Optical assessment of silicon nanowire arrays fabricated by metal-assisted chemical etching

Silicon nanowire (SiNW) arrays were prepared on silicon substrates by metal-assisted chemical etching and peeled from the substrates, and their optical properties were measured. The absorption coefficient of the SiNW arrays was higher than that for the bulk silicon over the entire region. The absorption coefficient of a SiNW array composed of 10-μm-long nanowires was much higher than the theoretical absorptance of a 10-μm-thick flat Si wafer, suggesting that SiNW arrays exhibit strong optical confinement. To reveal the reason for this strong optical confinement demonstrated by SiNW arrays, angular distribution functions of their transmittance were experimentally determined. The results suggest that Mie-related scattering plays a significant role in the strong optical confinement of SiNW arrays.     

Electrochemical corrosion and materials properties of reactively sputtered TiN/TiAlN multilayer coatings

TiN/TiAlN multilayers of 2 μm thickness were successfully prepared by reactive DC magnetron sputtering method. XRD pattern showed the (1 1 1) preferential orientation for both TiN and TiAlN layers. XPS characterization showed the presence of different phases like TiN, TiO₂, TiON, AlN and Al₂O₃. Cross sectional TEM indicated the columnar growth of the coatings. The average RMS roughness value of 4.8 nm was observed from AFM analysis. TiN/TiAlN coating showed lower friction coefficient and lower wear rate than single layer coatings. The results of electrochemical experiments indicated that a TiN/TiAlN multilayer coating has superior corrosion resistance in 3.5% NaCl solution.     

High Resistance of Cu–Ferrierite to Coke Formation During NH3-SCR in the Presence of n-Decane

Selective catalytic reduction of NO _x by NH₃ over Cu–FER and Cu–ZSM-5 in the presence of n-decane and SO₂ was investigated. NO _x conversion over Cu–ZSM-5 decreased in the presence of n-decane, owing to inhibition of the active sites by coke formation. In contrast, coke formation was negligible over Cu–FER, which maintained its NO _x conversion activity even in the presence of decane. Coke formation was negligible over H–ZSM-5 and H–FER supports, which suggests that Cu species were involved in coke formation. Temperature-programmed reduction by H₂ and electron spin resonance spectroscopy indicated that [Cu–O–Cu]²⁺ was probably the Cu species involved in coke formation over Cu–ZSM-5.     

Drying of Sewage Sludge During Composting in an Updraft Dryer with the Concept of Using Self-Energy Generated Within the System

An innovative technology for sewage treatment systems is proposed. A mixture of sewage sludge and char particle is subjected to drying in the progress of composting in an updraft column. Exothermic heat generated during composting is utilized for energy of sludge drying. The char particle in the mixture contributes to enhancement of composting and drying rate. This study presents drying and composting behaviors of sludge to examine the effect of char addition. A fundamental drying experiment was carried out by hot-air heating of the sample in a small vessel. The drying characteristic curve for a mixture of sludge and char was greater than the sample of only sludge over a whole period if the drying rates were compared with the same moisture content. The drying behavior could be analyzed with a reasonable agreement by the water front receding model. The enhancement effect of drying and composting of sludge by char addition was confirmed by examination using a pilot scale of the updraft column whose volume was 50 m³. Sludge with 400% dry base (80% wet base) in moisture content could be dried successfully to lower moisture content than 67% dry base (40% wet base) only by exothermic heat during composting without supplying any auxiliary energy from the outside, and the treatment time was reduced by mixing char in sludge. The behavior was analyzed with a satisfactory agreement by a theoretical model employing moisture diffusion parameters determined from the drying characteristic curve.     

Change in Oxygen Content of Y2O3-Nd2O3-Doped Silicon Nitride During Firing

The oxygen content of silicon nitride with 1 mol% Y₂O₃—Nd₂O₃ additive was measured after firing to determine the compositional change during gas-pressure sintering. Oxygen content decreases from 2.5 to 0.94 wt% during firing for 4 h at 1900°C and 10-MPa pressure in N₂. This decrease in oxygen results from the release of SiO gas generated by a thermaldecomposition reaction between Si₃N₄ and SiO₂. The resultant sintered silicon nitride material contains less than 1 wt% oxygen.     

The physical character of coal char formed during rapid pyrolysis at high pressure

Rapid pyrolysis was conducted in a drop tube reactor using seven coals under various operating conditions. In addition to dense char, porous chars (network char and cenospheric char) were formed by the rapid pyrolysis under certain conditions. Porous char was mainly composed of film-like carbon and skeleton carbon. The pyrolyzed coal char particles were characterized in detail. Morphology and bulk density of porous char were quite different from the dense char formed under the same conditions, but elemental composition and BET surface area were similar to each other. CO₂ gasification reactivity of porous char was lower than dense char in the later gasification stage, and this was ascribed to the low reactivity of skeleton carbon.     

Infrared study of catalytic reduction of lean NOx with alcohols over alumina-supported silver catalyst

Two intense IR absorption bands due to surface isocyanate (-NCO) species have been observed at 2262 and 2232 cm^–1 when an alumina-supported silver catalyst is exposed to a mixture of NO, O₂ and ethanol at 150°C and subsequently heated to > 300°C in vacuum. The intensity of the isocyanate band is hardly affected by the water existing in the mixture. Methanol is less reactive than ethanol for the formation of isocyanate species. The reaction mechanism of catalytic reduction of lean NOx with alcohols is discussed based on these IR spectroscopic findings.     

Sillimanite‐mullite transformation observed in synchrotron X‐ray diffraction experiments

High‐resolution synchrotron powder X‐ray diffraction (XRD) experiments were conducted to clarify the transformation of sillimanite to mullite (mullitization) and determine the mullitization temperature (T_c). We were able to distinguish sillimanite and mullite in the XRD patterns, despite their very similar crystallographic parameters, and to detect the appearance of small mullite peaks among sillimanite peaks. Analysis of the Johnson‐Mehl‐Avrami (JMA) equation for mullitization ratio (ζ) revealed that at temperatures T≥1240°C the mullitization had the same kinetics. The activation energy E at T≥1240°C obtained from the Arrhenius plot was 679.8 kJ mol^?1. In analysis using a time‐temperature‐transformation diagram for mullitization, a mullitization curve of ζ=1% can be described as where t is time, n is a reaction‐mechanism‐dependent parameter determined as 0.324 by JMA‐analysis, k₀ is the frequency factor, E_A is the activation energy for atomic diffusion, and represents the activation energy for nucleation. The results of fitting the data to this equation were T_c=1199°C, A=3.9×10⁶ kJ mol^?1 K^?2, E_A=605 kJ mol^?1, and k₀=3.65×10¹⁵. We conclude that the boundary between sillimanite and mullite+SiO₂ in the phase diagram is ~1200°C.     

Investigation of laser consolidation process for metal powder by two-color pyrometer and high-speed video camera

This paper deals with the measurement of surface temperature on metal powder during the laser consolidation process with two-color pyrometer. Additionally, the aspect of selective laser sintering (SLS) and selective laser melting (SLM) of metal powder is visualized with high speed video camera. As a result, the surface temperature during the laser irradiation was ranged 1520–1810 °C and the consolidation phenomena was classified according to the melting point of metal powder. The metal powder at the heating process cohered intermittently to the melt pool although the laser beam was continuously irradiated to the powder surface.     

Syntheses of group 4 transition metal complexes bearing 2-pyridinethiolate ligands and their catalytic activities for ethylene polymerization

Titanium bis(2-pyridinethiolate) complexes, Ti(6-R-SPy)₂(NMe₂)₂ (6-R-SPy = 6-R-2-pyridinethiolate, 3a: R = H; 3b: R = Me; 3c: R = Ph; 3d: R = C₆H₄-4-Me; 3e: R = C₆H₄-4-t-Bu; 3f: R = C₆H₃-3,5-Me₂), and the titanium bis(2-pyridinolate) complexes, Ti(6-Ph-OPy)₂(NMe₂)₂ (6-Ph-OPy = 6-phenyl-2-pyridinolate, 8) were prepared by treating Ti(NMe₂)₄ with 2 equiv. of 6-R-2-pyridinethiol or 6-Ph-2-pyridinol. The cis-configuration of the diamido moieties in the pseudo octahedral geometry was elucidated by X-ray crystallography for 3a. Reaction of M(NMe₂)₄ (M = Ti, Zr) with 4 equiv. of 2-pyridinethiol cleanly gave tetrakis(pyridinethiolate) complexes, M(6-H-SPy)₄·THF (6: M = Ti; 7: M = Zr). The triangular dodecahedral geometries of 6 and 7 were also revealed by X-ray crystallography. These complexes catalyzed ethylene polymerization upon activation with MAO (methylaluminoxane) or MMAO (modified MAO). The catalytic activities of titanium bis(6-aryl-pyridinethiolate) systems were found to be remarkably higher than that of titanium bis(6-methyl-pyridinethiolate) system. Among the complexes synthesized in this study, Ti[6-(C₆H₃-3,5-Me₂)-SPy]₂(NMe₂)₂ (3f)/MMAO showed the highest activity (1200 kg/Ti-mol h atm) for ethylene polymerization at 60 °C under atmospheric pressure. In contrast, the activity of the corresponding 6-aryl-pyridinolate system 8/MMAO was rather low (9.3 kg/Ti-mol h atm). Both the N-S chelating structure and the bulky aryl substituents are essential for the high activities of the 6-aryl-pyridinethiolate complexes.