Use Of Metals Research Articles

High temperature strength of YSZ joints brazed with palladium silver copper oxide filler metals

The Ag–CuO x system is being investigated as potential filler metals for use in air brazing high temperature electrochemical devices such as solid oxide fuel cells and gas concentrators. The current study examines the effects of palladium addition on the high temperature joint strength of specimens prepared from yttria stabilized zirconia (YSZ) bars brazed with the binary Ag–CuO x , and 15Pd–Ag–CuO. It was found that while the binary Ag–CuO x system exhibits stronger room temperature strength than the 15Pd system the strength is reduced to values equivalent of the 15Pd system at 800 °C. The 15Pd system exhibits a lower ambient temperature strength that is retained at 800 °C. In both systems the failure mechanism at high temperature appears to be peeling of the noble metal component from the oxide phases and tearing through the noble metal phase whereas sufficient adhesion is retained at lower temperatures to cause fracture of the YSZ substrate.

Calculated valence electronic structure of 3d metals for use in the X-ray intensity ratio studies

3d occupation numbers of the transition elements corresponding to various types of atomic configurations are calculated by means of the linear muffin-tin orbital (LMTO) method. This data is used with the multiconfiguration Dirac–Fock (MCDF) X-ray intensity ratios to estimate the electron populations of the 3d metals in alloys.

What are “heavy metals” in Plant Sciences?

Plants do not have the ability to sense physical properties of metals, e.g. specific weight. The term “heavy metal” was defined mainly by the specific weight of metals. The definition was often connected with the expectation that the substance should be toxic. This definition is not acceptable and also inconsistent in use as already stressed in literature. However, in Plant Sciences, the term is so widely used that it is hardly possible to eliminate it. We suggest instead defining the term in a more unequivocal way. This should be done on the basis of the periodic system of elements. Here, we suggest introducing the following three subgroups forming the group of heavy metals for use in Plant Sciences. 1st subgroup: all transition elements except La and Ac (Transition metals). 2nd subgroup: rare earth elements, subdivided in the series of lanthanides and the series of actinides including La and Ac themselves (Rare earth metals). 3rd subgroup: a heterogenous group p-elements including the metal Bi, the amphoterous oxides forming elements Al, Ga, In, Tl, Sn, Pb, Sb and Po, and the metalloids Ge, As and Te. We suggest using the term “lead-group” for this 3rd subgroup of heavy metals as in Toxicology and Environmental Sciences, Pb is the most prominent representative of this group.

Development of Carbon Materials for Energy and Environmental Applications

Methodologies for generating carbon materials from unusual natural sources like Limonea acidissima and Calotropis gigantea are reported. The carbon materials thus obtained have been characterized using a variety of tools. The possibility of modulating the textural properties of these materials has been examined. The carbon materials synthesized have been exploited for specific applications, such as support for noble metals for use in Direct Methanol Fuel Cells and as support for heteropoly acid for the production of gasoline additive. In addition, the utility of some of the activated carbon materials (from commercial sources) for the removal of sulphur from crude petroleum sources is also examined.

Effect of Filler Metal Composition on the Strength of Yttria Stabilized Zirconia Joints Brazed with Pd-Ag-CuO x

Various compositions in the Ag-CuOx system are being investigated as potential filler metals for use in air brazing high-temperature electrochemical devices such as solid oxide fuel cells and gas concentrators. Prior work has shown that the melting temperature, and therefore the potential operational temperature, of these materials can be increased by alloying with palladium. The current study examines the effects of palladium addition on the joint strength of specimens prepared from yttria stabilized zirconia (YSZ) bars brazed with three different families of filler metals: Ag-CuO, 5Pd-Ag-CuO, and 15Pd-Ag-CuO. In general, it was found that palladium leads to a small-to-moderate decrease in joint strength, particularly in low copper oxide containing filler metals. However, the declination in strength is likely an acceptable trade-off for increased use temperature. In addition, a critical composition was observed for each filler metal series at which the mechanism for joint failure underwent a transition, typically from ductile to brittle failure. In each case, this composition corresponds approximately to the silver-rich boundary composition of the liquid miscibility gap in each system at the temperature of brazing.

Ranges of ions in metals for use in particle treatment planning

In proton and ion radiotherapy, the range of particles is calculated from x-ray computed tomography (CT) numbers. Due to the strong absorption of x-rays in a metal and a cut-off for large Hounsfield units (HU) in the software of most CT-scanners, a range calculation in metals cannot be based on the measured HU. This is of special importance when metal implants such as gold fillings or hip prostheses are close to the treatment volume. In order to overcome this problem in treatment planning for heavy charged particles, the correct ranges of ions in the metal relative to water have to be assigned in the CT data. Measurements and calculations of carbon ion ranges in various metals are presented that can be used in treatment planning to allow for a more accurate range calculation of carbon ion beams in titanium, steel, tungsten and gold. The suggested values for the relative water-equivalent range and their uncertainties are 3.13 (±3%) for titanium, 5.59 (±3%) for stainless steel and 10.25 (±4%) for gold.

Metal equilibration in laboratory-contaminated (spiked) sediments used for the development of whole-sediment toxicity tests

The equilibration and bioavailability of metals in laboratory-contaminated sediments have been investigated in order to provide better guidance on acceptable procedures for spiking sediments with metals for use in the development of whole-sediment toxicity tests. The equilibration rates of Cd, Cu, Ni and Zn spiked into three estuarine surface sediments with varying properties were investigated. Changes to sediment pH, redox potential, porewater and acid-soluble metals, acid-volatile sulfide and bacterial activity during equilibration, effects of temperature and disturbances following equilibration are reported. The addition of metals to sediments caused major decreases in pH and increases in redox potential as metals displaced iron(II) into the porewaters and added metals and iron (following oxidation) were hydrolyzed. The rates of equilibration of metals in porewaters varied considerably and were dependent on sediment and metal properties. For the oxic/sub-oxic sediments studied, metal-spikes of Cd, Cu, Ni and Zn appeared near equilibrium after 25–45, 10–15, 30–70 and 20–40 days, respectively. Acid-soluble metal concentrations decreased during the equilibration period indicating that the metals become more strongly associated with the sediments with time (less bioavailable). Bacterial activity was greatest in the sediment equilibrated at pH 7 and decreased following the addition of metals. During the equilibration period, bacterial activity increased in sediments equilibrated at pH 6, remained low in sediments at pH 8 and varied erratically in sediments at pH 7. Spiked sediments were shown to equilibrate more slowly at lower temperatures resulting in high porewater metal concentrations. Disturbances to equilibrated sediments because of sample manipulation caused significant iron(II) oxidation and losses of metals from porewaters. The importance of documenting spiking and equilibration procedures and carefully measuring and reporting sediment parameters is highlighted so that contaminant bioavailability and exposure pathways can be interpreted and organism sensitivity accurately determined. Recommendations are given for the preparation of metal-spiked sediments for toxicity testing purposes.

Anode Materials for Low-Temperature Fuel Cells: A Density Functional Theory Study

Based on density functional calculations, we discuss the effect of alloying Pt with other metals for use as anode catalyst materials in low-temperature fuel cells. We discuss why a few parts per million of CO in the H2 fuel can poison Pt surfaces and how this problem can be alleviated by alloying, and an extensive data base of the effect of alloying on the reactivity that includes all binary combinations of the transition metals to the right in the periodic table is given. We also discuss the effect of surface segregation and give a calculated data base of segregation energies of binary transition metal alloys. Based on extensive Monte Carlo simulations we show that while the adsorbate-free surface of a Ru0.5Pt0.5 alloy has no Ru in the first layer, the presence of CO can move some Ru to the surface, but all these Ru atoms are covered by CO.

Electrochemical lithiation of tin and tin-based intermetallics and composites

This article gives an overview on lithium alloys and lithium alloying metals for use as anodes in ambient temperature rechargeable lithium batteries. After a brief introduction about advantages and drawbacks of lithium alloy anodes and a chronological review of their development, principle concepts to overcome the problems with the dimensional stability of the metallic host materials will be presented. Recent work on promising multiphase (composite and/or intermetallic) tin-based lithium alloying materials will be highlighted.

Materials selection for the in situ mirrors of laser diagnostics in fusion devices

When mirrors for the laser scattering diagnostic for large fusion devices need to be inside the vacuum chamber, they are subjected to irradiation by multiple high-energy laser pulses and bombardment by charge exchange atoms. Both of these assaults are known to degrade and eventually damage metal laser mirrors given sufficient time and flux. Our aim in this article is to use current data on these damage mechanisms to make design selections of metal mirror materials for application in fusion device diagnostics. We identify tradeoffs between low sputtering rates and multipulse laser damage resistance in candidate metals. The data for multipulse laser damage are incomplete and extend to a maximum of only 104 shots for a few metals. However, there is a clear trend of decreasing laser-damage threshold with increasing number of shots, and damage threshold fluences can fall to 10% of the single-pulse damaging laser fluence. Further experiments up to 106 or 108 laser shots need to be conducted on the likely mirror candidate metals for use in new plasma devices. We define a figure-of-merit based on current laser damage data and employ it in our analysis. Recent data on the sputtering yield and reflectance degradation of metal mirrors give a different priority ranking of candidate metals. Overall, the preferred material selection depends on the number of laser shots and the number of plasma pulses that the mirror must endure before replacement is allowed. For example, we find that for conditions typical of the LHD (10 s plasma pulses with a 10 Hz laser PRF), Au, Ag, and Cu are candidate materials if mirrors are replaced after 103 plasma pulses; Au and Rh are candidates if the replacement interval is 104 pulses; and if the replacement interval is further increased to 105 plasma pulses, then Mo is the candidate material. Other materials might also be candidates but the data on them are still insufficient.

Effectiveness of Thin‐film Barrier Metals for Eutectic Solder Bumps

This paper describes effective thin‐film structure barrier metals for use as eutectic solder bumps. Shear strength and bump interconnection resistance were evaluated. The mutual diffusion in metals was investigated. Barrier metal structures —Cu/Ti,Ni/Ti and Cu/Cr—were evaluated after ageing. The Ni/Ti structure has good reliability according to ageing test results. Pd is used for improvement of solder wettability and as an oxidisation barrier. Consequently, it was concluded that a thin‐film Pd/Ni/ Ti barrier metal is suitable for use as eutectic solder bumps. The broken interfaces of the solder bumps were analysed by scanning auger electron spectrometry. In the thin‐film Cu/Ti structure, decrease in the shear strength is caused by three mechanisms, as determined from the broken interface analysis. The three mechanisms are mixed metal formation, Ti oxidisation and diffusion between barrier metals and Al. Furthermore, TCT and PCT were carried out on these eutectic solder bumps to confirm the interconnection...

Study of paramagnetic ions in metals for use in cryogenic particle detection

We discuss a microcalorimeter for particle detection in which the absorbed energy is determined by the change in magnetization of paramagnetic spins in a metallic host. The magnetization is measured with a SQUID magnetometer. Results are presented for the system of erbium ions in gold.

Comparison of the behaviour of glassy carbon and some metals for use as nonconsumable anodes in alumina-cryolite melts

Current interest exists in development of nonconsumable anodes for the Hall-Heroult process of aluminium production and also in situ analytical probes for determination of Al2O3 content in the cryolite melts used in this process. A comparison of the behaviour of glassy carbon and metals such as tungsten, tungsten carbide, nickel and stainless steel (SS-316) used as anodes in alumina-cryolite melts is investigated by means of electrochemical transient techniques (cyclic voltammetry and chronoamperometry) and Tafel anodic polarization experiments. The results show that only glassy carbon could be used as a successful sensor electrode for an in situ determination of Al203 in alumina-cryolite melts and that the metals investigated are unresistant to anodic attack in such melts. Consequently, the metals investigated cannot be used as sensor electrodes for in situ electro-analytical determination of alumina in alumina-cryolite melts, nor as anodes in the production of aluminium by the Hall-Heroult process.

Noble Metal Alloys as Strain Gauge Materials

The development of materials which contain the noble metals for use in high temperature strain gauges is reviewed, with particular emphasis being placed upon work done by the Institute of Precious Metals, in China. Three alloy systems displaying excellent resistance to oxidation and good overall properties when used in high temperature strain gauges, are singled out for examination. These are platinum-tungsten-rhenium-nickel-chromium-yttrium, gold-palladium-chromium-platinum-iron-aluminium-yttrium and palladium-chromium. Their development and the suitability of these alloys for use in measuring high temperature static strain are discussed.

Spectroscopic studies of the chemical properties of thin metal films on poly(ether imide)

X-ray photoelectron spectroscopy studies were conducted on thin films of copper and nichrome (80:20 Ni:Cr) on neat poly(ether imide) (PEI) substrates. Evaporated copper thin films reacted mildly with PEI and formed metal carbides and oxides at the copper - PEI interface. In contrast, the chromium component of the nichrome alloy reacted strongly with PEI to generate a distribution of chromium oxides, nitrides, and carbides. However, the nickel component of nichrome exhibited little reactivity with the resin. Differences in the reactivities of metal thin films on PEI can be correlated to the heats of formation of the corresponding metal carbides, oxides, and nitrides. This information provides key insights into metals for use as adhesion promoters on printed circuit boards and molded circuits containing PEI.

Migration of alkyl groups from zirconium to various haloboranes

The hydrozirconations of acyclic alkenes are known to yield the dicyclopentadienyl-1-aklyl-zirconium chlorides regioselectively and in high yields. These alkyl groups may readily be transmetallated to the haloboranes forming regioisomeric pure alkylboranes in good yields. In principle, this migration reaction combines the facile hydrozirconation and unique isomerization reactions of organozirconiums with the established chemistry of boron, expanding the utility of both metals for use in organic synthesis.

New Applications of Weak Donor Atoms to Coordination, Organometallic and Materials Chemistry

Abstract Non-aqueous solvated transition metal cations are enjoying renewed popularity as precursors for new applications in molecular and materials chemistry. In two related projects, we are engaged in a general investigation of the syntheses, structures and reactivity of new compounds containing nitrile and ether ligands. A major effort is underway to synthesize homoleptic metal-metal bonded acetonitrile cations of second and third row metals for use in coordination and organometallic chemistry, photochemistry and materials chemistry. Dinuclear carboxylate, halide and halide-phosphine complexes are used to synthesize the metal-metal bonded acetonitrile cations [M2(MeCN)10]4+ (M = Re, Rh). The unusual partially solvated species [Mo2 IV,IV(μ-F)(MeCN)8O2]3+ was prepared from MoCl3(THF)3 in CH3CN. Reactions of the bulky ether-phosphine ligand tris(2,4,6-trimethoxyphenyl)phosphine (TMPP) with the dinuclear cation [Rh2(MeCN)10]4+ and with acetonitrile cations of 3d metals [M(MeCN)6]2+ (M = Co, Ni) produce bis...

X-ray photoelectron spectroscopic comparison of sputtered Ti, Ti6Al4V, and passivated bulk metals for use in cell culture techniques

In view of the reported differences in biological bone tissue reactions to Ti and Ti6Al4V the aim of the work described herein was to establish whether direct-current magnetron sputtered films would be realistic models of these materials which could then be used for in vitro studies of bone cell behavior. X-ray photoelectron spectroscopy (XPS) was used to compare the surface chemistries of bulk-passivated metals and the sputtered films. In the bulk passivated samples the predominant Ti oxide phase was 4+. However, Ti in its lower oxidation states was evident though closer to the bulk–oxide interface as seen by angle-resolved XPS. The Al content of the passivated alloy oxide film was seen to be greatly enhanced (26 wt. %) over that of the stoichiometric alloy while V was reduced (1 wt. %). The surfaces of the sputtered films were very similar to their bulk passivated counterparts. Although there was indication that the distribution of the various Ti oxide phases within the film differed to that in the passivated oxide layer, it was concluded that the sputtered films may be developed as realistic substrata to model bone cell reactions to bulk passivated metals.

Chemically modified metal surfaces—a new class of composite materials

AbstractThis promising method of chemically modifying reactive metal surfaces with organic molecules prior to the attachment of polymers could have a significant impact on work aimed at the optimization of the performance of composite materials. Strong chemical bonds can be formed between a suitably prepared metal surface and certain monomers, which resist even an electrochemical polarization of the interface at large cathodic or anodic overpotentials. These chemical bonds can, however, only be achieved if a suitable structure and reactivity is generated, for example, by using electrochemical techniques. Therefore, further technological progress in this important area requires the cooperation of scientists from rather different scientific disciplines like electrochemistry, surface science and organic chemistry, in order to optimize the structure of the organic monomers and to provide the best possible bonds to the different metals in use, taking into account the rather different reactivity of technologically important media.

Evaluation of Alkaline Earth and Transition Metals for Use in the Ion Moderated Partition Chromatography of Sugars

Abstract The elution behavior of 28 sugars and related compounds from high performance chromatography columns packed with alkaline earth and transition metals was investigated. As expected from the well-known chromatography of the commercially available calcium, silver, and lead form columns, elution behavior is highly metal-ion form specific. A significant data base of sugar elution versus column cationic-form was generated to permit the selection of new columns to enhance the separation of specific eluting species. Sugars resulting from the hydrolysis of wood were closely examined. Arabinose and galactose, known to be difficult to separate on commercially available lead and silver-form columns, were well separated on custom-packed rubidium and cesium-form columns.