Fluidized-bed synthesis of sub-millimeter-long single walled carbon nanotube arrays

The rapid growth method for vertically aligned, single walled carbon nanotube (SWCNT) arrays on flat substrates was applied to a fluidized-bed, using ceramic beads as catalyst supports as a means to mass produce sub-millimeter-long SWCNT arrays. Fe/Al₂O_x catalysts were deposited on the surface of Al₂O₃ beads by sputtering and SWCNTs were grown on the beads by chemical vapor deposition (CVD) using C₂H₂ as a feedstock. Scanning electron microscopy and transmission electron microscopy showed that SWCNTs of 2–4 nm in diameter grew and formed vertically aligned arrays of 0.5 mm in height. Thermogravimetric analysis showed that the SWCNTs had a catalyst impurity level below 1 wt.%. Furthermore, they were synthesized at a carbon yield as high as 65 at.% with a gas residence time as short as <0.2 s. Our fluidized-bed CVD, which efficiently utilizes the three-dimensional space of the reactor volume while retaining the characteristics of SWCNTs on substrates, is a promising option for mass-production of high-purity, sub-millimeter-long SWCNT arrays.     

One second growth of carbon nanotube arrays on a glass substrate by pulsed-current heating

We report the very rapid growth of carbon nanotubes (CNTs) at high temperatures that can be tolerated by glass substrates. Glass substrates with metal microelectrodes and sputtered catalysts are heated by a pulsed current in a chemical vapour deposition gas environment for 0.5–1 s to synthesize CNTs of several micrometres in height without damaging the glass substrate. CNTs with structures from single-walled to multi-walled and morphologies from entangled networks to vertically aligned forests are grown simply by changing the nominal thickness of the catalyst, and such CNTs grown selectively on the microelectrodes worked as field emitters for cathodoluminescence. Rapid, easy growth of patterned CNT arrays on glass substrates without using furnaces/heaters or vacuum pumps will be useful for various applications of CNTs.     

Vapor Pressure of Barium and Copper Components in YBa2Cu3O7−x Superconductor Ceramics

Purified air is passed over a specimen of YBa₂Cu₃O_{7– x} at 890°C; the vaporized substances are condensed in a pure alumina tube, then subjected to inductively controlled plasma analysis. Vapor pressure values of 2.5 × 10⁻⁵ Pa for BaO( g ), 1.2 × 10⁻⁴ Pa for Cu( g ), and 2.2 × 10⁻⁵ Pa for CuO( g ) are obtained under 2.1 × 10⁴ Pa (0.21 bar) of oxygen pressure. No Y vapor is detected at this temperature.     

Line identification of boron and nitrogen emissions in extreme-and vacuumultraviolet wavelength ranges in the impurity powder dropping experiments of the Large Helical Device and its application to spectroscopic diagnostics

An impurity powder dropper was installed in the 21 st campaign of the Large Helical Device experiment(Oct. 2019–Feb. 2020) under a collaboration between the National Institute for Fusion Science and the Princeton Plasma Physics Laboratory for the purposes of real-time wall conditioning and edge plasma control. In order to assess the effective injection of the impurity powders,spectroscopic diagnostics were applied to observe line emission from the injected impurity. Thus,extreme-ultraviolet(EUV) and vacuum-ultraviolet(VUV) emission spectra were analyzed to summarize observable impurity lines with B and BN powder injection. Emission lines released from B and N ions were identified in the EUV wavelength range of 5–300 ? measured using two grazing incidence flat-field EUV spectrometers and in the VUV wavelength range of 300–2400 ? measured using three normal incidence 20 cm VUV spectrometers. BI–BV and NIII–NVII emission lines were identified in the discharges with the B and BN powder injection, respectively. Useful B and N emission lines which have large intensities and are isolated from other lines were successfully identified as follows: BI(1825.89, 1826.40) ?(blended), BII 1362.46 ?, BIII(677.00, 677.14,677.16) ?(blended), BIV 60.31 ?, BV 48.59 ?, NIII(989.79, 991.51, 991.58) ?(blended), NIV765.15 ?, NV(209.27, 209.31) ?(blended), NVI 1896.80 ?, and NVII 24.78 ?. Applications of the line identifications to the advanced spectroscopic diagnostics were demonstrated, such as the vertical profile measurements for the BV and NVII lines using a space-resolved EUV spectrometer and the ion temperature measurement for the BII line using a normal incidence 3 m VUV spectrometer.     

A simple oxidation–reduction process for the activation of a stainless steel surface to synthesize multi-walled carbon nanotubes and its application to phenol degradation in water

Aligned multi-walled carbon nanotubes (MWCNTs) were synthesized directly on a stainless steel surface by surface activation by intense oxidation in air followed by a moderate reduction in H₂ without any wet process. This method is extremely simple compared with conventional ways that need catalyst loading steps or acid pre-etching steps to synthesize carbon nanotubes on stainless steel surfaces. It was found that the length of MWCNT bundles could reach 80 μm when the oxidation step was properly controlled. It was demonstrated that MWCNTs synthesized on stainless steel meshes could be used as a catalyst support to enhance ozone oxidation in the decomposition of phenol in water.     

Corrections and further comments to 'Equivalence relations between learnability,output-dissipativity and strict positive realness'

This correspondence presents corrections and further comments to our previous paper titled 'Equivalence relations between learnability, output-dissipativity and strict positive realness' (Arimoto and Naniwa 2000). It corrects (1) the previous definition of input?output 'invertibility' by assuming an additional continuity property of the system inverse operator, redefines exactly (2) the 'output-dissipativity' by adding a condition of invertibility, and presents (3) a further comment on the proof of Lemma 1. A diagram is given in order to clearly show interrelationships between these concepts.     

Cold-gas chemical vapor deposition to identify the key precursor for rapidly growing vertically-aligned single-wall and few-wall carbon nanotubes from pyrolyzed ethanol

Vertically-aligned carbon nanotubes (VA-CNTs) were rapidly grown from ethanol and their chemistry has been studied using a “cold-gas” chemical vapor deposition (CVD) method. Ethanol vapor was preheated in a furnace, cooled down and then flowed over cobalt catalysts upon ribbon-shaped substrates at 800 °C, while keeping the gas unheated. CNTs were obtained from ethanol on a sub-micrometer scale without preheating, but on a millimeter scale with preheating at 1000 °C. Acetylene was predicted to be the direct precursor by gas chromatography and gas-phase kinetic simulation, and actually led to millimeter-tall VA-CNTs without preheating when fed with hydrogen and water. There was, however a difference in CNT structure, i.e. mainly few-wall tubes from pyrolyzed ethanol and mainly single-wall tubes for unheated acetylene, and the by-products from ethanol pyrolysis possibly caused this difference. The “cold-gas” CVD, in which the gas-phase and catalytic reactions are separately controlled, allowed us to further understand CNT growth.     

The Non-isoplanatic Image Equation and the Effect of Not Satisfying the Sine Condition in the Scanning Microscope

Abstract

By considering lack of agreement with the sine condition and using the concept of image formation by interference of plane waves, we derive a new equation for non-isoplanatic image formation. Moreover, applying this equation and considering alignment errors between optical elements, a new equation for the image formation of the object-scan type scanning microscope is derived. This type of microscope also includes laser-disc optical systems. Effects of the sine condition not being satisfied both for the illumination lens and for the collector lens are discussed.     

Effect of centrifugal forces on the instability of the thermocapillary flow in partially confined half-zones

The stability of the axisymmetric steady thermocapillary flow in a cylindrical half-zone liquid bridge is investigated numerically for the case when the free surface is partially confined by a thin solid layer. A linear-stability and an energy analysis are performed to elucidate the dependence of the instability mechanism on the free-surface fraction which is defined as the length of the free part of the cylindrical surface relative to the full height of the zone. It is found that the balance of the elliptic instability and the centrifugal instability changes significantly, leading to three different types of instability depending on the free-surface fraction.     

Mechanical properties and microstructure of reaction sintered β′-sialon ceramics prepared by a slip casting method

Reaction sintered β′-sialon ceramics Si_6-zAl_zO_zN_8-z, were prepared by slip casting from α-Si₃N₄, Al₂O₃, and AlN starting powders. The mechanical properties and microstructures of sintered bodies were investigated as a function of composition (varying the z value). The maximum value of the flexural strength, ∼ 600 MPa, and fracture toughness, ∼ 4.1 MPa m^1/2 were observed in the z range of 0.5–1. In the z value range of 2–4, the mechanical properties decreased drastically. This phenomenon is attributed to the variation of fracture energy, which is greatly affected by the sintered crystallite size. This revised version was published online in November 2006 with corrections to the Cover Date.