Nanostrutured thick film sensors for CO (g) based on Al doped SnO2

in this work, the aluminium doping of sno2 lattice was studied, synthesising a semiconductive nanocrystalline doped material by a gel-combustion method with citric acid as fuel, to be used for thick film sensors to detect co (g). aluminium concentration was varied from 1 to 5 at %, nanocrystalline powders with crystallite mean size of 8-12 nm and low agglomeration were obtained. the semiconductive material was characterised with x-rays diffraction, energy dispersive electron microprobe and transmission electron microscopy. nanocrystalline powders were used to prepare conductive pastes with suitable organic solvents employing our own formulations different from those of commercial materials. pastes were deposited as serigraphic thick films on electronic purity alumina wafers provided with pt electrodes. sintering of thick sensing films was performed in a range of medium temperatures to avoid important crystallite growth since it is convenient to maintain the nanocrystalline structure in order to increase sensor sensitivity. sensors were characterised in mixtures of [co(g)+air] at temperatures from 300 to 400 °c. results indicated that aluminium was incorporated in the sno2 lattice in low proportions leaving low concentrations of amorphous al2o3 segregated. sensors showed a high sensitivity to the target gas. in addition, it was also found that the incorporation of aluminium to sno2 lowers the sensor operating temperature.