Surface characteristics of titanium–silver alloys in artificial saliva

Titanium and its alloys are widely used in biomedical and dental fields because of their excellent corrosion resistance and biocompatibility. It is well known that titanium is protected from corrosion because of the stability of the passive film that controls and determines the corrosion resistance and biocompatibility of titanium and its alloys. The purpose of this study was to evaluate the electrochemical properties of titanium–silver alloys and the surface characteristics of passive film in artificial saliva. We designed titanium–silver alloys with silver contents ranging from 0 to 5 at.%, in 1% increments. These alloys were arc‐melted, homogenized, hot‐rolled to 2 mm thickness, and finally solution heat‐treated for 1 h and quenched. Potentiostatic testing was performed, and the open circuit potentials of the alloys were measured in artificial saliva, at 37 °C. The passive films of the titanium–silver alloys were analyzed via XPS. Titanium–silver alloys maintained low current density and showed stable passive region and also had high open circuit potential as compared with pure titanium. The open circuit potential of titanium–silver alloys increased as silver addition increased. With regard to the fraction of oxygen species, a component of over 80% was found to be comprised of oxide. Therefore, the titanium surface mainly consisted of titanium oxide and, on the titanium–silver alloys, this film was composed of TiO₂, Ti₂O₃, and TiO. As silver content increased, the TiO₂ fraction also increased, as did the thickness of the titanium oxide layer formed. Copyright © 2005 John Wiley & Sons, Ltd.     

Some unusual features of the electrochemistry of silver in aqueous base

Multilayer oxide films were grown on silver in base by repetitive potential cycling; however, the type of oxide obtained, as assessed on the basis of its reduction behaviour, was dependent on the lower limit of the oxide growth cycles. Using limits of 1.03–2.60 V (RHE) the oxide film produced was assumed to be predominantly Ag₂O; reduction of the latter yielded a cathodic peak at ca. 0.8 V and a surface layer of silver microparticles of diameter ranging from ca. 100 to 227 nm which, although relatively stable, were prone to rapid, extensive reoxidation. Altering the oxide growth limits to 0.7–2.60 V resulted in the growth of a different type of oxide deposit which is assumed to be AgOH; reduction of the latter occurred in a negative sweep in a random manner, i.e. in the form of cathodic spikes extending to potentials as low as ca. –0.5 V. Both types of silver oxide species are assumed to be involved in premonolayer oxidation and electrocatalysis at silver in base and the nature of the former process is discussed in some detail. Electronic Publication     

Electrochemically induced reversible solid state transformations: electrosynthesis of Ag2Cu2O4 by room temperature oxidation of Ag2Cu2O3

Electrochemical oxidation at room temperature of a slurry of Ag₂Cu₂O₃ yields a new silver copper oxide, formulated as Ag₂Cu₂O₄, with one more atom of oxygen per unit formula, that can in turn revert to the original precursor. The resulting oxide presents a different electronic and crystal structure from its precursor, as shown by XPS, X-ray and electron diffraction. This phase transformation involves a radical structural change from a 3D to a 2D network, as well as electronic changes involving silver and oxygen. The potential of electrochemical techniques to induce crystal-chemical solid state transformations is analyzed.     

Anion-selective properties of alkali metal-free lead phosphate glasses containing silver chloride and their application in an ion-selective electrode

Alkali-free lead phosphate glasses containing silver chloride have been developed for anion responsive sensors. From measurements of the final glass compositions by electron probe microanalysis, it became clear that some of chloride ions in the glass bulk were not volatilized during the glass melting process. Compared with phosphate glasses containing silver oxide, the new glass electrodes containing silver chloride could respond more rapidly, although the response behaviour for anionic species were similar. From the electrode potential vs. time curve for the anionic species, the potential rapidly reached equilibrium when these concentrations varied from 10^?5 to 10^?2 M. The response times, t₉₅, to thiocyanate of the new glass electrode and the phosphate glass electrode containing silver oxide were 30 and 110 s, respectively. Moreover, the response time required for an initial potential change with a concentration jump of thiocyanate with the new glass electrode was found to be independent of the membrane thickness within about 2 mm and of the measuring temperature between 15 and 40°C. It is concluded that the diffusion process of species such as silver ion in the glass bulk does not take part in the initial part of the response behaviour.     

Synthesis of silver (II) oxide by oxidation of silver or silver oxide by means of ozone

The oxidation by ozone of a suspension of silver or silver oxide in an aqueous solution of sodium hydroxide is described. It has been shown that the oxidation proceeds in two steps:Ag^O₃→Ag₂O^O₃→AgO.The experimental results are in good agreement with a mechanism of dissolution and precipitation. The silver (II) oxide obtained has remarkable properties of stability in alkaline solution and of reducibility to metallic silver. These special properties are probably due to the large size of the particles.     

The influence of the conditions of the anodic formation and the thickness of Ag(I) oxide nanofilm on its semiconductor properties

The anodic formation of Ag(I) oxide nanofilms on polycrystalline silver and Ag–Au alloys as well as on low-index single crystals of silver in 0.1?М KOH was examined. By the methods of photocurrent i _ph and photopotential E _ph measurements, the n-type conductivity of Ag₂O film was established. Since the film (6–120 nm) is thinner than the space charge region, the dependence of photocurrent and photopotential appears on the film thickness L: i _ph ~L and E _ph ~L ². The transition from polycrystalline silver to single crystals as well as the addition of a small amount of gold (X _Au?≤?4 at.%) into the silver lattice decreases the degree of deviation from the stoichiometric composition Ag₂O. The parameters of Ag₂O film (optical absorption coefficient α, donor defects concentration N _D, space charge region W, and Debye’s length of screening L _D) depend on the index of a crystal face of silver, volume concentration of gold X _Au in the alloy, and film-formation potential E. At Е?=?0.52 V, the sequences of variation of these parameters correlate with the reticular density sequence. The growth of the potential disturbs these sequences. The band gap in Ag₂O formed on Ag_poly, Ag_hkl, and Ag–Au is 2.32, 2.23, and 2.19 eV. Flat band potential in Ag(I) oxide, formed on Ag_poly in 0.5 M KOH is 0.37 V. The appearance of the clear dependence between the state of the oxide/metal interface and the structure-sensitive parameters of semiconductor Ag(I) oxide phase allows considering the anodic formation of Ag₂O on Ag as a result of the primary direct electrochemical reaction, not of the precipitation from the near-electrode layer.     

Anodic silver (II) oxides investigated by combined electrochemistry,ex situ XPS and in situ X‐ray absorption spectroscopy

Silver (II) oxide layers (AgO) were prepared by anodic oxidation of pre‐oxidized, Ag₂O‐covered silver electrodes in 1 M NaOH (pH 13.8). The oxidized electrodes were investigated using a combination of electrochemical techniques, ex situ X‐ray photoelectron spectroscopy (XPS) and in situ surface‐sensitive grazing incidence X‐ray absorption spectroscopy (EXAFS) under full potential control. The application of these different techniques leads to a detailed, consistent picture of the anodic silver (II) oxide layer formation. The experiments have shown that the chemical composition of the AgO layer varies significantly with oxidation potential, revealing a decreasing oxygen deficiency with increasing anodization potential and oxidation time. XPS as well as EXAFS experiments support the interpretation of the oxide as a mixed valence Ag ⁺ Ag^{3 +} O₂ with different contributions of Ag ⁺ and Ag^{3 +} species, depending on potential and anodization time. Copyright © 2009 John Wiley & Sons, Ltd.     

Modification of catheter materials by coating with polymer layers containing silver

The surface of polyurethane based catheter material or of silicon wafers as model surfaces were modified by spin coating of solutions of poly(ethylene oxide) or poly(vinyl alcohol) in water. For the incorporation of silver ions, silver nitrate was added to some of the solutions or the as-cast surfaces were dipped into AgNO₃ solution. Furthermore, samples coated with a thin layer of metallic silver were prepared by deposition of silver vapor in vacuum. The as-prepared surfaces were studied by atomic force microscopy and X-ray photoelectron spectroscopy. During the spin coating of the solutions containing AgNO₃, clusters of the silver component were formed. They were well dispersed in a poly(vinyl alcohol) matrix but act as nucleation agents in poly(ethylene oxide) where then large spherulites are formed. The surface compositions of coated samples and the depth profiling were carried out by angle dependent X-ray photoelectron spectroscopy.     

Electrochemical behavior of silver thin films interfaced with yttria-stabilized zirconia

Thin silver films (100–800 nm) were deposited by physical vapor deposition (PVD) on yttria-stabilized zirconia solid electrolyte. The electric percolation as a function of the film thickness was studied during deposition and annealing using a two-electrode in-situ resistance measurement technique. Electrical percolation was achieved in as-deposited films greater than 5.4?±?0.4 nm; however, thermal treatment (550 °C in air) resulted in film dewetting for Ag films as thick as 500 nm and formation of electronically isolated Ag nanoparticles, as was confirmed by SEM and XPS. In thermally treated samples, stable electronic conductivity associated with a continuous percolated network was only observed in samples greater than 600 nm in thickness. The effect of polarization on the electrochemical reactions at the three-phase (electrode-gas-electrolyte) and two-phase (electrode-electrolyte) boundaries of the electrode was investigated by solid electrolyte cyclic voltammetry (SECV) at 350 °C and P _O2?=?6 kPa. With the application of positive potential, silver oxide (Ag₂O) was found to form along the three-phase boundary and then extends within the bulk of the electrode with increasing anodic potentials. By changing the hold time at positive potential, passivating oxide layers are formed which results in a shift in favor of the oxygen evolution reaction at the working electrode. This oxide forms according to a logarithmic rate expression with thick oxides being associated with decrease in current efficiency for subsequent oxide formation.     

Nano silver coated patterned silica thin film by sol–gel based soft lithography technique

We report the fabrication of nano silver coated patterned silica thin film by sol–gel based soft lithography technique. Initially, silica gel film on soda lime silica glass was prepared by dipping technique from a silica sol of moderate silica concentration. A PolydimethylSiloxane elastomeric stamp containing the negative replica of the patterns of commercially available compact disc was used for embossing the film and the embossed film was cured up to 450 °C in pure oxygen atmosphere for oxide film. Finally, a precursor solution of AgNO₃ in water containing polyvinyl alcohol as an organic binder was made and used for coating on the patterned silica film by dipping technique and cured the sample up to 450 °C in reducing gas atmosphere to obtain nano silver layer. The formation of only cubic silver (~4.0 nm) and both cubic silver (~5.2 nm) and silver oxide (~3.6 nm) crystallites at 350 and 450 °C film curing temperatures respectively were confirmed by XRD measurements. The % of nano silver metal and silver oxide were 75.4 and 24.6 respectively. The nano-structured surface feature was visualized by FESEM whereas AFM revealed the high fidelity grating structure of the films. Presence of both spherical and rectangular structure (aspect ratio, 2.37) of nano silver/silver oxide was confirmed by TEM. The films were also characterized by UV–Vis spectral study. The patterned film may find application in chemical sensor devices.     

Multicycle chronoamperometry at rotating ring-disc electrode as a method of current separation into partial currents of silver ionization,Ag<Subscript>2</Subscript>O formation and its chemical dissolution in alkaline medium

A method of multicycle chronoamperometry at rotating ring-disc electrode is suggested for experimental separation of the disc polarization current into its components that correspond to the substrate metal ionization, an oxide formation, and the oxide chemical dissolution. The method was validated by the example of the Ag|Ag₂O|OH^?(H₂O) system. At moderate anodic potentials of Ag-disc (0.48–0.51 V), silver active dissolution from open areas of its surface and through film’s pores dominates; the phase-forming current, hence, the current efficiency of this process drops down rapidly. At the potentials of the maximum at voltammograms (0.52–0.53 V), when the silver active dissolution current is suppressed, the phase-forming currents dominate; they exceed the oxide chemical dissolution rate significantly. The Ag₂O film thickness increases rapidly, the current efficiency of the oxide formation process approaches 100% during the entire disc polarization period. The Ag(I)-oxide chemical dissolution rate constant practically does not depend on the anodic phase-formation potential; however, it somewhat varies depending on the oxide film thickness, thus reflecting changes in the film structure and, possibly, chemical composition (from AgOH to Ag₂O).     

Sonoelectrochemistry at highly boron-doped diamond electrodes: silver oxide deposition and electrocatalysis in the presence of ultrasound

The use of boron-doped diamond has a considerable impact in electrochemistry owing to the wide potential range accessible, low background currents, extreme hardness, and the ease of chemical modification of diamond surfaces. It is shown here that, although the electrodeposition of silver metal is known to yield very poorly adhering films with a poor electrical contact, a silver oxysalt deposit formed on anodically pre-treated diamond surfaces adheres strongly with good electrical contact. The deposit is stable even in the presence of ultrasound. Voltammetric and XPS studies reveal that the silver oxide deposit, in contrast to the silver metal deposit, is efficiently stripped from the diamond surface by applying a sufficiently negative potential. The silver oxysalt Ag₇O₈NO₃, deposited onto two types of boron-doped diamond electrodes, a 50 μm thick polycrystalline thin film deposited on a tungsten substrate and a polished free standing diamond plate, is shown to act as an electrocatalyst for oxygen evolution and for the oxidation of toluene. This development opens up the possibility of boron-doped diamond being applied as an inert and conducting substrate material for a wide range of oxidic materials, which can then be utilised as active electrocatalysts at high applied potentials. Received: 17 March 2000 / Accepted: 10 April 2000     

Über die Flüchtigkeit von Silber im Sauerstoffstrom

Vaporization of Silver in a Stream of Oxygen Using a transport equipment the vaporization of silver at 611–721°C in a stream of oxygen has been measured. Experiments with detachable cuffs of silver or with wools of silver in a bulb made from quartzglass or silver lead to the same results. By variation of the O₂-pressure and the activity of silver is observed that the vaporization happens as Ag₂O,g, see “Inhaltsübersicht”. The solid was at first pure silver. During long lasting experiments, however, it is covered with a thin layer of oxygen or silver oxide, which lowers the concentration of Ag₂O,g in the equilibrium gas to a smaller, yet constant value. The following measurements using N₂ as carrier gas lead to the decomposition of this layer and ends with the very small vapor pressure of silver. The layer of oxygen or silver oxide on the metal could be shown after Davies [2] using mercury.     

Electroanalytical Study of the Composition of the Raw Pigment Mixtures that Yield the Metallic Lustre on Ceramics. A Link Between Composition and Final Result

Voltammetry of immobilized microparticles was used to study the electrochemistry of the raw pigments that produce the metallic lustre on ceramics after a successful firing. To study this influence of the mixture components on the reduction properties to achieve the metallic lustre, 14 mixtures of illitic clay, Fe₂O₃, HgS, CuO and AgNO₃ were prepared and studied in different media. Iron oxide improves the yield of the reduction of the metals and cinnabar helps a closer reduction of silver to copper reduction and prevents the Ag? Cu alloying because of the formation of silver–mercury adducts. The presence of one of the metals influences the peak position of the other metal. The use of vinegar as diluting agent is not casual, because in this media the reduction of silver takes place at a potential closer to the copper. This electroanalytical technique allowed to distinguish between powders of different composition and offered some information about the role of the components in the reduction of copper and silver and the selection of vinegar to prepare the raw pigment suspensions.     

Regularities of silver atom formation in gamma-irradiated aluminium silicates modified by lanthanum oxide(III)

The ESR-method was used to study the regularities of silver atom formation and stabilization in gamma-irradiated aluminium silicates modified by lanthanum oxide. Two types of silver atoms (Ag_I and Ag_II) stabilized at two different sites of the surface, and paramagnetic species Ag⁺₂ have been identified. ESR-spectrum parameters of paramagnetic silver species have been calculated. Under discussion are the nature of silver species Ag_I and Ag_II, and the influence of sample thermal and vacuum treatment prior to γ-irradiation, on the number of paramagnetic silver species observed. The thermal stability of silver species was found to increase with the temperature of sample vacuum pre-treatment. Under study was the dependence of silver species formed on the irradiation dose.     

电泳沉积制备氧化石墨烯-银电极及其氧还原催化性能

通过在1-甲基-2-吡咯烷酮(NMP)中超声剥离氧化石墨制备出稳定的氧化石墨烯(GO)分散液,添加AgNO3使氧化石墨烯吸附Ag+而带正电荷。采用电泳沉积法使GO沉积到阴极的玻璃碳电极上,Ag+被电化学还原为单质银,均匀的分散在GO片层当中。通过AFM、SEM、Raman、XRD及元素面扫分析对制备电极的形貌、结构进行表征。在碱性环境中进行氧还原测试,结果表明GO+Ag电极的氧还原起始电位较玻璃碳电极最大正移228 mV,还原电流密度最大为7.564 mA·cm-2,是玻璃碳电极的3.4倍。通过不同转速下的线性扫描曲线绘制Koutechy-Levich图,计算氧还原反应的电子转移数为3.3。     

The Construction and Transition of Supramolecular Hydrogels Induced by Cyclodextrin Inclusion

Soft hydrogel nano‐ and micro‐structures have great potential applications in the field of tissue engineering and chemical sensors. In this paper, a supramolecular hydrogel was constructed by combining a triblock copolymer poly(ethylene oxide)₁₀₀‐(propyleneoxide)₇₀‐(ethyleneoxide)₁₀₀ (PEO₁₀₀‐PPO₇₀‐PEO₁₀₀ ) (Pluronic F127), mono‐6‐thio‐β‐cyclodextrins (SH‐β‐CDs), and silver nanoparticles. Here, SH‐β‐CDs couple to the silver nanoparticles via thio groups and include PPO blocks of F127 using the hydrophobic cavity to form pseudo‐polyrotaxanes. Moreover, the hydrogel can be transformed to a homogenous solution by the addition of hydrochloride powder. These results are important for research related to the construction of soft hydrogel materials and control their mechanical properties.     

Magnetron sputtering of silver nanowires using anodic aluminum oxide template: a new active substrate of surface enhanced Raman scattering and an investigation of its enhanced mechanism

A high quality anodic aluminum oxide (AAO) template with ordered apertures about 50-80 nm was fabricated by anodizing aluminum in electrolytes through a two-step method, and silver nanowires with diameters from 40nm to 70nm were prepared on this AAO template by magnetron sputtering. On the glass covered with silver nanowires, high quality surface enhanced Raman scattering (SERS) spectra of sudan II (C₁₈H₁₆N₂O) with enhancement factors of 10⁵ were obtained. And comparison of SERS spectra on silver nanowires with the SERS spectra of silver colloids indicates that main enhanced mode is lightning rod effect of nanorods on the Sudan II/silver nanowires system.     

Natural rubber–based composites filled with bioglasses from a CaO‐SiO2‐P2O5‐Ag2O system. Effect of Ag2O concentration in the filler on composite properties

Bioactive glass was first synthesized by L. Hench in 1971. There are many studies on the properties of several metals and metal ions dopants used in the SiO₂‐CaO‐P₂O₅ system of bioglasses, such as Ag, Cu, Zn, and Fe. A number of authors have carried out research related to the influence of silver oxide on the properties of bioglasses . However, publications on the properties of elastomer‐based composites containing bioactive glasses are relatively scarce. We have not found in the literature studies discussing how silver oxide concentration in bioglasses of the CaO‐SiO₂‐P₂O₅‐Ag₂O system affects the significant properties of a natural rubber biocomposite. In this regard, the purpose of the present work is to investigate the aforementioned influence on the properties of this type of composites, namely, vulcanization, physicomechanical, thermal, dynamic, dielectric, electric, and thermoconductive characteristics. We have established those parameters of the composites to be impacted considerably by both degree of filling with bioglass and the silver oxide content in the latter. The improvement in the composites thermostability and some of their physicomechanical performance is the most significant. The volume resistance decreases, and the thermal conductivity coefficients increase. Results from scanning electron microscopy and energy‐dispersive X‐ray (EDX) analyses have confirmed the influence of silver oxide initially on the phase composition of the bioglass, hence on the properties of the biocomposites through changes in the bioglass used as filler. The dielectric characteristics of some of the biocomposites suggest that they can be used as substrates and insulating layers in flexible antennas for short‐range wireless communications.     

The Interaction of Oxygen with Silver Powders. A Comparison Between Esca Results and Volumetric Measurement

Interactions of oxygen with silver powders have been studied with a combination of angle-resolved ESCA and volumetric adsorption. Three states of adsorbed oxygen, i.e., atomically adsorbed oxygen, dissolved oxygen, and surface oxide, are characterized by 0(1s)-ESCA peaks at binding energies of 530.2, 532.0, and 529.3 eV respectivcly. The ESCA studies also suggest that atomically adsorbed oxygen dissolves into the subsurface of silver powders at temperatures above 100 °C, and then transforms into oxide (Ag₂O) at 175 °C. Adsorbed oxygen on the silver powders was partially desorbed at temperatures higher than 180 °C. The transformation and desorption information obtained from ESCA satisfactorily explains the variation of the adsorption isotherm with temperature obtained from the volumetric adsorption of oxygen on Ag/SiO₂ catalysts.