Fabrication of Ag/polypyrrole coaxial nanocables through common ions adsorption effect

According to the common ions adsorption effect, Ag⁺ ions will be adsorbed onto the closest surface of silver nanowires after being immersed in AgNO₃ solution. This makes the surface of silver nanowires become the active sites to oxidize pyrrole monomer to form PPy sheath without adding other oxidizing agent. The results of FT-IR and UV–vis spectra show the formation of PPy chain when pyrrole monomer was added to the reaction mixture containing the disposed silver nanowires. TEM images further prove that the Ag/polypyrrole (PPy) coaxial nanocables have been fabricated. The thickness of PPy sheath can be controlled by adjusting the concentration of AgNO₃ aqueous solution, which used to dispose silver nanowires. To some extent, the thickness of PPy layer would increase with the increasing of the concentration of AgNO₃ solution. After the adsorbed Ag⁺ ions on the surface of silver nanowires reach to the saturation, the thickness of PPy layer would not change greatly with continuously increasing of AgNO₃ concentration.     

Synthesis and photoactivity of the highly efficient Ag species/TiO2 nanoflakes photocatalysts

Ag species/TiO₂ nanoflakes photocatalysts with different relative contents (Ag⁺, Ag²⁺, Ag⁰) have been successfully synthesized by a simple template-free synthetic strategy. X-ray photoelectron spectroscopy, X-ray diffraction, and UV-vis diffuse reflectance spectra indicated that the dopant ions (Ag⁺ or Ag²⁺) were partly incorporated into the titanium dioxide nanoflakes. Meanwhile, part of the silver ions migrated to the surface after the subsequent calcination and aggregated into ultra-small metallic Ag nanoclusters (NCs) (1-2 nm), which are well dispersed on the surface of TiO₂ nanoflakes. The photocatalytic activities of the Ag species/TiO₂ materials obtained were evaluated by testing the photodegradation of the azo dye reactive brilliant X-3B (X-3B) under near UV irradiation. Interestingly, it was found that the maximum photocatalytic efficiency was observed when Ag species coexisted in three valence states (Ag⁺, Ag²⁺, Ag⁰ NCs), which was higher than that of Degussa P25. The high photocatalytic activity of the Ag species/TiO₂ can be attributed to the synergy effect of the three Ag species.     

Solution-based synthesis of ZnO nanoparticle/CdS nanowire heterostructure

The heterostructure of ZnO nanoparticle (NP)/CdS nanowire (NW) was successfully fabricated by a two-step chemical solution method. The first, CdS nanowires were synthesized by a simple solvothermal route. The second, ZnO nanoparticles were grown on the surface of CdS nanowires in a chemical solution of Zn(CH₃COO)₂·2H₂O and anhydrous ethanol at 200 °C. The heterostructure of synthesized ZnO NP/CdS NW was characterized by transmission electron microscopy (TEM). The effects of reaction conditions, such as different reaction time of CdS nanowires synthesized and deposition reaction time were investigated. Moreover, the formation mechanism of the ZnO NP/CdS NW heterostructure has been phenomenologically discussed.     

A study of the Ag(s)/Ag2SO4(l) high temperature reference electrode

Ag(s)/Ag₂SO₄(l) reference electrodes for use in hot corrosion research were fabricated and their properties were studied at 927°C (1200°K). The McDanel^TM MV 30 mullite tube was used as sheath of the reference electrode and concentrations of the tested electrolytes were varied from 0.1 to 10 m/o Ag₂SO₄ (l) + Na₂SO₄ (l). 10 m/o Ag₂SO₄ was always used as electrolyte in the reference electrode. The working electrodes with less than 2 m/o Ag₂SO₄ showed marked potential drift as the Ag₂SO₄ concentration was lowered, showing poor potential stability. However, the initial values of cell voltages obeyed Nernstian behavior for all range of Ag₂SO₄ concentrations in the working electrodes, which showed that Ag(s)/Ag₂SO₄(l) electrodes behaved reversibly. Galvanostatic polarization was performed on a pair of 10 m/o Ag₂SO₄ reference electrodes to test the reversibility. The polarizability was 3.5 mV/10 μA with no hysteresis loop on the polarization curve, showing that the reversibility was satisfactory. The potential of gold electrode in molten Na₂SO₄ was measured under pure oxygen atmosphere with 10 m/o Ag₂SO₄ electrode as a reference potential. The results showed that the potential of gold electrode could be explained by the 2 Na + SO₃ + 1/2 O₂ → Na₂SO₄ cell reaction.     

Mechanism of Ag3Sn grain growth in Ag/Sn transient liquid phase soldering

Transient liquid phase (TLP) bonding is a potential high-temperature (HT) electron packaging technology that is used in the interconnection of wide band-gap semiconductors. This study focused on the mechanism of intermetallic compounds (IMCs) evolution in Ag/Sn TLP soldering at different temperatures. Experimental results indicated that morphologies of Ag₃Sn grains mainly were scallop-type, and some other shapes such as prism, needle, hollow column, sheet and wire of Ag₃Sn grains were also observed, which was resulted from their anisotropic growths. However, the scallop-type Ag₃Sn layer turned into more planar with prolonging soldering time, due to grain coarsening and anisotropic mass flow of Ag atoms from substrate. Furthermore, a great amount of nano-Ag₃Sn particles were found on the surfaces of Ag₃Sn grains, which were formed in Ag-rich areas of the molten Sn and adsorbed by the Ag₃Sn grains during solidification process. Growth kinetics of the Ag₃Sn IMCs in TLP soldering followed a parabolic relationship with soldering time, and the growth rate constants of 250, 280 and 320 °C were calculated as 5.83×10^?15 m²/s, 7.83×10^?15 m²/s and 2.83×10^?14 m²/s, respectively. Accordingly, the activation energy of the reaction was estimated about 58.89 kJ/mol.     

磁性纳米材料Fe3O4-RGO-NH2对Ag+的吸附性能研究

采用一步溶剂热法成功制备了新型磁性纳米吸附剂Fe3O4-RGO-NH2,用透射电子显微镜(TEM)、X射线衍射(XRD)、振动样品磁力计(VSM)及Zeta电势对其形貌及晶型结构进行了表征,研究了Fe3O4-RGO-NH2纳米吸附剂对水溶液中Ag⁺的吸附性能。结果表明,水溶液pH值对Ag⁺吸附具有很大影响,pH=4.0时吸附效果最佳。Ag⁺最大吸附量随着初始浓度及吸附时间的增加而增加,Ag⁺的吸附符合准二级动力学模型。     

Phase separation and thermoelectric properties of Ag2Te-doped PbTe0.9S0.1

Spinodal decomposition is an ideal mechanism for producing bulk nanostructured materials with promising thermoelectric (TE) performance. In this contribution, the phase separation and TE properties of PbTe-PbS samples are investigated. Phase separation driven by spinodal decomposition is observed in PbTe_0.4S_0.6, PbTe_0.5S_0.5, PbTe_0.6S_0.4 and (PbTe_0.9S_0.1)_1?x(Ag₂Te)_x with x = 0, 0.01 and 0.03. The addition of Ag₂Te leads to a deterioration in electrical transport properties at low temperature but to a significantly enhanced higher-temperature power factor of the Ag₂Te-doped PbTe_0.9S_0.1 sample. The very low thermal conductivity of the Ag₂Te-doped sample is attributed to the doping effect of Ag₂Te, the precipitated Ag₂Te, and the nanoscale phase segregation driven by spinodal decomposition. In particular, the spinodal decomposition produces finely dispersed PbTe-rich and PbS-rich phases with solute atoms, coherent or semicoherent interfaces, lattice bending, and other lattice defects, which contribute to the phonon scattering and minimize the thermal conductivity. The highest TE figure of merit, ZT, is ～1.2 at 773 K for the sample with x = 0.03, and even larger ZT values at higher temperature might be expected based on its tendency to increase with the temperature.     

水溶液体系中制备纳米银线的研究

在水溶液体系中,以蔗糖为还原剂、NaCl为前驱体络合剂、PVP为表面活性剂,通过水热反应制备得到了直径大约为40 nm,线径分布均匀、分散性良好的纳米银线。有效解决了目前多元醇有机体系下制备纳米银线洗涤困难,反应条件苛刻,后处理繁琐等问题。系统研究了还原剂用量、还原剂种类、Cl^-/Ag⁺摩尔比、卤化物种类和表面活性剂种类对于产物形貌的影响。结果表明,当还原剂蔗糖的用量为0.18 g,PVP的相对分子质量为58000,选择Na Cl作为络合剂,且Cl^-/Ag⁺摩尔比控制在1.26时,制备的纳米银线形貌均一,纯度较高,纳米线长径比大于1000。     

离子液体辅助制备AgCl/Ag2O复合光催化剂

在离子液体[CPMIm]Cl辅助下,采用沉淀法原位制备了AgCl/Ag2O复合光催化剂。采用X射线衍射仪(XRD)、能量散射光电子能谱(EDS)、扫描电镜(SEM)、比表面仪(BET)和紫外-可见漫反射光谱(UV-Vis DRS)等对AgCl/Ag2O复合光催化剂结构、组成、形貌、比表面积和光吸收性能进行了表征;运用表面光电压谱(SPS)对异质结光催化剂的光生电荷分离特性进行了研究。考察了AgCl/Ag2O复合光催化剂对模拟污染物甲基橙的光催化降解性能。结果表明,AgCl的存在抑制了Ag2O颗粒的生长,增加了复合光催化剂的比表面积和孔容积。AgCl与Ag2O的原位复合有效提高了复合光催化剂光生e^-/h⁺对分离速率,增强了复合光催化剂对甲基橙的光催化降解。捕获测试表明?O2^-是光催化降解甲基橙的主要活性自由基。     

Experimental thermodynamic study of intermetallic phases in the binary Ag–Te system by an improved EMF method

A thermodynamic study of the solid two-phase regions of the binary Ag–Te system was made by an improved EMF method, using fast ion conductor RbAg₄I₅ as the solid electrolyte. The EMF measurements were made on three galvanic cells: [Ag | RbAg₄I₅ | Ag₅Te₃ + Te], [Ag | RbAg₄I₅ | Ag₅Te₃ + Ag_1.9Te] and [Ag | RbAg₄I₅ | Ag_1.9Te + Ag₂Te].Based on the results obtained, the EMF for each equilibrium phase assembly was expressed as a function of temperature, in the different regions of thermal stability of the substances. By using the observed EMF and temperature relations, the thermodynamic functions of the stoichiometric equilibrium phase assemblages: Ag₅Te₃–Te, Ag₅Te₃–Ag_1.9Te, Ag₅Te₃–Ag₂Te and Ag₂Te–Ag_1.9Te, in the low-temperature range 22–204 °C, as well as phase transformation temperatures, have been determined. Agreement between the results obtained and the literature values were established.     

Thermodynamic Properties of Superionic Phase Ag<Subscript>4</Subscript>HgSe<Subscript>2</Subscript>I<Subscript>2</Subscript> Determined by the EMF Method

Triangulation of the Ag-Hg-Se-I system in the vicinity of quaternary phase Ag₄HgSe₂I₂ was performed by differential thermal analysis, X-ray diffraction and electromotive force (EMF) methods. The spatial position of the phase region Ag₄HgSe₂I₂-Se-HgI₂ regarding the figurative point of silver was used to write the chemical reaction of formation of Ag₄HgSe₂I₂. The EMF measurements were carried out by applying an electrochemical cell: (–) C|Ag|Ag₂GeS₃ glass|Ag₄HgSe₂I₂, HgI₂, Se|C (+), where C is graphite and Ag₂GeS₃ glass is the fast purely Ag⁺ ions conducting electrolyte. The linear dependence of the EMF of the electrochemical cell on temperature was used to determine the standard thermodynamic values of Ag₄HgSe₂I₂ for the first time.     

Galvanically coupled process for the conversion of Ag2O to AgI

The conversion of Ag₂O, grown-on Ag substrates, to AgI has in been investigated, using open-circuit potential, linear polarization, and potentiostatic control measurements. Three distinct reaction stages were clearly identified from the time-dependent behaviour of the open-circuit potential, E_OC, and the corrosion currents measured by linear polarization. In the early stages, when the silver surface was covered with a coherent Ag₂O film with low porosity, E_OC∼(E^e)_Ag2O/Ag and only chemical conversion of Ag₂O to AgI was observed. As Ag₂O was consumed and the area of Ag exposed to I⁻ solution increased, galvanic coupling of Ag₂O reduction to Ag and the oxidation of the Ag substrate to AgI also occurred. Once all the Ag₂O has been reduced, AgI formation stopped and E_OC fell to (E^e)_AgI/Ag. Chemical conversion was shown to produce fine particulate AgI whereas that formed anodically via galvanic coupling was in the form of large crystals. Since few larger crystals were observed, conversion via galvanic coupling appeared to be a minor process.     

Investigation of the Interaction Between Cu2-x S +So Coatings and Pd(II) Ions by Cyclic Voltammetry and X-ray Photoelectron Spectroscopy

The interaction between Pd²⁺ ions and Cu_2-xS coating formed by three cycles and containing ~30 at.% of elementary S has been investigated by the methods of cyclic voltammetry and photoelectron spectroscopy (one cycle of coating formation includes treatment of the surface with Cu(I)+Cu(II) ammoniate solution, hydrolysis of the adsorbed copper compounds and sulphidation of copper oxygen compounds in Na₂S_n solution). After exposure of such a coating to Pd²⁺ ions (1.7 mM PdCl_2’ pH-2), an exchange as well as a redox interaction between the coating components and Pd²⁺ ions has been shown to occur. Due to this the amount of copper in the coating decreases from 2 to 4 times and that of sulphur from 1.5 to 5 times. The coating modified in such a way has been found to contain up to 75 at.% of palladium, ~90% of it being in a metallic state.

It has been determined that at the beginning S^o is bound into a soluble compound:

2Pd²⁺ + S^o + 3H₂O → 2Pd^o + H₂SO₃ + 4H⁺.

The Cu₂S present in the coating is considered to interact with Pd²⁺, with the formation of Pd⁰ and CuPdS_2’, while CuS reacts most likely according to the reaction:

CuS + 3Pd²⁺ + 3H₂O → 3Pd^o; + H₂SO₃ + Cu²⁺ + 4H⁺.

The Cu_2-xS +S^o coating formed on a dielectric and modified with Pd²⁺, contrary to the initial Cu_2-xS +S^o coating, can be plated with copper from any electrolyte for copper deposition.     

Morphology and growth kinetics of Ag3Sn during soldering reaction between liquid Sn and an Ag substrate

For the soldering of recycled Ag sputtering targets, the interfacial reaction between liquid Sn and an Ag substrate at temperatures ranging from 250 –425°C has been investigated. Experimental results show that a scallop-shaped layer of Ag₃Sn intermetallic compounds formed during the soldering reaction. Kinetics analysis indicated that the growth of such interfacial Ag₃Sn intermetallic compounds is diffusion-controlled with activation energy of 70.3kJ/mol. During the reaction, the Ag substrate dissolves into the molten Sn solder and causes the appearance of needle-shaped Ag₃Sn precipitates in the Sn matrix.     

Structure and stability of hcp bulk and nano-precipitated Ag2Al

We study the short- and long- range chemical ordering in hcp bulk Ag₂Al using the Monte Carlo method based on a Hamiltonian constructed via structural formation energies from ab initio electronic-structure calculations. We find that the ground-state structure of bulk Ag₂Al is that proposed from X-ray data, but there are several competing metastable hcp structures. Our results provide the structural and thermodynamic properties of Ag₂Al, with good agreement to experimental short-range order data (after reprocessing our data according to experimental procedure). We also discuss the influence of the Al:Ag₂Al interface, coherency strain, and off-stoichiometric disorder on the structure of metastable Ag₂Al γ′ nano-precipitates in an fcc Al matrix. We show that γ′ precipitates are off-stoichiometric and we provide a new structure that reproduces the observed transmission electron microscopy image while allowing for a distribution of Ag concentrations amongst the precipitates.     

Intermetallic Compounds Formed in Sn-20In-2.8Ag Solder BGA Packages with Ag/Cu Pads

The interfacial reactions in a Sn-20In-2.8Ag solder ball grid array (BGA) package with immersion Ag surface finish are investigated. After reflow, the Ag thin film dissolves quickly into the solder matrix, and scallop-shaped intermetallic layers, with compositions of (Cu_0.98Ag_0.02)₆(In_0.59Sn_0.41)₅, appear at the interfaces between Sn-20In-2.8Ag solder ball and Cu pad. No evident growth of the (Cu_0.98Ag_0.02)₆(Sn_0.59In_0.41)₅ intermetallic compounds was observed after prolonged aging at 100 °C. However, the growth accelerated at 150 °C, with more intermetallic scallops floating into the solder matrix. The intermetallic thickness versus the square root of reaction time (t ^1/2) shows a linear relation, indicating that the growth of intermetallic compounds is diffusion-controlled. Ball shear tests show that the strength of Sn-20In-2.8Ag solder joints after reflow is 4.4 N, which increases to 5.18 N and 5.14 N after aging at 100 and 150 °C, respectively.     

Influence of Silver Doping on Photocatalytic Activity of Liquid-Flame-Sprayed-Nanostructured TiO2 Coating

Silver ion was added to liquid feedstock to deposit Ag⁺-doped-nanostructured TiO₂ photocatalytic coatings through liquid-flame spraying. The coating microstructure was characterized by x-ray diffraction (XRD). The photocatalytic performance of coatings was examined by photodegradation of acetaldehyde. The XRD analysis showed that the phase structure of coatings was not significantly influenced by the silver ion doping. However, a shift was found for XRD peaks of anatase TiO₂. The photocatalytic activity of the TiO₂ coatings increased and then decreased with the increase of dopant concentration. The photocatalytic activity of doped coatings was higher than that of pure TiO₂ coating, regardless of the dopant concentration. The enhancement of photocatalytic performance of doped coatings is attributed to co-doping of Ag⁺ ion and metallic Ag. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

Sensitivity of composites based on gelatin and nanoparticles Cu<Subscript>2</Subscript>S and CdS to vapors of some organic compounds

The gas-sensitivity of gelatin/Cu₂S and gelatin/CdS samples under the effect of vapors of different solvents and ethyl alcohol has been investigated. It is shown that composites on the basis of polymers with Cu₂S and CdS nanoparticles are sensitive to vapors of different solvents. The gas sensitivity of the nanocomposites depends on the rate of matrix filling and the chemical data of the testing gas. These materials could be used as a sensitive element in different gas sensors and detectors.     

Interfacial reactions between high-Pb solders and Ag

Interfacial reactions between high-Pb solders (Pb-10Sn, Pb-5Sn, and Pb-3Sn, in wt.%) and immersion Ag layer at 350 °C are investigated. Upon decreasing the Sn concentration from 10 wt.% to 5 wt.%, the reaction product formed at the solder/Ag interface changes from the Ag₃Sn phase to the Ag₄Sn phase. When the Sn concentration reduces to only 3 wt.%, the reaction product is the Ag₄Sn phase at the initial stage of reaction but transforms to the (Ag) phase dissolved with Sn at the later stage of reaction. Pb penetrates across the (Ag) phase via grain boundary and forms a continuous Pb-rich layer between the (Ag) phase and the bottom Cu layer. The correlation between the phase transformation and the solder composition is discussed based on the calculated Sn-Pb-Ag isothermal section.     

Initial oxidation of Cr at 300–730 K in H2 18O/H2 16O/16O2 gas mixtures studiedin situ with18O/SIMS and XPS

The initial oxidation of pure, polycrystalline-chromium metal with gas mixtures of oxygen-labeled water, H₂ ¹⁸O, and oxygen,¹⁶O₂, at temperatures 300–730 K has been studied in situ with secondary ion mass spectrometry, SIMS. The fraction of O in secondary ion species: CrO⁺, Cr₂O⁺, CrOH⁺, Cr₂OH⁺, CrOH₂ ⁺, and Cr₂OH₂ ⁺ originating from water and oxygen was found. The reaction of water and oxygen in the oxygen/water gas mixture with Cr is then revealed. The dissociation of water in its reaction with Cr in such a gas mixture was analyzed. Oxide growth on cleaned Cr surfaces during the reaction with H₂O, O₂ and H₂O/O₂ gas was also studied in situ with X-ray photoelectron spectroscopy, XPS. A correlation between a chemical shift in XPS and the OH content in the oxide is discussed.