Mass production of multi-wall carbon nanotubes by metal dusting process with high yield

Carbon nanotube materials were synthesized over Fe-Ni nanoparticles generated during disintegration of the surface of alloy 304L under metal dusting environment. The metal dusting condition was simulated and optimized through exposing stainless steel samples during long term repetitive thermal cycling in CO/H₂ = 1/1, total gas flow rate 100 cm³/min, at 620 °C for 300 h. After reaction, surface morphology of the samples and also carbonaceous deposition which had grown on sample surfaces were examined by stereoscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results revealed that multi-wall carbon nanotubes could be formed over nanocatalyst generated on the alloy surface by exploiting metal dusting process. By optimization of reaction parameters the yields of carbon nanotube materials obtained were 700-1000%. Also it has been shown herein that the amount of carbon nanotube materials remarkably increases when the reaction time is extended up to 300 h, indicating a possibility of the mass production by this easy method.     

Carbonization and oxidation of metal–organic frameworks based on 1,4-naphthalene dicarboxylates

Three new isostructural metal–organic frameworks (MOFs), [V(OH)(NDC)] (1), [Cr(OH)(NDC)] (2), and [Ga(OH)(NDC)] (3) have been synthesized hydrothermally using 1,4-naphthalene dicarboxylate (NDC) as the linker. These MOFs (1, 2 and 3) have been used as a template for the synthesis of metal-oxide-inserted nanoporous carbon materials. The newly synthesized MOFs and the resulting porous carbon hybrid functional materials have been characterized using powder x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy dispersive x-ray spectroscopic analysis. Results show that compounds 2 and 3 form their respective metal oxide nanoparticles on the surface of the carbon materials during carbonization at 800 °C. The gas sorption properties of the new MOFs and their corresponding carbon frameworks have been reported.     

A one-step technique to prepare aligned arrays of carbon nanotubes

A simple effective pyrolysis technique has been developed to synthesize aligned arrays of multi-walled carbon nanotubes (MWCNTs) without using any carrier gas in a single-stage furnace at 700?°C. This technique eliminates nearly the entire complex and expensive machinery associated with other extensively used methods for preparation of CNTs such as chemical vapour deposition (CVD) and pyrolysis. Carbon source materials such as xylene, cyclohexane, camphor, hexane, toluene, pyridine and benzene have been pyrolyzed separately with the catalyst source material ferrocene to obtain aligned arrays of MWCNTs. The synthesized CNTs have been characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and Raman spectroscopy. In this technique, the need for the tedious and time-consuming preparation of metal catalysts and continuously fed carbon source material containing carrier gas can be avoided. This method is a single-step process where not many parameters are required to be monitored in order to prepare aligned MWCNTs. For the production of CNTs, the technique has great advantages such as low cost and easy operation.     

Magnetic-field-assisted solvothermal growth of single-crystalline bismuth nanowires

The magnetic-field-assisted approach has been used in the shape-controlled synthesis of single Bi nanocrystals. By tuning the magnetic field strength in the solvothermal process, Bi nanowires with dimension of 40-200?nm and lengths up to tens of micrometers were synthesized. Various techniques such as x-ray diffraction, scanning electron microscopy, transmission electron microscopy and Fourier transform infrared spectrometry have been used to characterize the products obtained. The results show that the magnetic field plays a key role in the crystal growth of the Bi nanowires. All nanowires were highly oriented single crystals with the growth direction along the c-axis.     

The Effect of Phosphate on the Properties of Copper Drinking Water Pipes Experiencing Localized Corrosion

Extensive localized or pitting corrosion of copper pipes used in household drinking water plumbing can eventually lead to pinhole water leaks that may result in water damage, mold growth, and costly repairs. Water chemistry has been recognized as the cause of some community-wide copper pinhole leak outbreaks. A large drinking water system in Florida recently switched from pH adjustment and orthophosphate addition to a blended ortho-polyphosphate chemical to address this problem. The objective of this study was to examine the impact of phosphates on the morphology and elemental composition of the interior surface of failed copper pipes removed from homes in the community. Scanning electron microscopy (SEM) and energy dispersive spectroscopy analysis of pipe surfaces revealed the build-up of phosphorus over time. Phosphorus was most greatly concentrated over areas of localized corrosion attack. Examination of the corrosion by-product mounds that covered corroding pits showed that phosphorus had migrated to the region adjacent to the copper pipe wall. Distinct copper–phosphorus solids were identified under SEM magnification; however, no crystalline copper–phosphate compound was identified by x-ray diffraction analysis.     

Carbonization and oxidation of metal–organic frameworks based on 1,4-naphthalene dicarboxylates

Abstract

Three new isostructural metal–organic frameworks (MOFs), [V(OH)(NDC)] (1), [Cr(OH)(NDC)] (2), and [Ga(OH)(NDC)] (3) have been synthesized hydrothermally using 1,4-naphthalene dicarboxylate (NDC) as the linker. These MOFs (1, 2 and 3) have been used as a template for the synthesis of metal-oxide-inserted nanoporous carbon materials. The newly synthesized MOFs and the resulting porous carbon hybrid functional materials have been characterized using powder x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy dispersive x-ray spectroscopic analysis. Results show that compounds 2 and 3 form their respective metal oxide nanoparticles on the surface of the carbon materials during carbonization at 800 °C. The gas sorption properties of the new MOFs and their corresponding carbon frameworks have been reported.     

高温碳氢气氛下Cr5Mo钢的尘化腐蚀状况

金属渗碳腐蚀(即尘化)是高温碳氢环境下常发生的灾难性腐蚀。Cr5Mo钢的工程应用量大面广,过去对其渗碳腐蚀研究不够。为此,研究了炉管材料Cr5Mo钢在600℃,50%CO-H2-3%H2O气氛下的尘化腐蚀行为,采用X射线衍射分析了腐蚀试样的物相组成,采用扫描电镜对试样进行了微观形貌分析。结果表明:Cr5Mo钢在试验条件下呈现均匀腐蚀,材料自表面向内依次析出Fe5C2和Fe3C脆性腐蚀产物,经560h尘化腐蚀后的试样平均腐蚀深度约为200μm,而基体材料性质无明显改变。因此Cr5Mo钢在尘化过程中出现的腐蚀减薄是由脆性碳化物层的析出引起的。     

Calibration of High-Resolution X-Ray Tomography With Atomic Force Microscopy

For two-dimensional x-ray imaging of thin films, the technique of scanning transmission x-ray microscopy (STXM) has achieved images with feature sizes as small as 40 nm in recent years. However, calibration of three-dimensional tomographic images that are produced with STXM data at this scale has not yet been described in the scientific literature, and the calibration procedure has novel problems that have not been encountered by x-ray tomography carried out at a larger scale. In x-ray microtomography, for example, one always has the option of using optical imaging on a section of the object to verify the x-ray projection measurements; with STXM, on the other hand, the sample features are too small to be resolved by light at optical wavelengths. This fact implies that one must rely on procedures with higher resolution, such as atomic force microscopy (AFM), for the calibration. Such procedures, however, generally depend on a highly destructive sectioning of the sample, and are difficult to interpret because they give surface information rather than depth information. In this article, a procedure for calibration is described that overcomes these limitations and achieves a calibration of an STXM tomography image with an AFM image and a scanning electron microscopy image of the same object.A Ge star-shaped pattern was imaged at a synchrotron with a scanning transmission x-ray microscope. Nineteen high-resolution projection images of 200 × 200 pixels were tomographically reconstructed into a three-dimensional image. Features in two-dimensional images as small as 40 nm and features as small as 80 nm in the three-dimensional reconstruction were resolved. Transverse length scales based on atomic force microscopy, scanning electron microscopy, x-ray transmission and tomographic reconstruction agreed to within 10 nm. Toward the center of the sample, the pattern thickness calculated from projection images was (51 ± 15) nm vs (80 ± 52) nm for tomographic reconstruction, where the uncertainties are evaluated at the level of two standard deviations.     

Electron microscopy of layered single crystals grown by direct vapour transport method

Besides interesting properties such as optical, transport, structure, etc. possessed by crystals of transition metal dichalcogenides, they have also been found to have a potential application in the fabrication ofpec solar cells. These crystals are normally grown by carrier gas transport technique but are always contaminated by carrier gases. A new method of direct vapour transport has been developed and successfully applied to grow these crystals including those of off-stoichiometric varieties. The crystals thus grown have been characterized structurally using the techniques of x-ray powder, rotation and Weissenberg photographs and electron diffraction. Perfection studies have been made by techniques like chemical etching and electron microscopy. This review describes the electron microscopic studies made on the single crystals of the layered compounds. High resolution technique of weak beam has been employed to study dislocation pattern. Dissociated dislocations have been used to estimate stacking fault energy. Such measurements have also been carried out at different temperatures and the variation of stacking fault energy with temperature has been worked out. Interesting information regarding phase transformation for TaS₂ and W₃Se₄ in the temperature range 109 to 580 K has been derived from the electron diffraction studies and the implications have been discussed.     

Synthesis and field emission of single-crystalline copper vanadate nanobelts

Single-crystalline nanobelts of a nonstoichiometric compound Cu(1.55)V(2)O(6.55), with a thickness of 40-60?nm, width of 50-300?nm and length of several micrometers, have been synthesized on a large scale by a hydrothermal method. The structures and morphologies of the nanobelts were characterized by x-ray powder diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and high-resolution transmission electron microscopy. A probable growth mechanism has also been discussed. The nanobelts exhibit a turn-on field of 11.0?V?μm(-1), which is defined as the macroscopic field required to produce a current density of 10?μA?cm(-2). It is anticipated that the nanobelts can serve as a candidate material for future field emitters.     

The role of metal nanoparticles and nanonetworks in alloy degradation

Oxide scale, which is essential to protect structural alloys from high-temperature degradation such as oxidation, carburization and metal dusting, is usually considered to consist simply of oxide phases. Here, we report on a nanobeam X-ray and magnetic force microscopy investigation that reveals that the oxide scale actually consists of a mixture of oxide materials and metal nanoparticles. The metal nanoparticles self-assemble into nanonetworks, forming continuous channels for carbon transport through the oxide scales. To avoid the formation of these metallic particles in the oxide scale, alloys must develop a scale without spinel phase. We have designed a novel alloy that has been tested in a high-carbon-activity environment. Our results show that the incubation time for carbon transport through the oxide scale of the new alloy is more than an order of magnitude longer compared with commercial alloys with similar chromium content.     

X-ray effects on the oxidation of Cu nanoparticles

X rays have been widely used for nondestructive analysis of nano-scaled materials for a long time; however, the effects of x-ray radiation have been less extensively discussed. In this work, by means of the in-situ x-ray diffraction and the ex-situ high-resolution electron microscopy, we have quantitatively investigated the x-ray effect on the oxidation behavior of Cu nanoparticles prepared by the vapor condensation method. Clear evidence shows that the x-ray irradiation increases the oxidation thickness as well as the oxidation rate. The results are of critical importance not only for the oxidation studies but also for the nanomaterial researches with x-ray related equipment.     

Poly(p-hydroxystyrene) grafted polystyrene nanospheres: excellent hosts for silver and ruthenium nanoparticles

A novel approach is described for the preparation of surface functionalized micro- and nanobeads using one pot synthesis by a core-shell method. Monodisperse poly(p-hydroxystyrene) is successfully prepared by grafting the p-acetoxystyrene monomer during the last 30 min of the fabrication of polystyrene bead core by emulsifier-free emulsion polymerization followed by hydrolysis of the acetoxy group by a base. The size of the resulting beads is dictated mostly by the size of the core. Hydroxyl derivatized polystyrene microspheres have been found useful as a high surface area and stable support for anchoring catalytically active silver and ruthenium nanoparticles. The bead formation, surface functionalization, and coating with metal nanoparticles have been studied using scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectrometry, Fourier transform infrared spectrometry, and Auger analysis.     

Effect of heat input and weld chemistry on mechanical and microstructural aspects of double side welded austenitic stainless steel 321 grade using tungsten inert gas arc welding process

Stainless steel 321 is a stabilized austenitic grade that prevents the formation of chromium carbides at the grain boundaries and subsequently reduces the risk of corrosion attack at the weld surface by forming titanium carbide. It is primarily used in industries such as pressure vessels, boilers, nuclear reactors, carburetors and car exhaust systems. In order to assess the effect of gas tungsten arc welding process parameters on weld penetration, the proposed Taguchi L₉ orthogonal matrix has been selected with two factors and three levels for welding austenitic stainless steel 321 by adjusting the welding current and welding speed. Bead-on-plate experiments were performed on base metal of 6 mm thick plate by changing the process parameters, and corresponding weld bead measurement and macrostructure images are examined. Maximum depth of penetration −3.3017 mm is achieved with a heat input −1.4058 kJ/mm, i. e., welding current-220 A and welding speed-120 mm/min. Double-side arc welding technique is used to obtain full penetration on 6 mm thick plate. The quality of the weldment was assessed using non-destructive radiography inspection. Mechanical integrity and microstructural characteristics of the weldments were studied using tensile (transverse and longitudinal), bend, impact, microhardness, optical microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction analysis, ferrite number measurement and scanning electron microscope. The results reveal that the double side-tungsten inert gas weldment have better mechanical properties. It is corroborated from the weld metal microstructure that it contains γ-austenite, δ-ferrite and titanium carbides (intermetallic compounds). X-ray diffraction analysis and energy dispersive x-ray spectroscopy plots confirm the increase in the ferrite phase in weld metal. The ferrite measurement results show that the ferrite volume in the base metal and weld metal is 1.2 percent and 6.1 percent respectively. In addition, the higher δ-ferrite volume in the weldment helps in attaining superior mechanical integrity. Fractography shows that the failure mode of the weld metal and the base metal is ductile.     

Deposition of metallic nanoparticles on carbon nanotubes via a fast evaporation process

A new technique was developed for the deposition of colloidal metal nanoparticles on carbon nanotubes. It involves fast evaporation of a suspension containing sonochemically functionalized carbon nanotubes and colloidal nanoparticles. It was demonstrated that metallic nanoparticles with different sizes and concentrations can be deposited on the carbon nanotubes with only a few agglomerates. The technique does not seem to be limited by what the nanoparticles are, and therefore would be applicable to the deposition of other nanoparticles on carbon nanotubes. PtPd and CoPt(3) alloy nanoparticles were used to demonstrate the deposition process. It was found that the surfactants used to disperse the nanoparticles can hinder the nanoparticle deposition. When the nanoparticles were washed with ethanol, they could be well deposited on the carbon nanotubes. The obtained carbon nanotube supported metal nanoparticles were characterized by transmission electron microscopy, energy dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, and cyclic voltammetry.     

Functionalization of nitrogen-doped carbon nanotubes with gallium to form Ga-CN(x)-multi-wall carbon nanotube hybrid materials

In an effort to combine group III-V semiconductors with carbon nanotubes, a simple solution-based technique for gallium functionalization of nitrogen-doped multi-wall carbon nanotubes has been developed. With an aqueous solution of a gallium salt (GaI(3)), it was possible to form covalent bonds between the Ga(3+) ion and the nitrogen atoms of the doped carbon nanotubes to form a gallium nitride-carbon nanotube hybrid at room temperature. This functionalization was evaluated by x-ray photoelectron spectroscopy, energy dispersive x-ray spectroscopy, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy.     

High spatially resolved morphological, structural and spectroscopical studies on copper oxide nanocrystals

Copper oxide nanocrystals decorated on multi-wall carbon nanotubes have been prepared. Comprehensive morphological, structural and spectroscopical studies have been carried out on the nanometre/atomic scale by the combination of high-resolution transmission electron microscopy and electron energy-loss near-edge structure in electron energy-loss spectroscopy, which has a high spatially resolved capacity advantage over the normally used analytical techniques such as x-ray powder diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). The result reveals that highly crystalline cubic Cu(2)O nanocrystals with highly uniform dispersion, homogeneous size of about 5.3?nm and nearly spherical morphology are synthesized as the predominant phase, while rare individual monoclinic CuO nanocrystals with irregular shape are still present as the minor phase. The analysis based on the survey result and the structural symmetry difference between Cu(2)O and CuO demonstrates that XRD underestimates the presence of the CuO phase with much lower structural symmetry while XPS overestimates the proportion of CuO phase.     

Microbial manufacture of chalcogenide-based nanoparticles via the reduction of selenite using Veillonella atypica: an in situ EXAFS study

The ability of metal-reducing bacteria to produce nanoparticles, and their precursors, can be harnessed for the biological manufacture of fluorescent, semiconducting nanomaterials. The anaerobic bacterium Veillonella atypica can reduce selenium oxyanions to form nanospheres of elemental selenium. These selenium nanospheres are then further reduced by the bacterium to form reactive selenide which could be precipitated with a suitable metal cation to produce nanoscale chalcogenide precipitates, such as zinc selenide, with optical and semiconducting properties. The whole cells used hydrogen as the electron donor for selenite reduction and an enhancement of the reduction rate was observed with the addition of a redox mediator (anthraquinone disulfonic acid). A novel synchrotron-based in situ time-resolved x-ray absorption spectroscopy technique was used, in conjunction with ion chromatography and inductively coupled plasma-atomic emission spectroscopy, to study the mechanisms and kinetics of the microbial reduction of selenite to selenide. The products of this biotransformation were also assessed using electron microscopy, energy-dispersive spectroscopy, x-ray diffraction and fluorescence spectroscopy. This process offers the potential to prepare chalcogenide-based nanocrystals, for application in optoelectronic devices and biological labelling, from more environmentally benign precursors than those used in conventional organometallic synthesis.     

Nb和N2在球磨过程中的固—气反应

利用改装后可充一定压力气体的球磨罐,装入一定量的高纯金属,经抽真空后充入一定压力的氮气,在室温下进行球磨产生固－气反应制备出金属氮化物的超细微粒,以金属铌为例,用XRD和TEM分别对生成物的晶粒尺度和相结合进行了分析测量,从热力学讨论了金属氮化的形成机制,在固－气反应中氮气分子在金属清洁表面的化学吸附起着重要作用,球磨过程中产生的大量缺陷对金属－氮气的反应有重要影响。     

Development and applications of an analytical electron microscope with a field emission electron gun

An analytical electron microscope with a field emission electron gun has been developed in order to improve the function of material identification, in order to obtain higher resolution of images, sharper electron diffraction patterns, and purer x-ray spectra with no effects of contamination from smaller areas than in the conventional instruments so far utilized. The performance capabilities of this newly developed analytical electron microscope, the Model H-600FE, have been examined and found to be very useful for the material characterization of nanometer-size areas. Various attributes of the microscope became apparent with reference to the results of different studies. These include better convergence of the electron beam (demonstrated by examination of an MoS₂ thin film), high-resolution transmission electron microscopy (using a gold film), high-resolution scanning electron microscopy (with a carbon film containing nanometer-size holes), high-angle resolution electron diffraction (of an iron carbide film), and precision x-ray analysis of nanometer-size areas (using a pyroxene crystal and a Cu---Zn---Al shape memory alloy).