Publications

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Conference Paper
ER, N., D. CJ, L. MC, I. R, I. P, and M. - M. JN, "Charge Carriers Injection/Extraction at the Metal-Polymer Interface and Its Influence in the Capacitive Microelectromechanical Systems-Switches Actuation Voltage", JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, vol. 10: Univ Nova Lisboa, pp. 2503-2511, Jan, 2010. Abstract
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ER, N., N. RM, D. CJ, L. MC, I. P, and M. - M. JN, Electrical Method to Study the Weak Molecular Movements at Nanometric Scale in Low Mobility Materials, , vol. 636-637, pp. 430-436, Jan, 2010. Abstract
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MC, L., P. S, N. ER, G. L, S. PC, and M. - M. S. J, "Electrical Properties Studies of a Cork/TetraPak (R)/Paraffin Wax Composite", Advanced Materials Forum Iv, vol. 587-588, no. 587-588, pp. 613-617, Jan, 2008. Abstract
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A., P., L. A. N. Ç. A. M.C., B. J.P., N. E. A. G. U. E.R., D. I. A. S. C.J., Marat-Mendes, and J.N., Influence of Polarization on the Bioactivity of Nanopowders of Hydroxyapatite, , pp. 55-56, Jan, 2011. Abstract
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A., P., L. A. N. Ç. A. M.C., B. J.P., N. E. A. G. U. E.R., D. I. A. S. C.J., Marat-Mendes, and J.N., "Influence of Polarization on the Bioactivity of Nanopowders of Hydroxyapatite", 14th International Symposium on Electrets, 2011. Abstract
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ER, N., D. CJ, L. MC, I. R, and M. - M. JN, Medium Electric Field Electron Injection/Extraction at Metal-Dielectric Interface, , no. 636-637, pp. 437-443, Jan, 2010. Abstract
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ER, N., D. CJ, L. MC, I. R, and M. - M. JN, Medium Electric Field Electron Injection/Extraction at Metal-Dielectric Interface, , vol. 636-637, pp. 437-443, Jan, 2010. Abstract
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RM, N., N. ER, L. MC, and M. - M. JN, "New Experimental Facts Concerning the Thermally Stimulated Discharge Current in Dielectric Materials", Advanced Materials Forum Iv, vol. 587-588, no. 587-588, pp. 328-332, Jan, 2008. Abstract
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ER, N., D. CJ, L. MC, I. R, I. P, and M. - M. JN, On the width of the thermally stimulated discharge current peak, , Jan, 2010. Abstract
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MC, L., N. ER, D. LA, and M. - M. S. J, "Space charge studies in XLPE from power cables using combined isothermal and thermostimulated current measurements", Advanced Materials Forum Iii, Pts 1 and 2, vol. 514-516, no. 514-516, pp. 935-939, Jan, 2006. Abstract
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MC, L., N. ER, and M. - M. JN, "Space charge studies of aged XLPE using combined isothermal and thermostimulated current measurements", Cross-Disciplinary Applied Research in Materials Science and Technology, vol. 480-481, no. 480, pp. 501-505, Jan, 2005. Abstract
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MC, L., N. ER, S. P, G. L, and M. - M. S. J, "Study of electrical properties of natural cork and two derivative products", Advanced Materials Forum Iii, Pts 1 and 2, vol. 514-516, no. 514-516, pp. 940-944, Jan, 2006. Abstract
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Journal Article
MC, L., N. ER, and M. - M. JN, "Combined isothermal and non-isothermal current measurements applied to space charge studies in low-density polyethylene", Journal of Physics D-Applied Physics, vol. 35, pp. L29-L32, Jan, 2002. Abstract
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ER, N., N. RM, D. CJ, L. MC, and M. - M. JN, "The determination of the metal-dielectric interface barrier height from the open-circuit isothermal charging current", Journal of Applied Physics, vol. 104, Jan, 2008. AbstractWebsite
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M.C., L. A. N. Ç. A., N. E. A. G. U. E.R., D. I. A. S. C.J., G. I. L. L., and M. A. R. A. T. - M. E. N. D. E. S. J.N., Electrical properties of cork and derivatives, , vol. 23, pp. 64-70, Jan, 2011. Abstract
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M.C., L. A. N. Ç. A., N. E. A. G. U. E.R., D. I. A. S. C.J., G. I. L. L., and M. A. R. A. T. - M. E. N. D. E. S. J.N., Electrical properties of cork and derivatives, , vol. 23, issue 3/4, 2011. Abstract
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MC, L., W. W, N. ER, G. R, and M. - M. S. J, "Influence of humidity on the electrical charging properties of cork agglomerates", Journal of Non-Crystalline Solids, vol. 353, pp. 4501-4505, Jan, 2007. AbstractWebsite
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MC, L., W. W, N. ER, G. R, and M. - M. S. J, "Influence of humidity on the electrical charging properties of cork agglomerates", Journal of Non-Crystalline Solids, vol. 353, issue 47-51, 2007. AbstractWebsite

Cork is a natural cellular and electrically insulating material which may have the capacity to store electric charges on or in its cell walls. Since natural cork has many voids, it is difficult to obtain uniform samples with the required dimensions. Therefore, a more uniform material, namely commercial cork agglomerate, usually used for floor and wall coverings, is employed in the present study. Since we know from our previous work that the electrical properties of cork are drastically affected by absorbed and adsorbed water, samples were protected by means of different polymer coatings (applied by spin-coating or soaking). Corona charging and isothermal charging and discharging currents were used to study the electrical trapping and detrapping capabilities of the samples. A comparison of the results leads to the conclusion that the most promising method for storing electric charges in this cellular material consists of drying and coating or soaking with a hydrophobic, electrically insulating polymer such as polytetraflouroethylene (Teflon (R)).

MC, L., F. M, N. E, D. LA, M. - M. S. J, T. A, and Z. S, "Space charge analysis of electrothermally aged XLPE cable insulation", Journal of Non-Crystalline Solids, vol. 353, pp. 4462-4466, Jan, 2007. AbstractWebsite
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MC, L., F. M, N. E, D. LA, M. - M. S. J, T. A, and Z. S, "Space charge analysis of electrothermally aged XLPE cable insulation", Journal of Non-Crystalline Solids, vol. 353, issue 47-51, 2007. AbstractWebsite

Cross-linked polyethylene (XLPE) is currently widely used as an insulating material for power cables due to its good physical properties, however when in use it undergoes an electrical ageing process. Its ability to trap electric charge can give rise to space charge accumulation in the bulk of the polymer and produce localised electric stresses that can lead to cable failure, since the electric field will be increased above the design stress in some regions favouring the initiation of degradation there. In this work the PEA (pulsed electro-acoustic) method was used to compare the charge dynamics in three samples (XLPE cable peelings) aged in different ways (electrothermally in the laboratory, field aged in service and thermally aged in the laboratory). Very different transient behavior was found depending upon the ageing history. This is related to differences in the migration of chemical species in the insulation layer, which are known to act as charge traps. All materials showed heterocharge peaks when the space charge reached stability, the magnitude of which seems to be related to the severity of the ageing.

MC, L., N. ER, N. RM, D. CJ, M. - M. JN, and D. - G. DK, "Space charge studies in LDPE using combined isothermal and non-isothermal current measurements", IEEE TRANSACTIONS ON DIELECTRICS AND ELECTRICAL INSULATION, vol. 11: Univ Wales, Univ Nova Lisboa, pp. 25-34, Jan, 2004. Abstract
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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. Abstract
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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. Abstract

During 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.

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. Abstract
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