In the current study, the evolution of the composition of fly ash (FA), since the beginning of op... more In the current study, the evolution of the composition of fly ash (FA), since the beginning of operation of the lignite-fired power station of Amynteon-Filotas [Steam Electric Station (SES) Amynteon-Filotas] in Greece, is presented. The respective evolution of the feedcoal-composition is also showed. This power station began to operate in 1987. Before that, it was predicted that lignite fly ash would turn from strongly calcareous to barely pozzolanic. Moreover, the variation of sulphur (%) (both total and volatile) in feedcoal had revealed that fly ash would not often meat the specifications to be used in the production process of concrete, due to the excessive percentage presence of SO3. These predictions were eventually confirmed in the 23 years of operation of the power station. During these years SO3 (%) kept alternating, rendering—in some cases—fly ash suitable for use in cement industry applications. The periodical changes of the SO3 concentration in fly ash were attributed to...
In this study, highly calcareous and siliceous fly ash particles were utilized for the fabricatio... more In this study, highly calcareous and siliceous fly ash particles were utilized for the fabrication of Al- and Al-alloy-based Metal-Matrix Composites (MMCs) by means of powder metallurgy. After compacting and sintering Al and Al/Si powders containing 10, 15, and 20wt. % ash particles, the homogenous (and with minimal amount of voids) microstructure of the produced composites was verified by means of Scanning Electron Microscopy (SEM). The composites were tested for their dry sliding wear behavior using a pin-on-disc machine against spheres of alumina. The worn surfaces of composites were then examined by using SEM and Energy Dispersive X-Ray Spectroscopy (EDS). It was shown that the addition of both types of FA enhanced the tribo-performance of Al, with the optimum metal powder replacement determined to the point of 15% wt., in the case of high-Si and 10% wt., in the case of high-Ca ash particles. Regarding alloy-matrix composites, although they generally presented worse tribological...
IEEE International Digest of Technical Papers on Magnetics Conference, 2002
ABSTRACT Summary form only given. We describe how a ferromagnetic metal employed as a conventiona... more ABSTRACT Summary form only given. We describe how a ferromagnetic metal employed as a conventional Schottky barrier contact provides a practical and robust means of injecting spin-polarized carriers into a semiconductor device heterostructure, with spin injection efficiencies of 30 % extending to room temperature. The Schottky barrier formed at the Fe/AlGaAs interface provides a natural tunnel barrier for injection of spin polarized electrons under reverse bias. These carriers radiatively recombine in an AlGaAs/GaAs quantum well, emitting circularly polarized light, and the quantum selection rules which relate the optical and carrier spin polarizations provide a quantitative, model-independent measure of spin injection efficiency. Electroluminescence spectra from an Fe/AlGaAs/GaAs spin-LED exhibit significant circular polarization. The temperature dependence of the optical polarization and corresponding spin injection efficiency are determined. These results demonstrate that spin injecting contacts can be formed using a widely employed contact methodology, providing a ready pathway for the integration for spin transport into semiconductor processing technology.
Digest of INTERMAG 2003. International Magnetics Conference (Cat. No.03CH37401), 2003
Electrical spin injection and band offsets in an n-type ferromagnetic semiconductor heterostructu... more Electrical spin injection and band offsets in an n-type ferromagnetic semiconductor heterostructure of CdCr2Se4-AlGaAs-GaAs are studied. Epitaxially grown CdCr2Se4 films exhibit hysteresis behavior with significant remanence, an in- plane easy axis with a coercive field of 125 Oe. The cross section of the LED and the band alignment were shown.
The energy balance of Greece is strongly dependent on imported oil. The rather late introduction ... more The energy balance of Greece is strongly dependent on imported oil. The rather late introduction of natural gas has increased the diversity of the energy mixture with the share of renewable sources still low and the need to increase according to the existing potential. Yet, Greece as the most of the EU countries encounters a serious task: the need to
A scalable method for controlled synthesis of luminescent compound semiconductor nanocrystals (qu... more A scalable method for controlled synthesis of luminescent compound semiconductor nanocrystals (quantum dots) using microemulsion-gas contacting at room temperature is reported. The technique exploits the dispersed phase of a microemulsion to form numerous identical nanoreactors. ZnSe quantum dots were synthesized by reacting hydrogen selenide gas with diethylzinc dissolved in the heptane nanodroplets of a microemulsion formed by self-assembly of a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) amphiphilic block copolymer in formamide. A single nanocrystal is grown in each nanodroplet, thus allowing good control of particle size by manipulation of the initial diethylzinc concentration in the heptane. The ZnSe nanocrystals exhibit size-dependent luminescence and excellent photostability.
In the current study, the evolution of the composition of fly ash (FA), since the beginning of op... more In the current study, the evolution of the composition of fly ash (FA), since the beginning of operation of the lignite-fired power station of Amynteon-Filotas [Steam Electric Station (SES) Amynteon-Filotas] in Greece, is presented. The respective evolution of the feedcoal-composition is also showed. This power station began to operate in 1987. Before that, it was predicted that lignite fly ash would turn from strongly calcareous to barely pozzolanic. Moreover, the variation of sulphur (%) (both total and volatile) in feedcoal had revealed that fly ash would not often meat the specifications to be used in the production process of concrete, due to the excessive percentage presence of SO3. These predictions were eventually confirmed in the 23 years of operation of the power station. During these years SO3 (%) kept alternating, rendering—in some cases—fly ash suitable for use in cement industry applications. The periodical changes of the SO3 concentration in fly ash were attributed to...
In this study, highly calcareous and siliceous fly ash particles were utilized for the fabricatio... more In this study, highly calcareous and siliceous fly ash particles were utilized for the fabrication of Al- and Al-alloy-based Metal-Matrix Composites (MMCs) by means of powder metallurgy. After compacting and sintering Al and Al/Si powders containing 10, 15, and 20wt. % ash particles, the homogenous (and with minimal amount of voids) microstructure of the produced composites was verified by means of Scanning Electron Microscopy (SEM). The composites were tested for their dry sliding wear behavior using a pin-on-disc machine against spheres of alumina. The worn surfaces of composites were then examined by using SEM and Energy Dispersive X-Ray Spectroscopy (EDS). It was shown that the addition of both types of FA enhanced the tribo-performance of Al, with the optimum metal powder replacement determined to the point of 15% wt., in the case of high-Si and 10% wt., in the case of high-Ca ash particles. Regarding alloy-matrix composites, although they generally presented worse tribological...
IEEE International Digest of Technical Papers on Magnetics Conference, 2002
ABSTRACT Summary form only given. We describe how a ferromagnetic metal employed as a conventiona... more ABSTRACT Summary form only given. We describe how a ferromagnetic metal employed as a conventional Schottky barrier contact provides a practical and robust means of injecting spin-polarized carriers into a semiconductor device heterostructure, with spin injection efficiencies of 30 % extending to room temperature. The Schottky barrier formed at the Fe/AlGaAs interface provides a natural tunnel barrier for injection of spin polarized electrons under reverse bias. These carriers radiatively recombine in an AlGaAs/GaAs quantum well, emitting circularly polarized light, and the quantum selection rules which relate the optical and carrier spin polarizations provide a quantitative, model-independent measure of spin injection efficiency. Electroluminescence spectra from an Fe/AlGaAs/GaAs spin-LED exhibit significant circular polarization. The temperature dependence of the optical polarization and corresponding spin injection efficiency are determined. These results demonstrate that spin injecting contacts can be formed using a widely employed contact methodology, providing a ready pathway for the integration for spin transport into semiconductor processing technology.
Digest of INTERMAG 2003. International Magnetics Conference (Cat. No.03CH37401), 2003
Electrical spin injection and band offsets in an n-type ferromagnetic semiconductor heterostructu... more Electrical spin injection and band offsets in an n-type ferromagnetic semiconductor heterostructure of CdCr2Se4-AlGaAs-GaAs are studied. Epitaxially grown CdCr2Se4 films exhibit hysteresis behavior with significant remanence, an in- plane easy axis with a coercive field of 125 Oe. The cross section of the LED and the band alignment were shown.
The energy balance of Greece is strongly dependent on imported oil. The rather late introduction ... more The energy balance of Greece is strongly dependent on imported oil. The rather late introduction of natural gas has increased the diversity of the energy mixture with the share of renewable sources still low and the need to increase according to the existing potential. Yet, Greece as the most of the EU countries encounters a serious task: the need to
A scalable method for controlled synthesis of luminescent compound semiconductor nanocrystals (qu... more A scalable method for controlled synthesis of luminescent compound semiconductor nanocrystals (quantum dots) using microemulsion-gas contacting at room temperature is reported. The technique exploits the dispersed phase of a microemulsion to form numerous identical nanoreactors. ZnSe quantum dots were synthesized by reacting hydrogen selenide gas with diethylzinc dissolved in the heptane nanodroplets of a microemulsion formed by self-assembly of a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) amphiphilic block copolymer in formamide. A single nanocrystal is grown in each nanodroplet, thus allowing good control of particle size by manipulation of the initial diethylzinc concentration in the heptane. The ZnSe nanocrystals exhibit size-dependent luminescence and excellent photostability.
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Papers by Grigorios Itskos