Platinum Metals Rev., 1963, 7, (3), 95
Longer Life for Iridium Crucibles
Rhodium Plating and Brazing
Iridium crucibles are frequently used in growing single crystals of high melting point materials but hitherto their lifetime has tended to be short. R. S. Horwath and C. Whiteley, of Sperry Electronic Tube Division, Sperry Rand Corporation, have now reported (J. Electrochem. Soc., 1963, 110, (5), 467) that rhodium plating extends the life of new or slightly used crucibles several times and that minor cracks can be repaired by brazing with either platinum or rhodium.
Rhodium plating was chosen because rhodium has a lower vapour pressure than iridium and a higher melting point than platinum. After plating with 0.0002 inch rhodium and heat treatment at 1650°C for 16 hours the cycle is repeated, and the crucible life may well increase from 50 up to about 300 hours.
Cracks may be repaired by spot welding platinum or rhodium wire into the filed-out defects, followed by R.F. heating of the crucible to melt the filler wire which then flows into the crack and seals it as in any other brazing operation.