Lanca, M. C., E. R. Neagu, R. M. Neagu, C. J. Dias, J. N. Marat-Mendes, and D. K. Das-Gupta,
"Space charge studies in LDPE using combined isothermal and non-isothermal current measurements",
Ieee Transactions on Dielectrics and Electrical Insulation, vol. 11, no. 1, pp. 25-34, 2004.
AbstractUsing a recently developed procedure combining isothermal and non-isothermal current measurements space charge trapping and transport in LDPE was successfully studied. Unaged, thermally and electrically aged samples were investigated. The samples were conditioned before each measurement in order to obtain reproducible results. In the non-isothermal measurements appeared a broad peak (40degreesC to 50degreesC) that was possible to decompose into two or three peaks (35, 45 and 65degreesC). At even higher temperature another peak was sometimes present (85degreesC) depending on the prior sample conditioning. The space charge is trapped near the surface in deep traps (maximum depth of approximate to 15 mum). Relaxation times, mobilities and activation energies have been calculated for different charging/discharging conditions. For unaged samples the reproducibility of the results was poor while for the aged polyethylene it was quite good, meaning that aging helps conditioning. In the electrically aged LDPE there is a decrease of conductivity and the broad peak of the non-isothermal spectra shows a slight shift towards higher temperatures when compared with the data found in the thermally aged polymer.
Neagu, E. R., C. J. Dias, M. C. Lança, and J. N. Marat-Mendes,
The study of molecular movements in dielectrics using isothermal and non- isotehermal current measurements,
, vol. 183, pp. –-, Jan, 2009.
Abstractn/a
ER, N., D. CJ, L. MC, I. R, I. P, and M. - M. J. N.,
The use of the final thermally stimulated discharge current technique to study the molecular movements around glass transition,
, vol. 354, pp. 385-390, Jan, 2011.
Abstractn/a
ER, N., D. CJ, L. MC, I. R, I. P, and M. - M. J. N.,
The use of the final thermally stimulated discharge current technique to study the molecular movements around glass transition,
, vol. 354, issue 2, 2011.
AbstractDuring electric polarization charge is injected into the material. The structure is decorated with space charge and during the subsequent heating an apparent peak and the genuine peaks that are related to dipole randomization and charge detrapping are observed. The method is used here to analyze the molecular movements in polyimide in the temperature range from 293 to 623K. Two weak relaxations have been observed around 337K and around 402K. The electrical conductivity changes with temperature in agreement with the Arrhenius law only below (W=(0.84±0.03) eV ) and above ( W=(0.82±0.03) eV) the temperature range where the β relaxation is observed. The variation of the electrical conductivity with temperature, in the range of the β relaxation, is controlled by the variation of the charge currier mobility with temperature and it shows a non-Arrhenius behavior. We suggest that the β1 sub-glass relaxation is related to the rotation or oscillation of phenyl groups and the β2 sub-glass relaxation is related to the rotation or oscillation of the imidic ring. At higher temperatures an apparent peak was observed. The relaxation time of the trapped charge, at 573K, is high than 8895s.
Neagu, E. R., C. J. Dias, M. C. Lanca, R. Igreja, P. Inacio, and J. N. Marat-Mendes,
"The use of the final thermally stimulated discharge current technique to study the molecular movements around glass transition",
Journal of Non-Crystalline Solids, vol. 357, no. 2, pp. 385-390, 2011.
AbstractDuring electric polarization charge is injected into the material. The structure is decorated with space charge and during the subsequent heating an apparent peak and the genuine peaks that are related to dipole randomization and charge detrapping are observed. The method is used here to analyze the molecular movements in polyimide in the temperature range from 293 to 623 K. Two weak relaxations have been observed around 337 K and around 402 K. The electrical conductivity changes with temperature in agreement with the Arrhenius law only below (W= (0.84 +/- 0.03) eV) and above ( W (0.82 +/- 0.03) eV) the temperature range where the beta relaxation is observed. The variation of the electrical conductivity with temperature, in the range of the beta relaxation, is controlled by the variation of the charge currier mobility with temperature and it shows a non-Arrhenius behavior. We suggest that the beta(1) sub-glass relaxation is related to the rotation or oscillation of phenyl groups and the beta(2) sub-glass relaxation is related to the rotation or oscillation of the imidic ring. At higher temperatures an apparent peak was observed. The relaxation time of the trapped charge, at 573 K, is high than 8895 s. (C) 2010 Elsevier B.V. All rights reserved.
M.C., L., C. I., M. J. Paulo, G. I. L. L., N. E. A. G. U. E.R., D. I. A. S. C.J., and M. - M. J. N.,
Water Content Control to Improve Space Charge Storage in a Cork Derivative,
, vol. 730-732, pp. 395-400, 2012.
Abstractn/a