Conducting polymer functionalized multi-walled carbon nanotubes with noble metal nanoparticles: Synthesis,morphological characteristics and electrical properties

We report the synthesis of conducting polyaniline-functionalized multi-walled carbon nanotubes (MWCNTs-f-PANI) containing noble metal (Au and Ag) nanoparticles composites (MWCNTs-f-PANI-Au or Ag-NC). MWCNTs-f-PANI was initially synthesized by functionalizing acyl chloride terminated carbon nanotubes (MWCNTs-COCl) with 2,5-diaminobenzenesulphonic acid (DABSA) via amide bond formation, followed by surface initiated in situ chemical oxidative graft polymerization of aniline in the presence of the ammonium persulphate (APS) as an oxidizing agent. MWCNTs-f-PANI was then dispersed into an aqueous Au or Ag metal salt solution followed by the addition of sodium citrate, which acted as a reducing agent. The resulting composite contained a high level of well dispersed Au or Ag nanoparticles (MWCNTs-f-PANI/Au-NC or MWCNTs-f-PANI-Ag-NC). Morphological and structural characteristics, as well as electrical conducting properties of the hybrid nanocomposites were characterized using various techniques including high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), UV–visible spectroscopy (UV–vis) and four-probe measurements. FT-IR spectra confirmed that PANI was covalently bonded to MWCNTs. TEM images revealed the presence of Au or Ag nanoparticles finely dispersed in the composites with a size of <15 nm. XRD analysis revealed the presence of strong interactions between the metal nanoparticles and MWCNTs-f-PANI, where the metal particles were present in a phase-pure crystalline state with face centered cubic (fcc) structure. The room temperature electrical conductivity of the MWNCTs-f-PANI/Au or Ag composites was 4.8–5.0 S/cm, respectively, which was much higher than that of CNTs-f-PANI (0.18 S/cm) or pure PANI (2.5 × 10^?3 S/cm). A plausible mechanism for the formation of nanocomposites is presented. We expect that the new synthesis strategy reported here will be applicable for the synthesis of other hybrid CNTs–polymer/metal nanocomposites with diverse functionalities. This new type of hybrid nanocomposite material may have numerous applications in nanotechnology, gas sensing, and catalysis.     

Mechanism of polypyrrole and silver nanorod formation in lauric acid–cetyl trimethyl ammonium bromide coacervate gel template: Physical and conductivity properties

Polypyrrole (PPy) and silver (Ag) nanorods are synthesized in cetyl trimethylammonium bromide–lauric acid (CTAB–LA) complex coacervate gel template. When PPy–CTAB–LA system is polymerized with AgNO₃, Ag nanorods are produced while use of ammonium persulphate (APS) as initiator yields PPy nanorods. Ag-nanorods are produced from the initial stage while PPy nanorods take a longer time. The average diameter of Ag nanorods varies from 60 to 145 nm by increasing AgNO₃ concentration from 0.27 M to 1.08 M and that of PPy varies from 145 nm to 345 nm by changing pyrrole concentration from 1 × 10^?4 to 2 × 10^?4 M, respectively. Fourier transformed infrared (FTIR) spectra indicate stabilization of Ag nanorods through complexation of PPy with adsorbed Ag⁺ ions. PPy nanoparticles are stabilized by adsorbed sulphate ions and lauric acid, both are acting as dopant to it. FFT pattern and EDX spectra clearly indicate the presence of Ag nanocrystals and PPy on the surface of Ag nanorods, respectively. The mechanism of nanorod formation is attributed from UV–Vis spectra showing a red shift of surface plasmon band of Ag and π–π* transition band of PPy with time. The highest dc conductivity of PPy–Ag composite is found to be 414.2 S/cm, 7 orders higher than that of PPy nanorods (9.3 × 10^?4 S/cm). PPy–Ag systems show Ohmic behavior while PPy nanorods exhibit semi-conducting behavior. The preferential formation of Ag nanorod in AgNO₃ initiated polymerization is attributed to the higher cohesive force of Ag than that of PPy. With two times higher LA and CTAB concentration in the gel the Ag nanorod diameter decreases only 12% while that of PPy nanorod decreases by 50%. Possible reasons are discussed from the hard and soft nature of the two nanorods and from the elasticity of the gel template.     

Amorphous Fe–B alloys in B–Fe–Ag multilayers studied by magnetization and Mössbauer measurements

Bulk and local magnetic properties were studied in [1 nm B + 1 nm ⁵⁷Fe + x nm Ag]₅, x = 1, 2, 4, 5 and 10, multilayer samples. Although Ag does not mix with either of the other two elements the magnetic properties of the multilayers are strongly influenced by the Ag thickness below x = 5, whereas no such effect is observed above this value. The Mössbauer measurements indicate a complete amorphization of the thin Fe layers in each sample, as a result of intermixing with the B layers. The variation of the magnetic properties is explained by the variation of the average B concentration of the amorphous Fe–B layers, which depends on the thickness of the Ag barrier layers. The magnetization measurements indicate ferromagnetic behaviour of the ultra-thin amorphous layers with the presence of less than 10% superparamagnetic moments for x = 5 and 10. The average B concentration of the amorphous Fe–B alloy, as estimated from the Fe hyperfine fields, is around 40 at%. It is significantly lower than the 60 at% nominal B concentration, suggesting the presence of an unalloyed B layer, as well. This picture is supported by transmission electron microscopy investigations which reveal two amorphous layers of different B concentration in between the crystalline Ag layers.     

Polypyrrole grafting onto the surface of pyrrole-modified silica nanoparticles prepared by one-step synthesis

The grafting of polypyrrole onto the surface of modified silica nanoparticles has been investigated. These silica nanoparticles were modified with pyrrole moieties prepared by the well-known Stober method in one-step starting from TEOS and a pyrrole-bearing trialkoxysilane compound. The effects of various reaction conditions, including reaction time, solvent, and molar ratio of water to alkoxy groups, have been investigated in order to obtain pyrrole-modified silica nanoparticles with the optimal core–shell structure and the smallest possible particle size. The grafting was carried out in aqueous FeCl₃ solution containing the modified silica nanoparticles, with pyrrole monomers already adsorbed on the surface of the particles by soaking. Several analytical tools have been employed to characterize the particles and to assess the degree of grafting, namely TEM, SEM, TGA, FTIR, and XPS. The final polypyrrole-grafted silica nanoparticles obtained had a mean diameter of about 220 nm and 50 wt.% of grafted polypyrrole with respect to the total weight of polypyrrole formed around the surface of the cores.     

Kinetics of Ag3Sn growth in Ag–Sn–Ag system during transient liquid phase soldering process

The kinetics of the interfacial reaction of a thin layer of Sn sandwiched between two pieces of Ag foil has been investigated at temperatures of 260 °C, 300 °C and 340 °C. A time dependence of the form t^1/n with n = 3 was obtained for the kinetics of both the consumption of the Sn remaining and the thickening growth of the Ag₃Sn scallops formed between Sn and Ag. Such a result can be explained well using the model of grain boundary/molten channel-controlled growth of intermetallic compounds. In this case, the diffusion of Ag atoms through the molten channels existing between the previously formed Ag₃Sn scallops is the controlling mechanism for the kinetics. We also report here the derived kinetic constants including reaction constants and the associated activation energy for guiding the practical transient liquid phase soldering of the Ag–Sn–Ag system.     

The formation and evolution of oxide particles in oxide-dispersion-strengthened ferritic steels during processing

The fabrication of oxide-dispersion-strengthened (ODS) steels is a multi-stage process involving powder ball milling, degassing and consolidation by hot isostatic pressing. Y is introduced by mechanical alloying (MA) with either Y₂O₃ or Fe₂Y so a high density of Y–Ti–O-based oxide nanoparticles is formed. The evolution of ～2 nm oxide nanoparticles and larger >5 nm grain boundary oxides has been studied at each step of the processing. The nanoparticle dispersions produced in material MA with Fe₂Y were comparable to those produced by alloying with Y₂O₃. Hence the majority of oxygen which forms the nanoparticles must be incorporated from the atmosphere during MA, rather than being introduced via the alloying additions. During mechanical alloying, a high density of subnanometer particles are formed (2.5 ± 0.5 × 10²⁴ m^?3). The oxygen content of the nanoparticles decreases slightly on annealing, and then the composition of the nanoparticles remains constant throughout subsequent processing stages. The nanoparticle size increases during processing up to ～2 nm radius, while the number density decreases to 4 ± 0.5 × 10²³ m^?3. Grain boundary oxides (>5 nm) have a Ti–Cr–O-rich shell, and contain no Y before consolidation, but have similar core composition to the matrix nanoparticles after consolidation. The formation of the larger grain boundary oxides is shown to take place during the degassing and consolidation stages, and this occurs at the expense of the nanoparticles in the matrix. This work provides a mechanistic understanding of the importance of controlling the oxygen content in the powder during MA, and the resulting impact on the formation of the ODS microstructure.     

Visible light-induced photocatalytic activity of Ag-containing TiO2/carbon nanofibers composites

TiO₂/carbon nanofiber (CNF) composites containing Ag nanoparticles (Ag–TiO₂/CNF) were prepared and their photocatalytic degradation ability upon visible light irradiation assessed. The reduction of methylene blue (MB) adsorption in an aqueous solution by the photocatalysts occurred due to the combined effects of MB adsorption in the pores of CNFs and decomposition by the photocatalysts throughout the process. The Ag–TiO₂/CNF photocatalyst degraded MB 17 times faster than the TiO₂/CNF composites with no Ag nanoparticles after 3 h under visible light illuminations.     

Electrospinning of carbon nanofiber supported Fe/Co/Ni ternary alloy nanoparticles

Polyacrylonitrile (PAN)-based carbon nanofiber supported Fe/Co/Ni ternary alloy nanoparticles were prepared by using the electrospinning technique for potential fuel cell applications. The solution was prepared by adding pre-solved catalytic precursor into PAN/DMF solution. The effect of PAN and catalyst precursor concentration on solution properties (viscosity and conductivity) and heat stabilization temperature has been investigated. Electrospun nanofibers were characterized by field emission scanning electron microscope, transmission electron microscope, energy dispersive spectrometer and X-ray diffractometer. It has been found that ternary nanoparticle size is in the range of 5–115 nm (average: 20 nm) and is a crystal alloy of Fe, Co and Ni. Also, TEM results demonstrate that in some regions metal nanoparticles tend to agglomerate into larger particles mainly due to the non-uniform distribution of nanoparticles in as-spun condition. PAN-derived carbon nanofiber mean diameter was measured as 200 nm by varying from 40 nm to 420 nm.     

Microstructure evolution of Ti–Si–C–Ag nanocomposite coatings deposited by DC magnetron sputtering

Nanocomposite coatings consisting of Ag and TiC_x (x < 1) crystallites in a matrix of amorphous SiC were deposited by high-rate magnetron sputtering from Ti–Si–C–Ag compound targets. Different target compositions were used to achieve coatings with a Si content of ～13 at.%, while varying the C/Ti ratio and Ag content. Electron microscopy, helium ion microscopy, X-ray photoelectron spectroscopy and X-ray diffraction were employed to trace Ag segregation during deposition and possible decomposition of amorphous SiC. Eutectic interaction between Ag and Si is observed, and the Ag forms threading grains which coarsen with increased coating thickness. The coatings can be tailored for conductivity horizontally or vertically by controlling the shape and distribution of the Ag precipitates. Coatings were fabricated with hardness in the range 10–18 GPa and resistivity in the range 77–142 μΩ cm.     

A study on the effects of silica particle size and milling time on synthesis of silicon carbide nanoparticles by carbothermic reduction

Silicon carbide nanoparticles were produced by a carbothermic reduction of nano and micro size silica with graphite at 1450 °C for 1 h. The SiC nanoparticles were characterized by XRD, SEM and TEM. The results showed that in the case of nano silica, milling up to 20 h could develop SiC particles of 5–25 nm with some residual SiO₂ particles. By extending milling time to 40 h, more energy was provided and produced Fe contamination, which could act as catalyst and increased SiC yield as well as Fe₂Si phase formation after heat treatment. Coarser particles of micro silica caused higher Fe erosion, more SiC formation with 20–70 nm size and presence of Fe₂Si phase at shorter milling times after heat treatment. Leaching treatment could purify SiC nanoparticles. Increase of milling from 20 to 40 h changed the morphology from polygonal shape to spherical with some reduction in the particle size.     

Electrical and magnetic properties of the composite pellets containing DBSA-doped polyaniline and Fe nanoparticles

DBSA-doped polyaniline powder (DBSA-PANI) was mixed with Fe nanoparticles to obtain the DBSA-PANI-Fe composite. Powder of the composite was compacted to the pellets to study the electrical property and magnetization characteristic by measuring the conductivity in 100–300 K and the magnetization curve at room temperature. The conductivity of the composite pellet is linearly decreased from 0.25 ± 0.02 to 0.07 ± 0.01 S/cm with increasing the Fe nanoparticle content from 0 to 70 wt.%. For the pellets containing the Fe nanoparticles less than 70 wt.%, the variation of conductivity with temperature reveals that the charge transport mechanism can be considered to be one-dimensional variable-range-hopping (1D-VRH). For the pellet with 70 wt.%-Fe nanoparticles, however, the charge transport mechanism cannot be well understood in terms of the VRH model. All the DBSA-PANI-Fe composite pellets show a magnetic hysteresis loop and a hard magnetization characteristic. The saturation magnetization monotonously increases from 32 to 78 emu/g with increasing the Fe nanoparticle content from 30 to 70 wt.%. The saturation field and the coercivity are estimated to be about 5500 and 385 Oe, respectively, independent of the Fe nanoparticle content.     

Photoinduced absorption of Ag nanoparticles deposited on ITO substrate

Substantial changes of absorption after illumination by 300 mW continuous wave green laser at 532 nm were observed. The effect of indium tin oxide (ITO) substrate was explored versus Ag nanoparticles (AgNPs) size, their regularity and surface plasmon resonance. The ITO substrate features play a crucial role for the formation of homogenous AgNPs. The attachments of AgNPs on ITO surface as well as their homogeneity are significantly changed under the influence of the laser treatment. We study the Ag NP deposited on the two different substrates which play a crucial role in the photoinduced absorption. The dependence of the photoinduced absorption versus the time of optical treatment is explained within a framework of the photopolarization of the particular trapping levels on the borders between the ITO substrate and the Ag NP.     

Effect of Ag–Au composition and acid concentration on dealloying front velocity and cracking during nanoporous gold formation

Nanoporous gold has many potential applications in various fields, including energy storage, catalysis, sensing and actuating. Dealloying of Ag–Au alloys under free corrosion conditions is a simple method to fabricate nanoporous gold. Here, we systematically investigate the dealloying rate of Ag–xAu alloy for a range of alloy compositions (x = 20–40 at.%) and nitric acid concentration (7.3–14.9 M) using in situ transmission X-ray microscopy. High-resolution in situ X-ray projections and ex situ tomographic reconstructions allow imaging of the dealloying front position during dealloying. The dealloying front velocity is constant with time, and depends exponentially on the alloy Ag/Au atomic ratio and the acid molar concentration. Only the leanest alloy, Ag–20 Au, shows a large macroscopic shrinkage in sample diameter (～38%) after dealloying, which leads to crack nucleation and growth observed in real time during dealloying. Finite element modeling is used to estimate dealloying-induced stresses and strains, and sheds light on the cracks created by the diameter shrinkage.     

An innovative method to perform maskless plain waterjet milling for pocket generation: a case study in Ti-based superalloys

This paper presents an innovative methodology/jet path on which plain waterjet (PWJ) can generate pockets of good dimensional/geometrical definition (minimised under/over-erosion) while the proposed method leads to the avoidance of grit embedment on the target workpiece and the elimination of extra cost and time related to the use of mask.The novelty of the paper relies on the proposal of jet-path strategy that minimises the variations in jet dwell time by providing “continuous” relative movement during the jet-part interaction (through minimisation of accelerations/decelerations of the machine head) and by removing a controlled amount of material in a series of layers using special techniques. The proposed method is powerful in its approach from which it ensures (quasi)equal exposure time for each zone of material over which the jet passes, so that the jet path is “totally contained” within the form to be generated; hence, no masking is necessary to define the contour/shape.This approach has been employed for generating pockets on two Ti-based superalloys commonly used in aerospace industries, followed by dimensional, geometrical and surface quality analysis. The results proved that this approach can produce milled surfaces of straightness of the pocket bottom (<200 μm), tolerance on depth of cut per layer (<20 μm), tolerance on the radii at the bottom of the pockets (<100 μm), surface roughness (Ra=4–14 μm) and waviness (Wa=10–13 μm) characteristics in conditions of high surface integrity (no cracks, contaminations, etc.).     

Charge transfer driven surface segregation of gold atoms in 13-atom Au–Ag nanoalloys and its relevance to their structural,optical and electronic properties

The structural, optical and electronic properties of 13-atom Ag–Au nanoalloys are determined by a combination of global optimization using semi-empirical potentials and density functional theory calculations. A family of Au surface-segregated structures are found for core–shell Ag_nAu_13−n (n = 1, 2, 3, 5, 7, 8, 9, 12) and hollow Ag_nAu_13−n (n = 4, 6, 10, 11) clusters, whose stability is enhanced by directional charge transfer. The atomic ordering in core–shell structures is related to the electric dipole moment and odd-numbered surface Au-atom clusters have high moments. Their ferroelectric and ferromagnetic properties provide a potential approach for tailoring their surface plasmonic modes.     

Structure and magnetoresistive properties of current-perpendicular-to-plane pseudo-spin valves using polycrystalline Co2Fe-based Heusler alloy films

We report current-perpendicular-to-plane giant magnetoresistance (CPP–GMR) of pseudo-spin valves (PSVs) with polycrystalline Co₂Fe(Al_0.5Si_0.5) (CFAS) and Co₂Fe(Ga_0.5Ge_0.5) (CFGG) Heusler alloy films. Strongly [0 1 1] textured polycrystalline Heusler alloy films grew on the Ta/Ru/Ag underlayer. Relatively large CPP–GMR values of ΔRA up to 4 mΩ μm² and ΔR/R up to 10% were obtained with 5 nm thick Heusler alloy films and Ag spacer layer by annealing CFAS PSV at 450 °C and CFGG PSV at 350 °C. Transmission electron microscopy revealed a flat and sharp interface between the [0 1 1] textured CFAS layers and the [1 1 1] textured Ag spacer layer. Annealing above an optimal temperature for each PSV led to reductions in MR values as a result of the thickening of the spacer layer induced by the Ag diffusion from the outer Ag layers.     

Fabrication and characteristics of composite containing HCl-doped polyaniline and Ni nanoparticles

HCl-doped polyaniline powder (HCl-PANI) was synthesized using a polymerization procedure and then Ni nanoparticles were deposited on the HCl-PANI at room temperature by direct current magnetron sputtering. After this process the HCl-PANI–Ni composite was obtained. Ni nanoparticle size ranges from 5 nm to 20 nm in the composite. HCl-PANI structure is not influenced by the Ni nanoparticles. The composite pellet exhibits room temperature ferromagnetism and a conductivity of about 0.66 S/cm. A temperature dependence of the conductivity from 160 K to 290 K reveals that a carrier transport mechanism in the composite is three-dimensional variable range hopping. Thermogravimetric analysis reveals that a weight loss of the HCl-PANI–Ni composite is larger than that of the HCl-PANI for the same heating temperature. The weight loss difference between the composite and the HCl-PANI increases with increasing the temperature.     

Elastic properties of hard cobalt boride composite nanoparticles

This paper reports on the determination of elastic and hardness properties of Co–B composite nanoparticles (CNP). Co boride materials is usually known for their functional properties (hydrogen catalysis, magnetism, corrosion, biomedics), but nanoscale dimensions also bring significant mechanical properties. In situ compression tests of 70–150 nm core–shell silica-coated Co₂B CNP (Composite nanoparticles) were performed for the first time with a nanoindenter in the load range 30–300 μN. The CNP modulus is comparable with the bulk material (E_CNP = 159–166 GPa), but the hardness is as much as 5 times higher (～4.5 ± 1.0 GPA). Both modulus and hardness (to a lesser extent) are found to increase with the applied pressure. The paper first addresses the limitations of ordinary contact analysis intended for single-phase NP, and then presents a hybrid Oliver–Pharr strategy suitable for CNP, where numerical modeling overcomes issues related to anisotropy and heterogenety of the composite nanostructure that hinder the direct application of basic contact models. An alternative regression-based approach for estimating modulus and hardness is also considered for comparison. The importance of the model selection for the contact area A for accurate modulus and hardness results is emphasized. Besides typical Hertzian, geometrical and cylindrical area models, a new one is formulated from a “rigid-sphere” approximation, which turned out to perform best and consistently in this study, on a par with the cylindrical model. Finally, evidence of the magnetic nature of CNP and, unexpectedly, reverse plasticity is provided.     

First-principles investigation of the structure and synergistic chemical bonding of Ag and Mg at the Al | Ω interface in a Al–Cu–Mg–Ag alloy

Density functional theory was used to characterize the atomic structure and bonding of the Al | Ω interface in a Al–Cu–Mg–Ag alloy. The most stable interfacial structure was found to be connected by Al–Al bonds with a hexagonal Al lattice on the surface of the Ω phase sitting on the vacant hollow sites of the Al {1 1 1} matrix plane. The calculations predict that when substituted separately for Al at this interface, Ag and Mg do not enhance the interface stability through chemical bonding. Combining Ag and Mg, however, was found to chemically stabilize this interface, with the lowest-energy structure examined being a bi-layer with Ag atoms adjacent to the Al matrix and Mg adjacent to the Ω phase. This study provides an atomic arrangement for the interfacial bi-layer observed experimentally in this alloy.     

Site preference of transition-metal elements in B2 NiAl: A comprehensive study

First-principles supercell calculations based on density functional theory were performed to study the T = 0 K site preference of 3d (Ti–Cu), 4d (Zr–Ag) and 5d (Hf–Au) transition-metal elements in B2 NiAl. By adopting a statistical-mechanical Wagner–Schottky model within the canonical ensemble, the effects of finite temperature on site preference were further considered. The calculations showed that, at all alloy compositions and temperatures, Co, Tc, Ru, Rh, Re, Os, Ir and Pt have a consistent preference for the Ni sublattice, while Ti, Zr, Nb, Hf and Ta have a consistent preference for the Al sublattice. In contrast, the site preference of V, Cr, Mn, Fe, Cu, Mo, Pd, Ag, W and Au was found to depend on both composition and temperature. The present calculated results compare favorably with existing theoretical and experimental studies in the literature.