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Environmental pollution, caused by traditional plastic packaging, has recently become more severe due to non-biodegradable nature of petroleum-based plastics. The present research studies the preparation of polyvinyl alcohol (PVOH)/Starch (ST)/Humic Acid (HA) contained sodium montmorillonite clay (MMT) as a plastic packaging method. It also investigates biodegradability of films in terms of microbial and thermal degradation and their residual effect on plant growth. For doing so, the research utilizes Broido Technique to obtain the activation energy of the films' thermal degradation. The influence of HA/MMT ratio on the surface morphology and physical characteristics has also been assessed, using the Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscope (SEM), and thermogravimetric analysis (TA). After 12 days of microbial degradation, the total remaining solids are 32.12 wt% (PVOH/ST/HA (3%)/MMT (1%)); 48.17 wt% (PVOH/ST/HA (3%)/MMT (3%)), and 58.82 wt% (PVOH/ST/HA (1%)/MMT (3%)). The research shows that the highest activation energy for PVOH/ST/HA (3%)/MMT (3%) is 75 kJ/mol. [ABSTRACT FROM AUTHOR]

Electrochemical noise (EN) can be used in situ to investigate corrosion processes and to detect and monitor the corrosion of metallic materials. EN data are largely influenced by the measurement mode, the surface area of the working electrodes, the electrolyte resistance, and the symmetry of the electrode system. Herein, the advantages and limitations of electrochemical kinetics, equivalent circuit, and shot noise methods for quantifying corrosion rates with EN are discussed. [ABSTRACT FROM AUTHOR]

Electrochemical probes and sensors have been developed to detect andmonitor atmospheric corrosion of metallic materials in the past 40 decades. Depending on the measurement methods, the electrodes and structures of probes and sensors can be different. Various mathematical methods andmodels have been developed to determine the time-dependent corrosion rate of metal under thin electrolyte film. Polarization techniques such as electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LRP) have the advantage of easy data interpretation but have a tendency to interfere with the corrosion system under investigation. Nonpolarized techniques such as electrochemical noise (EN) do not disturb the corrosion system but data interpretation can be problematic. To achieve long term and reliable corrosion monitoring, optimized electrode design and a multichannel electrochemical instrument are required. New corrosion models and novel data interpretation methods are needed in future work. [ABSTRACT FROM AUTHOR]

Passivity film breakdown on steam generator (SG) tubing alloys in Cl- + S2O32- solutions were investigated using a focused ion beam (FIB) and high resolution transmission electron microscopy (HRTEM), and a correlation between passivity film breakdown and film composition was established. Sulfur was not incorporated into the passive film that formed on the alloy. S2O32- adsorbed on the passive film surface was subsequently electrochemically reduced caused by SG alloy, leading to selective dissolution of Ni from the passive film. Fe, Ni, and Cr in the passive film have complex effects on corrosion resistance, which is highly dependent on temperature, and the Cl-/S2O32- concentration ratio. [ABSTRACT FROM AUTHOR]

The work presented in this review paper is part of a project to investigate corrosion degradation of steam generator (SG) tubing and tube support materials by sulfur compounds at reduced or intermediate oxidation levels (designated here as Sx). The stability of these Sx species in aqueous solutions is discussed, and the electrochemical and chemical interactions between Sx and metallic surfaces and the subsequent impact of these interactions on metal corrosion are reviewed. Factors influencing Sx-induced uniform corrosion, passivity breakdown and stress corrosion cracking (SCC) considered here include: pH, electrode potential, temperature, Sx species, alloy compositions and other impurity ions like Cl-. [ABSTRACT FROM AUTHOR]

The growth rate of pits formed on Alloy 800 in chloride solutions containing various thiosulphate concentrations was assessed by potentiostatic polarisation, in situ corrosion image observation, and image analysis. The pitting growth rate was a function of solution chemistry: in chloride solution pits were small but numerous, in chloride + thiosulphate solution, the pits were large. Competitive adsorption on Alloy 800 of chloride and thiosulphate ions affected the pitting potential and therefore the pitting growth rate on the metal. The reduction of thiosulphate to elemental sulphur accelerated the pitting growth rate in chloride + thiosulphate solutions. [ABSTRACT FROM AUTHOR]

Oxidation behavior of alloy 316L stainless steel static capsules were investigated by long-term exposure to the supercritical water at 500 °C and 25 MPa for various exposure times. It was found that the thickness and weight gain vs. exposure time followed parabolic law. Elemental and phase analyses indicated that long-term exposure to the SCW resulted in formation of scales identified as Fe 3 O 4 (outer layer), Mn-Fe-Ni-Cr spinel (inner layer) on the substrate, and Ni-enrichment (chrome depleted region) in the alloy 316L. Oxidation phenomena and scales grown on the Alloy 316L as the result of long term exposure to the supercritical water was discussed. [ABSTRACT FROM AUTHOR]

Corrosion behavior of alloy 316L stainless steel capsule was studied by exposure to the supercritical water (SCW) at 500 °C and 25 MPa for 20,000 h. The microstructural observations have been conducted on the cross section of the exposed surfaces to the SCW to perceive the internal oxidation of the grains and/or grain boundaries. Transmission electron microscopy (TEM) observations as well as elemental analyses such as energy dispersive spectroscopy (EDS) and Electron energy loss spectroscopy (EELS) were used to study the internal oxidation and micro-crack initiation on the surface. Elemental analyses indicated that long-term exposure to the SCW resulted in formation of scales identified as Fe 3 O 4 (outer layer), Fe-Cr spinel/(Fe,Ni)Cr 2 O 4 /(Mn,Cr) 2 O 3 /SiO 2 (inner layer) on the substrate, and Ni-enrichment (chrome depleted region) in the alloy 316L. Micro-crack initiation was observed ahead of the oxidized grain boundaries in which elemental enrichments happened ahead of the crack tip. The relevance of the observed oxidation phenomena on the crack susceptibility of Alloy 316L was discussed. Finally, prolonging the exposure time up to 20,000 h has shown that the alloy 316L might be susceptible to micro-crack initiation in the supercritical water. [ABSTRACT FROM AUTHOR]

The early stage atmospheric corrosion of T91 and Q235B steels exposed to Tianjin’s urban atmosphere over 20 days was studied using two electrochemical probes via an electrochemical noise (EN) technique. To identify the corrosion process and the corrosion form of the two steels, EN data were analysed by statistics and wavelet transform. The results revealed that the wavelet energy of decomposed EN mainly located at high-frequency level for Q235B steel, whereas it mainly located at the low-frequency level for T91 steel. Analyses of surface images confirmed that Q235B steel underwent uniform corrosion whereas T91 steel suffered from localised corrosion. The obtained noise resistance correlated well with weight loss data. [ABSTRACT FROM AUTHOR]

We study oxidation and crack susceptibility of alloy 310S stainless steel upon exposure to supercritical water (SCW) at 500 °C and 25 MPa for 20000 h. Electron microscopy observations and elemental analyses are conducted on the static capsule sample to investigate morphological features of the oxidation, micro-crack initiation as well as chemical composition along the micro-crack surface oxides and corrosion products around the micro-crack tip area. The elemental and phase analyses indicate that long term exposure to the SCW resulted in the formation of scales identified as Fe 3 O 4 (magnetite, outer layer), Fe-Cr spinel (FeCr 2 O 4 , inner layer), [Mn,Cr] 2 O 3 + SiO 2 (Cr-rich spinel and silicon dioxide, transition layer) on the substrate, and Ni-enrichment (chrome depleted region) in the alloy 310S. The presence of carbides along with chromium depletion region most probably result in grain boundary embrittlement around the micro-crack tip. Additionally, crack region is filled Cr-rich oxide, SiO 2 and lower amount of carbides. We believe that the intergranular crack initiation occurred through grain boundary oxidation, leading to stress concentration. The oxidation mechanism and scales grown on the alloy 310S stainless steel exposed to SCW and micro-crack initiation as the results of long term exposure at high temperature SCW are discussed. [ABSTRACT FROM AUTHOR]

This study concentrated on the investigation of oxide scale grown on alloys 304 and 304-oxide dispersion strengthened steel in supercritical water (650 °C/25 MPa) environment. The corrosion rate was evaluated by measuring the weight change of the samples and by cross-section examinations. Results showed that weight gains vs. supercritical exposure time follows a parabolic law for alloy 304-ODS contrary to alloy 304 which possibly follows a cubic rate law. The general weight gain after 550 h exposure to the SCW was 131.8 and 621.6 mg/dm 2 for alloys 304-ODS and 304, respectively. Electron microscopy observations and elemental analyses as well as X-ray diffraction and time-of-flight secondary ion mass spectrometry results revealed that the oxide scales formed on 304-ODS alloy composed of three distinct layers including Fe 3 O 4 (outer layer), FeCr 2 O 4 /(Fe,Cr) 2 O 3 spinel structures (inner layer) and Cr 2 O 3 (transition layer). However, alloy 304 had two layers including Fe 3 O 4 (outer layer) and Fe-Cr spinel structures (inner layer). It is believed that the formation of Cr 2 O 3 layer at the diffusion layer/metal interface becomes the rate-limiting step for oxide advancement, since this change in oxide structure also corresponds to a decrease in corrosion rate in the alloy 304-ODS compared to alloy 304. Based on the results and observations, the oxidation mechanisms are discussed. [ABSTRACT FROM AUTHOR]

This study investigates the oxidation behavior of several stainless steels and nickel-based superalloys exposed to supercritical water at 800 °C for 12 h. Characterization of the resulting oxide layers were conducted using weight change measurements, X-ray diffraction, scanning/transmission electron microscopy, and energy dispersive spectroscopy. Although the exposure time is only 12 h, the thickness of the oxide layers formed was as high as 1 μm, comprising different spinel structures. The influence of alloying elements such as Al, Nb, Mo, Mn and Ti on the corrosion behavior is investigated and possible corrosion mechanisms for each candidate alloy are discussed. [ABSTRACT FROM AUTHOR]

In the current study, a sol-gel-synthesized tricalcium magnesium silicate powder was coated on Ti-6Al-4V alloys using plasma spray method. Composition of feed powder was evaluated by X-ray diffraction technique before and after the coating process. Scanning electron microscopy and atomic force microscopy were used to study the morphology of coated substrates. The corrosion behaviors of bare and coated Ti-6Al-4V alloys were examined using potentiodynamic polarization test and electrochemical impedance spectroscopy in stimulated body fluids. Moreover, bare and coated Ti-6Al-4V alloys were characterized in vitro by culturing osteoblast and mesenchymal stem cells for several days. Results demonstrated a meaningful improvement in the corrosion resistance of Ti-6Al-4V alloys coated with tricalcium magnesium silicate compared with the bare counterparts, by showing a decrease in corrosion current density from 1.84 μA/cm2 to 0.31 μA/cm2. Furthermore, the coating substantially improved the bioactivity of Ti-6Al-4Valloys. Our study on corrosion behavior and biological response of Ti-6Al-4V alloy coated by tricalcium magnesium silicate proved that the coating has considerably enhanced safety and applicability of Ti-6Al-4V alloys, suggesting its potential use in permanent implants and artificial joints. [ABSTRACT FROM AUTHOR]

Semiconductive properties of the passive films formed on Alloy 800 in 0.1 M chloride solutions containing various concentrations of thiosulfate are investigated using Mott-Schottky analysis. The results indicate that when the concentration of the thiosulfate ions increases, the semiconductivity is converted from the n-type to the p-type. This conversion is postulated to be due to the incorporation of sulfur into the passive film, which changes the vacancy type. The breakdown behavior of the passive films is correlated with the semiconductivity of the film in this system. [ABSTRACT FROM AUTHOR]