Platinum Metals Review - Volume 9, Issue 4, 1965

The unique magnetic properties of the cobalt-platinum alloy Platinax II enable small permanent magnets to be made which will produce a high magnetic flux across a large air gap. A small cylinder of this alloy magnetised across its diameter, produces a two pole magnet with an ideal field geometry for the rotor of a synchro-transmitter. Used in conjunction with Hall effect elements the design of such devices can be simplified as the need for windings of very fine insulated copper wire on laminated rotors, used in conventional motors, is eliminated. The increasing demand for miniaturisation of electronic components may make it necessary to reduce still further the size of servo components, and the ductility and machining properties of cobalt-platinum make it an ideal material from which to make the permanent magnet rotors.

A systematic study of the electrochemical behaviour of platinum alloyed with other platinum metals has not previously been attempted. Some recent research directed to this end is briefly reported here, and shows the enhanced electrocatalytic activity of the alloys studied compared with bright platinum itself for the electrochemical reduction and evolution of oxygen in acid solution.

In the third and concluding part of this survey of the changes that occur when the platinum metals are heated in oxygen at temperatures up to their melting point the behaviour of palladium is considered. The gain in weight when commercial palladium is heated to around 1000°C in air or oxygen, reported by many experimenters, is probably the result of the internal oxidation of base metal impurities. At higher temperatures, the primary cause of the loss of weight then observed is almost certainly the very high vapour pressure of palladium itself. The reaction between palladium vapour and oxygen to form PdO gas has yet to receive the experimental study it demands.

In the second part of this paper it is shown that rhodium-platinum alloys are less readily wetted by glass than pure platinum, although the effect is marginal and disappears at temperatures above 1200°C. Gold additions are shown to increase the resistance to wetting much more effectively, the equilibrium contact angle between borosilicate glass and platinum containing 5 to 7 per cent of gold and 10 per cent of rhodium remaining above 75° up to 1500°C. This ternary alloy is stronger and more resistant to creep at high temperatures than the binary 10 per cent rhodium-platinum alloy.