Non-transferred Arc Torch Simulation by a Non-equilibrium Plasma Laminar-to-Turbulent Flow Model

Non-transferred arc torches are at the core of diverse industrial applications, particularly plasma spray. The flow in these torches transitions from laminar inside the torch to turbulent in the emerging jet. The interaction of the plasma with the processing gas leads to significant deviations from local thermodynamic equilibrium (LTE) far from the arc core. The flow from a non-transferred arc plasma spray torch is simulated using a non-LTE (NLTE) plasma flow model solved by variational multiscale (VMS) and nonlinear VMS (VMS_n) methods, which are suitable for unified laminar and turbulent flow simulations. Non-plasma turbulent jet simulations indicate that the VMS_n method produces results comparable to those by the dynamic Smagorinsky method, often considered the workhorse for turbulent incompressible flow simulations. VMS and VMS_n approaches are applied to the simulation of incompressible, compressible, and NLTE plasma flows in non-transferred arc torch operating at representative conditions found in plasma spray processes. The NLTE plasma flow simulations reproduce the dynamics of the arc inside the torch together with the evolution of turbulence in the produced plasma jet in a cohesive manner. However, the similarity of results by both methods indicates the need for numerical resolution significantly higher than what is commonly afforded in arc torch simulations.     

Sol-gel assisted synthesis of TiB2-B4C composite powder

Composite powders containing titanium diboride and boron carbide have been prepared by sol-gel method at 1450°C using titanium isopropoxide (titanium precursor), boric acid (Boron precursor), sucrose (carbon source), and acetic acid (AcOH) as a solvent. The effect of boron source (trimethyl borate and boric acid) and B₂O₃/TiO₂, C/B₂O₃ mole ratios of starting materials on the final phases has been studied. The progress of reactions was determined using thermal analysis (TGA-DTA). The resultant powders were characterized by X-ray diffraction (XRD) analysis and field-emission scanning electron microscope (FESEM). XRD patterns confirmed the formation of TiB₂, B₄C, and TiC phases after heat treatment at 1450°C at mole ratio of B₂O₃/TiO₂ = 4.5, C/B₂O₃ = 2.4. With increasing the content of boron oxide, the unwanted phases such as TiC and C were reduced. TiB₂ and B₄C composite powders (~5 µm diameter) containing residual carbon (<4 wt%) were synthesized using the mole ratio of B₂O₃/TiO₂ = 10 and C/B₂O₃ = 1.9 at low temperature of 1450°C.     

Analysis by mass spectrometry of the hydrolysis/condensation reaction of a trialkoxysilane in various dental monomer solutions

3‐Methacryloxypropyltrimethoxysilane (MPTMS) was converted to silsesquioxane oligomers by hydrolysis/condensation in three dental monomer solutions. The molecular mass distribution and molecular structures of these oligomers was studied by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry. Each dental monomer imparted distinct characteristics on the oligomeric silsesquioxane produced. Ethoxylated bisphenol A dimethacrylate (EBPADMA) produced low‐mass oligomer silsesquioxanes that showed complete hydrolysis and a very high degree of intramolecular condensation (i.e., there were no methoxy and few silanol groups remaining on the oligomers). 1,6‐Bis(methacryloxy‐2‐ethoxycarbonylamino) 2,4,4‐trimethylhexane also produced fully hydrolyzed oligomeric silsesquioxanes but with twice the average molecular mass as the EBPADMA. Finally, triethylene glycol dimethacrylate produced higher mass oligomeric silsesquioxanes than EBPADMA even though it showed incomplete hydrolysis. The degree of hydrolysis increased with increasing mass, as did the degree of intramolecular condensation. Oligomers with degrees of polymerization below 8 were poorly hydrolyzed and showed little if any intramolecular condensation. Those with degrees of polymerization of 9 or greater were almost completely hydrolyzed with a high level of intramolecular condensation. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1842–1847, 2006     

Characterization of Cold Spray Titanium Supersonic Jet

Titanium is widely used in aerospace, highly corrosive environments, and implants due to unique properties such as high strength to weight ratio and excellent corrosion resistance. Cold gas dynamic spray (cold spray) technology, in contrast to current fabrication technologies, has provided the potential for titanium to be utilized in broader industrial applications and at lower cost. Particle velocity is the most important parameter in the cold spray process that leads to successful deposition of titanium at supersonic speeds. In this study, particle image velocimetry (PIV) is utilized to characterize supersonic flow field for a commercially pure (CP) titanium powder. The results represent experimentally determined velocity for titanium particles under supersonic conditions with respect to propellant gas, spray temperature, and stagnation pressure. The high velocity flow region outside of the cold spray nozzle was significantly extended using helium. An increase in stagnation temperature results in a high velocity region close to the axis of the cold spray nozzle. In contrast, an increase in pressure expands the high velocity regions in the cold spray plume. The PIV that is a whole-flow-field process is a practical characterization technique for optimization of parameters and validation of the future models for the cold spray process.     

The use of biodegradable polymers for the stabilization of copper nanoparticles synthesized by chemical reduction method

Copper nanoparticles were synthesized by a convenient and rapid chemical reduction method in ambient condition using \(\hbox {Cu}(\hbox {NO}_{3})_{2}{\cdot } 3\hbox {H}_{2}\hbox {O}\) as a precursor, hydrazine hydrate as reducing agent and deionized water as solvent. The product was characterized by X-ray diffraction (XRD) patterns, field emission scanning electron microscopy, Fourier transform infrared spectroscopy and UV–Vis spectroscopy. However, agglomerated copper nanoparticles were obtained by this chemical reduction method. Hence, the effects of three polymers of polyvinyl pyrrolidone, polyethylene glycol (PEG) and starch as stabilizers on the size and size distribution of Cu nanoparticles were investigated. According to the results, smallest copper nanoparticles (30–50 nm) with a narrow size distribution were obtained using PEG as the stabilizing polymer. Zero-valent copper nanoparticles with high purity were obtained by this method and there was no peak related to the oxidized impurities such as CuO and \(\hbox {Cu}_{2}\hbox {O}\) in the XRD and UV–Vis studies, both in the presence and in the absence of stabilizer. On the other hand, by this method, zero-valent copper nanoparticles were obtained in the absence of any anti-oxidant agent and any inert gas flow. The effects of synthesis parameters including initial concentration of precursor, polymer concentration and the reaction temperature on the size and size distribution of copper nanoparticles were investigated using the UV–Vis analysis to determine the optimum synthesis conditions.     

Synthesis and characterization of nanowire-based anisotropic conductors

We investigated the potential of commercially available porous templates to be used for the fabrication of functional anisotropic conductors. A galvanostatic deposition technique was used to fabricate arrays consisting of 200 nm diameter nanowires inside the pores of polycarbonate membranes. A tape lift-off procedure allowed the complete removal of any residual metal from both sides of the polymer membrane to form an anisotropic conductive film. The 10 microm thick film has roughly 3 x 10(8) nanowires per cm2, and it showed near zero electrical resistance perpendicular to the surface while appearing completely open to circuits between any points on the surface. The preparation of the film, characterization using SEM, AFM, and resistance measurements are presented. The 1D conductivity of these membranes may have many potential applications for microelectronic interconnects for packaging technologies.     

Optimal design analysis of electrothermally driven microactuators

This paper explores a comparative study between different designs of electrothermal microactuators with emphasis on optimal design and performance key factors. For this purpose, two typical designs for electrothermal microactuators with the same material properties are studied: one with different beam lengths (design A), other one with different beam sections and a flexure part (design B). Analytical model and finite element model (FEM) have been developed and validated by comparison of simulation results with experimental results in literature. Optimal geometrical dimensions to achieve maximum deflection have been obtained using genetic algorithm (GA). As the key factors, temperature distribution, power consumption and deflection of these microactuators have been compared in the range of microactuator functionality. Design B is more sensitive to geometrical dimension variation. Using optimal geometrical dimensions, an increase of almost 40 and 55% has been achieved for design A and B tip deflections, respectively. The modified design A with a gold layer results to an increase of 70% for tip deflection comparing to its optimal design.     

Investigation of the electroactivity,conductivity, and morphology of poly(pyrrole‐co‐N‐alkyl pyrrole) prepared via electrochemical nanopolymerization and chemical polymerization

The copolymerization of pyrrole (Py) with N‐ethyl pyrrole, N‐butyl pyrrole, and N‐octyl pyrrole (NOPy) was carried out by electrochemical and chemical oxidation. In the electrochemical method, copolymer thin films with different feed ratios of monomers were synthesized by the cyclic voltammetry method in a lithium perchlorate (LiClO₄)/acetonitrile (CH₃CN) electrolyte on the surface of a glassy carbon working electrode. The deposition conditions on the glassy carbon, the influence of the molar ratios of the monomers on the formation of the copolymers, and the electroactivity of the copolymers were investigated with cyclic voltammetry. Nanoparticles made of a conjugate of the copolymers with different feed ratios of monomers were prepared by chemical polymerization (conventional and interfacial methods) in the presence of iron(III) chloride hexahydrate (FeCl₃·6H₂O) as the oxidant. Nanostructural copolymers with higher conductivities were synthesized by simple tuning of the preparation conditions in a two‐phase medium. Fourier transform infrared spectroscopy, scanning electron microscopy, and four‐probe conductivity measurement techniques were applied for the characterization of the obtained copolymers. The conductivity of the obtained copolymer by an interfacial method with chloroform as the organic phase was 20 times higher than the copolymer obtained via an interfacial method with toluene as the organic phase and 700 times higher than the copolymer prepared by the conventional method (for a molar ratio of 70 : 30 Py : NOPy). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012