Roles of precipitates on corrosion fatigue crack growth of high-strength steels in corrosive environments

The effect of microstructures on resistance to corrosion fatigue cracking and fracture surface morphology for age-hardened steels were investigated in a 3.5% NaCl aqueous solution under a cathodic potential of –0.85 V (Ag/AgCl). The free corrosion was about –0.63 V (Ag/AgCl). The resistance to corrosion fatigue cracking of materials containing coherent precipitates in the matrix (underaged conditions) was less than that of materials containing incoherent precipitates (reheated conditions) at equal strength levels. Accelerated fatigue crack growth rates of the underaged material in the aqueous solution were followed by cracking along prior-austenite grain boundaries, due to hydrogen embrittlement, while the overaged material did not show accelerated fatigue crack growth rates and had fracture surfaces similar to those in air. The difference in the fracture surfaces of both materials in air and in the aqueous solution was considered to depend on the ease of diffusion of hydrogen to the prior-austenite grain boundaries. It is concluded that incoherent precipitates in the matrix made hydrogen accumulation at prior-austenite grain boundaries much slower than for coherent precipitates.     

Evaluation of the stress corrosion cracking behaviour of damage-tolerant Al---Li sheet using the slow strain rate testing technique

Slow strain rate tests were performed on longitudinal tensile specimens of 8090-T81 sheet under permanent immersion conditions in various synthetic environments. Strain rates were in the range 10⁻⁷−10⁻⁴ s⁻¹. Environmentally assisted cracking is observed in aqueous chloride-carbonate-hydrogencarbonate solutions. Near neutral 3.5% NaCl solution and also 3% NaCl solution with hydrogen peroxide added do not promote stress corrosion cracking with 8090-T81 alloy sheet. The degradation of ductility found with tensile specimens immersed in the latter corrosive environments is caused by localized corrosion independent of stress. Fracture energy data obtained from slow strain rate tests in substitute ocean water reveal a large scatter. Again, the deterioration observed is not related to stress corrosion cracking. Slow strain rate tests were also carried out with longitudinal tensile specimens of 2091-T8X and 2091 CPHK-T8X alloy sheet using an aqueous solution of 3% NaCl + 0.3% H₂O₂. For the alloy 2091 CPHK-T8X, similar results were obtained to those with 8090-T81, whereas 2091-T8X sheet is prone to environment-induced cracking in the aqueous chloride-peroxide solution.     

Application of mid-infrared spectroscopy: measuring hydrogen peroxide concentrations in bleaching baths

The presented work applies mid-infrared attenuated total reflection (ATR) spectroscopy to the measurment of hydrogen peroxide in aqueous matrices. The performance of different ATR crystals mounted in flow cells was investigated in the presence of aqueous hydrogen peroxide solutions. Quantitative determination has been achieved by evaluation of specific OH stretching and deformation vibrations with linear correlation between peak areas or peak heights and hydrogen peroxide concentration in the range of 1-10% (weight in water). Important aspects such as chemical stability of the waveguide material and influences of pH and ionic strength on the performance are discussed. Feasibility for the investigation of real world samples is demonstrated by measuring industrial bleaching solutions with known concentrations of hydrogen peroxide fitting well with calibration graphs established with neat hydrogen peroxide solutions. The presented sensor system is capable of determining hydrogen peroxide within complex matrices and clearly corroborates the potential of providing an in situ measurement concept for on-line hydrogen peroxide detection.     

Generating nonlinear concentration gradients in microfluidic devices for cell studies

We describe a microfluidic device for generating nonlinear (exponential and sigmoidal) concentration gradients, coupled with a microwell array for cell storage and analysis. The device has two inputs for coflowing multiple aqueous solutions, a main coflow channel and an asymmetrical grid of fluidic channels that allows the two solutions to combine at intersection points without fully mixing. Due to this asymmetry and diffusion of the two species in the coflow channel, varying amounts of the two solutions enter each fluidic path. This induces exponential and sigmoidal concentration gradients at low and high flow rates, respectively, making the microfluidic device versatile. A key feature of this design is that it is space-saving, as it does not require multiplexing or a separate array of mixing channels. Furthermore, the gradient structure can be utilized in concert with cell experiments, to expose cells captured in microwells to various concentrations of soluble factors. We demonstrate the utility of this design to assess the viability of fibroblast cells in response to a range of hydrogen peroxide (H(2)O(2)) concentrations.     

Dealloying by metallic melt

Dealloying, which commonly involves corrosion processes in aqueous solutions, is a promising technique for preparing functional nanoporous metals. While this technique is ideal for preparing nanoporous noble metals such as of Au, it is not readily applicable to less-noble metals. Here, we propose a novel dealloying method employing a metallic melt, instead of an aqueous solution, as the dealloying liquid for a preparing of nanoporous metals. An atomic interaction among alloy components and metallic melt causes specific component to dissolve out from the alloy solid into the melt with self-organizing nanoporous structure by the remaining component. The dealloying method can be applied for preparation of nanoporous less-noble metal such as of Ti for the development of functional materials such as fluid filters, gas absorption media, and biomaterials.     

Degradation of bisphenol A and formation of hydrogen peroxide induced by glow discharge plasma in aqueous solutions

Degradation of bisphenol A (BPA) and simultaneous formation of hydrogen peroxide induced by glow discharge plasma in contact with aqueous solution were investigated. Experimental results indicated that the BPA degradation rate was higher in sodium chloride solution than that in sodium sulfate or phosphate solutions. However, the formation rates of hydrogen peroxide were on the opposite case. Both the BPA removal and the hydrogen peroxide production rates decreased in the presence of hydroxyl radical scavengers, indicating that hydroxyl radicals are the most probable oxidants responsible for BPA degradation and the precursors of hydrogen peroxide. Ferric ion showed better catalytic effect than that of ferrous ion, suggesting that the ferric ion was reduced by the intermediates formed during BPA degradation, which was confirmed by following the production of ferrous ion in the system. TOC of the solution gradually reduced with discharge time; however, without catalysts, the solution COD increased with discharge time and sharply decreased in the presence of iron salts. The major intermediate products were identified by LC/MS and the possible degradation mechanism was discussed.     

铁电存储器集成工艺中关键技术研究进展

铁电薄膜与半导体集成技术相结合而发展起来的铁电存储器与传统的半导体存储器相比有很多优点,其关键集成工艺技术有铁电薄膜制备技术、电极制备、刻蚀技术、氢阻技术、金属互连技术、钝化技术.简要介绍了这些工艺技术的研究现状,并讨论了相关工艺对性能的影响.     

Catalytic pyrolysis of oilsand bitumen over nanoporous catalysts

The catalytic cracking of oilsand bitumen was performed over nanoporous materials at atmospheric conditions. The yield of gas increased with application of nanoporous catalysts, with the catalytic conversion to gas highest for Meso-MFI. The cracking activity seemed to correlate with pore size rather than weak acidity or surface area.     

Nanoporous aluminum oxide as a novel support material for enzyme biosensors

To construct novel amperometric sensors for the detection of hydrogen peroxide and pyruvate, peroxidase and pyruvate oxidase were immobilized in self-supporting nanoporous alumina membranes those made by anodic oxidation. Pyruvate oxidase and other enzymes were enclosed in poly(carbamoylsulfonate) hydrogel and sucked into the nanoporous alumina structure before polymerization. The alumina membranes were investigated by scanning electron microscopy before and after the enzyme immobilization. In an amperometric flow detector cell, pyruvate and hydrogen peroxide were detected under flow injection analysis conditions in concentration ranges from 1 microM to 100 microM and 5 microM to 500 microM, respectively. The achieved operational stability showed that alumina membranes can be used to construct enzyme-modified electrodes.     

Photochemical treatment of phenol aqueous solutions using ultraviolet radiation and hydrogen peroxide

The potential of purifying phenol aqueous solutions (0.0006-0.0064 M) using ultraviolet (UV) radiation and hydrogen peroxide (H2O2; 0.005-0.073 M) was investigated. Although the direct photolysis of phenol and its oxidation by hydrogen peroxide (without ultraviolet light) were insignificant, the combination of UV and H2O2 was extremely effective on phenol degradation. However, the chemical oxygen demand was on no occasion entirely eliminated, indicating the resistance of the intermediate products formed to the photo-oxidation. Increasing the initial concentration of phenol had as a result lower phenol conversions achieved, whereas the increase in hydrogen peroxide initial concentration enhanced significantly the degradation of phenol. In contrast, COD removal was less sensitive to these changes.     

Hydrogen embrittlement of a low carbon steel during slow strain testing in chloride solutions containing sulphate reducing bacteria

Abstract

The paper presents results of a laboratory investigation of the microbiological environment assisted stress corrosion cracking of carbon steel in chloride solutions. Carbon steel specimens were subjected to slow strain rate testing (SSRT) in an aqueous solution of 3·5% sodium chloride, with and without a microbiological culture. Specimens tested in the biotic (microbiological) conditions showed a considerable loss of ductility, as compared to those tested in abiotic conditions. Fractography of the specimens tested in abiotic solutions suggested features of only ductile failure (dimples), whereas those tested in biotic conditions also had features of brittle cracking. Results of SSRT tests of the specimens pre-subjected to the electrochemical conditions for hydrogen charging have indicated susceptibility of the steel to hydrogen assisted cracking, and therefore suggesting a role of microbial environment in promoting hydrogen assisted cracking.     

Crack growth rates of Inconel 600 in aqueous solutions at elevated temperature

The effect of sulfate ions on the crack growth rates (CGRs) of notched specimens (CT) of Inconel 600 under constant load has been investigated in chloride containing aqueous solutions at 250 °C. The intergranular stress corrosion crack growth rates increased in chloride solutions while its hinder with increasing sulfate concentrations. Stress intensity factor (k) for stress corrosion cracking decreased with increasing of aggressivity of chloride ions while increased in the presence of sulfate solutions. At very low concentration of chloride (0.001 m), k-value retardation was observed. It is clear from the results that hydrogen in the aqueous solutions has a deleterious effect on crack propagation. The difference in crack growth rates in chloride ions and in chloride containing sulfate solution at high temperature can be recognized as caused by the difference in local environment conditions at a crack tip. The results indicate that the crack don't propagate under this conditions in the presence of sulfate ions. It is mainly due to a hinderance of chloride ions adsorption on active sites of the fracture surfaces and the formation of chromium oxide layer which is stable at higher temperature.     

Dispersibility‐Dependent Biodegradation of Graphene Oxide by Myeloperoxidase

Understanding human health risk associated with the rapidly emerging graphene‐based nanomaterials represents a great challenge because of the diversity of applications and the wide range of possible ways of exposure to this type of materials. Herein, the biodegradation of graphene oxide (GO) sheets is reported by using myeloperoxidase (hMPO) derived from human neutrophils in the presence of a low concentration of hydrogen peroxide. The degradation capability of the enzyme on three different GO samples containing different degree of oxidation on their graphenic lattice, leading to a variable dispersibility in aqueous media is compared. hMPO fails in degrading the most aggregated GO, but succeeds to completely metabolize highly dispersed GO samples. The spectroscopy and microscopy analyses provide unambiguous evidence for the key roles played by hydrophilicity, negative surface charge, and colloidal stability of the aqueous GO in their biodegradation by hMPO catalysis.     

Cracking of plain carbon steel in hydrogen sulfide solutions

The mechanism of cracking of high-strength steel in aqueous hydrogen sulfide solutions was studied. Certain preventive measures were proposed.     

WO3-PEO(聚环氧乙烷)溶胶-凝胶过程及表征

为提高WO3电致变色薄膜的循环使用寿命，采用过氧钨酸法将具有高离子电导率的高分子聚合物聚环氧乙烷与氧化钨复合，制备了相应的溶胶、凝胶与薄膜，利用XRD、FT—IR和TEM分析方法研究了体系的溶胶凝胶过程，并结合胶体化学原理讨论了制备条件对相应溶胶稳定性的影响。结果表明：醋酸与钨酸凝胶形成的较强相互作用，影响钨酸的溶胶凝胶过程；PEO在溶胶形成过程中对溶胶簇团的交联起导向作用；COOH^-离子对扩散双电层的影响和PEO的空间位阻效应使溶胶稳定。     

The rim zone of cement-based materials – Barrier or fast lane for chemical degradation?

Sophisticated evaluation models for the long-term stability of cement-based systems demand a precise knowledge of the mechanisms of deterioration reactions, particularly respecting a permanent exposure to aqueous environments. Commonly, insights into these mechanisms are deduced from long-term investigations. However, these chemical reactions start immediately after exposure to aggressive environments causing rapid changes of composition and structure. Consequently, properties of its rim zone change, which affects transport processes in aqueous solutions. In laboratory experiments, the influence of these surface processes on the stability of cement-based materials exposed to different chloride solutions was studied as a function of time and temperature. Analysis of compositional and structural changes beneath the surface reveal the role of crystalline covering layers for chemical resistance. Such layers are often described as protective barriers. However, these processes in the rim zone can accelerate chemical degradation and subsequently reduce the resilience of the cement-based materials to aggressive aqueous environments.     

Photochemical oxidation processes for the elimination of phenyl-urea herbicides in waters

Four phenyl-urea herbicides (linuron, chlorotoluron, diuron, and isoproturon) were individually photooxidized by monochromatic UV radiation in ultra-pure aqueous solutions. The influence of pH and temperature on the photodegradation process was established, and the first-order rate constants and quantum yields were evaluated. The sequence of photodecomposition rates was: linuron>chlorotoluron>diuron>isoproturon. The simultaneous photooxidation of mixtures of the selected herbicides in several types of waters was then performed by means of UV radiation alone, and by UV radiation combined with hydrogen peroxide. The types of waters used were: ultra-pure water, a commercial mineral water, a groundwater, and a lake water. The influence of the independent variables in these processes - the presence or absence of tert-butyl alcohol, types of herbicide and waters, and concentration of hydrogen peroxide - were established and discussed. A kinetic study was performed using a competitive kinetic model that allowed various rate constants to be evaluated for each herbicide. This kinetic model allows one to predict the elimination of these phenyl-urea herbicides in contaminated waters by the oxidation systems used (UV alone and combined UV/H2O2). The herbicide concentrations predicted by this model agree well with the experimental results that were obtained.     

General model of hydrogen transport through nanoporous membranes

A general model of transport of gases in solid nanoporous membranes was established. The model was developed based on Dusty Gas Model (DGM), solution diffusion and surface diffusion. As a result, solutions of the model for different transport conditions were derived. In this investigation, parameters of hydrogen gas transport of vinyl film (polymer) and vycor glass membranes were used to calculate semi-empirical solutions of the general model. In other words, the solutions of the general model were analytically obtained for different transport conditions, using experimentally obtained parameters of hydrogen gas transport in vinyl film (polymer) and vycor glass membranes. The obtained solutions of the general model were for the hydrogen transport of the membranes in the non-porous, nanoporous, microporous, and to macroporous range. The model was found useful for predictions of hydrogen transport through solid membranes. Additionally the model can be ready used for other gases for predictions of the transport of gases in nanoporous membranes.     

Atomic tritium as a surface nanoprobe in a structural investigation of molecular assemblies

Possibilities of atomic tritium application as surface nanoprobe for structural investigations of adsorption layers on the liquid–air interface have been demonstrated. Frozen aqueous solutions of a series of amino acids and their mixtures and one well-known surface-active substance (cetyltrimethylammonium bromide, CTAB) were exposed to bombardment by tritium atoms generated on hot tungsten wire in a special vacuum device. This procedure resulted in substitution of hydrogen atoms by radioactive tritium in the thin surface layer of investigated samples. Curves of radioactivity changes depending on bombardment time and solution concentration for applied compounds were obtained and analyzed.     

A silver nanoparticle thin film modified glass substrate as a colourimetric sensor for hydrogen peroxide

In this work, a silver nanoparticle (AgNP) coated glass slide was developed as a device for sensing hydrogen peroxide. AgNPs were synthesised using borohydride reduction with a citrate stabiliser, resulting in a negatively charged stabilised particle surface. The particles were attached to the glass surface using the layer-by-layer (LbL) technique. Poly (diallyldimethylammonium chloride) and poly (styrene sulphonate) were used as cationic and anionic polyelectrolyte layers, respectively. The glass slide was modified with polyelectrolytes leaving a cationic layer on the top surface. The AgNPs were subsequently deposited on the slide via electrostatic interaction. As a result, a dark yellow film of AgNPs was obtained with maximum absorption at 410 nm. Film fabrication based on LbL assembly provided acceptable reproducibility (relative standard deviation = 6.5%). The fabricated film had long-term stability (>6 weeks). A very small quantity of AgNPs was used in this method. Fabrication was performed under ambient conditions. Therefore this fabrication was considered as a green method. The AgNP modified slide was developed to sense hydrogen peroxide. Detection is based upon oxidation of AgNPs by hydrogen peroxide. This results in a change in colour of the film from dark yellow to colourless. Linear calibration was obtained over the range of 1.0--100.0 mM of hydrogen peroxide. The device was successfully used for measuring hydrogen peroxide in urine.