Fly ash from two lignite-fed power stations in Greece (Megalopolis and Meliti) has been utilized ... more Fly ash from two lignite-fed power stations in Greece (Megalopolis and Meliti) has been utilized to synthesize zeolitic materials with upgraded adsorption capacity. Two different siliceous fly ash samples were subjected to hydrothermal treatment at fixed solid / liquid ratio and constant temperature. The zeolitic products have been characterized for their microstructure, chemical, and mineralogical composition by means of SEM, AAS, and XRD, respectively. The primary zeolitic crystals identified were phillipsite and thomsonite, in Megalopolis and Meliti fly ash, respectively. In light of their prospective utilization as liquid-phase sorbents, the specific surface area and porosity of materials were also determined, by means of N 2 -porosimetry. The zeolitic samples were tested for their actual heavy metal-removal capacity by water sampled from active lignite mines in Northern Greece. Artificial aquatic samples with known concentration of heavy metals (Cd, Cr, Cu, Ni, Pb, and Zn) were also tested, showing that the synthetic zeolitic materials are good to uptake a wide variety of potential pollutants with up to 100% efficiency. The efficiency of the synthetic zeolitic materials was comparatively assessed, showing that the more intense the presence of phillipsite in the synthetic materials, the greater the uptake rates for certain groups of trace elements.
Two different fly ash (FA) samples were tested for their ability to give synthetic zeolitic produ... more Two different fly ash (FA) samples were tested for their ability to give synthetic zeolitic products. Polish bituminous (PB) and South African (SA) coal fly ash (FA) samples, derived from pilot-scale circulated fluidized bed (CFB) combustion facilities, have been utilized as raw materials. The two FAs underwent a hydrothermal activation with 1M NaOH solution at 90°C for 24 h. Two different FA/NaOH solution/ratios (50, 100 g/L) were applied for each sample and the following zeolitic materials were formed: Na-Al-Si Zeolite A (Na), K-Al-Si Zeolite A (K), Erionite, ZSM-18, K-Ca-Al-Si-Hydrate Unnamed Zeolite, Erionite and Linde (L). The experimental products were characterized by means of X-Ray Diffraction (XRD) and Energy Dispersive X-Ray coupled-Scanning Electron Microscope (EDX/SEM), while X-Ray Fluorescence (XRF) was applied for the determination of their chemical composition. The zeolitic products were also evaluated in terms of their cation exchange capacity (CEC), specific surface area (SSA), specific gravity (SG), particle size distribution (PSD), pH and the range of their micro-and macroporosity. The current work focuses on testing the synthesized zeolitic materials for their potential of retaining heavy metals from industrial wastewater. Therefore, the aforementioned products were tested for their ability of adsorbing Cr, Pb, Ni, Cu, Cd and Zn from contaminated liquids, by the use of instrumental analytical methodologies. It must be noticed that the main goal is the treatment of liquid waste with such by-products and the capability of the zeolitic material to inhibit the leaching of the metals. Main parameters, as it is concluded from the experimental results, are the mineralogical composition of the initial fly ashes, as well as the type and the amount of the produced zeolite and specifically the mechanism by which the metals ions are hold on the substrate.
In the present paper eight types of A356 Al-fly ash composites were synthesized using pressure in... more In the present paper eight types of A356 Al-fly ash composites were synthesized using pressure infiltration technique, by utilizing Class C fly ash (FA). Actually, such a strongly calcareous FA was for the first time used in MMCs-manufacturing by liquid metal infiltration techniques. After testing their mineralogy and chemistry, certain FA size-fractions were used for the fabrication of the composites and their particular properties were linked to the level of the successful synthesis of the materials, the development of their microstructure and their wear strengths. The effect of using ground FA particles on the structure of composites and their tribological performance was also investigated through this study. It was concluded that using fine FA particles can strongly advantage the properties of composites and that grinding of fly ash facilitates MMCs-manufacturing by pressure infiltration and it also advantages their wear properties.
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.
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 performance than pure Al/Si products, the additions of ashes up to 15% wt. resulted in only slight deterioration of the wear performance of composites.
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.
Archives of Industrial Hygiene and Toxicology, 2014
Wood fly ash is an industrial by-product of the combustion of different wood materials and is mos... more Wood fly ash is an industrial by-product of the combustion of different wood materials and is mostly disposed of as waste on landfills. In our preliminary experiments, wood ash exhibited antibacterial activity against urban wastewater bacteria and we focused on wood fly ash as a potential substrate for wastewater disinfection. The addition of ash at a concentration of 10 g L -1 (1 %) caused an instant increase of pH in urban wastewater and landfill leachate. High pH (10.1-12.7) inactivated bacterial populations in the wastewater and the removal of faecal coliforms and intestinal enterococci after 6 h of contact was 100 % (below the detection limit; <1 CFU per mL) with the most efficient ash sample (ash from combustion of beech) both in urban wastewater and landfill leachate. Properly chosen wood fly ash, i.e. one that tends to increase the pH to the greatest extent, proved to be a very effective disinfection substrate. Considering that water treated with wood ash has a high pH and needs to be neutralised before discharge, ash would be suitable for disinfection of leachates when smaller volumes are treated.
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
In this study, a fixed-bed downdraft gasifier (70 kW e -245 kW th ) with gas cooling and cleaning... more In this study, a fixed-bed downdraft gasifier (70 kW e -245 kW th ) with gas cooling and cleaning system, combined with a gas engine, was tested using olive kernel as fuel. The primary scope of this paper is to identify the most prominent utilization paths for the solid residues of the process. After a 3-day experimental work and the respective sampling campaigns, a thorough characterization study was conducted: the mineralogy of collected residues was examined by means of XRD, Loss on Ignition tests were carried out by the use of TGA up to 850°C, their morphology was examined by means of EDS-SEM, their energetic content and elemental composition were determined by means of proximate and ultimate analysis, respectively, while their major and trace metal characterization was conducted by means of AAS. Due to its high calorific value, relatively low moisture content, and high loss-on-ignition value, it has been concluded that the olive kernel gasification residue can be utilized as a primary fuel in combustion boilers. Moreover, its reduced chlorine and sulfur content suggest minimal corrosion-related problems. Alternative utilization options, based on their morphology, are also suggested in this study, while modifications in the current gasification conditions are proposed as well.
The aim of this work was to test CFB-derived fly ash for its potential to get utilised in ceramic... more The aim of this work was to test CFB-derived fly ash for its potential to get utilised in ceramic tilesmanufacturing by applying the sintering technique. The tested specimens were moulded using extrusion and fired at 1,050°C; a laboratory pilot-plant simulation of the industrial brick fabrication process was applied and the produced materials were afterwards tested for their microstructure and physical properties. Different types of clays were selected and characterised and various clay-ash mixtures were prepared. Plasticity after mixing with water as well as extrusion of the compact specimens and their drying behaviour were evaluated. Water absorption and mechanical strength of fired specimens were determined and evaluated as a function of the percentage FA content. Results showed that large-scale production of CFB FAcontaining bricks is feasible, as their mechanical properties were not significantly harmed, while any possible detrimental effect on the other properties of the synthetic bricks appeared to be relatively restricted.
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 SO 3 . These predictions were eventually confirmed in the 23 years of operation of the power station. During these years SO 3 (%) kept alternating, rendering-in some cases-fly ash suitable for use in cement industry applications. The periodical changes of the SO 3 concentration in fly ash were attributed to the free (volatile) sulphur of feedcoal as well as to the excess of FeS 2 , which had also a serious effect on the daily power production process (severe erosion of the metallic surfaces of boiler). A number of solutions for tackling this phenomenon are suggested in this study: discard of specific FA grain fractions, intense monitoring of the material and its effective mixture-homogenization and selective mining of lignite.
We have studied the room-temperature non-radiative energy transfer processes in hybrid structures... more We have studied the room-temperature non-radiative energy transfer processes in hybrid structures composed of (Ga, In)N/GaN single quantum wells and semiconducting polymer blend films placed in nanometre-scale proximity. The blends consist of three polyfluorene materials with concentrations adjusted so that they emit white light. Power-dependent photoluminescence (PL) measurements are used to investigate the process of energy transfer from the quantum wells to the different components of the polymer blend. We show that energy distribution among the hybrid structures involves competition between nanoscale range non-radiative energy transfer processes from the inorganic well to the polymer components and within the blend itself.
In the present paper, two Class C, lignite fly ashes (FAs) were utilized for the fabrication of A... more In the present paper, two Class C, lignite fly ashes (FAs) were utilized for the fabrication of Al/fly ash metal matrix composites (MMCs) using the powder metallurgy (PM) technique. Aluminum-fly ash and aluminum/silicon alloy (Al-12% Si)-fly ash mixtures, containing 5, 10 and 15 wt.% of -both pozzolanic and hydraulic -FAs were prepared and compacted. The green products were tested for their thermal behavior in order for the sintering temperature to be determined. Then, they were sintered for 2 and 6 h. The density of composites was decreasing with the increase of the percentage participation of fly ash particles into them. Apart from that, although FA clusters had been developing in the metal matrix, there was a significant enhancement in the hardness of MMCs when increasing FA content, which is mainly attributed to the intense calcareous nature of the reinforcement material. Volume and mass changes throughout calcination were also estimated as a function of increasing FA weight percent and it seems that CaO (%) of FAs plays a crucial role regarding the post-sintering raise in the mass and volume of composites. Microscopic studies of green and sintered compacts clearly indicated the effectiveness of the sintering process. Additionally, the composites were characterized in terms of their chemical composition and mineralogical structure. The rise of Ca-Si-and Si-mineral phases is intense, particularly for the composites with the highest percentage presence of CaO in FAs (15 wt.%) and does not differentiate as a function of the sintering time.
In this paper, two different ASTM C 618 Class C fly ashes (FA) were used for the production of al... more In this paper, two different ASTM C 618 Class C fly ashes (FA) were used for the production of aluminum metal matrix composites (MMCs) using powder metallurgy (PM) technology.
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.
Eight types of A356 Al-fly ash composites were produced by pressure infiltration of high-Ca ligni... more Eight types of A356 Al-fly ash composites were produced by pressure infiltration of high-Ca lignite fly ash. This type of ash was used for the first time in Al-composites synthesis, and particularly by liquid metal infiltration techniques. After examining mineralogy and chemistry, specific, narrow ash size fractions were used for the synthesis of composites, and properties linked to microstructure and wear strength of the materials. The effect of using ground ash particles on the microstructure and tribological performance of the composites was also investigated. It was concluded that using fine, high-Ca ash particles can improve the properties of composites, and that using ash particles in a ground form can better facilitate the production process of MMCs.
Fly ash from two lignite-fed power stations in Greece (Megalopolis and Meliti) has been utilized ... more Fly ash from two lignite-fed power stations in Greece (Megalopolis and Meliti) has been utilized to synthesize zeolitic materials with upgraded adsorption capacity. Two different siliceous fly ash samples were subjected to hydrothermal treatment at fixed solid / liquid ratio and constant temperature. The zeolitic products have been characterized for their microstructure, chemical, and mineralogical composition by means of SEM, AAS, and XRD, respectively. The primary zeolitic crystals identified were phillipsite and thomsonite, in Megalopolis and Meliti fly ash, respectively. In light of their prospective utilization as liquid-phase sorbents, the specific surface area and porosity of materials were also determined, by means of N 2 -porosimetry. The zeolitic samples were tested for their actual heavy metal-removal capacity by water sampled from active lignite mines in Northern Greece. Artificial aquatic samples with known concentration of heavy metals (Cd, Cr, Cu, Ni, Pb, and Zn) were also tested, showing that the synthetic zeolitic materials are good to uptake a wide variety of potential pollutants with up to 100% efficiency. The efficiency of the synthetic zeolitic materials was comparatively assessed, showing that the more intense the presence of phillipsite in the synthetic materials, the greater the uptake rates for certain groups of trace elements.
Two different fly ash (FA) samples were tested for their ability to give synthetic zeolitic produ... more Two different fly ash (FA) samples were tested for their ability to give synthetic zeolitic products. Polish bituminous (PB) and South African (SA) coal fly ash (FA) samples, derived from pilot-scale circulated fluidized bed (CFB) combustion facilities, have been utilized as raw materials. The two FAs underwent a hydrothermal activation with 1M NaOH solution at 90°C for 24 h. Two different FA/NaOH solution/ratios (50, 100 g/L) were applied for each sample and the following zeolitic materials were formed: Na-Al-Si Zeolite A (Na), K-Al-Si Zeolite A (K), Erionite, ZSM-18, K-Ca-Al-Si-Hydrate Unnamed Zeolite, Erionite and Linde (L). The experimental products were characterized by means of X-Ray Diffraction (XRD) and Energy Dispersive X-Ray coupled-Scanning Electron Microscope (EDX/SEM), while X-Ray Fluorescence (XRF) was applied for the determination of their chemical composition. The zeolitic products were also evaluated in terms of their cation exchange capacity (CEC), specific surface area (SSA), specific gravity (SG), particle size distribution (PSD), pH and the range of their micro-and macroporosity. The current work focuses on testing the synthesized zeolitic materials for their potential of retaining heavy metals from industrial wastewater. Therefore, the aforementioned products were tested for their ability of adsorbing Cr, Pb, Ni, Cu, Cd and Zn from contaminated liquids, by the use of instrumental analytical methodologies. It must be noticed that the main goal is the treatment of liquid waste with such by-products and the capability of the zeolitic material to inhibit the leaching of the metals. Main parameters, as it is concluded from the experimental results, are the mineralogical composition of the initial fly ashes, as well as the type and the amount of the produced zeolite and specifically the mechanism by which the metals ions are hold on the substrate.
In the present paper eight types of A356 Al-fly ash composites were synthesized using pressure in... more In the present paper eight types of A356 Al-fly ash composites were synthesized using pressure infiltration technique, by utilizing Class C fly ash (FA). Actually, such a strongly calcareous FA was for the first time used in MMCs-manufacturing by liquid metal infiltration techniques. After testing their mineralogy and chemistry, certain FA size-fractions were used for the fabrication of the composites and their particular properties were linked to the level of the successful synthesis of the materials, the development of their microstructure and their wear strengths. The effect of using ground FA particles on the structure of composites and their tribological performance was also investigated through this study. It was concluded that using fine FA particles can strongly advantage the properties of composites and that grinding of fly ash facilitates MMCs-manufacturing by pressure infiltration and it also advantages their wear properties.
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.
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 performance than pure Al/Si products, the additions of ashes up to 15% wt. resulted in only slight deterioration of the wear performance of composites.
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.
Archives of Industrial Hygiene and Toxicology, 2014
Wood fly ash is an industrial by-product of the combustion of different wood materials and is mos... more Wood fly ash is an industrial by-product of the combustion of different wood materials and is mostly disposed of as waste on landfills. In our preliminary experiments, wood ash exhibited antibacterial activity against urban wastewater bacteria and we focused on wood fly ash as a potential substrate for wastewater disinfection. The addition of ash at a concentration of 10 g L -1 (1 %) caused an instant increase of pH in urban wastewater and landfill leachate. High pH (10.1-12.7) inactivated bacterial populations in the wastewater and the removal of faecal coliforms and intestinal enterococci after 6 h of contact was 100 % (below the detection limit; <1 CFU per mL) with the most efficient ash sample (ash from combustion of beech) both in urban wastewater and landfill leachate. Properly chosen wood fly ash, i.e. one that tends to increase the pH to the greatest extent, proved to be a very effective disinfection substrate. Considering that water treated with wood ash has a high pH and needs to be neutralised before discharge, ash would be suitable for disinfection of leachates when smaller volumes are treated.
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
In this study, a fixed-bed downdraft gasifier (70 kW e -245 kW th ) with gas cooling and cleaning... more In this study, a fixed-bed downdraft gasifier (70 kW e -245 kW th ) with gas cooling and cleaning system, combined with a gas engine, was tested using olive kernel as fuel. The primary scope of this paper is to identify the most prominent utilization paths for the solid residues of the process. After a 3-day experimental work and the respective sampling campaigns, a thorough characterization study was conducted: the mineralogy of collected residues was examined by means of XRD, Loss on Ignition tests were carried out by the use of TGA up to 850°C, their morphology was examined by means of EDS-SEM, their energetic content and elemental composition were determined by means of proximate and ultimate analysis, respectively, while their major and trace metal characterization was conducted by means of AAS. Due to its high calorific value, relatively low moisture content, and high loss-on-ignition value, it has been concluded that the olive kernel gasification residue can be utilized as a primary fuel in combustion boilers. Moreover, its reduced chlorine and sulfur content suggest minimal corrosion-related problems. Alternative utilization options, based on their morphology, are also suggested in this study, while modifications in the current gasification conditions are proposed as well.
The aim of this work was to test CFB-derived fly ash for its potential to get utilised in ceramic... more The aim of this work was to test CFB-derived fly ash for its potential to get utilised in ceramic tilesmanufacturing by applying the sintering technique. The tested specimens were moulded using extrusion and fired at 1,050°C; a laboratory pilot-plant simulation of the industrial brick fabrication process was applied and the produced materials were afterwards tested for their microstructure and physical properties. Different types of clays were selected and characterised and various clay-ash mixtures were prepared. Plasticity after mixing with water as well as extrusion of the compact specimens and their drying behaviour were evaluated. Water absorption and mechanical strength of fired specimens were determined and evaluated as a function of the percentage FA content. Results showed that large-scale production of CFB FAcontaining bricks is feasible, as their mechanical properties were not significantly harmed, while any possible detrimental effect on the other properties of the synthetic bricks appeared to be relatively restricted.
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 SO 3 . These predictions were eventually confirmed in the 23 years of operation of the power station. During these years SO 3 (%) kept alternating, rendering-in some cases-fly ash suitable for use in cement industry applications. The periodical changes of the SO 3 concentration in fly ash were attributed to the free (volatile) sulphur of feedcoal as well as to the excess of FeS 2 , which had also a serious effect on the daily power production process (severe erosion of the metallic surfaces of boiler). A number of solutions for tackling this phenomenon are suggested in this study: discard of specific FA grain fractions, intense monitoring of the material and its effective mixture-homogenization and selective mining of lignite.
We have studied the room-temperature non-radiative energy transfer processes in hybrid structures... more We have studied the room-temperature non-radiative energy transfer processes in hybrid structures composed of (Ga, In)N/GaN single quantum wells and semiconducting polymer blend films placed in nanometre-scale proximity. The blends consist of three polyfluorene materials with concentrations adjusted so that they emit white light. Power-dependent photoluminescence (PL) measurements are used to investigate the process of energy transfer from the quantum wells to the different components of the polymer blend. We show that energy distribution among the hybrid structures involves competition between nanoscale range non-radiative energy transfer processes from the inorganic well to the polymer components and within the blend itself.
In the present paper, two Class C, lignite fly ashes (FAs) were utilized for the fabrication of A... more In the present paper, two Class C, lignite fly ashes (FAs) were utilized for the fabrication of Al/fly ash metal matrix composites (MMCs) using the powder metallurgy (PM) technique. Aluminum-fly ash and aluminum/silicon alloy (Al-12% Si)-fly ash mixtures, containing 5, 10 and 15 wt.% of -both pozzolanic and hydraulic -FAs were prepared and compacted. The green products were tested for their thermal behavior in order for the sintering temperature to be determined. Then, they were sintered for 2 and 6 h. The density of composites was decreasing with the increase of the percentage participation of fly ash particles into them. Apart from that, although FA clusters had been developing in the metal matrix, there was a significant enhancement in the hardness of MMCs when increasing FA content, which is mainly attributed to the intense calcareous nature of the reinforcement material. Volume and mass changes throughout calcination were also estimated as a function of increasing FA weight percent and it seems that CaO (%) of FAs plays a crucial role regarding the post-sintering raise in the mass and volume of composites. Microscopic studies of green and sintered compacts clearly indicated the effectiveness of the sintering process. Additionally, the composites were characterized in terms of their chemical composition and mineralogical structure. The rise of Ca-Si-and Si-mineral phases is intense, particularly for the composites with the highest percentage presence of CaO in FAs (15 wt.%) and does not differentiate as a function of the sintering time.
In this paper, two different ASTM C 618 Class C fly ashes (FA) were used for the production of al... more In this paper, two different ASTM C 618 Class C fly ashes (FA) were used for the production of aluminum metal matrix composites (MMCs) using powder metallurgy (PM) technology.
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.
Eight types of A356 Al-fly ash composites were produced by pressure infiltration of high-Ca ligni... more Eight types of A356 Al-fly ash composites were produced by pressure infiltration of high-Ca lignite fly ash. This type of ash was used for the first time in Al-composites synthesis, and particularly by liquid metal infiltration techniques. After examining mineralogy and chemistry, specific, narrow ash size fractions were used for the synthesis of composites, and properties linked to microstructure and wear strength of the materials. The effect of using ground ash particles on the microstructure and tribological performance of the composites was also investigated. It was concluded that using fine, high-Ca ash particles can improve the properties of composites, and that using ash particles in a ground form can better facilitate the production process of MMCs.
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Papers by Grigorios Itskos