Microscopic Mechanisms of Damage Caused by Degradants

Wypych, George

doi:10.1016/b978-1-927885-25-3.50007-0

Cited by 6 publications

(2 citation statements)

References 378 publications

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“…Ozone and N 2 O, on the other hand, are reported to have very large electron attachment crosssections at electron energies in the range of 0 − 4 eV [18]. However, N 2 O is less likely to be responsible for the large increase in breakdown voltage as it is a stable compound with a long atmospheric lifetime of around 150 years [19]. In this study, it was observed that the increased value of impulse breakdown voltage of air lowered down to the initial level within several hours after the test.…”

Section: Discussionmentioning

confidence: 99%

Lightning Impulse Testing in Short Air-Gaps and Memory Effect of Previous Discharges

Subhana,

Støa-Aanensen,

Gammelsæter

et al. 2024

IEEE Trans. Dielect. Electr. Insul.

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This paper reports on an observed phenomenon of increasing breakdown voltage while performing standard up and down lightning impulse (LI) testing in short air-gaps with weakly non-uniform field in an enclosed volume. The phenomenon could occur due to accumulation of space charges in the gap, changes in the chemical composition of the insulation gas, and/or changes in electrode surface due to discharges. To investigate the effect of these factors, LI tests are carried out in a 10 mm rod-plane air gap using four different methods: 1) ion flushing by DC voltage application in between LI shots, 2) with opposite polarity LI intertwined, 3) using forced air flow by a fan during the test, and 4) a reference test without any fan or voltage application. Results indicate that the phenomenon is more likely to be caused by formation of electronegative byproducts, e.g., ozone. Ozone was also experimentally detected near the test gap followed by consecutive LI breakdowns. It was found that air circulation rapidly reduces ozone concentration, which may explain why the increasing trend is not observed when a fan is used. Calculation of electron transport coefficients indicates that lack of primary electrons might be the prime reason of the increased impulse breakdown voltage of the air gap in presence of ozone.

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Section: Discussionmentioning

confidence: 99%

Lightning Impulse Testing in Short Air-Gaps and Memory Effect of Previous Discharges

Subhana,

Støa-Aanensen,

Gammelsæter

et al. 2024

IEEE Trans. Dielect. Electr. Insul.

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“… 5 , 6 Degradation of PP mesh is considered to be the result of the synergistic effects of corrosive chemicals such as reactive oxygen species (ROS) produced by inflammatory cells and tensile stress in the mesh fibers in vivo. 7 , 8 Degraded PP mesh has reduced tensile strength and elastic modulus, the altered morphology of the mesh surface also affects the interaction with the immune cells. 9 , 10 Therefore, the concern about the long‐term safety of PP mesh implants is growing.…”

Section: Introductionmentioning

confidence: 99%

Characterization in respect to degradation of titanium‐coated polypropylene surgical mesh explanted from humans

2023

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Titanium-coated polypropylene (Ti-PP) mesh was introduced in 2002 as a surgical mesh for the treatment of hernias and shortly after for pelvic floor surgery, with the aim of improving biocompatibility when compared to non-titanised/regular PP mesh implants. The application of a titanium coating could also be beneficial to address concerns regarding the exposure of PP in an in vivo environment. Many studies have shown that PP, although it is widely accepted as a stable polymer, is subject to oxidation and degradation, such degradation affects the mechanical behavior, that is, the stiffness and tensile strength of PP mesh. Despite the wide clinical use of Ti-PP surgical meshes, no study has yet investigated the residual material properties post clinical deployment and subsequent explantation. In this study, two explanted Ti-PP mesh samples each having different incorporation durations from two patients were examined. Material analysis conducted within this study includes the following techniques: attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), Raman spectroscopy, low voltagescanning electron microscopy (LV-SEM), backscattered electron (BSE) imaging, energy dispersive X-ray spectroscopy (EDS) and secondary election hyperspectral imaging (SEHI). The hypothesis of this study is that the Ti coating successfully shields the PP mesh from oxidative stress in vivo and thus protects it from degradation. The results of this analysis show for the first time evidence of bulk oxidation, surface degradation, and environmental stress cracking on explanted Ti-PP meshes.

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