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Commercial purity aluminum was reinforced with different percentages of carbon nanohorns (CNH) using ball milling (1 h) followed by spark plasma sintering (SPS) at 550 °C for 5 min under 50 MPa pressure with heating rate 100 °C/min. The microstructure, hardness and compression properties of the spark-plasma-sintered carbon-nanohorns-reinforced aluminum (Al-CNH) composites were evaluated. Transmission electron microscopy revealed a uniform distribution of 0.3% CNH in Al, but above 0.3% CNH, agglomeration occurred. The compression strength of Al-0.3%CNH composites increased by 44% compared to the milled Al sample without CNH.

Cobalt-rich alloys of various compositions (Co33Fe33Ni33, Co40Fe40Ni20, Co50Fe25Ni25 and Co60Fe20Ni20) were synthesized from their respective precursor salts using a novel hydrazine reduction method. The synthesized nanosized powders were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM) techniques. XRD phase analysis results revealed that the Co33Fe33Ni33 alloy was formed with a pure FCC phase. Whereas, Co40Fe40Ni20, Co50Fe25Ni25 and Co60Fe20Ni20 alloys were composed of both FCC and BCC phases. The average particle size of the alloys was estimated to be in the range of 107–280 nm. The synthesized cobalt-rich alloys exhibited ferromagnetic properties at room temperature with a high saturation magnetization value up to 138 emu/g. The mixed phase Co40Fe40Ni20 alloy showed higher saturation magnetization and higher coercivity as compared to the other alloy compositions. In mixed phase alloys, the dominance of the BCC phase over the FCC phase seems to has resulted in the enhancement of the saturation magnetization value. The obtained results indicate that the hydrazine reduction method was effective in synthesizing cobalt-rich alloys with excellent soft magnetic properties. Keywords: Cobalt-rich alloys, Hydrazine reduction method, Electron microscopy, Magnetic properties

Carbon nanotubes (CNT) are synthesized using arc discharge method in an open air. Various amounts of carbon nanotubes-reinforced AA7075 composites are prepared by powder metallurgy route and then hot extrusion at 450 °C. Hot-extruded composites are characterized, and mechanical properties are measured. Dry sliding wear properties of hot-extruded samples were evaluated using a pin-on-disk method for various loads (5-20 N) at room temperature and for various temperatures (100-400 °C) at the applied load 10 N as a function of CNT amount. Grain size of the composites is decreased compared with Al alloy matrix. Transmission electron microscopy of the composites revealed that the CNT are uniformly distributed in the composites. Mechanical properties of the hot-extruded composites are enhanced with an increase in CNT content. The wear performance is improved with an increased CNT amount, but decreases with an increase in the applied load and temperature as well. The wear damage is mild at lower applied loads and temperatures, whereas the damage is severe at 400 °C. The wear mechanism was plowing in the initial stages which is transformed to severe sliding and chipping with increasing load and temperature. The enhanced wear behavior of composites is attributed to self-lubricating nature of carbon nanotubes.

Magnetic nanoparticles of cobalt ferrite are synthesized via a simple reduction route. These synthesized nanoparticles were characterized using x-ray diffraction (XRD), Scanning Electron Microscopy, Raman Spectroscopy, Fourier Transform Infrared studies and their magnetic properties were measured using Vibrating-sample magnetometer. The XRD analysis confirms the formation of single phase CoFe2O4 nanoparticles, with cubic spinel structure, having crystalline size of 5-10 nm, depending on the annealing temperature. Raman spectra analysis confirmed that all the synthesized powders are phase pure. The maximum magnetic saturation of 268 A m(-1) has been observed for the sample calcined at 600 degrees C and correspondingly the magnetic anisotropic constant values are reported. The proposed hydrazine reduction synthesis route is simple in execution and cost effective, which makes it economically adaptable for large scale production of CoFe2O4 nanoparticles.

Magnesium (Mg)-based biomaterials are widely investigated for degradable implant applications. Developing Mg-based composites is one of the strategies adopted to increase the bioactivity and to reduce the degradation rate of Mg. In the present study, hydroxyapatite (fHA) has been produced from fish bones and incorporated into pure Mg sheets by friction stir processing (FSP). Microstructures of the composites clearly revealed the grain refinement in the stir zone up to $$10\,\upmu \hbox {m}$$ from the starting size of $$2000\,\upmu \hbox {m}$$ . Measurements of microhardness also indicated the effect of a smaller grain size and the presence of fHA on increasing the hardness in composites. Interestingly from the tensile tests, mechanical properties, such as yield strength and ultimate tensile strengths were measured as they decreased for the composite due to the presence of fHA particles. However, the observed % elongation of the composite was similar to that of a natural bone. From the electrochemical tests, the composite exhibited an enhanced corrosion performance. From the results, it can be concluded that the cost-effective Mg–fHA composites can be developed by FSP for degradable scaffold applications in biomedical fields.

Carbon nanohorns (CNHs) are synthesized by DC arc-discharge method in helium atmosphere. The synthesized CNHs are heat treated and then functionalized with Nafion. Platinum is reduced onto Nafion functionalized CNHs through ethylene glycol reduction method. Pt/Nafion-CNHs catalysts are prepared by varying deposition times from 1 to 7 h. Detailed characterization of CNHs and the catalyst is performed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, X-ray diffraction (XRD) and thermo gravimetric analysis (TGA). Membrane electrode assemblies are prepared by decal method and electrode performance is analyzed using hydrogen pumping technique. SEM and TGA analysis of soot indicates relatively high level purity of CNHs. TEM and XRD analysis of catalyst with 6 h deposition time reveals that Pt nanoparticles are uniformly deposited on multiwall CNHs surface with particle size of 3–4 nm. Hydrogen pumping studies reveals that Nafion functionalized CNHs act as good catalyst support without hindering electron transfer at electrodes. Hence, these graphitic carbon supports have potential application for high power density applications.

In this study, Titania (TiO 2 ) 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 TiO 2 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 TiO 2 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 TiO 2 matrix. The hardness and modulus of the CNT reinforced TiO 2 increased by 22% and 5.4% respectively while that of the SWNH reinforced TiO 2 increased by 11% and 23% respectively. GNP and CNT reinforced TiO 2 exhibited superior photocatalytic activity for the degradation of methylene blue dye compared to pure TiO 2 .

In the present work, multi walled carbon nanotubes (MWCNT) reinforced magnesium (Mg) matrix composite was fabricated by friction stir processing (FSP) with an aim to explore its mechanical and electrochemical behavior. Microstructural observations showed that the thickness of the produced composite layer was in the range of 2500 µm. FSP resulted uniform distribution of CNT near the surface while agglomerated layers in the subsurface. Grain refinement of Mg achieved by FSP improved the hardness but significant enhancement in the hardness value was observed for FSPed MWCNT/Mg composites. Potentiodynamic polarization studies revealed that the increase in corrosion current density was observed for MWCNT/Mg composite compared with grain refined Mg and pure Mg, implying the significance of secondary phase (MWCNT) in decreasing the corrosion resistance of the composite. Keywords: Friction stir processing, MWCNT/Mg composite, Hardness, Basal texture, Corrosion resistance

Cost-effective synthesis of single walled carbon nanotube (SWCNT) and single walled carbon nanohorn (SWCNH) hybrids, in a single step, by electric arc discharge technique in open air, at lower current densities is reported. The rate of production of the hybrids is 3-5 g/h. The presence of SWCNTs and SWCNHs is confirmed by a transmission electron microscope (TEM). In addition to conventional larger Dahlia-like aggregates of nanohorns, unique nearly-spherical shaped and relatively smaller sized aggregates (mean size ? 25 nm) of nanohorns are formed along with thin bundles (mean diameter ? 5.7 nm) of SWCNTs. � 2015 Elsevier B.V. All rights reserved.

Electroless nickel (EN) plating was performed on arc discharge synthesized multiwalled carbon nanotubes for various deposition times. X-ray diffraction (XRD), Transmission electron microscopy (TEM), and Raman spectroscopy characterization techniques are used to identify the presence of nickel deposition on the carbon nanotubes (CNTs) and the degree of graphitization. The results indicate that impurities are less in the purified CNTs as compared to raw carbon soot. Increasing deposition time up to 60 min increases uniform deposition of nickel throughout the length of the CNTs. However, for deposition time longer than 60 min, nickel particles are seen separated from the surface of the CNTs. Uniformly coated nickel CNTs throughout their length are potential candidates for reinforcements in composite materials. Magnetic properties of the nickel coated CNTs, with deposition time of 30 and 60 min were also evaluated. The magnetic saturation of nickel coated CNTs with deposition time of 30 min is less compared to nickel coated CNTs with deposition time of 60 min. � 2014 Elsevier B.V. All rights reserved.

Graphene sheets have been synthesized from single walled carbon nanohorns by one-step reaction with hydrogen peroxide. The obtained graphene sheets are in pure form and shows good electrical properties. As-synthesized graphene acts as dual function of support as well as reducing agent to prepare graphene-silver nanoparticle composite having uniform particle size of 6 nm. This method can easily be scalable to prepare graphene or graphene supported metal nanoparticle composites for versatile applications.

Horizontally aligned and densely packed multiwalled carbon nanotubes (MWCNTs) were synthesized in an open air, without the need for a controlled atmosphere, using a rotating cathode arc discharge method with the help of a metal scraper. The physical force exerted by the scraper results in in-situ alignment of MWCNTs along the direction of scrape marks. This strategy, which enables the alignment of nanotubes in a controlled fashion to any length and direction of interest, was examined to determine the force required to align a nanotube. A model is developed to understand the alignment process. Using the nanoscratch technique to mimic this strategy, and incorporating the data obtained from the nanoscratch technique into the model developed, the minimum force required to align a MWCNT, as well as the energy required to align a gram of nanotubes, has been estimated. The method demonstrated represents an economical approach for large-scale synthesis of aligned MWCNTs at low costs. � Indian Academy of Sciences.

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. � 2015 Elsevier B.V.

Upcycling polymer wastes into useful, and valuable carbon based materials, is a challenging process. We report a novel catalyst-free and solvent-free technique for the formation of nano channeled ultrafine carbon tubes (NCUFCTs) and multiwalled carbon nanotubes (MWCNTs) from polyethylene terephthalate (PET) wastes, using rotating cathode arc discharge technique. The soot obtain from the anode contains ultrafine and nano-sized solid carbon spheres (SCS) with a mean diameter of 221. nm and 100. nm, respectively, formed at the lower temperature region of the anode where the temperature is approximately 1700. �C. The carbon spheres are converted into long "Y" type branched and non-branched NCUFCTs and MWCNTs at higher temperature regions where the temperature is approximately 2600. �C, with mean diameters of 364. nm and 95. nm, respectively. Soot deposited on the cathode is composed of MWCNTs with a mean diameter of 20. nm and other nanoparticles. The tubular structures present in the anode are longer, bent and often coiled with lesser graphitization compared to the nanotubes in the soot on the cathode. � 2014 Elsevier Ltd.

Electrode structure plays an important role in the performance of proton exchange membrane fuel cells. To get high electrochemical active area in the electrode, perfluorosulfonate-ionomer is loaded in stage wise. Single-wall carbon nanohorns (SWCNHs) are synthesized by DC arc-discharge method in Helium atmosphere and these synthesized SWCNHs were functionalized with Nafion. Platinum was reduced onto Nafion functionalized SWCNHs through colloidal method. Pt/Nafion-SWCNHs catalysts were prepared by varying deposition times. Detailed characterization of the catalyst was carried out using Transmission Electron Microscopy (TEM), X-ray diffraction (XRD), infrared spectroscopy (IR), and Thermo Gravimetric Analysis (TGA). TEM of Pt decorated SWCNHs revealed uniformly dispersed Pt nano particles with an average particle size of 3 nm in the SWCNHs. IR studies of catalyst confirm the presence of Nafion on Pt/Nafion-SWCNHs. Nafion membrane and Pt/Nafion-SWCNHs catalyst were used to construct fuel cell in decal method and tested in fuel cell testing facility. Cyclic voltammetry tests of the catalyst also confirm the high electrochemical active area of the catalyst. Pt reduction onto Nafion functionalized SWCNHs leads to an increase in electrochemically active surface area. High platinum utilization due to increased electrochemical surface area with efficient SWCNHs support of Pt/Nafion-SWCNHs catalyst makes it a promising electrocatalyst for fuel cells.