Boron Nitride-Based Overcoat Thick Films for MoSi2 Planar Heating Elements

This work first reports a boron nitride-based dielectric system that is designed for MoSi₂–based planar heating elements patterned on a regular 96% alumina substrate. The dielectric system is expected to function as an overcoat layer mainly to protect the printed heating elements from environments and to reduce thermal stress induced during thermal heating through improved heat dissipation. The boron nitride (BN) pastes mixed with a low softening glass of calcium barium aluminoborosilicate were screen printed onto MoSi₂ thick films and then fired at a temperature of 900°C. The addition of BN was found to increase the thermal conductivity considerably without detrimental chemical reactions with glass constituents. For instance, the thick film containing 30 wt% BN was regarded as a promising composition from the supporting evidences of good adhesion with MoSi₂, an increased thermal conductivity of ∼31 W·(m·K)⁻¹, and a high electrical resistance of 4.7 × 10¹⁰Ω.     

Effects of gamma irradiation on the thermal and mechanical properties of chitosan/PVA nanofibrous mats

Chitosan/poly(vinyl alcohol) (PVA) nanofibrous mats were prepared by the electrospinning method. The morphology and structure of electrospun nanofibers were investigated by scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. SEM images showed that the uniform and bead-free fibers were obtained at concentrations greater than 8 wt%. Chitosan/PVA mats were irradiated with different doses (50–200 kGy) of ⁶⁰Co gamma rays. The effect of irradiation dose on the mechanical and thermal properties of these films was also investigated. Increasing the irradiation dose led to a decrease in tensile strength. FT-IR and DSC demonstrated that there were strong intermolecular hydrogen bonds between the chitosan and PVA molecules.     

Incorporation of carbon nanotube into direct-patternable ZnO thin film formed by photochemical solution deposition

Direct-patterning of ZnO hybrid films containing MWNT was realized without using photoresist and dry etching. Photosensitive 2-nitrobenzaldehyde was introduced into the solution precursors as a stabilizer and contributed to form a cross-linked network structure during photochemical reaction. According to the incorporation of multi-walled nanotube (MWNT) into ZnO films, the transmittance of ZnO hybrid film containing MWNT did not change but the sheet resistance was improved due to the enhancement of charge mobility due to π-bonding nature of MWNT. These results suggested a possibility that a micro-patterned system can be fabricated relatively easily and without high-cost processes, for example, by conventional etching procedure.     

Hole injection improvement by doping of organic material in copper phthalocyanine

Hole injection properties of copper phthalocyanine (CuPc) layer doped with hexaazatriphenylene–hexacarbonitrile (HAT) were studied by changing the doping concentration of HAT. Hole injection efficiency of CuPc layer was improved by doping of HAT as a p-dopant and a maximum current density was obtained at a HAT doping concentration of 10%. The use of HAT doped CuPc layer as a hole injection layer improved the current efficiency of green phosphorescent organic light-emitting diodes.     

Effect of reduction conditions on electrocatalytic activity of a ternary PtNiCr/C catalyst for methanol electro-oxidation

The effect of reduction conditions on a Pt₂₈Ni₃₆Cr₃₆/C catalyst was investigated by using two different reduction methods: hydrogen reduction and NaBH₄ reduction. In hydrogen reduced catalysts, dissolution of metallic Ni and Cr was observed during cyclic voltammetry (CV) tests, and a larger amount of Ni and Cr was dissolved when reduced at higher temperatures. For methanol electro-oxidation, the highest specific current density of 1.70 A m⁻² at 600 s of the chronoamperometry tests was observed in the catalyst reduced at 300 °C, which was ∼24 times that of a Pt/C catalyst (0.0685 A m⁻²). In NaBH₄ reduced catalysts, formation of an amorphous phase and a more Pt-rich surface was observed in X-ray diffraction and CV results, respectively, with increasing amounts of NaBH₄. When reduced by 50 times of the stoichiometric amount of NaBH₄, the PtNiCr/C catalyst (PtNiCr-50t) showed a current density of 34.1 A g_{noble metal}⁻¹, which was 81% higher than the 18.8 A g_{noble metal}⁻¹ value of a PtRu/C catalyst at 600 s of the chronoamperometry tests. After 13 h of chronoamperometry testing, the activity of the PtNiCr-50t (15.0 A g_{noble metal}⁻¹) was 110% higher than the PtRu/C catalyst (7.15 A g_{noble metal}⁻¹). The PtNiCr/C catalyst shows promise as a Ru-free methanol oxidation catalyst.     

Physical degradation of MEA in PEM fuel cell by on/off operation under nitrogen atmosphere

The durability of PEMFCs is one of the most important issues for application in automotive vehicles with a repeated start-up and shut-down system. The understanding of degradation phenomena such as causes, mechanisms and influence of working condition is essential to improving the performance and lifetime of PEMFC. We conducted on/off cyclic operation in a single cell configuration with ultra purity nitrogen gas to investigate the physical degradation of membrane electrode assembly (MEA). After on/off cycle operation for 100,000 cycles under different humid condition, the characteristics of the MEAs were examined by in situ and ex situ analyses techniques. The physical degradation of MEA by on/off cycling led to a change in the membrane-electrode interfacial structure, which is mainly attributed to the loss of cell performance.     

Combinatorial Search for Quaternary Methanol Tolerant Oxygen Electro‐Reduction Catalyst

A combinatorial library containing 645 different compositions was synthesised and characterised for methanol tolerant oxygen electro‐reduction reaction (ORR) catalytic performance. The library was composed of compositions involving between 1 and 4 metals among Pt, Ru, Fe, Mo and Se. In an optical screening test, Pt(50)Ru(10)Fe(20)Se(10) composition exhibited the highest ORR activity in the presence of methanol. This composition was further investigated by synthesis and characterisation of a powder version catalyst [Pt(50)Ru(10)Fe(20)Se(10)/C]. At 0.85 V [vs. reversible hydrogen electrode (RHE)] in the absence of methanol, the Pt/C catalyst exhibited higher ORR current (0.0990 mA) than the Pt(50)Ru(10)Fe(20)Se(10)/C catalyst (0.0902 mA). But much higher specific activity (12.7 μA cm_pt^–2) was observed in the Pt(50)Ru(10)Fe(20)Se(10)/C catalyst than for the Pt/C catalyst 6.51 μA cm_pt^–2). In the presence of methanol, the ORR current decreased by 0.0343 and 0.247 mA for the Pt(50)Ru(10)Fe(20)Se(10)/C and Pt/C catalysts, respectively, which proved the excellent methanol tolerance of the Pt(50)Ru(10)Fe(20)Se(10)/C catalyst.     

Degradation of TiN Coatings on Inconel 617 and Silicon Wafer Substrates Under Pulsed Laser Ablation

The degradation behavior of TiN coatings on Inconel 617 and silicon (Si) wafer substrates was compared following Nd:YAG pulsed laser ablation to apply thermomechanical stress. Surface cracks and pores were observed on the TiN coating on the Inconel 617 after five pulses, and melting of the coating was occurred over ten pulses. The TiN coating on the Si wafer also showed surface cracks and pores, but there was no surface melting. As the pulses were increased, the surface roughness of the TiN coating on Inconel 617 increased more than the TiN coating on the Si wafer, and interfacial cracking was the dominant degradation behavior on the Si wafer. The hardness of the TiN coating decreased below 50% of its initial value (2200 HK) after five pulses on the Inconel 617, whereas over 70% of the initial value (2400 HK) was maintained on the Si wafer. The TiN coating on Inconel 617 showed diffusion of substrate atoms to the surface, while Si was not found in the TiN coating on the Si wafer even after 25 pulses. It was determined that the decrease in hardness was influenced by the cracking behavior and the diffusion of atoms from the substrate.     

Die quenching limit of AA2024 aluminum alloy billet on servo press

Die quenching of AA2024 aluminum alloy billets was carried out on a servo press with ram-motion control of WC-20 mass%Co dies directly after solution heat treatment (SHT). To clarify the dependence on billet size for die quenching, two billets with a height of h₀ = 8 mm or 16 mm and with the same diameter of 16 mm were prepared. The cylindrical billets were heated in an electric furnace at 823 K and transferred to the press. Then the billets were uniaxially compressed with a reduction in height (Δh/h₀) of 2% or 5%, and further held between the dies. The sandwiching duration by dies (t_d.q.) was varied from 0 to 8 s. Based a measured temperature change, hardness and TG–DTA analysis, it is found that die quenching is successfully carried out without precipitation hardening only in the case of the billet with a height of 8 mm and t_d.q. > 6 s. The reduction in height is limited less than 5% by intergranular fracture on side surface of billet during the die quenching process.