Prathap Haridoss

Alignment of multi-walled carbon nanotubes (MWCNTs) is demonstrated using physical forces both during synthesis, as well as post-synthesis through the arc discharge technique. The arc discharge process results in relatively straight and defect free MWCNTs compared to other techniques such as chemical vapor deposition. A scraper enables alignment of these straight MWCNTs during synthesis. Additional tailoring of the direction of alignment is seen to be possible even at room temperature, using physical forces in the form of scratch marks on the soot. Using a hand operated roller, on the surface of the soot, also results in the alignment of MWCNTs along the rolling direction. Alignment of MWCNTs is confirmed using scanning electron microscopy and it results in distinct changes in X-ray diffraction and energy dispersive spectroscopy data. These results are significant from the perspective of obtaining aligned MWCNTs, in large quantities, in a relatively inexpensive manner. © 2012 Elsevier Ltd. All rights reserved.

Nanoclusters of CdS and PbS were prepared using two different organic solvents as stabilizers in order to understand the factors affecting their formation and stabilization. Growth of the nanoclusters was monitored by optical absorption spectroscopy at regular intervals of time. Mean cluster size was characterized by X-ray diffraction (XRD). The surface structure of nanoclusters was analyzed using infrared (IR) spectroscopy. Spectroscopic studies under identical experimental conditions reveal interesting correlations between the stability of the nanoclusters formed, the nature of the solvent and the size of metal ion involved, leading to a better understanding of nanocluster formation. © 2004 Elsevier B.V. All rihgts reserved.

Carbon nanotubes (CNT) have received huge attention from the scientific community in the last two decades due to their unique structure and properties. They have been considered for potential applications in various areas of science and technology. One of the major applications of CNT is as reinforcement for fabrication of light weight high strength composite materials for use in automobile and aerospace applications. Aluminium and its alloys are natural choices for such applications due to their low density, high specific strength and modulus. In the last decade, there have been significant advances in the processing of carbon nanotube reinforced aluminium matrix (Al-CNT) composites. New understanding has emerged due to research on several aspects such as damage to CNTs during processing, interfacial phenomena, novel methods of processing for improving CNT dispersion, tensile behaviour, numerical modelling and in situ tensile testing. This review summarizes the present status of the tensile properties of pure Al-CNT and Al alloy-CNT composites. The various processing routes for fabrication of Al-CNT composites have been compared in terms of the resulting microstructure, degree of CNT dispersion, extent of interfacial reaction and its effect on the tensile properties. Factors affecting strengthening efficiency and the strengthening mechanisms in Al-CNT composites are discussed.

Sluggish kinetics and catalyst instability in oxygen reduction reaction are the central issues in fuel cell and metal-air battery technologies. For that, highly active, stable, and low-cost non-platinum based electrocatalysts for oxygen reduction reaction are an immediate requirement in fuel cell and metal-air battery technologies. A new composite (S,N-GQD/TiO2/C-800) is synthesized, made of sulfur (S) and nitrogen (N) co-doped graphene quantum dot (GQD) with TiO2. This composite is supported on carbon on heating at 800 °C under N2 atmosphere and is explored for oxygen reduction reaction (ORR) catalyst. The synthesized composite S,N-GQD/TiO2/C-800, shows outstanding catalytic activity with an onset potential of 0.91 V and a half-wave potential of 0.82 V vs. RHE, an alkaline medium. The Tafel slope of the catalyst is 61 mV dec−1. The catalyst is an excellent methanol tolerant and shows good stability in an alkaline medium. The excellent ORR activity of S,N-GQD/TiO2/C-800 is ascribed to well-built interactivity between the S,N-GQD/TiO2, and the carbon support. The unique structure offers advantages, with outstanding electrical conductivity, high surface area, and excellent charge transfer kinetics between the doped GQD and TiO2 interface and subsequently from the carbon surface to the S,N-GQD/TiO2.

Electroless copper coatings were performed on purified carbon nanotubes (CNT), with varying deposition time and the optimum deposition time in terms of uniform deposition was determined to be 45. min. Different amounts of optimized Cu coated CNT (CNT (Cu)) and Al powders were ball milled. CNT (Cu) reinforced Al (Al-CNT (Cu)) composites were prepared by spark plasma sintering (SPS). Pure CNT reinforced Al (Al-CNT) composites were also prepared by SPS. The ball milled powders and composites were characterized using X-Ray diffraction, scanning electron microscopy, Raman spectroscopy, and transmission electron microscopy (TEM). Microhardness and compression properties of the composites were measured. TEM images of ball milled powders and composites revealed uniform distribution of CNT in matrix. Mechanical properties of Al-CNT (Cu) composites are superior to Al-CNT composites. The maximum enhancement in compressive strength of Al-CNT (Cu) composites is 154% for 2. wt% reinforcement; this enhancement is attributed to the copper coating on CNT surface.

Semiconductor nanocrystals doped in stable matrices such as polymers are of interest due to fundamental scientific aspects as well as their scope for technological applications. In the present investigation, PbS nanocrystals are synthesized in polyvinyl alcohol (PVA) matrix using a simple technique based on colloidal chemistry. Various concentrations of nanocrystalline PbS (with an average size of 4.5 nm) are loaded into the polymer to study the effect of PbS concentration on the optical, thermal and electrical properties of the composite. An increase in PbS content results in decrease in thermal stability and an increase in electrical conductivity, presumably resulting from interactions between the nanofiller and polymer. Considerations for designing composites with desired combinations of electrical, thermal, and optical properties to suit specific device operating environments are studied systematically. © 2006 Elsevier B.V. All rights reserved.

In this work, the rheological properties, thermal stability and the lap shear strength of epoxy adhesive joints reinforced with different carbon nano-fillers such as multi-walled carbon nanotubes (CNT), graphene nanoplatelets (GNP) and single-walled carbon nanohorns (CNH) have been studied. The nano-fillers were dispersed homogeneously using Brabender® Plasti-Corder®. The epoxy pre-polymer with and without the nano-fillers exhibited shear thinning behavior. The nano-filler epoxy mixtures exhibited a viscoplastic behavior which was analyzed using Casson's model. Thermo-gravimetric analysis indicated an increase in the thermal stability of the epoxy with the addition of carbon nano-fillers. Carbon nano-fillers resulted in increased lap shear strength having high Weibull modulus. The joint strength increased by 53%, 49% and 46% with the addition of 1 wt.% CNT, 0.5 wt.% GNP and 0.5 wt.% CNH, respectively. The strength of the joints having high filler content (>1 wt.%) was limited by mixed mode type of failure.

In this study, Titania (TiO2) based composites reinforced with 2 wt% of various carbon nanomaterials were prepared using spark plasma sintering (SPS). Prior to SPS, the samples were ball milled. The reinforcements used in the composites were graphene nanoplatelets (GNP), carbon nanotubes (CNT) and single walled carbon nanohorns (SWNH). The ball milled powders and SPS compacts were characterized using various techniques. Mechanical and photocatalytic properties of the SPS composites were evaluated and compared for different nano-carbon reinforced TiO2 composites. X-ray diffraction and Raman spectroscopy studies confirmed that the milled powders comprised of Anatase phase which transformed into Rutile phase during SPS. Nano transformation twins were observed in Rutile grains. Fractured surfaces showed that the reinforcements were well bonded with the TiO2 grains and the SWNH reinforcement resulted in comparatively finer grain size. Nanoindentation studies showed that the hardness and elastic modulus of GNP reinforced composites was 78% and 30% respectively higher compared to TiO2 matrix. The hardness and modulus of the CNT reinforced TiO2 increased by 22% and 5.4% respectively while that of the SWNH reinforced TiO2 increased by 11% and 23% respectively. GNP and CNT reinforced TiO2 exhibited superior photocatalytic activity for the degradation of methylene blue dye compared to pure TiO2.

Proton exchange membrane fuel cell (PEMFC) performance with a cross-linked poly (vinyl alcohol)/sulfosuccinic acid (PVA/SSA) polymer is compared with Nafion® N-115 polymer. In this study, PVA/SSA (≈5 wt. % SSA) polymer membranes are synthesized by a solution casting technique. These cross-linked PVA/SSA polymers and Nafion are used as electrolytes and ionomers in catalyst layers, to fabricate different membrane electrode assemblies (MEAs) for PEMFCs. Properties of each MEA are evaluated using scanning electron microscopy, contact angle measurements, impedance spectroscopy and hydrogen pumping technique. I-V characteristics of each cell are evaluated in a H2-O2 fuel cell testing fixture under different operating conditions. PVA/SSA ionomer causes only an additional ≈4% loss in the anode performance compared to Nafion ionomer. The maximum power density obtained from PVA/SSA based cells range from 99 to 117.4 mW cm-2 with current density range of 247 to 293.4 mA cm-2. Ionic conductivity of PVA/SSA based cells is more sensitive to state of hydration of MEA, while maximum power density obtained is less sensitive to state of hydration of MEA. Maximum power density of cross-linked PVA/SSA membrane based cell is about 35% that of Nafion® N-115 based cell. From these results, cross-linked PVA/SSA polymer is identified as potential candidate for PEMFCs.

Electronic waste, in the form of printed circuit boards (PCBs) or printed wiring boards (PWBs), represents a significant and growing fraction of the waste generated in many communities. It is necessary to identify schemes to manage and dispose this waste in an environmentally safe manner. The present work, examines the use of mechanical means to separate the metallic and non-metallic components present in PCBs. The unique characteristics of PCB construction pose challenges to the mechanical means of separation. In view of these unique characteristics of PCBs, an empirical approach is suggested to evaluate the effectiveness of the mechanical separation process. Two milling operations were used to obtain the feed for the separation using elutriation. Compositions of different size fractions from the milling operations are presented. Experimental data from the separation process is presented and the extent of use of mechanical means that results in optimum separation is identified. The separation efficiency is analyzed in terms of composition, particle size and operating condition of the elutriation flow rate. A probabilistic analysis based on single particle settling velocity shows that separation results with uniform particle size fraction can be described effectively. However, the probabilistic analysis captures only the qualitative features with mixed particle sizes and components. © 2007 Elsevier B.V. All rights reserved.