The thermal degradation of PVC in air ambience was investigated by the thermogravimetric analysis (TGA). The experiments were carried out at different heating rate of 5, 10, 20 and 40°C/min, respectively. The activation energy was calculated by the Friedman method. The pyrolysis mechanism of PVC in air was discussed and compared with that in Nitrogen atmosphere. The pyrolysis process of PVC in air could be divided into two main stages: 200 °C ~ 380 °C and 400 °C ~ 600 °C, which obtained by TGA at the heating rate of 5°C/min. The second stage could be further subdivided into two parts by 465 °C. It can be concluded that the oxygen in air affected the second stage more obviously than that of the first one, in comparison with inert atmosphere. The activation energy of the second stage was still larger than the first stage.
Tungsten-rhenium thin film thermocouples (TFTCs) are well suited for the surface temperature monitoring of hot components due to their small size, rapid response and low cost. In this study, a tungsten-rhenium TFTC with SiC protective film on all parts except the pads was fabricated by a microelectromechanical system (MEMS) process. During the low to medium temperature (−40 °C to 500 °C) repeatability test phase, the thermal voltage from the TFTC agreed well with that of the standard tungsten-rhenium thermocouple. However, during the high temperature test phase, the TFTC lost electronic response at around 620 °C. Failure analysis of the TFTC tested at 620 °C was performed by microscopy, scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), laser scanning confocal microscope (LSCM) and statistics. The results showed that the pads were oxidized without the protective layer, the number of oxidized protrusions distributed in this TFTC from the pad to the node decreases more and more slowly and the size of the oxidized protrusions also becomes smaller and smaller. This demonstrates the presence of horizontal oxidation diffusion in TFTCs, further illustrating the importance of pad protection and provides a direction for the subsequent structural optimization and the extension of the service life of TFTCs and other sensors.
The thermal degradation of PVC resin was examined by the thermogravimetric analysis (TGA). The pyrolysis volatile products were analyzed by Fourier transform infrared spectrometer synchronized with TG test (TG-FTIR). Based on the TG results, the kinetics of thermal degradation was studied by Friedman method. The pyrolysis mechanism was discussed also. The results indicate that the pyrolysis process of PVC can be divided into two main stages: 220°C - 380°C and 380°C - 560°C. By the calculation of mass conservation and TG-FTIR results, it can be supposed that not only HCl, but also some unsubstituted aromatics such as benzene were released during the first stage. The comparison of activation energy shows that the second stage exhibited higher activation energy than the first stage. Two activation energy values in the first stage confirm that there arose two reactions in the first stage.
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