Surface Analysis Measurements Research Articles

Corrosion of carbon steel in clay environments relevant to radioactive waste geological disposals, Mont Terri rock laboratory (Switzerland)

Carbon steel is widely considered as a candidate material for the construction of spent fuel and high-level waste disposal canisters. In order to investigate corrosion processes representative of the long term evolution of deep geological repositories, two in situ experiments are being conducted in the Mont-Terri rock laboratory. The iron corrosion (IC) experiment, aims to measure the evolution of the instantaneous corrosion rate of carbon steel in contact with Opalinus Clay as a function of time, by using electrochemical impedance spectroscopy measurements. The Iron Corrosion in Bentonite (IC-A) experiment intends to determine the evolution of the average corrosion rate of carbon steel in contact with bentonite of different densities, by using gravimetric and surface analysis measurements, post exposure. Both experiments investigate the effect of microbial activity on corrosion. In the IC experiment, carbon steel showed a gradual decrease of the corrosion rate over a period of 7 years, which is consistent with the ongoing formation of protective corrosion products. Corrosion product layers composed of magnetite, mackinawite, hydroxychloride and siderite with some traces of oxidising species such as goethite were identified on the steel surface. Microbial investigations revealed thermophilic bacteria (sulphate and thiosulphate reducing bacteria) at the metal surface in low concentrations. In the IC-A experiment, carbon steel samples in direct contact with bentonite exhibited corrosion rates in the range of 2 µm/year after 20 months of exposure, in agreement with measurements in absence of microbes. Microstructural and chemical characterisation of the samples identified a complex corrosion product consisting mainly of magnetite. Microbial investigations confirmed the limited viability of microbes in highly compacted bentonite.

Corrosion inhibition and anti-bacterial efficacy of benzalkonium chloride in artificial CO2-saturated oilfield produced water

Corrosion inhibition by benzalkonium chloride (BKC) against anaerobic CO2 corrosion and microbiologically influenced corrosion was studied using surface analysis, weight loss and electrochemical measurements. Results showed that the minimal bactericidal concentration of BKC against Desulfotomaculum nigrificans (D. nigrificans) was 40mgL−1. While at this concentration the planktonic D. nigrificans cell count could recover after 21-day incubation, it resulted in 4 log reduction in sessile D. nigrificans cell count. When 80mgL−1 BKC was used, both planktonic and sessile D. nigrificans became undetectable. It was found that at these concentrations, BKC reduced both uniform corrosion and pitting corrosion.

The corrosion behavior and mechanism of carbon steel induced by extracellular polymeric substances of iron-oxidizing bacteria

In this work, the corrosion behavior and mechanism of carbon steel induced by extracellular polymeric substances (EPS) extracted from an iron-oxidizing bacterium culture were studied using surface analysis and electrochemical measurements in 3.5wt% NaCl solutions. Results of electrochemical measurements showed that 7day-old EPS at 240mgL−1 inhibited the corrosion of carbon steel, especially after the EPS solution was heat treated to deactivate the enzymes in the EPS. However, 7day-old EPS at much higher and much lower concentrations accelerated corrosion. Furthermore, 14day-old EPS and 28day-old EPS at 240mgL−1 also accelerated corrosion.

Influence of chloride concentration and pre-passivation on the pitting corrosion resistance of low-alloy reinforcing steel in simulated concrete pore solution

The effect of chloride concentration and pre-passivation on the pitting corrosion resistance of low-alloy steel and conventional low-carbon steel in simulated concrete pore solution was investigated using electrochemical techniques and surface analysis measurements. The results show that the passive film could enhance the pitting corrosion resistance for both investigated steels. Low-alloy steel exhibits slightly lower pitting corrosion resistance at low chloride concentration compared to low-carbon steel, regardless of the passivation condition. However, at high chloride concentration, low-alloy steel shows higher pitting corrosion resistance due to the formation of Cr-enriched protective rust layer.

Corrosion inhibition of carbon steel in CO2-containing oilfield produced water in the presence of iron-oxidizing bacteria and inhibitors

Inhibition effect of an imidazoline derivative, dodecanoic acid and dodecylamine against CO2 corrosion and microbiologically influence corrosion in a CO2-containing oilfield produced water was studied using surface analysis, weight loss and electrochemical measurements. Results indicated that dodecanoic acid could inhibit the adhesion of iron-oxidizing bacteria (IOB) significantly on carbon steel coupons, but had no effect on the planktonic IOB growth. Its inhibition efficiency reached 88.2% after 43 days of incubation. An imidazoline derivative was found to inhibit the adhesion of IOB on the steel surface, and contributed to lower inhibition effect.

The effect of magneticfield on biomineralization and corrosion behavior of carbon steel induced by iron-oxidizing bacteria

In this paper, the effect of a magneticfield (MF) on biomineralization and corrosion behavior of Q235 carbon steel were studied using surface analysis, weight loss and electrochemical measurements. Experimental results showed that MF inhibited the growth of iron-oxidizing bacteria (IOB) and the corrosion of Q235 carbon steel. MF reduced the largest pit depth by half, while it reduced pit population density from 50pitscm−2 to 10pitscm−2. MF also altered the morphology of biomineralization film, leading to the formation of a more compact biomineralization film which contributed to the lower corrosion rate.

Study of corrosion behavior and mechanism of carbon steel in the presence of Chlorella vulgaris

In this paper, the corrosion behavior of Q235 carbon steel in the presence of Chlorella vulgaris (C. vulgaris) was investigated by surface analysis, weight loss and electrochemical measurements. Results showed that the average corrosion rate in the presence of C. vulgaris was approximately 4 times as high as that in the absence of C. vulgaris. The corrosion rate in the daytime was higher than that in the night in the presence of C. vulgaris. The local corrosion was observed and the corrosion process of specimen was closely related to the activity of C. vulgaris.

Corrosion behavior of copper under biofilm of sulfate-reducing bacteria

The effect of sulfate-reducing bacteria (SRB) on corrosion behavior of copper was investigated using surface analysis and electrochemical measurements in seawater. Results demonstrated that SRB adhere onto copper surface to form biofilm and that the resulting corrosion product is mainly composed of cuprous sulfide. Cuprous sulfide and EPS are helpful for SRB adhesion on copper by providing a barrier against copper toxicity. In SRB growth cycle, corrosion rate is related to metabolic activity. Especially during exponential growth and stationary phases, SRB metabolism decreases the anodic zone area and promotes localized corrosion of copper.

Comparative surface analysis and TAP measurements to probe the NO adsorptive properties of natural gas vehicle Pd–Rh/Al2O3 catalyst

Thermal ageing has a significant detrimental effect on the behavior of bimetallic Pd–Rh natural gas fuelled vehicle (NGV) catalysts toward NO adsorption and its dissociation recognized as structure-sensitive. The ageing procedure at the lab-scale consisted of a thermal treatment under wet atmosphere (10vol.% H2O in air) at 980°C that would induce comparable surface reconstructions taking place under real exhaust conditions of Pd–Rh/Al2O3 catalysts. XPS and FTIR of CO adsorption highlight the occurrence of simultaneous particle sintering and preferential surface Rh enrichment. Temporal analysis of product (TAP) experiments have been implemented for in situ characterization that allows the elucidation of surface reactions and diffusion processes taking place at the surface of Pd–Rh/Al2O3 when single NO pulse is introduced. It was found that the relative rates of those processes are strongly affected by the dispersion and the Rh composition on freshly-prepared and aged catalysts. Interestingly, Rh recognized as the most suitable noble metal to convert NO to N2 would also slow down the agglomeration on Pd further protecting the metal/support interface.

Polystyrene-b-poly(2-vinyl phenacyl pyridinium) salts as photoinitiators for free radical and cationic polymerizations and their photoinduced molecular associations

• PS- b -PVPP photoinitiator initiates radical and cationic polymerizations. • The initiation of the polymerization involves homolytic and heterolytic scission. • Photoinduced switching behavior of PS- b -PVPP was demonstrated by surface analysis. Polystyrene- b -poly(2-vinyl phenacyl pyridinium hexafluorophosphate) (PS- b -PVPP) was synthesized by reacting polystyrene- b -poly(2-vinyl pyridine) prepared by living anionic polymerization with phenacyl bromide followed by counter anion exchange reaction. The ability of PS- b -PVPP to act as a photoinitiator for both free radical and cationic polymerizations is demonstrated. In the free radical polymerization, the initiation step involves the decay of the excited state of the salt with homolytic bond rupture of the nitrogen–carbon bond. For the cationic polymerization, homolytic cleavage followed by electron transfer and/or heterolytic scission reactions are responsible for the generation of reactive species. Photoinduced switching behavior of PS- b -PVPP from ionic to neutral state was also demonstrated by surface analysis, particle size and film thickness measurements.

Au-TiO2Nanocomposites and Efficient Photocatalytic Hydrogen Production under UV-Visible and Visible Light Illuminations: A Comparison of Different Crystalline Forms of TiO2

nanocomposites were prepared by the solvated metal atom dispersion (SMAD) method, and the as-prepared samples were characterized by diffuse reflectance UV-visible spectroscopy, powder XRD, BET surface analysis measurements, and transmission electron microscopy bright field imaging. The particle size of the embedded Au nanoparticles ranged from 1 to 10 nm. These Au/TiO2 nanocomposites were used for photocatalytic hydrogen production in the presence of a sacrificial electron donor like ethanol or methanol under UV-visible and visible light illumination. These nanocomposites showed very good photocatalytic activity toward hydrogen production under UV-visible conditions, whereas under visible light illumination, there was considerably less hydrogen produced. Au/P25 gave a hydrogen evolution rate of 1600 μmol/h in the presence of ethanol (5 volume %) under UV-visible illumination. In the case of Au/TiO2 prepared by the SMAD method, the presence of Au nanoparticles serves two purposes: as an electron sink gathering electrons from the conduction band (CB) of TiO2 and as a reactive site for water/ethanol reduction to generate hydrogen gas. We also observed hydrogen production by water splitting in the absence of a sacrificial electron donor using Au/TiO2 nanocomposites under UV-visible illumination.

Corrosion behavior of 3C magnesium alloys in simulated sweat solution

AbstractAZ series Mg alloys AZ31, AZ61, and AZ80 are widely applied in 3C (computer, communication, and consumer electronic) industry. Their corrosion characters in simulated sweat solution have been investigated by electrochemical technology, surface analysis, and pH measurements. Electrochemical test results showed that the three magnesium alloys revealed different corrosion resistance (Rt) in simulated sweat solution, Rt(AZ31) < Rt(AZ61) < Rt(AZ80). Three major components of simulated sweat solution played different roles during corrosion processes. Lactic acid was a kind of strong erosive medium for the magnesium alloys, and NaCl can induce pitting corrosion on alloys surface, while urea acted as a corrosion inhibitor. The corroded surface morphology of the three magnesium alloys was observed using scanning electron microscopy (SEM) and corrosion products were analyzed by X‐ray diffraction (XRD). Result of pH measurement tests showed that there were differences in climbing speed and final values of pH for the three magnesium alloys in simulated sweat solution.

SiO2 coated pure and doped titania pigments: low temperature CVD deposition and quantum chemical study

We report the in-flight CVD coating with smooth 1-2 nm thick SiO(2) of pure and doped rutile particles via the oxidation of SiCl(4) vapour introduced in the high temperature zone of a purpose built thermal reactor. The effectiveness of the coatings was determined by a combination of electron microscopy, surface analysis and photocatalytic measurements. No excess Cl was detected on the coated pigment particles indicating the complete oxidation of the SiCl(4) precursor. In conjunction with the experimental outcomes of this optimised deposition process, we use first-principles density functional and semi-empirical quantum chemical calculations to examine the underlying electronic processes which determined the morphology and photocatalytic properties of the coated titania. We highlight the presence of low lying valence electronic states which reduce photocatalytic activity, and as a consequence decrease the population of photo-excited titania electrons which transfer to the surrounding matrix. Born-Oppenheimer molecular dynamics (MD) simulations indicate that the coating process is completed within the order of 10 ps.

Bonding of composite resin to dentin using rigid rod polymer modified primers.

This study was conducted to evaluate the microtensile bond strength of composite resin to dentin with experimental rigid rod polymer (RRP) modified primers. RRP fillers are based on long stiff molecules specifically designed to create long polymers with restricted chain movement. Experimental primers were fabricated by dissolving RRP into dichloromethane (DCM) and further mixing it with monomers: ethylene glycol methacrylate phosphate (EGMP), bis[2-(methacryloyloxy)-ethyl]phosphate (BMEP) and 3(methacryloyloxy)propyltrimethoxysilane (MPS). Eight experimental primers were prepared with different proportions for each dentin substrate. A commercial etch-and-rinse adhesive was used as a control. Surfaces of human molar teeth were wet ground occlusally. The experimental primers were applied onto dentin prior to light polymerization of the incremental composite resin build-up. After 48 hours of water storage, teeth were sectioned and tested with the microtensile tester. Fracture surface analysis and contact angle measurements of adhesive resin were performed. Scanning electron micrographs were taken. 3-way ANOVA revealed that all factors, monomer type, solvent-monomer ratio and RRP, had a significant effect (p < 0.05) on bond strength. Primer with a combination of MPS and dimethacrylate BMEP revealed higher bond values than a mixture of MPS and monomethacrylate EGMP. Increase of the solvent-monomer ratio and addition of RRP into primers increased the microTBS. The contact angle measurements showed that RRP containing primers enhanced adhesive resin penetration into dentin similar to that of the control primer. Within the limitations of this study, it was concluded that an experimental type of modified RRP-silane-phosphate-acrylate primer was developed with comparable bonding properties to a commercial control.

Evidence for surface cleaning of sulphide minerals by attritioning in stirred mills

Recent developments in large scale stirred milling technology using ceramic media have allowed its application to relatively coarse particle streams. Apart from benefits in grinding finer more efficiently, benefits may also be derived from the surface cleaning action of stirred mills. This paper discusses evidence for the cleaning action of a stirred mill on the surfaces of chalcocite and effects on its subsequent flotation. Single mineral samples of chalcocite were ground with either stainless or mild steel grinding media. The effects of surface contamination by iron hydroxide on chalcocite floatability were studied using ethylene diamine-tetra acetic acid (EDTA) extraction, X-ray photoelectron spectroscopy (XPS) surface analysis and contact angle measurements. Depression of both coarse (+75 μm) and fine (−10 μm) size fractions was attributed to the surface precipitation of iron hydroxide species. Transfer of iron hydroxides from coarse particles to fine particles was observed with XPS analysis. Recovery of coarse particles (+75 μm) was improved by attritioning, while additional collector was needed to fully restore chalcocite recovery in both fine and coarse size fractions.

High fieldQslope and the baking effect: Review of recent experimental results and new data on Nb heat treatments

The performance of superconducting radio-frequency (SRF) cavities made of bulk Nb at high fields (peak surface magnetic field greater than about 90 mT) is characterized by exponentially increasing rf losses (high-field $Q$ slope), in the absence of field emission, which are often mitigated by low-temperature ($100--140\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, 12--48 h) baking. In this contribution, recent experimental results and phenomenological models to explain this effect will be briefly reviewed. New experimental results on the high-field $Q$ slope will be presented for cavities that had been heat treated in a vacuum furnace at high temperature without subsequent chemical etching. These studies are aimed at understanding the role of hydrogen on the high-field $Q$ slope and at the passivation of the Nb surface during heat treatment. Improvement of the cavity performances, particularly of the cavities' quality factor, have been obtained following the high-temperature heat treatments, while secondary ion mass spectroscopy surface analysis measurements on Nb samples treated with the cavities revealed significantly lower hydrogen concentration than for samples that followed standard cavity treatments.

A study of mechanisms affecting molybdenite recovery in a bulk copper/molybdenum flotation circuit

Molybdenite flotation in the bulk copper/molybdenum flotation circuit at Kennecott Utah Copper was studied by means of a combination of plant metallurgical surveys, laboratory flotation tests, mineralogical analysis (QEM-Scan), surface analysis (ToF-SIMS) and contact angle measurements. It was demonstrated that molybdenite recovery is influenced by flotation feed solids percent and by the mineralogy of the host rock. Molybdenite recovery was consistently higher at reduced flotation feed solids percent. Furthermore, the recovery of molybdenite was significantly lower from flotation feeds with high limestone skarn ore content. The major factors affecting the flotation recovery of molybdenite from both porphyry and skarn copper ores are discussed. It is suggested that the lower flotation recovery of molybdenite compared to the copper sulphide is determined by several factors, including particle morphology, inherent hydrophobicity and possible formation of slime coatings in the presence of gangue minerals typical of skarn ores. Implications on plant performance are discussed, and solutions to restore molybdenite recovery presented.

Ultrathin amorphization of single-crystal silicon by ultraviolet femtosecond laser pulse irradiation

The mechanisms of amorphization for crystalline Si (c-Si) induced by ultraviolet femtosecond laser irradiation are described in this paper. The wavelength of the laser pulse was 267 nm, which is the third harmonics of a Ti:sapphire laser. We performed a laser scanning microscopy and a transmission electron microscopy for surface and structural analysis and imaging pump-probe measurements to investigate the dynamics of the process. From the analyses, we confirmed that the thickness of the amorphized layer was quite uniform and there is no lattice defect under the amorphized section. The thickness of the amorphous Si (a-Si) layer was 7 nm and the threshold fluence of the amorphization was 44 mJ/cm2. From the Imaging Pump-Probe measurement it was revealed that the melting time is less than 1 ns and ultra high speed melting and re-solidification process was occurred. The melting depth estimated by the Imaging Pump-Probe measurement was 7 nm. The melted portion completely corresponded to the amorphized section.

Surface passivation and implications on high mobility channel performance (Invited Paper)

We review our recent studies of the passivation of the GaAs and InGaAs surface using a combination of in situ and ex situ surface analysis and capacitor measurements. We find that the control of Ga-oxides in particular appears to play an important role in understanding the characteristics of III–V MOS devices.

Failure analysis of the draft tube connecting bolts of a Francis-type hydroelectric power plant

In this paper, the failure of the bolts that fasten the draft tube of a 95-MW Francis turbine is presented. The fracture of the bolts is especially frequent when the machine operates at partial load. Fracture surface analysis and stress measurements under several power levels were done. Stress was also measured, while pressure relief in the spiral case was performed. Finally, stress measurements were conducted while pressured air was injected at the stay vanes and the machine was operating at partial load. With the strain measured, stress on the bolts was calculated. The fracture surface analysis showed that fatigue is the failure mechanism. Stress measurements revealed that strong vibration and broad stress variation is present when the machine operates at powers below 80 MW. Air injection effectively decreases vibration and stress fluctuation, but pressure relief in the spiral case did not show any beneficial effect.