Platinum Alloys

alloys (usually binary alloys) based on platinum; usually solid solutions of the alloying element in platinum. The most important alloying elements in platinum alloys are metals of Group VIII of the Mendeleev periodic system (rhodium, iridium, palladium, ruthenium, nickel, and cobalt), as well as copper, tungsten, and molybdenum.

Platinum alloys are characterized by a high melting point; good corrosion resistance in many aggressive media, particularly by high oxidation resistance at high temperatures; and good mechanical properties and wear resistance. Several platinum alloys have catalytic action in oxidation, hydrogenation, and iso-merization reactions. Most platinum alloys are suitable for pressure working; objects made of them may be produced by forging, rolling, drawing, and stamping.

Platinum alloys are used in the production of thermocouples (5–40 percent Rh); break and sliding contacts (10–25 percent Rh or 5–15 percent Ru, 5–30 percent Ir, 10–20 percent Pd, or 5 percent Ni); parts for small, critical instruments, such as potentiometers (4–8 percent W or 3–10 percent Cu, 10–20 percent Ir, 10 percent Ru, or 5–10 percent Mo); springs and spring elements (25–30 percent Ir); permanent magnets (23 percent Co); and high-temperature solders (10–20 percent Pd).

Platinum alloys are used as catalysts in the oxidation of ammonia to nitric acid and in the production of prussic acid from ammonia and methane (5–10 percent Rh or 3–5 percent Pd and 3–5 percent Rh), insoluble anodes (5 percent Ir or 20–50 percent Pd), material for glass-melting vessels and dies for the production of viscose fiber (3–10 percent Rh), laboratory ware and apparatus (1–30 percent Rh, 5 percent Ir, or 10 percent Ru), and heaters for high-temperature furnaces (10–40 percent Rh).