Effect Of Silver Addition Research Articles

Long-Time Stability vs Deactivation of Pd–Ag/Al2O3 Egg-Shell Catalysts in Selective Hydrogenation of Acetylene

Industrial relevant Pd–Ag/Al2O3 egg-shell catalysts with varying Pd/Ag mole ratios were prepared, characterized (CO chemisorption, DRIFTS, EPMA, STEM, coupled with EELS and EDX, as well as TPR) and tested for selective hydrogenation of acetylene under tail-end conditions. Characterization suggests a reduction of the total number of Pd surface atoms nPd,surf as well as an isolation of large Pd ensembles. The effect of silver addition on byproduct formation and deactivation behavior was investigated, representing a higher long time stability of Pd5–Ag95/Al2O3 in comparison to silver free Pd100/Al2O3 egg-shell catalysts, due to a decrease of green oil and coke formation. The selectivity to C6 compounds is a fundamental indicator for long-term stability of palladium catalysts that is often overlooked in the literature. Furthermore, this study implicates selective hydrogenation of acetylene as a structure sensitive reaction originating from a geometric effect.

Preparation and antibacterial property on silver incorporated mesoporous bioactive glass microspheres

In this study, the antibacterial property of silver-incorporated mesoporous bioactive glass microspheres (Ag-MBGMs) was investigated. The samples belonging to the 80SiO2·(15 − x)CaO·5P2O5·xAg2O system where 0 ≤ x ≤ 5 mol% were successfully prepared for bone regeneration and drug carrier applications. The obtained samples were evaluated by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope, Fourier transform infrared spectroscopy, and N2 adsorption/desorption measurements. All Ag-MBGMs had spherical particles with particle size 6–10 µm. TEM images showed mesopore structure. The textural properties showed a decrease in surface area and pore volume with an increase in silver content. XRD patterns exhibited the presence of pseudowollastonite and hydroxyapatite phase for silver-incorporating MBGMs, which might increase its bioactivity and bone bonding ability. Finally, all Ag-MBMGs had an antibacterial effect against both Escherichia coli and Staphylococcus aureus. Therefore, Ag-MBGMs may provide more potential for use as injectable, anticancer and drug-loading biomaterials for bone tissue engineering applications. In this study, the mesoporous bioactive glass microspheres (MBGMs) belonging to the system 80SiO2·(15 − x)CaO·5P2O5·xAg2O (x = 1, 3, and 5) were successfully prepared by the sol–gel process with surfactant-assisted mesoporous template. Effects of silver addition in MBGMs system were investigated for the first time such as particle shape and size, textural analysis, phase composition, in vitro bioactivity, and antibacterial effect. All prepared MBGMs have uniform microspherical particle (2–5 µm) with hierarchically structure. The textural analysis revealed that all prepared MBGMs had high porosity and relatively high surface area. The incorporation of apatite, pseudowollastonite, and metallic silver crystals were found for adding silver content more than 1 mol%. All prepared MBGMs can induce the crystalline hydroxyl carbonate apatite layer on the surface after soaking in simulated body fluid solution for 7 days. All silver-containing MBGMs had a very good antibacterial effect against Staphylococcus aureus and Escherichia coli. In addition, silver-incorporated MBGMs exhibited anticancer property against HepG2 cells.

Effects of Silver Addition on Critical Current Densities and Mechanical Properties in Bulk MgB2

The present study focuses on the effects of Ag addition on the critical current density (Jc) and the mechanical performance of disk‐shaped MgB2 bulk superconductors. MgB2 samples with varying Ag contents of 0, 2, 4, 6, 8, and 10 wt% were sintered at 775 °C for 3 h in Ar atmosphere. The Jc values were improved with Ag addition, in that the sample with 4 wt% Ag showed the highest Jc value of 295 kA cm−2 at 20 K and self‐field. The respective Jc values of the same sample were 430, 360, and 238 kA cm−2 in self‐field, 0.5 T, and 1 T at 7 K. These values are the highest so far reported in bulk MgB2 materials. Scanning electron microscopy showed that silver and silver oxide particles are embedded in the voids. As a result, the mechanical performance at room temperature was improved with Ag addition. We also confirmed the presence of nanometer‐sized AgMg3 particles, which may be responsible for high flux pinning and improved mechanical performances.

Effects of silver addition on Cu–Sn microjoints for chip-stacking applications

The solid-state reactions under confined space between Cu substrate and Sn and Sn–Ag solders are systematically investigated, with the objective of providing fundamental data that are critical to the design of robust microjoints for chip-stacking applications. Sandwich structures of Cu/Sn/Cu and Cu/Sn3.5Ag/Cu are prepared by thermal compression bonding. The thickness of Sn and Sn3.5Ag layer is controlled at 10μm. High temperature storage tests are conducted at 120°C, 150°C, 180°C, and 200°C for different time periods. Unlike the well-known void formation in the Ni/Sn/Ni system, there is no such void at all in the Cu/Sn/Cu system. The addition of Ag consistently slows down the growth kinetics of intermetallics. The time-to-impingement of intermetallics is established for the first time for both systems under solid-state reactions.

Effect of Silver Addition to Superconducting SmFeAsO1−x F x

We investigate the effect of silver addition to polycrystalline Sm-1111 superconductor. We show that Ag improves the phase homogeneity of the samples drastically reducing the weight of the low temperature, hence, leading to less fluorinated phases. The intragranular critical current density is enhanced by adding a small amount of Ag in all pinning regimes but a higher content of Ag leads to a decrease of this quantity. A tentative explanation for this dependence is proposed.

Effect of Silver Ions on the Structural and Antibacterial Properties of Bone Replacement Material

Antibacterial materials based on calcium phosphates have wide range of biomedical applications in the prevention of microbial infections. The synthesis of inorganic mineral component of bone i.e. hydroxyapatite was done with the addition of silver (Ag) (5-15 wt %) as antibacterial agent. The wet precipitation synthesis was carried out using diammonium hydrogen phosphate and calcium nitrate as P and Ca precursors. The presence and effect of silver addition on the structure was studied using Fourier Transform-Infrared (FTIR) spectroscopy and Energy Dispersive X-ray (EDX) techniques. The antibacterial properties of all samples were evaluated using Disc Diffusion Technique (DDT) againstS. aureus,B. subtilis, P. aeruginosaandE. coli. Antibacterial activities of samples were found to vary depending on the bacterial species and Ag loading percentage. The antibacterial assay suggested that the addition of Ag ions within hydroxyapatite can be effectively provided the required level of antibacterial activity against bacteria.

Effect of silver incorporation in phase formation and band gap tuning of tungsten oxide thin films

Silver incorporated tungsten oxide thin films are prepared by RF magnetron sputtering technique. The effect of silver incorporation in micro structure evolution, phase enhancement, band gap tuning and other optical properties are investigated using techniques such as x-ray diffraction, micro-Raman spectroscopy, atomic force microscopy, scanning electron microscopy, energy dispersive x-ray spectroscopy, and UV-Visible spectroscopy. Effect of silver addition in phase formation and band gap tuning of tungsten oxide thin films are investigated. It is found that the texturing and phase formation improves with enhancement in silver content. It is also found that as the silver incorporation enhances the thickness of the films increases at the same time the strain in the film decreases. Even without annealing the desired phase can be achieved by doping with silver. A broad band centered at the wavelength 437 nm is observed in the absorption spectra of tungsten oxide films of higher silver incorporation and this can be attributed to surface plasmon resonance of silver atoms present in the tungsten oxide matrix. The transmittance of the films is decreased with increase in silver content which can be due to increase in film thickness, enhancement of scattering, and absorption of light caused by the increase of grain size, surface roughness and porosity of films and enhanced absorption due to surface plasmon resonance of silver. It is found that silver can act as the seed for the growth of tungsten oxide grains and found that the grain size increases with silver content which in turn decreases the band gap of tungsten oxide from 3.14 eV to 2.70 eV.

Effect of silver addition on the microstructures and electrical responses of La(1.7)Sr(0.3)Mo(2)O(9 − δ) ceramics

Different amounts of silver (3–15wt.% Ag2O) have been mixed with ceramic powders based on La1.7Sr0.3Mo2O9−δ (LSM). XRD analysis indicated that the silver was chemically stable in LSM. TEM observation and XPS analysis showed that some metallic silver atoms presented random distribution in the LSM ceramic, while others entered into crystal lattice in the form of Ag+, efficiently stabilizing the cubic phase at the room temperature. And there were a great enhancement on conductivity in Ag added (<10wt.% Ag2O) LSM ceramics. Also addition of Ag had a significant influence on the surface oxygen exchange properties with electrode components.

Effect of silver addition on structural, electrical and magnetic properties of Fe3O4 thin films prepared by pulsed laser deposition

The structural, electrical, and magnetic properties of Agx-(Fe3O4)1−x (x = 0, 0.02, 0.10) composite films were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), resistivity as well as magnetization measurements. The samples used in the present work were prepared by the pulsed laser deposition (PLD) technique on a single crystal Si (111) substrate. XRD spectra reveal that Ag added samples show polycrystalline growth on the Si substrate in distinction to oriented growth of Fe3O4 on a similar substrate. XRD and XPS data confirm that silver is present in metallic form. Temperature dependent resistivity data corresponding to all the three samples show a characteristic Verway transition (Tv) around 121 K. However, the resistivity pattern of the Ag added sample with x = 0.10 shows the tunneling behavior below Tv, which is attributed to the accumulation of silver clusters across the boundary of Fe3O4 grains. Both Ag added (x = 0.02, 0.10) Fe3O4 films show positive magnetoresistance which is in contrast to negative magnetoresistance observed in pure Fe3O4 at room temperature. Magnetization measurements reveal that Ag granules reduce the saturation magnetization of Fe3O4.

Electrochemical Characteristics of Eutectoid AlZnAg Alloys

Aluminium-zinc alloys were added with silver micro-constituent by vortex method and hot-rolled. The understanding of microstructure-chemistry relationship during the electrochemical oxidation and the effect of silver additions on the corrosion behavior have been investigated. The results of potentiodynamic polarization curves and transmission electron microscopy (TEM) with energy-dispersive X-ray (EDX) revealed the importance of the silver addition in the microstructure. Ag content significantly influences the corrosion behavior of a-Al, h-Zn and e-AgZn3 phases. The electrochemical investigations showed that the corrosion rate increased with the additions of Ag micro-constituent. Furthermore, it was also evidenced the formation of a passive layer for the highest Ag content alloys. The passivity of this layer could be broken down due to the presence of the intermetallic compounds (IMCs) AgZn3. The AgZn3 particles are responsible for the localized corrosion because they act as local anodes. All this indicate that AgZn3 particles and microstructural features play an important role in the corrosion process for AlZnAg alloys

Cold Workability, Mechanical Properties, Pseoudoelastic and Shape Memory Response of Silver Added Ti-5Cr Alloys

In order to develop new nickel-free biomedical Ti-based alloys, effect of silver additions on mechanical properties of Ti-5Cr (mol%) alloy was investigated. Cold workability of Ti-5Cr alloy was 5% in thickness reduction and the cold rolling reduction was improved to be 38% by 2mol% Ag addition and 96% by 4mol%Ag addition. The improvement was due to β phase stabilization. From the XRD results, α’ martensite was the dominant phase in Ti-5Cr-2Ag alloy and β phase was the dominant phase in Ti-5Cr-4Ag alloy. By tensile tests, Ti-5Cr-4Ag alloy showed good strength of 447 MPa in ultimate tensile strength (UTS) and ductility of 13% in fracture strain. Ti-5Cr-4Ag showed higher hardness of HV398 than Ti-5Cr-2Ag with HV288. The hardening by increase of Ag is probably due to the solid solution strengthening. By the cyclic loading-unloading tensile tests with a constant strain increment, Ti-5Cr-4Ag showed pseoudoelastic behavior. Ti-5Cr-4Ag also showed shape memory effect with 57% in shape recovery ratio. It is concluded that Ti-5Cr-4Ag is hopeful as a new non-allergic shape memory material for biomedical applications.

Effects of silver addition on microstructure and electrical properties of barium titanate ceramics

Barium titanate–silver composites were prepared by using a solid state reaction process with silver contents ranging from 0 mol% to 20 mol%. XRD results and Raman spectra indicated that there was no phase other than BaTiO 3 and Ag in the ceramics and tetragonality of barium titanate reduced with increasing Ag content. SEM images illustrated that Ag influenced densification and microstructure of BaTiO 3 ceramics. Besides, addition of Ag led to increase in dielectric permittivity and broadening of ferroelectric–paraelectric phase transition peak. Also addition of Ag had effects on dielectric loss and dc conductivity. Dielectric and conductivity properties as a function of Ag volume fraction were explained by the percolation theory.

Effect of silver addition in gamma titanium aluminide

The influence of sliver on the oxidation resistance and relative fracture toughness of aluminum rich gamma titanium aluminide was studied. The titanium aluminide buttons were prepared in argon protected environment. The samples were tested and characterized with the help of Vickers hardness testing machine, optical and scanning electron microscope and energy dispersive spectrometer. The relative fracture toughness was determined by indentation method. It was observed that for a certain alloying addition the oxidation resistance and the relative fracture toughness can be improved.

Effects of Silver Addition on Properties and Performance of Plasma Sprayed La0.6Sr0.4Co0.2Fe0.8O3−δ Interconnect Layer

Interconnect layers on stainless steel substrates (STS430) for solid oxide fuel cells (SOFC) were built up by atmospheric plasma spraying (APS) using spray dried La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) and blended LSCF/Ag composites. The microstructure and phase of each coating were analyzed using scanning electron microscopy (SEM) and x-ray diffraction (XRD) studies, respectively. Furthermore, bond strength, microhardness, performance in a thermal cycle test and in an oxidation test, and electrical conductivity were measured and compared. The coatings prepared from spray dried LSCF have higher porosity and more cracks within the splats and at intersplat boundaries. In contrast, the coatings prepared from LSCF/Ag had fewer cracks and less porosity due to the relatively high ductility of silver. After oxidation testing at 800 °C for 200 h, the weight change of the STS430 substrate and the LSCF and LSCF/Ag-coated alloys were found to be 0.06833, 0.01950, and 0.01656 mg/cm2, respectively. Also the electrical conductivity of LSCF and LSCF/Ag coatings were higher than that of STS430 by two orders.

Effect of silver addition on the properties of combustion synthesized nanocrystalline LiCoO 2

Nanocrystalline (∼50 nm) LiCoO 2 powders containing 0–10 mol% of Ag have been prepared by combustion synthesis using citrate–nitrate combustion route. Thermal analyses show a sharp decomposition of the gel at ∼177 °C for pristine LiCoO 2. With addition of silver, the decomposition becomes sluggish and it completes only above 430 °C. X-ray powder diffraction analyses show an increase in lattice parameter, c, with increasing Ag content suggesting the occupation of Ag within LiCoO 2 interlayer spacings. Transmission electron microscopy indicates diffusion of Ag into LiCoO 2 grains. It has been observed that adding 1.0 mol% silver increases the room temperature electrical conductivity by more than two orders of magnitude (1.5 × 10 −3 S cm −1). Galvanostatic charge–discharge profiles of coin cells fabricated with the synthesized powders show a two-fold enhancement in the discharge capacity for 1.0 mol% Ag-added LiCoO 2 cathode (140 mAh g −1) compared to that for pristine LiCoO 2 (70 mAh g −1).

Effect of Silver Additions on the Ageing Behavior and Mechanical Properties of Mg-Al-Si-Sn-Sr Alloy

Mg is one of the most promising structural materials for lightweight applications due to its low density, good castability and damping capacity. In this study, we investigated the effect of silver (Ag) addition on alloy ageing behavior and mechanical properties of Mg-Al-Si-Sn-Sr-Ag alloys with variation of Ag contents (0.1, 0.5, 1.0, 2.0wt%). The ageing kinetics of Ag added alloys was determined and affected by Ag addition. Although the precipitation of platelets of Mg17Al12 within α-Mg matrix was not significantly affected by the silver, mechanical properties such as hardness and tensile properties were improved with increasing Ag contents.

Effect of silver addition on the creep parameters of Sn–7 wt.% Bi alloy during transformation

The strain–time relations of Sn–7 wt.% Bi and Sn–7 wt.% Bi–1 wt.% Ag alloys have been obtained under different constant stresses (8.7–19.1 MPa) in the temperature range (313–373 K). The results showed that the transient and the steady state creep parameters n, β and ε st depend on both the deformation temperature and the applied stress. The temperature dependence of these parameters indicates a transition temperature at 343 K. The Ag-free samples are more hard than those with Ag addition. This is explained by precipitation of Bi atoms which segregate to form a non-coherent cubic α-phase Sn–7 wt.% Bi samples. While, Ag addition prevents precipitation segregate on the grain boundaries. The analysis of the X-ray diffraction patterns shows that, Ag addition increases the Sn crystallite size but decreases Bi crystallite size. The energy activating the steady state creep in the two alloys in the low and high temperature ranges (before and after transformation temperature) were found to be 51.2 ± 1.6 and 88.1 ± 1.4 kJ/mol for Sn–7 wt.% Bi alloy and 34.3 ± 1.9 and 57 ± 1.8 kJ/mol for Sn–7 wt.% Bi–1 wt.% Ag alloy, respectively.

Effect of silver addition on the formation and deposition of titania nanoparticles produced by liquid flame spray

In this study, liquid flame spray (LFS) was used to produce titania, silver and silver–titania deposits of nanoparticles. Titanium(IV)ethoxide (TEOT) and silver nitrate in ethanol solutions were used as precursors and sprayed into turbulent hydrogen–oxygen flame. Production rates of 1.5–40 mg/min of titania were used with silver additions of 1, 2, 4, and 8 wt% compared to titania. Nanoparticle deposits were collected by thermophoretic sampling at six different axial distances from the flame torch head: 3, 5, 10, 12, 15, and 20 cm, of which the all but the last one occurred inside the flame. The deposit samples were analysed by TEM and SAED analysis. The powder samples of the particles were also collected by electric precipitator to XPS and specific surface area analysis. Particle size and effective density after the flame in the aerosol were analysed with SMPS and ELPI. The results from the previous studies i.e. controlling the particle size by setting the production rates of the particles were seen to apply also for this binary system. Characterisation of the deposits showed that when the substrate is inserted into the flame, in the beginning of the flame the deposit is formed by gas phase deposition whereas further down the flame the particles are first formed in the gas phase and then deposited. The location of the transition from gas phase deposition to gas phase nucleation prior to deposition depends on chemical/physical properties (e.g. thermodynamics and gas phase interactions) of the precursor, precursor concentration in the flame and also flame temperature profile. Therefore, the deposit collection distance from the burner also affected the collected particle size and degree of agglomeration. The two component deposits were produced in two different ways: one-step method mixing both precursors in the same solute, and two-step method spraying each precursor separately. The particle morphology differs between these two cases. In one-step method the primary (dTEM) and agglomerate particle size (dSMPS) decreased with the amount of silver addition, verifying the fact that when present, the silver has a clear effect on the titania nanoparticle formation and growth.

Effect of silver addition on the properties of nickel–titanium alloys for dental application

Effect of silver addition on the properties of nickel–titanium alloys for dental application

Melting Equilibria of the Bi-Sr-Ca-Cu-O (BSCCO) System in Air: The Primary Crystallization Phase Field of the 2212 Phase and the Effect of Silver Addition

The subsolidus and primary crystallization phase field of the 2212 (Bi:Sr:Ca:Cu) phase in the BSCCO system have been investigated. At 830 C, this phase was observed to be in equilibrium with ten phases. Sixteen four-phase equilibrium regions that surround the 2212 phase have been identified at this temperature. The melting events associated with these four-phase regions were studied with differential thermal analysis, quenching experiments, and wicking experiments, in which samples of the liquid for analysis were absorbed by capillary action. The melt compositions were obtained by using quantitative energy-dispersive X-ray spectrometry. The 2212 phase melts incongruently, beginning at {minus}825 C. Its primary crystallization field encompasses a compositional range of 24--42 mol% BiO{sub 1.5}, 7--33 mol% SrO, 2--27 mol% CaO, and 19--43 mol% CuO. The compositions of melts in equilibrium with the 2212 phase were mostly on the calcium-deficient side of the 2212 solid solution. An approximate polygonal model of the 2212 primary crystallization field has been presented. The addition of silver depresses the melting temperatures in the vicinity of the 2212 phase, from 4 C to 22 C. Silver entered the melt at a saturation level of 2--8 mol%. In the more copper-rich liquids, silver replaced some of the copper,more » which resulted in a shift of the 2212 crystallization field away from the copper oxide corner.« less