Biofouling and microbially influenced corrosion of stainless steels

Stainless steels are among the most investigated materials on biofouling and microbially-influenced corrosion (MIC). Although, generally corrosion-resistant owing to tenacious and passive surface film due to chromium, stainless steels are susceptible to extensive biofouling in subsoil, fresh water and sea water and chemical process environments. Biofilms influence their corrosion behavior due to corrosion potential ennoblement and sub-surface pitting. Both aerobic and anaerobic microorganisms catalyse microbial corrosion of stainless steels through biotic and abiotic mechanisms. MIC of stainless steels is common adjacent to welds at the heat-affected zone. Both austenite and delta ferrite phases may be susceptible. Even super stainless steels are found to be amenable to biofouling and MIC. Microbiological, electrochemical as well as physicochemical aspects of MIC pertaining to stainless steels in different environments are analyzed.

Experimental study of thermocapillary convection on a liquid bridge consisting of fluid with low Prandtl number in a floating half-zone

A device of mercury liquid bridge of floating half-zone is designed to experimentally explore thermocapillary convection and its instability of a low Prandtl number liquid. Noncontacted diagnostic techniques were developed to monitor surface flow and surface deformation. The surface flow and the influence of a growing surface film (or skin) on the flow were observed. It is shown that the film is a key factor in changing the behavior associated with the thermocapillary convection. The experiment indicates that the critical Marangoni number should be much higher than that expected by the numerical simulation. The condition and process of surface film growth are discussed. The surface oscillation of the mercury bridge wrapped with ''dirt-film'' was observed, and the characteristics and the frequency associated with this oscillation are given.

Experiment on the thermocapillary convection of a mercury liquid bridge in a floating half zone

A liquid bridge of a floating half zone consisting of liquid mercury sealed in a glass tube with nitrogen atmosphere was used for the experiment of thermocapillary convection with a low Prandtl number liquid. A non-contacted diagnostic method was developed to monitor the surface flow and the surface oscillation. A growing surface film (or skin) is a crucial source to suppress thermocapillary convection, and is discussed in this paper. For the case of a mercury Liquid bridge, the critical Marangoni number was obtained as 900, and the oscillatory frequency was around 5 Hz.

Measurement of w-InN/h-BN Heterojunction Band Offsets by X-Ray Photoemission Spectroscopy

X-ray photoelectron spectroscopy has been used to measure the valence band offset (VBO) of the w-InN/h-BN heterojunction. We find that it is a type-II heterojunction with the VBO being -0.30 +/- A 0.09 eV and the corresponding conduction band offset (CBO) being 4.99 +/- A 0.09 eV. The accurate determination of VBO and CBO is important for designing the w-InN/h-BN-based electronic devices.

Polyaniline-coated carbon particles and their electrode behavior in organic carbonate electrolyte

In an attempt to increase the interface stability of carbon used in Li-ion batteries, a thin conducting polyaniline (PANI) film was fabricated on the surface of carbon by in situ chemical polymerization. The chemical and electrochemical properties of the composite material were characterized using X-ray diffraction, Raman spectroscopy, scanning electron microscope, cyclic voltammetry, and electrochemical impedance spectroscopy. It was confirmed that the PANI film has an obvious effect on the morphology and the electrochemical performance of carbon. The results could be attributed to the electronic and electrochemical activity of the conducting PANI films.

Acid-stable amperometric soybean peroxidase biosensor based on a self-gelatinizable grafting copolymer of polyvinyl alcohol and 4-vinylpyridine

A peroxidase was extracted from Chinese soybean seed coat, and its thermostability and acid-stability were characterized. This peroxidase was immobilized into a self-gelatinizable grafting copolymer of polyvinyl alcohol with 4-vinylpyridine(PVA-g-PVP) to construct an acid-stable hydrogen peroxide biosensor. The effect of pH was studied for optimum analytical performances by amperometric and spectro-photometric methods, also the K-m(app) and the stability of the soybean peroxidase-based biosensor are discussed. At pH 3.0, the soybean peroxidase maintained its bioactivity and the enzyme electrode had a linear range from 0.01 to 6.2 mM with a detection limit of 1.0 x 10(-7) M. In addition, the main characteristics of different hydrogen peroxide sensors were compared.

Irreversible capacity loss of graphite electrode in lithium-ion batteries

The irreversible capacity loss of the carbon electrode in lithium-ion batteries at the first cycle is caused mostly by surface film growth. We inspected an unknown irreversible capacity loss (UICL) of the natural graphite electrodes. The charge/discharge behavior of graphite and meso-phase carbon microbeads heat-treated at 2800 degrees C (MCMB28) as the materials of the carbon anode in the lithium-ion battery were compared. It was found that the capacity loss of the natural graphite electrode in the first cycle is caused not only by surface film growth, but also by irreversible lithium-ion intercalation on the new formed surface at the potential range of lithium intercalation, while the capacity loss of the MCMB28 electrode is mainly originated from surface film growth. The reason for the difference of their irreversible capacity losses of these two kinds of carbon material was explained in relation to their structural characteristics. (C) 1997 Published by Elsevier Science S.A.

Improvements in the selectivity of electrochemical detectors for liquid chromatography and flow injection analysis using the self-assembled n-alkanethiol monolayer-modified au electrode

4-Aminophenol (4-AP), paracetamol (PRCT), norepinephrine (NE), and dopamine (DA) (all somewhat hydrophobic compounds) were HPLC electrochemically detected while the signals from uric acid (UA) and ascorbic acid (AA) (both hydrophilic compounds at the pH studied) were minimized, taking advantage of the permselectivity of the self-assembled n-alkanethiol monolayer (C-10-SAM)-modified Au electrodes based on solute polarity, The effects of various factors, such as the chain length of the n-alkanethiol modifier, modifying time, and pH value, on the permeability of C-10-SAM coatings were examined, The calibration curves, linear response ranges, detection limits, and reproducibilities of the EC detector for 4-AP, PRCT, NE, and DA were obtained, The result shows that the EC detector can be applied in the chromatographic detection of 4-AP, PRCT, NE, and DA in urine, effectively removing the influence of UA and AA in high concentrations existing in biological samples. As a result, a great improvement in the selectivity of EC detectors has been achieved by using Au electrodes coated with neutral n-alkanethiol monolayer.

Polymer nanotubes by wetting of ordered porous templates

We have developed a simple technique for the fabrication of polymer nanotubes with a monodisperse size distribution and uniform orientation. When either a polymer melt or solution is placed on a substrate with high surface energy, it will spread to form a thin film, known as a precursor film, similar to the behavior of low molar mass liquids. Similar wetting phenomena occur if porous templates are brought into contact with polymer solutions or melts: A thin surface film will cover the pore walls in the initial stages of wetting. This is because the cohesive driving forces for complete filling are much weaker than the adhesive forces. Wall wetting and complete filling of the pores thus take place on different time scales. The latter is prevented by thermal quenching in the case of melts or by solvent evaporation in the case of solutions, thus preserving a nanotube structure. If the template is of monodisperse size distribution, aligned or ordered, so are the nanotubes, and ordered polymer nanotube arrays can be obtained if the template is removed. Any melt-processible polymer, such as polytetrafluoroethylene (PTFE), blends, or multicomponent solutions can be formed into nanotubes with a wall thickness of a few tens of nanometers. Owing to its versatility, this approach should be a promising route toward functionalized polymer nanotubes.

YBACUO PRBACUO MULTILAYERS BY EXCIMER LASER ABLATION

YBaCuO films with (001) orientation have been deposited on MgO by laser ablation at 248 and 193 nm wavelengths. Transitions to zero resistance at 87 K and 90 K have been reproducibly achieved in the respective cases. Optical spectroscopic studies of the plume show the importance of molecular species in the ablation if good superconducting films are to be formed. The substrate position in the plume and substrate temperature are important in determining film quality. The influence of oxygen gas pressure can be significant. SEM studies show the occurrence of second-phase outcrops with a needle-like morphology aligned over the whole area of the film along two mutually perpendicular directions on the film surface. Film orientation is determined by XRD and R against T is measured down to 80 K in a hydrogen exchange gas cryostat. Characterization studies of device-related multilayer YBaCuO/PrBaCuO structures by XRD are presented.

Exploring corrosion protection of Mg via ionic liquid pretreatment

We present the development of a 10–100 nanometer thick surface film upon pure Mg on exposure to an ionic liquid (IL) based on the bis(trifluoromethanesulfonyl)amide (TFSA) anion. This film formation is the result of the oxidative reactivity of the metal in the IL, with the subsequent effect of ultimately protecting the underlying metal from corrosion in aqueous chloride containing solution. Film formation was studied in the IL using an electrochemical droplet cell. It was seen that this film is adherent and subsequently facilitates appreciable protection against corrosion as judged by subsequent electrochemical testing in the form of potentiodynamic polarization and impedance spectroscopy, along with direct observation. The physical film morphology was studied by electron microscopy and focused ion beam.

Phosphonium ionic liquids as lubricants for aluminium-steel

The performance of a series of novel room temperature ionic liquids (ILs) based on the trihexyl(tetradecyl)phosphoniumcation (P66614 +) and a number of novel anions have been studied in pin-on-disk tests using a 100Cr6 steel ball on AA2024 aluminium disks.

The anions coupled to the (P66614 +) cation include diphenyl phosphate (DPP-), dibutyl phosphate (DBP-), bis (2,4,4-trimethyl pentyl) phosphinate (M3PPh-) and bis(2-ethyl hexyl) phosphate (BEH-).

More traditional anions such as bis(trifluoromethanesulfonyl) amide (NTf2 -) and bromide (Br-) were also investigated. Experiments were conducted at various loads to assess the IL film forming abilities.

The results suggest that the structure of the anion is important in forming a surface film that reduces the friction and wear of the aluminium disk. At 30N five of the six ILs tested showed a 30-90% reduction in wear, as determined from wear scar depth measurements, compared to fully formulated diesel oil.

The IL lubricant with a diphenyl phosphate anion achieved the lowest wear coefficient, showing a better performance than a typical fluorine-containing IL anion, NTf2.

To further investigate wear mechanisms and surface interactions the wear scars were analysed using a scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS).

Clinical evaluation of long-term users of two contact lens care preservative systems

Purpose: To clinically evaluate long-term users of two different contact lens care preservative systems and to investigate whether prolonged use is associated with an increase in the prevalence of dry eye.

Methods: Eighty-nine wearers of group IV hydrogel or silicone hydrogel lenses participated in this one-visit, investigator-masked study. Subjects were required to have consistently used a polyhexamethylene biguanide (PHMB) or polyquaternium-1 (PQT) based solution for 2 years. Consistent use was defined as 80% for the past 2 years and 100% for the past year. Clinical assessments included: average and comfortable wear time; overall and end-of-day comfort; signs of dryness, discomfort, burning or stinging, grittiness or scratchiness and visual changes; non-invasive and fluorescein break-up-time; pre-ocular tear film lipids, tear meniscus height, Schirmer and fluorescein clearance tests; limbal and bulbar hyperemia; palpebral roughness; corneal and conjunctival staining; lens front surface wetting; and lens film deposits.

Results: Significantly more grittiness or scratchiness was reported by subjects using a PHMB-containing system (67% vs. 44%; P = 0.02). Palpebral roughness and hyperemia were significantly greater in the PHMB group wearing group IV lenses (P = 0.01 and P = 0.05, respectively). Corneal staining was significantly higher in the PHMB users in all four peripheral sectors (P < 0.01). Nasal and temporal conjunctival staining was also significantly higher for users of PHMB-containing systems (P < 0.05). Front surface lens wettability was significantly better for group IV PQT users compared to PHMB users (P = 0.008), with 84% vs. 72%, respectively, with lenses graded by the investigator as having good or excellent wettability. Significantly higher levels of lens front surface film deposits were noted with PHMB users (P = 0.007), with 58% of group IV lenses treated with PHMB compared with 38% of group IV lenses treated with PQT showing some lens front surface film deposition. No significant differences between the two preservative system groups were noted for the range of dry eye evaluations nor the remaining clinical assessments.

Conclusions: Differences in both ocular and lens characteristic were observed between long-term users of two preservative systems used in many contact lens multi-purpose solutions. The findings from this study did not support the hypothesis that prolonged use of PHMB-containing solutions leads to dry eye. Additional studies including a larger sample size and perhaps longer use of the systems could help to further elucidate differences in clinical performance between systems.

The corrosion inhibition of aluminium alloy 7075-T651 with cerium and Mischmetal di phenyl phosphate

Previous studies have shown that cerium diphenyl phosphate (Cedpp) 3 is a very effective inhibitor of corrosion of aluminium alloys in chloride solutions. This paper describes the results of further studies using electrochemical and constant immersion corrosion tests to compare the effectiveness of Ce(dpp) 3 and Mischmetal diphenyl phosphate Mm(dpp) 3 as inhibitors of corrosion pitting on AA7075-T651 aluminium alloy. The results shows that both Ce(dpp) 3 and Mm(dpp) 3 are excellent inhibitors of pitting corrosion of this alloy in very aggressive environments of continuously aerated 0.1M and 1.0M sodium chloride (NaCl) solutions. Polarisation tests indicate that these compounds act as a cathodic inhibitors by reducing the rate of the oxygen reduction reaction, which results in a decreased corrosion current density and a separation of the corrosion potential from the pitting potential. This inhibition is thought to be due to the formation of a surface film consisting of rare earth metal oxide, aluminium oxide and a cerium-aluminium organo-phosphate complex. Surface analysis data from scanning electron microscopy and X-ray Energy Dispersive Spectroscopy show the complex nature of this protective film. This work further develops our understanding about the mechanisms through which these complex films form, and how inhibition occurs in the presence of these compounds.

Corrosion of mg alloy ZE41 and its mitigation using ionic liquids

Magnesium alloy ZE41 (Mg-Zn-RE-Zr), which is used extensively in the aerospace industry, possesses excellent mechanical properties albeit poor corrosion resistance. This work investigates the mechanism of corrosion, and the interaction between the grain boundary intermetallic phases, the zirconium (Zr)-rich regions within the grains and the bulk Mg rich matrix in both the as-cast and heat-treated conditions. The results of optical and scanning electron microscopy (SEM) show the importance of the microstructure in the initiation and propagation of corrosion in an aqueous environment. The Zr-rich regions play a distinct role in the early stages of corrosion with this alloy. The second part of this work investigates the interaction of two different ionic liquids (ILs) with the surface of the ZE41 alloy. ILs based on trihexyltetradecylphosphonium (P 6,6,6,14) coupled with either diphenylphosphate (DPP) or bis(trifluoromethanesulfonyl) amide (Tf 2N) have been shown to react with Mg alloy surfaces, leading to the formation of a surface film that can improve the corrosion resistance of the alloy. The interaction of the ILs with the ZE41 surface has been investigated by optical microscopy and SEM. Surface characterization has been performed using Time of Flight-Secondary Ion Mass Spectrometry (ToF-SIMS) and X-ray Photoelectron Spectroscopy (XPS). The surface characterization and microscopy revealed the preferential interaction with the grain boundaries and grain boundary phases. Thus the morphology and microstructure of the Mg surface seems critical in determining the nature of the interaction with the IL. The corrosion protection of the IL films formed on the ZE41 surface was investigated by SEM and potentiodynamic polarisation.