Preparation and properties of poly(N-vinylcarbazole) and MWCNT nanocomposites

N-vinylcarbazole (NVC) was polymerized in bulk through the interaction of multi-walled carbon nanotube (MWCNT) without any extraneous catalyst. A PNVC-MWCNT composite was isolated by MeOH precipitation of a polymerization system containing NVC and MWCNT at melting temperature of the monomer. The inclusion of PNVC in the composite was endorsed by the FTIR study. TG analysis revealed the thermal stability trend as MWCNT > PNVC-MWCNT composite > PNVC. DTA showed two exothermic peaks at 427 degrees C and 607 degrees C in the PNVC-MWCNT composite. Transmission electron microscopic analyses of MWCNT revealed presence of tubular MWCNT particles with diameters in nm range while the corresponding analysis for the composite showed the formation of spherical dark polymer particles encapsulating cylindrical MWCNT moieties with some ends of uncoated MWCNT tubes (light shades) protruding out of the dark spherical particles. Scanning electron microscopic analysis revealed presence of tubular CNT particles entangled with the composite particles of irregular shapes and sizes. XRD analysis revealed no additional crystalline peaks for PNVC in the composite. In contrast to PNVC homopolymer (10(-12)-10(-16) S/cm), the dc conductivity values of the composite varied form 1.3 to 33 S/cm depending upon the weight ratio of MWCNT and PNVC in the composite. Current-voltage characteristics of the composite showed a linear variation and conductivity-temperature studies revealed an increase in conductivity by 35% in the temperature range 150-220 degrees C.     

Conducting nanocomposites of poly(N-vinylcarbazole) with single-walled carbon nanotubes

The in situ solid-state polymerization of N-vinylcarbazole (NVC) at an elevated temperature in the presence of single-walled carbon nanotubes (SWCNTs) leads to the formation of new types of composite materials, the morphology and properties of which were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and electrical property measurements. FTIR spectroscopy and XPS studies confirmed the ability of SWCNTs to initiate the in situ polymerization of NVC monomers. FE-SEM and TEM results showed the coating of the outer surfaces of SWCNTs by the PNVC hompolymer with separation of individual SWCNTs from the bundles. Thermogravimetric analysis revealed a moderate improvement in the thermal stability of the nanocomposites at a higher temperature region relative to the base polymer. The electrical conductivity of neat polymer dramatically improved in the presence of SWCNTs. For example, dc electrical conductivity increased from 10(-16)-10(-12) S x cm(-1) for neat PNVC to approximately 10(-6) S x cm(-1) for nanocomposite containing 9 wt% SWCNTs.     

Optimal shape design of three‐dimensional MEMS with applications to electrostatic comb drives

A comb drive is one of the most important microactuators in Microelectromechanical (MEM) systems. In a standard comb drive, the capacitance varies linearly with displacement, resulting in an electrostatic driving force which is independent of the position of the moving fingers (relative to the fixed ones) except at the ends of the range of travel. It is of interest in some applications to have force profiles such as linear, quadratic or cubic. Such shaped comb drives could be useful, for example, for electrostatic tuning or to get actuators with longer ranges of travel than those of standard comb drives. This paper presents a methodology for solving three‐dimensional design (inverse) problems in MEM systems. Design of variable shape comb drives (shape motors) is presented as an application of the general methodology. It addresses issues of simulation, sensitivity analysis and then design of three‐dimensional comb drives. Direct simulation is carried out by the exterior, indirect boundary element method and shape sensitivities are obtained by the direct differentiation approach. The inverse problem determines the height profile of the moving fingers of a comb drive such that the driving force is a desired function of its travel distance. An available optimization code (‘E04UCF’ from the NAG package) is used to solve the inverse problem. Numerical results are presented for shape motors that produce linear or cubic force profiles as functions of travel of the moving fingers. Copyright © 1999 John Wiley & Sons, Ltd.     

Simulation of abrasive flow machining process for 2D and 3D mixture models

Improvement of surface finish and material removal has been quite a challenge in a finishing operation such as abrasive flow machining (AFM). Factors that affect the surface finish and material removal are media viscosity, extrusion pressure, piston velocity, and particle size in abrasive flow machining process. Performing experiments for all the parameters and accurately obtaining an optimized parameter in a short time are difficult to accomplish because the operation requires a precise finish. Computational fluid dynamics (CFD) simulation was employed to accurately determine optimum parameters. In the current work, a 2D model was designed, and the flow analysis, force calculation, and material removal prediction were performed and compared with the available experimental data. Another 3D model for a swaging die finishing using AFM was simulated at different viscosities of the media to study the effects on the controlling parameters. A CFD simulation was performed by using commercially available ANSYS FLUENT. Two phases were considered for the flow analysis, and multiphase mixture model was taken into account. The fluid was considered to be a Newtonian fluid and the flow laminar with no wall slip.     

SST-1 Refurbishment Progress: an Update

Refurbishment of steady state tokamak (SST-1) primarily focused at addressing the issues and bottle-necks involving various subsystems of SST-1 as observed during earlier commis- sioning attempts, have progressed significantly. Under the refurbishment spectrum, all joints in the superconducting magnet system have been re-fabricated as low DC leak tight joint resistances, all toroidal field (TF) magnets have been equipped with 5 K radiation shields on the inner side and successfully tested for their rated parameters in cold under nominal currents, all vessel sectors and modules have been baked and tested under representative conditions, supporting helium and ni- trogen cryogenic facilities have been made > 99% reliable in various envisaged operating scenarios of SST-1. The reassemblies of the critical subsystems of the SST-1 machine shell have progressed aggressively and are nearing completion. Auxiliaries such as the baking facility for the vacuum vessel and first wall components, current leads assembly distributions, synchronized timing sys- tem, reliable data acquisition and plasma control systems as well as essential diagnostics have also been readied towards the first plasma. A detailed engineering validation of the assembled SST-1 machine shell including field error measurements has been planned prior to first plasma attempts.     

Electro-conductive Palmyra Fibers By In Situ Polymerization of Pyrrole

Palmyra (Borassus flabellifer L.) is one of the natural fruit fibers that are available in plenty. This fiber has many advantages, such as biodegradability, renewability, low density, and low cost, which offer greater opportunities to develop new applications. Imparting electrical conductivity to this fiber may open up avenues for various novel applications. In the present study, Palmyra fibers are made electro-conductive by in situ chemical polymerization of pyrrole with FeCl₃ oxidant and PTSA dopant. Prepared electro-conductive fibers show average electrical resistivity 2.96 kΩ cm^?1. A positive correlation is found between fiber-length and electrical resistance, whereas a negative correlation is found in between fiber-diameter and electrical resistance. FTIR study is conducted to understand the chemical interaction between lingo-cellulose and polypyrrole. Tensile properties and thermal degradation behavior of the prepared electro-conductive fibers are evaluated, and significant deterioration of both tensile properties and thermal stability is observed. Due to this reason, these electro-conductive fibers are unsuitable for mechanical processing and high-tech applications. But the response of these fibers in different pH solution is investigated, and their possible application as a pH sensor has been explored.     

On the Development of Thermo-Kinetic Eh-pH Diagrams

It is shown that thermo-kinetic Eh-pH diagrams can be generated through electrochemical measurements. These diagrams offer an accurate method of determining stability regions for leaching without relying on thermodynamic calculations, which may be inaccurate or for which data may be difficult to obtain. The Fe-NH₃-CO₃-H₂O system is studied here. Potentiodynamic polarization experiments were performed on an iron sample in ammoniacal solution in de-aerated condition at different temperature and pH. Polarization plots show that both active anodic dissolution and passive regions are present for pure iron in ammoniacal solution depending on the potential. The electrochemically obtained potential-pH data were used to generate the thermo-kinetic Eh-pH diagrams for the Fe-NH₃-CO₃-H₂O system.     

Efficient Recovery of Combustibles From Coking Coal Fines

The processing of three Indian coking coal fines with feed ash values of 25.12% (S1), 22.97% (S2), and 30.38% (S3) was studied. Substantial improvement in the overall recovery of combustible could be obtained by splitting sample S1, exhibiting good washability but poor release behavior, into a coarser and a finer fraction and treating them by gravity and Jameson cell flotation, respectively. Sample S2 had over 70% of the material below 100 µm and had excellent release characteristics. The Jameson cell flotation indeed resulted in very high recovery of combustibles at the desired target ash values and split processing was not required for this sample. The floatability and washability characteristics of sample S3 indicated that gravity-based methods might improve combustible recovery in terms of theoretical yield at the desired product ash values. A combination of spiral concentration of the coarser fraction and froth flotation of the finer fraction using a Jameson cell showed some improvement in the combustible recovery of this sample. It was established in this study that if the floatability is poor or moderate, then split processing improves coal cleaning performance. Flotation alone may be recommended only when samples exhibit excellent floatability.     

Segregation and Process Features in a Teeter Bed Separator as Revealed by High-Speed Videography and Image Processing

Gravity concentration in a liquid fluidized bed floatex density separator (FDS) was investigated through high-speed videography and image analysis. Process performance in terms of yield and grade of the product for fine coal beneficiation in the FDS was established experimentally. The feed coal (?1.18 mm) with 36% ash was enriched to 24% ash at a mass yield of 65%. Coarsest underflow with a d₅₀ of 700 μm was obtained at 5.8 kPa bed pressure, 120 kg/h feed rate, and 12 lpm teeter water flow. The lowest SG₅₀ of 1.62 was obtained at 5.4 kPa, 15 lpm, and 80 kg/h. At 9 lpm water flow, steady state was achieved in 400 sec when the voidage and suspension density distributions became constant. From the suspension density distribution, the SG₅₀, 1.69 under this set of conditions, was estimated with reasonable accuracy. Increase in teeter water was shown to increase the time required for attaining steady state. It was established that particle size distribution at the bottom of the bed in the column offers a good indication of the separation performance. The influences of the operating variables on the axial steady state profile of the suspension density and voidage were also established. Image analysis is shown to be quite useful in collecting quantitative transient and steady state data that may be difficult to obtain otherwise. The process performances were adequately described using such transient and steady state observations.