In order to impart resistance against water vapor, a promising C14 Laves phase AB2 type alloy, (Ti0.5Zr0.5)(Fe0.2Mn0.8)1.5, was encapsulated by softened ceramic overlayers derived from tetraethoxysilane (TEOS) with dimethyldimethoxysilane (DMDMOS) incorporated as an elastic segment. DMDMOS containing sol did not solidify to hard matters, but kept soft properties similar to silicone rubbers after prolonged exposure to air. While TEOS treated conventional samples were lacking in cyclic durability, the present samples showed substantially no extrinsic capacity loss under humidified hydrogen (partial pressure of water: 0.61 kPa) through 50 hydriding-dehydriding cycles. Furthermore, fully hydrided alloys did not lose their hydrogen through XRD measurements under air, after the softened sol-gel encapsulation was applied.
XRD Rietveld analysis showed that cell volume of hydride phase (β phase) slightly increased on encapsulation. It is likely that crystallites surrounded by elastic matters could expand through hydriding to full extent, while those surrounded by hard alloys themselves could not. Formation of cracks on hydriding was scarcely observed for encapsulated samples by SEM, while that was frequent for as-activated samples. Encapsulation through the softened sol-gel method thus brought about water resistance, its cyclic durability and free motion on volume changes through hydriding and dehydriding to release mechanical stress. XRD results additionally showed that the stoichiometric change from B/A = 2 to 1,5 lowered the expanding ratio of β phase to alloy phase (α phase). That would give an additional tool to design specific alloys on demand.