A Theoretical Formula for the Solubility of Hydrogen in Palladium

It is known that the amount of hydrogen dissolved by Pt, Mo, Cu, Co, Fe, and Ni is directly proportional to the square root of the hydrogen pressure p . Furthermore, these metals take up hydrogen without changing their lattice structure. It has been shown by Fowler and Smithells (1937) that one can get a theoretical interpretation of the observed solubility, if one assumes that the hydrogen dissolves as protons which are free to move throughout practically the whole volume of the metal. The theory has been extended, using slightly different assumptions, to include the metals V, Ta, Ti, and Zr. In these cases definite metallic hydrides are formed having lattice structures differing from that of the pure metal, and at higher pressures the amount of absorbed hydrogen saturates, being no longer proportional to √ p . In the present paper we shall give a statistical interpretation of the solubility of hydrogen in palladium. Palladium seems to offer an advan­tageous starting-point for an attempt at a more profound extension of the theory outside the region where the √ p law is valid. It has been thoroughly investigated experimentally and is capable of taking up large volumes of hydrogen without changing its lattice structure (Linde and Borelius 1927; Kruger and Gehm 1933)