Platinum Rhodium foil, 0.025mm (0.001in) thick, 99.9% (metals basis) is used as a standard for calibration of base metal thermocouples. It is also used in the glass industry for furnace linings and complex fabrications.
The addition of rhodium to platinum also providesimproved mechanical properties to platinumand increases its resistance to corrosion.For applications at high temperatures, the platinum–rhodium alloys are preferred because ofretention of good mechanical properties includinggood hot strength and very little tendencytoward volatilization or oxidation.
Platinum–rhodium alloys are used for thermocouplesfor temperatures above 1100°C. Thestandard thermocouple is platinum vs. platinum–10% rhodium. Other thermocouples forhigher operating temperatures use platinum–rhodium alloys in both elements. Thealloys of platinum–rhodium are widely used inthe glass industry, particularly as glass-fiberextrusion bushings. Rhodium increases thehigh-temperature strength of platinum withoutreducing its resistance to oxidation. Platinum–rhodium gauze for use as a catalyst inproducing nitric acid from ammonium contains90% platinum and 10% rhodium.
