Characterization of silver and silver/nickel composite particles prepared by spray pyrolysis

Pure silver and silver/nickel composite particles were prepared by spray pyrolysis of aqueous solutions of AgNO₃, and mixed salts of AgNO₃ and Ni(NO₃)₂·6H₂O, respectively. In the case of pure silver, reduction to metallic silver and subsequent sintering to highly spherical and dense particles took place immediately and almost simultaneously once favorable conditions for the former were imposed, irrespective of the nature of the carrier gas. For the composite particles, the high rates of reduction and sintering of the silver were still maintained, while crystallization of the silver, and the reduction and sintering of the nickel were considerably retarded, compared to the spray pyrolysis of each pure salt. Once the counterpart salt was added, the size of the composite particles increased compared to that of each pure metallic particles, but it was little affected by the furnace set temperature, the residence time and the molar ratio of the two precursor salts. Within single particles, an increase in either the temperature or the residence time caused segregation—silver in the shells and nickel in the cores—and improved the particles' surface smoothness and sphericity accordingly.     

The effect of thermal stresses on the EMI (electromagnetic interference) shielding of conductive plastics

The electrical properties of a number of filled and coated plastics were examined after subjecting the materials to rigorous thermal cycling between −20 and 80°C. Filled compounds that obtained their conductivity through the addition of carbon based conductive fillers maintained their conductivity throughout the thermal cycling. Compositions which contained metal fillers were able to maintain their conductivity only when a high temperature thermally stable polymer was used as the polymer matrix. Plaques coated by a zinc arc spray or with acrylic paints containing graphite, silver, and nickel particles were unaffected by thermal cycling. Plaques coated with an acrylic paint containing copper particles lost most of their conductivity during the changes in sample temperature.     

On the magnetic, mechanical and rheological properties of rubber–nickel nanocomposites

Rubber–nickel nanocomposites were synthesized by incorporating freshly prepared nanometric nickel particles in two different matrices namely natural rubber and neoprene rubber according to specific recipes for various loadings of nano nickel and the cure characteristics of these composites were evaluated. The maximum torque values register an increase with the increase in loading of nickel in both composites and this is attributed to the non-interacting nature of nickel nanoparticles with rubber matrices. The cure time of natural rubber composites decreases with increase in the content of nickel, and in neoprene rubber cure, time increases with increase in filler content. In natural rubber, the curing reaction seems to be activated by the presence of nickel particles. The magnetization studies of the composites reveal that the magnetic properties of nickel are retained in the composite samples. The elastic modulus of natural rubber and neoprene rubber are largely improved by the incorporation of nickel particles.     

Effects of oxidation and particle shape on critical volume fractions of silver‐coated copper powders in conductive adhesives for microelectronic applications

The effects of oxidation and particle shape on critical volume fractions of silver‐coated copper powders in conductive adhesives are investigated. Silver‐coated copper powders with spherical and flake‐shaped particles were oxidized at temperatures of 30°C, 175°C and 240°C for two hours and dispersed in an epoxy matrix. As silver‐coated copper powders are oxidized at 30°C and 175°C, the critical volume fractions of the conductive adhesives are slightly affected by oxidation and particle shape at these temperatures. As the oxidation temperature approaches 240°C, the critical volume fractions of the conductive adhesives are strongly affected by oxidation temperature and particle shape, owing to the formation of oxides such as Cu₂O on the surface of silver‐coated copper powder—Cu diffuses from the interior to the surface of silver‐coated copper powder and reacts with the oxygen in the air. Silver‐coated copper powder with flake‐shaped particles shows lower critical volume fractions in conductive adhesives than silver‐coated copper powder with spherically shaped particles. Polym. Eng. Sci. 44:2075–2082, 2004. © 2004 Society of Plastics Engineers.     

Silver-Containing Carbon Fibers,Preparation and Properties

Fibre Chemistry - Various methods for preparing fibrous materials [substrates in which polymer filaments of various nature are decorated with particles and/or layers of metallic silver (Ag)] are...     

玻璃微珠/银核壳纳米复合粒子的制备及表征

通过添加聚合物表面活性剂,采用原位复合法制备了具有面心立方结构壳层的草莓状银包玻璃微珠核壳纳米复合粒子.用X射线衍射、扫描电镜及透射电镜等表征了复合粒子的形貌和结构.结果表明:随着溶液pH值的升高,反应速率加快,银的析出量增大,壳层银纳米粒子的特征峰也越强.十二烷基硫酸钠的加入使得表面呈蓬松态,而聚乙烯吡咯烷酮则使表面均匀致密,羧甲基纤维素钠使壳层颗粒生长呈不对称分布.随着银氨溶液浓度的增加,经液相还原的银纳米粒子相应增多,复合粒子壳层厚度也逐渐从30nm增大到52nm左右.     

Reductive crystallization of each metal in composite particles spray-pyrolyzed from silver/nickel mixed nitrates

Composite particles prepared by spray pyrolysis of aqueous solution of AgNO₃ and Ni(NO₃)₂·6H₂O with 10 vol%H₂-N₂ were characterized and compared with the particles similarly prepared from their pure nitrates. The composite particles were composed of metallic silver, nickel oxide or metallic nickel, depending on the condition, with no trace of alloy. The existence of nickel ions dispersed throughout the particles did not affect the rate of reduction to the highly reducible silver but retarded its subsequent crystal growth. On the other hand, both the reduction to nickel and its crystal growth were all retarded due to the existence of the more reducible silver ions. In addition to these, the incompatibility also increased the size of the composite particles from the corresponding single component particles and kept it almost constant with respect to the preparation temperature.     

The hydrogenation of triglycerides using supported alloy catalysts. I. Silica-supported Ni—Ag catalysts

Silica-supported Ni-Ag catalysts with a loading of 2·1·0.6% (w/w) total metal have been prepared using the precursors nickel dimethylglyoxime and silver nitrate by means of a simple impregnation method. The resulting catalysts were activated by calcination at 260°C in air, followed by hydrogen reduction at 450°C. They were then employed for soyabean oil hydrogenation at 1 bar H2 pressure and 160°C in a stirred batch reactor. Characterisation of the catalysts using temperature-programmed reduction and electron microscopy indicated that alloying of nickel and silver had occurred, but metal particle composition, for a given overall composition, varied with metal particle size and smaller metal particles were nickel rich. The hydrogenation activity and selectivity measurements revealed that the catalysts were more active and selective than a commercial nickel catalyst. Furthermore, the specific activities of the alloy catalysts were a maximum for alloys in the range 70–90 at. % Ni. However, the supported alloy catalysts also gave rise to greater trans isomerisation than the commercial catalyst. This is attributed to hydrogen deficiency caused by large triglyceride molecules blocking hydrogen chemisorption on small nickel particles (10–50 Å in diameter), leading to enhanced cis-trans isomerisation.     

Al/NiO复合粒子的制备与表征

以N i(NO3)2.6H2O和CO(NH2)2为主要原料,通过均匀沉淀法,90℃恒温12 h,异相成核,在片状金属铝粉表面包覆一层N i2CO3(OH)2,制备出包覆式复合粒子A l/N i2CO3(OH)2。将复合粒子在马弗炉中400℃恒温灼烧2 h,制备出了A l/N iO复合粒子。通过SEM、XRD及粒度测试等分析方法,对复合粒子的形貌、晶体结构及粒径进行了表征。     

Effect of synthesis conditions on preparation of nickel metal nanopowders via hydrothermal reduction technique

Synthesis of nickel nanopowders from aqueous solution using hydrothermal reduction method with hydrazine hydrate as a reducing agent and Cetyl trimethyl ammonium bromide (CTAB) as a surfactant was investigated. Statistical design was used to study the effects of reaction time, concentration of nickel chloride, and concentration of surfactant on the nickel particles size. Formed nickel particles were characterized using XRD and SEM. The formation of nickel single phase was revealed from XRD patterns. On the other hand, SEM showed that the nickel particles are in nanosized ranges from 55 nm to 250 nm. The analysis of the results indicated that the reaction time and surfactant addition were the controlling factors. The reduction of nanocrystalline nickel hydroxide Ni(OH)₂ into Ni is the possible formation mechanism.     

Effect of metallic impurities on the gasification of graphite in water vapor and hydrogen

The catalytic effects of metallic impurities on the reactivity of graphite towards water vapor and hydrogen in the temperature range 25° to 1100°C have been investigated as a function of the oxidation state of the impurity. Iron, cobalt and nickel are active catalysts for the former reaction between 600° and 1000°C when the metal is kept in the reduced state by means of added hydrogen. Motion of the metallic particles on the basal plane surface of the graphite during the reaction leads to the formation of channels which with the smallest catalyst particles are oriented mostly in the 〈112̄0〉 directions. Vanadium and molybdenum are weak catalysts under these conditions, whereas copper, zinc, cadmium, silver, chromium, manganese and lead are inactive. When hydrogen is absent so that the metal remains in the oxidized state, the catalytic activity of all these impurities is low or negligible. The reaction of graphite with dry hydrogen occurs less readily but is again strongly catalyzed by metallic iron, cobalt and nickel. Manganese, chromium, molybdenum and vanadium show a slight catalytic effect in the hydrogenation reaction at temperatures around 1000°C, whereas copper, zinc, cadmium, silver and lead are inactive.     

Synthesis of CoO/Ni Composite Powders for Molten Carbonate Fuel Cells

CoO/Ni composite particles were prepared by the advanced mechanical-coating method called Mechanofusion™. These composite particles were composed of nickel particles uniformly covered with fine CoO particles. A new cathode structure for molten carbonate fuel cells (MCFCs), where the NiO core was coated with an outer layer of lithiated cobalt and nickel solid-solution oxide (Li(Co,Ni) oxide), was formed by oxidation and lithiation using these CoO/Ni composite particles. The solubility of nickel in this Li(Co,Ni) oxide layer into carbonate melt decreased to two-thirds of that of NiO when used as a cathode for MCFCs.     

水热合成法制备高长径比的银纳米线

以季铵盐型阳离子Gemini表面活性剂[C16H33(CH3)2N+(CH2)3N+(CH3)2C16H33]×2Br-(16-3-16)为结构导向剂和稳定剂,以六次甲基四胺为还原剂,用水热合成法由硝酸银制备了直径约30 nm、长约50 mm的银纳米线. 用X射线衍射(XRD)、紫外-可见吸收光谱和透射电子显微镜(TEM)等手段对制备产物的表征结果表明,所得银纳米线具有面心立方结构,并且是沿着{111}晶面生长的. 银纳米线的长度与反应时间有关,而直径则变化不大. 反应温度对产物的形貌有较大影响,在100和120℃下得到的是纳米线,而在150℃下得到的多为不规则的纳米颗粒.     

γ射线辐射法制备石墨/镍复合材料及其电磁性能

为提高鳞片状石墨在电磁波吸收方面的应用性能,采用γ辐射一步法制备了鳞片状石墨/镍复合材料。实验在常温常压下进行,将鳞片状石墨置于镍盐溶液内,控制溶液的镍盐浓度,再加入氧化性自由基清除剂并将该混合溶液置于钴60辐照室辐照,获得了纳米金属镍包覆在鳞片状石墨表面的复合材料。通过XRD、SEM对复合材料进行了结构和形貌的表征,复合材料为核壳结构、由纯纳米镍与石墨构成,同时提出了γ辐射法合成该复合材料的复合机理,并且研究了复合材料在2～18GHz频段的电磁性能。     

Novel and efficient electrochemical way for silver nanoparticles deposition onto solid conductors: a new concept of metal-silver cathodes

The deposit of very small silver particles onto a very large palette of solid electronic conductors was achieved by means of the cathodic reduction of alkyl iodides RIs in the presence of a suspension of silver–palladium alloy particles (diameter >250 μm). The potential applied to the conductor is so that RIs are not directly reduced at its surface. The observed cathodic reaction is then the discharge of silver grains reacted in surface and covered by a transient assigned to be [RAg⁺, I⁻]. The main heterogeneous products are homo-dimers R–R while the deposition of silver aggregates of very small size (nanometric scale) occurs onto the conductor. By this way, the efficient silverization of many surfaces is possible. Stable layers of Ag particles were made onto many solid surfaces like platinum, palladium, copper, nickel, iron, gold, graphite, and glassy carbon. Preliminary evidences for the use of those new silvered electrodes are presented.     

紫外光辐照法制备纳米银的研究

以硝酸银为反应物,N,N-二甲基甲酰胺为溶剂、聚乙烯吡咯烷酮为分散剂,用紫外光辐照法制备纳米银,研究了反应条件对纳米银粒径的影响。实验结果表明,当辐照时间为2.5h,硝酸银和聚乙烯吡咯烷酮比例为1∶1,反应温度为40℃时,可以制备得到粒径为80nm且分散性良好的纳米银。     

Nickel catalysts supported on carbon nanofibers: structure and activity in methane decomposition

Structures of Ni catalysts supported on filamentous carbon (CFC) produced by methane decomposition over coprecipitated Ni and Ni-Cu/alumina catalysts were studied by EXAFS and TEM. Thermal pre-treatment in N₂ at 350°C of samples impregnated by nickel nitrate precursor was found to produce either NiO or nickel carbide, Ni₃C, phase. This was explained by different reducing properties of the carbon nanofibers which depend on the surface structure. High stability of the Ni/C catalysts in methane decomposition reaction at 550°C was found with those prepared from only nickel chloride precursor, due to the formation of large (30-70 nm) Ni particles further leading to new carbon filaments growth. Data implies a common mechanism of the filamentous carbon deposition in all Ni-based catalysts, independent of the support (silica, alumina, carbon) being used. However, accumulation of filamentous carbon is strongly influenced by morphology and texture of the support. This revised version was published online in July 2006 with corrections to the Cover Date.     

Polyaniline-coated silver nanowires

Two non-conducting chemicals, aniline and silver nitrate, dissolved in formic acid solutions, yielded a composite of two conducting products, polyaniline and silver. As the concentration of formic acid increased, an alternative reaction, the reduction of silver nitrate with formic acid to silver became dominant, and the content of silver in the composites increased. The formation of polyaniline was confirmed by UV–visible, FTIR, and Raman spectroscopies. The typical conductivity of composites was 43 S cm^?1 at 84 wt.% of silver. Silver nanowires coated with polyaniline nanobrushes are produced at low concentrations of formic acid, the granular silver particles covered with polyaniline dominate at high acid concentrations.     

Oxidation and reduction characteristics of oxygen carrier particles and reaction kinetics by unreacted core model

The reaction kinetics of the oxygen carrier particles, which are used as bed material for a fluidized bed chemical looping combustor (CLC), has been studied experimentally by a conventional thermal gravimetrical analysis technique. The weight percent of nickel and nickel oxide in oxygen carrier particles and reaction temperature were considered as experimental variables. After oxidation reaction, the pure nickel particle was sintered and unsuitable to use as fluidizing particles. The oxidation reaction rate increased with increasing weight percent of nickel in oxygen carrier particles and reaction temperature. The rate of reduction shows maximum point with weight percent of nickel oxide (57.8%) and reaction temperature (750 or 800 °C) increased. In this work, the reaction between air and Ni/ bentonite particle was described by a special case of unreacted core model in which the global reaction rate is controlled by product layer diffusion resistance. However, the reaction between CH₄ and NiO/bentonite particle was described by unreacted core model in which the global reaction rate is controlled by chemical reaction resistance. The temperature dependence of the effective diffusivity of oxidation reaction and reaction rate constant of reduction reaction could be calculated from experimental data and fitted to the Arrhenius equation. Presented at the Int’l Symp. on Chem. Eng. (Cheju, Feb. 8-10, 2001), dedicated to Prof. H. S. Chun on the occasion of his retirement from Korea University.     

Electrically conductive composites prepared from polymer particles coated with metals by electroless deposition

Polystyrene particles were coated by electroless deposition of copper, nickel or copper and nickel. The metal-coated polystyrene particles were molded at high temperature and pressure into plaques, in which the metallic shell continuity was preserved and a continuous conducting metal network was formed. Very high conductivities at low metal concentrations (less than 1 percent v/v) are obtained by this procedure. The resistivity, dielectric constant, and dissipation factor of these metal containing composites are presented as functions of the metal concentration, frequency, and temperature. The metal containing composites exhibit reasonable flexural properties.