1,721,004 research outputs found
On the influence of chemical defects and structural factors on charge transport and failure in polyethylene
No full textA blend of high and low density polyethylene was aged at 160 °C in air and the impact of the chosen aging protocol on local chemistry, crystallinity and charge transport dynamics was considered. The aging conditions were chosen in order to exploit oxygen diffusion effects, such that the resulting systems could be considered as bi-layer specimens, containing two regions: a uniform lightly aged layer and a more spatially varying highly aged layer, which vary in the concentrations of aging-related defects such as carbonyl groups and unsaturation. For aging periods up to 3 h, little space charge was found within both the highly and lightly aged layers. However, after aging for about 3.5 h, an abrupt change in behavior was observed, whereby charges move rapidly through the highly aged layer, accumulating at the interface with the lightly aged layer. Sample melting behavior, as determined by differential scanning calorimetry, was found to depend on aging time, as a result of impeded crystallization and retarded reorganization kinetics. We suggest that this abrupt change in charge transport behavior is a consequence of the local concentration of chemically related trapping sites exceeding some critical threshold. The consequence of the resulting space charge distribution is a dramatic increase in the local electric field across the lightly aged layer and a consequent reduction in the overall DC breakdown strength. However, while further aging exacerbates these space charge effects, counter to expectations, the breakdown strength then recovers somewhat, suggesting a change in the underlying mechanism of electrical failure
Electrical breakdown strength of boron nitride polyethylene nanocomposites
No full textThere is a growing demand for the design of high-performance insulators for high voltage applications. It was proposed that the addition of nanofillers to a polymer could potentially enhance the electrical properties of insulators when compared to the conventional unfilled or microfilled polymers [1]. These materials have captured the interest of many researchers worldwide since then, as present dielectric materials could benefit from improvements in properties such as dielectric strength, dielectric loss, electrical and thermal conductivity, and permittivity that nanodielectrics offer. However, many of the underlying principles remain uncertain, such as the polymer/nanofiller interface, and researchers are still exploring solutions to common challenges faced by nanodielectrics such as nanoparticle agglomeration [2].The work presented in this paper is based on a hexagonal boron nitride nanocomposite in a polyethylene blend host polymer. A polyethylene blend composed of 80% low density polyethylene (LDPE) and 20% high density polyethylene (HDPE) is chosen as the polymer matrix since it has a higher electrical breakdown strength than pure LDPE. Hexagonal boron nitride was chosen as a nanofiller because of its attractive properties for high voltage applications such as high dielectric strength, high thermal conductivity, and mechanical robustness [3]. A solution blending method is used to mix the nanoparticles in the polymer as better quality materials and nanoparticle dispersion are achieved.This paper will investigate the AC electrical breakdown behaviour of the prepared polymer nanocomposite materials. The electrical breakdown strength of the unfilled polymer will be compared to the untreated hexagonal boron nitride filled polymer at different loading levels. The addition of this nanofiller is expected to alter the dielectric strength due to changes in the material’s structure. The chemical structure of hexagonal boron nitride is illustrated in Figure 1, where there is an equal number boron and nitrogen atoms firmly bound together. The breakdown results will then be analysed using a two-parameter Weibull distributio
Impact of particle thermal treatment on dielectric properties of core-shell filled epoxy nano-composites
No full textThis paper presents the effect of Silica-Titania (SiO2@TiO2) core-shell nano-particles added into amine-cured epoxy composites, under three different particle treatment conditions: untreated, calcined at 250 ∘C and 450 ∘C , on the dielectric and structural properties of the bulk composite. Characterization was conducted using a range of methods Transmission Electron Microscopy (TEM), Fourier Transform Infra-Red Spectroscopy (FTIR), Raman Spectroscopy, Differential Scanning Calorimetry (DSC) and Broadband Dielectric Spectroscopy (BDS). TEM confirmed the synthesis of the core-shell architecture with denser shells at higher calcination temperatures. Raman spectroscopy showed an increase in the Ti-O-Ti network formation and orderliness with elevated temperature treatment. Incorporating untreated filler into epoxy reduces the bulk real permittivity, while the inclusion of calcined fillers leads to an increase. An additional ω relaxation was observed in imaginary permittivity spectra of nano-composites pointing towards altered molecular dynamics within the epoxy due to nano-particle addition. These findings highlight the role of core-shell nano-particles in modifying the dielectric properties of epoxy composites, whilst differentiating them from conventional nano-particles
The effect of exfoliation on the breakdown strength of polystyrene boron nitride composites
No full textResearch on polymer nanocomposites promises to create a new class of materials with enhanced dielectric properties. This paper reports on the study of polystyrene systems filled with hexagonal boron nitride (BN) nanoparticles. The polymer nanocomposite materials were produced using a solvent blending procedure, where some of the materials were produced using dichloromethane (DCM) as the solvent and others using isopropyl alcohol (IPA). The breakdown strength was measured at different loading levels; the breakdown strength was found to decrease at the 5 wt% loading level, but increased again with 10 wt% and higher loadings of BN. The effect of exfoliation by solvent choice and sonication on the breakdown strength was investigated; sonication in IPA produced the best results. However, micrographs obtained from the scanning electron microscope show no apparent change of the dispersion of BN in the sonicated systems with the different solvents
On the post-curing thermal treatment of silicone rubbers: a study on electrical performance
No full textSilicone rubbers, particularly poly(dimethylsiloxane) (PDMS), are popular across various industrial applications, however notable issues arise from volatile cyclic siloxanes and their tendency to compromise their performance. This study investigates the electrical performance (DC conductivity, dielectric spectroscopy, DC breakdown) of two commercial PDMS products, before and after a post-curing treatment (200◦C, 4h). The tested materials, named PDMS A (RTV) and PDMS B (LSR), are chosen as they display distinct characteristics: they differ in terms of outgassing behavior and structural alterations during treatment. In particular, thermogravimetric analysis (TGA) reveal pronounced volatile removal in PDMS B, while Fourier transform infrared (FTIR) and Raman spectroscopy demonstrate pronounced structural alterations in PDMS A (crosslinking of unreacted long chains) promoted by post-curing. As expected, the electrical insulation performance is enhanced in both post-cured materials: the magnitude of this depends on the extent of two abovementioned aspects. The DC conductivity reduction follows the volatiles removal pattern (larger scale in PDMS B), while the ε’ and ε’’ values reduce following the structural alteration pattern (elimination of a relaxation peak in PDMS A). The DC breakdown strength enhancements are driven by structural variations rather than removal of volatiles
Permittivity in epoxy based syntactic foam nanocomposites
No full textFollowing previous work, this paper focuses on a new type of epoxy based syntactic foam, a lightweight material which is known to electrical engineering since the seventies, but so far couldn't live up to it's potential in high voltage applications. This is mainly because of the basic structure of syntactic foam, which provides closed cell porosity. The porosity, which gives syntactic foam its weight reduction, unfortunately leads to shortcomings in terms of dielectric strength and PD resistance. However: with recent advances in material science and the dawn of nanotechnology, there is a new take on this unique material, which can be used as insulating material for HV-applications, where weight is of vital importance. Four different types of epoxy based syntactic foam nanocomposites are presented, whose respective dielectric behavior were studied with help of dielectric spectroscopy. The measurement results, with emphasis on the complex permittivity, are presented in this work. Also the advantages and shortcomings of the various composites are discussed, as they are compared with both unmodified syntactic foam, as well as the unmodified base epoxy
Influence of nano-SiO2 and BN on space charge and AC/DC performance of epoxy nanocomposites
No full textIn this paper, the high purity bisphenol-A diglycidyl ether (DGEBA) epoxy resin (D.E.R 332), which is mainly used as filament winding, electrical laminates and encapsulation applications, was used as a host. The epoxy resins were loaded with nano-SiO2 and nano-BN in different loading concentrations, and then test of the AC/DC breakdown strength has been performed. It has been observed that the presence of untreated nano-fillers will decrease the AC/DC breakdown strength of nanocomposites. This may be caused by field enhancement resulting from agglomeration of un-treated nano-fillers. The influence of filler concentration and surface treatment, especially the filler type, of particles on AC, DC breakdown strength and space charge has been investigated. Moreover, it has been widely recognised that the presence of moisture in nanocomposites has detrimental effect on the electrical performance. Therefore, the water absorption of epoxy nanocomposites and its impact on electrical performance has also been considered
Comparison of the dielectric response of alumina-epoxy composites with nano- and conventional sized filler
No full textThe effect of material processing on the dielectric properties of polystyrene boron nitride nanocomposites
Get PDFExtensive experimental work in the area of polymer nanocomposites has been done over the past two decades to explore their potential. In this study, a range of related polymer nanocomposite materials was prepared using a solvent blending method, using dichloromethane (DCM), toluene (TOL) and chlorobenzene (CB) to dissolve the polymer, atactic polystyrene (a-PS), and disperse the filler, hexagonal boron nitride (hBN). Where TOL and CB were used, heat was used in material processing, whereas the material was processed at room temperature with DCM. The largest increase in breakdown strength is observed in the materials processed with TOL and CB. The hBN appears to be well dispersed in these systems and more agglomerated in the DCM system as shown from SEM
Modelling of the thermal conductivity in polymer nanocomposites and the impact of the interface between filler and matrix
Get PDFIn this paper the thermal conductivity of epoxy-based composite materials is analysed. Two and three-phase Lewis–Nielsen models are proposed for fitting the experimental values of the thermal conductivity of epoxy-based polymer composites. Various inorganic nano- and microparticles were used, namely aluminium oxide, aluminium nitride, magnesium oxide and silicon dioxide with average particle size between 20 nm and 20?m. It is shown that the filler–matrix interface plays a dominant role in the thermal conduction process of the nanocomposites. The two-phase model was proposed as an initial step for describing systems containing 2 constituents, i.e. an epoxy matrix and an inorganic filler. The three-phase model was introduced to specifically address the properties of the interfacial zone between the host polymer and the surface modified nanoparticles.Electrical Sustainable EnergyElectrical Engineering, Mathematics and Computer Scienc
- …
