Quantifying time-dependent structural and mechanical properties of UV-aged LDPE power cables insulations

This paper reports effects of ultraviolet (UV) light radiation on the physicochemical, electrical and mechanical properties of low-density polyethylene (LDPE) cable insulating materials. Changes in structural and morphological properties of UV-aged samples were characterized by various analytical methods such as attenuated total reflection Fourier transform infrared spectroscopy (ATRFTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Additionally, elongation at break, tensile strength, dielectric strength, and optical properties were also evaluated. Changes in some physical properties of LDPE after exposing to UV irradiation clearly highlighted that the polymer underwent the structural degradation. In addition, it was also found that such degradation yielded both crosslinking and chain scission as two competing processes during UV aging

Low Loss Sol-Gel TiO2 Thin Films for Waveguiding Applications

TiO2 thin films were synthesized by sol-gel process: titanium tetraisopropoxide (TTIP) was dissolved in isopropanol, and then hydrolyzed by adding a water/isopropanol mixture with a controlled hydrolysis ratio. The as prepared sol was deposited by “dip-coating” on a glass substrate with a controlled withdrawal speed. The obtained films were annealed at 350 and 500 °C (2 h). The morphological properties of the prepared films were analyzed by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The optical waveguiding properties of TiO2 films were investigated for both annealing temperature using m-lines spectroscopy. The refractive indices and the film thickness were determined from the measured effective indices. The results show that the synthesized planar waveguides are multimodes and demonstrate low propagation losses of 0.5 and 0.8 dB/cm for annealing temperature 350 and 500 °C, respectively

Effect of co-solvent on structural and morphological properties of ZnO aerogel prepared by a modified sol-gel process

Nanocrystalline zinc oxide (ZnO) aerogel powders were synthesized using a modified sol-gel process. Ethanol, acetone and methanol were used as supercritical drying fluids. Effects of co-solvent on morphological and structural properties were investigated. The as prepared powders were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The XRD results show that drying in solvents mixture affects the crystalline quality and acts as a compression agent by exerting stress on the lattice parameters. SEM micrographs demonstrate that co-solvent plays a key role in controlling ZnO nucleation and favors the particles agglomeration with increasing the pressure and the temperature. The EDAX analysis shows that the obtained ZnO nanopowder with ethanol and acetone as co-solvent is pure with different stoichiometries (an excess of oxygen (O) with ethanol and zinc (Zn) atoms with acetone). However, when methanol is used as supercritical drying fluid, the obtained nanopowder contains an excess of carbon (C) atoms. FTIR absorption bands are more intense for aerogel synthesized by drying in methanol indicating the presence of more C-H bounds responsible of the low rate agglomeration of the ZnO crystallites

Correlation between structural changes and dielectric behavior of UV-Aged LDPE

Low-density polyethylene (LDPE) is widely employed as insulator for high and medium voltage cable, due to its excellent dielectric, mechanical and other characteristics However, like all other insulating materials, LDPE properties deteriorate after working under different service conditions. One of the most dangerous stressing factors causing a serious degradation for the LDPE insulation properties is UV radiation. In this work, the influence of UV radiation constraint on the LDPE dielectric properties is studied. In order to support this investigation, ATR-FTIR spectroscopy is also performed. The findings indicate that UV radiation influences significantly the material insulating properties

AZO Thin Films by Sol-Gel Process for Integrated Optics

coating

Effects of dip-coating speed and annealing temperature on structural, morphological and optical properties of sol-gel nano-structured TiO

We reported material characterization of the nano-structured TiO2 thin films prepared by the sol-gel dip-coating process on glass substrates. The dependence of the structural, morphological and optical properties of the synthesized films on the fabrication parameters such as withdrawal velocity and annealing temperature were investigated by the techniques of X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV-visible spectrophotometry. The results indicate that for the TiO2 films annealed at 500 °C there exhibits (1 0 1) XRD peak corresponding to the anatase phase of TiO2. The latter is consistent with the recorded Raman signal observed at 142 cm-1 (Eg mode) and 391 cm-1 (B1g mode), respectively. From the analyses made on the SEM micrographs and AFM images, it was revealed that the morphology and surface roughness of the thin films would depend on the withdrawal speed and the heat treatment temperature. The UV-visible spectroscopy analyses show that all the films were transparent in the visible region with an average transmittance of more than 70%. With an increase on the dip-coating speed from 1 cm/min to 3 cm/min, we observed a spectral red shift of the absorption edge from 3.76 eV to 3.71 eV, indicating a decrease in the bandgap energy (Eg) of the films

Effects of sol concentration on structural, morphological and optical waveguiding properties of sol-gel ZnO nanostructured thin films

Nanostructured ZnO thin films with different precursor concentrations (0.5–0.8 M) have been deposited on glass substrates by sol-gel dip coating technique. X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV-visible spectrophotometer, and m-lines spectroscopy have been employed to investigate the effect of solution concentration on structural, morphological, optical and waveguiding properties of the ZnO thin films. XRD spectra have shown that all the films are polycrystalline and exhibit the wurtzite hexagonal structure. SEM micrographs and AFM images have revealed that morphology and surface roughness of the thin films depend on sol concentration. The UV-visible transmittance results show a high transparency in the visible range and a shift of the maximum transmittance to the higher wavelength with increasing sol concentration. Waveguiding properties such as refractive index, number of propagating modes and attenuation coefficient measured at 632.8 nm wavelength by m-lines spectroscopy indicate that our ZnO slab waveguides are single mode and demonstrate optical losses estimated around 1.5 decibel per cm (dB/cm) for the thin film prepared with a sol concentration of 0.7 M

Comprehensive characterization of Al-doped ZnO thin films deposited in confocal radio frequency magnetron co-sputtering

Al-doped ZnO thin films with varying Aluminium (Al) content were deposited by radio frequency magnetron cosputtering of two ZnO and Al targets in confocal configuration. A comprehensive study of the effect of Al content variation on the structural, optical and electrical properties were studied for as-deposited films and after an annealing step under controlled argon atmosphere. Chemical composition analyses, performed by both X-ray photoelectron spectroscopy and energy dispersive X-ray spectrometry, show an Al content variation in the deposited films in the 0-14 at.% range by varying the Al target power from 0 to 30 W, while the Zn target power was kept constant at 200 W. All deposited films exhibit a wurtzite crystalline structure and a decreasing crystalline quality for Al content above 5 at.% as shown by grazing incidence X-ray diffraction patterns. Atomic Force Microscopy analysis revealed films with homogeneous and dense surface morphology with roughness in the one nm range. Carrier concentration, resistivity and photoluminescence vary significantly with Al content in the ZnO films and appear optimized for an Al content window ranging from 1.5 to 5.5 at. %. Both optical and electrical properties are improved by a post-annealing at 300 degrees C under argon. A high figure of merit of 43.6 x 10-4 sq.& omega;-1 was obtained for the ZnO film with Al content of 3.6 at.% after annealing at 300 degrees C. Optimized properties are obtained for a higher Al content than the standard value of 2 at. % widely used in published works