Microstructure and oxidation behaviour of Ir-rich Ir–Al binary alloys

In the current study, alloys of Ir–11Al, Ir–23Al, Ir–30Al, Ir–41Al and Ir–45Al (at.%) were prepared to investigate the microstructure and oxidation behaviour of Ir-rich Ir–Al alloys. Ir(Al)_ss and/or β-IrAl intermetallic phases were found to exist in the prepared alloys. During isothermal oxidation at 1100 °C, the Ir(Al)_ss and β-IrAl individually changed to porous and dense Al₂O₃. The microstructure of the oxide scale formed on Ir–23Al was similar to that of its former alloy which possessed a dendrite-like configuration. It was found that the mass change of Ir–45Al followed a parabolic law, showing the best oxidation resistance among the Ir–Al alloys.     

High-throughput study of binary thin film tungsten alloys

Combinatorial magnetron co-sputtering from elemental sources was applied to produce W-alloy thin film composition spread materials libraries with well-defined, continuous composition gradients (film thicknesses between 1 and 2.5 μm). Three systems were studied: W-Fe (0–7 at.%), W-Ti (0–15 at.%) and W-Ir (0–12 at.%). High-throughput characterization of the materials libraries comprised of chemical, morphological and microstructural analyses. Scanning electron microscope investigations revealed that the films have a columnar structure of inverted cone-like units separated by voided boundaries, with a strong correlation to the alloying element content. Significant morphological changes occurred with an increase in the amount of the added element; W films with lower at.% of the alloying element had higher density and tighter grain boundaries, altering towards an increased amount of voids as the concentration of the alloying element increased. Electron backscatter diffraction scanning was used to determine microstructural components (grain size, grain shape, texture evolution), in dependence on the concentration of the alloying element.     

High-temperature tensile and creep deformation of cross-weld specimens of weld joint between T92 martensitic and Super304H austenitic steels

The high-temperature mechanical behavior of cross-weld specimens prepared from a dissimilar weld joint between T92 martensitic and Super304H austenitic heat-resistant steels incorporating Ni-based weld metal was evaluated at temperatures up to 650 °C. For both high temperature tensile and creep tests, failure took place in T92 due to its faster degradation with temperature increase. The heat-affected zone of T92 played a critical role during creep deformation, resulting in type IV failure under the long-term creep condition. For the creep specimens, the location of failure shifted from the base metal region to the fine-grained heat-affected zone as the creep duration time increased from the short-term to the long-term condition. The massive precipitation of Laves phase on the grain boundaries of the fine-grained heat-affected zone during creep deformation was observed and found to be responsible for the accelerated void formation in the area leading to the premature failure.     

Unique cyclic performance of post-treated carbide-derived carbon as an anode electrode

Carbide-derived carbon (CDC) is an attractive anode material for Li-ion battery applications because diverse pore textures and structures from amorphous to highly ordered graphite can be controlled by changing the synthesis conditions and precursor, respectively. To elucidate the unique cycling behavior of the post air-treated CDC anode, electrochemical performance was studied under variation of C-rates with structural changes before and after cycling. By tailoring the pore texture of CDCs as removal of amorphous phase by post air-activation, the anode electrode showed a high increase of capacity under prolonged cycling and under high C-rate conditions such as 0.3–1.0 C-rates. The discharge capacities of the treated CDC increased from 400 mAh g⁻¹ to 913 mAh g⁻¹ with increasing cycle number and were close to high initial irreversible value, 1250 mAh g⁻¹, at the 220th cycle under a 0.1C-rate condition, which are unique and unusual cyclic properties in carbon anode applications. Under high C-rate conditions, the discharge capacities started to increase from around 160 mAh g⁻¹ and values of 415 mAh g⁻¹, 372 mAh g⁻¹, and 336 mAh g⁻¹, were observed at 0.3, 0.5, and 1.0 C-rates, respectively, at 600 cycles, demonstrating stable capacity performance.     

‘Two way’ shape memory composites based on electroactive polymer and thermoplastic membrane

A practical and facile strategy was proposed to fabricate composites that not only use the properties of individual components (commercial electroactive polymer and thermoplastic resin) to their advantage, but also produce synergy effect of ‘two way’ shape memory properties. In this design, electroactive polymer is treated as soft segment which provides actuation force via converting electrical energy to dynamic energy. Thermoplastic material serves as ‘hard segment’ to help with fixation of temporary shape thanks to its re-structuring and stiffness/modulus changing abilities through the reversible transitional temperature. Compared with traditional one way and two way shape memory materials, this composite material has the capability of changing shape without pre-programming. High shape recover property (99 ± 0.3%.) has been obtained due to the rubber elasticity of electroactive polymer matrix. Many features could be brought up based on this design, such as accurate control over deformation by changing strength of applied electric field as well as tailorable stimulus temperature and mechanical properties.     

Non-fullerene organic solar cells with 7% efficiency and excellent air stability through morphological and interfacial engineering

We report on the fabrication of the poly{[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]} (PTB7) and poly{[N,N-9-bis(2-octyldodecyl)- naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,59-(2,29-bithiophene)}(P(NDI2OD-T2)) active layer combination employing air brush spray coating technique in 2-methyl anisole. Optical absorption characteristics of the blend layer were examined utilizing UV–visible spectra in the wavelength sweep varying from 300 to 900 nm. Atomic force microscopy was utilized to analyze the surface characteristics of the fabricated active layer. Under the radiance of simulated solar light with 100 mW cm⁻² (AM 1.5G), the current density voltage (J-V) characteristics were determined by employing a solar simulator. Fullerene-free organic solar cells were build using a combination of P(NDI2OD-T2) acceptor and a polymer donor PTB7 with SnO₂ acting as an interlayer, which showed power conversion efficiency (PCEs) of more than 7.0%, which is considered as the best PCEs been reported for the chosen donor and the acceptor. The device is extremely stable, holding 75% of its unique effectiveness subsequent to being put away in air for 72 days even without encapsulation. These outcomes demonstrate that the spray-coated film is a feasible contrasting option to the vacuum-deposited ITO film in terms of cost for mass production and for roll-to-roll based organic solar cells.     

Anchoring of Pt and PtRu to carbon nanofibers studied by density functional theory calculations

PtRu particles supported on carbon nanofibers have been reported to have higher activity as anode catalysts in proton exchange membrane fuel cells than conventional catalysts. In the present work, density functional theory calculations are used to investigate the metal–carbon interface for different crystal facets of mono-metallic Pt and the PtRu alloy. The carbon side is modeled by graphene sheets with either zigzag or armchair termination. The strongest metal–carbon interaction is predicted for a (1 1 1) facet attached to a zigzag edge. The anchoring of the PtRu metal is found to have pronounced effects on the surface composition of the alloy. Whereas the bare surface is rich in Pt, the interface with carbon favors the stoichiometric bulk composition. Core level binding energies of carbon, platinum and ruthenium are found to provide valuable signatures of the interface and give means to interpret future high resolution photoemission core level spectroscopy experiments.     

Catalyst faceting during graphene layer crystallization in the course of carbon nanofiber growth

The low temperature catalytic growth of multiwall carbon nanotubes (MWCNTs) rests on the continuous nucleation and growth of graphene layers at the surface of crystalline catalyst particles. Here, we study the atomic mechanisms at work in this phenomenon, by observing the growth of such layers in situ in the transmission electron microscope, in the case of iron-based catalysts. Graphene layers, parallel to the catalyst surface, appear by a mechanism of step flow, where the atomic layers of catalyst are “replaced” by graphene planes. Quite remarkably, catalyst facets systematically develop while this mechanism is at work. We discuss the origin of faceting in terms of equilibrium particle shape and graphene layer nucleation. Step bunching due to impeded step migration, in certain growth conditions, yields characteristic catalyst nail-head shapes. Mastering the mechanisms of faceting and step bunching could open up the way to tailoring the structure of low temperature-grown MWCNTs, e.g. with highly parallel carbon walls and, ultimately, with controlled structure and chirality.     

Erosion resistance of CO2 corrosion scales formed on API P110 carbon steel

The erosion resistance of CO₂ corrosion scales formed on carbon steel was investigated in water–sand two-phase flow utilizing weight loss test, scanning electron microscopy, and X-ray diffraction. The effects of CO₂ partial pressure, stirring speed, test time, and grain size on the erosion resistance of the scales were analysed. Results show that several characteristics of CO₂ corrosion scales are key factors affecting erosion resistance. Cubic polynomials are used to fit the erosion rate data, and effectively evaluate the ability of CO₂ corrosion scales to resist erosion. An erosion mechanism, based on fluid dynamics and CO₂ corrosion scales characteristics, is discussed.     

Influence of temperature on the pitting corrosion behavior of AISI 316L in chloride–CO2 (sat.) solutions

The paper discusses the pitting corrosion behavior of AISI (American iron and steel institute) 316L stainless steel in aerated chloride solutions (0.1–2 M NaCl) at 25, 50 and 80 °C using potentiodynamic polarization technique. A comparison is made with CO₂-saturated chloride solutions. The results have revealed that pitting potential decreased in a logarithmic relationship with the chloride concentration, and decreased linearly with temperature. The influence of CO₂ on the chloride pitting of AISI 316L stainless steel is quite complex and found to be dependent on chloride concentration and test temperature. At 25 °C the presence of CO₂ appears to have insignificant effect on E_p irrespective of chloride concentration. As the temperature is raised to 50 or 80 °C the additions of CO₂ has caused marked negative shifts in pitting potential. The detrimental effect of CO₂ increases with NaCl concentration and temperature. The results indicate that pitting potential (E_p) is influenced by a synergy between chloride, CO₂ and temperature, and that this synergy depends on the chloride concentration and test temperature.