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Tutorial MenueThe World of the Platinum MetalsLearning Unit 1 of 5

Platinum as a Metallic Material

Platinum-rhodium Alloys

The platinum materials used in the largest quantities – in particular for applications at high temperatures – are the alloys of platinum with rhodium, and the most commonly used alloys have rhodium contents of 10 or 20 %. Compositions with up to 30 % rhodium are also used. The phase diagram of the platinum-rhodium alloy system shows a continuous solid solution with no tendency to phase separation above approx. 760 °C. Because of the relatively low temperature of the phase separation, it does not normally arise under practical conditions. Whereas platinum has a Young’s modulus of 165 GPa, the Young’s modulus of rhodium is 372 GPa1). As one would expect on the basis of these values, platinum-rhodium alloys have substantially higher mechanical strength at all temperatures than chemically pure platinum. Even at temperatures immediately below the melting temperature, the platinum-rhodium alloys demonstrate oxidation resistance that is similar to that of platinum.

Phase diagram of the alloy system platinum-rhodium
© "Binary Alloy Phase Diagrams plus Updates", ASM International 1996
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