Dielectric Loss Index Research Articles

Study of the Effect of Doping with Alumina and Silica the Structural and Electrical Properties of Epoxy

Crystalline structure of a sample of Alumina (Al2O3 – reinforced epoxy) at (4% and 8%) has two prominent peaks at point (17°) and (19.5°) with miller vectors (111) and (220), respectively. These results are corresponding to crystalline cubic and notes growing of crystallization. The spectrum of (XRD) showed increase in crystalline size which means an increase in randomization and a lack of crystallization amorphous at (6%) (Al2O3). This result showed increase in crystalline size which means an increase in randomization and a lack of crystallization amorphous. Epoxy matrix reinforced by particles of silica (SiO2) and alumina (Al2O3) with different fractions were investigated for electrical properties such as dielectric constant, conductivity and dielectric loss index. This result showed effect of additional (SiO2, Al2O3) is small concentration except (2% SiO2) has large effect.

INVESTIGATION OF STRUCTURAL, OPTICAL, AND DIELECTRIC PROPERTIES OF PVA-KI FOR TEMPERATURE SENSOR APPLICATIONS

Polyvinyl alcohol (PVA) films doped with potassium iodide (KI) have been prepared by casting from their aqueous solutions. The structure of the doped samples was investigated using Fourier transform infrared spectroscopy. The addition of KI to PVA structure leads to form crosslinking as well as the increase of the amorphous ratio within the investigated sample. The optical measurements were recorded at room temperature in the range of 200–2500[Formula: see text]nm. It was found that the optical energy gap of the investigated sample increases with increasing KI ratio. The effect of the addition increment of KI on the optical parameters of PVA has been investigated. Dielectric spectra of PVA doped with KI were studied in the temperature and the frequency ranges of 303–373[Formula: see text]K and 100[Formula: see text]Hz–5[Formula: see text]MHz, respectively. The behavior of dielectric constant ([Formula: see text]) and dielectric loss index ([Formula: see text]) of PVA sample doped with KI exhibits good linearity with temperature. The obtained results suggest strongly the applicability of these materials in the temperature sensor applications.

STRUCTURAL, OPTICAL, ELECTRICAL AND DIELECTRIC PROPERTIES OF PVA-YCl3 FILMS

Polyvinyl alcohol (PVA) films doped with 10[Formula: see text]wt.% of yttrium chloride (YCl[Formula: see text] have been made by casting from their aqueous solutions. The structure of un-annealed and annealed PVA-YCl3 films was studied using X-ray diffraction (XRD) patterns and Fourier-transform infrared spectroscopy (FTIR). Both FTIR and XRD revealed that the crystalline ratio of the studied samples increased due to the effect of annealing. The effect of annealing on the optical properties has been studied. Dispersion of the refractive index was described using the single oscillator model. The single oscillator energy and the dispersion energy were estimated. The calculated optical band gap of all PVA-YCl3 films was 5.0[Formula: see text]eV. The behavior of ac conductivity showed that the conduction mechanism of PVA-YCl3 films was correlated barrier hopping model. The dielectric constant and dielectric loss index were decreased with the increase of the field frequency. The electric modulus granted a straightforward technique for assessing the dielectric relaxation time. The calculated activation energy obtained from the electric modulus mechanism was 0.172[Formula: see text]eV.

Dielectric Relaxation Behavior and AC Electrical Conductivity Study of 2-(1,2-Dihydro-7-Methyl-2-Oxoquinoline-5-yl) Malononitrile (DMOQMN)

Dielectric relaxation and alternative current conductivity of a new organic compound 2-(1,2-dihydro-7-methyl-2-oxoquinoline-5-yl) malononitrile (DMOQMN) have been investigated. X-ray diffraction (XRD) at room temperature reveals that DMOQMN samples have a polycrystalline structure of the triclinic system. The analysis of the dielectric constant and dielectric loss index suggested the dominant polarization is performed and the Maxwell–Wagner–Sillar type polarization is dominating at low frequency and high temperature. These results have been confirmed by the XRD and dielectric modulus. The estimated relaxation time and the activation energy are 9 × 10−13 s and 0.43 eV, respectively. Our results indicated that the conduction mechanism of DMOQMN is controlled by the correlation barrier hopping (CBH) model.

AC Conductivity and Dielectric Relaxation Behavior of Sb2S3 Bulk Material

The Sb2S3 bulk material was used for next-generation anode for lithium-ion batteries. Alternative current (AC) conductivity, dielectric properties and electric modulus of Sb2S3 have been investigated. The measurements were carried out in the frequency range from 40 Hz to 5 MHz and temperature range from 293 K to 453 K. The direct current (DC) conductivity, σDC, shows an activated behavior and the calculated activation energy is 0.50 eV. The AC conductivity, σAC, was found to increase with the increase of temperature and frequency. The conduction mechanism of σAC was controlled by the correlated barrier hopping model. The behavior of the dielectric constant, e′, and dielectric loss index, e′′, reveal that the polarization process of Sb2S3 is dipolar in nature. The behavior of both e′ and e′′ reveals that bulk Sb2S3 has no ferroelectric or piezoelectric phase transition. The dielectric modulus, M, gives a simple method for evaluating the activation energy of the dielectric relaxation. The calculated activation energy from M is 0.045 eV.

Development of synthetic electrical insulating paper

The analysis of modern high requirements to paper features that used for electric insulation, among which it is highlighted a number of key features such as heat resistance, dielectric strength, water absorption, tangent of the angle of dielectric losses is presented in the article. Some results of our research in this area are given. The research is conducted by manufacturing of laboratory samples of 100 % synthetic paper using a composition of polyester fibers as main and two binding options. It is developed a composition of paper that have a high thermal stability and gives an electric insulation synthetic paper with low water absorbency, low dielectric loss tangent. The synthetic paper made using a matrix of polypropylene fiber has low dielectric loss index value, which will use this paper for insulation in high voltage cables. Using of such paper will reduce losses during electricity transmission.

Dielectric and electrical conductivity studies of bulk lead (II) oxide (PbO)

The dielectric properties, the impedance spectroscopy and AC conductivity of bulk PbO have been investigated as a function of frequency and temperature. The measurements were carried out in the frequency range from 40 to 5×106 Hz and in temperature range from 313 to 523K. The frequency response of dielectric constant, ε1, and dielectric loss index, ε2, as a function of temperature were studied. The values of ε1 and ε2 were found to decrease with the increase in frequency. However, they increase with the increase in temperature. The presence of a single arc in the complex modulus spectrum at different temperatures confirms the single-phase character of the PbO. The AC conductivity exhibited a universal dynamic response: σAC=Aωs. The AC conductivity was also found to increase with increasing temperature and frequency. The correlation barrier hopping (CBH) model was found to apply to the AC conductivity data. The calculated values of s were decreased with temperature. This behavior reveals that the conduction mechanism for PbO samples is CBH. The activation energy for AC conductivity decreases with increasing frequency. This confirms that the hopping conduction to the dominant mechanism for PbO samples.

Dielectric analysis of α‐relaxation process of chlorinated poly(vinyl chloride) stabilized with nitro‐phenyl maleimide

AbstractNitro‐phenyl maleimide (NPM), is the organic stabilizer for poly (vinyl chloride) (PVC), has been investigated as thermal plasticization for rigid chlorinated poly (vinyl chloride) (CPVC). Dielectric relaxation of CPVC stabilized with 10 wt% of NPM has been studied in temperature and frequency ranges of 300–450 K and 10 kHz–1 MHz, respectively. An analysis of the dielectric constant, ε′ and dielectric loss index, ε″, was performed assuming a plasticization effect of NPM molecules. The plasticization effect of NPM molecules was confirmed by the behavior of the dielectric modulus M′ and M″ spectra. A clear dielectric α‐relaxation process has been obtained in the studied temperature range. The results showed that NPM reduce the glass transition temperature, Tg, of CPVC by about 20 K. This effect has been assigned to the plasticization effect of NPM. At lower temperatures, dielectric modulus spectra reveal that there is a role of the effect of the electrode polarization in the relaxation process. The behavior AC conductivity, σac, indicated that the conduction mechanism in all CPVC samples is hopping type conduction. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

Dielectric relaxation and Poole–Frenkel conduction in poly(vinyl chloride) blends with bisphenol A/Egyptian corncob resin

AbstractThe dielectric constant (ε′), dielectric loss index (ε″), direct‐current conductivity, and current–voltage (I–V) characteristics of pure poly(vinyl chloride) (PVC) and blends of PVC and bisphenol A/Egyptian corncobs (BCC) were investigated at different temperatures. The relaxation processes for PVC and its blends revealed that PVC and BCC had an incompatible phase. PVC blends with 5 wt % BCC exhibited a peculiar I–V behavior. Both ε′ and ε″ were used to study miscibility and phase behavior in blends of PVC. The activation energies of all PVC samples were calculated. At higher voltages, the conduction mechanism could be identified as the Poole–Frenkel type. In addition, the ionic groups of BCC could enhance the PVC conductivity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

The effect of silica surface modification on the dielectric properties of silica-filled epoxy compounds

Crystalline silica was modified by annealing at temperatures ranging up to 1000 °C and by treating with a silane coupling agent (γ-glycidoxypropylotrietoxysilane) at concentrations up to 1 wt.%. The silica was dispersed in a matrix of diglycidyl ether of bisphenol-A epoxy resin. The dielectric properties of the composite samples were measured in the frequency range from 0.6–300 kHz. The results reveal that the dielectric loss index values of the samples are associated with water molecules adsorbed on the silica surface. An interpretation in terms of the cluster model of dielectric relaxation is provided. A relationship between the parameters pertaining to the silica modification and those describing the effects of the boiling water treatment on one hand and the dielectric loss index of the composites on the other has been determined.

Dielectric properties of halar, an alternating copolymer of ethylene and chlorotrifluoroethylene

AbstractDielectric properties of Halar, a predominantly alternating 1 : 1 copolymer of ethylene (E) and chlorotrifluoroethylene (CTFE), have been obtained as a function of temperature (−100 to +175°C), frequency (102–106 Hz), and thermal history. The dielectric loss index (ε″), related to heat dissipation in electrical applications, shows no major change between 25 and 175°C. However, a significant increase in (ε″) between +25°C and −100°C is not considered detrimental for the applications. Activation energies (δE) for the three major relaxations (α‐, β‐, and γ‐) in both mechanical and dielectric experiments are similar, thus suggesting a similar phase origin of the molecular relaxations in the two techniques. In dielectric analysis, the lowest temperature γ‐relaxation is the strongest while it is the weakest in mechanical technique. It is proposed that, in dielectric experiments, only the CTFE groups participate and due to restricted mobility at low temperatures (i.e., γ‐relaxation), the dissipation factor or relaxation strength is maximum.

Dielectric properties of semicrystalline polychlorotrifluoroethylene

The dielectric properties of polychlorotrifluoroethylene (Tm = 224 °C, Tg=52 °C) have been measured at temperatures between —50 and +250 °C, and at frequencies between 0.1 c/s and 8.6 kMc/s. Specimens of known crystallinities, ranging from %=0.80 to x=0.00 (pure liquid) were studied. Comprehensive tables of data are presented. The experimental techniques employed to measure the dielectric properties over these wide ranges of temperature, frequency, physical state, and sample type (disks, cylinders, and thin films), are discussed. The operation and calibration of the specimen holder, bridges, resonant circuits, and waveguide apparatus used are discussed in detail. When the dielectric loss index, e, at 1 c/s is plotted as a function of temperature for a highly crystalline specimen (%=0.80), where the crystallinity consists largely of lamellar spherulites, three distinct loss peaks are readily apparent. These peaks occur at about — 40 °C (low-temperature process), 95 °C (intermediate-temperature process), and 150 °C (high-temperature process). The dielectric data are compared with the mechanical loss data obtained at 1 c/s by McCrum. Mechanical loss peaks at temperatures virtually identical to those in the e versus Tplot are found. The high-temperature process is attributed to the presence of well-formed chain-folded lamellar spherulites. Some evidence points to the surfaces of the lamellae as the site of the loss^mechanism. The high-temperature loss peak does not appear in resolved form in nonspherulitic specimens even when the crystallinity is high. The intermediate-temperature process originates in the normal supercooled amorphous phase, and is due to the complex dipole relaxation effects involving motions of large numbers of polymer chain segments that are associated with the onset of the glass transition at Tg=52 °C. As determined by V— T data, the glass transition temperature at Tg=52 °C that is associated with this relaxation effect does not shift appreciably with increasing crystallinity. The low-temperature dielectric loss process, which is active far below Tg, originates principally in the supercooled amorphous regions, and evidently corresponds to a fairly simple motion involving a small number of chain segments. This process tends to exhibit anomalous behavior in highly crystalline specimens, particularly at low temperatures. A large dipolar contribution of the crystals to the static dielectric constant was observed. This contribution increased with increasing temperature, and corresponded to a very rapid dipole reorientation process ( T ^ I O 1 1 sec at 23 °C).