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This article is a literature survey on the fabrication of novel H2 sensors based on titania nano-tubes prepared using anodization and annealed in an oxygen atmosphere. The as prepared nano-tubes are amorphous but they crystallize on annealing at elevated temperatures and are structurally stable (which is a requirement of any sensor) to at least 600 °C.Titania nano-tubes are grown from titanium foil (≈99.5% pure) of thickness 0.25 mm. The anodization is performed in an electrolyte medium of 0.5% hydrofluoric acid in water, using a platinum foil cathode. A well defined nano-tube architecture results, with nano-tube length of 400 nm in approximately 20 minutes.Measurement of H2 concentration is based on the increase in conductivity of the nano-tube surface in a hydrogen ambient as compared to its original conductivity, and this is quantified by ’sensitivity’ ratio, S = (R0 – Rgas)/Rgas (where R0 is the electrical resistance of the sensor before passing the gas and Rgas that after passing gas and reaching the saturation value). The sensor shows significant hydrogen sensitivity, with a three order of magnitude change in resistance as compared to its original resistance. The major process behind the interaction between the nano-tubes and hydrogen is the chemisorption of the dissociated hydrogen on the titania surface.These sensors find application in industrial process control, combustion control, gas leak detection from hydrogen-powered cars and fueling stations and in medical applications with hydrogen indicating certain types of bacterial infection. These nano-tube sensors can monitor hydrogen levels from parts per billion to about 1000 ppm.These sensors have a special ability to ‘clean’ themselves up. The photocatalytic properties of titania nano-tubes are so large (a factor of 100 times greater than any other form of titania) that sensor contaminants are efficiently removed with exposure to ultraviolet light, so that the sensors effectively recover or retain their original hydrogen sensitivity in real world application. These sensors have also been shown to be completely reversible, with respect to their original conductivity, which means that when the hydrogen gas exposure is cut-off, they regain their original resistance without any hysteresis.

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Hydrogen  sensors  titania  nano  tubes  carbon  
 About This Document
 Subject Mechanical Engineering
 Category White Paper
 Views 3504
 Downloads 341
 Added 12-08-09
 Contributor   sidpatel
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