side is an active part of power devices and is normally coated with a stack of Ti-Ni-Au or Ti-Ni-Ag layers to ensure the best electrical contact with the frame on which the device is attached prior to the packaging. An important failure mechanism related to this particular process step is related to the diffusion of Ni to the surface of the stack that causes its oxidation on the back metal surface, inhibiting the correct connection to the metallic frame.Auger Electron Spectroscopy (AES) is a powerful analytical technique that can be used to detect this failure mechanism for its very high sensitivity in the characterization of surface layers. Unfortunately, its results are mainly qualitative. Quantitative extrapolations can be inaccurate using library Elemental Relative Sensitive Factor (ERSF) because they are mainly referred to a silicon substrate and could be not valid for a different matrix. A most accurate evaluation of the ERSF is based on the analysis, under identical experimental condition, of standard materials (with known concentration) that should be similar to the unknown sample and having the same matrix. However, the production of this kind of standard is not easy due to the mobility of Ni in Au and Ag.Another commonly used technique is the Energy Dispersive X-ray Spectrometry (EDS) which is less sensitive than the Auger and not sufficiently adequate for a quantitative analysis due to the limitation of the matrix correction methods. Recently, a new method to perform quantitative analysis by using Transmission Electron Microscopy (TEM) EDS was proposed, starting from bi-layers of pure elements.In this work we show how the use of TEM-EDS quantification of Ni in Ag could be a successful method for ERSF evaluation in order to overcome matrix effect in Auger quantification. For this purpose suitable foils of Ag/Al and Ni/Al were used. The validation of the method was performed on a sample with a tri-metal stack of Ti/Ni/Ag previously stimulated by means of a thermal budget to induce Ni migration on Ag surface. The quantitative analysis allowed us to use this characterized sample as AES standard for ERSF calculation.

Cu and Ag additions affecting the solidification microstructure and tensile properties of Sn-Bi lead-free solder alloys

Over the past few years Sn-based solders containing third and fourth elements have become of great interest to try and improve the consistency of solders during application. In most reported cases this involved the addition of either Ni in Sn-Cu or Ag in Sn-Bi solder alloys. Still there is a lack of research showing how the combination of third element additions and varying cooling rates affect the mechanical properties of Sn-Bi-X solder alloys. As such the present investigation examines the effects of minor additions of Ag and Cu on a Sn-34wt%Bi solder alloys produced by directional solidification. Directional solidification was used as the transient regime attained during directional solidification in a water-cooled mold may allow for similar cooling rates to those found in industrial reflow soldering operations. Microstructural analysis on the Sn-Bi-X alloys was conducted using eutectic spacing (λE), Bi precipitates spacing (λp) and the secondary dendritic spacing (λ2) measurements. These measurements represented the complex eutectic growth, the solid-state precipitation of Bi within the β-Sn phase and the length-scale of the Sn-rich dendritic array respectively. In conjunction with these measurements the evolution of tensile strength and ductility as a function of λ2 was examined. Considering the Sn-34wt%Bi, Sn-34wt%Bi-0.1wt%Cu, Sn-34wt%Bi-0.7wt%Cu and Sn-33wt%Bi-2wt%Ag alloys, it was found that the modified alloys containing 0.7wt%Cu and 2.0wt%Ag showed lower tensile properties and lower ductility. In contrast, the addition of 0.1wt%Cu increased the ductility for λ2 < 14µm while preserving the tensile strength, representing the best alternative of all alloys examined.

Trace element distribution in primary sulfides and Fe–Ti oxides from the sulfide-rich pods of the Lac des Iles Pd deposits, Western Ontario, Canada: Constraints on processes controlling the composition of the ore and the use of pentlandite compositions in exploration

There is an on-going debate as to whether the Lac des Iles Pd deposits (Ontario, Canada) are of magmatic or hydrothermal origin. An aspect of the deposits that has not yet been documented is the presence of sulfide-rich pods which occur throughout the host intrusion (the Mine Block Intrusion). The ore mineralogy of the sulfide-rich pods consists of pyrrhotite, pentlandite, chalcopyrite, ±pyrite, magnetite and ilmenite. We present the trace element concentrations of pyrrhotite, pentlandite, chalcopyrite, magnetite, and ilmenite from the pods and compare these results with results from other Ni–Cu–platinum-group element (PGE) deposits. The low concentrations of Si and Ca and high concentrations of V, Ni, and Cr in magnetite are consistent with a magmatic origin of the magnetite. Variations in the V and Cr concentrations indicate that magnetite crystallized from a magmatic sulfide liquid during crystal fractionation of the sulfide liquid. The enrichments in Ni, Co, Os, Ir, Ru, and Rh and depletions in Cu, Ag, Cd, and Zn in pentlandite and pyrrhotite relative to chalcopyrite are also consistent with the formation of the pods by crystallization of a magmatic sulfide liquid. Comparison of pyrrhotite and pentlandite compositions from Lac des Iles with those from other Ni–Cu–PGE deposits shows that pyrrhotite and pentlandite derived from evolved magmas have distinct compositions relative to those derived from more primitive magmas. In addition, this comparison shows that pentlandites from PGE-dominated deposits are richer in Pd and Rh than pentlandites from Ni–Cu sulfide deposits. A plot of Pd vs Rh appears to be effective at distinguishing pentlandites of PGE-dominated deposits from those of Ni–Cu sulfide deposits and could possibly be used to adapt exploration strategies.

Amla ( Phyllanthus emblica L.) Enhances Iron Dialysability and Uptake in In vitro Models

Phyllanthus emblica L. (Indian gooseberry or amla ) is a well-known dietary supplement ( Rasayana ) in Ayurveda used in the management of iron deficiency anaemia ( Pandu ). Amla is said to act by regulating the 'metabolic fire' ( agni ), which is important for proper digestion and absorption of nutrients. In the present study standard cell-free and cell-based models that are employed in biomedical sciences to study digestion and bioavailability of nutrients were used to examine the influence of amla fruit juice on iron dialysability and uptake. Amla juice contained 0.35% ascorbic acid (AA), 0.33% tannins (gallic acid equivalent), 0.13% gallic acid, 0.58% total organic acid and 0.002% iron on a w/w basis. Amla juice exhibited a dose response to iron dialysability with an optimum at 1 : 0.25 molar ratio of Fe : amla juice (AA equivalent) in the cell-free digestion model and 1 : 0.5 in both Caco-2 and HepG2 cell lines. Amla juice increased the dialysable iron three times more than the FeSO 4 alone control in the cell-free digestion model. Iron uptake in Caco-2 and HepG2 cell lines increased 17.18 and 18.71 times more than the control respectively, in the presence of amla juice. AA, a known Fe bioavailability enhancer, at the same molar ratios showed an enhancement only by 1.45 times in the cell-free model and 13.01 and 12.48 times in the Caco-2 and HepG2 models respectively. As a dietary supplement that enhances iron dialysability and uptake, amla fruits can be explored further as a low-cost intervention in the management of iron deficiency anaemia.

Size and Solid Solubility in Electrodeposited Ag-Ni Nanoparticles

Owing to a large difference in atomic sizes and a positive enthalpy of mixing, Ag and Ni form an immiscible system. In the current work, we report on the electrodeposition of Ag-Ni nanoparticles with a solid solution structure. Effect of current on the relative changes in composition and sizes of solid solution nanoparticles is illustrated. It is shown that with increase in the deposition current, size of Ag-Ni nanoparticles decreases due to an increased nucleation rate. With decrease in size the extent of miscibility of Ni in Ag increases due to increased energetic contribution from the particle curvature.

Electrodeposition of Ag–Ni films from thiourea complexing solutions

Ag–Ni alloy films were electrodeposited from thiourea-based acidic solutions. Electrochemical studies confirmed the strong polarization of Ag deposition due to the strong complexation of Ag+ with thiourea, bringing the onset of Ag and Ni deposition closer, potentially favoring alloy formation. The as-deposited films were very fine grained (less than 20nm) and consisted of various phases: a supersaturated solid solution of Ni in Ag and a Ni-rich nanocrystalline or amorphous phase, preferentially formed at grain boundaries. Ag-rich films were smooth, while a higher Ni content resulted in increasingly rough and porous films. Decomposition of the metastable phase and precipitation of the pure elemental phases occurred upon thermal annealing at 600°C. Reduction of thiourea induced by Ni deposition led to sulfur incorporation in the films, up to 20at.%.

The distribution of platinum group elements (PGE) and other chalcophile elements among sulfides from the Creighton Ni–Cu–PGE sulfide deposit, Sudbury, Canada, and the origin of palladium in pentlandite

Concentrations of platinum group elements (PGE), Ag, As, Au, Bi, Cd, Co, Mo, Pb, Re, Sb, Se, Sn, Te, and Zn, have been determined in base metal sulfide (BMS) minerals from the western branch (402 Trough orebodies) of the Creighton Ni–Cu–PGE sulfide deposit, Sudbury, Canada. The sulfide assemblage is dominated by pyrrhotite, with minor pentlandite, chalcopyrite, and pyrite, and they represent monosulfide solid solution (MSS) cumulates. The aim of this study was to establish the distribution of the PGE among the BMS and platinum group minerals (PGM) in order to understand better the petrogenesis of the deposit. Mass balance calculations show that the BMS host all of the Co and Se, a significant proportion (40–90%) of Os, Pd, Ru, Cd, Sn, and Zn, but very little (<35%) of the Ag, Au, Bi, Ir, Mo, Pb, Pt, Rh, Re, Sb, and Te. Osmium and Ru are concentrated in equal proportions in pyrrhotite, pentlandite, and pyrite. Cobalt and Pd (∼1 ppm) are concentrated in pentlandite. Silver, Cd, Sn, Zn, and in rare cases Au and Te, are concentrated in chalcopyrite. Selenium is present in equal proportions in all three BMS. Iridium, Rh, and Pt are present in euhedrally zoned PGE sulfarsenides, which comprise irarsite (IrAsS), hollingworthite (RhAsS), PGE-Ni-rich cobaltite (CoAsS), and subordinate sperrylite (PtAs2), all of which are hosted predominantly in pyrrhotite and pentlandite. Silver, Au, Bi, Mo, Pb, Re, Sb, and Te are found predominantly in discrete accessory minerals such as electrum (Au–Ag alloy), hessite (Ag2Te), michenerite (PdBiTe), and rhenium sulfides. The enrichment of Os, Ru, Ni, and Co in pyrrhotite, pentlandite, and pyrite and Ag, Au, Cd, Sn, Te, and Zn in chalcopyrite can be explained by fractional crystallization of MSS from a sulfide liquid followed by exsolution of the sulfides. The early crystallization of the PGE sulfarsenides from the sulfide melt depleted the MSS in Ir and Rh. The bulk of Pd in pentlandite cannot be explained by sulfide fractionation alone because Pd should have partitioned into the residual Cu-rich liquid and be in chalcopyrite or in PGM around chalcopyrite. The variation of Pd among different pentlandite textures provides evidence that Pd diffuses into pentlandite during its exsolution from MSS. The source of Pd was from the small quantity of Pd that partitioned originally into the MSS and a larger quantity of Pd in the nearby Cu-rich portion (intermediate solid solution and/or Pd-bearing PGM). The source of Pd became depleted during the diffusion process, thus later-forming pentlandite (rims of coarse-granular, veinlets, and exsolution flames) contains less Pd than early-forming pentlandite (cores of coarse-granular).

Process Development of Low-Cost AgNi and AgFe Contact Materials with no Range of Solid Solubility

AgNi and AgFe are known as contact materials with high workability and low contact resistance for medium to weak current contacts. However, AgNi and AgFe contact materials are difficult to manufacture using conventional melting and casting procedure because they exhibit no range of solid solubility of Ni and Fe in Ag for all temperature range. The purpose of this research is to develop a process for low-cost AgNi and AgFe contact materials based on solidification process control. AgNi and AgFe contact materials were produced by rotation cylinder method (RCM). The hardness value of AgNi and AgFe contact materials by RCM were higher than that of AgNi and AgFe contact materials produced by conventional powder metallurgy and co-precipitation processes. The higher hardness values of contact materials produced by RCM may be attributed to the uniform distribution and small size of Ni and Fe particles in Ag matrix.

Microstructural properties of bulk nanocrystalline Ag-Ni alloy prepared by hot pressing of mechanically pre-alloyed powders

A bulk nanocrystallined Ag50Ni alloy has been prepared by hot-pressing the mechanically pre-alloyed powders at 620degreesC under a normal pressure of 58 MPa in vacuum. The microstructural characteristics of the alloy were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results of the precise determination of the lattice parameters of the phases in the powders and in the alloy by XRD show that, after mechanical alloying for 200 h, the solid solubility of Ag in Ni reaches 4.85 0.21 at %, while that of Ni in Ag reaches 0.84 +/- 0.30 at %. After hot pressing, the Ag- and Ni-rich phases in the alloy still show a certain degree of supersaturation, with a solid solubility of 0.45 +/- 0.11 at % of Ag in Ni. After further annealing of the alloy at 700 degreesC for 24 h, the solubility decreases to a value of 0.21 0.11 at % for Ag in Ni and to less than 0.1 at % for Ni in Ag. The grain size of the mechanically alloyed powders was of ca 6 nm. After hot pressing, the grain size of the alloy increased to 40-60 nm and then grew further to 100-110 nm after annealing. The influence of the variation of the grain size and the internal stress on the line breadth of the X-ray diffraction peaks has been evaluated in detail. Finally, the role of the nanocrystalline structure in the fast densification process of the powders is also discussed.

Formation of supersaturated solid solutions in the immiscible Ni–Ag system by mechanical alloying

The mechanical alloying process in the immiscible Ni–Ag system with a positive heat of mixing was investigated by x-ray diffraction and differential scanning calorimetry. High energy ball milling of mixed elemental powders, with nominal composition NixAg100−x (x=95, 90, 70, 50, and 30), results in the formation of mixtures of supersaturated, nanocrystalline Ni-rich and Ag-rich solid solutions. The solubilities and final grain sizes of these phases depend on the nominal composition of the powder. The maximum solubilities were determined using Vegard’s law to be 4.3 at. % Ni in Ag and 6.6 at. % Ag in Ni for samples milled at room temperature. The effect of milling temperature on mechanical alloying was examined in the range −195 to 250 °C. Lower temperature milling leads to a larger solubility of Ni in the Ag-rich samples, up to 7.1 at. % for the Ni30Ag70 composition. Indications for the existence of a concentrated solid solution (Ni36Ag64-Ni44Ag56) were also found. Milling at higher temperatures leads to lower solubilities. A study of the thermal stability of supersaturated Ag-rich and Ni-rich phases shows that milling at high temperature can be understood in terms of a competition between mechanical mixing and thermal decomposition. At room temperature, nonequilibrium vacancies are responsible for decomposition. The results give new insight into the general characteristics of the mechanical alloying process in thermodynamically unstable systems.

Deviation from Matthiessen's rule at high temperatures: Theoretical interpretation

Theoretical interpretation is given for the deviation from Matthiessen's rule (DMR) at high temperatures on dilute alloy systems Au in Cu, Cu in Au, and Ni in Cu, and Cu, Ag, and Ge in Al, measured with the use of the new experimental techniques developed by Fujita and others. The measured deviation from this rule, $\ensuremath{\Delta}(c, T)$, can be fitted to curves of $Y+AT$ ($Y\ensuremath{\approx}0$), where $T$ is the absolute temperature, and the numerical constant $A(Y)$ can be calculated using a standard lowest-order (higher-order) variational scheme. $Y$ is always positive and gives a measure of the anisotropy of the scattering at high temperatures. For most of the Al-based and noble-metal-based dilute alloys, $Y$ is small and the anisotropy scattering is unimportant. The proportionality factor $A$ has been evaluated, within the standard variational formalism, using an atomistic model calculation for the electron-phonon spectral function. It is shown that the leading contribution to the high-temperature DMR is due to the change in the phonon spectral function $F(\ensuremath{\omega})$ for Cu in Al, Ge in Al, Cu in Au, and Au in Cu alloys, while it comes from the change in the electron-phonon coupling function ${\ensuremath{\alpha}}_{\mathrm{tr}}^{2}(\ensuremath{\omega})$ (electron-mass-enhancement parameter ${\ensuremath{\lambda}}_{\mathrm{tr}}$) for the Ag in Al alloy.

Supersaturated metastable Ag-Ni solid solutions formed by ion beam mixing

Extension of terminal solid solubilities has been achieved by ion beam mixing in the almost completely immiscible Ag-Ni system. Multi-layered samples of thin deposited Ag-Ni films of various compositions were bombarded with energetic Xe ions at temperatures from −190 to 250 °C. Supersaturated Ag- and Ni-rich fcc solid solutions were obtained, as indicated by x-ray and electron diffraction. Analyses of lattice parameters showed that the solubility range for the metastable solid solutions produced by low-temperature bombardment was wider than for those formed at high temperature. Maximum solubilities were determined to be 4.5 at. % Ni in Ag and 16 at. % Ag in Ni if one assumes the ion-induced fcc phases to be ideal solid solutions. The effects of implantation temperature on the formation of metastable phases are discussed.

Kinetics of oxide formation in liquid copper and silver

The process of formation of oxide phases in liquid copper and liquid silver has been studied by pumping oxygen into the liquid alloy with the use of a solid-electrolyte electrochemical cell. The oxygen potential at the electrolyte-metal interface is monitored simultaneously by the electrochemical cell. A wide range of effects were observed ranging from the very rapid formation of a layer of oxide at the electrolyte-metal interface to what appears to be homogeneous nucleation of the oxide in the metal. The results may help to explain some of the difficulties that sometimes have been observed in using this type of cell to measure the oxygen potential of a liquid metal. The results indicate that a supersaturation ratio of about 9 is necessary for homogeneous nucleation of iron oxide (most probably Fe3O4(s)) in liquid copper containing 0.01 to 0.07 pct iron. The interfacial tensionσCu-Fe3O4 is calculated to be 0.74 J/m2. In experiments with higher concentrations of deoxidant (0.2 pct Fe in Cu and 0.2 to 0.4 pct Ni in Ag) equilibrium precipitation of oxides apparently predominates over homogeneous nucleation for the experimental conditions employed. A mathematical model which partly explains the different effects observed is presented.

ARSENIDES OF THE TRANSITION METALS: VIII. SOME BINARY AND TERNARY GROUP VIII DIARSENIDES AND THEIR MAGNETIC AND ELECTRICAL PROPERTIES

The diarsenides of the cobalt and nickel families have been synthesized for magnetic susceptibility studies. The diffraction pattern of the low-temperature modification of nickel diarsenide differs from that of the mineral pararammelsbergite, although the space group is apparently identical and the unit cell dimensions comparable (orthorhombic [Formula: see text] a = 5.770 ± 0.007, b = 5.838 ± 0.006, c = 11.419 ± 0.008 Å). These binary diarsenides exhibit temperature dependent diamagnetic or weakly paramagnetic behavior. Temperature dependence of electrical resistivity indicates that PdAs2 is metallic while PtAs2 is a semiconductor with an energy gap of ~0.17 eV.Substitutional solid solution limits have been determined for various Group VIII transition metal atoms in the pyrite phases PdAs2 and PtAs2, and in the skutterudites RhAs3 and IrAs3. There is no substitution by Ru or Os in PdAs2, by Ni or Pt in PdAsa, by Ru or Ag in RhAs3, or by Os in IrAs3. Very limited substitutions were observed for Rh and Ag in PdAs2, Pd in PtAs2, Pd in RhAs3, and Pt in IrAs3. The limit of Co substitution in PdAs2 is 8.2 ± 0.3 atom %, and of Ni in PdAs2, 56.7 ± 0.3 atom %.In the CoxPd1−xAs2 system, a temperature-dependent paramagnetic contribution corresponding to approximately one uncompensated spin per cobalt ion has been attributed to the t52g low-spin configuration of the Co ion in the pyrite structure. In the NixPd1−xAs2 system, the temperature-independent paramagnetic contribution by the nickel ions is not completely understood.