Characterization of film failures by bismuth electrodeposition—Application to thin deformed fluorocarbon films for stent applications

A new approach for the detection and visualization of nano-scaled film defects, such as fissures and holes is described. The procedure is based on a selective electrochemical deposition of bismuth onto uncovered parts of stainless steel substrates due to film cracking after deformation. Cyclic voltammetry experiments enabled the identification of the bismuth redox signals, necessary for the subsequent potentiostatic electrodeposition. A combination of XPS and ToF-SIMS analyses demonstrated that deposition with commonly used acidified electrolytes led to a significant film degradation, by defluorination and chain scission. When an identical procedure was performed in neutral conditions, which was realized by the addition of a bismuth chelating agent, no influence onto the integrity of the fluorocarbon coatings was observed. By SEM, XPS and ToF-SIMS analyses, the deposition of bismuth on the film defects was clearly demonstrated and the failures were evidenced. The identification of nano-scaled coating failures, which was extremely difficult before using common characterization tools, was now realized. This work makes part of a strategy to cover stent materials with a protective fluorocarbon layer and to examine the influence of stent expansion onto the film cohesive properties.     

Quantification of the relationship between fuser roller temperature and laser printer emissions

Recently published studies not only demonstrated that laser printers are often significant sources of ultrafine particles, but they also shed light on particle formation mechanisms. While the role of fuser roller temperature as a factor affecting particle formation rate has been postulated, its impact has never been quantified. To address this gap in knowledge, this study measured emissions from 30 laser printers in chamber using a standardized printing sequence, as well as monitoring fuser roller temperature. Based on a simplified mass balance equation, the average emission rates of particle number, PM_2.5 and O₃ were calculated. The results showed that: almost all printers were found to be high particle number emitters (i.e. >1.01×10¹⁰ particles/min); colour printing generated more PM_2.5 than monochrome printing; and all printers generated significant amounts of O₃. Particle number emissions varied significantly during printing and followed the cycle of fuser roller temperature variation, which points to temperature being the strongest factor controlling emissions. For two sub-groups of printers using the same technology (heating lamps), systematic positive correlations, in the form of a power law, were found between average particle number emission rate and average roller temperature. Other factors, such as fuser material and structure, are also thought to play a role, since no such correlation was found for the remaining two sub-groups of printers using heating lamps, or for the printers using heating strips. In addition, O₃ and total PM_2.5 were not found to be statistically correlated with fuser temperature.     

Ultra-STEM-EELS characterization of MgB<Subscript>2</Subscript> superconductor synthesized by different routes: Comparative study

We report a comparative study on the synthesis of MgB₂ by electrothermal explosion (ETE), self-propagating high temperature synthesis (SHS), and high-temperature sintering. Advantages of these methods are demonstrated by comparing the structural and electronic properties of final MgB₂ with a superconducting transition temperature of above 39 K. The structural properties of materials were studied by XRD and SEM/EDS (chemical cartography), while imaging and electronic properties were investigated by Ultra-STEM microscopy and electron energy loss spectroscopy (EELS), respectively. The results show that the synthesized bulk compounds are highly dense, with strong intergrain connections. The EEL spectra show the peaks of σ- and anti-bonding bonds, which is in good agreement with the theoretically calculated band structure, Fermi surface, and de Haas-van Alphen frequencies.     

Decomposition of ethylene carbonate on electrodeposited metal thin film anode

Metals capable of forming alloys with Li are of great interest as an alternative to present carbon electrodes, hence the importance of knowing their interactions with electrolytes is necessary. Herein we report further on the high-voltage extra irreversibility of Sn electrodeposited thin films vs. Li in EC-DMC 1 M LiPF₆ electrolytes. We show that this high-voltage irreversibility is strongly dependent upon the electrolyte composition as demonstrated by its disappearance in EC-free electrolytes. This finding coupled with IR spectroscopy measurements provides direct evidence for the tin-driven catalytic degradation of EC during the discharge of Sn/Li cells. From an electrochemical survey of various metals, capable of alloying with Li, we found that Bi and Pb behaved like Sn while Si and Sb did not act as catalysts towards EC degradation. A rationale for such behaviour is proposed, a procedure to bypass EC degradation with the addition of VC is presented, and an explanation for the non-observance of catalytic-driven EC degradation for Sn/C composites is provided.     

蕾切尔住宅

项目地点:加拿大,蒙特利尔建筑师:Sid Lee建筑事务所摄影:Stephane Brugger Location:Montreal,Canada Architects:Sid Lee Architecture Photos:Stéphane Brügger     

The structure-function relationship of the lipases from Pseudomonas aeruginosa and Bacillus subtilis

Within the BRIDGE T-project on lipases we investigate the structure-functionrelationships of the lipases from Bacillus subtilis and Pseudomonasaeruginosa. Construction of an overproducing Bacillus. strainallowed the purification of > 100 mg lipase from 30 l culturesupernatant. After testing a large variety of crystallizationconditions, the Bacillus lipase gave crystals of reasonablequality in PEG-4000 (38-45%), Na₂SO₄ and octyl-ß-glucosideat 22°C, pH 9.0. A 2.5 Å; dataset has been obtainedwhich is complete from 15 to 2.5 A resolution. P.aeruginosawild-type strain PAC1R was fermented using conditions of maximumlipase production. More than 90% of the lipase was cell boundand could be solubilized by treatment of the cells with TritonX-100. This permitted the purification of 50 mg lipase. So far,no crystals of sufficient quality were obtained. Comparisonof the model we built for the Pseudomonas lipase, on the basisof sequences and structures of various hydrolases which werefound to possess a common folding pattern (/ß hydrolasefold), with the X-ray structure of the P.glumae lipase revealedthat it is possible to correctly build the structure of thecore of a protein even in the absence of obvious sequence homologywith a protein of known 3-D structure.     

As oxidation by Thiomonas arsenivorans in up-flow fixed-bed reactors coupled to As sequestration onto zero-valent iron-coated sand

The combined processes of biological As^III oxidation and removal of As^III and As^V by zero-valent iron were investigated with synthetic water containing high As^III concentration (10 mg L⁻¹). Two up-flow fixed-bed reactors (R1 and R2) were filled with 2 L of sieved sand (d = 3 ± 1 mm) while zero-valent iron powder (d = 76 μm; 1% (w/w) of sand) was mixed evenly with sand in R2. Thiomonas arsenivorans was inoculated in the two reactors. The pilot unit was studied for 33 days, with HRT of 4 and 1 h. The maximal As^III oxidation rate was 8.36 mg h⁻¹ L⁻¹ in R1 and about 45% of total As was removed in R2 for an HRT of 1 h. A first order model fitted well with the As^III concentration evolution at the different levels in R1. At the end of the pilot monitoring, batch tests were conducted with support collected at different levels in R1. They showed that bacterial As^III oxidation rate was correlated with the axial length of reactor, which could be explained by biomass distribution in reactor or by bacterial activity. In opposition, As^III oxidation rate was not stable in R2 due to the simultaneous bacterial As^III oxidation and chemical removal by zero-valent iron and its oxidant products. However, a durable removal of total As was realized and zero-valent iron was not saturated by As over 33 days in R2. Furthermore, the influence of zero-valent iron and its oxidant corrosion products on the evolution of As^III-oxidizing bacteria diversity was highlighted by the molecular fingerprinting method of PCR-DGGE using aoxB gene as a functional marker of aerobic As^III oxidizers.