Chemical Composition Of Surface Films Research Articles

Investigation of the formation mechanism of the fluorocarbon film in CF4 plasma processing of fused silica

In this work, the formation mechanism of the fluorocarbon film in CF4 plasma etching of fused silica has been explored. The chemical characteristics of the film were analyzed by x-ray photoelectron spectroscopy (XPS). In addition, the formation mechanism of surface deposition film was analyzed based on the chemical composition of surface film and emitting species of CF4 plasma. The roles of gas-phase excited, especially F atoms and CF2 radicals, were examined by optical emission spectroscopy (OES) as they contribute to SiO2 etching and fluorocarbon film formation respectively. Moreover, the effect of addition O2 on chemical reactions were investigated, the OES measurement and XPS analysis were compared between CF4 and O2/CF4 plasma processed. And the optical transmittance with different O2/CF4 ratios was carried out by ultraviolet-visible-near infrared (UV–vis-NIR) spectrometer to confirm the effect of O2 on inhibition of fluorocarbon film.

Synergistic inhibition behavior of sodium tungstate and penicillin G as an eco-friendly inhibitor on pitting corrosion of 304 stainless steel in NaCl solution using Design of Experiment

In this study the synergistic behavior of sodium tungstate and penicillin G as an environmental-friendly co-inhibitor on pitting corrosion of 304 stainless steel in 3.5 wt% NaCl solution has been investigated. The simultaneous effect of temperature and inhibitor on inhibition efficiency has been evaluated by employing Design of Experiment technique according to Central Composite Design method. The temperature and concentration of inhibitors were selected as independent factors, while the extent of passive region and inhibition efficiency were considered as the responses of independent factors. Cyclic potentiodynamic polarization and electrochemical impedance spectroscopy were employed to determine the responses experimentally. The surface morphology and chemical composition of surface film were characterized by a Scanning Electron Microscope. The electrochemical measurements showed that increase in the concentration of penicillin G up to 50 ppm as co-inhibitor in the presence of 2.5 mM sodium tungstate resulted in the highest possible extent of passive region and inhibition efficiency. The increase in the extent of passive region and inhibition efficiency due to addition of penicillin G as co-inhibitor to sodium tungstate showed the synergistic behavior of the mixed inhibitors in controlling pitting corrosion of 304 stainless steel. It was revealed that the extent of passive region and inhibition efficiency decrease by increase in temperature of the solution due to increase in the kinetics of corrosion reactions and desorption of inhibitor from surface. The SEM observations indicated that the mixed inhibitors could provide a smooth and uniform surface due to formation of a protective film.

The Effect of Hydrogen on the Corrosion and Anodic Behavior of 13Cr Stainless Steel in Chloride Solution

Hydrogen evolution is one of the common cathodic reactions involved in corrosion of metals and alloys in aqueous solutions. The reduction of hydrogen ions is a source of atomic hydrogen on the surfaces of metals. Corrosion reactions, the application of cathodic protection and electroplating, etc., can introduce hydrogen into metals via diffusion. The presence of hydrogen in metals can have a significant influence on the mechanical properties and electrochemical behavior of metals depending on the environments. Stainless steels generally corrode at very low rates in high temperature aqueous environments because of their tendency to form a protective oxide film. Hydrogen is incorporated into the structural alloys during production, fabrication, processing, from in service conditions, and from the electrochemical reaction during corrosion. The transport of hydrogen through passive films is involved in many corrosion processes such as pitting, stress corrosion cracking and corrosion fatigue. The nature of passive films on metals and alloys is a decisive factor that controls their corrosion behavior. Mmuch work has been devoted to the study of the electronic properties and chemical composites of passive films on metals and alloys. Based on the fact that the potential-dependent transpassive dissolution varies with the electronic properties of the passive film, Sato proposed a breakdown mechanism of the passive film on metals, the electrochemical stability of a passive film strongly depends on the electron energy band structure in the film. Bianchiet al. concluded that the high susceptibility of stainless steel to pitting nucleation was connected to n-type conductivity of the oxide film. Cr-bearing stainless steels have been widely used in power generation systems and other industrial systems. The effects of hydrogen on the surface film and electrochemical behavior of 13Cr stainless steel in a chloride solution were investigated in the present work. Hydrogen was introduced into the samples by cathodic charging under galvanostatic condition at 25 oC in sulfuric acid solution with thiourea. The specimens were charged at a current density 2 mA/cm2 for 2 h. Electrochemical measurements were carried out on both uncharged and hydrogen charged specimens for evaluating their corrosion resistance. Potentiodynamic anodic polarization curves were carried out in 200 ppm wt.% NaCl solution at 25 oC, as shown in Figure. 1. Pre-charged hydrogen specimen showed a significantly lower open-circuit potential of about -0.67 V(SCE), and the non-charged specimen showed OCP of about -0.11V (SCE). Anodic current density in the anodic polarization curves of the hydrogen-charged specimen was significantly higher than that of the non-charged specimen. These results indicate that the corrosion resistance of 13Cr steel was significantly reduced by charged-hydrogen. Figure 2 show the electrochemical impedance spectra (EIS) for hydrogen-charged and non-charged specimens after different immersion periods in 200ppm wt.% NaCl solution at 25 oC. EIS diagrams of hydrogen-charged and non-charged specimens exhibited two parts: a capacitive loop in the high-frequency region and a capacitive loop in the low-frequency region. The second capacitive arc radius for the hydrogen-charged specimen was significantly less than that of the non-charged specimen. The scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) was used for the element and surface morphology analysis of the specimens after immersion tests in 200ppm wt.% NaCl solution at 25 oC for 68 h. Little corrosion product could be found on the non-charged specimen surface while more corrosion product appeared on the hydrogen-charged specimen surface, as shown in Fig. 3. Cr content in the film formed on hydrogen-charged specimen was lower than that on non-charged specimen, indicating the effect of hydrogen on the chemical composition of surface film. Figure 1

A facile electrodeposition process to fabricate corrosion-resistant superhydrophobic surface on carbon steel

Superhydrophobic Fe film with hierarchical micro/nano papillae structures is prepared on C45 steel surface by one-step electrochemical method. The superhydrophobic surface was measured with a water contact angle of 160.5±0.5° and a sliding angle of 2±0.5°. The morphology of the fabricated surface film was characterized by field emission scanning electron microscopy (FE-SEM), and the surface structure seems like accumulated hierarchical micro-nano scaled particles. Furthermore, according to the results of Fourier transform infrared spectra (FT-IR) and X-ray photoelectron spectroscopy (XPS), the chemical composition of surface film was iron complex with organic acid. Besides, the electrochemical measurements showed that the superhydrophobic surface improved the corrosion resistance of carbon steel in 3.5wt.% NaCl solution significantly. The superhydrophobic layer can perform as a barrier and provide a stable air–liquid interface which inhibit penetration of corrosive medium. In addition, the as-prepared steel exhibited an excellent self-cleaning ability that was not favor to the accumulation of contaminants.

Corrosion and passivation behavior of Mg–Zn–Y–Al alloys prepared by cooling rate-controlled solidification

Highly corrosion-resistant nanocrystalline Mg–Zn–Y–Al multi-phase alloys have been prepared by consolidation of rapidly solidified (RS) ribbons. The relation between corrosion behavior and microstructure evolution of Mg–Zn–Y–Al alloys with a long period stacking ordered phase has been investigated. In order to clarify the influence of rapid solidification on the occurrence of localized corrosion such as filiform corrosion, several Mg 96.75Zn 0.75Y 2Al 0.5 (at.%) alloys with different cooling rates are fabricated by the gravity casting, copper mould injection casting and melt-spinning techniques and their corrosion behavior and microstructures are examined by the salt water immersion test, electrochemical measurements, GDOES, XRD, SEM and TEM. To clarify the effect of aluminium addition on the improvement in corrosion resistance of the alloys, several Mg 97.25− x Zn 0.75Y 2Al x alloys with different aluminium contents are fabricated by consolidating RS ribbons and the formation of corroded films on the Mg–Zn–Y–Al alloys have been investigated. Rapid solidification brings about the grain refinement and an increase in the solid solubility of zinc, yttrium and aluminium into the magnesium matrix, enhancing microstructural and electrochemical homogeneity, which in turn enhanced corrosion resistance. The addition of aluminium to magnesium can modify the structure and chemical composition of surface films and improves the resistance to local breakdown of the films.

The relationship between building characteristics and the chemical composition of surface films found on glass windows in Brisbane, Australia

Films found on the windows of residential buildings have been studied. The main aim of the paper was to assess the roles of the films in the accumulation of potentially toxic chemicals in residential buildings. Thus the elemental and polycyclic aromatic hydrocarbon compositions of the surface films from the glass windows of eighteen residential buildings were examined. The presence of sample amounts of inorganic elements (4.0–1.2 × 10 6 μg m −2) and polycyclic aromatic hydrocarbons in the films (BDL - 620.1 ng m −2) has implications for human exposure and the fate of pollutants in the urban environment. To facilitate the interpretation of the results, data matrices consisting of the chemical composition of the films and the building characteristics were subjected to multivariate data analysis methods, and these revealed that the accumulation of the chemicals was strongly dependent on building characteristics such as the type of glass used for the window, the distance from a major road, age of the building, distance from an industrial activity, number of smokers in the building and frequency of cooking in the buildings. Thus, building characteristics which minimize the accumulation of pollutants on the surface films need to be encouraged.

Chemical composition of surface films on glass windows and implications for atmospheric chemistry

Atmospherically derived surface films that cover impervious surfaces in cities, have areas comparable to that of atmospheric particulate matter (PM). The films compete with PM for sorption of volatile and semi-volatile organic compounds and alter the functionality of urban surfaces. The determination of surface-film composition is therefore vital to understanding their role in mediating chemical fate and transport within cities. Here, we show the composition of urban surface films collected from windows in downtown Toronto (Ontario, Canada) to be comprised of ∼94% inorganic compounds of which 8% are sulfate, 7% nitrate and 18% metals. Approximately 5% of the urban film mass is organic carbon, with ∼35% of the organic carbon mass corresponding to carbohydrates, ∼35% aliphatics, ∼20% aromatics and ∼10% carbonyls. The composition of surface films differs significantly from that of PM, suggesting differential accumulation, depositional degradation, and/or processes within films differing from those affecting PM. A rigid polymeric component comprising a small fraction of the organic carbon was also found, which may suggest direct deposition from environmental sources, or possible secondary in situ reactions within the film. Here, we suggest a potential mechanism for the oxidation of surface films to form organic polymers via radical initiation processes. Thus, the composition of surface films has important implications for chemical fate of contaminants within cities and presents a significant aspect of contaminant uptake that has not been considered in many air-quality models.

Composition and thermal stability of thin native oxides on InP

The chemical composition of surface films formed on air exposed bromine/methanol etched InP were investigated in both the ’’as etched’’ condition and after in situ heat treatment. Both UPS and XPS spectra were obtained in order to probe at two different depths into the surface (≊5 and 15 Å, respectively). The as etched surface appears to be composed primarily of In2O3 with a small concentration of a phosphate compound, presumably either InPO4 or H3PO4. Prolonged exposure to water or water vapor causes additional film growth. The new growth increases the phosphate concentration and an In compound which, by the location the In3d5/2 peak at 445.6 eV, indicates either InPO4 or In(OH)3. Heating the as etched surface in situ also causes film growth. The phosphate is found to evaporate from the outer surface of the film but to grow underneath the In2O3 skin as the substrate is heated. It is suspected that excessive H2O on CO background in the vacuum chamber caused a rapid oxidation of the surface as the sample was heated.

Chemical composition of surface film in the coastal sea area and in freshwater lakes.

Chemical composition of surface film were studied in the coastal waters and in freshwater lakes. In the coastal sea areas, considerable concentrations of particulate and dissolved organic carbon and nitrogen as well as dissolved inorganic nitrogen and phosphorus were observed in the surface film relative to 1m layer. Our results suggest the presence of “surface film” in freshwater lakes as well. The concentration was, however, more conspicuous in oligotrophic lakes and was not evident in eutrophic lakes. Urea in remarkable concentrations was found in the surface film of both the coastal waters and freshwater lakes.

On the chemical composition of surface films produced on germanium in different etchants

Measurements of the infrared absorption of surface films have been performed, using the technique of attenuated total reflection. These films have been produced in different etchants, and their thicknesses amounted to several hundred ångströms. It is shown that the films produced in HF/HNO 3 consist mainly of amorphous germanium dioxide, while those prepared in HF/H 2O 2 have the approximate chemical composition GeOH 2.