A simple route to large-scale production of tungsten trioxide nanoparticles

Tungsten trioxide particles in high yield were prepared via a simple solid evaporation route with ammonium paratungstate hydrate as precursor and Ar gas as carrier gas. Detailed characterization by scanning electron microscopy has shown that increasing carrier gas flow rate promotes morphological evolution from large and irregular semi-spherical particles to non-agglomerated quasi-spherical particles, and finally to single-crystalline nanoparticles with an average diameter of 60 nm. The adsorption activity of the tungsten trioxide particles is size-dependent and increased with decreasing particle size. The present method could readily produce large-scale tungsten trioxide nanoparticles with ideal adsorption performance, and can be utilized to fabrication of various semiconductor oxides with advanced properties.     

Analysis of methods of attaching a semiconductor sensor to the substrate

It is shown that correct selection of the method used to attach the sensor (SR) of a microtransducer to the frame (substrate) of the latter is an important element in sensor design and fabrication. Microtransducers for measuring pressure are used as an example in an analysis of methods of attaching semiconductor SRs to the substrate of the transducer. Translated from Izmeritel'naya Tekhnika, No. 12, pp. 27–30, December, 1998.     

A novel route to the synthesis of silica nanowires without a metal catalyst at room temperature by chemical vapor deposition

Silica nanowires were synthesized by employing inherent directionality of chemical vapor reaction between bis(ethylmethylamino)silane (H(2)Si[N(C(2)H(5))(CH(3))](2)) precursor and water without a metal catalyst at room temperature. The difference in the oxidation reactivity between Si-H and Si-N bonds with water leads to the formation of silica nanowires. The mean diameter and length of the silica nanowires grown for 10 min were 60-80 nm and 1.9 μm, respectively. Transmission electron microscopy revealed that the obtained nanowires had the concave tip, differing from other silica nanowires produced by a conventional vapor-liquid-solid method, and were amorphous. Energy dispersive X-ray spectroscopy, Fourier transform infrared, and X-ray photoelectron spectroscopy results also proved that the nanowires have a close composition to stoichiometric SiO(2). Silica nanowires were successfully synthesized on a poly(ethylene terephthalate) film. The nanowires can emit strong blue light and ultraviolet light under excitation at 266 nm.     

Continuous nanoparticles production through a combination of a micro electro mechanical system and an electromagnetic resonator cavity

In the present work, a reliable, rapid, and controllable method is developed for the continuous generation of pharmaceutical curcumin and loratadine nanoparticles (NPs). Micro droplets of curcumin and loratadine were generated by atomization of their corresponding solutions by a combination of a micro electro mechanical system and an electromagnetic resonator cavity. After evaporation of the solvent of micro droplets by electromagnetic waves, the NPs were collected by a polytetrafluoroethylene (PTFE) filter. NPs were characterized by scanning electron microscopy. Results showed that this method can be an effective way to produce amorphous NPs with narrow particle size distribution, where particle size can be easily controlled by solution concentration. Particles size varies from 152 to 446?nm and from 116 to 719?nm for loratadine and curcumin, respectively.     

A convenient route for the synthesis of hydroxyapatite through a novel microwave-mediated metathesis reaction

Microwave synthesis of ceramics offers the advantage of efficient transformation of energy and heating throughout the volume efficiently in a shorter period. In this communication, we report the first example of a novel metathesis reaction performed in the presence of microwave irradiation. Nanocrystaline particles of hydroxyapatite (HAP) could be readily synthesized by microwave treatment of calcium chloride (CaCl₂) and sodium phosphate (Na₃PO₄) in solid phase. Use of sodium carbonate or sodium fluoride in addition to calcium chloride resulted into the formation of carbonate- or fluoride-substituted hydroxyapatite.     

On the general solution by a direct method of a large-scale singular system of linear equations: application to the analysis of floating structures

Finding the general solution of a singular system of linear equations requires computing a particular solution and a basis of the null space of the corresponding singular matrix. In this paper, we consider the case where the singular matrix is large and sparse, and the application calls for a direct solution method. We highlight the dependence of straightforward factorization algorithms on an arbitrary constant that can influence the correctness of the computed solution, and describe a family of improved direct solution methods that alleviate this problem. For structural mechanics applications, we propose a hybrid geometric–algebraic method that is more robust than the purely algebraic direct methods that are currently used for solving singular sparse systems of equations. We illustrate the potential of our proposed solution algorithms with examples from structural mechanics and domain-decomposition-based iterative solvers. © 1998 John Wiley & Sons, Ltd.     

A new route to mass production of metal hydroxide/oxide hydroxide nanoparticles

Aluminum hydroxide/oxide hydroxide nanofibers were self-assembled by hydration of highly activated aluminum powder using no surfactants or templates. The activation was performed by milling aluminum powder with sodium chloride as nano-miller. Transmission electron microscopy images and X-ray diffraction patterns confirm that this method leads to smaller size of aluminum particles (less than 50 nm) and increases the lattice strain. These factors provide conditions under which hydration procedure proceeds until it reaches the core of aluminum particles. The synthesized powder consists of nanofibers with thickness less then 10 nm and average length of 120 nm and specific surface area of 309 m² g⁻¹. The process is convenient, highly efficient and capable to be implemented in mass production. It may be extended to produce hydroxide/oxide hydroxide nanopowders of other metals, as well.     

The effect of sulfur on the structure of carbon nanotubes produced by a floating catalyst method

The effect of sulfur on the structures (shell number and diameter distribution) of carbon nanotubes (CNTs) was investigated in detail using high resolution transmission electronic microscopy (HRTEM) and Raman spectroscopy. Single-walled (SWNTs), double-walled (DWNTs), and multi-walled carbon nanotubes (MWNTs) with different diameter distributions were obtained only by increasing the sulfur addition amount with methane as carbon source. A similar structure change was found for ethanol as carbon source with changing the sulfur addition amount. These results indicate that addition of sulfur is necessary to enhance the growth of SWNTs and DWNTs, independent of the carbon source for our method. Based on the growth parameter study, HRTEM observations and kinetic considerations, the role of sulfur in the nucleation and growth of CNTs was discussed.     

A method for estimating muon production and penetration through a shield

An approximate expression is derived that describes muon production by high-energy protons and the subsequent attenuation of the muons in a shield. It is shown that the muon flux at x ahead of an interaction by a proton of energy ? GeV and where pions have a path length of Δ m in which to decay, will be given by:

$\text{φ=8.5×10}{}^{\mathrm{?2}}\text{εΔ}\text{x}{}^2\text{e}{}^{\mathrm{<mtext>?(</mtext><mtext>\alpha t</mtext><mtext>\epsilon </mtext><mtext>)</mtext>}}\text{μ/}\text{m}{}^2$

, where t is the shield thickness in m and α is an effective muon energy loss rate which has a value of 22 GeV/m for iron and 7.8 GeV/m for concrete. It is further shown that the effective muon attenuation mean-free path is equivalent to $\text{1}\text{16}$ of the range of a muon with the energy of the interacting proton.The width of the muon beam that passes through the shield is also considered and it is shown that the beam profile approximates a Gaussian distribution with a diameter at half-maximum intensity of:

$\text{d=}\text{4.6x}\text{εαt}\text{m}$

.Calculated muon fluxes are shown to correspond reasonably with those obtained by more sophisticated computer methods for proton energies up to at least 30 GeV and over the entire range of shield thicknesses of interest for radiation safety. Results of measurements of muon levels behind beam dumps under various conditions are presented and are shown to be in reasonable agreement with predictions based on the above model.     

Preparation of gallium oxynitride in the presence of iron through a citrate route

Gallium oxynitrides were prepared in the copresence of various amounts of Fe³⁺ by ammonia nitridation of oxide precursors. Their crystallinity reduced in a compositional range up to 3 mol% and improved again above 4 mol% with an appearance of a nitride impurity. The product with 2 mol% of Fe³⁺ showed the maximum oxygen content of 21 mol% and minimum nitrogen content of 24 mol%. X-ray absorption spectroscopy, Mössbauer and magnetic measurements suggested a small amount of Fe₃O₄-like clusters in the oxynitride products. Density-functional calculations supported that the Fe-O-clustered system is more preferable than the statistical distribution of iron in the hexagonal gallium oxynitride structure.     

Synthesis and characterization of mesoporous silica thin films as a catalyst support on a titanium substrate

Mesoporous silica films with a thickness of 500-900 nm were synthesized on a titanium substrate by the evaporation-induced self-assembly method (with 900-1200 rpm for 90 s) using cetyltrimethylammonium bromide (CTAB) as structure-directing agent and tetraethyl orthosilicate as the silica source. Prior to coating deposition, the titanium substrate was oxidized to increase the surface roughness up to 500 nm and to produce a thin titania layer. Just before the synthesis, the titania layer was made super hydrophilic by an UV treatment for 2 h to provide a better adhesion of the silica film to the substrate. Films with hexagonal and cubic mesostructures with a uniform pore size of 2.8 nm and a surface area of 1080 m²/g were obtained and characterized by different methods. An alternative approach for surfactant removal by gradual heating up to 250 °C in vacuum was applied. Complete removal of CTAB from the as-synthesized silica films was confirmed by infrared spectroscopy.     

Effect of substrate and catalyst on the transformation of carbon black into nanotubes

Structural transformation of carbon black (CB) into nanotubes and nano-onion like structures in the presence of bimetallic catalysts (Fe and Ni) is reported and the influence of the substrate (alumina and stainless steel) in the structural transformation is studied. In addition, the importance of a specific weight ratio of CB to catalyst in the transformation of amorphous CB into graphitic nanostructures is verified. The experiments were carried out at 1,000 °C in a horizontal tube furnace under N₂ atmosphere. The samples were characterized by transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, Raman spectroscopy and also thermomagnetic analysis (Curie-temperature determinations) were done to assess thermally induced magnetic phase changes. All the characterization techniques showed the resulting structures were influenced by the substrate and weight ratio for CB to catalysts. However, there was no significant difference in the magnetic performance of the resulting structures obtained on different substrates.     

A capacity-oriented hierarchical approach to single-item and small-batch production planning using project-scheduling methods

Most production planning and control (PPC) systems used in practice have an essential weakness in that they do not support hierarchical planning with feedback and do not observe resource constraints at all production levels. Also, PPC systems often do not deal with particular types of production, for example, low-volume production. We propose a capacity-oriented hierarchical approach to single-item and small-batch-production planning for make-to-order production. In particular, the planning stages of capacitated master production scheduling, multi-level lot sizing, temporal and capacity planning, and shop floor scheduling are discussed, where the degree of aggregation of products and resources decreases from stage to stage. It turns out that the optimization problems arising at most stages can be modelled as resourceconstrained project scheduling problems.     

High-yield synthesis and magnetic property of hematite nanorhombohedras through a facile solution route

Through a relatively low temperature solution route, hematite (α-Fe₂O₃) nanorhombohedras with average particle size of 35 nm were synthesized in high yield. The final products were investigated by a variety of characterization techniques, such as X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM) and Raman spectrum. As a steric stabilizer and capping agent, the roles of PVP played in the whole process were discussed. And the magnetic property of the nanorhombohedras at low temperature was examined, exhibiting weakly ferromagnetic characteristic, which deviates from the behavior of the corresponding bulk material and might be ascribed to the presence of small crystals in a few regions of the sample.     

A novel route to large-scale and robust free-standing TiO2 nanotube membranes based on N2 gas blowing combined with methanol wetting

We present a novel and straightforward approach to fabricate large-scale and robust free-standing TiO(2) nanotube (TNT) membranes. Simply by blowing N(2) gas onto as-anodized TNTs that are wetted with methanol, free-standing TNT membranes are produced. The approach also provides homogeneous and honeycomb-like Ti substrates after the detachment of TNT membranes. Through the second anodization of the honeycomb-like Ti substrates following the N(2) blowing, TNT membranes comprising hexagonally close-packed and regularly ordered TNTs with clear open ends can be achieved. Characterization of the free-standing TNT membranes using Raman spectroscopy and a high-resolution transmission electron microscope reveals that anatase TiO(2) and crystalline graphitic carbon are embedded in the bottom surface of the free-standing TNT membranes.     

Microwave treatment and fluorine addition on Co-B catalyst to improve the hydrogen production rate

In this paper, microwave heating treatment process and fluorine addition over Co-B-F catalyst was applied to produce hydrogen via the hydrolysis of NaBH₄. The effects of microwave heating treatment time, microwave heating treatment power, microwave inert gases and temperature on the catalyst were studied. X-ray absorption spectrometer, scanning electron microscopy coupled to energy-dispersive spectroscopy, nitrogen adsorption analyzer and infrared spectrometer were performed for the chemical characterization of the catalysts. It was found that Co-B-F and microwave-treated Co-B-F catalysts exhibited excellent catalytic activity to produce hydrogen. The rates of the maximum hydrogen production for untreated and microwave-treated Co-B-F catalysts are 1868 and 3400?mL/g/min, respectively.     

Novel approach to the fabrication of an artificial small bone using a combination of sponge replica and electrospinning methods

Abstract

In this study, a novel artificial small bone consisting of ZrO₂-biphasic calcium phosphate/polymethylmethacrylate-polycaprolactone-hydroxyapatite (ZrO₂-BCP/PMMA-PCL-HAp) was fabricated using a combination of sponge replica and electrospinning methods. To mimic the cancellous bone, the ZrO₂/BCP scaffold was composed of three layers, ZrO₂, ZrO₂/BCP and BCP, fabricated by the sponge replica method. The PMMA-PCL fibers loaded with HAp powder were wrapped around the ZrO₂/BCP scaffold using the electrospinning process. To imitate the Haversian canal region of the bone, HAp-loaded PMMA-PCL fibers were wrapped around a steel wire of 0.3 mm diameter. As a result, the bundles of fiber wrapped around the wires imitated the osteon structure of the cortical bone. Finally, the ZrO₂/BCP scaffold was surrounded by HAp-loaded PMMA-PCL composite bundles. After removal of the steel wires, the ZrO₂/BCP scaffold and bundles of HAp-loaded PMMA-PCL formed an interconnected structure resembling the human bone. Its diameter, compressive strength and porosity were approximately 12 mm, 5 MPa and 70%, respectively, and the viability of MG-63 osteoblast-like cells was determined to be over 90% by the MTT (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide) assay. This artificial bone shows excellent cytocompatibility and is a promising bone regeneration material.     

A novel precursor route for the production of Si―B―N ceramic fibers

A novel polymeric precursor to SiBN ceramic fiber was synthesized by reaction of tetramethylaminosilane ((CH₃NH)₄Si) and trimethylaminoborane ((CH₃NH)₃B). It was shown that the polymer contains an Si―N―B bridge bond connecting the linear silicon and borazon ring parts. This structure imparts sufficient viscosity for the material to be processed by melt spinning, so that for the first time it was easily spun into green fibers using laboratory scale equipment. SiBN ceramic fibers with diameter 35 μm were obtained after pyrolysis at 1600 °C in an NH₃ atmosphere. The thermal decomposition behavior of the polymer during pyrolysis was also investigated.