experimentally explored by Sun et al. who studied the influence of the interface on the dielectricproperties of epoxy/silica composites [ 7 ].
A dielectric material has an arrangement of electric charge carriers that can be displaced by an electric field
Authors:H. W. Starkweather, P. Avakian, J. J. Fontanella, and Mary C. Wintersgill
Dielectric measurements have been made at frequencies from 10 Hz to 100 kHz and temperatures from 4 K to at least 300 K on a number of polymers containing units of hexafluoropropylene (HFP). These included copolymers of tetrafluoroethylene (TFE) and HFP, the homopolymer of HFP, elastomeric copolymers of HFP and vinylidene fluoride, and alternating copolymers of methyl vinyl ether with TFE and HFP. The effect of an ether linkage between the CF3 group and the chain was also considered. Most of these polymers exhibited a main chain local mode relaxation near 228 K and a side group relaxation near 93 K.
Authors:Eszter Vozáry, Kinga Ignácz, and Bíborka Gillay
-dependent dielectricproperties of honey associated with dielectric heating . Journal of Food Engineering , 102 : 209 – 216 . 10.1016/j.jfoodeng.2010.08.016 Guo , W. , Zhu , X. , Liu , Y. , and Zhuang , H. ( 2010 ). Sugar and water contents of honey with
Authors:G. Parkes, P. Barnes, E. Charsley, and G. Bond
This paper describes a new instrument for performing thermal analysis using microwaves both as a form of heating and as a
novel means of detecting thermally induced transformations in materials. Results are presented for a selection of processes
including decompositions, dehydrations and phase changes. The capability of the instrument to be coupled with ancillary techniques
such as EGA is also demonstrated.
Authors:J. Binner, G. Dimitrakis, D. Price, M. Reading, and B. Vaidhyanathan
of the β to α phase transition in silver iodide was investigated
by conventional and modulated temperature DSC and dielectric property measurements.
On cooling, the high temperature phase remained stable 2.5C below its
normal transition temperature even at a very slow cooling rate 0.2C h–1.
Dielectric property measurements under conventional and microwave heating
suggested an anomalous effect of the latter on the β to α phase
transition in this material.
Authors:Lisardo Núñez-Regueira, M. Villanueva, I. Fraga, C. A. Gracia-Fernández, and S. Gómez-Barreiro
The thermal degradation
of an epoxy system consisting of a diglycidyl ether of bisphenol A (DGEBA, n=0) and m-xylylenediamine (m-XDA)
was studied by both thermogravimetric analysis (TG) and dielectric analysis
(DEA). It has been checked a deviation of the typical behaviour in the Arrhenius
plot expected for this kind of systems, owing to the thermal degradation.
Both, structural relaxation time and conductivity values, were represented
as a function of the mass loss, that allow a relationship to be obtained between
characteristic relaxation time and the degree of degradation at the beginning
of the degradation process.
In the present manuscript, freshly prepared and also pure chemical grade (BDH) antimony trioxide specimens were investigated. Numerous measurements were carried out on these specimens, comprising chemical, spectral and X-ray analyses, pycnometric and X-ray density measurements and observations of the behaviour of the dielectric constant and dielectric loss factor (∈′ and ∈″) as functions of temperature and frequency. The results obtained gave values of 12.4 and 10 for the dielectric constant for the freshly prepared and commercial antimony trioxide specimens, respectively. The results were compared in correlation with the phase constitution and degree of compactness for both specimens. Finally, the data are discussed on the basis of the interactions of the field frequency and temperature with the electric dipoles and electronic polarization of the test specimens.
Authors:P. Bowen, M. Daglish, G. Frenzer, J. -F. Ricard, and Y. Wyser
Aluminate sodalite ceramics, (Sr8Al12O24)(CrO4)2) — SACR, have been prepared from solution spray-dried precursors. The spray drying of a mixed aqueous nitrate solution gave an anhydrous powder which was thermally decomposed in air at 1350 °C to give a crystalline SACR powder with a median volume diameter of 4–6 μm. The SACR powder was dry pressed and sintered to >90% density. The yellow SACR powder showed two phase transitions between 10 and 45 °C with a 25 ° intermediate phase region indicative of a low defect concentration in the crystalline structure. A colour change observed in the sintered ceramic (changing to a mixed green/yellow) and a narrowing of the phase transition region (15–40 °C) are discussed. Dielectric measurements were consistent with the presence of two extrinsic ferroelectric transitions at 17 and 35 °C.
Composites made from E-glass/epoxy or aramid/epoxy are frequently used in aircraft and aerospace industries. These materials are prone to suffer from the presence of delamination, which can reduce severely the performance of aircrafts and even threaten their safety. Since electric conductivity of these composites is rather small, they can propagate electromagnetic waves. Detection of delamination damage can then be monitored by using an electromagnetic penetrating radar scanner, which consists of emitting waves having the form of short time pulses that are centered on a given work frequency. While propagating, these waves undergo partial reflection when running into an obstacle or a material discontinuity. Habitually, the radar is moved at constant speed along a straight path and the reflected signal is processed as a radargram that gives the reflected energy as function of the two-way time and the antenna position.In this work, modeling of electromagnetic wave propagation in composites made from E-glass/epoxy was performed analytically. The electromagnetic wave reflection from a delamination defect was analyzed as function of key intervening factors which include the defect extent and depth, as well as the work frequency. Various simulations were performed and the obtained results have enabled to correlate the reflection pattern image features to the actual delamination defect characteristics which can provide quantification of delamination.