Platinum alloying element

Platinum and Platinum Alloys. Platinum has excellent resistance to strong acids and, at elevated temperatures, to oxidation. Under reducing conditions at high temperatures it must be protected from low-fusing elements or their oxides. Easily reduced metals at high temperatures may form low-fusing alloys with platinum. 

Platinum, as an alloying element, is used in many dental casting golds (Tables 6 and 7) to improve hardness and elastic qualities. Platinum in combination with palladium and iridium has limited use for dental pins and wires. 

The corrosion behaviour of amorphous alloys has received particular attention since the extraordinarily high corrosion resistance of amorphous iron-chromium-metalloid alloys was reported. The majority of amorphous ferrous alloys contain large amounts of metalloids. The corrosion rate of amorphous iron-metalloid alloys decreases with the addition of most second metallic elements such as titanium, zirconium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, copper, ruthenium, rhodium, palladium, iridium and platinum . The addition of chromium is particularly effective. For instance amorphous Fe-8Cr-13P-7C alloy passivates spontaneously even in 2 N HCl at ambient temperature ". (The number denoting the concentration of an alloy element in the amorphous alloy formulae is the atomic percent unless otherwise stated.)... 

Ruthenium nowadays finds many uses in the electronics industry, particularly for making resistor tracks. It is used as an ingredient in various catalysts and, importantly, in electrode materials, e.g. Ru02-coated titanium elements in the chloralkali industry. Osmium tetroxide is a very useful organic oxidant and, classically, is used as a tissue stain. Both elements are employed in making certain platinum alloys. 

Silvery, shiny, and hard. Unique metal, gives off an odor as it forms volatile 0s04 on the surface (oxidation states 81). Osmium is the densest element (22.6 g cm3 record ). Was replaced in filaments (Osram) by the cheaper tungsten. Used in platinum alloys and as a catalyst. Haber s first catalyst in ammonia synthesis was osmium, which fortunately could be replaced by doped iron. The addition of as little as 1 to 2 % of this expensive metal increases the strength of steel (e.g. fountain-pen tips, early gramophone needles, syringe needles). 

Researchers are looking at ways to reduce the amount of platinum yet retain the catalytic activity. Peter Strasser, a researcher at the University of Houston in Texas, and his colleagues are trying to develop a platinum alloy that will do the job. An alloy such as bronze is a combination of elements, which in the case of bronze are tin and copper. Engineers often use alloys because they offer properties that are superior to those of a single metal, as described in chapter 1. A platinum alloy that acts as an effective catalyst in fuel cell electrodes yet contains less platinum would save a substantial amount of money. 

Figure 9. Plot of the isomeric shift of platinum alloys vs. the electronegativity of the host element.

J. Begerow, L. Dunemann, Internal platinum and palladium exposure of the general population with emphasis on the exposure from automobile exhaust and dental restorative alloys, in F. Zereini, F. Alt (eds), Anthropogenic Platinum-group Element emissions. Their Impact on Man and Environment, Springer, Berlin, 2000, pp. 227 D 236. 

Alloying elements exert a very important influence upon the occlusion of hydrogen by palladium. The absorptive power of commercial palladium is from 10 to 20 per cent, less than that of the pure metal, a fact that is attributed to the presence of small quantities of platinum and ruthenium.6... 

Another approach is to use a carefully selected standard platinum alloy for which the constants in Eqs. (6) and (8) are well known. In the mid-1980s, the International Electrotechnical Commission (lEC) recommended that ITS-90 be based on the Callendar-van Dusen interpolation formula and proposed constants for a Ft resistor with = 100 O A = 3.90802 X 10 5=-5.802 X 10 C =-4.27350 X 10 (or a = 0.00385, 8 = 1.50701, /3 = 0.111). The platinum wire used in platinum resistance thermometers that conform to this proposed standard is a platinum alloy containing small amounts of several different elements (mostly noble metals) adjusted so as to achieve the required a = 0.00385 K . This alloy is now widely used in Europe and by some American manufacturers of resistance thermometers note, however, that other American firms use a wire for which a = 0.00392 K . In spite of the fact that this lEC proposal was not adopted, the Callendar-van Dusen constants given above are a guide to appropriate values, which can always be checked by calibration. 

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. 

Osmium is an element in Group 8 (VIIIB) of the periodic table. The periodic table is a chart showing how chemical elements are related to one another. Osmium is also a member of the platinum family. This family consists of five other elements ruthenium, rhodium, palladium, iridium, and platinum. These elements often occur together in Earth s cmst. They also have similar physical and chemical properties, and they are used in alloys. 

ELEMENTS (Metals and intermetallic alloys metalloids and nonmetals carbides, silicides, nitrides, phosphides) l.A Metals and Intermetallic Alloys l.AA. Copper-cupalite family TAB. Zinc-brass family l.AC. Indium-tin family l.AD. Mercury-amalgam family l.AE. Iron-chromium family l.AF. Platinum group elements l.AG. PGE-metal alloys... 

Direct Reaction Calorimetry (DRC) works slightly different. It is a form of calorimetric measurements where you synthesize the alloys directly in the crucible (container), where you also measure the heats. The method will be described very quickly here, for further reading one could consult Refs. [122, 123, 124]. In this method you have a crucible made of ceramic aluminium, in which several thermoelectric elements (usually made of a platinum alloy) are lodged. With the help of these one can then measure the heat of the reaction and get the mixing enthalpy from... 

Kumagai K., Samata Y., Kawashima A., Asami K. and Hashimoto K. (1987) Anodic characteristics of amorphous nickel-valve metal alloys containing small amounts of platinum group elements in 0.5 M NaCl. J. appl. J. electrochem. 17, 347-356. 

The first catalytic converters used mainly platinum, but palladium is now the predominant catalyst metal. Sixty percent of the palladium manufactured worldwide is used in catalytic converters. Other uses are as the electrodes in MLCCs and other electronic components, and a small amount is used in jewelry (for example, an alloying element in white gold). 

Platinum and Platinum Alloys Applications. Platinum and platinum alloys are important constituents of catalysts (chemistry, automotive exhaust gas cleaning, fuel cells), sensor materials (thermocouples, resistance thermometers), strong permanent magnet alloys, magnetic and magnetooptical (memory) devices, high temperature and corrosion resistant stmctural parts, and electrical contacts and connecting elements. Classical applications are jewelry and dentistry alloys. 

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