Boron carbide nanowires with uniform CNχ coatings

Boron carbide nanowires with uniform carbon nitride coating layers were synthesized on a silicon substrate using a simple thermal process. The structure and morphology of the as-synthesized nanowires were characterized using x-ray diffraction, scanning and transmission electron microscopy and electron energy loss spectroscopy. A correlation between the surface smoothness of the nanowire sidewalls and their lateral sizes has been observed and it is a consequence of the anisotropic formation of the coating layers. A growth mechanism is also proposed for these growth phenomena.

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Tensile behaviour of non-uniform fibres and fibrous composites

This work investigates the tensile behaviour of non-uniform fibres and fibrous composites. Wool fibres are used as an example of non-uniform fibres because they're physical, morphological and geometrical properties vary greatly not only between fibres but also within a fibre. The focus of this work is on the effect of both between-fibre and within-fibre diameter variations on fibre tensile behaviour. In addition, fit to the Weibull distribution by the non-brittle and non-uniform visco-elastic wool fibres is examined, and the Weibull model is developed further for non-uniform fibres with diameter variation along the fibre length. A novel model fibre composite is introduced to facilitate the investigation into the tensile behaviour of fibre-reinforced composites. This work first confirms that for processed wool, its coefficient of variation in break force can be predicted from that of minimum fibre diameters, and the prediction is better for longer fibres. This implies that even for processed wool, fibre breakage is closely associated with the occurrence of thin sections along a fibre, and damage to fibres during processing is not the main cause of fibre breakage. The effect of along-fibre diameter variation on fibre tensile behaviour of scoured wool and mohair is examined next. Only wet wool samples were examined in the past. The extensions of individual segments of single non-uniform fibres are measured at different strain levels. An important finding is the maximum extension (%) (Normally at the thinnest section) equals the average fibre extension (%) plus the diameter variation (CV %) among the fibre segments. This relationship has not been reported before. During a tensile test, it is only the average fibre extension that is measured. The third part of this work is on the applicability of Weibull distribution to the strength of non-uniform visco-elastic wool fibres. Little work has been done for wool fibres in this area, even though the Weibull model has been widely applied to many brittle fibres. An improved Weibull model incorporating within-fibre diameter variations has been developed for non-uniform fibres. This model predicts the gauge length effect more accurately than the conventional Weibull model. In studies of fibre-reinforced composites, ideal composite specimens are usually prepared and used in the experiments. Sample preparation has been a tedious process. A novel fibre reinforced composite is developed and used in this work to investigate the tensile behaviour of fibre-reinforced composites. The results obtained from the novel composite specimen are consistent with that obtained from the normal specimens.

Needleless electrospinning of uniform nanofibers using spiral coil spinnerets

Polyvinyl alcohol nanofibers were prepared by a needleless electrospinning technique using a rotating spiral wire coil as spinneret. The influences of coil dimension (e.g., coil length, coil diameter, spiral distance, and wire diameter) and operating parameters (e.g., applied voltage and spinning distance) on electrospinning process, nanofiber diameter, and fiber productivity were examined. It was found that the coil dimension had a considerable influence on the nanofiber production rate, but minor effect on the fiber diameter. The fiber production rate increased with the increased coil length or coil diameter, or the reduced spiral distance or wire diameter. Higher applied voltage or shorter collecting distance also improved the fiber production rate but had little influence on the fiber diameter. Compared with the conventional needle electrospinning, the coil electrospinning produced finer fibers with a narrower diameter distribution. A finite element method was used to analyze the electric field on the coil surface and in electrospinning zone. It was revealed that the high electric field intensity was concentrated on the coil surface, and the intensity was highly dependent on the coil dimension, which can be used to explain the electrospinning performances of coils. In addition, PAN nanofibers were prepared using the same needleless electrospinning technique to verify the improvement in productivity.

Studying non-uniform electrodeposition using the wire beam electrode method

Nonuniform electrodeposition is a major concern in almost every practical electrodeposition application. The ablility to control nonuniformity in electrodeposition is the key to successful plating for corrosion resistance, and more especially to meeting the very exacting requirements of electroforming, electrodeposition. This paper presents a novel technique namely the wire beam electrode (WBE) for characterizing and monitoring nonuniform electroplating processes. For the first time, the nonuniform distribution of electroplating currents (NDEC) has been mapped. Preliminary experimental results indicated that electrochemical heterogeneity was the key factor affecting NDEC. The secondary current distribution, rather than the primary current distribution, played a major role in determining the NDEC. This work suggests that the WBE is a practical tool for characterizing and optimizing electrodeposition processes and for verifying the accuracy and completeness of mathematic modelling of electrodeposition processes.