Platinum Metals Review - Volume 14, Issue 4, 1970

The growth of single crystal oxides for optical and magnetic purposes is commonly carried out using platinum containers. Modifications to container design have been important factors in improving growth conditions. A new composite three-layer crucible has been fabricated in platinum and iridium for growing crystals of sodium barium niobate, and a platinum container which can be drained of flux has been developed for growing rare earth iron garnets.

Platinum reacts exothermically with aluminium, zirconium and thorium, but is very reluctant to alloy with magnesium. It dissolves 2.2 per cent by weight of aluminium at 1500°C and 10 per cent by weight of zirconium at 1650°C. These wide solid solutions are in equilibrium with very stable inter-metallic compounds, thus accounting for the severe reactions which can occur when platinum is heated in contact with alumina and zirconia. Zirconium reacts peritectically with platinum. The effects of these refractory decomposition processes on the long-term stability of platinum thermocouples will be discussed in the fourth and concluding article in this series.

Interest in the absorption of hydrogen by palladium and its alloys continues at a high level. A symposium on this subject was held in Poland in July and is reported here, while a further meeting on the subject is planned there for next year. Papers included studies on the diffusion coefficient of hydrogen in gold-palladium alloys, the variation of electrical resistance with hydrogen content of palladium at low temperatures, and the absorption by palladium alloys of hydrogen at extremely high pressures. The symposium also dealt with hydrogen absorption by nickel alloys. Some of these papers parallel work on palladium and are also briefly reported here.

Applications of molecular sieve materials have become of increasing interest in catalysis. The ability of these materials to differentiate on the basis of molecular size gives them a unique form of selective catalytic action with the additional benefit of high resistance to sorption of large poison molecules. Hitherto their major application has been realised with zeolites but new platinum catalysts possessing similar properties and based on a carbonaceous structure have now been developed in the Johnson Matthey Research Laboratories.