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Probes a study which used the z-scan technique in measuring the nonlinear absorption coefficient of continuous gold films, deposited onto surface-modified quartz substrates. Experimental procedure of the study; Characteristics of continuous metal films; Scanning tunneling microscopy (STM) images obtained with a platinum/iridium tip at a specific scan size; Effectivity of the z-scan.

The present work had attempted to develop rice straw black liquor based porous carbon-poly (aniline-co-methoxy aniline) composite added catalysts for alcohol oxidation. In this aspect, nanoparticles of platinum-iridium and platinum were deposited on poly(aniline-co-methoxy aniline)-rice straw black liquor based porous carbon (Poly(Ani-co-MAni)-RSBLPC) composite. The electrochemical test has been carried out using Pt-Ir/Poly(Ani-co-MAni)-RSBLPC and Pt/Poly(Ani-co-MAni)-RSBLPC electrocatalysts in an alkaline solution of methanol, ethylene glycol, and glycerol. For comparison, the electrochemical performance test is also done using Pt/Poly(Ani-co-MAni) and Pt/RSBLPC catalysts in basic solution of methanol. From electrochemical studies, it was noticed that platinum nanoparticles decorated Poly(Ani-co-MAni)-RSBLPC reveals a significant enhancement towards the oxidation of methanol in comparison with Pt/Poly(Ani-co-MAni) and Pt/RSBLPC catalysts, which will be expected from the synergic effect of rice straw black liquor based porous carbon and conductive polymer material. Furthermore, the bimetallic Pt-Ir/Poly(Ani-co-MAni)-RSBLPC catalyst showed enhanced catalytic activity in comparison with monometallic Pt/Poly(Ani-co-MAni)-RSBLPC catalyst. The above results suggested that Poly(Ani-co-MAni)-RSBLPC composite is a potent support and could be used as a potent low cost support for catalyst deposition towards fuel cell industries that include the applications of sensor and super capacitor. [ABSTRACT FROM AUTHOR]

Conducting polymers, specifically poly (3,4-ethylenedioxythiophene) (PEDOT), have recently been coated onto Pt/Ir electrodes intended for neural applications, such as deep brain stimulation (DBS). This modification reduces impedance, increases biocompatibility, and increases electrochemically active surface area. However, direct electropolymerization of PEDOT onto a metallic surface results in physically adsorbed films that suffer from poor adhesion, precluding their use in applications requiring in vivo functionality (i.e. DBS treatment). In this work, we propose a new attachment strategy, whereby PEDOT is covalently attached to an electrode surface through an intermediate phenylthiophene layer, deposited by electrochemical reduction of a diazonium salt. Our electrodes retain their electrochemical performance after more than 1000 redox cycles, whereas physically adsorbed films begin to delaminate after only 40 cycles. Additionally, covalently attached PEDOT maintained strong adhesion even after 10 minutes of ultrasonication (vs. 10 s for physically adsorbed films), confirming its suitability for long-term implantation in the brain. The simple two-step covalent attachment strategy proposed here is particularly useful for neural applications and could also be adapted to introduce other functionalities on the conducting surface. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) crumpled reduced graphene oxide supported Pt-Ir alloys that served as bifunctional oxygen catalysts for use in untized regenerative fuel cells were synthesized by a facile spray pyrolysis method. Pt-Ir catalysts supported on rGO (Pt-Ir/rGOs) were physically characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA) to observe change in composition by heat treatment, alloying, and morphological transition of the catalysts. Their catalytic activities and stabilities for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) conditions were electrochemically investigated using cyclic voltammetry (CV), linear sweep voltammetry (LSV), potential cycling and hold tests on the rotating disk electrode (RDE). Pt-Ir/rGO with no post heat-treatment (Pt-Ir/rGO_NP) showed a lower activity for ORR and OER although metal nanoparticles decorated on the support are relatively small. However, Pt-Ir/rGO showed remarkably enhanced activity following heat treatment, depending on temperature. Pt-Ir/rGO heat-treated at 600 °C after spray pyrolysis (Pt-Ir/rGO_P600) exhibited a higher activity and stability than a commercially available Pt/C catalyst kept under the ORR condition, and it also revealed a comparable OER activity and durability versus the commercial unsupported Ir catalyst. [ABSTRACT FROM AUTHOR]

Accurate prediction of triplet excitation energies for transition metal complexes has proven to be a difficult task when confronted with a variety of metal centers and ligand types. Specifically, phosphorescent transition metal light emitters, typically based on iridium or platinum, often give calculated results of varying accuracy when compared to experimentally determined T1 emission values. Developing a computational protocol for reliably calculating OLED emission energies will allow for the prediction of a complex's color prior to synthesis, saving time and resources in the laboratory. A comprehensive investigation into the dependence of the DFT functional, basis set, and solvent model is presented here, with the aim of identifying an accurate method while remaining computationally cost-effective. A protocol that uses TD-DFT excitation energies on ground-state geometries was used to predict triplet emission values of 34 experimentally characterized complexes, using a combination of gas phase B3LYP/LANL2dz for optimization and B3LYP/CEP-31G/PCM(THF) for excitation energies. Results show excellent correlation with experimental emission values of iridium and platinum complexes for a wide range of emission energies. The set of complexes tested includes neutral and charged complexes, as well as a variety of different ligand types. [ABSTRACT FROM AUTHOR]

With the capability of MgAl 2 O 4 spinel {111} nano-facets in stabilizing small Rh, Ir and Pt particles, bimetallic Ir-Pt catalysts on the same support were investigated, aiming at further lowering the catalyst cost by substituting expensive Pt with cheaper Ir in the bulk. Small Pt-Ir nano-alloy particles (< 2 nm) were successfully stabilized on the spinel {111} nano-facets as expected. Interestingly, methanol oxidative dehydrogenation (ODH) rate on the surface Pt atoms increases with oxidizing aging but decreases upon reducing treatment, where Ir is almost inactive under the same reaction conditions. Up to three times enhancement in Pt exposure was achieved when the sample was oxidized at 800 °C in air for 1 week and subsequently reduced by H 2 for 2 h, demonstrating successful surface enrichment of Pt on Pt-Ir nano-alloy particles. A dynamic stabilization mechanism involving wetting/nucleation seems to be responsible for the evolution of surface compositions upon cyclic oxidizing and reducing thermal treatments. [ABSTRACT FROM AUTHOR]

Monometallic Pt- and bimetallic Pt-Ir-modified Ti-SBA-15 were used in the hydrogenation of tetralin to decalin in the presence of 150 ppm of N as quinoline and indole at 250 °C and 15 atm of pressure of hydrogen, using a Parr reactor. The catalyst was synthesized using sol-gel method and Ti was added during the synthesis using Tetraethyl Orthotitanate. Pt/Ir was added by wetness impregnation. The catalysts prepared were extensively characterized by X-ray diffraction (XRD), N 2 adsorption isotherms, UV–vis-DRS, Raman spectroscopy, XPS, TEM-EDS and TPR. UV–vis-DRS and Raman spectroscopy confirmed that Ti was incorporated in tetrahedral coordination in the framework of the SBA-15. The analysis showed that the mesoporous structure was maintained after metal incorporation and Ti incorporation helps to reduce significantly the size of the metals clusters and improves its dispersion considerably. Pt-Ir/Ti-SBA-15 was the most active catalyst. The experimental data were quantitatively represented by a modified Langmuir-Hinshelwood type rate equation. The preliminary results show these materials as a promising catalyst for HDT reactions. [ABSTRACT FROM AUTHOR]

Herein we report a Prussian Blue modified carbon fiber electrode (CFE/PB) to be used in microbiosensors for glutamate monitoring in physiological applications as an alternative to the classical Pt and Pt-Ir transducers. Their low dimensions (∼250 μm CFE length and ∼10 μm diameter) are advantageous for measuring in living tissues. In addition, PB-modified microelectrodes allow the detection of enzyme-generated hydrogen peroxide at a low applied potential (∼0.0 V against SCE), contrasting the high potential used in many previous designs (∼0.7 V), decreasing the endogenous interference contributions. Moreover, the electrosynthesized polymer, poly- o -phenylenediamine (P o PD), was used to improve biosensor stability and selectivity. CFE/PB was conveniently characterized using impedance, Raman and XPS spectroscopies. Optimization of the fabrication procedure and analytical conditions is described, including activation of CFE/PB, enzyme enrichment, cross-linking, stabilization and anti-interference. A range of analytical parameters were also characterized such as sensitivity, limit of detection, linear range, and enzymatic loading. Finally, an optimized biosensor displaying a linear sensitivity of 135 ± 2 nA μM −1 cm −2 (n = 3), LOD of <2 μM, linear range up to 150 μM and effectively free of interference, is proposed as a suitable candidate for in-vivo glutamate monitoring in the central nervous system. [ABSTRACT FROM AUTHOR]

38% to 93% selectivity enhancement toward sulfur-free products was observed upon iridium addition to a palladium-only catalyst in the hydrodesulfurization of a refractory sulfur compound 4,6-dimethyldibenzothiophene (4,6-DMDBT) at the same 40% conversion from a 300 ppm, S-containing feed at 5 MPa and 300 °C. Pd promoted hydrogenation to sulfurous intermediates, while Ir catalyzed C S hydrogenolysis and also improved Pd resistance to sintering. The selectivity in the direct desulfurization path for the Ir-containing catalysts increased up to 26% versus 5% for the Pd-only catalyst. The bimetallic catalyst allowed for a decrease in S from 300 ppm to 11 ppm. It can be used at reduced pressure (3 MPa) with only a 15% decrease in hydrodesulfurization conversion as compared to the operation at 5 MPa. [ABSTRACT FROM AUTHOR]

N-heterocyclic carbene (NHC) ligands with naphthyl side chains were employed for the synthesis of unsaturated, yet isolable [(NHC)Ir(cod)]+ (cod=1,5-cyclooctadiene) complexes. These compounds are stabilised by an interaction of the aromatic wingtip that leads to a sideways tilt of the NHC−Ir bond. Detailed studies show how the tilting of such N-heterocyclic carbenes affects the electronic shielding properties of the carbene carbon atom and how this is reflected by significant upfield shifts in the 13C NMR signals. When employed in the intramolecular hydroamination, these [(NHC)Ir(cod)]+ species show very high catalytic activity under mild reaction conditions. An enantiopure version of the catalyst system produces pyrrolidines with excellent enantioselectivities. [ABSTRACT FROM AUTHOR]

Minimally invasive therapies are increasingly in demand for organ-confined prostate tumors. Electrochemical therapy (EChT) is attractive, as it relies on locally-induced reduction–oxidation reactions to kill tumor cells. Its efficacy for prostate cancer was assessed in human PC-3 and LNCaP tumor xenografts growing subcutaneously in nude mice (n = 80) by applying 2 Stainless Steel vs. 4 Platinum–Iridium (Pt–Ir) electrodes to deliver current densities of 10 to 35 mA/cm 2 for 30 or 60 min. The procedure was uneventful in 90% of mice. No difference in tumor vs. body temperature was observed. Changes at electrode-tumor junctions were immediate, with dryness and acidity (pH 2–3) at the anode and oedema and alkalinity (pH 10–12) at the cathode. This was accompanied by cellular alterations, found more pronounced at the cathode. Such acidic and alkaline conditions were cytotoxic in vitro and dissolved cells at pH > 10. In mice, tumor destruction was extensive by 24 h with almost undetectable blood prostate specific antigen (LNCaP model) and covered the whole tumor surface by 4 days. EChT was most efficient at 25–30 mA/cm 2 for 60 min, yielding the longest recurrence-free survival and higher cure rates, especially with 4 Pt–Ir electrodes. EChT is a promising option to optimize for organ-confined prostate tumors. [ABSTRACT FROM AUTHOR]

Electrodes for cortical stimulation need to deliver current to neural tissue effectively and safely. We have developed electrodes with a novel annular geometry for use in cortical visual prostheses. Here, we explore a critical question on the ideal annulus height to ensure electrical stimulation will be safe and effective. We implanted single electrodes into the motor cortex of anesthetized rats and measured the current required to evoke a motor response to stimulation, and the charge injection capacity (CIC) of the electrodes. We compared platinum iridium (PtIr) electrodes with different annulus heights, with and without a coating of porous titanium nitride (TiN). Threshold charge densities to evoke a motor response ranged from 12 to 36 μC.cm-2.ph-1. Electrodes with larger geometric surface areas (GSAs) required higher currents to evoke responses, but lower charge densities. The addition of a porous TiN coating did not significantly influence the current required to evoke a motor response. The CIC of both electrode types was significantly reduced in vivo compared with in vitro measurements. The measured CIC was 72 and 18 μC.cm-2.ph-1 for electrodes with and without a TiN coating, respectively. These results support the use of PtIr annular electrodes with annulus heights greater than 100 μm (GSA of 38, 000 μm2). However, if the electrodes are coated with porous TiN the annulus height can be reduced to 40 μm (GSA of 16,000 μm2). [ABSTRACT FROM AUTHOR]

Numerous natural Os-Ir-Ru and Os-Ir-Ru-Pt alloys have been found in iron quartzites and their weathered rocks. The Ir-Os alloys in the Mikhailovka and Staryi Oskol KMA iron regions are characterized by the densest hexagonal packing. Almost all of them contain a low amount of Fe and Ni at a relatively higher amount of Pt, Ru, and, locally, Rh. The highest Rh contents are typical of minerals with Ir dominant over Os or with a high Pt content. [ABSTRACT FROM AUTHOR]

In this study, the phase-separation phenomenon of non-ionic surfactants was used for separation and preconcentration of Pd(II). The cloud point extraction (CPE) method is based on the formation of PdI2 which is then entrapped in the non-ionic surfactant Triton X-114. Ethanol acidified with 0.5 M HNO3 was added to the surfactant-rich phase prior to its analysis by flame atomic absorption spectrometry. The main factors affecting CPE efficiency, such as sample solution pH, concentration of iodide ion and Triton X-114, equilibration temperature and time, were all investigated and optimized. At optimum conditions, a calibration curve was constructed for the determination of palladium according to the ligandless CPE procedure. Linearity was maintained between 1.0 to 500.0 ng/mL. The LOD based on three times the SD of the blank divided by the slope of analytical curve, (3Sb/m) was 0.3 ng/mL. Seven replicate determinations of a solution containing of 4.0 µg palladium gave a mean absorbance of 0.359 with RSD ±1.85%. The high efficiency of CPE to carry out the determination of palladium in complex matrixes was demonstrated. The proposed method has been applied to the determination of trace amounts of palladium in a platinum-iridium alloy, water, and dust samples, with satisfactory results. [ABSTRACT FROM AUTHOR]

Abstract: In this work we report the impregnation of 16wt.% Pt and Ir on titania nanotubes. The metal load was fully dispersed on nanotubular support as Pt–Ir bimetallic particles of subnanometric size around 0.9nm and polyhedral morphologies. Larger Pt or Ir phase segregation was not observed. The impregnation and dispersion of the metals were made through the co-impregnation method by chemical vapor deposition modified. The reduction of both metallic salts was carried out under inert atmosphere at 400°C. The samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy using a relatively new technique as high angle annular dark field scanning transmission electron microscopy (STEM) with corrected-aberration and energy dispersive X-ray spectroscopy in the STEM mode. Concentrations of 8.94wt.% Ir and 7.27wt.% Pt in the sample were detected by SEM-EDX. Statistical analysis of the chemical composition performed on 50 single nanoparticles by STEM-EDX showed that all were bimetallic. The average chemical composition was around 56.6wt.% Ir and 43.4wt.% Pt. Nevertheless, the compositional distribution varied from 15 to 95wt.% Ir. [Copyright &y& Elsevier]

The National Institute of Standards and Technology (NIST) is responsible for the dissemination of the unit of mass within the United States of America through the national prototype kilogram K20 and its check standard K4. These platinum-iridium artifacts have been in use since 1889 and are periodically sent to the International Bureau of Weights and Measures (BIPM) for recalibration. The following is a brief description of the roles of the national prototype kilograms in the dissemination of mass in the United States of America, and the implications for NIST mass calibration customers of the most recent recalibrations of K20 and K4. [ABSTRACT FROM AUTHOR]

Abstract: Pt-Ir/HY and Pt-Mg-Ir/Al2O3 catalysts were studied and tested in the reaction of ring opening of decalin. The acidity of the alumina support was modified by addition of 3% Mg and the acidity of the zeolite by ion exchange with NH4Cl. The Pt content of the catalysts was fixed at 1% (mass basis) while the Ir content was adjusted between 0.1 and 0.6%. The catalysts were characterized by temperature programmed reduction, temperature programmed desorption of pyridine and FTIR of adsorbed CO. They were further tested with the reactions of cyclohexane dehydrogenation, cyclopentane hydrogenolysis and n-C5 isomerization. It was found that the Pt-Ir/HY catalyst was substantially more acid than Pt-Mg-Ir/Al2O3. Increasing the Ir content produced an increase of the hydrogenolytic activity and a decrease of the dehydrogenating activity of both catalysts. The n-pentane isomerization reaction results revealed that in the case of the alumina catalyst increasing the Ir content promoted both the catalyst stability and the cracking selectivity to C5 isomers. The opposite was found for the Pt-Ir/HY zeolite catalysts. The zeolite supported Pt-Ir catalysts performed better for decalin ring opening than those supported on alumina. Higher Ir content favored the formation of ring-opening products in all cases. [Copyright &y& Elsevier]

We present a near-field scanning microwave microscope (NSMM) that has been configured for imaging photovoltaic samples. Our system incorporates a Pt-Ir tip inserted into an open-ended coaxial cable to form a weakly coupled resonator, allowing the microwave reflection S11 signal to be measured across a sample over a frequency range of 1 GHz - 5 GHz. A phase-tuning circuit increased impedance-measurement sensitivity by allowing for tuning of the S11 minimum down to -78 dBm. A bias-T and preamplifier enabled simultaneous, non-contact measurement of the DC tip-sample current, and a tuning fork feedback system provided simultaneous topographic data. Light-free tuning fork feedback provided characterization of photovoltaic samples both in the dark and under illumination at 405 nm. NSMM measurements were obtained on an inhomogeneous, third-generation Cu(In,Ga)Se2 (CIGS) sample. The S11 and DC current features were found to spatially broaden around grain boundaries with the sample under illumination. The broadening is attributed to optically generated charge that becomes trapped and changes the local depletion of the grain boundaries, thereby modifying the local capacitance. Imaging provided by the NSMM offers a new RF methodology to resolve and characterize nanoscale electrical features in photovoltaic materials and devices. [ABSTRACT FROM AUTHOR]

With the increasing complexity of medical devices and with efforts to reduce manufacturing costs, challenges arise in joining dissimilar materials. In this study, the laser weldability of dissimilar joints between Pt-10 pct Ir and 316 low-carbon vacuum melted (LVM) stainless steel (SS) crossed wires was investigated by characterizing the weld geometry, joint strength, morphology of weld cross sections, and differences in joining behavior, depending on which material is subject to the incident laser beam. With the Pt-Ir alloy on top, a significant amount of porosity was observed on the surface of the welds as well as throughout the weld cross sections. This unique form of porosity is believed to be a result of preferential vaporization of 316 LVM SS alloying elements that become mixed with the molten Pt-10 pct Ir during welding. The joining mechanism documented in micrographs of cross-sectioned welds was found to transition from laser brazing to fusion welding. It is inferred that the orientation of the two dissimilar metals ( i.e., which material is subject to the incident laser beam) plays an important role in weld quality of crossed-wire laser welds. [ABSTRACT FROM AUTHOR]

Precise positioning of a stimulating electrode in the eye is not possible by simple visualization. However, reliable measurement of responses to retinal stimulation requires consistent positioning. The present study focuses on impedance measurement techniques to sense the proximity of the electrode to the retina. A platinum-iridium stimulation electrode was placed inside the rat eye and impedance was recorded at different positions of the stimulating electrode relative to the retina. The presence of robust electrically evoked response in the superior colliculus indicates that the electrode may not have to be in absolute contact in order to elicit a neural response. Optical coherence tomography imaging confirmed the distance-impedance relationship. [ABSTRACT FROM AUTHOR]

Abstract: A series of Pt–Ir thin films envisaged for application as fuel cell cathodic catalysts are deposited by dc co-sputtering from pure metal targets. To achieve different metal ratios, the sputtering power applied on the iridium target (P Ir) is varied in the range 0–100W at constant power of the Pt target (P Pt). The influence of the sputtering power on the film composition, morphology, and surface structure is analysed by energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The catalytic activity towards oxygen reduction reaction (ORR) is evaluated in sulphuric acid solutions applying the methods of cyclic voltammetry and potentiodynamic polarization curves. The performed morphological and electrochemical investigations reveal that catalytic efficiency of the co-sputtered Pt-Ir films is superior compared to pure Pt. The ORR is most intensive on the sample deposited at power ratio P Pt:P Ir =100:30W containing 11at.% Ir that has also the most developed active surface. The ORR current density for this film achieved at 0.825V in acid solution (4.1mAcm−2) is about 6 times higher than for pure Pt (0.67mAcm−2). The improved activity of the thin co-sputtered Pt-Ir over Pt allows for essential reduction of the catalyst loading at preserved performance. [Copyright &y& Elsevier]

The goal of this paper is to develop a quantitative understanding about the shape and the volume of tissue activated (VTA) and stimulation sites by deep brain stimulation (DBS) in deep brain area like subthalamic nucleus (STN) to improve neural stimulation. Monopolar current steering approach has been studied in cochlear implants and deep brain stimulation. In this paper, novel bipolar and tripolar current steering schemes are applied to deep brain stimulation. Finite-element models of deep brain stimulation are used to study the volume of tissue activated for monopolar, bipolar, and tripolar current steering configurations. [ABSTRACT FROM PUBLISHER]

Abstract: In this study co-sputtered layers of platinum–iridium (PtIr) are investigated as stimulation electrode material. The effects of different sputter parameters on the morphology and the electrochemical behavior are examined. It is shown that films sputtered at the lowest incident energy possess the highest charge storage capacity (CSC). At a Pt:Ir atomic-ratio of 55:45 the obtained CSC of 22mC/cm2 is enhanced compared to the standard stimulation material platinum (16mC/cm2) but inferior to iridium which has a CSC of 35mC/cm2. Long term cyclic voltammetry measurements show that PtIr can be activated which increases the CSC to 29mC/cm2. Also a change in the film morphology is observed. Sputtered platinum–iridium films promise to combine high mechanical strength and increased charge storage capacity. [Copyright &y& Elsevier]

The phase-shift method and correlation constants, which are unique electrochemical impedance spectroscopy techniques for studying the linear relationship between the phase shift (90° ≥ −φ ≥ 0°) versus electric potential (E) behavior for the optimum intermediate frequency and the fractional surface coverage (0 ≤ θ ≤ 1) vs Ebehavior, are proposed and verified to determine the Frumkin, Langmuir, and Temkin adsorption isotherms and related electrode kinetic and thermodynamic parameters. On a Pt−Ir [90:10 % (by weight)] alloy in 0.5 M H2SO4aqueous solution, the Frumkin and Temkin adsorption isotherms (θ vs E), equilibrium constants [K= 3.3 · 10−5exp(2.5θ) mol−1for the Frumkin and K= 3.3 · 10−4exp(−2.1θ) mol−1for the Temkin adsorption isotherm], interaction parameters (g= −2.5 for the Frumkin and g= 2.1 for the Temkin adsorption isotherm), standard Gibbs energies of adsorption of overpotentially deposited (OPD) H [(25.6 ≥ ΔGθ0≥ 19.4) kJ·mol−1for K= 3.3 · 10−5exp(2.5θ) mol−1and 0 ≤ θ ≤ 1 and (20.9 0) interaction between the adsorbed OPD H species appears. On Pt, Ir, and Pt−Ir alloys in 0.5 M H2SO4aqueous solution, the values of Kfor the Frumkin adsorption isotherms of OPD H decrease with increasing mass ratio of Ir. Negative values of gfor the Frumkin adsorption isotherms of OPD H on the Pt, Ir, and Pt−Ir alloys in acidic and alkaline H2O and D2O solutions are experimentally and consistently determined. The duality of the lateral attractive and repulsive interactions is a unique feature of the adsorbed OPD H species on the Pt, Ir, and Pt−Ir alloys in acidic and alkaline H2O and D2O solutions. [ABSTRACT FROM AUTHOR]

Abstract: Plating bath concentrations of Pt(IV) and Ir(III) have been optimized as well as the total catalytic loading of bimetallic Pt–Ir alloy for the electro-oxidation of ammonia in alkaline media at standard conditions. This was accomplished using cyclic voltammetry, scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and statistical optimization tools. Concentrations of Pt(IV) and Ir(III) of the plating bath strongly influence electrode surface atomic compositions of the Pt–Ir alloy directly affecting the electro-oxidation behavior of ammonia. Several anode materials were studied using cyclic voltammetry, which demonstrated that Pt–Ir was the most active catalyst for the electro-oxidation of ammonia. Criteria for optimization were minimizing the climatic oxidation overpotential for ammonia and maximizing the exchange current density. Optimized bath composition was found to be 8.844±0.001gL−1 Pt(IV) and 4.112±0.001gL−1 Ir(III) based on electrochemical techniques. Physical characterization of the electrodes by SEM indicates that the plating bath concentrations of Pt and Ir influence the growth and deposition behavior of the alloy. [Copyright &y& Elsevier]

Abstract: Pt based catalysts are commonly used in several industrial processes involving hydrogenation and dehydrogenation reactions. New deposition methods as well as support materials are being investigated to generate new catalysts with superior catalytic activity. In this work, platinum-iridium (Pt-Ir) nanoparticles of about 5nm in size were supported on titania (TiO2) nanotubes by metal organic chemical vapor deposition (MOCVD). The TiO2 nanotubes were prepared by an alkali hydrothermal method using sodium hydroxide solution at 100°C, during 64.8ks. Pt-Ir nanoparticles were obtained by controlling the MOCVD conditions at 400°C and 66.6kPa. Textural properties and particle size were investigated by nitrogen physisorption (BET method), X-ray diffraction, Raman spectroscopy and high resolution transmission electron microscopy. Catalytic activity was measured in cyclohexene disproportion as the test molecule for hydrogenation/dehydrogenation reactions. The TiO2 nanotubes exhibit a considerable high surface area of about 425,000m2/kg, however, after calcination at 400°C their nanotubular morphology was partially transformed. In spite of this change, the 5nm Pt-Ir nanoparticles supported on TiO2 nanotubes were more active in the cyclohexene disproportion reaction than conventional Pt-Ir/alumina catalysts in the whole range of temperatures investigated (50–250°C). Hydrogenation reactions (high selectivity to cyclohexane) predominate at temperatures below 150°C. [Copyright &y& Elsevier]

Abstract: Surface reconstructions on Pd, Pd/5wt.% Ni, Ag, Ir, Pt/10wt.% Ir, Pt/20wt.% Ir, and Au wire-shaped specimens have been studied after ammonia oxidation at 900°C and atmospheric pressure. The tested specimens were examined by powder X-ray diffraction, electron microprobe analysis, and scanning electron microscopy. Extensive surface reconstructions, with numerous pits, well developed facets, and “cauliflower”-like excrescences were, except for Au, observed on all tested specimens. Neglecting Au, the tested catalyst materials were active for oxidation of NH3 to NO, however, the selectivity and effective lifetime of these catalysts are strongly composition dependent. Au did not catalyze ammonia oxidation and its surface reconstructions are negligible. Solid oxides of NiO, PdO and IrO2 were identified on the surfaces of Pd–Ni, Pd, and Ir specimens, respectively. The results are discussed in relation to findings for Pt–Rh alloy catalysts, for which surface reconstruction is attributed to chemical-vapor-transport reactions driven by local temperature gradients between hotspots and colder regions on the catalyst surface. [Copyright &y& Elsevier]

High-frequency stimulation (HFS) of deep brain structures is a powerful therapeutic tool for the treatment of various movement disorders in patients. However, the pathophysiological mechanisms of this therapeutic approach on basal ganglia network function are still largely unknown. Hitherto, experimental studies have focused on short-term stimulation. Since patients receive HFS for many years, animal studies which reproduce the conditions of long-term stimulation will be necessary to accurately investigate the effects of HFS.However, stimulation parameters of acute HFS cannot be easily transferred to long-term conditions. Accordingly, for this purpose we studied the influence of different charge densities (0, 3, 6.5, 13 and 26 μC/cm2/phase) and duration (4 h or 3 days) of subthalamic nucleus (STN)-HFS using stainless-steel and platinum–iridium (Pt/Ir) electrodes on neuronal tissue damage in rats.Our data demonstrate the advantage of Pt/Ir over stainless-steel electrodes when used in short-term HFS (frequency 130 Hz, pulse width 60 μs) and indicate that HFS using Pt/Ir-electrodes pulsed with 3 μC/cm2/phase over 3 days did not produce any relevant tissue damage in the STN. [Copyright &y& Elsevier]

Electrochemical processes at the electrode–electrolyte (body fluid) interface are of ultimate importance for stimulating/sensing electrode function. A high electrode surface area is desirable for safe stimulation through double-layer charging and discharging. Pt and Pt–Ir alloys have been the most common electrode materials. The use of TiN coating as the surface layer on the electrode has found increasing interest because of its metal-like conductivity, excellent mechanical and chemical properties, and the fact that it can be deposited with a high surface area. In this work, electrochemical impedance spectroscopy (EIS), which is a sensitive and non-destructive technique and widely used for characterization of electrical properties of electrode–electrolyte interfaces, was applied to investigate pure Pt and Ti, and TiN coated electrodes exposed to a phosphate-buffered-saline (PBS) solution. Platinized Pt and Ti were also studied for comparison. The capacitance value of the electrodes in PBS was obtained through quantitative analysis of the EIS spectra. The results reveal that the capacitance of the TiN coated electrodes with a rough surface is several hundreds times higher than that of a smooth Pt surface. Platinization of Ti can also increase the capacitance to the same extent as platina. EIS has been shown to be a powerful technique for characterization of stimulating/sensing electrodes. [Copyright &y& Elsevier]

(1) Oxygen flux in waterlogged forest soils can be measured using the platinum microcathode technique. By automatically scanning a predetermined voltage range applied to each set of up to twenty-four microcathodes in turn, the instrument described produces a set of polarograms from which a flux-derived current can be unambiguously determined. (2) Examples of different types of polarogram are given and the degree of desaturation is indicated by the shape of the polarogram. (3) The robust microcathodes are made of a hard platinum-iridium alloy cased in resin-impregnated glass fibre, the whole instrument being rugged, portable and capable of running unattended in adverse environments. (4) Applied potential and scanning rate can be preselected, usually 0 to --500 mV at 33 mV min[sup-1]. (5) Difficulty in extrapolating transient to steady state diffusion and the uncertainty associated with the exact cathodic process involved are discussed. [ABSTRACT FROM AUTHOR]

The application of low level direct current with a current density of 50 μa/cm2 within the mandible of mature Beagle dogs results in an increased osteogenesis about the negative electrode (cathode). Significant differences observed between the use of platinum-iridium and stainless-steel electrodes suggest careful consideration of appropriate current density and electrode composition when direct current stimulation is to be used. [ABSTRACT FROM AUTHOR]

The charge-injection limits of activated iridium oxide electrodes (AIROF) and PtIr microelectrodes with similar geometric area and shape have been compared in vitro using a stimulation waveform that delivers cathodal current pulses with current-limited control of the electrode bias potential in the interpulse period. Charge-injection limits were compared over a bias range of 0.1-0.7 V (versus Ag∣AgCI) and pulse frequencies of 20, 50, and 100 Hz. The AIROF was capable of injecting between 4 and 10 times the charge of the PtIr electrode, with a maximum value of 39 mC/cm² obtained at a 0.7 V bias and 20 Hz frequency. [ABSTRACT FROM AUTHOR]

Objective . The implantation of intraneural electrodes in amputees has been observed to be effective in providing subjects with sensory feedback. However, this implantation is challenging and time consuming. Surgeons must be especially trained to execute the implantation. Therefore, we aimed at developing a novel peripheral intraneural electrode and insertion mechanism, which could drastically reduce the overall implantation time while achieving a high neural selectivity. Approach. A new insertion method based on hollow microneedles was developed to realize the prompt and effective simultaneous implantation of up to 14 active sites in a transversal manner. Each needle guided two Pt/Ir microwires through the nervous tissue. After the insertion, the microneedles were released, leaving behind the microwires. Each microwire had one active site, which was coated with poly-3,4-ethylenedioxythiophene (PEDOT) to enhance the electrochemical properties. The active sites were characterized by evaluating the impedance, charge storage capacity, and maximum injectable charge. Twelve quick to implant peripheral intraneural electrodes (Q-PINEs) were implanted in four pig sciatic nerves to evaluate the implantation time and neural selectivity. We compared the stimulation of the sciatic nerve with that of its branches. Main results . The average surgical access time was 23 min. The insertion time for 12 electrodes was 6.7 min (std. ±1.6 min). The overall implantation time was reduced by 40.3 min compared to the previously reported values. The Q-PINE system demonstrated a satisfactory performance during in vitro and in vivo characterization. The electrochemical results showed that the PEDOT coating successfully increased the electrochemical parameters of the active sites. Significance. With an average impedance of 1.7 kΩ, a maximum charge level of 76.2 nC could be achieved per active site. EMG recruitment curves showed that 46% of the active sites exhibited selective stimulation of four out of six muscles. The histological analysis indicated that the microwires successfully penetrated the nerve and single fascicles., (Creative Commons Attribution license.)

Two absolute composition depth profiles of single atomic layer depth resolution have been obtained for the (001) surface of a Pt-20% Ir alloy. Pt segregates only to the top two surface layers. A feature of a diffusion kinetic effect has also been observed from which diffusion parameters of alloy species in the near surface layers are estimated. [ABSTRACT FROM AUTHOR]

In this paper, we present the synthesis, characterization, catalytic and computational studies of Composites of Platinum-Iridium Alloy Nanoparticles and Graphene Oxide (PtIr@GO) for dimethylamine borane (DMAB) dehydrogenation. The prepared PtIr@GO nanocatalysts were synthesized using an ethanol super-hydride method, and the characterization procedures for PtIr@GO alloy nanoparticles were carried out by various advanced spectroscopic methods like X-ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Transmission Electron Microscopy(TEM) and high-resolution transmission electron microscopy (HRTEM). Additionally, catalytic activity, reusability, substrate concentration, and catalyst concentration experiments were performed for DMAB dehydrogenation catalyzed by PtIr@GO alloy nanomaterials. According to the results obtained in this study, PtIr@GO NPs catalyst was found to be active and reusable for the DMAB even at ambient conditions. Besides, DFT-B3LYP calculations have been utilized on PtIr@GO cluster to reveal the prepared catalyst activity. The calculated findings based on DFT was found to be a good agreement with experimental results. [ABSTRACT FROM AUTHOR]

The article offers a list of scientific research papers from several Chinese academic journals and includes 'New digital simulation of a quantum system', 'Platinum–iridium nanocubes with enhanced catalytic activity', and 'Trapping light to improve efficiency of solar cells'.

Platinum-iridium films (Ir = 0, 32, 46, 83, 100 at.%) were deposited on the nickel-base single crystal superalloy through magnetron sputtering. After annealing and aluminizing, the Pt-Ir modified aluminide coatings mainly consisted of PtAl2 and β-(Ni,Pt,Ir)Al phases. Hot corrosion resistance of Pt-Ir modified aluminide coatings with the different Ir contents were evaluated by exposure at 1173 K in the presence of the 90%Na2SO4 + 10%NaCl (wt%) salt deposits. The corrosion kinetics curves of the specimens were plotted up to 100 h heating time. The phase constitution, morphology of corrosion products, and element concentrations along the cross section were also measured. The lowest mass gain (0.299 mg/cm2, after 100 h) was observed for Pt-46Ir aluminide coating because the dense and continuous protective Al2O3 scale formed. Phase transformation from β-(Ni,Pt)Al to ?'-(Ni,Pt) 3Al, characteristics of the scale, and protection by Pt/Ir enriched layer had the important effects on the hot corrosion behavior of modified aluminide coatings. [ABSTRACT FROM AUTHOR]

A new method of producing Pt-Ir tips for use in scanning tunneling microscopy is described. This reproducible method is simple, cheap, fast, and avoids the use of hazardous chemicals common in many other methods. Scanning electron microscopy, time of flight-secondary ion mass spectroscopy, and x-ray photoelectron spectroscopy have been applied to understand both the chemical and morphological changes that occur as a result of the etching. The method has been demonstrated on both stock Pt-Ir wire and commercial tips and has been found to dramatically enhance image quality. It is also reusable on the same tip extending the lifetime of a single tip indefinitely. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The clinical use of chronic electrode implants for measurement or stimulation of neuronal activity has increased over the past decade with the advent of deep brain stimulation and the use of brain-computer interfaces. However, despite the wide-spread application of electrode implants, their chronic use is still limited by technical difficulties. Many of the reported issues, ranging from short-circuits to loss of signal due to increased electrical impedance, may be traced back to the reaction of the cortical tissue to the implanted devices: the foreign body response (FBR). This response consists of several phases that ultimately result in neuronal loss and the formation of a dense glial sheath that encapsulates the implant. Empirical evidence suggests that reducing the FBR has a positive effect on the electrical properties of implants, which can potentially expand their clinical use by improving their chronic usability. The primary focus of this work is to review the consequences of the FBR and recent developments that can be considered to control and limit its development. We will discuss how the choice of device material and electrode-architecture influences the tissue reaction, as well as modifications that allow for less stiff implants, increase electrode conductivity, or improve the implant-tissue integration. Several promising biological solutions include the local release of anti-inflammatory compounds to weaken the initial inflammatory phase of the FBR, as well as methods to diminish the negative effects of the glial sheath on neuronal regrowth., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Reports that scientists at the National Institute of Standards and Technology are exploring ways to replace Le Gran K, the platinum-iridium cylinder that has served as the standard for the kilogram. Disadvantages of using an artifact as a standard; Use of x-ray techniques to measure the lattice spacing of silicon crystals; Determining Avogradro's number.