Noble Alloys Research Articles

アルミニウム合金の局部溶解形態と溶解電位の関係

To investigate pitting growth characteristics of aluminum alloys observations of dissolution morphology within the pits formed after immersion corrosion test in tap water were carried out, and they were discussed in comparison with the anodic dissolution morphology in AlCl3 solution assuming localized corrosion environment. Dissolution morphology within the pits after immersion corrosion test could be well simulated with that after anodic dissolution in AlCl3 solution. The morphology was closely related with the electrochemical properties of the alloys, such as the level of pitting potential. For example, in aluminum and the more noble alloys (100) type of crystallographic pits, while, in the less noble alloys less crystallographic dissolutions were observed, respectively. On the other hand, (100) type of crystallographic pits could be observed even in the less noble alloys after the dissolution in the sufficiently noble potentials. With these results it can be concluded that the difference of dissolution morphology of aluminum alloy is caused, not by the additional elements themselves, but by variation of dissolution potentials.

Al-0.1 mass%Sn合金の電気化学的性質に及ぼす各種添加元素の影響

Effects of addition of a small amount of Fe, Si, Cu, Mn or Mg on the electrochemical property and the corrosion resistance of an Al-0.1 mass%Sn alloy were examined. The corrosion potential of the alloy was remarkably less noble, when it was water-quenched after the solution treatment, while it became noble when furnace-cooled, because of the precipitation of Sn. The addition of Cu, Si or Mn made the corrosion potential of quenched alloy noble, while that of Mg or Fe gave little effect. The additional elements had essentially no effect on the precipitation of Sn of the alloy. These suggest the effect of Cu, Si or Mn in the solid solution is greater than that of Sn on the electrochemical property of aluminum.Corrosion rates of less noble alloys in an acidified chloride solution which simulated the solution of anodic area were unusually high, but those of noble ones were sufficiently low. The anodic efficiency in galvanostatic dissolution was lower in the less noble ones, but much higher in the noble ones. These results show that the anodic efficiency is controlled by the corrosion rate of anodic area which is closely related with the electrochemical property of the alloys and that an alloy with both a higher efficiency and an excellent sacrificial anode effect can be hardly obtained in these ternary alloys examined.

Ａｌ‐０．１％Ｓｎ合金の電気化学的性質に及ぼす微量亜鉛含有の効果

Anodic polarization characteristics and corrosion resistance of Al-0.1%Sn alloys containing Zn up to 0.3% were examined in NaCl and AlCl3 solutions. Remarkably less noble characteristics and abnormally low corrosion resistance of solution treated Al-Sn alloys are greatly improved by an addition of Zn0.2% or more. Localized dissolution morphology of Al-Sn-Zn alloys is controlled mainly by dissolution potential, that is, canal-like and (100) type of crystallographic pits are observed in the solution treated and precipitation treated noble alloys respectively. Zn addition has little effect on the microstructure of Al-Sn alloys both solution treated and precipitation treated. A small amount of Zn addition is effective to improve electrochemical properties of Al-Sn alloys in practical use.

A comparison of the bond strength of two ceramometal systems

T he ceramometal restoration has been a major advancement in restorative dentistry. The metal component provides the fit and strength, while the porcelain veneer affords ihe esthetics. The bonding of the two materials is of major importance in the fabrication of the ceramometal restoration. The theory of ceramicto-metal bonding has focused on four possible mechanisms: (1) van der Waals’s forces, (2) compressive forces generated in thermal expansion, (3) mechanical bonding with surface geometry, and (4) chemical bonding with the oxides in the ceramic and the metal. Various test methods have been developed to measure the bond strength at the ceramic-metal interface and to understand the bonding roles of the four mechanisms. The most commonly used test was developed by Shell and Nielsen.’ This was a shear test in which an alloy rod was pulled out of a porcelain block. Anthony et aL2 modified the Shell and Nielsen test using a ring of porcelain instead of a block to reduce the notch effect at the free surface of the bond. With the Shell and Nielsen method or variations, studies have reported bond strengths with 10,000 to 20,000 psi.lv3 The variables include the types of porcelain, the alloy, coating agents, trace elements, degree of roughness, and the type of firing atmosphere. With polished rods of 100% noble alloy, Shell and Nielsen’ measured bond

Fretting of electrical contacts: An investigation of palladium mated to other materials

The contacts of electrical connectors that are made of palladium can develop a high contact resistance during fretting because of the formation of insulating polymeric solids which originate in adsorbed organic pollutants from the atmosphere. A fretting study was conducted with palladium mated to a large variety of noble metals and alloys involving gold, palladium, silver, rhodium, ruthenium, nickel and other metals to determine whether there are systems that do not degrade as does palladium mated to itself. Fretting was modeled with bench equipment using wipes 20 μm long and a contact force of 50 gf for runs of 10 5 cycles at 8 Hz. It was found that the contact resistance can be stable, can rise quickly to high values, can increase gradually to intermediate levels or can be stable until a wear-out process is completed after which the contact resistance rises. These behaviors are determined by the film-forming tendency of the interface materials which, in turn, depends on the composition of the metals in the contact pair and their tendency to transfer during fretting. The composition of the interface of a dissimilar metal pair changes from the initiation of fretting until an equilibrium is attained when both surfaces are identical. To avoid high resistance during fretting with a palladium contact, the opposing member should be non- or low-polymer forming such as gold, silver or alloys of these metals which can contain up to about one-third palladium. A second condition is that the mating contact should be softer so that the direction of metal transfer is to the palladium. Finally, if the opposing material is a thin gold layer on a base metal or a substrate that forms polymer, its thickness should be sufficiently large to resist wear-through during the service life of the connector.

A pseudopotential approach to the electronic structure of dilute transitional and noble metal impurity systems

A generalised pseudopotential formalism for calculating the change in electronic structure Delta N(E) of transitional impurity systems has been employed to recast the Green function analysis of Riedinger (1971) for dilute transitional impurity systems into a pseudopotential framework. The required pseudo Green's functions are evaluated from a model Hamiltonian representation of the host metal band structure. For the difference pseudopotential at the impurity site the authors employ a parametrised, optimised model potential which is made partially self-consistent through the application of the Friedel sum rule. This pseudopotential method is then applied to a variety of dilute transitional impurity systems in an endeavour to assess its overall validity. The first systems considered are the dilute noble metal-palladium alloys CuPd, AgPd and AuPd and the resulting Delta N(E) are found to yield Pd virtual bound state (VBS) resonance peaks whose positions and widths are in fairly good agreement with experiment. The method is then applied to the dilute PdAu alloy system and produces a Au VBS resonance near the bottom of the Pd d band as supported by photoemission studies. Finally the authors consider the dilute noble alloys for which the difference in chemical valence of the two components is zero. Calculations for both AgAu and AuAg confirm that there is an effective charge transfer in these systems of around 0.3 e.

Microhardness of alloys for porcelain veneering

R e s t o r a t i v e materials for fixed prosthodontics must be capable of withstanding masticatory forces. The mechanical properties of the high-fusing gold alloys differ from those of type III and type IV dental casting alloys. '-'~ The microstructure and mechanical properties of the noble dental alloys are dependent on the composition of the alloy.' There is a systematic relationship between the proportional limit, tensile strength, and hardness of noble alloys for porcelain veneering. :~-~ Chemical composition and microstructure of a high-fusing gold alloy varies depending on the location within the metal, s 'n The purpose of this study was to determine the microhardness of three high-fusing alloys at the metal/porcelain interface and centrally in the fused specimen during different stages of alloy preparations.

Pre-service corrosion control in multiflash desalination plants

Multiflash Desalination Plants are characterized by large heat exchange surfaces and presence of noble alloys which might be sensitive to localized corrosion attack during manufacturing, transportation and commissioning. To avoid premature failure, all surfaces must be preserved clean and free from corrosion nucleation until the plant starts its normal operation. A detailed analysis is given of possible corrosion causes and available remedies. Some Pre-conditioning treatments are outlined, especially for stainless steel and copper alloys.

Anisotropic [formula omitted] interactions from spin-orbit coupled 5 d intermediate states

The anisotropy of the conduction electron-4ƒ local moment interaction ( k-ƒ) gives rise to anisotropic transport effects. The contribution from the orbital character of the 4ƒ moment has been well documented by magnetotransport studies on noble metals containing non- S state rare-earth ions. To determine whether there is an additional contribution to the anisotropy from the spin-orbit coupled 5 d electron states we have studied the magnetoresistivity of Ag: Gd alloys. We have not found any significant anisotropy of the magnetoresistivity. By comparing this result and previous Hall effect and magnetoresistivity data on noble metal-rare earth alloys with our model calculation, we come to the conclusion that the spin-orbit splitting of the 5 d virtual bound state is relatively small. We discuss the details of the resulting anisotropy of the k-ƒ interaction.

Susceptibility maximum of AuFe, CuFe and AgFe alloy films

In noble metal base alloy films, produced by quench condensation, the temperature of the maximum of the initial susceptibility increases with the Fe concentration and with annealing. For AuFe films, annealed at 1100 K, this temperature is nearly the same as for bulk AuFe.

ChemInform Abstract: THE OXYGEN EVOLUTION REACTION ON PLATINUM, IRIDIUM, RUTHENIUM AND THEIR ALLOYS AT 80°C IN ACID SOLUTIONS

AbstractDie kinetischen Parameter für die O2‐Entwicklung an den 50:50‐Atom‐%‐Legierungen Ru‐Ir, Ru‐Pt und Ir‐Pt in l M H280; und 1 M CF3‐ SO3H‐Lösungen werden mit denen von Ru‐, Ir‐, Pt‐ und RuO,/TiO,(auf Ti‐Substrat)‐ Elektroden verglichen (potentiostatische und cyclisch voltammetrische Untersuchungen).

The oxygen evolution reaction on platinum, iridium, ruthenium and their alloys at 80°C in acid solutions

Kinetic parametes were determined for the oxygen evolution reaction on 50–50 atom percent alloys of RuIr, RuPt, and IrPt and compared with results obtained using ruthenium, iridium, platinum, and RuO 2/TiO 2 electrodes. The potentiostatic studies were made on oxide covered electrodes at 80°C in both 1.0 M H 2SO 4 and 1.0 M CF 3SO 3H. Cyclic voltammetric studies showed that while these noble metals and alloys are about equally effective as electrocatalysts for the hydrogen evolution reaction, striking differences in activity are found for the oxygen evolution reaction. The order of electrocatalytic activity towards oxygen evolution in H 2SO 4 is Ru > RuIr alloy ∼ RuO 2/TiO 2 ∼ Ir > IrPt alloy > RuPt alloy > Pt. The type of acid used had very little effect on the kinetic parameters. The lower electrocatalytic activities when platinum is present is probably due to the formation of a platinum oxide film. The dual barrier model is used to interpret the results for the electrodes containing platinum. The best electrocatalysts for oxygen evolution in acid solutions consist of noble metals which form oxide films (RuO 2, IrO 2) possessing metallic characteristics.

Measurement of the critical pitting potential of aluminium

The electrochemical methods for the measurement of the critical pitting potential have been analyzed in terms of their applicability to aluminium and its alloys. Interpretation of data for these alloys may follow different guidelines than those developed for more noble alloys like steel in order to obtain meaningful results. Present work and a literature survey show that most methods give fairly accurate results with careful data analysis with the exception of fast-scan methods. Experimental difficulties associated with different methods are reviewed. The critical pitting potential of aluminium varies appreciably with chloride concentration, other factors such as surface treatment, temperature, and small additions of alloying elements being of minor importance. The significance of the critical potential for aluminium is discussed in view of this result.

Semiprecious alloys for cast restorations: A preliminary report

A previous clinical evaluation indicated that semiprecious metals had a definite place in the construction of dowels and cores in endodontically treated teeth. 2 The results from the present in vitro study suggest that those alloys do have a place in the fabrication of single castings as type III and IV gold alloy substitutes. Although when compared with a type III gold alloy the behavior of the semiprecious alloys tested was less like that of a noble alloy, the semiprecious alloys appeared less active than the base-metal alloy. This suggests that the semiprecious alloys should be acceptably resistant to corrosion in the oral environment.

A Test of Noble Metal Slip-Ring Alloys for Use in Inertial Guidance Platforms

Lubricated slip-ring contact materials were life-tested in a nitrogen atmosphere and in a multichemical atmosphere that simulated the gases in an inertial guidance platform. The test mode was one that maximized the effects of debris accumulations and the generation of resistive films on infrequently wiped surfaces. The contacts that were lubricated with a four-ring polyphenyl ether had lower noise than ones lubricated with a blend of diester and chlorofiuorocarbon oils. The alloys grouped in decreasing order of performance as sliding contacts for inertial guidance platforms are as follows: Group I-ASTM B477; 4 Ni, Au; 1 Ni, Au electrodeposit; Group II-ASTM B541; 10 Cd, Au; Group III-54.5 Au, 37.5 Ag, 4 Cd, 4 In.

On the electrical resistivity of noble based transition metal dilute alloys

We apply the CPA expression of the electrical conductivity to the case of Au-based alloys containing 3 d and 4 d transition impurities. In this approach, a s-diagonal disorder larger for the 3 d case than for the 4 d one can explain the measured differences in resistivity between these two cases.

Evaluation of alternative alloys to type III gold for use in fixed prosthodontics

A study was done to evaluate the fit of castings made from commercially available alloys promoted by their manufacturers as cheaper alternatives to type III gold for use in fixed prosthodontics. Two nickel-chromium alloys, two silver-palladium alloys, two gold-silver-palladium alloys, a 50% gold alloy, and a type III conventional gold alloy (used as a basis of comparison) were evaluated. After optimum conditions for waxing, investing, and casting were determined experimentally, four crowns (two full crowns and two three quarter crowns) were cast from each alloy. The castings were cleaned by pickling or sandblasting and placed on their respective dies. Only one casting was made from each die. Ten judges were asked to evaluate the marginal fit and completeness of each casting on its die. The judges rated each casting and the ratings were converted into rankings. Type III gold and Forticast tied and were ranked first; Paliney CB was ranked second; Alborium and Albacast tied and ranked third; Aurolite CB was ranked fourth; and Jelenko Experimental and Howmedica III tied and ranked fifth. It was found that the nickel-chromium alloys produced castings that had a tight fit and showed marginal discrepancies even under conditions designed to yield maximum expansion of the investment. These nonprecious metal castings were judged inferior in terms of fit when compared with castings made from noble metal-and precious metal-containing alloys. Existing investments and techniques were adequate for all castings except those made from the nonprecious alloys. It was concluded that low (approximately lambda 50%) gold alloys and palladium-silver-gold alloys that are commerically available can be used as substitutes for type III gold alloy without any loss inthe quality of casting fit.

Optical properties of silver-palladium alloys

Thin films of Ag rich Ag-Pd alloys are prepared by cathodic sputtering. Reflectivity of pure metals and alloys is measured using four monochromators to successively cover the whole energy range between 0.1 and 90 eV. Optical and dielectric constants are deduced by a Kramers-Kronig analysis. It is obvious for the results obtained on Ag rich Ag-Pd alloys in the 1-6 eV energy range, that the virtual bound state model is appropriate for describing the alloy density of state. The virtual bound state is found to be centred at 2.35 eV below the Fermi level; the halfwidth of the states due to s-d interaction is equal to delta 0sd=0.2 eV. The interactions between Pd d states gives an important contribution to the observed width. When the palladium concentration reaches 45 at.% the Pd d states form a true band; Friedel's theory therefore seems limited to the noble metal rich alloys.

Microsyntaxy and polytypism in SiC

An interesting type of syntaxy has been observed by transmission electron microscopy where two different polytypes of SiC, 6H and 15R in one case and 6H and 4H in another case, coexist as alternating parallel bands of 200∼500 A ̊ in width with the common c-axis. It is pointed out that this phenomenon is very closely related to an extensive formation of twin bands during the growth of β-SiC and to the coexistence of two kinds of martensite of close packed structure as alternating parallel bands in the transformation products of β-phase noble metal base alloys.

The effect of d electrons on crystal field potentials in rare earth metals and dilute alloys

The effect of 5d character on the crystalline electric field in noble metal rare earth alloys and in pure rare earths has been investigated. The change in sign of the fourth order CEF coefficient in the noble metal alloys can be interpreted in terms of this d character. From symmetry this d like component has no effect on the sixth order coefficients whose varying magnitude in these alloys can be explained using the f like contribution. In the pure rare earth metals it is likely that d character will predominate.