A nanostructured sensor based on double wall carbon nanotubes (DWNTs) was fabricated and assessed for hydrogen gas
detection. DWNT networks were used as an active substrate material evaporated with layers of palladium nanoparticles
of three thicknesses 1, 3 and 6 nm. The electrical resistance change of nanosensor with hydrogen gas exposure in
compressed air at room temperature was monitored. The nanostructures were characterized using high resolution
transmission electron microscopy (HRTEM) and atomic force microscopy (AFM). Hydrogen concentrations as low as
0.05 vol% (500 ppm) can be detected at room temperature. Sensitivity values as high as 65% and response times of
about 3 seconds were obtained. The results indicate that DWNT- based sensors exhibit comparable performance as that
for SWNT-based high performance hydrogen sensors, but with potential improvement in mechanical and thermal
resistance associated with the double layer structure.
A nanostructured sensing element based on anodic aluminum oxide (AAO) nanowells was fabricate and assessed for
hydrogen gas sensing. AAO nanowells with an average diameter of 73 nm and depth proportional to the anodization
time were immersed in a surfactant solution and coated with an 8 nm film of palladium nanoparticles. The electrical
resistance change of the nanostructure with hydrogen gas exposure was used as the sensing parameter. The AAO
nanowells-Pd nanostructures were characterized using atomic force microscopy (AFM), field-emission scanning electron
microscopy (FESEM), and contact angle test. Hydrogen concentrations as low as 0.05 vol% (500 ppm) can be detected
at room temperature. Response times as fast as 1.15 seconds were obtained. Compared to current devices and
nanostructures in development, the AAO nanowell-Pd nanostructure is found to be considerably fast without
compromising sensitivity and selectivity.
The capability and sensitivity of an electromagnetic (EM) sensor to be used as a non destructive evaluation (NDE) technique to detect and monitor corrosion in structural steels has been evaluated. Three structural carbon steels: AISI 1018, AISI 1045, and Stress Proof, were used for the study. The effect of corrosion on the magnetic properties of the steels was evaluated. Correlation curves and equations relating mass loss due to corrosion at early stages and magnetic property are presented. Based on the results it is established that the EM sensor has the potential to be used as a reliable NDE tool to detect corrosion at early stages based on the variation in magnetic saturation. These results are used to estimate and monitor the degree of damage in terms of mass loss.