The CNTs have a multi-wall structure with purity of more than 95%. The tube diameter ranges from 20 to 30 nm, whereas the tube lengths range from 10 to 30 ��m. The specific surface area of 4 ? molecular sieve is about 800 g/m2 in the paper. Filtered by 5,000 mesh sub-sieve, the ground 4 ? molecular sieve has micrometer dimensions, with a powder particle diameter of approximately 1 ��m.First, the MWNTs and the ground micrometer size 4? molecular sieve were weighed at different mass ratios. In this paper, the following mass ratios were selected: 1:1, 3:1, 5:1, 10:1, and 20:1. The MWNTs were placed in anhydrous ethanol and the mixed solution was dispersed for 90 min using an ultrasonic oscillator to obtain a uniformly dispersed suspension. A certain amount of the solution was taken and placed it in anhydrous ethanol.

The mixed solution was then dispersed several times for 60 min to obtain a clearer solution.The MWNT sensor substrate is made of printed circuit boards. Copper interdigital electrodes are etched in the substrate. Foil thickness is approximately 30 ��m, whereas the width and spacing of the electrodes are both 1 mm.Trace solution was dropped onto the surface of the interdigital electrodes, until the initial resistance values of the sensors meet the needs, and then placed in an oven at 80 ��C to prepare a uniform, dense, and smooth film to serve as the gas membrane for the detection of characteristic SF6 decomposition products.Figure 2 shows a comparison of the intrinsic MWNTs and the adsorbent-mixed MWNTs recorded using a Nicolet 5DXCFT-IR infrared spectrometer.

From the infrared spectra in Figure 2, an evident silicon-oxygen bond absorption peak is observed at 1,000 to 1,100 cm?1 (circled in Figure 2) of in the adsorbent-mixed MWNTs. Silicon-oxygen bonds exist in the adsorbent, but not in MWNTs. This proves the adsorbent is mixed into the MWNTs. Figure 3a,b shows the SEM images of the intrinsic MWNTs and adsorbent mixed MWNTs, respectively.Figure 2.Infrared absorption spectra of MWNTs and mixed MWNTs.Figure 3.SEM images of MWNTs.According to SEM image, the 4 ? zeolite powders are present in the mixture. Meanwhile, it could be observed that the powder has micrometer dimensions.3.?Results and Discussion3.1. Procedures for Detecting SF6 Decomposition ProductsThe prepared MWNT sensor was placed in a sealed chamber, as shown in Figure 4.

The MWNT sensor was then connected to an impedance analyzer through a wire. Finally, screws were used to seal the gas chamber.Figure 4.Structure Anacetrapib of the gas chamber used for testing sensors.The experimental steps were as follows:(1)The inlet valve was closed, the vacuum gauge and the outlet valves were opened, and the vacuum pump was switched on to pump air from the cylinder. The ball valves and vacuum pump were then closed after the cylinder became a vacuum.