Ag/Au-decorated Fe3O4/SiO2 composite nanospheres for catalytic applications

Noble metal particles in nanoscale (Au, Ag, Pt, etc.) have attracted intensive research interest due to their promising catalysis properties. However, the practical applications of these nanoparticle catalysts are always jeopardized by two problems. One is the difficulty in recovering the used nanoparticles and the other arises from the low catalytic efficiency due to the aggregation of the nanoparticles. In this work, Ag/Au nanoparticles were distributed onto spherical superparamagnetic carriers (SSCNs), which were fabricated through a facile oil-in-DEG emulsion route. The Ag/Au nanoparticles were attached onto the SSCNs by two steps. The Au seeds were attached onto the silica surface through electrostatic attraction first, and the Ag nanoparticles were grown on the basis of the Au seeds. The obtained Ag/Au–SSCN composite nanospheres demonstrated promising catalytic properties, which could also be recycled very easily by using a magnet.     

Pd effect on reliability of Ag bonding wires in microelectronic devices in high-humidity environments

We investigated the effect of Pd concentration in Pd-doped Ag wires on the humidity reliability and interfacial corrosion characteristics between Ag wire and Al metallization. Additionally, we confirmed no corrosion problem between Ag wire and noble metal (Pd, Au) metallization, even after a pressure cooker test (PCT). The chemical composition of the tested Ag wires was pure Ag, Ag-1wt% Pd and Ag-3wt% Pd. These wires were bonded to Al and noble metal (Au, Pd) metallization using a thermo-sonic bonder. The interfaces were characterized by focused ion beam (FIB), high resolution transmission electron microscope (HRTEM) and energy dispersive X-ray spectroscopy (EDS). The interface corrosion of Pd doped Ag wires was significantly reduced as the Pd concentration in the Ag wires increased. Furthermore, the Ag wires on the noble metal (Au, Pd) metallization exhibited stable reliability during the PCT.     

Comparative study of ZnO nanostructures grown on silicon (1 0 0) and oxidized porous silicon substrates with and without Au catalyst by chemical vapor transport and condensation

ZnO tetrapods and rods were grown on silicon and thermally oxidized porous silicon substrates with and without Au catalyst layer by carbothermal reduction of ZnO powder through chemical vapor transport and condensation method (CVTC). Porous silicon was fabricated by electrochemical etching of silicon in HF solution. The effect of substrates on morphology, structure and photoluminescence spectra of ZnO nanostructures has been studied. The texture coefficient (TC) of each sample was calculated from XRD data that demonstrated random orientation of ZnO nanostructures on the oxidized porous silicon substrate. Moreover, TC indicates the effect of Au catalyst layer on formation of more highly oriented ZnO nanorods. The morphology of the samples was investigated by SEM which confirms formation of ZnO nanostructures on oxidized porous silicon substrates with and without catalyst. A blue-green emission has been observed in ZnO nanostructures grown on Si and the oxidized PS substrates without Au catalyst layer by PL measurements.     

(Au,Ag,Cu)/SiO_2二元金属单分散复合薄膜非线性光吸收性的Mie理论模拟

采用修正的Mie理论模拟计算了(Ag, Cu)/SiO₂, (Au, Cu)/SiO₂和(Ag, Au)/SiO₂二元单质金属纳米颗粒分散体系的理论吸收光谱. 研究发现, 二元金属纳米颗粒分别以单质金属形式存在时, 吸收光谱分别在2个波段处出现表面等离子共振吸收峰, 二元金属的相对含量影响吸收峰的峰强, 与峰位无关. 理论模拟吸收光谱与前人实验结果符合良好.     

New Sorption Materials Based on Organosilicon Derivatives of Thiosemicarbazides

The synthesis of organosilicon derivative monomers and polymers characterized with sorption properties has been performed. The synthesized organosilicon polymers have been investigated as sorbents for heavy (Hg(II)) and noble (Ag(I), Au(III), Rh(II), Pd(II), and Pt(IV)) metals. The coefficients of the interphase metal distribution have been estimated.     

一种合成PS/Ag复合微球的简便方法

本文提出一种制备具有高金属覆载率及良好均匀性的PS/Ag复合微球的简便方法,可以避免PS微球的表面修饰。首先通过多元醇法制备具有良好单分散性的PVP覆盖的Ag纳米颗粒, 然后通过溶胀-异质凝聚法将这些Ag纳米颗粒负载于PS球上。对Ag纳米颗粒的尺寸分布及PS/Ag复合微球的表面形貌进行了研究,结果表明这种方法制得的PS/Ag复合微球具有良好的分散性与均一性,并且Ag颗粒的负载率可以通过Ag溶胶的加入量来调控。     

镀层金属对钒合金与不锈钢电子束焊接头组织与性能的影响

采用高真空电子束阻隔熔化连接异种金属V-5Cr-5Ti钒合金和HR-2不锈钢,通过焊缝成型、微观组织和接头性能的对比分析,研究不同镀层金属(Au、Ag、Cr和Ni)的影响。结果表明:通过电子束流的偏移均可实现V-5Cr-5Ti/Au(Ag、Cr、Ni)/HR-2异种金属的连接,接头平滑过渡,焊缝正反面成型良好;V-5Cr-5Ti与熔化区的界面较为平直,在靠近钒合金一侧形成一个明显的镀层金属富集带;熔化区内部晶粒细小均匀,在靠近HR-2处形成取向明显的树枝晶。Au和Ag起到了很好的阻隔作用,V-5Cr-5Ti/HR-2接头的抗拉强度明显增加,达到400 MPa,X射线探伤未发现裂纹和气孔缺陷;镀层金属为Cr、Ni时,接头抗拉强度低于100 MPa。     

硫代硫酸盐浸出脱铜阳极泥中金、银和钯的研究

密度泛函计算和热力学分析表明,相较于Au(I)和Ag(I)离子,Pd(II)离子更容易与S2O3^2-发生配位反应,3种元素均可被氨性硫代硫酸盐溶液浸出。脱铜阳极泥中高含量的锡和锑对硫代硫酸盐浸出贵金属无明显影响,但铅以PbO形态存在时会覆盖在贵金属表面抑制浸出。硫代硫酸盐对脱铜阳极泥中贵金属的直接浸出率低;阳极泥先经氢氧化钠预处理去除部分铅后浸出率有所提高;经碳酸盐转化-醋酸预处理可去除阳极泥中93.8%的铅,硫代硫酸盐对金、银和钯的浸出率达到88.0%、93.4%和80.7%。X射线衍射(XRD)和X射线光电子能谱(XPS)分析表明,醋酸预处理后阳极泥颗粒表面没有出现PbO钝化层。     

Partial phase diagram of Au-Ag-Dy ternary system

On the basis of Au-Ag, Au-Dy and Ag-Dy binary phase diagrams, the 700 ℃ isothermal section of Au-Ag-Dy ternary system（Dye≤35 %, mole fraction） was established by X-ray diffraction analysis, differential thermal analysis and optical microscopy. It is found that there is a long single-phase region, Au（Ag） or Ag（Au）, along the Au-Ag binary isomorphous system on the gold-silver-rich side of the 700 ℃ isothermal section and between the binary compound Au2Dy and Ag2 Dy there is the all proportional solid solution, （Au2 Dy） or （Ag2 Dy）. It is confirmed that the partial 700 ℃ isothermal section consists of six single-phase regions： solid solution Au（Ag） or Ag （Au）, （Au2 Dy） or （Ag2 Dy）, Au6 Dy, Au51 Dy14, Au3 Dy and Ag51 Dy14 ; nine binary-phase regions; （Au2 Dy） ＋ Au （Ag）, Au6Dy＋ Au（Ag）, Au（Ag） ＋Ag51 Dy14 , Ag51 Dy14 ＋ （Au2Dy）, Au3Dy＋（Au2Dy）, Au3Dy＋ Au51 Dy14, Au51 Dy14＋Au6Dy, Au51 Dy14＋Au（Ag） and Au（Ag） ＋Au3Dy; four ternary regions： Ag51 Dy14＋ （Au2Dy）＋ Au （Ag）, （Au2 Dy） ＋ Au（Ag） ＋ Au3 Dy, Au（Ag） ＋ Au3 Dy＋ Au51 Dy14 and Au51 Dy14＋ Au （Ag）＋ Au6 Dy. No new ternary compound is formed in the gold-silver-rich field（Dy≤35 %） of the Au-Ag-Dy ternary system.     

Physical properties of selected brazing filler metals

Abstract

A suitable selection of the filler metal is vital for producing satisfactory brazed joints. The wettability of brazing alloys with base metals depends on physical properties such as surface tension, density, melting point, and viscosity. Thermal conductivity and electrical resistivity are also important since the filler metal is frequently required to have similar values to those of the base metal. In the present paper, the physical properties of liquid alloys relevant to brazing have been evaluated. Six different filler metal systems were analysed, comprising alloys based on Ag, Al, Au, Cu, Ni, and Ti. Results show that the viscosity values for most binary brazing filler alloys are of the order of 2–8 mPa s, with Cu and Al alloys exhibiting the lowest viscosities. The surface tensions of brazing alloys vary from 800 to 1800 mN m^-1, with the lowest surface tension values corresponding to the Ag and Al alloys. Thermal conductivity and electrical resistivity values fall in the range 10–200 W m^-1 K^-1 and 17–300 μΩ cm, respectively.     

Photoluminescence Properties of Porous Silicon Based on FZ(H) Si Wafer

1 IntroductionThe visible ltiminescence at room temperatUre of porous silicon (PS) has been attractivefor the pmpose of using it in Photo-electronicdevices. The large stirface area of PS has focused attentions not only on surface modificationdirected toward coevalling Photo-electronicProperties but also on new exciting applicationsin the sensors and biomaterials areas [l]. For thesolid-state contact, semitranspared conductingmaterials have been formed on PS by Physical orchemical vapor dep…     

Laser brazing of alloy 600 with precious filler metals

Abstract

The diode laser brazing of Ni base heat resistant alloy with precious filler metals has been conducted using the tandem beam for preheating and brazing. A couple of 1 mm thick plates of alloy 600 (Inconel 600) were butt brazed using Au–18Ni, Ag–10Pd and Ag–21Cu–25Pd filler metals of 0·5 mm diameter with a brazing flux. Sound butt joints which were free from brazing defects such as porosity and lack of penetration could be obtained at brazing clearances of 0·1–1·5 mm. The tensile strength of the braze joint produced using Ag–Pd filler metal increased with decreasing brazing clearance and reached ～70% of the base metal strength at a brazing clearance of 0·1 mm while those obtained by using Au–Ni and Ag–Cu–Pd filler metals were comparable with the base metal strength at any clearances between 0·1 and 1·5 mm. The laser brazing technique could be successfully applied to the brazing of Ni base superalloy to attain a joint with high performance and reliability.     

Deciphering anomalous Ag enrichment recorded by galena in Dayingezhuang Au(-Ag) deposit,Jiaodong Peninsula,Eastern China

Texture, geochemistry, and in-situ Pb isotope of galena were investigated to probe the origin of anomalous Ag enrichment in the DayingezhuangAu(-Ag) deposit. Silver enrichment postdates the main Au mineralization and occurs in the south of the Dayingezhuang deposit. It is primarily associated with galena and the exsolution of Ag-rich sulfosalts (e.g., matildite) in distal vein-ores related to steeply dipping brittle fractures. Silver-rich galena is characterized by the least radiogenic Pb isotope signature (²⁰⁶Pb/²⁰⁴Pb 17.195–17.258 and ²⁰⁸Pb/²⁰⁴Pb 37.706–37.793), possibly indicating a metasomatized lithospheric mantle or modified lower crustal source for Pb and Ag. Both of these mafic and ultramafic source regions have been previously suggested as Au reservoirs for other Jiaodong Au deposits, implying that the metal reservoir has only a weak control on the uneven Ag-enrichment. Since the Ag-enrichment areas are located in the footwalls of both the Dayingezhuang and Zhaoping faults, the enrichment was most likely dominated by local rotational stress during coeval movements of the two faults in a NE–SW compression and NW−SE extension regime. This work highlights the shallow-crust structural deformation responsible for controlling the flow of late ore-forming fluid resulting in local anomalous metal enrichment.     

Gold/oxide heterostructured nanoparticles for enhanced SERS sensitivity and reproducibility

In surface-enhanced Raman scattering(SERS),it is highly desirable to obtain Raman signals with high sensitivity and reproducibility from noble metal nanoparticle substrates,which remains a great challenge due to the inhomogeneity of the plasmonic coupling that is sensitive to the interparticle nanogaps.In this work,we report that the interparticle plasmonic coupling could be circumvented by first synthesizing Au/metal or nonmetal oxide heterostructured nanoparticles and then depositing them uniformly onto the substrates,leading to high reproducibility of the Raman signals.Strong plasmonic coupling has been found at the Au/oxide interface,which enables high sensitivity of the SERS analysis that accompanies the excellent signal reproducibility.Among different oxides investigated(SiO_2,TiO_2 and Fe_2O_3),the Au/Fe_2O_3 heterostructured nanoparticles demonstrate the highest Raman enhancement effect.We believe our strategy opens a promising route to fabricate SERS substrates that are capable of sensitively and quantitatively detecting molecules of interest in a much reliable manner.     

铈基钝化法在金属防护中的应用研究进展

铈盐由于其自身无污染、成本低、性能好、用途广等优点,已成为代替铬酸盐钝化的重要方法之一.简要总结了国内外研究人员的发现,得出铈盐可以自行成膜,且铈盐有着良好的自愈能力.同时,也发现纯铈膜的防腐效果不是很理想,易出现裂纹、附着力差等问题.为解决此问题,可以将铈盐与其他金属盐结合,得到混合钝化液,所得到的复合膜效果较好,能减少裂纹的形成;也可以在铈盐钝化液中加入有机化合物,形成的有机和无机复合钝化膜效果更佳,防腐效果甚至高于铬酸盐技术.铈盐以及铈盐复合钝化膜能广泛地应用在各类金属及金属合金表面,极大程度地扩展了铈盐钝化液的应用范围,提高了在工业上的使用率.对铈盐钝化液的机理、钝化方法、应用领域等方面的最新进展进行简单地总结与探讨.为解决铈盐钝化液在钝化机理以及钝化方法方面存在的不足,对最新的工艺方法或配方改善方法进行了提炼,并对未来铈盐钝化液能有效解决原铬基钝化液的污染问题和提高涂层的防腐能力进行了展望.     

Photocatalytic and Antibacterial Activities of Ag/ZnO Nanocomposities Fabricated by Co-Precipitation Method

A Ag/ZnO nanocomposite has been synthesized and characterized for investigating its photocatalytic activity.The morphology and particle size of the Ag/ZnO was studied by scanning electron microscope(SEM) and the microstructure of the as-synthesized nanocomposite was confirmed by X-ray diffraction(XRD) analysis.The elemental composition of the metal oxide was determined by energy dispersion spectrometry(EDS).Diffuse reflectance spectra(DRS),Photoluminescence(PL) spectra,and Fourier transform infrared spectroscopy(FTIR) were also studied for characterizing the nanocomposite.The average particle size was found to be around 20–30 nm.Photocatalytic activity of Ag/ZnO has been investigated over methyl violet(6B) dye under UV and visible light irradiation.The degradation of methyl violet(6B)dye using ZnO and Ag/ZnO was compared and found that Ag/ZnO composite is more efficient than ZnO.The rate of disappearance of dye was monitored spectrophotometrically in the maximum visible absorption wavelength and the extent of degradation was discussed in terms of Langmuir–Hinshelwood model.The Ag/ZnO composite was found capable of degrading the industrial dye effluent.Effect of H2O2addition on dye degradation by the Ag/ZnO was investigated and Ag/ZnO was found to be an effective antimicrobial agent.Reusability of Ag/ZnO catalyst was also tested.     

核-壳结构Ag-Au纳米颗粒合金化行为的分子动力学

利用分子动力学方法和改进分析型嵌入原子势函数模拟了核-壳结构Ag-Au纳米颗粒的合金化行为,从原子扩散、微观结构演变以及合金化程度等方面对比分析了壳层厚度对合金化行为的影响。结果表明,壳层较薄时,核-壳界面处原子扩散现象显著,内核表现出多面体形貌,表层Au、Ag原子完全混合。壳层较厚时,表面原子以扩散为主,整个颗粒表面为多面体结构,但内核保持初始球状结构。通过层错生长方式使形貌发生了改变。壳层越薄,体系合金化程度越高     

Structural properties of some conducting polymers and carbon nanotubes investigated by SERS spectroscopy

In this paper, we present Surface Enhanced Raman Scattering (SERS) experiments performed successfully on some conducting polymers and carbon nanotubes deposited in thin films on rough metallic surfaces. The enhancement mechanism in SERS has a twofold origin: electromagnetic and chemical. The electromagnetic enhancement is, however, the dominant mechanism and consists in the excitation of localized and delocalized surface plasmons (SP). The second enhancing mechanism for SERS, not yet convincingly supported by experimental data, is of chemical origin. This mechanism is due to the increase of the polarizability of the molecules on the metal surface under the action of the incident radiation, leading to the formation of new chemical bonds between the molecules and the metal surface. Unfortunately, the experimental data available to argue the presence of a chemical process are scarce and scattered. In this paper, we try to present some details regarding this aspect. In order to do so, we studied poly 3-hexylthiophene (3-PHT) and polyaniline (PAN) as a function of the type of the rough metallic support (Ag, Au or Cu), the oxidization state and thickness of the polymer layer. We studied also carbon single walled nanotubes. Our experiments reveal the existence of a chemical surface effect. The results obtained for 3-PHT show that SERS spectra depend on the oxidizing properties of the metal surface and on the nature of the solvent. This dependence is explained by the existence of some interfacial reactions that lead to the formation of interface compounds. The SERS measurements reported here reveal an increase of the intensities of the Raman lines, accompanied by a modification of the corresponding intensity ratios, when the degree of doping is increased. We observe for the first time by SERS spectroscopy that doping of 3-PHT with FeCl₃ leads to the appearance of a state of disorder in the structure of the macromolecular chain, as a result of steric hindrance effects. The type of the rough metallic support can modify SERS spectra and such an effect is clearly shown for the polyaniline case. No such dependence on metallic support type is observed on the SERS spectra of carbon nanotubes.     

Hot cracking in laser braze joint of high strength stainless steel using gold brazing filler metal – prevention of hot cracking by controlling thermal cycle

Abstract

The hot cracking behaviour in the diode laser braze joint of 13Cr–4Ni stainless steel using Au–18Ni, Ag–10Pd and Ag–21Cu–25Pd filler metals has been investigated. The types of joint investigated were the T fillet joint and the L fillet joint which simulated the second braze bead in the T fillet joint. Tandem beam brazing was also carried out in order to prevent the hot cracking by post-heating treatment with a trailing beam. A centreline crack, characterised as a ductility dip crack, occurred in the second braze bead of the T fillet joint using Au–Ni filler metal. On the other hand, no cracks occurred in either the first or the second braze bead in T fillet braze joints using Ag–Pd and Ag–Cu–Pd filler metals. The hot cracking susceptibility of the Au–Ni braze metal was evaluated by the spot Varestraint test. Most of the cracks observed in the spot Varestraint test specimen were also characterised as ductility dip cracks, and the susceptibility to such cracking increased with increasing the augmented strain. The ductility dip temperature range (DTR) was estimated from the crack position and length to be 1000–1250 K at strains over 0·4%. Numerical analyses of the thermal stress and strain revealed that the plastic strain–temperature curve intersected the DTR in the single beam brazing, but did not intersect the DTR with post-heating during the laser brazing. The effect of post-heating on the crack prevention was verified by tandem beam brazing of L fillet joint with a trailing beam. No cracks occurred in the braze bead made with a trailing beam at laser powers of 200–300 W. The authors concluded that hot cracking in the Au–Ni braze metal could be successfully prevented by controlling the thermal cycle during the laser brazing process.     

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.