What is the meaning of occlusion with respect to hydrides of hydrogen?
Occlusion means the absorption of a substance from a gaseous medium by solids or melts. During occlusion, gases are absorbed by the entire volume of the absorbent rather than by the surface layer. In this way, occlusion is similar to absorption, which is the dissolution of gases in liquids.
The most common type of occlusion is the absorption of gases by metals; for example, hydrogen is occluded by metals of Group VIII of the periodic table of elements. At room temperature, one volume of iridium absorbs more than 800 volumes of hydrogen, while one volume of palladium absorbs more than 700 volumes of hydrogen. The occluded gas interacts with the metal to form a solid solution; or sometimes a part of the gas combines with the metal to yield other chemical compounds, for example, hydrides.