HDPE films were treated in the post-discharge region of N2/O2 plasma, powered by a radio frequenc... more HDPE films were treated in the post-discharge region of N2/O2 plasma, powered by a radio frequency power supply. Therefore, in this paper, it was investigated the role of pressure in molding the nano-topography of the polymer. The treatment was carried out in low temperature (T <40 ° C) and time of 5.0 min, in order to preserve the integrity of the polymer bulk. It is well known that the production and recombination rate of reactive species in the plasma depends on the working gas pressure. Results show that the surface nano-roughness is very sensitive to pressure, between 0.01Torr and 0.5Torr, making it possible to use as a fine control parameter for polymer nano-texturing. In the lower pressure treatment it was observed regular nano-peaks and nano-troughs on the surface of the sample. Contact angle measurements show that, in general, the surface becomes hydrophilic after N2/O2 plasma treatment. In addition, samples treated in higher pressure generate oxidized islands by the act...
Energy dispersive spectroscopy (EDS) experiments were carried out in the scanning electron micros... more Energy dispersive spectroscopy (EDS) experiments were carried out in the scanning electron microscope (SEM) on top of either stainless steel (SS), silicon or glass substrates covered with TiN nitride coatings. The nominal coating thicknesses were 0.43, 1.1, 2.1 and 3.0 μm. From the EDS spectra obtained, the ratio between the strongest peak coming from the substrate and the Tik peak, from the coating, was assessed at an increasing microscope accelerating voltage (V0) between 10 and 30 kV. This ratio is afterward called Intensity-ratio (IR). A methodology was developed for assessing the coating thickness from the experimental IR and the V0 by using Monte Carlo simulations of the dispersion of electrons inside the covered samples and the concomitant emission of characteristic X-ray photons. Three freeware Monte Carlo graphical user interfaces were used, and the predicted thicknesses were compared between them, namely Casino, MC-Xray and DTSA. At fixed V0, numerical simulations predict a mono-valued and smooth relationship between IR and coating thickness. Monte Carlo predictions on the coating thickness were compared with reference thicknesses independently assessed by cross-sectional micrographs obtained in the SEM. Absolute value of percentage discrepancy between the predicted and the reference thicknesses was lower than 30 %, wherein the lower the V0, the less accurate the predicted thickness. In general, none of the three pieces of software compared outperformed the others, although predicted thicknesses significantly varied between them. For V0 higher than 20 kV, 90 % of predicted thicknesses deviated less than 15 % from the reference value. Predicted thicknesses for TiN coatings onto Si substrates presented the largest discrepancy regarding reference values.
Mechanical systems being designed nowadays operate in ever more severe conditions, sustaining hig... more Mechanical systems being designed nowadays operate in ever more severe conditions, sustaining high applied loads, higher temperatures, greater sliding speeds and much more severe environments. The combination of usually con icting properties is required in order to achieve higher productivity, high power ef ciency, low energy consumption, and low levels of emissions. The design of these mechanical systems involves the combination of properties such as low friction, high wear resistance, high load bearing capacity, and fatigue resistance. When subjected to high intensity loading, a thin coating may collapse, mainly due to substrate elastic and plastic deformation, resulting in premature failure of the coating. For many applications the performance of a coating is limited by the mechanical properties of the substrate material itself. Thin lms require a mechanical support given by the substrate material to avoid the so called ‘eggshell effect’, granting good adhesion to the hard coatin...
This contribution presents a theoretical discussion on phase hierarchy stability between face-cen... more This contribution presents a theoretical discussion on phase hierarchy stability between face-centered cubic (FCC), austenite, and body-centered cubic (BCC), ferrite, lattice structures of stainless steel (SS) films that are sputter-deposited from austenitic targets under non-reactive atmospheres. Data published in literature on both phase characterization and chemical composition of diverse SS films are interpreted anew in this contribution in the light of lattice stability thermodynamic simulations. For films obtained from 304 and 316 steel targets, thermodynamic simulations predict that the ferrite phase is more stable than the austenite phase at low thermal energies. In contrast, simulations forecast thermodynamic stability at low thermal energies of the austenite phase in films that are sputtered from 330 steel targets. The criterion of lattice stability reveals that structures observed in the experiments cannot be described comprehensively by thermodynamic states where either ...
An active screen plasma system (ASPS) was used for the surface activation of poly(lactic acid) (P... more An active screen plasma system (ASPS) was used for the surface activation of poly(lactic acid) (PLA) as a pretreatment before the oxidative graft polymerization of polyaniline (PANI). In ASPS, the plasma glow discharge occurs outside the grid, and the samples to be treated are placed inside the cage where they are subjected to a floating potential (about −12 V). An increase in hydrophilicity was observed for all samples after Ar plasma treatment. In addition, a decrease in thermal stability and changes in crystallization behavior were observed for PLA samples treated for a longer time. After PANI graft polymerization, smoothing of the surface topography was noticed in samples treated for short time periods. Such a change in the topography, in addition to surface activation, provides better conditions for subsequent PANI grafting.
RESUMO O processo de recobrimento por pulverização catódica é uma técnica amplamente utilizada pa... more RESUMO O processo de recobrimento por pulverização catódica é uma técnica amplamente utilizada para produção de revestimentos metálicos e cerâmicos, devido a versatilidade no controle das propriedades com pequenas mudanças nos parâmetros de processo, como densidade de potência aplica ao cátodo magnetron e atmosfera de trabalho. Sendo assim, as propriedades mecânicas dos filmes que estão altamente relacionadas à estrutura cristalina e composição química podem ser controladas, tornando o processo viável para aplicações nas mais diversas áreas. Utilizando-se um alvo de aço inoxidável AISI 316 foram depositados filmes com quatro valores diferentes de densidade de potência aplicada ao cátodo e com três porcentagens diferentes de N2 na atmosfera de deposição. O objetivo é determinar a influência destes parâmetros na estabilização das fases alfa e gama com estrutura cristalina cúbica de corpo centrado (CCC) e cúbica de face centrada (CFC), respectivamente. Os filmes obtidos foram caracteri...
In this study, films of graphene oxide and chemically or thermally reduced graphene oxide were pr... more In this study, films of graphene oxide and chemically or thermally reduced graphene oxide were produced by a simple vacuum filtration method and submitted to a thorough characterization by X-ray diffraction (XRD), Raman and infrared spectroscopies, field-emission scanning electron microscopy, transmission electron microscopy, atomic force microscopy, confocal microscopy, and contact angle measurements. Graphene oxide (GO) was produced from graphite by the modified Hummers method and thereafter reduced with NaBH4 or by heating under argon in a tubular furnace. The films were produced from aqueous solutions by vacuum filtration on a cellulose membrane. Graphite presents two characteristic XRD peaks corresponding to d=0.34 nm and d=0.17 nm. After oxidation, only a peak at d=0.84 nm is found for powder GO, confirming the insertion of oxygen groups with an increase in the interplanar distance of graphene nanoplatelets. However, for GO films, other unexpected peaks are observed at d=0.63 ...
RESUMO Filmes de polietileno de alta densidade (PEAD) foram tratados por plasma radiofrequência (... more RESUMO Filmes de polietileno de alta densidade (PEAD) foram tratados por plasma radiofrequência (RF) de N2/O2. Foi investigado o efeito da pressão do gás de trabalho N2/O2, do plasma, na texturização superficial do filme. O plasma gerado em baixa potência (20W) permite manter a amostra em baixa temperatura (T<40°C) durante o tratamento de superfície. Os resultados mostram que a rugosidade superficial, em escala nanométrica, é muito sensível à pressão do gás de trabalho, entre 0,01Torr e 0,5Torr. Quando o material é tratado em pressão mais baixa (0,01Torr), observa-se a formação de uma estrutura superficial nanométrica de vales e picos com elevada regularidade. Por outro lado, quando o tratamento é feito em pressão mais alta (0,5 Torr), observa-se a formação de uma textura mais grossa na superfície da amostra, além da formação de ilhas de moléculas oxidadas. Em todos as condições estudadas, as amostras tornaram-se hidrofílicas após o tratamento por plasma, mantendo a característic...
HDPE films were treated in the post-discharge region of N2/O2 plasma, powered by a radio frequenc... more HDPE films were treated in the post-discharge region of N2/O2 plasma, powered by a radio frequency power supply. Therefore, in this paper, it was investigated the role of pressure in molding the nano-topography of the polymer. The treatment was carried out in low temperature (T <40 ° C) and time of 5.0 min, in order to preserve the integrity of the polymer bulk. It is well known that the production and recombination rate of reactive species in the plasma depends on the working gas pressure. Results show that the surface nano-roughness is very sensitive to pressure, between 0.01Torr and 0.5Torr, making it possible to use as a fine control parameter for polymer nano-texturing. In the lower pressure treatment it was observed regular nano-peaks and nano-troughs on the surface of the sample. Contact angle measurements show that, in general, the surface becomes hydrophilic after N2/O2 plasma treatment. In addition, samples treated in higher pressure generate oxidized islands by the act...
Energy dispersive spectroscopy (EDS) experiments were carried out in the scanning electron micros... more Energy dispersive spectroscopy (EDS) experiments were carried out in the scanning electron microscope (SEM) on top of either stainless steel (SS), silicon or glass substrates covered with TiN nitride coatings. The nominal coating thicknesses were 0.43, 1.1, 2.1 and 3.0 μm. From the EDS spectra obtained, the ratio between the strongest peak coming from the substrate and the Tik peak, from the coating, was assessed at an increasing microscope accelerating voltage (V0) between 10 and 30 kV. This ratio is afterward called Intensity-ratio (IR). A methodology was developed for assessing the coating thickness from the experimental IR and the V0 by using Monte Carlo simulations of the dispersion of electrons inside the covered samples and the concomitant emission of characteristic X-ray photons. Three freeware Monte Carlo graphical user interfaces were used, and the predicted thicknesses were compared between them, namely Casino, MC-Xray and DTSA. At fixed V0, numerical simulations predict a mono-valued and smooth relationship between IR and coating thickness. Monte Carlo predictions on the coating thickness were compared with reference thicknesses independently assessed by cross-sectional micrographs obtained in the SEM. Absolute value of percentage discrepancy between the predicted and the reference thicknesses was lower than 30 %, wherein the lower the V0, the less accurate the predicted thickness. In general, none of the three pieces of software compared outperformed the others, although predicted thicknesses significantly varied between them. For V0 higher than 20 kV, 90 % of predicted thicknesses deviated less than 15 % from the reference value. Predicted thicknesses for TiN coatings onto Si substrates presented the largest discrepancy regarding reference values.
Mechanical systems being designed nowadays operate in ever more severe conditions, sustaining hig... more Mechanical systems being designed nowadays operate in ever more severe conditions, sustaining high applied loads, higher temperatures, greater sliding speeds and much more severe environments. The combination of usually con icting properties is required in order to achieve higher productivity, high power ef ciency, low energy consumption, and low levels of emissions. The design of these mechanical systems involves the combination of properties such as low friction, high wear resistance, high load bearing capacity, and fatigue resistance. When subjected to high intensity loading, a thin coating may collapse, mainly due to substrate elastic and plastic deformation, resulting in premature failure of the coating. For many applications the performance of a coating is limited by the mechanical properties of the substrate material itself. Thin lms require a mechanical support given by the substrate material to avoid the so called ‘eggshell effect’, granting good adhesion to the hard coatin...
This contribution presents a theoretical discussion on phase hierarchy stability between face-cen... more This contribution presents a theoretical discussion on phase hierarchy stability between face-centered cubic (FCC), austenite, and body-centered cubic (BCC), ferrite, lattice structures of stainless steel (SS) films that are sputter-deposited from austenitic targets under non-reactive atmospheres. Data published in literature on both phase characterization and chemical composition of diverse SS films are interpreted anew in this contribution in the light of lattice stability thermodynamic simulations. For films obtained from 304 and 316 steel targets, thermodynamic simulations predict that the ferrite phase is more stable than the austenite phase at low thermal energies. In contrast, simulations forecast thermodynamic stability at low thermal energies of the austenite phase in films that are sputtered from 330 steel targets. The criterion of lattice stability reveals that structures observed in the experiments cannot be described comprehensively by thermodynamic states where either ...
An active screen plasma system (ASPS) was used for the surface activation of poly(lactic acid) (P... more An active screen plasma system (ASPS) was used for the surface activation of poly(lactic acid) (PLA) as a pretreatment before the oxidative graft polymerization of polyaniline (PANI). In ASPS, the plasma glow discharge occurs outside the grid, and the samples to be treated are placed inside the cage where they are subjected to a floating potential (about −12 V). An increase in hydrophilicity was observed for all samples after Ar plasma treatment. In addition, a decrease in thermal stability and changes in crystallization behavior were observed for PLA samples treated for a longer time. After PANI graft polymerization, smoothing of the surface topography was noticed in samples treated for short time periods. Such a change in the topography, in addition to surface activation, provides better conditions for subsequent PANI grafting.
RESUMO O processo de recobrimento por pulverização catódica é uma técnica amplamente utilizada pa... more RESUMO O processo de recobrimento por pulverização catódica é uma técnica amplamente utilizada para produção de revestimentos metálicos e cerâmicos, devido a versatilidade no controle das propriedades com pequenas mudanças nos parâmetros de processo, como densidade de potência aplica ao cátodo magnetron e atmosfera de trabalho. Sendo assim, as propriedades mecânicas dos filmes que estão altamente relacionadas à estrutura cristalina e composição química podem ser controladas, tornando o processo viável para aplicações nas mais diversas áreas. Utilizando-se um alvo de aço inoxidável AISI 316 foram depositados filmes com quatro valores diferentes de densidade de potência aplicada ao cátodo e com três porcentagens diferentes de N2 na atmosfera de deposição. O objetivo é determinar a influência destes parâmetros na estabilização das fases alfa e gama com estrutura cristalina cúbica de corpo centrado (CCC) e cúbica de face centrada (CFC), respectivamente. Os filmes obtidos foram caracteri...
In this study, films of graphene oxide and chemically or thermally reduced graphene oxide were pr... more In this study, films of graphene oxide and chemically or thermally reduced graphene oxide were produced by a simple vacuum filtration method and submitted to a thorough characterization by X-ray diffraction (XRD), Raman and infrared spectroscopies, field-emission scanning electron microscopy, transmission electron microscopy, atomic force microscopy, confocal microscopy, and contact angle measurements. Graphene oxide (GO) was produced from graphite by the modified Hummers method and thereafter reduced with NaBH4 or by heating under argon in a tubular furnace. The films were produced from aqueous solutions by vacuum filtration on a cellulose membrane. Graphite presents two characteristic XRD peaks corresponding to d=0.34 nm and d=0.17 nm. After oxidation, only a peak at d=0.84 nm is found for powder GO, confirming the insertion of oxygen groups with an increase in the interplanar distance of graphene nanoplatelets. However, for GO films, other unexpected peaks are observed at d=0.63 ...
RESUMO Filmes de polietileno de alta densidade (PEAD) foram tratados por plasma radiofrequência (... more RESUMO Filmes de polietileno de alta densidade (PEAD) foram tratados por plasma radiofrequência (RF) de N2/O2. Foi investigado o efeito da pressão do gás de trabalho N2/O2, do plasma, na texturização superficial do filme. O plasma gerado em baixa potência (20W) permite manter a amostra em baixa temperatura (T<40°C) durante o tratamento de superfície. Os resultados mostram que a rugosidade superficial, em escala nanométrica, é muito sensível à pressão do gás de trabalho, entre 0,01Torr e 0,5Torr. Quando o material é tratado em pressão mais baixa (0,01Torr), observa-se a formação de uma estrutura superficial nanométrica de vales e picos com elevada regularidade. Por outro lado, quando o tratamento é feito em pressão mais alta (0,5 Torr), observa-se a formação de uma textura mais grossa na superfície da amostra, além da formação de ilhas de moléculas oxidadas. Em todos as condições estudadas, as amostras tornaram-se hidrofílicas após o tratamento por plasma, mantendo a característic...
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