Multilayer fiber optic sensors for in situ gas monitoring in harsh environments

This paper reports the fabrication and test of multilayer fiber optic sensors (FOSs) for hydrogen gas monitoring at high temperature. The FOS is a long-period fiber grating (LPFG) coated with a proton-conducting SrCe0.8Zr0.1Y0.1O2.95 (SCZY) nanocrystalline thin film and a chemically inert and thermally stable nanoporous silicalite protective layer. The multilayer sensors were tested for their responses to the variation of H2 partial pressure at 500 °C. The sensor's H2-sensitivity increased with increasing the thickness of the SCZY sensing film and decreased with the thickness of the silicalite film. The silicalite overcoat had no appreciable influence on the sensor's response time because of the fast diffusion of the small H2 molecules in the zeolitic channels. Because of the uniform subnanometer sized pore opening, the silicalite layer is inaccessible to any fine particles or large contaminating molecules. The multilayer FOS is thus potentially useful for in situ H2 monitoring in the dusty syngas streams from coal or biomass gasification.