Fiber optic hydrogen detectors containing Mg-based metal hydrides

We report on the implementation of Pd-capped chemo-chromic metal hydrides as a sensing layer in fiber optic hydrogen detectors. Due to the change in optical properties of Mg-based alloys on hydrogen absorption, a drop in reflectance by a factor of 10 is demonstrated at hydrogen levels down to 15% of the lower explosion limit. The switching takes place in only a few seconds. Comparing Mg–Ni and Mg–Ti based alloys, we find that the latter has superior optical and switching properties. Using a 50 nm thick Mg70Ti30 film capped with a 30 nm Pd catalytic layer as the sensing layer, we report on the sensitivity of the fiber optic detector for hydrogen both in argon and oxygen, the temperature behavior and the reversibility.