Crystallization of Amorphous Tris(8‐hydroxyquinoline)aluminum Nanoparticles and Transformation to Nanowires

Amorphous tris(8‐hydroxyquinoline)aluminum (AlQ₃) nanoparticles can be grown directly into α‐phase crystalline nanowires in a one‐step heat treatment. At the most appropriate Ar pressure, heating time, and heating temperatures (between 150 and 190 °C), fine and long nanowires are obtained. The growth of the nanowires is dictated by the anisotropic bonding in α‐AlQ₃ crystals. The growth mechanism is illustrated by the concept of nucleation and molecular migration. Two exotherms are revealed, from differential scanning calorimetry analyses, in the transformation process of AlQ₃ amorphous nanoparticles to crystalline nanowires. The first exotherm is the transition from amorphous nanoparticles to the γ‐phase, and the second exotherm is the transition from the γ‐ to the α‐phase. By means of Kissinger plots, the activation energies for the crystallization of the γ‐phase and the transition from the γ‐ to the α‐phase are calculated, for the first time, to be 9.7 and 12.1 kJ mol^–1, respectively. A blue‐shift and higher intensity of photoluminescence after heat treatment are also demonstrated.     

Effect of quenching temperature on the morphology and separation properties of polypropylene microporous tubular membranes via thermally induced phase separation

Polypropylene microporous tubular membranes were prepared by using camphene as solvent and through thermally induced phase separation at various quenching temperatures. Characterization of the resulting membrane included scanning electron microscopy, differential scanning calorimetry, and wide angle X-ray scattering. Microscopic observation showed that the membrane was composed of spherical clusters and had a leafy structure. The crystallinity increased with the quenching temperature. The crystalline structure was of smectic form. Permeation performance was also determined, including pure water permeability and retention of dextran. The results showed that at lower quenching temperatures, the structure of membrane was denser. Therefore, the permeability was lower and the retention was higher.     

Numerical predictions of design and operating parameters of reformer on the fuel conversion and CO production for the steam reforming of methanol

SIMPLE-C algorithm and Arrhenius form of reaction model were employed to simulate the three-dimensional laminar flow field and the chemical reaction in a cylindrical methanol reformer under steam reforming. The effects of geometrical and thermo-fluid parameters on the CO and CO₂ productions as well as the heat and mass transfer in a cylindrical methanol reformer with a constant-volume catalyst bed will be observed in the present study. Low CO concentration in hydrogen-rich gas denotes a low load of CO removal in purifying processes. The results indicate that the smaller diameter-to-length ratio of chamber with a thicker catalyst bed enhances the methanol conversion and reduces the overall CO concentration in the cylindrical methanol reformer. This is because that a lower temperature distribution restrains the reverse water–gas-shift reaction to reduce the production of CO with a thicker catalyst bed.     

Environmentally assisted cracking of two-phase Fe-Mn-Al alloys in NaCl solution

Three two-phase Fe-Mn-Al alloys with nominal compositions, Fe-24Mn-9Al, Fe-27Mn-9Al-3Cr,. and Fe-27Mn-9Al-6Cr, were prepared in the solution-treated and cold-rolled conditions. The fractions of ferrite in the solution-treated condition were controlled at 46 to 60 pct, mainly by adjusting the carbon content and the relative amounts of Mn and Al. The ferrite fractions were reduced to 30 to 37 pct after 75 pct deformation by cold-rolling. Specimens were tensile tested at open circuit in aerated 3.5 pct NaCl solution at slow strain rates ranging from 4 × 10^-7 to 4 × 10^-5 s^-1 at room temperature. All of the alloys were quite susceptible to environmentally assisted cracking (EAC). The deformed specimens showed less susceptibility, presumably because the plasticity was already too limited. The EAC appeared to occur at or after the onset of plastic deformation. In this alloy system, the ferritic phase was less resistant to EAC than the austenitic phase, in contrast to the Fe-Cr-Ni stainless steels. The crack propagated preferentially through the ferrite grains or along the ferrite/austenite grain boundaries. The addition of up to 6 pct Cr did not improve the EAC resistance. Formerly Graduate Student, Department of Materials Science and Engineering, National Tsing Hua University     

Studies of phosphonate‐containing bismaleimide resins. I. Synthesis and characteristics of model compounds and polyaspartimides

Two phosphonate‐containing bismaleimide (BMI) [(4,4′‐bismaleimidophenyl)phosphonate] monomers with different melting temperatures and similar curing temperatures were synthesized by reacting N‐hydroxyphenylmaleimide with two kinds of dichloride‐terminated phosphonic monomers. The BMI monomers synthesized were identified with ¹H‐, ¹³C‐, and ³¹P‐nuclear magnetic resonance (NMR) spectroscopy and elemental analysis. The phosphonate‐containing BMI monomers react with a free‐radical initiator to prepare phosphonate‐containing BMI polymers and also with various aromatic diamines to prepare a series of polyaspartimides as reactive flame retardants. The polymerization degrees of polyaspartimides depend on the alkalinity and nucleophility of diamines as chain extenders. Differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA) were used to study the thermal properties of the phosphonate‐containing BMI resins such as the melting temperature, curing temperature, glass transition temperature (T_g), and thermal resistance. All the phosphonate‐containing BMI resins, except the BMI polymers, have a T_g in the range of 210–256°C and show 5% weight loss temperatures (T_5%) of 329–434 and 310–388°C in air and nitrogen atmospheres, respectively. The higher heat resistance of cured BMI resin relative to the BMI polymer is due to its higher crosslinking density. Since the recrosslinking reactions of BMI polymers and polyaspartimides occur more easily in an oxidation environment, their thermal stabilities in air are higher than are those in nitrogen gas. In addition, the thermal decomposition properties of polyaspartimides depend on the structures and compositions of both the diamine segments and the BMI segments. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1919–1933, 2002     

Modulation of wall thickness of Al-doped ZnO nanotubes by nanolamination of atomic layer deposition for oxygen sensing

The high surface-to-volume ratio and feature dimensions of the gas sensors are the key factors for improving the gas response. In this study, a novel method to prepare an Al-doped ZnO (AZO) nanotube oxygen sensor with tunable wall thickness is reported via the ZnO–Al₂O₃ nanolamination of atomic layer deposition (ALD) using tris(8-hydroxyquinoline) gallium nanowire (GaQ₃NW) as a template. The ALD of Al₂O₃ significantly enhances wall uniformity and decreases the wall thickness of the AZO nanotubes. In addition, the incorporation of Al₂O₃ allows full coverage of AZO on GaQ₃NWs. With an increase in the Al₂O₃ fraction, the carrier concentration increases, but the depth of the depletion layer and gas response of the nanotube sensor are reduced. The gas response of the nanotubes is inversely proportional to wall thickness, suggesting that it is a function of the surface-to-volume ratio. When the wall thickness is decreased to 12 nm, the gas response of AZO nanotubes with 2% Al increases significantly to 7. This can be explained by the grain control model, because thin wall leads to the formation of fully charge-depleted nanotubes.     

Genetic algorithm-based decision support for the restoration budget allocation of historical buildings

Historical building preservation is becoming increasingly important world-wide due to the emphasis on cultural heritage and its potential benefits. Restoration management and cost allocation for these valuable buildings have been constant concerns. This study discusses problems concerning restoration budget allocation for historical buildings of the Tainan local government. A new contracting method based on genetic algorithm (GA) is presented to support decision makers in determining the optimal budget allocation and relevant contracting methods. Compared with traditional contracting methods, the result of a pilot test shows that the new method provides more effective and economical decision suggestions. Lessons learned in Tainan city could be useful for many other cities that are facing similar problems.     

One-dimensional organic and organometallic nanostructured materials

One-dimensional (1D) organic and organometallic nanomaterials are of considerable interests for both fundamental research and potential applications. They are likely to play critical roles in improving the efficiency of various electronic, photonic, biosensing devices, etc. In this context, the authors present a comprehensive review of current research on 1D organic and organometallic nanostructures. The synthetic strategies for achieving the 1D growth are elucidated by four categories: (1) template-based synthesis, (2) vapor-solid method, (3) solution-based self-assembly, and (4) dictation by the anisotropic nature. The unique thermal, optical, electronic, field emission properties and biocidal activity of 1D organic and organometallic nanostructures are consequently highlighted. Some promising applications in (integrated) molecular electronic, optoelectronic and photonic devices are also discussed.     

Nano-structured Cu2O solar cells fabricated on sparse ZnO nanorods

Nano-structured Cu₂O/ZnO nanorod (NR) heterojunction solar cells fabricated on indium tin oxide (ITO)-coated glass are studied. Substrate film and NR density have a strong influence on the preferred growth of the Cu₂O film. The X-ray diffractometer (XRD) analysis results show that highly (2 0 0)-preferred Cu₂O film was formed when plating on plain ITO substrate. However, a highly (1 1 1)-preferred Cu₂O film was obtained when plating on sparse ZnO NRs. SEM, TEM and XRD studies on sparse NR samples indicate that the Cu₂O nano-crystallites mostly initiate its nucleation on the peripheral surfaces of the ZnO NRs, and are also highly (1 1 1)-oriented. Solar cells with ZnO NRs yielded much higher efficiency than those without. In addition, ZnO NRs plated on a ZnO-coated ITO glass significantly improve the shunt resistance and open-circuit voltage (V_oc) of the devices, with consistently much higher efficiency obtained than when ZnO NRs are directly plated on ITO film. However, longer NRs do not improve the efficiency due to low short-circuit current (J_sc) and slightly higher series resistance. The best conversion efficiency of 0.56% was obtained from a Cu₂O/ZnO NRs heterojunction solar cell fabricated on a 80 nm ZnO-coated ITO glass with V_oc=0.514 V, J_sc=2.64 mA/cm² and 41.5% fill factor.     

On the processes of photo-induced hydrogen generation from methanol solution by Ta3N5 and WO3

The hydrogen production rates from deionized water and 20% methanol solution, with or without the presence of Ta₃N₅, WO₃, and the indirect Z-scheme Ta₃N₅/WO₃, were investigated. Under irradiation of a 300 W Xe lamp, all of these three catalysts assisted hydrogen generation in deionized water. In the methanol solution, Ta₃N₅, and WO₃ reduced the hydrogen generation, but Ta₃N₅/WO₃ significantly enhanced the hydrogen production rate by seven times. Under visible light irradiation, the effects of the three catalysts are different from those under full spectrum irradiation. The mechanisms based on the competition of methanol decomposition and water reduction in the presence of catalyst under different irradiation conditions are proposed to explain the different hydrogen generation behaviors.