Ag Nanopowders Research Articles

Al2O3–Ag nanopowders: new method of synthesis, characterisation and biocidal activity

The present paper describes an innovative method of producing silver nanoparticles incorporated into an aluminium nano‐oxide substrate. The method utilises thermal decomposition and reduction, which yields an Al2O3–Ag nanopowder with the average size of particles ranging from 43 to 60 nm and the average size of agglomerates between 330 and 870 nm. The average size of the silver nanoparticles incorporated in the aluminium nano‐oxide carrier ranges from 22 to 60 nm. The Al2O3–Ag nanopowders thus produced have a largely developed surface area (above 200 m2 g−1) with a great number of open pores (above 5×10−4 m3 g−1), which gives evidence that their tendency to agglomeration is only slight and that the possible agglomerates have a loose structure. Moreover, the nanopowders show good bactericidal and fungicidal properties. The results obtained in the present experiments show that the Al2O3–Ag nanopowders produced by the proposed method can be used successfully as the raw material in the production of biocidal biomaterials.

Interaction of silver nanopowder with copper substrate

Addition of lead into tin based solders represents a serious health risk and environmental problem. Lead-free solders represent one of the ways to remove pollution of lead into environment, nevertheless, new advanced joining methods have to be considered. Aggregation effect of nanoparticles studied in this work seems to be an interesting alternative. It was found experimentally that Ag nanopowder annealed at temperatures above silver oxide decomposition forms continuous Ag layer and yields a firm junction between copper plates. Oxide layer is observed at the Cu-Ag interface. The oxide interlayer thickness reflects the temperature and annealing time. Microstructure of prepared experimental joints, composition profiles and local mechanical properties were studied on cross-sectional samples by analytical electron microscopy and depth-sensing indentation technique.

Measurement of Nanoparticle Concentration Using Quartz Crystal Microgravimetry

Various nanoscale items (e.g., nanoparticles and nanotubes) have been actively investigated due to their unique physicochemical properties. A common issue encountered in such studies is accurate expression of nanoparticle concentration. Given the critical importance of the dose-response relationship, we present the use of quartz crystal microgravimetry (QCM) to accurately measure nanoparticle concentration in a colloidal suspension. Application of a small drop of the nanoparticle suspension in a volatile solvent to the crystal surface leaves a dry nanoparticle residue after solvent evaporation after which the shift in the crystal resonant frequency is recorded. The instrument was calibrated using a set of serial dilutions of Si and Ag nanopowder in methanol, rhodamine B in methanol, and ferrocene in cyclohexane. Using QCM, a linear response for nanoparticle concentrations up to 1300 μg/mL was determined. The developed method was used to determine the concentrations of size-selected, octyl-terminated Si nanocrystal samples with median diameters in the range 1.1-14.8 nm and also to calculate size-dependent nanocrystal extinction coefficients.

Characterization of spark plasma sintered Ag nanopowders

The low temperature sintering behaviour of nanocrystalline Ag powder (with anaverage size of 70 nm) was characterized. Using spark plasma sintering (SPS), the Agnanopowders can be successfully sintered at low pressure for only 5 min without externalheating, and the sintering density increases and porosity decreases significantlywith increase in the sintering temperature. Nanoindentation has been used tocharacterize the SPS sintered Ag samples. The mechanisms of the low sinteringtemperature behaviour of the nano-Ag powder and the nanoscale mechanicalperformance have been discussed. Compression tests were also used to characterize themechanical properties of the sintered Ag sample with a maximum strain up to 15%.

Self-assembly of Ag nanopowder on OTS-patterned glass

Ag ink was spontaneously patterned on glass substrate by using the surface energy difference of a pre-patterned octadecyltrichlorosilane (OTS) layer. Ag ink was confined into the hydrophilic area, where OTS layer was not formed. OTS layer was selectively transferred by micro-contact printing (μCP) method and significantly decreased surface energy. As a result, surface of glass substrate was separated as hydrophobic and hydrophilic with and without OTS layer, respectively. Ag line could be successfully patterned with the width of below 10 μm on the glass. The patterned Ag line was dense and abrupt on the edge and the thickness was about 0.25 μm. Ag film showed good adhesion on a glass substrate after anneal above 200 °C. The minimum resistivity was about 4 μΩ cm.

The Speciation of Silver Nanoparticles in Antimicrobial Fabric Before and After Exposure to a Hypochlorite/Detergent Solution

Because of their antibacterial properties, silver nanoparticles are often used in consumer products. To assess environmental and/or human health risks from these nanoparticles, there is a need to identify the chemical transformations that silver nanoparticles undergo in different environments. Thus an antimicrobial sock material containing Ag nanoparticles was examined by X-ray absorption spectroscopy to identify the speciation of Ag. The material was exposed to a hypochlorite/detergent solution and subjected to agitation. An elemental Ag nanopowder was also exposed to the hypochlorite/detergent solution or to a 1 mol L(-1) NaCl solution. Results showed that the sock material nanoparticles consisted of elemental Ag. After exposure to the hypochlorite/detergent solution, a significant portion (more than 50%) of the sock nanoparticles were converted, in situ, to AgCl. Results from exposures to elemental Ag nanopowder suggest that an oxidation step is necessary for the elemental Ag nanoparticles to transform into AgCl as there was no evidence of AgCl formation in the presence of chloride alone. As a result, if Ag ions leach from consumer products, any chloride present may quickly scavenge the ions. In addition, the efficacy of Ag, as an antimicrobial agent in fabrics, may be limited, or even negated, after washing in solutions containing oxidizers as AgCl is much less reactive than Ag ion.

Die-attachment solutions for SiC power devices

Silicon carbide has become a very attractive material for high temperature and high power electronics applications due to its physical properties, which are different than those of conventional Si semiconductors. However, the reliability of SiC devices is limited by assembly processes comprising die attachment and interconnections technology as well as the stability of ohmic contacts at high temperatures. The investigations of die to substrate connection methods which can fulfill high temperature and high power requirements are the main focuses of the paper. This work focuses on die attach technologies: solder bonding by means of gold–germanium alloys, adhesive bonding with the use of organic and inorganic conductive compositions, as well as die bonding with the use of low temperature sintering with silver nanoparticles. The applied bonding technologies are described and obtained results are presented. Of the methods tested, the best solutions for high temperature application are two die attach technologies: silver glass die attach and die bonding with the use of low temperature sintered Ag nanopowders.

High precision determination of silver isotope ratios in commercial products by MC-ICP-MS

Silver isotope ratios in several fortified commercial products were determined by multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS). Mass discrimination and instrument drift were corrected for by a combination of internal normalization with Pd and standard-sample-standard bracketing, without assuming identical mass bias for Pd and Ag. The certified value of 1.07638 for 107Ag/109Ag in NIST SRM 978a was used for mass bias correction of 106Pd/108Pd in two adjacent solutions of SRM 978a. Their average was then used for mass bias correction to calculate the mass bias corrected Ag isotope ratio in the sample. An approximately 2.5-fold improvement in precision of determination of δ107/109Ag was obtained with the use of the proposed technique compared to data obtained solely with a standard-sample-standard bracketing approach. Internal and external precisions (2SD) of ±0.05‰ (n = 10) and ±0.04‰ (n = 19) for δ107/109Ag were obtained, suitable for the detection of varying Ag isotope abundances in commercial products fortified with Ag. Amongst the commercial products examined, no significant differences were detected in Ag isotopic compositions among NIST 978a standard, Ag high purity metal (Johnson Matthey Plc), Ag Nanopowder (Sigma-Aldrich) and Silversoft socks. Significant differences in Ag isotope ratios were found among NIST SRM 978a standard, a colloidal Ag dietary supplement, decanethiol functionalized Ag nanoparticles and X-static socks. The X-static socks and decanethiol functionalized Ag nanoparticles have negative δ107/109Ag values of −0.08 ± 0.05‰ and −0.15 ± 0.02‰ (2SD, n = 4), respectively, and the colloidal Ag dietary supplement has +0.83 ± 0.06‰ (2SD, n = 4). These observations suggest that such data may provide a useful tool for fingerprinting sources of Ag in the environment.

질소가스흡착법을 이용한 금속 나노분말의 프랙탈 차원 결정 및 표면 특성 평가

The surface roughness of Al, Ag and Ni nano-powders which were prepared by pulsed wire evaporation method was quantified based upon the fractal theory. The surface fractal dimensions of metal nano-powders were determined from the linear relationship between In <TEX>$V/V_{mono}$</TEX> and Inln (<TEX>$P^o/P$</TEX>) using multi-layer gas adsorption theory. Moreover, the fractal surface image was realized by computer simulation. The relationship between preparation condition and surface characteristics of metal nano-powders was discussed in detail.

A novel design and fabrication of multilayered ionic polymer-metal composite actuators based on Nafion/layered silicate and Nafion/silica nanocomposites

Recently, we prepared Nafion/layered silicate and Nafion/silica nanocomposites and used them as starting materials in the fabrication of ionic polymer-metal composites (IPMCs). Experimental data indicated that Nafion/silica-based IPMCs exhibited almost three times higher blocking force with 200% larger displacement than the pure Nafion-based IPMC. On the other hand, due to the barrier property of well-dispersed silicate platelets, the response rate of Nafion/layered silicate-based IPMCs under an electric voltage was lower than that of Nafion-IPMC. However, these samples showed a complete lack of relaxation, which appeared to be a good sign of a prolonged service life of IPMC. In this work, the high blocking force and the lack of relaxation during operation period observed, respectively, for Nafion/silica- and Nafion/layered silicate-based IPMCs were combined in a multilayer configuration, which contained a main Nafion/silica nanocomposite layer sandwiched between two outer layers of Nafion/layered silicate nanocomposites. Two designs for multilayered IPMCs were proposed. In the first design, the electrode layer of IPMCs was prepared by a conventional electroless plating process, while in the second design a flexible electrode layer was made by recasting of a mixture containing Nafion solution, layered silicate and a conductive material (e.g. Ag nano-powder). The multilayered IPMC exhibited a greatly improved blocking force with a very limited relaxation. The IPMC of the second design showed a blocking force of 6 and 9 g f at 2 and 3 V dc, respectively. A remarkable improvement in tip displacement of IPMC was also obtained, where multilayered IPMCs demonstrated a 250% increase in tip displacement compared to that of Nafion-IPMC. Furthermore, the response rate of multilayered IPMCs was also higher than that of conventional Nafion-based IPMC. Results and highlights of our present study are presented in this paper.

Production of nanopowders by wire explosion in liquid media

The technology of wire explosion has been used to produce nanopowders. A new concept was proposed to produce nanosized powder, which is wire explosion in liquid media. We have exploded the Ag wires with 0.3-mm diameter and 25-mm length, in the de-ionized water. Electrical energy of 1.1 kJ was stored in a 10-uF capacitor and released to the wires through a triggered spark gap switch. The process was observed by high-speed camera. Those images showed that the powders were generated by vapor condensation in the shell formed by the shock wave in the water. The particles were directly dispersed into the water with the collapse of the shell. The pure Ag nanopowder was produced by this method.

Hydrothermal synthesis and characterization of silver and antimony co-doped PbSe nanopowders

Silver and antimony co-doped PbSe (AgPb 10SbSe 12) nanopowders were hydrothermally synthesized at 160 °C, using selenium powder, lead nitrate, silver nitrate and antimony nitrate as starting materials, and NaBH 4 as a reductant. X-ray diffraction (XRD), scanning electron microscope (SEM) equipped with X-ray energy-dispersed spectroscopy (EDS), and transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS) were respectively used for characterization of the nanopowders. The formation mechanism of the Ag and Sb co-doped PbSe nanopowders was proposed.

The effect of nano-powder additions on the superconducting properties of MgB/sub 2/

To investigate the effect of Ag or SiC nano-powder additions on the superconducting properties of MgB/sub 2/, a series of superconducting (Ag)/sub (x)wt.-%/(MgB/sub 2/)/sub (100-x)wt.-%/(Ag/sub x/-MgB/sub 2/) and (SiC)/sub (x)wt.-%/(MgB/sub 2/)/sub (100-x)wt.-%/((SiC)/sub x/-MgB/sub 2/)(0/spl les/x/spl les/20), containing Ag and SiC nano-powders, respectively, of different diameters (30 nm and 130 nm), were prepared by a simple solid-state reaction route, cold-pressed into a pellet form and investigated. To maintain the same environment of MgB/sub 2//stainless-steel tapes/wires, Ag/sub x/-MgB/sub 2/ and (SiC)/sub x/-MgB/sub 2/ pellets made out of the mixed powders were put inside stainless steel tubes and then sintered at 900/spl deg/C for two hours in Ar atmosphere. Characterization performed included both X-ray diffraction and magnetization. No impurity phase was identified for as-rolled samples. However, both the Ag/sub x/-MgB/sub 2/ and (SiC)/sub x/-MgB/sub 2/ composite pellets, when sintered, contain various impurity phases. The isothermal magnetizations M(H) of a series of samples were measured at temperatures between 5 and 50 K in fields up to 5 T, using a PPMS-9 (Quantum Design). The optimal amounts of Ag and SiC nano-powder in Ag/sub x/-MgB/sub 2/ and (SiC)/sub x/-MgB/sub 2/ to obtain the largest flux pinning effect are /spl sim/8 and /spl sim/4 wt.-%, respectively. The two-step structures in ZFC M(T) curves of (SiC)/sub x/-MgB/sub 2/ were more developed than Ag/sub x/-MgB/sub 2/. The best flux pinning centers can be created by adding a suitable size and amount of SiC nano-powder, not too large to increase the decoupling between the MgB/sub 2/ grains.

Li Storage Properties of Ag and SnO &lt;sub&gt;2&lt;/sub&gt; Nanopowders Synthesized from Reverse Micelles

Ag and SnO2 nanopowders were synthesized by reverse-micelle method. The reverse micelles were prepared to form tiny aqueous droplets dispersed in oil-based solvents. Two reverse micelles containing metallic salts and reductive agents were rigorously mixed to form nanoparticles inside aqueous droplets by a reductive reaction. The spherical powders of 20~50 nm were formed during the process. The resulting Ag and SnO2 nanopowders were examined as the anode electrode for lithium-ion cells. The reversible discharge capacity of the Ag and SnO2 nanopowders after 25 cycles were 315 and 380 mAh/g, respectively.

Synthesis of Ag Nanopowders from Reverse Micelles

Synthesis of Ag Nanopowders from Reverse Micelles

Effect of production parameters on the structure and morphology of Ag nanopowders produced by inert gas condensation

Polymer-based materials can be made electrically conductive by adding reinforcing particulate conductive material. Instead of using high aspect-ratio conventional fillers, such as fibres and flakes, highly porous silver nanopowders can be used in polymer matrix composites. Such porous morphology contributes to improving electrical conductivity and mechanical properties of nanopowders-polymer matrix composite due to its irregularly shaped surface which prevents or minimises delimitation in the composite structure. In this study, porous nanopowders were produced by the inert gas condensation method with various production parameters such as, different O 2 amount, wire feeding rates, gas types and pressures. Effect of those parameters on the size, morphology and specific surface area of the nanoparticles were determined.