Study Of Process And Properties Of Porous Tin Dioxide Gas Sensors

In this paper, anodic oxidation technology and electrophoretic depositiontechnology were used to fabricate gas sensor, the properties of the sensors and gassensing mechanism were deeply reached.The quantitative relationship between the sensing properties of porous SnO₂materials and the specific surface area was studied, with conclusion that the responsecan be improved by increasing specific surface area. SnO₂film with a porousstructure was obtained by drawing the experience of mature technology ofaluminum’s anodic oxidation. The gas sensing properties of films oxidized bydifferent voltages were studied. For4.1ppm H2S at room temperature, with theincreasing of anodic voltage, the response increased, at3V the response was only2.5and the response time was as longer as5min, at10V the response reached thehighest value of53, and then with oxidizing voltage of12V, the response began todecrease, however, the recovery property began to get better. SEM graphs showed thefilms had a porous structure with pore diameter of1²μm.The nanometer SnO₂were synthesised by method of precipitation. The TEMshowed the diameter of grains were8¹5nm, consistent with average particlediameter10.2nm calculated by the Scherrer formula according to the XRD testresults of the three main peaks. The optical electrophoretic depositon was studied.Deposition voltage, deposition time, the suspension concentration substantiallyrepresented the linear relationship within a certain range. BET test showed that thefilms have a large specific surface area, after sintering at400℃for2hours, thespecific surface area reduced from57.5m2/g to44.2m2/g, pore diameter increasedfrom4.4nm to8.7nm. Primary particles with150³00nm were found in the SEMimages, these primary particles agglomerated into secondary particles with diameterof2³μm, the film had a porous structure.The resistance of films by EPD changed from87KΩ to17ΜΩ after400℃sintering, the response towards4.1ppm H2S changed from13to201, and the highestresponse was obtained after500℃sintering. Improving the working temperature can improve the recovery property towards H2S. Continuous response and recoverycurve towards13.7ppm NO₂at different temperatures was studied. When the sensorswere working above80℃, the resistance of sensors can restore to the initial stateafter the test gas was extracted. With the increasing of working temperature, responsetowards NO₂increased, response and recovery time decreased. The gas sensingmechanism towards NO₂was studied by the law of mass action and gas diffusiontheory.