Continuous synthesis of colloidal silver nanoparticles by electrochemical discharge in aqueous solutions

This article presents an electrochemical discharge (ECD) method that consists of a combination of chemical methods and electric arc discharges. In the method, 140 V is applied to an Ag electrode from a DC power supply. The arc-discharge between the electrodes produces metallic silver nanoparticles and silver ions in the aqueous solution. Compared with the original arc discharge, this ECD method creates smaller nanoparticles, prevents clumping of the nanoparticles, and shortens the production time. The citrate ions also reduce the silver ions to silver nanoparticles. In addition, the citrate ions cap the surface of the produced silver nanoparticles and the zeta potential increases. In this article, the weight loss of the electrodes and the reduction of silver ions to silver nanoparticles as a function of citrate concentration and electric conductivity of the medium are discussed. Furthermore, the properties of the colloidal silver prepared with ECD are analyzed by UV–Vis spectroscopy, dynamic light scattering, electrophoresis light scattering, and scanning electron microscopy. Finally, a continuous production apparatus is presented for the continuous production of colloidal silver.     

Dual-jet plasmatron for medical applications

We present a design for a dual-jet arc plasmatron operating at a frequency of 66 kHz in an argon flow at atmospheric pressure. We present the results of determination of the temperature, electron concentration, and electrode erosion obtained by atomic emission spectral analysis. The proposed convenient design for a dualjet plasmatron and the low erosion of the copper electrodes in the plasma make it possible to use it for medical purposes. Report given at the Fifth International Conference on Plasma Physics and Plasma Technologies (PPPT-5), 18–22 September 2006, Minsk, Belarus. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 139–140, January–February, 2007.     

Uncapped silver nanoparticles synthesized by DC arc thermal plasma technique for conductor paste formulation

Uncapped silver nanoparticles were synthesized by DC arc thermal plasma technique. The synthesized nanoparticles were structurally cubic and showed wide particle size variation (between 20–150 nm). Thick film paste formulated from such uncapped silver nanoparticles was screen-printed on alumina substrates and the resultant ‘green’ films were fired at different firing temperatures. The films fired at 600 °C revealed better microstructure properties and also yielded the lowest value of sheet resistance in comparison to those corresponding to conventional peak firing temperature of 850 °C. Our findings directly support the role of silver nanoparticles in substantially depressing the operative peak firing temperature involved in traditional conductor thick films technology.     

Comparison between the parameters of a one-phase arc with copper and steel electrodes ignited in nitrogen and in air

The characteristics of an open one-phase arc with gas stabilization in electrode units are studied. The arc is ignited between copper and steel electrodes in nitrogen and in air. The amplitude values of the current and voltage reach 9–10 A and 650–1600 V, respectively. Current and voltage oscillograms, as well as dynamic I–V characteristics, are presented. The time variation of the conductivity, the discharge power, and the spectral composition and integral radiation losses of the arc column are compared when the electrodes are made of copper and steel.     

Experimental investigation of the anode region of a free-burning atmospheric-pressure inert-gas arc. II. Intermediate current regime—multiple anode constriction

This paper reports the experimental investigation of multiple anode constriction in atmospheric-pressure arcs in argon and xenon. The investigations were carried out in a free-burning arc with water-cooled electrodes. Results are presented from spectroscopic measurements of the electron temperature and density in the arc column and near the anode in various regimes of burning. Analysis of the experimental data leads to the conclusion that the constriction occurs because of the development of an overheating instability near the anode due to the disruption of the balance between Joule heating of the plasma and its cooling via the emission of radiation. Zh. Tekh. Fiz. 67, 41–45 (January 1997)     

Raman study of oxidation-reduction dispersion of silver

We have examined the process of redox dispersion of silver, using a solution simultaneously containing an oxidizing agent (potassium ferricyanide) and a reducing agent (sodium borohydride). We have studied the changes over time in the Raman spectra of the indicated solution when no silver particles are present and when such particles are added to the solution. We have established that the silver particles have a catalytic effect on the reaction between potassium ferricyanide and sodium borohydride, kinetically slowed down in alkaline medium. The original silver particles (1–20 μm) undergo redox dispersion as a result, and Ag particles are formed with sizes 1–10 nm. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 182–186, March–April, 2006.     

Production of fullerenes in an arc discharge in the presence of hydrogen and oxygen

The production of fullerenes in an arc with graphite electrodes in mixtures of helium with oxygen and hydrogen as well as in pure oxygen and hydrogen is investigated. The radiation spectra of the arc and the mass spectra of the soot obtained in the arc are recorded; the content of fullerenes in the soot is determined. It is shown that fullerenes are formed in appreciable quantities (∼1%) even in pure hydrogen. Zh. Tekh. Fiz. 69, 48–51 (December 1999)     

Rotating high current arc

A high current arc (1–16 kA) of 5–20 ms duration is investigated, which rotates between two annular electrodes of variable distance (5–16 mm) at elevated pressures (0.1–1 MPa) in SF₆. The are is driven by the magnetic field of two ring-shaped coils in cusp geometry, one on either side of the electrodes. Both experiments and theoretical models concentrate on the investigation of the hot wake. The temperature, velocity, and size of the wake are determined by schlieren photography, streak records, and shock waves. A simple model is developed which yields a quantitative picture. The immediate surroundings of the transversely blown are can be described in terms of sucking in cold gas with associated heating and expansion, whereas the far-field region is governed by turbulent entrainment. The model involves only one empirical parameter: the entrainment coefficient α, which turns out to have a value of about 10⁻³.     

Gradient multilayer tribilogical coatings based on Mo–S–Ti–C formed by hybrid ion-plasma methods

Mechanical, physical and tribological properties of layer-gradient multi-component coatings based on the Mo–S–Ti–C composition are investigated. The coatings are formed by combining the magnetron sputtering and the hybrid magnetron and vacuum arc deposition assisted by a gas plasma generator. A correlation is established between the physic mechanical and tribological properties of the resulting coatings, which allows identifying their potential applications. The physical principles of the combined technologies of lowtemperature ion-plasma deposition of tribological Mo–S–Ti–C coatings onto hardened steel machine parts are developed.     

Laser-induced modification of composite Cu-C nanosized particles synthesized using a pulsed electrical discharge in a liquid

Composite copper-containing carbon nanosized structures were synthesized in the plasma of a pulsed electrical discharge, initiated between two graphite electrodes in an aqueous copper chloride solution. We studied the effect of laser radiation on the morphology of the nanoparticles formed, whose properties we studied by optical absorption spectroscopy and transmission electron microscopy. We discuss the mechanisms for nanoparticle formation in a discharge submerged in a liquid, and the possibilities for laser-induced modification of the nanoparticles. We estimated the temperature of the nanoparticles when exposed to laser radiation pulses. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 3, pp. 372–378, May–June, 2008.     

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讨论了在相距25.0mm长度40.0mm的平行电极间的由强度可达6040Gs的外磁场驱动的滑移弧功率变化过程,分析了滑移弧等离子体所处的状态。当电弧运行在电极平行段时,电弧功率在0.65kW附近剧烈振荡;当电弧接近平行电极顶端时,电弧功率由约0.65kW迅速增加到约2.0kW。在一个放电周期内,电弧功率基本上是从小到大持续增加的,由弧电源提供能量来维持滑移弧等离子体的平衡状态。根据Ozlem Mutaf-Yardimici等人的理论,此时滑移弧等离子体仍处于平衡态。     

Carbon nanotubes as nanoparticles collector

This communication reports on a new method for the collection of nanoparticles using carbon nanotubes (CNT) as collecting surfaces, by which the problem of agglomeration of nanoparticles can be circumvented. CNT (10–50 nm in diameter, 1–10 μm in length) were grown by thermal CVD at 923 K in a 7 v/v% C₂H₂ in N₂ mixture on electroless nickel-plated copper transmission electron microscopy (TEM) grids and Monel coupons. These samples were then placed downstream of an arc plasma reactor to collect individual copper nanoparticles (5–30 nm in diameter). It was observed that the Cu nanoparticles preferentially adhere onto CNT and that the macro-particles (diameter >1 μm), a usual co-product obtained with metal nanoparticles in the arc plasma synthesis, are not collected. Cu–Ni nanoparticles, a catalyst for CNT growth, were deposited on CNT to grow multibranched CNT. CNT-embedded thin films were produced by re-melting the deposited nanoparticles.     

Photoionization spectra of silver atoms adsorbed on the surface of a ZnS single crystal

We have used photostimulated flash luminescence to study deep electronic states arising when silver ions Ag⁺ are deposited under high vacuum onto the surface of a ZnS single crystal, followed by creation of the conditions for neutralization of the silver ions. The flux density of the silver ion beam was 10⁷ cm⁻²·sec⁻¹. We have observed the appearance of two types of deep electronic states with photoionization energies 1.60 eV and 1.80 eV, arising after depositing the silver ions onto the surface of the ZnS single crystal. We have hypothesized that there may be two different preferred sites for adsorption of silver atoms on the zinc sulfide surface. The corresponding photoionization spectra of the adsorbed silver atoms have maxima at 775 nm and 690 nm. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 335–338, May–June, 2006.     

Investigation of Saha-Boltzmann equilibrium in the analyte zone of a two-jet plasma generator

Relative populations of the excited levels for Cr(I), Cr(II), Fe(I) and Fe(II) in the argon plasma flow of an arc two-jet plasma generator used in spectrochemical analysis were measured. The range of the total energy E of excitation and ionization was 4.5–8.0 and 12.5–16.0 eV, respectively. It is shown that the populations of atom and ion levels are linear with respect to energy lower than E∼15 eV. For ionic lines with energy close to 15.5–16.0 eV the line intensities behave anomalously against equilibrium values. This can be associated with charge transfer between the analyte and argon ions. Deviation of I from LTE values increases in the plasma zones below and above the site of jet confluence, where the plasma temperature decreases. A. P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, 1a Favorskii St., Irkutsk, 664033, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 575–581, September–October, 1997.     

EELS plasmon studies of silver/carbon core/shell nanocables prepared by simple arc discharge

A method for the fabrication of large quantities of high quality silver nanocables encapsulated in carbon nanotubes (Ag@C) using a hydrogen arc is presented. A growth mechanism based on the generation of poly-aromatic hydrocarbons by the hydrogen arc is proposed. The size-dependent electronic structures of the resultant materials are investigated using electron energy loss spectroscopy (EELS). The surface plasmon and bulk-excitation character observed by EELS are discussed. As the diameter of Ag@C nanocable decreases, the surface and bulk plasmons of the silver core shift to lower energy and the peaks broaden. Measurements of electrical conductivity exhibits a liner current–voltage character with a conductivity of 0.5×10⁴ S/cm for the nanocable structure. PACS 81.05.Tp; 81.07.-b     

Probe diagnostics of strongly ionized inert-gas plasmas at atmospheric pressure

The technique of probe measurements (experiment and theory) is applied in a dense, strongly ionized inert-gas plasma at atmospheric pressure. The measurements are performed in a high-current (250–550 A) free-burning argon arc with a thermionic cathode. As a control technique we used spectroscopic measurements. Comparison of calculation with experiment reveals good agreement. The possibility of determining the plasma potential from the measured floating-probe potential is demonstrated. Zh. Tekh. Fiz. 68, 51–55 (June 1998)     

A novel method for synthesis of colloidal silver nanoparticles by arc discharge in liquid

This paper presents a novel, inexpensive and one-step approach for synthesis of silver nanoparticles (Ag NPs) using arc discharge between titanium electrodes in AgNO₃ solution. The resulting nanoparticles were characterized using UV–Vis spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Silver nanoparticles of 18 nm diameter were formed during reduction of AgNO₃ in plasma discharge zone. Optical absorption spectroscopy of as prepared samples at 15 A arc current in AgNO₃ solution shows a surface plasmon resonance around 410 nm. It was found that sodium citrate acts as a stabilizer and surface capping agent of the colloidal nanoparticles. SEM images exhibit the increase of reduced nanoparticles in 6 min arc duration compared with 1 min arc duration. TEM image of the sample prepared at 6 min arc duration shows narrow size distribution with 18 nm mean particle size. Antibacterial activities of silver nanoparticles were investigated at the presence of Escherichia coli (E-coli) bacteria.     

Synthesis of mixed metallic nanoparticles by spark discharge

Short spark discharges (2 μs) were successfully applied to generate mixed particles a few nanometres in diameter by fast quenching. Alloyed Cr–Co electrodes were applied to demonstrate this. Further it was shown that if the anode and the cathode are different materials, the discharge process mixes the vapour of both materials, forming mixed nanoparticles. Electron microscopy (TEM, SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analyses were performed on the collected particles to study their size, morphology, composition and structure. The average compositions of the particles were measured by inductively coupled plasma (ICP). In addition, online measurements of the particle size distribution by mobility analysis were carried out. In the case of alloyed electrodes (Cr–Co), the relative concentration of the elements in the nanoparticulate sample was consistent with the electrode composition. When using electrodes of different metals (Au–Pd and Ag–Pd) the individual nanoparticles showed a range of mixing ratios. No surface segregation was observed in these mixed noble metal particles. Crystalline nanoparticulate mixed phases were found in all cases.     

Argentite–Acanthite Transition in Silver Sulfide as a Two-Sublattice Ordering

We propose a model of phase transformation cubic argentite–monoclinic acanthite in silver sulfide Ag2S (AgS0.5) as ordering in two argentite sublattices. We have determined the channel of the disorder–order transition including four nonequivalent superstructure vectors of stars {k9} and {k4}. For monoclinic acanthite α-Ag2S, we have calculated the distribution function for silver atoms occupying b positions in argentite, as well as the distribution function for sulfur atoms. Ordering in both sublattices is complicated by static atomic displacements. The displacement of S atoms distort the body-centered cubic (bcc) nonmetallic argentite sublattice, forming a monoclinic lattice in which silver atoms are at large distances from one another and occupy their crystallographic positions with unit probability. We have determined the range of admissible values of long-range order parameters η9 and η4 for the model monoclinic ordered α-Ag2S phase.     

Effect of metallic nanoparticle sizes on the local field near their surface

We have used numerical calculations based on Mie theory to analyze the near field distribution patterns for 4–150 nm spherical silver nanoparticles (nanospheres). We have shown that as the nanoparticle sizes increase, the region where “hot spots” are concentrated is shifted to the forward hemisphere. We have observed a nonmonotonic dependence of the maximum attainable local field enhancement factor on the size of the silver nanospheres. We have determined a correlation between the optimal nanosphere size for the maximum attainable local field enhancement factor and the optical absorption efficiency factor. We have established a nonmonotonic dependence of the optimal size of the nanoparticles and the maximum attainable local field enhancement factor on the refractive index of the surrounding medium. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 831–837, November–December, 2008.