Interaction Between Thiourea and Palladium Electrodes

Interction of thiourea (THU) with Pd electrodes (geometrical surface area 1.5 cm²,roughness factor $\text{f}\text{?}$_w =3-600) has been studied at 20°C. The roughness factor was measured by krypton adsorption. The interaction occurs by the following steps:(1) reversible adsorption of THU molecules on the surface of Pd electrode according to a simple Langmuir isotherm, in neutral medium and (2) surface hydrolosis of adsorbed THU molecules followed by the formation of a monolayer of strongly adsorbed sulphur on the surface of the Pd electrode in acidic or alkaline medium. The THU molecules are precursors of the adsorbed sulphur and an equivalence between their amounts has been found. The adsorbed sulphur has been determined by anodic oxidation by linear sweep voltammetry in 1 M NaOH. Brief comments on the interaction of Pd electrodes with other sulphur compounds (Na₂S, H₂S, CS₂, cysteine and cystine) are also given.     

Interaction of BiNbO4-Based Low-Firing Ceramics with Silver Electrodes

Several commercial silver electrode pastes have been evaluated for use with BiNbO₄-based low-firing ceramics. After electrode application and subsequent cofiring, the electrode pattern on the ceramic was no longer visible. A bismuth-rich second phase was present at the electrode/BiNbO₄ interface, and silver was detected in the second phase. Systematic X-ray diffractometry analysis of the mixtures between different silver pastes and doped/undoped BiNbO₄ revealed an interaction between the silver and the BiNbO₄. This reaction was responsible for the disappearance of the silver electrode patterns.     

Solubility of Silver and Palladium in BaTiO3

Silver, palladium, and their alloys are frequently used as electrode materials for BaTiO₃ (BT) based dielectrics. However, the electrodes and dielectrics usually are cofired at high temperatures, and silver and palladium can dissolve into the BT during cofiring. In the present study, the solubility of silver and palladium into BT after cofiring was determined. Three measurement techniques were used to determine solubility: chemical analysis, structural analysis, and dielectric analysis. The solubility of the silver in the BT was low, 450 ppm, after cofiring at 1290°C for 2 h in air. The diffusion distance of the silver ions into the BT was >5 μm. The solubility of the palladium in the BT was even lower, 50 ppm at 1290°C, and the diffusion distance was ∼1 μm. The solubility of both the silver and the palladium in the BT decreased as the oxygen partial pressure of the sintering atmosphere decreased. These results demonstrated that both silver and palladium solutes act as acceptors for BT.     

电镀银/钯/硬金组合耐磨镀层工艺研究

为了提高镀硬金导电环的耐磨性,在黄铜基材上电镀铜/钯/硬金、镍/钯/硬金和银/钯/硬金三种组合镀层,通过工艺实验,组合镀层的外观、厚度、结合力、硬度、接触电阻及表面微观形貌等性能测试,以及装配后耐磨性能考核试验,发现银/钯/硬金组合镀层耐磨性最好。结果表明,该镀层耐磨可达100万次,能够满足产品抗磨性要求。     

Behavior of Silver and Palladium Mixtures during Heating

The behavior of mixtures of silver and palladium during heating in both air and an inert atmosphere was studied using X-ray diffractometry (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dilatometry, and scanning electron microscopy (SEM). In situ high-temperature XRD studies on a commercial 20% palladium material with submicrometer-sized particles indicated that an intermetallic phase, most likely Ag₃Pd, formed in air between 300° and 400°C, the same temperature range where a 13% linear expansion was measured by dilatometry. The DSC data indicated an exothermic peak at 340°C, a temperature where the TGA results indicated that the material had picked up only 0.2% oxygen, compared with the maximum of 1.4% at 525°C. No PdO was detected by XRD at 400°C, which suggests that oxygen was being incorporated in the intermetallic. Microstructural examination using SEM indicated that larger particles, with internal pores, had formed after heating in air to 375°C. When the material was heated in argon for 1 h at 400°C, no intermetallic phase or alloy formed, and minimal expansion occurred. When mixtures of larger silver particles (5–30 μm) with palladium particles (1–3 μm) were heated in air, the maximum amount of expansion that occurred increased from 0% for pure palladium up to a maximum of 18% at 75% silver. This result supports the conclusion that expansion is a result of formation of this new phase, in the presence of oxygen, not of the oxidation of the palladium.     

银条中钯含量的不确定度评估

电感耦合等离子体发射光谱法(ICP-OES)可对银条中钯含量进行分析,该方法简便、快速。文章中,钯在银条中的含量通过该方法进行测定,并且钯含量的测量被建立了数学模型。通过分析、计算模型中各参数的不确定度,给出合成不确定度及扩展不确定度,银条中钯含量可以表示为50.8 mg/kg±2.0 mg/kg(k=2)。     

Oxidation and Reduction of Palladium in the Presence of Silver

The silver/palladium ratio, alloy form, and heating rate cause significant changes in the oxidation and reduction behavior of palladium powder as determined by thermogruvimetric analysis. Surface area and airflow had little effect on oxidation and reduction. Possible models to explain the changes are considered.     

Studies on Interaction of Polysaccharide-Templated Silver Nanoparticles with Bovine Serum Albumin

In the present work, the interaction between bovine serum albumin (BSA) and as-synthesized silver nanoparticles (Oc-AgNPs) by using 4-acetamido-TEMPO-oxidized curdlan (Oc), as a reducing and stabilizing agent, was studied through fluorescence quenching method, ultraviolet visible spectrum (UV–Vis), and circular dichroism measurement. The results presented clearly indicate that the intrinsic fluorescence of BSA molecule was effectively quenched after the interaction with Oc-AgNPs by a static mechanism, which is further confirmed by UV–Vis analysis. The apparent binding constant (K), number of binding sites (n), and dissociation equilibrium constant (K_D) were calculated to be 7.5 × 10⁵ M^?1, 1.03, and 3.0 ± 0.6 μM, respectively. Furthermore, a conformational change of BSA was also observed when the Oc-AgNPs–BSA interactant formed.     

金属钯负载对氰氨银光催化性能的影响

以氰氨银（Ag2NCN）、活性艳红X-3B和罗丹明B为目标降解物,考察钯纳米粒子负载对Ag2NCN的光催化性能的影响。结果表明,钯纳米粒子负载可显著增强Ag2NCN的光催化活性,最佳负载量为0．6％。     

Chemical Compatibility between Silver Electrodes and Low-Firing Binary-Oxide Compounds: Conceptual Study

The chemical compatibility of silver electrodes and low-firing ceramics has been considered, in terms of the existence of a tie line between silver (and/or Ag₂O) and the binary oxide compound in the corresponding ternary phase diagram. The probability of the existence of the tie line is related to the conditions in the subordinated silver-based isothermal binary systems. Greater probabilities have been calculated for the systems with fewer silver-based binary compounds. Based on the concepts that have been developed, several silver-based isothermal binary systems have been investigated to identify the oxides suitable for the development of low-temperature cofired ceramics. The developed concept has been tested by investigating the phase relations in the Bi₂O₃–Nb₂O₅ and Bi₂O₃–V₂O₅ ternary systems with silver. X-ray and microstructural investigations of bismuth niobates and bismuth vanadates reveal that, as a result of the inertness of Bi₂O₃ and the reactivity of Nb₂O₅ and V₂O₅ toward silver, compounds that are rich in niobium or vanadium react with silver to form ternary Nb/V-Bi-Ag oxide compounds, whereas for compounds that are rich in bismuth, tie lines to silver and Ag₂O do exist.     

Separation of Palladium and Silver from a Nitric Acid Solution by Liquid Surfactant Membranes

Abstract

The recovery of palladium from a nitric acid solution containing silver has been conducted by application of liquid surfactant membranes (LSMs) containing LIX 860, a β-hydroxyoxime, as a mobile carrier in a stirred tank. The extraction equilibria of palladium and silver using several different extractants were also studied. Palladium was selectively extracted from a silver-containing liquor with LIX 860 while it was also observed that both palladium and silver were extractable with a sulfur-containing extractant. The recovery of palladium with LIX 860 was selectively achieved by using perchloric acid solution as the LSM internal phase dosed with thiourea. In the LSM operation, the effects of several chemical parameters on the selective recovery of palladium were studied. The use of hydrochloric acid as an internal receiving phase prevented the transport of silver into the emulsion due to the formation of silver chloride in the external feed solution. Commercially available Span 80 was found suitable for the selective extraction of palladium as a surfactant in LSM operation. Under optimum conditions, palladium was successfully separated from silver and concentrated into a receiving phase in W/O emulsions.     

Design of Electroceramics for Solid Oxides Fuel Cell Applications: Playing with Ceria

Nanostructured samaria- and gadolinia-doped ceria (SDC and GDC) powders were synthesized at low temperature (400°C) using diamine-assisted direct coprecipitation method. Fast-firing (f.f.) processes, where sintering temperatures are reached in a short time to promote lattice diffusion, were compared with conventional sintering, for the formation of dense microstructures from the nanostructured powders. Highly dense SDC and GDC samples (96%) with reduced grain size (150 nm) were obtained by f.f. even at 1300°–1400°C and, unexpectedly, high electrical conductivity and low blocking effect at grain boundary was obtained. Conventionally sintered samples showed that the grain boundary resistivity decreased with increasing the grain size, in agreement with the increase in geometrical bulk volume/grain boundary area ratio. Conversely, f.f. samples showed grain boundary resistivity smaller for small grain size. The above effect was observed only for high dopant (>10% molar) contents. The combined effect of powder grain size, dopant content, and sintering temperature–time profile, can be exploited to tune ceria microstructures for specific ionic device applications.     

Morphological Effects of Grinding on Bismuth-Based Cuprate Superconductors

Morphological changes of bismuth-based cuprate superconductors, such as the 2223 phase, via a small mechanical force were studied mainly by means of high-resolution transmission electron microscopy and atomic force microscopy. Even light mechanical grinding of the sintered 2223 samples led to the formation of superfine particles that had a width of ∼5 nm. Moreover, we found first that the superfine particles had a discrete thickness of odd numbers of a half unit length c /2 of the 2223 phase, e.g. 1.9 nm, 5.6 nm, and so on. The formation of the superfine particles was due to cleavage at Bi—O double layers that were bound weakly to each other in a unit cell.     

Reactive Sintering and Retrograde Densification of Bulk Bismuth-Based Superconductors

Densification was observed when bulk ceramic superconductors with a composition of Bi_1.8Pb_0.4Sr₂Ca₂Cu₃O_10+δ were sintered for short times (<4 h) near the incongruent melting temperature. The initial shrinkage of the powder compacts was correlated with the existence of a transient liquid phase. Retrograde densification, which is a decrease in density, occurred for longer sintering times and was attributed to changes in pore structure. The results provide direction for future processing of bulk bismuth-based superconductors and powder-in-tube tapes for the fabrication of long-length wire.     

Fabrication and Characterization of Colossal Electroresistance Chip Devices Composed of Polycrystalline Lanthanum-Doped Strontium Titanate and Palladium Electrodes

A colossal electroresistance (CER) multilayered chip device composed of polycrystalline 0.8-at% La-doped SrTiO₃ and Pd electrodes has been successfully fabricated. Polycrystalline SrTiO₃ devices exhibit large hysteresis in their current–voltage ( I – V ) characteristics after the forming process. Further, their resistance states can be switched by applying voltage pulses above ±50 V, and the resistance changes by approximately two orders of magnitude (from ∼600 Ω to ∼80 kΩ). These resistance-switching behaviors demonstrate that even ceramics can exhibit resistance changes as large as thin-film devices and provide the possibility of new switching devices with the memory effect composed of ceramics.     

载银煤/LLDPE抗菌复合材料

采用固-液吸附及熔融挤出相结合的方法制备一种新型的栽银煤/LLDPE抗菌复合材料(ACCPE).利用现代分析测试手段如IR、XRD、SEM对制备的复合材料进行表征.探讨复合材料的机械性能、流变性能、Ag~+释放特性及抗菌性能.结果表明:复合材料具有良好的机械性能、加工性能和抗菌性能,并且在大肠杆菌的抗菌实验中,Ag~+与煤显示出良好的加合作用.     

Enhancement of Tc(0) by Substitution of Gallium in the Bismuth-Based High-Tc Superconducting Material

We report the enhancement of the zero resistivity T _c(0) by 5.5 K i.e. from 104 to 109.5 K by substitution of gallium 1.34% of copper in the bismuth 2223 compound. A series of Ga-containing compounds Bi₂Pb_0.4Sr₂Ca₂Cu_{3− x} Ga _x O _y ( x =0.00, 0.02, 0.04, 0.06, and 0.08) are synthesized by the solid-state reaction method. The samples are characterized by measurements of their dc electrical resistivity and ac magnetic susceptibility and by the powder X-ray diffraction analysis. It is noted that the high- T _c (2223) phase increases from 57.55% in an undoped sample to 92.99% in samples containing a low concentration of gallium i.e. x ≤0.04.     

Iodothiocyanation/Nitration of Allenes with Potassium Thiocyanate/Silver Nitrite and Iodine

Direct strategies for the iodothiocyanation and iodonitration of allenes have been developed. In this process, potassium thiocyanate/silver nitrite and molecular iodine are used as the source of SCN, ONO₂ and iodine to provide the desired products in moderate to good yields with high stereoselectivity.

     

On Homogeneous Gold/Palladium Catalytic Systems

Two substrates containing an aryl iodide and an allenoate ester were prepared and the gold‐induced cycloisomerisation to vinylgold(I) species and their proto‐deauration as well as the intramolecular palladium‐catalysed cross‐coupling reactions were investigated. Switching to catalytic amounts of gold and palladium and stoichiometric amounts of silver did indeed furnish the product of a cycloisomerisation/intramolecular cross‐coupling. Control experiments revealed that silver cannot substitute for gold or palladium in these reactions, but a different palladium catalyst in a different oxidation state also afforded the cycloisomerisation/intramolecular cross‐coupling products in only slightly reduced yields. By ICP analysis the palladium was shown to contain gold only at the sub‐ppm level. This shows how carefully results obtained with such systems have to be interpreted. Then a series of allylic and benzylic o‐alkynylbenzoates were investigated in gold‐ and palladium‐catalysed reactions. For esters of benzyl alcohol and cinnamyl alcohol no palladium co‐catalyst was needed for the conversion. All reagents were thoroughly checked for palladium traces by ICP analysis in order to thoroughly exclude a gold/palladium co‐catalysis. Optimisation of the gold complex, counter ion and solvent showed that gold(I) isonitrile pre‐catalysts and silver triflate as activator in dioxane are suitable to convert a number of substrates with aryl, alkyl and even cyclopropyl substituents. Crossover experiments proved an intermolecular allyl transfer.