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Lanca, M. C., J. Domingues, and I. Franco, Study of fractal properties in Lichtenberg figures, , pp. 133-144, 1995. AbstractWebsite
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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. Abstract
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Neagu, E. R., C. J. Dias, M. C. Lanca, R. Igreja, P. Inacio, J. N. Marat-Mendes, and Ieee, "The Study of the Molecular Movements in the Range of Glass Transition by the Final Thermally Stimulated Discharge Current Technique", Proceedings of the 2010 Ieee International Conference on Solid Dielectrics (Icsd 2010), 2010. Abstract
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Neagu, E. R., C. J. Dias, M. C. Lanca, R. Igreja, P. Inacio, J. N. Marat-Mendes, and Ieee, "The Study of the Molecular Movements in the Range of Glass Transition by the Final Thermally Stimulated Discharge Current Technique", Proceedings of the 2010 Ieee International Conference on Solid Dielectrics, 2010. Abstract

The electrical methods used to study the molecular movements are based on the movement of the dipoles under DC or AC electric field. We have proposed recently a combined measuring protocol to analyze charge injection/extraction, transport, trapping and de-trapping in polar or non-polar dielectric materials. The method is used here to analyze the molecular movements in polyimide in the temperature range from 293 to 572 K. A strong relaxation was observed around 402 K and a very weak relaxation around 345 K. This is the beta relaxation which is quite complex. As concern the behavior at high temperatures, above the beta relaxation, a high peak was observed that shifts continuously to higher temperatures as the charging temperature and/or the charging field increase. The maximum current of the peak increases and the temperature corresponding to the maximum current increases as the charging temperature and/or the charging field increase, given a direct observation of the so called cross-over effect related to current decay for sample charged at high fields and/or high temperatures.

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Neagu, E. R., R. M. Neagu, M. C. Lanca, and J. N. Marat-Mendes, The time as a parameter to investigate the landscape of the apparent activation energies in the final thermally stimulated discharge current measurements, , pp. 292-295, 2005. AbstractWebsite

The experimental results obtained in a wide range of temperatures, for polyethylene terephthalate, demonstrate that the apparent activation energy changes when the charging (polarization) time or the isothermal discharging time, prior to the final thermally stimulated discharge current measurement, are used as variable parameters. Consequently, the charging and/or discharging time can be used as a variable parameter to investigate the landscape of the apparent thermal activation energies. A continuous distribution of the traps in the range from 0.4 to 3 eV was observed. The experimental results demonstrate that there is a range of experimental conditions for which the thermal activation energy is independent of the experimental parameter values. This is the activation energy value which should be used to characterize a certain mechanism.

Neagu, E. R., R. M. Neagu, M. C. Lanca, and J. N. Marat-Mendes, "The time as a parameter to investigate the landscape of the apparent activation energies in the final thermally stimulated discharge current measurements", 12th International Symposium on Electrets (ISE 12), Proceedings, pp. 292-295, 2005. AbstractWebsite

The experimental results obtained in a wide range of temperatures, for polyethylene terephthalate, demonstrate that the apparent activation energy changes when the charging (polarization) time or the isothermal discharging time, prior to the final thermally stimulated discharge current measurement, are used as variable parameters. Consequently, the charging and/or discharging time can be used as a variable parameter to investigate the landscape of the apparent thermal activation energies. A continuous distribution of the traps in the range from 0.4 to 3 eV was observed. The experimental results demonstrate that there is a range of experimental conditions for which the thermal activation energy is independent of the experimental parameter values. This is the activation energy value which should be used to characterize a certain mechanism.

Prezas, P. R., B. M. G. Melo, L. C. Costa, M. A. Valente, M. C. Lança, J. M. G. Ventura, L. F. V. Pinto, and M. P. F. Graça, "TSDC and impedance spectroscopy measurements on hydroxyapatite, β-tricalcium phosphate and hydroxyapatite/β-tricalcium phosphate biphasic bioceramics", Applied Surface Science, vol. 424, issue 1, pp. 28-38, 2017. Abstract

Bone grafting and surgical interventions related with orthopaedic disorders consist in a big business, generating large revenues worldwide every year. There is a need to replace the biomaterials that currently still dominate this market, i.e., autografts and allografts, due to their disadvantages, such as limited availability, need for additional surgeries and diseases transmission possibilities. The most promising replacement materials are biomaterials with bioactive properties, such as the calcium phosphate-based bioceramics group. The bioactivity of these materials, i.e., the rate at which they promote the growth and directly bond with the new host biological bone, can be enhanced through their electrical polarization.In the present work, the electrical polarization features of pure hydroxyapatite (Hap), pure β-tricalcium phosphate (β-TCP) and biphasic hydroxyapatite/β-tricalcium phosphate composites (HTCP) were analyzed by measuring thermally stimulated depolarization currents (TSDC). The samples were thermoelectrically polarized at 500. °C under a DC electric field with a magnitude of 5. kV/cm. The biphasic samples were also polarized under electric fields with different magnitudes: 2, 3, 4 and 5. kV/cm. Additionally, the depolarization processes detected in the TSDC measurements were correlated with dielectric relaxation processes observed in impedance spectroscopy (IS) measurements.The results indicate that the β-TCP crystalline phase has a considerable higher ability to store electrical charge compared with the Hap phase. This indicates that it has a suitable composition and structure for ionic conduction and establishment of a large electric charge density, providing great potential for orthopaedic applications.

Dias, I. J. G. J. G., A. S. S. Pádua, E. Pires, J. P. M. R. Borges, J. C. Silva, and M. C. Lança, "TSDC and surface potential measurements of charged hydroxyapatite/BaTiO 3 biocoatings deposited by CoBlast", ISE19-19th Int Symp on Electrets, 18-22 Sept., Linz, Austria, Johannes Kepler Univ., pp. 77, 2023. Abstract

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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. AbstractWebsite

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 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.

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Inês, C., M. J. Paulo, G. Luís, N. E. R., D. C. J., M. - M. J. N., and L. M. C., Water Content Control to Improve Space Charge Storage in a Cork Derivative, , pp. 395-400, Jan, 2012. Abstract
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Inês, C., M. J. Paulo, G. Luís, N. E. R., D. C. J., M. - M. J. N., and L. M. C., "Water Content Control to Improve Space Charge Storage in a Cork Derivative", Materiais2011, 2012. Abstract
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Lanca, M. C., I. Cunha, J. P. Marques, E. R. Neagu, L. Gil, C. J. Dias, and J. N. Marat-Mendes, "Water Content Control To Improve Space Charge Storage in a Cork Derivative", Advanced Materials Forum Vi, Pts 1 and 2, vol. 730-732, pp. 395-400, 2013. Abstract
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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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Gavinho, S. R., P. R. Prezas, D. J. Ramos, I. Sá‐Nogueira, J. P. Borges, C. M. Lança, J. C. Silva, C. M. R. Henriques, E. Pires, J. S. Kumar, and M. P. F. Graça, "{Nontoxic glasses: Preparation, structural, electrical and biological properties}", International Journal of Applied Ceramic Technology: John Wiley {&} Sons, Ltd (10.1111), pp. ijac.13243, apr, 2019. AbstractWebsite
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