Thermodynamic stabilization of nanocrystalline aluminum

Journal of Materials Science - Nanocrystalline metals are generally unstable due to a large volume fraction of high-energy grain boundaries associated with a small grain size. Preferential dopant...     

Spectroscopic evidence for the presence of internal silanols in highly siliceous ZSM-5

FTi.r. and MAS n.m.r. evidence is presented which establishes the presence of internal silanols in ZSM-5. The concentration of internal silanols is shown to increase as aluminium content decreases and they are believed to be responsible for the phenomenon of excess ion exchange previously reported.     

Spectroscopic evidence and control of compensating native defects in doped ZnSe

Electron paramagnetic resonance spectroscopy combined with photoexcitation is used to identify and characterise the defects responsible for the compensation in iodine or aluminium doped ZnSe bulk crystals. The principal g-values of the Al_ZnV_Zn complex are reported for the first time. The acceptor levels of both A-centres observed are determined at 0.50 and 0.54 eV above the valence band edge for I_SeV_Zn and Al_ZnV_Zn, respectively. Annealing of these samples in Zn vapour is shown to be suitable for reproducible adjustments of the electron concentration at room temperature up to a few 10¹⁸ cm⁻³. The tight coupling of these vapour phase equilibrations with the electrical and spectroscopic analysis allows to propose a simple defect-chemical model.     

Frequency stabilization of distributed-feedback laser diodes at 1572 nm for lidar measurements of atmospheric carbon dioxide

We demonstrate a wavelength-locked laser source that rapidly steps through six wavelengths distributed across a 1572.335 nm carbon dioxide (CO(2)) absorption line to allow precise measurements of atmospheric CO(2) absorption. A distributed-feedback laser diode (DFB-LD) was frequency-locked to the CO(2) line center by using a frequency modulation technique, limiting its peak-to-peak frequency drift to 0.3 MHz at 0.8 s averaging time over 72 hours. Four online DFB-LDs were then offset locked to this laser using phase-locked loops, retaining virtually the same absolute frequency stability. These online and two offline DFB-LDs were subsequently amplitude switched and combined. This produced a precise wavelength-stepped laser pulse train, to be amplified for CO(2) measurements.     

Effect of pulsed dye-laser wavelength stabilization on spectral overlap in atmospheric NO fluorescence studies

We introduce an inexpensive application of a Fabry-Perot etalon to control long-term UV-laser line drift in atmospheric NO laser-induced fluorescence (LIF) measurements by monitoring the visible fundamental of a pulsed dye laser. A linear image sensor captures the interference pattern, and the dye grating can be adjusted to maintain a fixed wavelength through an interface with labview software. Results indicate that the laser wavelength can be fixed to an accuracy of +/-0.0001 nm in the dye fundamental and +/-0.00003 nm in the UV beam. Hence the average error in the LIF signal owing to fluctuations in spectral overlap between the laser and the NO absorption transition decreases from ~5 to ~0.05%, which results in improved measurement accuracy.     

Microstructural evidence for counter-diffusion of aluminum and oxygen during the growth of alumina scales

Abstract

A novel, two-stage oxidation experiment is described that enables the outward diffusion of cations in alumina scales during high-temperature oxidation to be analyzed on the basis of microstructural changes in the surface morphology of the scale. Using this technique, observations of aluminum out-diffusion along α-Al₂O₃ grain boundaries during oxidation of Fe–Cr–Al alloys, nickel aluminides and platinum-modified NiAl bond-coats are made. Although microstructural evidence for the inward grain boundary diffusion of oxygen is more difficult to obtain, it still can be demonstrated by the growth of the oxide above interface cavities on nickel aluminides and inside internal cracks in the alumina scales during cyclic oxidation of zirconia top-coated material. SEM examination of the crack surfaces after scale spallation provides a vivid illustration of two simultaneous processes, aluminum outward and oxygen inward diffusion along grain boundaries in the scale.     

Spectroscopic characterization of two different microwave (2.45 GHz) induced argon plasmas at atmospheric pressure

A surface-wave-sustained discharge created by using a surfatron device in a tube open to the atmosphere can be used to maintain a microwave (2.45 GHz) plasma at atmospheric pressure at powers of less than 300 W. The TIA (Torche a Injection Axiale) is a device also producing a plasma that, moreover, permits us to work at high power (higher than 200 W and up to 1000 W). A study of the departure from the thermodynamic equilibrium existing in the argon plasmas created by both devices has been done by using optical emission spectroscopy techniques in order to characterize them and to evaluate their possible advantages when they are used for applied purposes.     

Embedding variable micro-capacitors in polydimethylsiloxane for enhancing output power of triboelectric nanogenerator

Nano Research - Polydimethylsiloxane (PDMS) is an excellent material for investigating the mechanism of triboelectricity as it can easily be used to construct various microstructures. In this...     

Ru-B催化剂催化NaBH4水解制氢研究

利用化学浸渍-还原法制备出了Ru-B催化剂,考察了催化剂的制备条件和反应条件对Ru-B催化剂催化NaBH4水解制氢性能的影响。结果表明:当活性组分前体RuCl3·6H2O和还原剂NaBH4的物质的量比为1∶7,还原温度为303K时,制得的Ru-B催化剂催化NaBH4水解制氢性能最佳。当催化剂浓度为0.17g/L,反应温度为303K,NaBH4浓度为0.22mol/L,NaOH浓度为0.01mol/L,转速为540r/min时,Ru-B催化剂催化NaBH4水解产氢的速率可达1740mL H2/(min·g)。还发现Ru-B催化剂催化NaBH4水解产氢的速率与催化剂用量呈线性关系,计算得到Ru-B催化剂催化NaBH4水解产氢反应的活化能为23.58kJ/mol。     

Kinetics of aluminum dross dissolution in sec-butyl alcohol for aluminum sec-butoxide

Al sec-butoxide (ASB) has been used as a precursor for activated aluminas but its cost is higher than any other type of precursor. This study was carried out on the dissolution kinetics for synthesis of the ASB from Al dross waste. The reaction was performed under the molar ratio of Al dross and sec-butyl alcohol (SBA) of 3 mol SBA/mol Al with a catalyst of 10^?3 mol HgI₂/mol Al and three different dissolution temperatures of 80, 90 and 100 °C. The Al reactant was used with Al dross of 3–5 mm size range. As a result of the experiment, the dissolution reaction gave a 65% yield after 24 h. The dissolution mechanism was determined by the shrinking core model assumed by the shape of spherical particles. Especially, the kinetic data were well fitted by a chemical reaction in the model. By the Arrhenius equation, the apparent activation energy was determined to be 40.9 kJ mol^?1 at the given reaction temperatures.     

Comparison of in vivo biocompatibilities between parylene-C and polydimethylsiloxane for implantable microelectronic devices

Implantable devices are often composed of or coated with different biologically compatible materials based on their requirements. Selecting a surface material for an implantable device is not an easy task, and it is necessary to compare the biocompatibilities of the available surface materials. In this study, we perform a comparison of the in vivo biocompatibilities of polydimethylsiloxane (PDMS) and para-xylyene polymer (parylene-C) as they are considered to be candidates for a coating material for implantable microelectronic devices. For in vivo biocompatibility testing, fifty four male Sprague-Dawley rats were used for testing, and they were divided into three groups (PDMS, parylene-C and a positive control). At one, four and twelve weeks after implantation of the test object, the density of inflammatory cells and the granulation layer thickness were recorded for each group and compared with other groups using visible light and fluorescence microscopy. The thickness of the granulation layer tended to decrease over time for all of the experimental groups, whereas the granulation layer thickness remained constant in the positive control group. The thinnest capsular layer was observed for the parylene-C group and fewest inflammatory cells were observed in this group during the entire experimental period. Macrophage infiltration was minimal, even at one week, and was not observed thereafter. The parylene-C group showed better biocompatibility than the PDMS groups, both for acute and chronic implantation. Thus, parylene-C is the best candidate of the tested materials for applications involving permanent implantable micro-devices.     

Effect of grain-boundary stabilization on the strength, thermal conductivity, and dielectric properties of aluminum nitride

The thermal conductivity, dielectric properties, and strength of A1N ceramics were studied. The ceramics were prepared by semidry pressing and sintering. Increasing the sintering time was found to increase the thermal conductivity of the ceramics up to 200 W/(m K). A nonequilibrium-phonon-propagation method was used to analyze the effect of grain boundaries and processing conditions on the thermal conductivity of the ceramics.     

Nanoconfinement in activated mesoporous carbon of calcium borohydride for improved reversible hydrogen storage

Mesoporous carbon frameworks were synthesized using the soft-template method. Ca(BH(4))(2) was incorporated into activated mesoporous carbon by the incipient wetness method. The activation of mesoporous carbon was necessary to optimize the surface area and pore size. Thermal programmed absorption measurements showed that the confinement of this borohydride into carbon nanoscaffolds improved its reversible capacity (relative to the reactive portion) and performance of hydrogen storage compared to unsupported borohydride. Hydrogen release from the supported hydride started at a temperature as low as 100?°C and the dehydrogenation rate was fast compared to the bulk borohydride. In addition, the hydrogen pressure necessary to regenerate the borohydride from the dehydrogenation products was reduced.     

Biocompatible composites of fibrous nanohydroxyapatite embedded in a polydimethylsiloxane

Silicone elastomers have the potential to be a valuable biomaterial due to their mechanical and chemical properties, easy processing, and high gas permeability. Some inherent properties of the pure silicone implant such as high hydrophobicity and low load bearing capacity can be problematic for biomedical applications. The issues were addressed by fabricating hydroxyapatite nanofiber/polydimethylsiloxane nanocomposites. The morphology of nanocomposite structures was visualized by high resolution transmission electron microscopy and field emission scanning electron microscopy. Improved mechanical strength and compliance of the prepared nanocomposite structures were obtained by frequency sweep and creep measurements. Surface hydrophilicity of polydimethylsiloxane was enhanced by hydroxyapatite nanofiber incorporation into the polymer matrix. The cytotoxicity and biocompatibility of the structures were analyzed using breast epithelial cells (MDA MB 231 cell line). These studies showed that the nanocomposite scaffold did not leach any cytotoxic material and showed better cell adhesion and cell proliferation compared to the unfilled elastomer.     

聚二甲基硅氧烷膜分离甲醇/碳酸二甲酯混合物的渗透汽化研究

制备了一系列聚二甲基硅氧烷(PDMS)均质膜,用于渗透汽化法分离甲醇/碳酸二甲酯混合物,此系列PDMS均质膜优先脱除碳酸二甲酯.考查了PDMS均质膜在甲醇和碳酸二甲酯液体中的溶胀性能,并研究了PDMS预聚体的黏度、交联剂浓度、操作温度及料液浓度对渗透汽化分离性能的影响.结果表明,对于不同黏度的PDMS预聚体均表现出随交联剂浓度增加分离因子先增加后减小,而渗透通量则逐渐减小;随操作温度增加分离因子减小而渗透通量增大;随料液中碳酸二甲酯浓度增加分离因子先增加后减小,而渗透通量则逐渐增大.对于碳酸二甲酯浓度为30%的甲醇/碳酸二甲酯混合物,40℃时渗透侧碳酸二甲酯浓度为59.7%,分离因子为3.46,渗透通量为1.41 kg/(m2·h).     

Spectroscopic evidence and molecular simulation investigation of the pi-pi interaction between pyrene molecules and carbon nanotubes

The pi-pi interaction between pyrene molecules and single-walled carbon nanotubes (SWNTs) or multi-walled carbon nanotubes (MWNTs) was studied by fluorescence, FTIR, Raman spectroscopy and molecular simulation. The carbon nanotubes were incubated in pyrene solution and dried for characterization. A broadband fluorescence emission at 463 nm of the incubated samples was observed, which is similar to that of pyrene excimers but shifts to shorter wavelength. The typical FTIR bands of pyrene shift to lower wavenumbers in the incubated samples. D- and G-bands in Raman spectra of SWNTs also shift to low frequencies. All these spectroscopic evidences reveal the stronger pi-pi stacking interaction between the nanotubes and pyrene molecules over the pyrene dimers, which leads to the formation of pyrene-carbon nanotube complexes. The systems of SWNTs and pyrene molecules were also studied with molecular simulation. It was found from the binding energy calculation that a stronger interaction presents between the pyrene molecule and the nanotube. In addition, the simulation gives some structural information about the pyrene-nanotube complex, such as the staggered conformation of pyrene on nanotube. The effect of defects in carbon nanotube sidewall was also discussed.