Hawker Hart by Francis K. Mason

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At any given temperature rhenium is far stronger than the other metals in this group. Rhodium and iridium have comparable tensile strengths at temperatures up to 500° C, although iridium becomes progressively stronger at higher temperatures. ~ Electrical properties :::!! (17) The effect of temperature on resistance at higher temperatures is shown in Table 4. Over the range 0°-1 400°C the resistivities of both platinum and palladium increase by a factor of 5. Although palladium begins with a slightly higher resistivity than platinum, its temperature coefficient is lower, so that it has a lower resistivity at 1 400° C.

59) Resistance to oxidation and corrosion Although the mechanical and physical properties of gold are very similar, gold is considerably more resistant to corrosion, and being completely immune to attack by oxygen, can be safely melted in air. Silver, on the other hand, dissolves about ten times its own volume of oxygen when melted in air, although much of this is released on solidification when the metal 'spits' very violently and sets in the form of metallic sponge. The solubility of oxygen in both I Q _j _j ~ ;:!

All the platinum metals remain clean in air when the rate of oxide volatilisation exceeds the rate of oxide formation. The temperature at which this balance occurs depends upon the stability of the oxide and also upon the partial pressure of oxygen above the metal surface. Thus in one atmosphere of oxygen, platinum remains clean at all temperatures above 20° C. This is because of the volatility of PtO 2 , 38 which in one atmosphere of oxygen dissociates only between 280°-450°C. Compact ruthenium, rhodium, palladium, osmium, and iridium show obvious signs of oxidation when heated in air above about 400° C.