ABSTRACT The main purpose of this study is to investigate the nano-indentation test method and va... more ABSTRACT The main purpose of this study is to investigate the nano-indentation test method and validation of its finite element simulation. In the first stage, the nano-indentation experiment was performed on aluminum 1100 series by using Triboscope system and Berkovich indenter and the Young's modulus and hardness of the material were determined. In order to verify the results of nano-indentation experiment, the uniaxial tensile test was also performed on the same material and its Young's modulus was measured. Good agreement was found between the values of Young's modulus obtained from the two test methods. Then in the second stage, the nano-indentation process on aluminum 1100 was simulated by an axisymmetric finite element (FE) model. Using the same projected area to depth function as the standard Berkovich indenter, a conical rigid indenter with half-angle of 70.3 degrees was considered in the simulation. The results showed that the load-displacement curve obtained from the finite element simulation of non-sharp indenter was in very good agreement with that obtained from the nano-indentation experiment. Based on the load and displacement data obtained from the finite element simulation, the material hardness was also calculated. The difference between the hardness values obtained from the finite element simulation and the nano-indentation experiment was negligible.
Polymer matrix composites filled with carbon nanoparticles are promising materials for many appli... more Polymer matrix composites filled with carbon nanoparticles are promising materials for many applications, but their properties strongly depend on the particle features, concentration and distribution within the matrix. Here we present a study of the electrical resistivity and the low-frequency voltage fluctuation of composites based on epoxy resin filled with onion-like carbon (OLC) of different sizes (40–250 nm) above the percolation threshold, which should clarify the electrical transport characteristics in these materials. Electrical measurements were performed in the temperature range of 78 to 380 K, and voltage noise analysis was carried out from 10 Hz to 20 kHz. At low temperatures (below 250 K), thermally activated tunneling, variable-range hopping and generation–recombination of charge carriers take place. Above 250 K, the rapid expansion of the matrix with the temperature increases the resistivity, but above ~330 K, the conductivity of the matrix becomes significant. Quasi ...
The microwave-absorbing properties of a heterostructure consisting of an ordered monolayer of por... more The microwave-absorbing properties of a heterostructure consisting of an ordered monolayer of porous glassy carbon spheres were experimentally and theoretically investigated in the Ka-band (26–37 GHz) frequency range. The electromagnetic response of such a “moth-eye”-like all-carbon metasurface at a normal incidence angle was modelled on the basis of long-wave approximation. Modelling parameters in the Ka-band were used to estimate and predict the absorption properties of monolayers in free space in the range 1–40 GHz. Experimental and theoretical results demonstrate that a metasurface based on porous glassy carbon spheres is an inert, lightweight, compact, and perfectly absorbing material for designing new effective microwave absorbers in various practically used frequency ranges.
The electromagnetic shielding properties of thin films comprising different types of carbon nanot... more The electromagnetic shielding properties of thin films comprising different types of carbon nanotubes (CNTs) were analysed in the microwave frequency range (26–36 GHz). A comparative analysis of the shielding properties was achieved for films based on long and short single-, double- and multi-walled CNTs. The experimental results proved that long-length single-walled CNTs demonstrate the highest interaction with the electromagnetic (EM) field, thereby providing the best shielding efficiency. At the same time, double-walled CNTs demonstrate a higher level of absorption ability (50%) along with the overall high EM shielding efficiency (88%), which makes them attractive for using in nanoelectronics screens as they produce the smallest secondary EM pollution.
A charcoal prepared by pyrolyzing stones of awara, a nut from a common Guyanese palm tree, was ph... more A charcoal prepared by pyrolyzing stones of awara, a nut from a common Guyanese palm tree, was physically activated with water according to two different procedures. Either superheated steam (SHS) at 600, 700 or 800°C and atmospheric pressure, or supercritical water (SCW) at 600°C and 250 or 350 bar, was used. The main characteristics of the resultant activated carbons were
ABSTRACT Highly porous organic aerogels have been prepared for the first time from a mixed lignin... more ABSTRACT Highly porous organic aerogels have been prepared for the first time from a mixed lignin–phenol–formaldehyde (LPF) resin. Six different P/L weight ratios and two (L + P)/F weight ratios have been tested, leading most of times to nice and reproducible hydrogels which were subsequently either supercritically of freeze-dried. A broad family of aerogels and cryogels, respectively, was thus obtained. These materials were thoroughly investigated in terms of porous structure, based on pycnometry, adsorption and electron microscopy studies. The pore-size distributions were found to depend strongly on the initial composition, but not on the method of drying. The thermal conductivity of aerogels and cryogels has been measured and found to be minimal in materials combining both high mesopore volume and ideal pore sizes.
ABSTRACT The main purpose of this study is to investigate the nano-indentation test method and va... more ABSTRACT The main purpose of this study is to investigate the nano-indentation test method and validation of its finite element simulation. In the first stage, the nano-indentation experiment was performed on aluminum 1100 series by using Triboscope system and Berkovich indenter and the Young's modulus and hardness of the material were determined. In order to verify the results of nano-indentation experiment, the uniaxial tensile test was also performed on the same material and its Young's modulus was measured. Good agreement was found between the values of Young's modulus obtained from the two test methods. Then in the second stage, the nano-indentation process on aluminum 1100 was simulated by an axisymmetric finite element (FE) model. Using the same projected area to depth function as the standard Berkovich indenter, a conical rigid indenter with half-angle of 70.3 degrees was considered in the simulation. The results showed that the load-displacement curve obtained from the finite element simulation of non-sharp indenter was in very good agreement with that obtained from the nano-indentation experiment. Based on the load and displacement data obtained from the finite element simulation, the material hardness was also calculated. The difference between the hardness values obtained from the finite element simulation and the nano-indentation experiment was negligible.
Polymer matrix composites filled with carbon nanoparticles are promising materials for many appli... more Polymer matrix composites filled with carbon nanoparticles are promising materials for many applications, but their properties strongly depend on the particle features, concentration and distribution within the matrix. Here we present a study of the electrical resistivity and the low-frequency voltage fluctuation of composites based on epoxy resin filled with onion-like carbon (OLC) of different sizes (40–250 nm) above the percolation threshold, which should clarify the electrical transport characteristics in these materials. Electrical measurements were performed in the temperature range of 78 to 380 K, and voltage noise analysis was carried out from 10 Hz to 20 kHz. At low temperatures (below 250 K), thermally activated tunneling, variable-range hopping and generation–recombination of charge carriers take place. Above 250 K, the rapid expansion of the matrix with the temperature increases the resistivity, but above ~330 K, the conductivity of the matrix becomes significant. Quasi ...
The microwave-absorbing properties of a heterostructure consisting of an ordered monolayer of por... more The microwave-absorbing properties of a heterostructure consisting of an ordered monolayer of porous glassy carbon spheres were experimentally and theoretically investigated in the Ka-band (26–37 GHz) frequency range. The electromagnetic response of such a “moth-eye”-like all-carbon metasurface at a normal incidence angle was modelled on the basis of long-wave approximation. Modelling parameters in the Ka-band were used to estimate and predict the absorption properties of monolayers in free space in the range 1–40 GHz. Experimental and theoretical results demonstrate that a metasurface based on porous glassy carbon spheres is an inert, lightweight, compact, and perfectly absorbing material for designing new effective microwave absorbers in various practically used frequency ranges.
The electromagnetic shielding properties of thin films comprising different types of carbon nanot... more The electromagnetic shielding properties of thin films comprising different types of carbon nanotubes (CNTs) were analysed in the microwave frequency range (26–36 GHz). A comparative analysis of the shielding properties was achieved for films based on long and short single-, double- and multi-walled CNTs. The experimental results proved that long-length single-walled CNTs demonstrate the highest interaction with the electromagnetic (EM) field, thereby providing the best shielding efficiency. At the same time, double-walled CNTs demonstrate a higher level of absorption ability (50%) along with the overall high EM shielding efficiency (88%), which makes them attractive for using in nanoelectronics screens as they produce the smallest secondary EM pollution.
A charcoal prepared by pyrolyzing stones of awara, a nut from a common Guyanese palm tree, was ph... more A charcoal prepared by pyrolyzing stones of awara, a nut from a common Guyanese palm tree, was physically activated with water according to two different procedures. Either superheated steam (SHS) at 600, 700 or 800°C and atmospheric pressure, or supercritical water (SCW) at 600°C and 250 or 350 bar, was used. The main characteristics of the resultant activated carbons were
ABSTRACT Highly porous organic aerogels have been prepared for the first time from a mixed lignin... more ABSTRACT Highly porous organic aerogels have been prepared for the first time from a mixed lignin–phenol–formaldehyde (LPF) resin. Six different P/L weight ratios and two (L + P)/F weight ratios have been tested, leading most of times to nice and reproducible hydrogels which were subsequently either supercritically of freeze-dried. A broad family of aerogels and cryogels, respectively, was thus obtained. These materials were thoroughly investigated in terms of porous structure, based on pycnometry, adsorption and electron microscopy studies. The pore-size distributions were found to depend strongly on the initial composition, but not on the method of drying. The thermal conductivity of aerogels and cryogels has been measured and found to be minimal in materials combining both high mesopore volume and ideal pore sizes.
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