A review on the mechanical methods for evaluating coating adhesion

Coatings have been applied widely in aerospace, biomedical, electronic, and many other industries. The performance of a coating is dictated by the adhesion between the coating and the underlying substrate. Thus, the evaluation of coating adhesion is critical for the assessment of the quality of a coating and its fitness for service. However, this evaluation is not straightforward, and various mechanical and non-mechanical evaluation methods have been developed. This paper presents a comprehensive review of the currently most widely employed mechanical methods. The interface fracture mechanics that provides the fundamental knowledge for conducting adhesion assessment and analysis is briefly introduced. Detailed discussions are presented on various sandwich specimen-based and bimaterial specimen-based testing methods, with emphasis on the principles, merits, limitations, typical applications, and recent improvements of each method.     

An experimental overview of the effects of hydrogen impurities on polymer electrolyte membrane fuel cell performance

Hydrogen quality is critical for increasing the reliability, stability, and durability of polymer electrolyte (PEM) fuel cells. In this work, several hydrogen impurities have been studied to understand their effects on PEM fuel cell performance at various operating concentrations. Our studies have shown that the following impurities suggested by industry stakeholders do not result in substantial fuel cell degradation when they are the sole impurity in hydrogen: 5 ppm formaldehyde, 2 ppm formic acid, 19 ppm chloromethane, 30 ppm acetaldehyde, 5% ethylene, 20 ppm toluene, and 10 ppm benzene. In addition, a specific mixture of impurities called the “specification concentration level cocktail” consisting of 0.2 ppm carbon monoxide, 4 ppb hydrogen sulphide, 0.2 ppm formic acid, 2 ppm benzene, and 0.1 ppm ammonia in hydrogen, also does not show significant effects on cell performance. In comparison, when a cocktail having five times the specification concentration is introduced into the cell, significant performance loss is evident.     

Effect of contaminants from flue gas on CO2 sequestration in saline formation

Deep saline aquifers are reported to have the largest estimated capacity for CO₂ sequestration. Most geochemical studies on CO₂ storage in saline formations are focused on the interactions of pure CO₂ and do not consider the potential impacts of contaminants such as SO₂ found in typical post‐composition flue gas streams. This paper reports on results of a combined CO₂–co‐contaminant–brine–rock experimental and a simple modeling study of the potential impact of flue gas contaminants on saline formations. Chemical reactions of the sandstone from Mount Simon formation exposed to CO₂ mixed with other gas species under sequestration conditions were studied (i.e. solid material — representative Mount Simon sandstone; liquid — synthetic Illinois Basin brine; T and P — 50 °C, 110 bar; gas composition — 1% SO₂, 4% O₂, 95% CO₂). The experimental study indicates that the co‐injection of 1% SO₂ would lead to substantially reduced brine pH due to the formation of sulfuric acid and the formation of bassanite (major) and anhydrites. Preliminary equilibrium computational modeling yielded similar results. Copyright © 2013 John Wiley & Sons, Ltd.     

Atomistic study of edge and screw 〈c + a〉 dislocations in magnesium

The gamma surfaces in the pyramidal I {1 ?1 0 1} and II {1 1?2 2} planes for hexagonal close packed Mg have been calculated using two embedded-atom-method potentials and by ab initio methods, and reasonable agreement is obtained for key stacking fault energies. Screw and edge 〈c + a〉 dislocation core structures and Peierls stresses at 0 K and finite temperature have been examined using the embedded-atom-method potentials. Screw 〈c + a〉 dislocations glide in the {1 ?1 0 1} pyramidal plane I, and in the prism plane for larger stresses, but not in the {1 1 ?2 2} plane as observed in experiments. However, the preference for pyramidal I glide correlates well with the gamma surfaces. New low energy edge 〈c + a〉 dislocation cores were found in addition to the sessile Type I and Type III cores observed in previous simulations while the Type II core was not observed. The lowest energy core is a glissile core that lies in the {1 1 ?2 2} plane and has a 3 nm long {1 1 ?2 1} twin embryo, rather than the sessile Type III core found in previous simulations. As the temperature increases from 0 to 300 K, the Peierls stresses in compression/tension drop from ?80 MPa/+140 MPa and ?140 MPa/+220 MPa for the most glissile screw and edge dislocations to ?5/+2.5 MPa and ?27/+5 MPa, and dislocation glide changes from kink motion to face-centered-cubic-like motion. At 300 K and under an applied stress, almost all the edge cores found at low temperature transform into a glissile core denoted IT, which glides at low stresses. Thus, at 300 K both screw and edge 〈c + a〉 dislocations were found to glide at stresses smaller than the ～40 MPa measured experimentally.     

Reengineered BI‐DIME Ligand Core Based on Computer Modeling to Increase Selectivity in Asymmetric Suzuki–Miyaura Coupling for the Challenging Axially Chiral HIV Integrase Inhibitor

Through a computer‐guided approach, new series of monophosphine ligands were designed and developed for asymmetric Suzuki–Miyaura couplings of challenging heterocyclic substrates. Computer modeling pointed to a tunable, yet unexplored quadrant in BI‐DIME, leading to the discovery of the 3′,5′‐dimethyl‐substituted ligand which improved the atropisomeric selectivity of the Suzuki–Miyaura reaction from the previously reported 5:1 dr to 15:1 dr for the synthesis of a challenging HIV integrase intermediate, and up to 24:1 dr with various other quinoline substrates.

     

Controlled CVD growth of Cu-Sb alloy nanostructures

Sb based alloy nanostructures have attracted much attention due to their many promising applications, e.g. as battery electrodes, thermoelectric materials and magnetic semiconductors. In many cases, these applications require controlled growth of Sb based alloys with desired sizes and shapes to achieve enhanced performance. Here, we report a flexible catalyst-free chemical vapor deposition (CVD) process to prepare Cu-Sb nanostructures with tunable shapes (e.g. nanowires and nanoparticles) by transporting Sb vapor to react with copper foils, which also serve as the substrate. By simply controlling the substrate temperature and distance, various Sb-Cu alloy nanostructures, e.g. Cu(11)Sb(3) nanowires (NWs), Cu(2)Sb nanoparticles (NPs), or pure Sb nanoplates, were obtained. We also found that the growth of Cu(11)Sb(3) NWs in such a catalyst-free CVD process was dependent on the substrate surface roughness. For example, smooth Cu foils could not lead to the growth of Cu(11)Sb(3) nanowires while roughening these smooth Cu foils with rough sand papers could result in the growth of Cu(11)Sb(3) nanowires. The effects of gas flow rate on the size and morphology of the Cu-Sb alloy nanostructures were also investigated. Such a flexible growth strategy could be of practical interest as the growth of some Sb based alloy nanostructures by CVD may not be easy due to the large difference between the condensation temperature of Sb and the other element, e.g. Cu or Co.     

A sustainable city environment through child safety and mobility—A challenge based on ITS?

Our cities should be designed to accommodate everybody, including children. We will not move toward a more sustainable society unless we accept that children are people with transportation needs, and ‘bussing’ them around, or providing parental limousine services at all times, will not lead to sustainability. Rather, we will need to make our cities walkable for children, at least those above a certain age. Safety has two main aspects, traffic safety and personal safety (risk of assault). Besides being safe, children will also need an urban environment with reasonable mobility, where they themselves can reach destinations with reasonable effort; else they will still need to be driven. This paper presents the results of two expert questionnaires focusing on the potential safety and mobility benefits to child pedestrians of targeted types of intelligent transportation systems (ITS). Five different types of functional requests for children were identified based on previous work. The first expert questionnaire was structured to collect expert opinions on which ITS solutions or devices would be, and why, the most relevant ones to satisfy the five different functional requests of child pedestrians. Based on the first questionnaire, fifteen problem areas were defined. In the second questionnaire, the experts ranked the fifteen areas, and prioritized related ITS services, according to their potential for developing ITS services beneficial to children. Several ITS systems for improving pedestrian quality are discussed. ITS services can be used when a pedestrian route takes them to a dangerous street, dangerous crossing point or through a dangerous neighborhood. An improvement of safety and other qualities would lead to increased mobility and a more sustainable way of living. Children would learn how to live to support their own health and a sustainable city environment. But it will be up to national, regional and local governments, through their ministries and agencies and public works departments, to promote, fund, and possibly mandate such systems. It is clear that we need to offer an acceptable level of convenience, efficiency, comfort, safety and security to pedestrians but it is less clear if society will prioritize resources toward this.