Platinum Metals Rev., 1975, 19, (2), 47
Platinum Alloys in Corrosive Environments
High Temperature Resistance to Molten Glass and Air
The ability of platinum and its alloys to resist the corrosive effects of a wide variety of media that rapidly cause other metals to decay has been the basis of their use in many industries, and especially in the glass industry. However, the mechanism by which molten glass and air attempt to attack platinum alloys has not been completely worked out as yet. Certainly some platinum alloys resist attack better than others and so a report on Russian studies on three important platinum alloys is particularly interesting.
E. I. Rytvin and L. A. Medovoi (Vliyanie Fiz.–Khim. Sredy Zharoproch. Metal. Mater., 1974, 87–94) investigated the corrosion of the alloys 10 per cent Rh–Pt, 10 per cent Rh–25 per cent Pd–Pt and 1.5 per cent Ru–10 per cent Rh–25 per cent Pd–Pt in air and in a molten glass of composition 54 per cent SiO2, 14.5 per cent Al2O3, 10 per cent B2O3, 16 per cent CaO, 4 per cent MgO.The ductility and high temperature strength of the alloys were assessed by measuring the rate of sublimation and dissolution at 1400°C in the unstressed state and during creep induced by an initial stress of 0.5 kg/mm2.
It was discovered that the corrosion which occurs is intergranular in nature. This is illustrated by a series of photomicrographs and the results are tabulated. It appears that the rate of intergranularcorrosion mainly depends upon the alloying elements and that dissolution of the alloys in glass is slower when tensile stress is applied. Molten glass affects the high temperature strength and ductilityof the platinum alloys so that, when the degree of intergranular corrosion is greater, then the reduction in the ductility of the platinum alloys also increases.
It can be concluded from examination of the results that 10 per cent rhodium-platinum is superior to either of the alloys containing palladium in its ability to withstand the corrosive conditions met with when in contact with molten glass, as well as when exposed to air at high temperature.