Platinum-iridium alloy

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. 

Alloys with ruthenium Additions of ruthenium have a most marked effect upon the hardness of platinum, but the limit of workability is reached at about 15% ruthenium, owing to the fact that ruthenium belongs to a crystallographic system different from that of platinum. Apart from a somewhat greater tendency to oxide formation at temperatures above 800°C, the resistance to corrosion of ruthenium-platinum alloys is comparable to that of iridium-platinum alloys of similar composition. 

Platinum and rhodium-platinum and iridium-platinum alloys are frequently employed to line and sheath autoclaves, reactor vessels and tubes, and a wide range of equipment. Linings are generally 0-13 mm to 0- 38 mm thick, and for certain applications co-extruded platinum-lined Inconel or other metal reactor or cooling tubes are fabricated. In such cases the platinum is bonded to the base metal, but in all other instances platinum linings are of the loose type. 

Iridium-platinum alloys, 79 602 Iripallidal degradation products, 24 577 Irish moss, common and scientific names, 3 188t... 

Gaudin fused lo per cent iridium-platinum alloy and commented on the lustre, malleability, and great corrosion resistance of the metal, but iridium was generally regarded as a troublesome impurity in platinum. ... 

Two metallurgical problems exist. The first is to find a suitable material for the leads which connect to the electrodes, as they must withstand the mechanical flexure of the beating heart. Several stainless steel alloys have been developed. These, available under the trade names Ethicon and Surgaloy, are used in the form of multifilament wires about 0.013 in. in diameter. The second problem relates to electrolysis of the electrodes, as mentioned in Section 1.1. The stimulative signal may be considered as pulsed direct current. As a result, considerable electrolytic action may occur in the electrolyte environment of the heart tissue. It has been reported that stainless steel is eroded very rapidly but that iridium-platinum alloy is quite stable (Rowley, 1963). A possible solution to the problem, in addition to... 

The pacemaker itself is a device planted in the chest and connected to the heart muscles a programmed electrical pulse is periodically administered, which assures regularity in the heart beat. Heart pacemakers that operate from chemical batteries have a limited life, and must be replaced periodically by a surgical procedure. A nuclear power source increases the time between repowering the pacemaker by a factor of at least S. A typical nuclear-powered heart pacemaker contains about 160 mg of Pu encased in a tantalum-iridium-platinum alloy. Several thousand such devices are in use world-wide. 

Nitric acid reacts with all metals except gold, iridium, platinum, rhodium, tantalum, titanium, and certain alloys. It reacts violentiy with sodium and potassium to produce nitrogen. Most metals are converted iato nitrates arsenic, antimony, and tin form oxides. Chrome, iron, and aluminum readily dissolve ia dilute nitric acid but with concentrated acid form a metal oxide layer that passivates the metal, ie, prevents further reaction. 

Iridium [7439-88-5] Ir, and rhodium [7440-16-6] Rh, iadividually iacrease corrosion resistance, hardness, and strength of platinum alloys. They can be used to reduce grain size (140). 

Alloys of zinc with iridium, platinum or rhodium, after extraction with acid, leave residues which explode on warming in air, owing to the presence of occluded hydrogen (or oxygen) in the catalytic metal powders so produced. 

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. ... 

Alloys.—With the exception of those obtained with allied metals, the alloys of iridium are unimportant. Osmiridium has already been described, and platinum alloys are dealt with in the sequel (see p. 208). On heating to redness with tin, the compound IrSn2 is obtained in cubical crystals which may be isolated from the excess of tin by treatment with hydrochloric add, in which the latter dissolves.6... 

Detection of Ruthenium in Platinum Alloys.—In order to detect the presence of ruthenium in platinum alloys, a portion of the alloy is fused with lead. The melt is extracted with nitric acid and the residue ignited in contact with air in order to volatilise the osmium. The mass may now contain platinum, iridium, rhodium and ruthenium, and is fused with potassium nitrate and hydroxide. The whole is dissolved in water, treated with excess of nitric acid and allowed to stand in a flask covered with filter-paper. In a few hours (12-24) the filter-paper darkens if ruthenium is present, in consequence of the evolution of vapour of its tetroxide. To confirm the presence of ruthenium, the paper is ignited and the ash fused with potassium nitrate and hydroxide. On extraction with water the orange colour of potassium ruthenate is obtained.1... 

Iridium is a third-row d-block metal and is the heaviest element in group 9. It is a hard, lustrous, silvery metal, discovered by Tennant in 1803 the name iridium derives from the Latin iris (rainbow). The element occurs as a native platinum alloy and in osmiridium (a native alloy of osmium, 15-40%, and iridium, 50-80%). Selected physical and chemical properties of Ir are given in Table 1. It is considered both as a platinum metal and as a precious metal. At room temperature, Ir is particularly resistant to corrosion. 

Rhodium and iridium are very unreactive metals, not being attacked by aqua regia (a mixture of nitric acid and sulfuric acid). Iridium is alloyed with platinum to produce a ery hard alloy, which is used for the tips of gold pens, surgical tools, and scientific apparatus. Representative compounds are Rb.Og, KgRbCl, Iro 3 and... 

Osmium metal has few uses. It is sometimes added to platinum or iridium to make them harder. The osmium-platinum alloy is harder than pure platinum. Some alloys of osmium and platinum are used to make... 

The DSA-type anodes are inert , coated anodes made of a valve metal (titanium, niobium, or tantalum) base coated with an electrochemically active coating. The active coating is made either of noble metals or of mixed metal oxides. Noble metals in active coatings are usually platinum or platinum alloys. Mixed metal-oxide coatings contain active oxides and inert oxides the active components are usually ruthenium dioxide (R.UO2) and iridium dioxide (IrC>2) and the inert components are mostly titanium dioxide (TiC>2) and other oxides such as tantalum... 

Figure 4.29 Test of method of accounting for the overlapping of iridium Lm EXAFS in the analysis of platinum Zm EXAFS data on a physical mixture of platinum and iridium and on a platinum-iridium bulk alloy (48). (Reprinted with permission from the American Institute of Physics.)...

The interatomic distance determined from X-ray diffraction data on the alloy is 2.751 A, which is very close to the average of the two distances derived from Figure 4.29. If one assumes a linear relation between interatomic distance and alloy composition (Vegard s law), the value of 2.751 A would correspond to an alloy composition of 60% platinum, 40% iridium. The alloy composition as determined by X-ray fluorescence is 58% platinum, 42% iridium (48). 

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