Role of additives as recombination centres in polyethylene materials as probed by luminescence techniques

Abstract

The long-term electrical stability and dielectric breakdown of insulating polymers is largely determined by the density and energy distribution of the conduction and trapping levels. Although these materials are widely used in technical applications very little is known about the nature of the deep trapping centres which are responsible for charge storage. We show that luminescence techniques can be used to gather information on their nature. The proposed approach relies on photo- and recombination-induced luminescence experiments. The latter has been specifically developed to record the optical spectrum of the emission radiated by a deep trapping centre during a recombination event. The work concerns low-density polyethylene, doped or undoped, and cross-linked polyethylene. It is shown that the implication of a given chemical in the trapping process can be probed by using the recombination-induced luminescence technique.

Photoluminescence of ultra-high molecular weight polyethylene modified by fast atom bombardment

“…The maximum in the excitation spectra, observed at¨290 nm (Fig. 1), is consistent with the presence of chromophoric carbonyl group (C=O), which exhibits an absorption maximum at that wavelength [11]. The long wavelength tail of the luminescence spectra, however, originates from fluorescence transition, rather than from phosphorescence.…”

“…4) prove the presence of C=O group, with an increased amount in the FAB-treated samples, as compared to reference material. In case of eventual presence of separated carbonyl chromophore groups, maximal luminescence efficiency at~290 nm excitation would be expected [11]. Since the luminescence intensity was found to be weak at this excitation, the possibility of the presence of isolated carbonyl group as a new chromophore can be rejected.…”

Correlation between trapping parameters and surface insulation strength of solid dielectric under pulse voltage in vacuum

“…Because of the limitations of the experimental method and device, it is difficult to obtain a full energy distribution of traps. The traps at the deeper energy level can only be scanned, and this mainly reflects the status of chemical traps [28]. In contrast, the shallow traps are quickly detrapped and hard to be detected due to the relatively slow response time of probe system and the influence of ambient.…”

“…According to the molecular formulae of epoxy resin in Figure 1, its spatial network structure is made up of plenty of molecule chains with branches and includes abundant unsaturated bonds. These asymmetric molecular constitution and unsaturated links form a great deal of trapping centers, which is generally regarded as the deep trapping centers [28]. In the process of adding fillers, the agglomeration phenomena are difficult to be avoided, as shown in Figure 2b.…”

“…Figure 13 demonstrates an electron (with a kinetic energy E et ) trapped in a potential well formed by the immobile positive ion, and a trapped hole in certain outer layer orbit of the ion. The trapped electron in deep trap could penetrate the barrier of the coulombic potential by means of tunneling effect and recombine with the trapped hole [28,33]. Thus, with the increase of the hole trap density, the more recombination opportunities are provided and the distortion of the surface electric field is relaxed more, which could promote the insulation performance (after the surface being charged) to some extent.…”