Alloy iridium

It is the most corrosion-resistant metal known, and was used in making the standard meter bar of Paris, which is a 90 percent platinum and 10 percent iridium alloy. This meter bar was replaced in 1960 as a fundamental unit of length (see under Krypton). 

Mass kilogram kg Mass of a cylinder of platinum-iridium alloy kept at Paris. 

Iridium on valve metals is suitable if the consumption rate of platinum is too high at elevated temperatures or critical composition of the medium. Mostly platinum-iridium alloys are used with about 30% Ir, because coating valve metals with pure iridium is somewhat complicated. For the same reason, other noble metals such as rhodium cannot be used [21]. At present there is little price difference between platinum and iridium. 

Alloys with iridium Iridium alloys with platinum in all proportions, and alloys containing up to about 40% iridium are workable, although considerably harder than pure platinum. The creep resistance of iridium-platinum alloys is better than that of rhodium-platinum alloys at temperatures below 500°C. Their stability at high temperatures, however, is substantially lower, owing to the higher rate of formation of a volatile iridium oxide. 

Rhodium and iridium have a resistance to anodic corrosion comparable with that of platinum, and are more resistant to the influence of alternating currents. A platinum-iridium alloy, in the form of a coating on titanium, is preferred to pure platinum for the production of chlorine from brine , due to its improved corrosion resistance and lower overvoltage. 

For scientific work the fundamental standard of mass is the international prototype kilogram, which is a mass of platinum-iridium alloy made in 1887 and deposited in the International Bureau of Weights and Measures near Paris. Authentic copies of the standard are kept by the appropriate responsible authorities in the various countries of the world these copies are employed for the comparison of secondary standards, which are used in the calibration of weights for scientific work. The unit of mass that is almost universally employed in laboratory work, however, is the gram, which may be defined as the one-thousandth part of the mass of the international prototype kilogram. 

Because of- the similarity in the backscattering properties of platinum and iridium, we were not able to distinguish between neighboring platinum and iridium atoms in the analysis of the EXAFS associated with either component of platinum-iridium alloys or clusters. In this respect, the situation is very different from that for systems like ruthenium-copper, osmium-copper, or rhodium-copper. Therefore, we concentrated on the determination of interatomic distances. To obtain accurate values of interatomic distances, it is necessary to have precise information on phase shifts. For the platinum-iridium system, there is no problem in this regard, since the phase shifts of platinum and iridium are not very different. Hence the uncertainty in the phase shift of a platinum-iridium atom pair is very small. 

Figure 5.33. Impurity and Th concentrations on intergranular and transgranular areas of an iridium alloy containing 6000 ppm Th and (a) 5000 ppm Fe, (b) 4000 ppm Al, (c) 3000 ppm Ni, (d) 5000 ppm Cr and (e) no added impurities. (After Heatherly and George 2001).

Unfortunately, platinum-iridium alloy was a poor choice, for it has the unusual property of shrinking (albeit microscopically) with time. This SI metre rule is now about 0.3 per cent too short. King Edgar s yardstick, being made of gold, would still be the same length today as when it was made, but gold is too ductile, and could have been stretched, bent or re-scored. 

Platinum-group minerals, classes of, 79 603 Platinum halides, 79 657 Platinum-iridium alloy electrodes, medical applications for, 79 629... 

The material of the nebulizer must be highly corrosion resistant. Commonly, the plastic capillary is fixed to a platinum-iridium alloy (90 10) capillary mounted in stainless-steel gas supply inlets. The impact bead is sometime made of a similar alloy or smooth borosilicate glass. 

A dilatometer is used to measure the intrusion and extrusion volumes and several methods are used to measure the change in mercury level within the dilatometer stem as intrusion and extrusion take place. One method involves the use of platinum or platinum-alloy resistance wire placed coaxially in the stem of dilatometer tube. As the mercury level decreases, the amount of resistance wire exposed increases, thereby providing a voltage which increases linearly with decreasing mercury level. Very small current is used to minimize resistive heating of the mercury. Platinum or platinum-iridium alloy may be employed as the resistance wire because they do not amalgamate with mercury. 

Platinum alloys containing from 0 5 to 20 per cent, of tantalum are hard, withstand heat, as well as the action of adds and fused potassium hydrogen sulphate, and are more resistant to the action of aqua-regia than platinum.8 They possess the mechanical properties off platinum-iridium alloys and are less expensive the relative quantities, of tantalum and iridium required to produce the same hardness and mechanical resistance are stated to be 1 5. Platinum-tantalum alloys, hence have been recommended for various purposes in place of platinum or platinum-iridium. Tantalum can also be coated with platinum, andl can then be utilised in high-temperature work. ... 

KILOGRAM (kg). A unit of mass and is based upon a cylinder of platinum-iridium alloy kept by the International Bureau of Weights and Measures at Paris. A duplicate in the custody of the National Bureau of Standards at Washington is the mass standard for the United States. The kilogram is the only base unit still defined by an artifact. (A kilogram equals (1) 1,000 grams (2) 2.205 pounds (3) 9,842 x 10-4 long tons or (4) 1 102 x 10-3 short tons. 

The standard kilogram is defined as the mass of a cylindrical bar of platinum-iridium alloy stored in a vault in a suburb of Paris, France. There are 40 copies of this bar distributed throughout the world, with two (Numbers 4 and 20) stored at the U.S. National Institute of Standards and Technology near Washington, D.C. 

The acute recording of evoked potentials and the stimulation at the spinal cord has been a well-established method for more than 20 years. The procedures require electrodes that are similar to pacemaker electrodes. Applications can be found in the field of skoliosis correction [38, 39] and the repair of aorta aneurysms [40]. An intraoperative stimulation of fibers of the sacral spinal cord was performed during dissection of unilateral testicle tumors to preserve ejaculation [41]. The main application of implants for chronic stimulation of the spinal cord is the handling of chronic pain [42]. There are two types of electrodes the percutaneous electrodes resemble the pacemaker electrodes. They consist of a mandrel with up to four ring electrodes of a platinum iridium alloy (Fig. 6). They have a length of 3 mm with an interelectrode distance of 6 mm or a length of 6 mm with an interelectrode distance of 12 mm. 

It is well known that contact between the bottom of the tip and the sample surface will not be between two smooth, regular surfaces. In particular, the bottom of the tip may contain many asperities, and one of these asperities will serve as the probe. In STM experiments the most common tip is made from a tungsten poly-crystalline wire, and other tip materials are commonly transition metals (platinum, iridium, alloys) [21]. It is generally agreed today that only a very sharp tip with a single atom at its pinnacle is suitable to obtain atomic resolution on close-packed surfaces. But, such a tip is highly unstable. Therefore, the fabrication and characterization of defined tips, e.g. by field ion microscopy, have not been achieved, nor can it... 

In August 1978, a Bulgarian defector living in Paris was shot with a tiny pellet made of 90% platinum-iridium alloy which was only 1.7 mm in... 

Some of the materials that have been examined as catalysts include Pure Platinum, Platinum-Iridium Alloys, Various Compositions of Platinum-Rhodium Alloys, Platinum-Palladium Alloys, Platinum-Ruthenium Alloys, Platinum-Rhenium Alloys, Platinum-Tungsten Alloys, FejOj-M CVI Oj (Braun Oxide), CoO-Bi20j, CoO with AI2O3, Thorium, Cerium, Zinc and Cadmium. 

J Cf is encapsulated and shipped in eight standard Special Form capsules and packages to meet the needs of the different medical, industrial, and research applications used. The isotope is available as californium oxide, californium-palladium cermet wire or pellets, and, in the case of medical therapy sources, californium-palladium cermet sheathed in platinum-iridium alloy. Capsules are available in a variety of metals and alloys (Table 1, Figures 1 through 8). 

Osmium Tetroxide, 0s04, frequently but incorrectly known as osmic acid, is the highest oxide of osmium known, and is formed in a variety of ways. Finely divided metallic osmium slowly oxidises in air to the tetroxide, and more rapidly on heating in air or, better, in oxygen.1 At high temperatures the compact metal yields vapours of the volatile tetroxide, and this affords a useful means of quantitatively separating osmium from its iridium alloy (p. S38). 

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