Gas Sensitivity Studies On Conductive Polyaniline Detecting SF₆ Decomposed Components

Sulfur hexa?uoride(SF6), has excellent chemical stability under room temperature, high electronegativity, extreme electrical insulating and arcing performance that make it applicable in gas-insulated switchgear(GIS). During long term operation, the inevitable faults in GIS may cause different degree of partical discharge(PD) and partial over-thermal fault, which lead to SF6 decomposition and produced a variety of unstable low fluorine sulphr. Then reacted with trace amount of water and oxygen that generate H2S、SO2、SOF2 and SO2F2. The SF6 decomposition gases generated by these faults should be detected to effectively predict, detect, and locate faults in GIS. In this paper, conductive polymer polyaniline(PANI) gas sensor was used to detect SF6 decomposition gases. And the synthesis of materials, gas-sensing properties and gas sensitive mechanism are studied.Using chemical oxidative polymerization, aniline monomers, ammonium persulfate(APS) as the oxidant, then in an acidic medium synthesis three doping state of PANI material PANI-HCl, PANI-SSA and PANI-HCl/SSA, and fork refers to the electrode based gas sensors were prepared. The chemical composition and structure of doped state PANI were characterized using FTIR, XRD, SEM and TGA-DTA methods.The gas-sensing properties of PANI-HCl sensors to 100 μL/L H2S、SO2、SOF2 and SO2F2 were tested, and found that this sensors is the most sensitive to H2S(-89%). With the increase of concentration of H2 S the gas sensor response become saturate, which indicate that PANI-HCl sensor is suitable for detecting low concentration of H2 S. The sensitivity of PANI-HCl sensor to 25 μL/L H2 S is-72% is greater than 100 μL/L SO2, SOF2 and SO2F2(-65%,-24.5% and-10%), and showed a better selectivity to H2 S. In the recovery experiment, gas sensors after tested H2 S and SO2 required N2 cleaning and auxiliary heating conditions to obtain a completely desorption and the recovery time is longer. However, SOF2 and SO2F2 can easily dissociative from gas sensitive material surface. Through the FTIR analysis before and after contact with gas, and found that the sensitivity of sensors and the speed of gas molecules desorption is closely related to its chemical properties.In order to improve the environmental stability of PANI-HCl, PANI-SSA and PANI-HCl/SSA sensors were prepared to tested different concentration H2 S and SO2 under the same experimental conditions. The results showed that the sensitivity of PANI-SSA to 100 μL/L H2 S and SO2 are-15.6% and-13.2%, respectively, and showed a poor sensitivity and selectivity. Meanwhile, the sensitivity of PANI-HCl/SSA sensor to 100 μL/L H2 S and SO2 are-61.8% and-43.6%, both showed sensitive and obtained certain of selectivity. Literature has suggested that H2 S is a characteristic decomposition product during a serious discharge and over-thermal fault occurs at a certain stage of development. However, SO2 as a main breakdown products, the beginning produce time and the rate of producing of this two kinds of gases are different, and the detection will not result in a cross interference. Moreover, the response and recovery time is shorter than PANI-HCl sensor, and have a good environmental stability, which is suitable as a kind of SF6 decomposition components detecting devices at room temperature.