Electrochemical preparation of poly(2,5-dimethoxy-1,4-phenylene)

Summary p-Dimethoxybenzene was electro-oxidatively polymerized to give poly(2,5-dimethoxy-1,4-phenylene) with high yield. 1,4-Structure of polyphenylene was confirmed by ¹³C-NMR and IR spectrum. The polymer was deposited on electrode, and electrolysis solvent affected the polymer yield and morphology of the polymer. In a strongly basic solvent the polymerization was inhibited, which suggests that cation radical of p-dimethoxybenzene is an active species of this polymerization.     

Magneto-thermo-elastic problem of a conducting rectangular cylinder subjected to sinusoidal change in time of magnetic field

This study is concerned with a magneto-thermo-elastic problem of a conducting rectangular cylinder in an external magnetic field which varies sinusoidally in time. Analytical solutions of eddy currents induced in the cylinder are derived on the basis of a theory of the quasi-stationary current. Two-dimensional transient temperature change produced by the eddy current loss is derived by means of the Green’s function method. The stresses in the infinitely long cylinder in a plane state are derived by making use of the Airy’s stress function. The effect of a frequency in a sinusoidal change in time of the external magnetic field on behaviors of eddy current loss, temperature change and stresses in the cylinder is examined by numerical calculation. The skin effect with an increase in a frequency of the external magnetic field on the transient response of temperature change and stresses in the cylinder is discussed.     

Spontaneous emission from a planar microcavity below threshold and the wolf effect

Abstract

Equivalence between a planar microcavity below threshold and a partially coherent primary source is pointed out for the first time. Spatial coherence properties of spontaneous emission from the planar microcavity are controllable by varying two cavity parameters of the cavity length and the mirror reflectivity. The spontaneous emission gives rise to the Wolf effect which is spectral changes induced by the spatial coherence. It is clearly shown from our theoretical analyses that the spectrum in the far field shifts toward higher frequencies than that on the emitting plane of the planar microcavity. In particular, the blue shift of the far-field spectrum takes a maximum value at the centre of the far-field plane and decreases gradually far away from the centre. Moreover, the blue shift increases with decreasing values of the two cavity parameters.     

Cold Spraying of TiO<Subscript>2</Subscript> Photocatalyst Coating With Nitrogen Process Gas

Titanium dioxide (TiO₂) is a promising material for photocatalyst coatings. However, it is difficult to fabricate a TiO₂ coating with anatase phase by conventional thermal spray processes due to a thermal transformation to rutile phase. In this paper, anatase TiO₂ coatings were fabricated by the cold spray process. To understand the influence of process gas conditions on the fabrication of the coatings, the gas nature (helium or nitrogen) and the gas temperature are investigated. It was possible to fabricate TiO₂ coatings with an anatase phase in all spraying conditions. The process gas used is not an important factor to fabricate TiO₂ coatings. The thickness of the coatings increased with the process gas temperature increasing. It indicates that the deposition efficiency of the sprayed particles can be enhanced by controlling the spray conditions. The photocatalytic activity of the coatings is similar or better than the feedstock powder due to the formation of a large reaction area. Concludingly, cold spraying is an ideal process for the fabrication of a TiO₂ photocatalyst coating.     

Strength of self-organized TiO2 nanotube arrays

Self-organized titanium oxide (TiO₂) nanotube arrays were formed by an anodic oxidization technique. Nanoindentation experiments were conducted using three different indenters (i.e. flat punch, cone and triangular pyramid) to explore the mechanics governing the strength of the TiO₂ nanotubes. The force–displacement responses were strongly dependent on the tip geometry and size of the nanotubes. A stress-based fracture model considering graded, porous and discrete structures of the nanotube arrays is proposed, and fracture stress was estimated based on the model. The experimental fracture stresses obtained using different indenters were almost the same, regardless of the indenter shape, which indicates the validity of the model. The evaluated compressive strength of the TiO₂ ligament was approximately 3 GPa, and no clear size effects were observed for the 55–110 nm diameter nanotubes.     

Tribology of helical scan tape drive systems

The future direction of the designs of the metal evaporated tape for higher density recording in the helical scan tape drives which use MR heads was investigated. Static friction force between a tape and a roller guide increases the force with which the tape edge is pressed against the flange of the roller guide and wear debris is produced from the tape edge. The wear debris is driven to the recording area on the tape and increases a rewrite ratio, which indicates the ratio of failure of reading data. A solid lubricant at operating temperature was found to reduce the coefficient of static friction. However, the combination between the solid lubricant and MR heads which are heated by sense current may cause tape damage in dwell tests at low temperature. The increase in a melting temperature of the solid lubricant was found to improve the durability in dwell tests at low temperature.     

Effects of thermal contact resistance on film growth rate in a horizontal MOCVD reactor

Effects of thermal contact resistance between heater and susceptor, susceptor and graphite board in a MOCVD reactor on temperature distribution and film growth rate were analyzed. One-dimensional thermal resistance model considering thermal contact resistance and heat transfer area was made up at first to find the temperature drop at the surface of graphite board. This one-dimensional model predicted the temperature drop of 18K at the board surface. Temperature distribution of a reactor wall from the three-dimensional computational fluid dynamics analysis including the gap at the wafer position showed the temperature drop of 20K. Film growth rates of InP and GaAs were predicted using computational fluid dynamics technique with chemical reaction model. Temperature distribution from the three-dimensional heat transfer calculation was used as a thermal boundary condition to the film growth rate simulations. Temperature drop due to the thermal contact resistance affected to the GaAs film growth a little but not to the InP film growth.     

Grain boundary tracking: A four-dimensional visualization technique for determining grain boundary geometry via local strain mapping

A procedure for determining three-dimensional grain boundary geometry and its change under external loading is proposed for evaluating crystallographic deformation behaviours in polycrystalline materials, and the feasibility of this approach is confirmed for an aluminium alloy. X-ray microtomography has been combined with gallium-enhanced microscopy, in which grains are visualized in three dimensions by decorating grain boundaries with liquid gallium. Grain boundary particles are then extracted by comparing tomographic images with and without the gallium application. Three-dimensional reconstruction of grains is achieved using a connection scheme based on triplets of non-aligned points on grain boundaries. The deformation of the closed polygonal grains is visualized by combining the above technique with a microstructural tracking technique, in which the paths of particles are reconstructed by matching each pair of particles in consecutive images. This process also enables high-density four-dimensional strain mapping by tracking particles located in grains, providing direct interpretation of localized deformation caused by interaction between neighbouring grains.     

ω Transformation in cold-worked Ti–Nb–Ta–Zr–O alloys with low body-centered cubic phase stability and its correlation with their elastic properties

The ω transformation and its correlation with elastic properties were investigated in cold-worked Ti–36Nb–2Ta–3Zr–xO mass% alloys with low body-centered cubic (β) phase stability, known as gum metal. Analysis of the temperature dependence of the ω (hexagonal) phase formation using transmission electron microscopy and of the elastic properties of solution-treated and cold-worked alloys using resonant ultrasound spectroscopy revealed that in the solution-treated 0.36% and 0.51% O alloys, the high concentration of oxygen suppressed ω-phase formation from room temperature to a fairly low temperature of ～13 K. However, the ω phase was formed by cold working at room temperature in the 0.30% and 0.47% O alloys. Importantly, the fraction of the ω phase clearly increased upon cooling, which indicates that the formation of the ω phase is thermodynamically favorable near and below room temperature in the cold-worked 0.30% and 0.47% O alloys. This formation of the ω phase and the low stability of the β phase related to the low electron/atom (e/a) ratio were the dominant factors determining the elastic properties near and below room temperature in the cold-worked Ti–Nb–Ta–Zr–O alloys.     

Grain size refinement through gas bubble stirring in AC4CH cast aluminium alloy

A comparison has been made of the mechanical properties of gravity and squeeze cast aluminium alloys that have been grain refined using gas bubbling and those that have not. To find the optimum gas bubbling conditions, the alloy melt temperature, the gas flow rate and the gas bubbling times were varied over wide ranges. The microstructure of the gas bubbled gravity and squeeze cast materials is fine, equiaxed and non-dendritic with an average primary α size of 52 μm and 163 μm respectively. However, gas bubbling has no effect on the morphology of the eutectic Si. There seems to be no noticeable difference between the measured mechanical properties of the gravity and squeeze cast materials with or without the gas bubbling. The lack of improvement in the mechanical properties of the gravity cast alloy is due to casting defects and porosity, which offset the effects of the grain refinement. The crystal separation and showering mechanisms are operative for the formation of equiaxed grains.