Iridium Alloy Research Articles

Field-ion microscopy of dilute substitutional solid solutions

A systematic field-ion microscopy study of several iridium-based dilute substitutional solid solutions has been performed. Alloys of iridium with zirconium, tungsten, rhodium, platinum and ruthenium, having solute concentrations of between 0.1 and 5 at. %, have been examined by directscreen methods in order to establish the viability of differentiating atomic species solely by image contrast features arising from their differing response to the field-ionization-evaporation processes. Reliable species recognition in this way allows the structural and crystallographic relations between the solvent and solute species to be determined collectively from careful field-evaporation sequences. A method of manual numerical analysis of micrographs has been developed which allows the salient contrast features from any one alloy system to be deduced. Further, the order of priority of various experimentally observed contrast features has been determined as a function of several parameters. The reliability of such investigations is discussed in terms of both experimental techniques used and the presence of artefact contrast events (e.g. field-induced surface vacancies) created by the technique itself. As a direct means of investigating such structures at the atomic level, it is found that field-ion microscopy can supply information concerning the location of particular species and may also reveal some aspects of the surface electronic state of each atom species with respect to its coordinating surroundings.

Vibrational spectra of CO adsorbed on iridium alloys

The vibrational spectra of carbon monoxide chemisorbed on alloys of Ir-Rh, Ir-Pd, Ir-Pt and Ir-Cu of different composition have been investigated at temperatures from 30 to 400°C. It has been shown that the surface of an alloy does not correspond in its properties to a simple mixture of the two components concerned. In the case of CO chemisorbed on Ir-Rh, Ir-Pd and Ir-Cu, a lowering of the frequency of CO has been observed. This effect is probably due to electron transitions between the alloy components.

Dissociated dislocations in field-ion microscope images of iridium and iridium-based alloys

Abstract The geometrical contrast theory for dislocations emerging in the imaged surface of field-ion specimens has been extended in order to analyse several new observations of dissociated perfect dislocations in specimens of both pure iridium and some iridium-based dilute alloys. It is shown that these dissociation patterns are often not of the simple ‘stepped-ring’ type because of the frequent occurrence of q values for the bounding partial dislocations which are integral, zero, or of magnitude greater than p for the perfect dislocation. The recognition of such patterns and their distinction from artefacts are discussed, together with the metallurgical significance of the fault patterns observed, including a possible solute interaction and the probable fault configuration of dissociated perfect dislocation loops. No significant variation in the stacking-fault energy of iridium on alloying has been observed, the fault energy being deduced as between 230 and 400 ergs cm−2. The correlation of the observed...

Shape of the Field-ion Image Points for Certain Solute Atoms—the “Halo” Effect

Platinum and rhodium solutes in dilute iridium alloys give rise to characteristic field-ion image points which have weak structure outside the main circular core (the “halo” effect). This effect arises in some way from the charge distribution around these solute atoms and can be used as a diagnostic test for the presence and distribution of these solutes.

Study of the Instability of Noble Metal Thermocouples in Vacuum

Thermoelectric instabilities of noble metal thermocouples and individual thermoelements (platinum, rhodium, iridium, platinum-rhodium, and iridium-rhodium alloys) have been studied in vacuum in the temperature range 800 to 1600°C. These studies are an extension of previous work performed in oxidizing and neutral atmospheres. As in that work, the principal source of instability was found to be contamination of the thermoelements by impurities from ceramic protection tubes. Thermocouple errors associated with this contamination are reported and compared with the previous data.

The nomenclature of the natural alloys of osmium and iridium

SummaryAn historical review of the nomenclature of the natural Os-Ir alloys suggests that the most suitable names are: For the cubic alloys, osmiridium (Steffens, 1824), i.e. osmian iridium; and for the hexagonal alloys, iridosmine (Breithaupt, 1827), i.e. iridian osmium, for alloys with 20% or more Ir, and native osmium for the very rare alloys with little or no Ir. Iridosmine may, if desired, be divided into two varieties, nevyanskite and sysertskite, following Rose and Haidinger.

Glass Insulated Platinum Microelectrode

Microelectrodes for electrophysiological use have been prepared easily and quickly by electrolytically sharpening platinum iridium alloy wire and coating with molten glass. The desirable combination of the electrical characteristics and strength of the platinum iridium wire with the exceptional durability of glass insulation has long been known, but earlier methods of fabrication were difficult and tedious.

Points from Foregoing Letters

Mass spectrograms of platinum and platinum following cycle occurs: visual purple iridium alloy obtained by means of a high-frequency spark are submitted by Prof. A. J. Dempster. They confirm the existence of two iridium isotopes of mass numbers 191 and 193, the existence of which was recently deduced by Venkatesachar and Sibaiya from the arc spectrum of iridium. These two isotopes fill the only gaps in the mass number scale in this region.

XV.—On the Thermo-Electric Properties of Charcoal and certain Alloys, with a Supplementary Thermo-Electric Diagram

The determination by experiment of the thermo-electric relations of any one substance belonging to the electromotive series to all other such substances is sufficient to fix all mutual thermo-electric relations among these. The first endeavour of the experimenter is then to obtain as convenient a substance for this purpose as possible. In investigating charcoal and certain alloys, we have in almost all cases employed one or other of two alloys of platinum and iridium, which have been already used by Professor Tait for a like purpose. The wires we used were the same which he discusses in his “First Approximation to a Thermo-Electric Diagram,” under the names of M and N. Their complete freedom from oxidation, their elasticity, and the high temperatures of their fusing points, rendered them peculiarly suitable for thermo-electric investigations through long ranges of temperature.Generally both the M and N wires were firmly bound, each by its one extremity to the end or ends of the wire or wires respectively which were under investigation, in a multiple junction. This triple or, as it was in some cases, quadruple junction constituted the “hot junction.” The free extremities of the wires thus united were each bound to a moderately thin copper wire by very thin wire of the same metal, and the copper wires were led from these “cold junctions” to a commutator, which was in connection with a galvanometer. The commutator consisted of an arrangement of small mercury pools, into which the galvanometer and circuit wires, carefully amalgamated to ensure contact, dipped. All the junctions were formed in the manner indicated above, namely, by tightly binding the extremities of the wires together by thin copper wire.

Laboratory Notes by Professor Tait. 3. On the Thermo-Electric Relations of Pure Iron

By the kindness of Dr Russell, of Bartholomew's Hospital, I have been enabled to experiment upon a ribbon of pure iron prepared by the late Dr Matthiessen. I reserve details until I can obtain the history and mode of preparation of the specimen examined, but I may state now that, when formed into thermo-electric circuits with various alloys of Platinum and Iridium (Proceedings, 1871–2, p. 773) it gives results, as to the position of neutral points, not differing more from those given under the same circumstances by various iron wires of commerce, than the latter do among themselves. Thus it appears that, in the thermo-electric diagram, the line even for pure iron is sinuous; and that the specific heat of electricity in it changes sign somewhere about a low red heat.

3. Laboratory Notes by Professor Tait - 1. On Thermo-electricity: Circuits with more than one Neutral Point

Having lately obtained from Messrs Johnson & Matthey some wires of platinum, and of alloys of platinum and iridium, I formed them into circuits with iron wire of commerce; and noticed that with all, excepting what is called “soft” platinum, there is more than one neutral point situated below the temperature of low white heat, and that at higher temperatures other neutral points occur. This observation is, in itself, highly interesting; but my first impression was one of disappointment, as I imagined it depended on some peculiarity of the platinum metals, which I had hoped would furnish me with the means of accurately measuring high temperatures (by a process described in previous notes of this series). As this hope may possibly not be realised, I can as yet make only rough approximations to an estimation of the temperatures of these neutral points.