Pantelitsa Georgiou | National Technical University of Athens (original) (raw)
Papers by Pantelitsa Georgiou
Polymer international, Apr 12, 2024
The demands of cost-driven industrial applications can be satisfied by manufacturing composites w... more The demands of cost-driven industrial applications can be satisfied by manufacturing composites with a low volume fraction of carbon fibres as phenolic carbon fibre-reinforced composites and C/C composites, both with acceptable performances, for lowor high-temperature applications, respectively. Polymeric composites reinforced with a low volume fraction (7.5% v/v) of carbon fibres were fabricated using laboratory-produced phenolic resins, novolac (N) and resole (R), as matrices after different curing/post-curing temperature profiles. By optimising the manufacturing conditions, the N-based polymeric composites exhibited higher flexural strength, whereas the R-based composites showed higher shear strength. C/C composites, namely N-based and R-based, were manufactured by pyrolysis of the previously prepared polymeric composites up to 1000°C. The pyrolysed composites were then densified by impregnation with an appropriate resin solution, followed by curing and new pyrolysis, and particularly by employing 1 up to 4 consecutive cycles of 'impregnation-curing/pyrolysis'. Weight changes resulting from the impregnation-curing and pyrolysis stages were determined. The curing of both resins was verified by Fourier Transform Infrared Analysis. The apparent density and X-ray diffraction data of the C/C composites were used to calculate their total percent porosities. The morphology and elemental composition of the C/C composites at their failure region (after flexural testing) were examined by Scanning Electron Microscopy/Energy-Dispersive X-ray Analyses. In comparison to the N-based C/C composites, the R-based ones exhibited: higher shear strength, lower flexural strength, higher Shore D hardness, slightly higher surface conductivity and lower volume conductivity. The optimum conditions for the manufacture of C/C composites were achieved by applying two consecutive cycles of 'pyrolysis-impregnation-pyrolysis' to the polymeric composites.
Polymer International, 2024
The demands of cost-driven industrial applications can be satisfied by manufacturing composites w... more The demands of cost-driven industrial applications can be satisfied by manufacturing composites with a low volume fraction of carbon fibres as phenolic carbon fibre-reinforced composites and C/C composites, both with acceptable performances, for lowor high-temperature applications, respectively. Polymeric composites reinforced with a low volume fraction (7.5% v/v) of carbon fibres were fabricated using laboratory-produced phenolic resins, novolac (N) and resole (R), as matrices after different curing/post-curing temperature profiles. By optimising the manufacturing conditions, the N-based polymeric composites exhibited higher flexural strength, whereas the R-based composites showed higher shear strength. C/C composites, namely N-based and R-based, were manufactured by pyrolysis of the previously prepared polymeric composites up to 1000°C. The pyrolysed composites were then densified by impregnation with an appropriate resin solution, followed by curing and new pyrolysis, and particularly by employing 1 up to 4 consecutive cycles of 'impregnation-curing/pyrolysis'. Weight changes resulting from the impregnation-curing and pyrolysis stages were determined. The curing of both resins was verified by Fourier Transform Infrared Analysis. The apparent density and X-ray diffraction data of the C/C composites were used to calculate their total percent porosities. The morphology and elemental composition of the C/C composites at their failure region (after flexural testing) were examined by Scanning Electron Microscopy/Energy-Dispersive X-ray Analyses. In comparison to the N-based C/C composites, the R-based ones exhibited: higher shear strength, lower flexural strength, higher Shore D hardness, slightly higher surface conductivity and lower volume conductivity. The optimum conditions for the manufacture of C/C composites were achieved by applying two consecutive cycles of 'pyrolysis-impregnation-pyrolysis' to the polymeric composites.
Hydrothermally grown ZnO nano-crystals were deposited on nickel substrates in the form of ZnO nan... more Hydrothermally grown ZnO nano-crystals were deposited on nickel substrates in the form of ZnO nano-thorn-flower formations by the spin-coating technique. The resulting semiconducting films were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). According to XRD spectra the synthesized ZnO powder was mainly characterized by (m) side structures, with ends of regular hexagonal pyramid structures (+p). The deposited ZnO film with nano-thorn-flower formations on the Ni (111) substrate had an average crystalline size of 48 nm. The SEM images confirmed the nano-thorn-flower formations. A metal-ZnO-metal structure was formed by positioning a Au electrode on top of the ZnO surface and the I-V characteristics of the resulting device were investigated in the dark and under low intensity diffused illumination. The experimental I-V data imply that the device is capable of producing electric power in the dark due to electrochemical surface interactions with gaseous polarizing molecules or ions, and also under low-energy lowintensity (0.2 mW cm −2) diffused solar radiation. The advantages offered on energy conversion efficiency by the presence of deep electronic states that are spatially confined on the nano-crystal semiconductor surface are experimentally and theoretically investigated. A potential energy diagram is proposed to present the operation principles of the structure (under dark or illumination) and link the deep level parameters to the obtained I-V characteristics. The investigated structure might be practically implemented on top of 1st G photovoltaic (PV) cells to reduce heating of PV cells by converting low energy photons of the electromagnetic spectrum to electrical energy (instead of heat).
Materials research express, Apr 16, 2015
ABSTRACT
Journal of Nano Research, Jun 1, 2009
ZnO was synthesized by the hydrothermal method using proper aqueous solutions of ZnCl 2 and NaOH,... more ZnO was synthesized by the hydrothermal method using proper aqueous solutions of ZnCl 2 and NaOH, as the main raw materials, corresponding to the molar ratio of Zn 2+ : OH-= 1 : 20 (solution 'A'), and a proper proportion of water as solvent, ethanol (EtOH) as non solvent and polyethylene glycol (PEG) as nonionic surfactant (solution 'B'). The reaction takes place in an autoclave at 200 °C for a defined period of time (1-20 h). The solid ZnO products received after centrifugation, washing and drying were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The percentage of unreacted Zn present after the reaction in the liquid phase (incumbent solution) was determined by Atomic Absorption Spectroscopy. The parameters of processing (i.e., temperature, pressure, residence time) and the raw materials parameters (i.e. proportion of 2 Solution 'A' mL H O + mL EtOH , amount of PEG) influence the morphology and the dimensions of the product. Increasing the residence time from 1 h → 3 h → 20 h, the amorphous regions illustrated in SEM images are decreased and the number and dimensions of the obtained single or branched rods of the final product are increased. Avoiding the use of additional water, i.e. the denominator in the aforementioned ratio, mL, water, is equal to zero, but simultaneously using ethanol, the ZnO material is mainly amorphous. Increasing the amount of the additional water without ethanol, no amorphous material is observed and single rods or flowerlike/starlike structures having ends of regular hexagonal pyramid structure, are formed. Increasing the proportion of PEG, many flowerlike or starlike branched structures having ends of regular hexagonal prismatic structure, are formed. The ZnO materials having much of amorphous regions do not show XRD peaks. On the other hand, the crystalline ZnO materials show many XRD peaks, which are indexed and they correspond to the wurtzite-structured (hexagonal) ZnO. Furthermore, the lattice constants and c are determined.
Electrocatalysis, Aug 1, 2022
Applied sciences, Jan 20, 2023
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Applied Sciences
An as-produced epoxy material reinforced with ZnO (nano)rods for outdoor use was produced for the... more An as-produced epoxy material reinforced with ZnO (nano)rods for outdoor use was produced for the purpose of enclosing VHF/early UHF transceiving elements. Three different ZnO (nano)rod percentages were dispersed (0.1 wt%, 0.5 wt% and 2 wt%) in epoxy samples and were consequently exposed to an artificial weathering environment for a total period of 2880 h. SEM and XRD characterizations were followed by gravimetric, colorimetric and dielectric measurements that were conducted every 576-h AWE treatment intervals and were complemented by FTIR, UV-Vis, contact angle and gloss measurements. The composite exhibited favourable dielectric behaviour: ZnO presence inflicted minimal impact to the composites’ loss tangent, while dielectric permittivity was reduced for low ZnO content (0.1 wt%/0.5 wt%), especially until the 1152-h interval, while it suffered an increase for 2 wt% samples that was maintained from the beginning until the end of the experiment. Hence, the low-k (4–5.2) constructed ...
The scope of the doctoral thesis is the surface modification of commercial and laboratory-produce... more The scope of the doctoral thesis is the surface modification of commercial and laboratory-produced carbon fibres with electrochemical treatment by cyclic voltammetry and their characterization and the correlation of the parameters / conditions with their structure. To achieve this goal, commercial carbon fibres are used as working electrodes in a suitable electrochemical cell and they are surface modified by cyclic voltammetry, choosing various redox conditions based on the concentration of electrolyte solution, the sweep scan range, the sweep scan rate and the number of treatment cycles and subsequently they are characterized. Since commercial carbon fibres bear oxygen-containing groups in their structure by unknown origin of surface modification from the industry, they are not chemically inert and therefore they are subjected to pyrolysis anew and afterwards they are electrochemically treated and characterized. In addition, laboratory-produced carbon fibres, after appropriate batc...
Polymers, 2020
The present paper deals with the use of polymeric matrix composite materials reinforced with carb... more The present paper deals with the use of polymeric matrix composite materials reinforced with carbon fiber as concrete shear reinforcement materials. Accordingly, cement specimens were manufactured and coated with various types of carbon fabrics and epoxy resin in liquid and solid form (paste). Additionally, composite materials of epoxy resin matrix reinforced with carbon fiber fabrics were manufactured. In all the specimens, the mechanical properties were estimated; the cement samples coated with composite materials of epoxy resin matrix reinforced with carbon fiber fabrics were tested for compressive strength, while the other specimens were tested for shear and bending strength. The specimens were subjected to artificial aging through heat treatment for 8, 12 and 16 days. During the process of artificial aging, the temperature in the chamber reached the range of 65–75 °C. These composite materials exhibited high mechanical properties combined with adaptability. Both an external det...
Journal of Materials Science, 2015
Electrochimica Acta, 2010
Commercial carbon fibres were pyrolyzed up to 1000 • C and were then electrochemically treated by... more Commercial carbon fibres were pyrolyzed up to 1000 • C and were then electrochemically treated by cyclic voltammetry in aqueous electrolyte solutions of H 2 SO 4 , in two potential sweep ranges: a narrow region, N, and a wide region, W, avoiding and including water decomposition, respectively. The anodic and cathodic peaks were correlated with oxide formation and their partial reduction, respectively. The nature of oxygen containing groups on the fibre surfaces was determined by XPS. Wide scan spectra and high energy resolution spectra were recorded through the C 1s, O 1s, N 1s and S 2p photoelectron regions. The ability of the fibres to adsorb methylene blue and alizarin yellow dyes from their aqueous solutions indicates the presence of electron acceptor or donor groups on the fibres, respectively. The carbon fibres were classified into two categories. The first includes electrochemically untreated and treated in the N region, and the second those treated in the W region. The high oxygen concentration and effective dye adsorption on the carbon fibres in the second category indicates that their surfaces were effectively modified. The adsorption of dyes on carbon fibres constitutes a complementary method to XPS for an indirect estimation of oxygen and other groups present on the carbon fibre surfaces.
Materials Research Express
ABSTRACT
– Manufacturing of nanomaterials is an interdisciplinary field covering physics, chemistry, biolo... more – Manufacturing of nanomaterials is an interdisciplinary field covering physics, chemistry, biology, mate-rials science and engineering. The interaction between scientists with different disciplines will undoubtedly lead to the production of novel materials with tailored properties. The success of nanomanufacturing depends on the strong cooperation between academia and industry in order to be informed about current needs and future challenges, to de-sign products directly transferred into the industrial sector. It is of paramount importance the selection of the appropri-ate method combining synthesis of nanomaterials with required properties and limited impurities as well as scalability of the technique. Their industrial use faces many obstacles as there is no suitable regulatory framework and guidance on safety requirements; specific provisions have yet to be established in EU legislation. Moreover, regulations related to the right of intellectual properties as well as the absence ...
Abstract. ZnO was synthesized by the hydrothermal method using proper aqueous solutions of ZnCl 2... more Abstract. ZnO was synthesized by the hydrothermal method using proper aqueous solutions of ZnCl 2 and NaOH, as the main raw materials, corresponding to the molar ratio of Zn , amount of PEG) influence the morphology and the dimensions of the product. Increasing the residence time from 1 h → 3 h → 20 h, the amorphous regions illustrated in SEM images are decreased and the number and dimensions of the obtained single or branched rods of the final product are increased. Avoiding the use of additional water, i.e. the denominator in the aforementioned ratio, mL, water, is equal to zero, but simultaneously using ethanol, the ZnO material is mainly amorphous. Increasing the amount of the additional water without ethanol, no amorphous material is observed and single rods or flowerlike/starlike structures having ends of regular hexagonal pyramid structure, are formed. Increasing the proportion of PEG, many flowerlike or starlike branched structures having ends of regular hexagonal prismatic ...
Polymers and Polymer Composites
The purpose of this study is to investigate a novel exploitation approach for a mass livestock by... more The purpose of this study is to investigate a novel exploitation approach for a mass livestock byproduct, namely sheep wool fibres. In order to fulfil this aim, wool fibre toughened epoxy composites with an amount of 2.4, 4.1 and 5.7 phr were prepared via the hot press method. Initially, mechanical assessment of the composites was executed, in order to evaluate their mechanical integrity. The flexural and shear strength tests showed that the wool fibre-epoxy composites maintain their mechanical properties for up to 4.1 phr and no degradation is detected. Subsequently, the thermal properties were tested. Thermogravimetric analysis proved that adding wool fibres as toughening agent in epoxy matrix can prolong the endurance of the material while reaching high temperatures. The coefficient of thermal conductivity decreased by 30% compared to neat epoxy, something that is also confirmed through simulation, proving that wool fibre-epoxy composites can be considered as a promising insulati...
MDPI, 2020
The present paper deals with the use of polymeric matrix composite materials reinforced with carb... more The present paper deals with the use of polymeric matrix composite materials reinforced with carbon fiber as concrete shear reinforcement materials. Accordingly, cement specimens were manufactured and coated with various types of carbon fabrics and epoxy resin in liquid and solid form (paste). Additionally, composite materials of epoxy resin matrix reinforced with carbon fiber fabrics were manufactured. In all the specimens, the mechanical properties were estimated; the cement samples coated with composite materials of epoxy resin matrix reinforced with carbon fiber fabrics were tested for compressive strength, while the other specimens were tested for shear and bending strength. The specimens were subjected to artificial aging through heat treatment for 8, 12 and 16 days. During the process of artificial aging, the temperature in the chamber reached the range of 65–75 °C. These composite materials exhibited high mechanical properties combined with adaptability. Both an external det...
Polymer international, Apr 12, 2024
The demands of cost-driven industrial applications can be satisfied by manufacturing composites w... more The demands of cost-driven industrial applications can be satisfied by manufacturing composites with a low volume fraction of carbon fibres as phenolic carbon fibre-reinforced composites and C/C composites, both with acceptable performances, for lowor high-temperature applications, respectively. Polymeric composites reinforced with a low volume fraction (7.5% v/v) of carbon fibres were fabricated using laboratory-produced phenolic resins, novolac (N) and resole (R), as matrices after different curing/post-curing temperature profiles. By optimising the manufacturing conditions, the N-based polymeric composites exhibited higher flexural strength, whereas the R-based composites showed higher shear strength. C/C composites, namely N-based and R-based, were manufactured by pyrolysis of the previously prepared polymeric composites up to 1000°C. The pyrolysed composites were then densified by impregnation with an appropriate resin solution, followed by curing and new pyrolysis, and particularly by employing 1 up to 4 consecutive cycles of 'impregnation-curing/pyrolysis'. Weight changes resulting from the impregnation-curing and pyrolysis stages were determined. The curing of both resins was verified by Fourier Transform Infrared Analysis. The apparent density and X-ray diffraction data of the C/C composites were used to calculate their total percent porosities. The morphology and elemental composition of the C/C composites at their failure region (after flexural testing) were examined by Scanning Electron Microscopy/Energy-Dispersive X-ray Analyses. In comparison to the N-based C/C composites, the R-based ones exhibited: higher shear strength, lower flexural strength, higher Shore D hardness, slightly higher surface conductivity and lower volume conductivity. The optimum conditions for the manufacture of C/C composites were achieved by applying two consecutive cycles of 'pyrolysis-impregnation-pyrolysis' to the polymeric composites.
Polymer International, 2024
The demands of cost-driven industrial applications can be satisfied by manufacturing composites w... more The demands of cost-driven industrial applications can be satisfied by manufacturing composites with a low volume fraction of carbon fibres as phenolic carbon fibre-reinforced composites and C/C composites, both with acceptable performances, for lowor high-temperature applications, respectively. Polymeric composites reinforced with a low volume fraction (7.5% v/v) of carbon fibres were fabricated using laboratory-produced phenolic resins, novolac (N) and resole (R), as matrices after different curing/post-curing temperature profiles. By optimising the manufacturing conditions, the N-based polymeric composites exhibited higher flexural strength, whereas the R-based composites showed higher shear strength. C/C composites, namely N-based and R-based, were manufactured by pyrolysis of the previously prepared polymeric composites up to 1000°C. The pyrolysed composites were then densified by impregnation with an appropriate resin solution, followed by curing and new pyrolysis, and particularly by employing 1 up to 4 consecutive cycles of 'impregnation-curing/pyrolysis'. Weight changes resulting from the impregnation-curing and pyrolysis stages were determined. The curing of both resins was verified by Fourier Transform Infrared Analysis. The apparent density and X-ray diffraction data of the C/C composites were used to calculate their total percent porosities. The morphology and elemental composition of the C/C composites at their failure region (after flexural testing) were examined by Scanning Electron Microscopy/Energy-Dispersive X-ray Analyses. In comparison to the N-based C/C composites, the R-based ones exhibited: higher shear strength, lower flexural strength, higher Shore D hardness, slightly higher surface conductivity and lower volume conductivity. The optimum conditions for the manufacture of C/C composites were achieved by applying two consecutive cycles of 'pyrolysis-impregnation-pyrolysis' to the polymeric composites.
Hydrothermally grown ZnO nano-crystals were deposited on nickel substrates in the form of ZnO nan... more Hydrothermally grown ZnO nano-crystals were deposited on nickel substrates in the form of ZnO nano-thorn-flower formations by the spin-coating technique. The resulting semiconducting films were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). According to XRD spectra the synthesized ZnO powder was mainly characterized by (m) side structures, with ends of regular hexagonal pyramid structures (+p). The deposited ZnO film with nano-thorn-flower formations on the Ni (111) substrate had an average crystalline size of 48 nm. The SEM images confirmed the nano-thorn-flower formations. A metal-ZnO-metal structure was formed by positioning a Au electrode on top of the ZnO surface and the I-V characteristics of the resulting device were investigated in the dark and under low intensity diffused illumination. The experimental I-V data imply that the device is capable of producing electric power in the dark due to electrochemical surface interactions with gaseous polarizing molecules or ions, and also under low-energy lowintensity (0.2 mW cm −2) diffused solar radiation. The advantages offered on energy conversion efficiency by the presence of deep electronic states that are spatially confined on the nano-crystal semiconductor surface are experimentally and theoretically investigated. A potential energy diagram is proposed to present the operation principles of the structure (under dark or illumination) and link the deep level parameters to the obtained I-V characteristics. The investigated structure might be practically implemented on top of 1st G photovoltaic (PV) cells to reduce heating of PV cells by converting low energy photons of the electromagnetic spectrum to electrical energy (instead of heat).
Materials research express, Apr 16, 2015
ABSTRACT
Journal of Nano Research, Jun 1, 2009
ZnO was synthesized by the hydrothermal method using proper aqueous solutions of ZnCl 2 and NaOH,... more ZnO was synthesized by the hydrothermal method using proper aqueous solutions of ZnCl 2 and NaOH, as the main raw materials, corresponding to the molar ratio of Zn 2+ : OH-= 1 : 20 (solution 'A'), and a proper proportion of water as solvent, ethanol (EtOH) as non solvent and polyethylene glycol (PEG) as nonionic surfactant (solution 'B'). The reaction takes place in an autoclave at 200 °C for a defined period of time (1-20 h). The solid ZnO products received after centrifugation, washing and drying were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The percentage of unreacted Zn present after the reaction in the liquid phase (incumbent solution) was determined by Atomic Absorption Spectroscopy. The parameters of processing (i.e., temperature, pressure, residence time) and the raw materials parameters (i.e. proportion of 2 Solution 'A' mL H O + mL EtOH , amount of PEG) influence the morphology and the dimensions of the product. Increasing the residence time from 1 h → 3 h → 20 h, the amorphous regions illustrated in SEM images are decreased and the number and dimensions of the obtained single or branched rods of the final product are increased. Avoiding the use of additional water, i.e. the denominator in the aforementioned ratio, mL, water, is equal to zero, but simultaneously using ethanol, the ZnO material is mainly amorphous. Increasing the amount of the additional water without ethanol, no amorphous material is observed and single rods or flowerlike/starlike structures having ends of regular hexagonal pyramid structure, are formed. Increasing the proportion of PEG, many flowerlike or starlike branched structures having ends of regular hexagonal prismatic structure, are formed. The ZnO materials having much of amorphous regions do not show XRD peaks. On the other hand, the crystalline ZnO materials show many XRD peaks, which are indexed and they correspond to the wurtzite-structured (hexagonal) ZnO. Furthermore, the lattice constants and c are determined.
Electrocatalysis, Aug 1, 2022
Applied sciences, Jan 20, 2023
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Applied Sciences
An as-produced epoxy material reinforced with ZnO (nano)rods for outdoor use was produced for the... more An as-produced epoxy material reinforced with ZnO (nano)rods for outdoor use was produced for the purpose of enclosing VHF/early UHF transceiving elements. Three different ZnO (nano)rod percentages were dispersed (0.1 wt%, 0.5 wt% and 2 wt%) in epoxy samples and were consequently exposed to an artificial weathering environment for a total period of 2880 h. SEM and XRD characterizations were followed by gravimetric, colorimetric and dielectric measurements that were conducted every 576-h AWE treatment intervals and were complemented by FTIR, UV-Vis, contact angle and gloss measurements. The composite exhibited favourable dielectric behaviour: ZnO presence inflicted minimal impact to the composites’ loss tangent, while dielectric permittivity was reduced for low ZnO content (0.1 wt%/0.5 wt%), especially until the 1152-h interval, while it suffered an increase for 2 wt% samples that was maintained from the beginning until the end of the experiment. Hence, the low-k (4–5.2) constructed ...
The scope of the doctoral thesis is the surface modification of commercial and laboratory-produce... more The scope of the doctoral thesis is the surface modification of commercial and laboratory-produced carbon fibres with electrochemical treatment by cyclic voltammetry and their characterization and the correlation of the parameters / conditions with their structure. To achieve this goal, commercial carbon fibres are used as working electrodes in a suitable electrochemical cell and they are surface modified by cyclic voltammetry, choosing various redox conditions based on the concentration of electrolyte solution, the sweep scan range, the sweep scan rate and the number of treatment cycles and subsequently they are characterized. Since commercial carbon fibres bear oxygen-containing groups in their structure by unknown origin of surface modification from the industry, they are not chemically inert and therefore they are subjected to pyrolysis anew and afterwards they are electrochemically treated and characterized. In addition, laboratory-produced carbon fibres, after appropriate batc...
Polymers, 2020
The present paper deals with the use of polymeric matrix composite materials reinforced with carb... more The present paper deals with the use of polymeric matrix composite materials reinforced with carbon fiber as concrete shear reinforcement materials. Accordingly, cement specimens were manufactured and coated with various types of carbon fabrics and epoxy resin in liquid and solid form (paste). Additionally, composite materials of epoxy resin matrix reinforced with carbon fiber fabrics were manufactured. In all the specimens, the mechanical properties were estimated; the cement samples coated with composite materials of epoxy resin matrix reinforced with carbon fiber fabrics were tested for compressive strength, while the other specimens were tested for shear and bending strength. The specimens were subjected to artificial aging through heat treatment for 8, 12 and 16 days. During the process of artificial aging, the temperature in the chamber reached the range of 65–75 °C. These composite materials exhibited high mechanical properties combined with adaptability. Both an external det...
Journal of Materials Science, 2015
Electrochimica Acta, 2010
Commercial carbon fibres were pyrolyzed up to 1000 • C and were then electrochemically treated by... more Commercial carbon fibres were pyrolyzed up to 1000 • C and were then electrochemically treated by cyclic voltammetry in aqueous electrolyte solutions of H 2 SO 4 , in two potential sweep ranges: a narrow region, N, and a wide region, W, avoiding and including water decomposition, respectively. The anodic and cathodic peaks were correlated with oxide formation and their partial reduction, respectively. The nature of oxygen containing groups on the fibre surfaces was determined by XPS. Wide scan spectra and high energy resolution spectra were recorded through the C 1s, O 1s, N 1s and S 2p photoelectron regions. The ability of the fibres to adsorb methylene blue and alizarin yellow dyes from their aqueous solutions indicates the presence of electron acceptor or donor groups on the fibres, respectively. The carbon fibres were classified into two categories. The first includes electrochemically untreated and treated in the N region, and the second those treated in the W region. The high oxygen concentration and effective dye adsorption on the carbon fibres in the second category indicates that their surfaces were effectively modified. The adsorption of dyes on carbon fibres constitutes a complementary method to XPS for an indirect estimation of oxygen and other groups present on the carbon fibre surfaces.
Materials Research Express
ABSTRACT
– Manufacturing of nanomaterials is an interdisciplinary field covering physics, chemistry, biolo... more – Manufacturing of nanomaterials is an interdisciplinary field covering physics, chemistry, biology, mate-rials science and engineering. The interaction between scientists with different disciplines will undoubtedly lead to the production of novel materials with tailored properties. The success of nanomanufacturing depends on the strong cooperation between academia and industry in order to be informed about current needs and future challenges, to de-sign products directly transferred into the industrial sector. It is of paramount importance the selection of the appropri-ate method combining synthesis of nanomaterials with required properties and limited impurities as well as scalability of the technique. Their industrial use faces many obstacles as there is no suitable regulatory framework and guidance on safety requirements; specific provisions have yet to be established in EU legislation. Moreover, regulations related to the right of intellectual properties as well as the absence ...
Abstract. ZnO was synthesized by the hydrothermal method using proper aqueous solutions of ZnCl 2... more Abstract. ZnO was synthesized by the hydrothermal method using proper aqueous solutions of ZnCl 2 and NaOH, as the main raw materials, corresponding to the molar ratio of Zn , amount of PEG) influence the morphology and the dimensions of the product. Increasing the residence time from 1 h → 3 h → 20 h, the amorphous regions illustrated in SEM images are decreased and the number and dimensions of the obtained single or branched rods of the final product are increased. Avoiding the use of additional water, i.e. the denominator in the aforementioned ratio, mL, water, is equal to zero, but simultaneously using ethanol, the ZnO material is mainly amorphous. Increasing the amount of the additional water without ethanol, no amorphous material is observed and single rods or flowerlike/starlike structures having ends of regular hexagonal pyramid structure, are formed. Increasing the proportion of PEG, many flowerlike or starlike branched structures having ends of regular hexagonal prismatic ...
Polymers and Polymer Composites
The purpose of this study is to investigate a novel exploitation approach for a mass livestock by... more The purpose of this study is to investigate a novel exploitation approach for a mass livestock byproduct, namely sheep wool fibres. In order to fulfil this aim, wool fibre toughened epoxy composites with an amount of 2.4, 4.1 and 5.7 phr were prepared via the hot press method. Initially, mechanical assessment of the composites was executed, in order to evaluate their mechanical integrity. The flexural and shear strength tests showed that the wool fibre-epoxy composites maintain their mechanical properties for up to 4.1 phr and no degradation is detected. Subsequently, the thermal properties were tested. Thermogravimetric analysis proved that adding wool fibres as toughening agent in epoxy matrix can prolong the endurance of the material while reaching high temperatures. The coefficient of thermal conductivity decreased by 30% compared to neat epoxy, something that is also confirmed through simulation, proving that wool fibre-epoxy composites can be considered as a promising insulati...
MDPI, 2020
The present paper deals with the use of polymeric matrix composite materials reinforced with carb... more The present paper deals with the use of polymeric matrix composite materials reinforced with carbon fiber as concrete shear reinforcement materials. Accordingly, cement specimens were manufactured and coated with various types of carbon fabrics and epoxy resin in liquid and solid form (paste). Additionally, composite materials of epoxy resin matrix reinforced with carbon fiber fabrics were manufactured. In all the specimens, the mechanical properties were estimated; the cement samples coated with composite materials of epoxy resin matrix reinforced with carbon fiber fabrics were tested for compressive strength, while the other specimens were tested for shear and bending strength. The specimens were subjected to artificial aging through heat treatment for 8, 12 and 16 days. During the process of artificial aging, the temperature in the chamber reached the range of 65–75 °C. These composite materials exhibited high mechanical properties combined with adaptability. Both an external det...