Morphology and constitution of the compound layer formed on nitrided Fe–4wt.%V alloy

The microstructure of the compound (“white”) layer formed on the surface of Fe–4wt.%V alloy, by nitriding in a gas mixture of ammonia and hydrogen at 580 °C, has been investigated by employing light and scanning electron microscopy, X-ray diffraction and electron probe microanalysis. The compound layer is dominantly composed of γ^|-Fe₄N nitride. Quantitative analysis of the composition data demonstrated that V is present in the compound layer as VN precipitates, i.e. V is not taken up significantly in (Fe, V) nitrides. A mechanism for compound-layer formation has been proposed.

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Dynamics of nanoscale grain-boundary decohesion in aluminum by molecular-dynamics simulation

The dynamics and energetics of intergranular crack growth along a flat grain boundary in aluminum is studied by a molecular-dynamics simulation model for crack propagation under steady-state conditions. Using the ability of the molecular-dynamics simulation to identify atoms involved in different atomistic mechanisms, it was possible to identify the energy contribution of different processes taking place during crack growth. The energy contributions were divided as: elastic energy—defined as the potential energy of the atoms in fcc crystallographic state; and plastically stored energy—the energy of stacking faults and twin boundaries; grain-boundary and surface energy. In addition, monitoring the amount of heat exchange with the molecular-dynamics thermostat gives the energy dissipated as heat in the system. The energetic analysis indicates that the majority of energy in a fast growing crack is dissipated as heat. This dissipation increases linearly at low speed, and faster than linear at speeds approaching 1/3 the Rayleigh wave speed when the crack tip becomes dynamically unstable producing periodic dislocation bursts until the crack is blunted.

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A quantitative characterization of the optical absorption spectrum associated with hydrogenated amorphous silicon

We propose a quantitative means of characterizing the optical absorption spectrum associated with an amorphous semiconductor. In particular, for a representative hydrogenated amorphous silicon optical absorption experimental data set, through a series of least-squares linear fits of an exponential function to this experimental data set, taken over a number of optical absorption ranges, we determine how the breadth of the optical absorption tail varies along the optical absorption spectrum of hydrogenated amorphous silicon. We find that the quantitative variations in the breadth of the optical absorption tail that are found provide for a clear delineation between the different regions of the optical absorption spectrum of hydrogenated amorphous silicon. We complete this analysis by theoretically determining the form of the optical absorption spectrum using a recently developed empirical model for the density of states functions corresponding to hydrogenated amorphous silicon, this analysis providing a theoretical basis for the interpretation of our results.

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Optical switching of a photochromic bis-phenylazo compound in PMMA films

We present our results on a newly synthesized bis-phenylazo derivative, namely bisperfluoroalkylsulfonylamino- arylazomethylene-triphenyl-phosphorane (BAM-TPP). Thin films of BAM-TPP in polymethylmethacrylate (PMMA) matrix were prepared. The films (thickness, d < 60 μm) were exposed to UV-vis light with variable intensity in order to stimulate the photochromic reaction of BAM-TPP. The resulting absorption changes of the BAM-TPP/PMMA films were investigated by spectrophotometry. The absorption spectra reveal that BAM-TPP molecules in PMMA undergo photoisomerization with resulting decrease of absorbance in the range 500–700 nm. Finally, the time response of film transmittance at 514 nm under increasing CW light intensity was recorded, showing that the reverse photochromic process brings the absorbance back to its pristine value. The obtained films thus proved to be suitable for optical switching applications.

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Nitrogen absorption by Fe-1.04at.%Cr alloy: uptake of excess nitrogen

By dedicated pre-nitriding (at 580 °C in an ammonia/hydrogen gas atmosphere) and de-nitriding (at 470 °C in a hydrogen gas atmosphere) experiments, performed on Fe-1.04at.%Cr alloy, it could be demonstrated that the uptake of “excess” nitrogen by the nitrided ferritic matrix is not due to the presence of iron in chromium-nitride precipitates, as it was suggested previously. The determination of nitrogen-absorption isotherms for these pre-nitrided and de-nitrided Fe-1.04at.%Cr alloy specimens revealed that the total amount of excess nitrogen in the alloy is composed of two parts: (a) nitrogen adsorbed at the precipitate/matrix interface, and (b) nitrogen dissolved interstitially in the ferrite matrix strained by the misfit between (coherent) the CrN precipitates and the matrix.

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Sub-solidus melting of directionally solidified Rene 80 superalloy during solution heat treatment

The microstructure of directionally solidified Rene 80 (DS Rene 80) superalloy in the standard solution heat treated condition was examined. Sub-solidus incipient melting was observed, which was found to be caused by the liquation of terminal solidification reaction products present in front of the γ–γ′ eutectic in the as-cast alloy. Based on the differential scanning calorimetry (DSC) measurements, and microstructural examination of heat-treated and water-quenched specimens, sub-solidus incipient melting in the alloy is likely to occur below 1,160 °C, and this is a key factor to be considered in the development of a suitable solution heat treatment scheme for DS Rene 80.

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Composite bond inspection

After 50+ years of research to discover a way of determining the in situ strength of an adhesive bond, a method has been found to probe this key parameter. The initial testing on composite joints has shown it to be accurate and reliable. While effective, it is expensive to implement in a production environment and then during the final stages of assembly. A second method of probing the adherent surface prior to bonding is presented that offers the promise of determining adhesion potential before final bond consolidation. These new inspection methods should enable significant increases in structural performance for structures that utilize composite materials. Before examining these two new methods a brief review of past work on adhesive bond strength determination is presented.

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The synthesis and characterisation of grafted random styrene butadiene for biomedical applications

The work undertaken investigates the spectral, thermal and surface characteristics of a random styrene butadiene rubber (SBR) with monomeric graft(s) of acrylic acid (AA), N-vinyl-2-pyrrolidinone (NVP) or N-isopropylacrylamide (NIPAAm) synthesised using UV polymerisation. The grafted materials were characterised by differential scanning calorimetry (DSC), modulated differential scanning calorimetry (MDSC), attenuated total reflectance infrared Fourier transform spectrometry (ATR-FTIR) and atomic force microscopy (AFM). Thermograph analysis has shown an endothermic transition occurring at ~75 °C for all random SB-g-NVP copolymers, whereas the T _g value for random SB copolymer was found at 60 °C, thus suggesting that a chemical reaction between styrene and NVP had occurred. Similar thermal profiles to that of random SB-g-NVP copolymers were evident when random SB was UV polymerised with AA. When NIPAAm was grafted onto random SB, a notable exothermic transition was evident in all samples tested using DSC. It was established using MDSC that this exothermic transition was caused by the breakdown of crosslinks as a result of UV polymerisation.

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Physical, electrical, and optical properties of SF-PECVD-grown hydrogenated microcrystalline silicon with growth surface electrical bias

Characterization results on hydrogenated microcrystalline silicon (μc-Si:H) thin films grown in a Saddle Field (SF) PECVD system are presented. The microcrystalline content of the films is controlled by the application of a positive electrical bias to the film growth surface. The results of photoluminescence, atomic force microscopy, infrared-absorption, and electrical conductivity studies are presented. The results correlate to the changing microcrystalline content of the films in the same way as when microcrystalline content is influenced through growth parameters such as hydrogen dilution in other CVD techniques.

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Mechanics of the hysteretic large strain behavior of mussel byssus threads

Natural fibers are particularly interesting from a materials point of view since their morphology has been tailored to enable a wide range of macroscopic level functions and mechanical properties. In this paper, we focus on mussel byssal threads which possess a morphology specifically designed to provide a hysteretic yet resilient large strain deformation behavior. X-ray diffraction studies have shown that numerous natural fibers have a multi-domain architecture composed of folded modules which are linked together in series along a macromolecular chain. This microstructure leads to a strong rate and temperature dependent mechanical behavior and one which exhibits a stretch-induced softening of the mechanical response as a result of the underlying morphology evolving with imposed stretched. This paper addresses the development of a constitutive model for the stress–strain behavior of the distal portion of mussel byssal threads based on the underlying protein network structure and its morphology evolving with imposed stretched. The model will be shown to capture the major features of the stress–strain behavior, including the highly nonlinear stress–strain behavior, and its dependence on strain rate and stretch-induced softening.

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Self-assembled nanowires on semiconductor surfaces

A number of different families of nanowires which self-assemble on semiconductor surfaces have been identified in recent years. They are particularly interesting from the standpoint of nanoelectronics, which seeks non-lithographic ways of creating interconnects at the nm scale (though possibly for carrying signal rather than current), as well as from the standpoint of traditional materials science and surface science. We survey these families and consider their physical and electronic structure, as well as their formation and reactivity. Particular attention is paid to rare earth nanowires and the Bi nanoline, both of which self-assemble on Si(001).Further information within the topic of this review article, including an up-to-date list of relevant publications, can be found on our Website. The address is:

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A review of sealing technologies applicable to solid oxide electrolysis cells

This article reviews designs and materials investigated for various seals in high temperature solid oxide fuel cell “stacks” and how they might be implemented in solid oxide electrolysis cells that decompose steam into hydrogen and oxygen. Materials include metals, glasses, glass–ceramics, cements, and composites. Sealing designs include rigid seals, compressive seals, and compliant seals.

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Stretching a stiff polymer in a tube

The present paper investigates the force-extension behavior of a stiff polymer under stretching inside a small tube. We develop a theory and perform Brownian dynamic simulations based on a recently developed generalized bead-rod model (GBR) to show that the force-extension relation of such a strongly confined polymer chain can be described by that of an unconfined polymer subject to an effective force which is derived based on Odijk’s theory of a confined polymer chain.

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Amorphous and nano crystalline phase formation in Ni<Subscript>2</Subscript>MnGa ferromagnetic shape memory alloy synthesized by melt spinning

Melt spinning technique was used to synthesize Ni₂MnGa ferromagnetic shape memory alloy ribbons. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) analysis of the ribbon synthesized at lower wheel speed (20 m/s) reveal the formation of very fine clusters of austenitic phase of Ni₂MnGa. However at higher wheel speed (30 m/s) the formation of martensite and nanoparticles of Ni₂MnGa with a size range of 10–20 nm in the amorphous matrix is observed. Also an amorphous phase was observed at higher wheel speed in some areas of the ribbon. Annealing (1000 °C, 1 h) of the ribbon synthesized at higher wheel speed resulted in martensite and γ (gamma) phases. Amorphous phase, Ni₂MnGa nanoparticles, and the martensite phase are analyzed in detail.

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A quenching apparatus for the gaseous products of the solar thermal dissociation of ZnO

Rapid cooling for avoiding the recombination of Zn vapor and O₂ derived from the solar thermal dissociation of ZnO is investigated using a thermogravimeter coupled to a quenching apparatus. The ZnO sample, which is placed in a cavity receiver and directly exposed to concentrated solar irradiation, underwent dissociation in the temperature range 1,820–2,050 K at a rate monitored by on-line thermogravimetry. The product gases were quenched by water-cooled surfaces and by injection of cold Ar at cooling rates from 20,000 to 120,000 K/s, suppressing the formation of ZnO in the gas phase and at the walls. Zinc content of the collected particles downstream varied in the range 40–94% for Ar/Zn(g) dilutions of 170 to 1,500.

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Refined model of elastic nanoindentation of a half-space by the blunted Berkovich indenter accounting for tangential displacements on the contact surface

Elastic contact between a non-ideal Berkovich indenter and a half-space is investigated. The derived mathematical model of the contact allows for tangential displacements of the boundary points of the half-space. The tip of the blunted indenter is simulated as a smooth surface. The boundary element method is implemented in the model for numerical simulation of nanoindentation. The relative deviation function is introduced and calculated to quantify the influence of the tangential displacements on the load–displacement curves. A simple expression is derived for the impact of the tangential displacements on the values of the reduced Young’s modulus determined due to nanoindentation studies. The refined model was successfully applied to simulate the experimental load–displacement curves gained by elastic nanoindentations of flat LiF and KCl samples. Such values of the indenter bluntness (the varying parameter) were found that the simulated load–displacement curves coincided with those of the experimental data at displacements higher than 7.5 nm. The model neglecting tangential displacements gives slightly differing values for the parameter of the indenter bluntness.

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Woolrock—a material for technical use consisting of keratin

This article debates the production of mouldings made of keratin. It is demonstrated that the properties of keratin allow for being processed with heat and pressure to manufacture tough mouldings without chemical preprocessing of the used wool. This material thus has a high potential as a bioplastic, because it potentially can be used with conventional plastic manufacturing techniques. Additionally, it might also serve as an adhesive in various applications. The biobased material might become a sustainable source for mouldings.

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