Athanasios Kanapitsas | UNIVERSITY OF THESSALY, GREECE (original) (raw)
Papers by Athanasios Kanapitsas
Journal of Physics and Chemistry of Solids
Abstract Nanocomposites of poly (vinylidene fluoride), PVDF, and magnetite (Fe3O4) nanoparticles ... more Abstract Nanocomposites of poly (vinylidene fluoride), PVDF, and magnetite (Fe3O4) nanoparticles were prepared using the twin screw compounding method and the effect of filler concentration (5–15 wt%) on the thermal stability, dielectric properties and dielectric strength were investigated. It was observed that the dynamic characteristics of crystalline αc-relaxation peak remain almost constant for the composites studied; while the activation energy plots almost coincide indicating that the time scale of this relaxation process is independent of the Fe3O4 filler loading. Ferrite particles alter Maxwell-Wagner-Sillars (MWS) mechanism behaviour. In the isochronal diagrams of electric modulus dielectric function, at the lower ferrite concentration 5 wt% and the lowest frequency 0.1 Hz, two contributions to MWS process were clearly detected. For ferrite concentrations higher than 5 wt%, it seems that the contribution of amorphous-crystalline interfaces to the MWS relaxation drastically decreases and their effect is the broadening of the MWS peak at higher temperatures, while the effect of Fe3O4-PVDF matrix interfaces dominate in the formation of MWS relaxation. Herein, the nanocomposites dielectric strength performance was investigated by means of switching impulse high voltage stressing and AC (50 Hz) high voltage; from the results the nanocomposites demonstrated high levels of dielectrics strength accompanied with stable performance.
Procedia Structural Integrity, 2018
2008 26th International Conference on Microelectronics, 2008
In this paper test techniques for RFICs are presented. A Built-In Test (BIT) circuit is applied f... more In this paper test techniques for RFICs are presented. A Built-In Test (BIT) circuit is applied for a 1.9-GHz double balanced Gilbert-cell CMOS active mixer. The BIT circuit operation is based on the observation that the presence of catastrophic faults, like resistive bridgings, shorts and opens, or parametric faults, result in the attenuation of the output voltage amplitude (gain reduction). The BIT circuit along with an active down-conversion mixer have been designed in a 90 nm UMC CMOS technology to evaluate the efficiency of the proposed approach and experimental results are presented.
Science of Advanced Materials, 2015
ABSTRACT The dielectric and thermal response of epoxy resin (ER) based nanocomposites filled with... more ABSTRACT The dielectric and thermal response of epoxy resin (ER) based nanocomposites filled with semi-conductive zinc–oxide (ZnO) nanoparticles, were studied in the present work. Dielectric Relaxation Spectroscopy (DRS) technique was used, in the frequency range of 0.1 Hz – 10 MHz and temperature range of 30–160 °C, for the investigation of the effect of ZnO nanoparticles on the dynamics of the molecular mobility of ER/ZnO system. On the other hand Differential Scanning Calorimetry (DSC) and Thermogravimetric/Differential Thermal Analysis (TGA/DTA) techniques have been used in order to examine the effect of ZnO nanoinclusions upon the molecular mobility, in relation to the thermal stability of the studied system. Four distinct relaxation mechanisms have been recorded in the spectra of all the systems under study. They were attributed to conductivity relaxation, interfacial polarization (IP), glass to rubber transition of the polymer matrix (α-relaxation) and re-orientation of polar side groups of the main polymer chain (β-relaxation). Dielectric and thermal response could be interpreted by the simultaneous action of two opposite effects: (a) the addition of ZnO nanoparticles leads to a decreasing of the cross-linking density of the epoxy matrix which has as a result an increase of the fractional free volume and of the corresponding molecular mobility, and (b) the strong interactions between filler and epoxy matrix results to a reduction of the mobility of a fraction of the polymer chains at the interfaces of the constituents.
10th International Symposium on Electrets (ISE 10). Proceedings (Cat. No.99 CH36256), 1999
ABSTRACT The low temperature relaxation mechanisms of epoxy networks and blends were investigated... more ABSTRACT The low temperature relaxation mechanisms of epoxy networks and blends were investigated by thermally stimulated discharge current (TSDG) techniques in the temperature range of 77 to 300 K. Two series of specimens, based on DGEBA cured with either TETA or DDM, were prepared. Specimens in the first series were mixed with different amounts of plasticizer thiocol. The influence of the absorbed water on the low temperature relaxations, and its plasticizing capability were studied, both affected by the presence of plasticizer and water in the specimens. In the second series, blends of CTBN with epoxy resin ER were prepared. Four dispersions are observed and ascribed to the CTBN phase, the ER phase and their interfaces
Spectroscopy of Biological Molecules: Modern Trends, 1997
Abstract The preparation of epoxy nanocomposites is very complex procedure. The effect of process... more Abstract The preparation of epoxy nanocomposites is very complex procedure. The effect of processing conditions and of each parameter involved , such as different types of filler, different types of curing agent, and processing conditions (temperature, time, speed), on dispersion and consequently on the physicochemical properties of the nanoparticles is complex one [ ]. In this work, we have prepared epoxy resin (ER) composites filled with fly ash (FA). The fly ash was produced at the power stations of Kozanis region in northern Greece and it is rich in CaO due to the origin of the burned lignite. The dynamic mechanical properties (storage (E΄) and loss (E΄΄) moduli and glass transition (Tg)) of composites were assessed by dynamic mechanical analysis (DMA). Scanning electron microscopy (SEM) was used to observe the fractured surfaces of the composites and clarify the dispersion and deaggregation of fly ash particulates in the matrix, whereas μ-Raman spectroscopy and FT-IR microscopy...
Journal of Physics and Chemistry of Solids
Abstract Nanocomposites of poly (vinylidene fluoride), PVDF, and magnetite (Fe3O4) nanoparticles ... more Abstract Nanocomposites of poly (vinylidene fluoride), PVDF, and magnetite (Fe3O4) nanoparticles were prepared using the twin screw compounding method and the effect of filler concentration (5–15 wt%) on the thermal stability, dielectric properties and dielectric strength were investigated. It was observed that the dynamic characteristics of crystalline αc-relaxation peak remain almost constant for the composites studied; while the activation energy plots almost coincide indicating that the time scale of this relaxation process is independent of the Fe3O4 filler loading. Ferrite particles alter Maxwell-Wagner-Sillars (MWS) mechanism behaviour. In the isochronal diagrams of electric modulus dielectric function, at the lower ferrite concentration 5 wt% and the lowest frequency 0.1 Hz, two contributions to MWS process were clearly detected. For ferrite concentrations higher than 5 wt%, it seems that the contribution of amorphous-crystalline interfaces to the MWS relaxation drastically decreases and their effect is the broadening of the MWS peak at higher temperatures, while the effect of Fe3O4-PVDF matrix interfaces dominate in the formation of MWS relaxation. Herein, the nanocomposites dielectric strength performance was investigated by means of switching impulse high voltage stressing and AC (50 Hz) high voltage; from the results the nanocomposites demonstrated high levels of dielectrics strength accompanied with stable performance.
Procedia Structural Integrity, 2018
2008 26th International Conference on Microelectronics, 2008
In this paper test techniques for RFICs are presented. A Built-In Test (BIT) circuit is applied f... more In this paper test techniques for RFICs are presented. A Built-In Test (BIT) circuit is applied for a 1.9-GHz double balanced Gilbert-cell CMOS active mixer. The BIT circuit operation is based on the observation that the presence of catastrophic faults, like resistive bridgings, shorts and opens, or parametric faults, result in the attenuation of the output voltage amplitude (gain reduction). The BIT circuit along with an active down-conversion mixer have been designed in a 90 nm UMC CMOS technology to evaluate the efficiency of the proposed approach and experimental results are presented.
Science of Advanced Materials, 2015
ABSTRACT The dielectric and thermal response of epoxy resin (ER) based nanocomposites filled with... more ABSTRACT The dielectric and thermal response of epoxy resin (ER) based nanocomposites filled with semi-conductive zinc–oxide (ZnO) nanoparticles, were studied in the present work. Dielectric Relaxation Spectroscopy (DRS) technique was used, in the frequency range of 0.1 Hz – 10 MHz and temperature range of 30–160 °C, for the investigation of the effect of ZnO nanoparticles on the dynamics of the molecular mobility of ER/ZnO system. On the other hand Differential Scanning Calorimetry (DSC) and Thermogravimetric/Differential Thermal Analysis (TGA/DTA) techniques have been used in order to examine the effect of ZnO nanoinclusions upon the molecular mobility, in relation to the thermal stability of the studied system. Four distinct relaxation mechanisms have been recorded in the spectra of all the systems under study. They were attributed to conductivity relaxation, interfacial polarization (IP), glass to rubber transition of the polymer matrix (α-relaxation) and re-orientation of polar side groups of the main polymer chain (β-relaxation). Dielectric and thermal response could be interpreted by the simultaneous action of two opposite effects: (a) the addition of ZnO nanoparticles leads to a decreasing of the cross-linking density of the epoxy matrix which has as a result an increase of the fractional free volume and of the corresponding molecular mobility, and (b) the strong interactions between filler and epoxy matrix results to a reduction of the mobility of a fraction of the polymer chains at the interfaces of the constituents.
10th International Symposium on Electrets (ISE 10). Proceedings (Cat. No.99 CH36256), 1999
ABSTRACT The low temperature relaxation mechanisms of epoxy networks and blends were investigated... more ABSTRACT The low temperature relaxation mechanisms of epoxy networks and blends were investigated by thermally stimulated discharge current (TSDG) techniques in the temperature range of 77 to 300 K. Two series of specimens, based on DGEBA cured with either TETA or DDM, were prepared. Specimens in the first series were mixed with different amounts of plasticizer thiocol. The influence of the absorbed water on the low temperature relaxations, and its plasticizing capability were studied, both affected by the presence of plasticizer and water in the specimens. In the second series, blends of CTBN with epoxy resin ER were prepared. Four dispersions are observed and ascribed to the CTBN phase, the ER phase and their interfaces
Spectroscopy of Biological Molecules: Modern Trends, 1997
Abstract The preparation of epoxy nanocomposites is very complex procedure. The effect of process... more Abstract The preparation of epoxy nanocomposites is very complex procedure. The effect of processing conditions and of each parameter involved , such as different types of filler, different types of curing agent, and processing conditions (temperature, time, speed), on dispersion and consequently on the physicochemical properties of the nanoparticles is complex one [ ]. In this work, we have prepared epoxy resin (ER) composites filled with fly ash (FA). The fly ash was produced at the power stations of Kozanis region in northern Greece and it is rich in CaO due to the origin of the burned lignite. The dynamic mechanical properties (storage (E΄) and loss (E΄΄) moduli and glass transition (Tg)) of composites were assessed by dynamic mechanical analysis (DMA). Scanning electron microscopy (SEM) was used to observe the fractured surfaces of the composites and clarify the dispersion and deaggregation of fly ash particulates in the matrix, whereas μ-Raman spectroscopy and FT-IR microscopy...