Iridium Alloy Research Articles

Surface morphology and oxidation products of DOP-26 iridium alloy upon high-temperature exposure to air

The DOP-26 Ir alloy is employed for fuel sealing in isotope batteries and exhibits superior oxidation resistance at high temperatures under low oxygen conditions. This study investigated the oxidation behavior of the DOP-26 Ir alloy in air, focusing on the correlation between the oxidation temperature and time. X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy were conducted to examine the phase, morphology, and valence of the alloy upon oxidation. The findings provide a comprehensive understanding of the high-temperature oxidation kinetics of DOP-26 Ir alloy in the air, and these results could potentially be applied to the design and application of radioisotope thermoelectric generators.

Magnetic Field Enhanced Cobalt Iridium Alloy Catalyst for Acidic Oxygen Evolution Reaction.

Magnetic field mediated magnetic catalysts provide a powerful pathway for accelerating their sluggish kinetics toward the oxygen evolution reaction (OER) but remain great challenges in acidic media. The key obstacle comes from the production of an ordered magnetic domain catalyst in the harsh acidic OER. In this work, we form an induced local magnetic moment in the metallic Ir catalyst via the significant 3d-5d hybridization by introducing cobalt dopants. Interestingly, CoIr nanoclusters (NCs) exhibit an excellent magnetic field enhanced acidic OER activity, with the lowest overpotential of 220 mV at 10 mA cm-2 and s long-term stability of 120 h under a constant magnetic field (vs 260 mV/20 h without a magnetic field). The turnover frequency reaches 7.4 s-1 at 1.5 V (vs RHE), which is 3.0 times higher than that without magnetization. Density functional theory results show that CoIr NCs have a pronounced spin polarization intensity, which is preferable for OER enhancement.

Effect of Y on Arc Breaking Behavior of Platinum–Iridium Alloy Contact Materials at Different Voltages

The Pt–Ir alloy is an important electrical contact material in the aerospace field, and its electrical contact performance directly affects the reliability and stability of the circuit system. In order to elucidate the effect of Y on the breaking arc behavior of Pt–Ir alloys at different voltages, Pt-10Ir-1Y and Pt-25Ir-1Y alloys were prepared using melting and thermal processing, and the electrical contact tests were carried out at DC 15 A 12 V, 24 V, and 36 V. When comparing the results of Pt-10Ir and Pt-25Ir electrical contact tests, they showed that Y doping provided a tendency to concentrate individual arc erosion regions. Meanwhile, the comparative study showed that the addition of Y could inhibit the tendency of the Pt–Ir arc time to increase with voltage. At 36 V, the overall arc time of Pt–Ir–Y was significantly lower than that of Pt–Ir, and the fluctuation in arc time and arc energy was reduced. In addition, Y reduced the welding force of Pt–Ir alloys at 12 V, while Y improved the stability of the welding force of Pt–Ir alloys at 24 V. It could be seen that Y was favorable to improving the arc erosion resistance of the Pt–Ir alloy under certain conditions. The contact resistance analysis showed that there was an obvious partitioning phenomenon in the contact resistance of Pt–Ir alloys, and Y changed in this phenomenon at a certain voltage range. In addition, the material transfer direction of the Pt–Ir alloy was from the anode to the cathode, which was not affected by the voltage change, while the addition of Y changed the material transfer direction from the cathode to the anode, which was likely caused by the change from the metal-phase arc dominance to gas-phase arc dominance.

Iridium and gold alloy beta gallium oxide expected to achieve p-type conductivity

The beta monoclinic gallium oxide (β-Ga2O3) is a wide-bandgap material with promising applications in high-power electronics, but bottleneck problem of p-type conductivity has become the biggest obstacle to device performance improvement. The effective p-type doping can be achieved in β-(Ir x Au y Ga1-x-y )2O3 alloys, promising to be synthesised in the laboratory, from an energy perspective. The β-(Ir x Ga1-x )2O3 exhibits an extended valence band with a maximum of 1.94 eV at the edge of the valence band. The location and bandwidth of the extended valence band can be changed with the Ir concentration. The Au substitution at the Ga(2) site actually creates a relatively shallow level, contrary to the expected deep acceptors. The 2p orbital of the O atom easily coupling with the doped atomic orbital to appear as a hole-polaronic state, while the higher energy of the Au-doped hole state avoids coupling with the valence band maximum of the host material. Theoretical feasibility of p-type doping of β-(Ir x Au y Ga1-x-y )2O3 is achieved.

Optimization of process parameters for hot isostatic pressing of Ir–Rh alloys based on first-principles calculations

In this paper, the effect of Rh content on the mechanical properties of Ir–Rh alloys was investigated based on first-principles density functional theory. The calculated results show that when the Rh content is small, the three elastic moduli (elastic modulus (B), shear modulus (G), and Young’s modulus (E)) of Ir–Rh alloy increase rapidly with the increase of Rh content. They reach a maximum value at Ir–10Rh and then decrease, before rising slowly at Ir–40Rh and then gradually decreasing again. This shows that adding a small amount of rhodium to iridium can effectively improve the strength and hardness of iridium. Among all the components of the selected Ir–Rh alloys, Ir–10Rh has the highest hardness and strength. The addition of Rh can cause the embrittlement of Ir–Rh alloys, and its brittleness first increases and then decreases with the increase of Rh content, and reaches the highest at Ir–50Rh. Considering the results obtained from theoretical calculations and experiments, Ir–20Rh was selected as the alloy composition for the study of hot isostatic pressing technology. The effects of mixing time, whether to mix powder with balls, and degassing temperature on the properties of metal powders were studied to find the best mixing and degassing process parameters. In the experiment of mixing powder for the iridium and rhodium alloy, it is found that the time required for mixing powder with balls to reach uniformity was shorter than that without balls. The oxygen content of the final mixed powder obtained by the two processes is the same. The nitrogen content of the metal powder mixed with the ball is slightly higher than that without the ball, but it can be reduced to below 0.001% after the degassing process. During the sintering process, with the increase in temperature, the mutual diffusion speed between iridium powder and rhodium powder increases, the sintering neck grows, the internal pores decrease, and the density of the sintered body increases. Therefore, the final decision process is to select mixing with balls for 10 h, degas at 1200 °C for 2 h, and then raise the temperature to 1800 °C for sintering. With the increase of hot isostatic pressing temperature and pressure, the density of the alloy increases. When the highest temperature (1300 °C) and highest pressure (140 MPa) are used for hot isostatic pressing for 2 h, the density can reach 95.7% of the theoretical density.

Performance of in situ oxidized platinum/iridium alloy Schottky contacts on (001), (2¯01), and (010) β -Ga2O3

The performance of β-Ga2O3 Schottky contacts (SCs) fabricated using amorphous, intentionally oxidized platinum–iridium alloys was investigated as a function of alloy composition and β-Ga2O3 crystal orientation. PtyIr(1−y)Ox SCs with Pt fractions of y = 0.8, 0.5, and 0.3 were deposited on (001), (2¯01), and (010) single-crystal β-Ga2O3 substrates via the reactive rf and dc co-sputtering of Pt and Ir targets using oxygen–argon plasmas. In each case, the PtyIr(1−y)Ox SCs were highly rectifying with current rectification ratios (at ±3 V) of 11/10/9 orders of magnitude (at 300 K) for the (001)/(2¯01)/(010) β-Ga2O3 substrates. Current–voltage (I–V) and capacitance–voltage (C–V) measurements revealed that the Pt0.5Ir0.5Ox SCs contained the highest Schottky barriers on all β-Ga2O3 crystal faces, with the best contacts having ideality factors of 1.05 and image-force-corrected I–V and C–V determined barrier heights of 2.10 and 2.20 eV, respectively. These were consistently higher by ∼0.2 eV than the corresponding barriers for the Pt0.8Ir0.2Ox and Pt0.3Ir0.7Ox SCs, with the Pt0.5Ir0.5Ox SCs also having significantly lower reverse leakage currents (in the 0 to −100 V range). In comparison, the barrier heights of the best unoxidized plain-metal Pt0.5Ir0.5 SCs were only ∼1.2 eV, illustrating the effectiveness of in situ oxidation in improving the performance of PtIr SCs. All PtyIr(1−y)Ox SCs on (2¯01) β-Ga2O3 showed excellent high-temperature performance with rectification ratios (at ±3 V) of 109 at 300 °C and of 106 at 500 °C.

Controllable fabrication of a nickel–iridium alloy network by galvanic replacement engineering for high-efficiency electrocatalytic water splitting

A Ni–Ir alloy network electrocatalyst, which is prepared via a galvanic replacement engineering route, presents remarkable electrocatalytic properties for both the HER and the OER due to its porous architecture and synergistic effect between Ni and Ir.

Thermal analyses of high-power advanced thermoacoustic radioisotope power system for future space exploration missions

This paper presents the results of 3-D thermal analyses of the heat source assembly of a 440 We advanced radioisotope power system (RPS) for future space exploration missions. This high thermal efficiency RPS employs a heat source assembly of eight Step 2 General Purpose Heat Source (GPHS) modules and four Thermoacoustic Power Converter (TAPC) units. Each unit is thermally coupled to two GPHS modules. The analyses investigated the temperatures of the Iridium (Ir) alloy cladding of the 238PuO2 fuel pellets and the surface of the Fine Weave Pierced Fabric (FWPF) aeroshell in the GPHS modules to ensure reliable operation and safety in case of an unlikely reentry. Conductive coupling of the GPHS modules to the heater heads of the TAPC units produces relatively uniform axial and azimuthal distributions of heat flux and temperature. However, for this case the temperature of the Ir alloy cladding is lower than the desired values of 1173 K to maintain sufficient ductility. Adding a 5 mm wide He filled gap and decreasing the thickness of the graphite sleeve to 10 mm increased Ir cladding temperature to 1197–1174 K, which are in the desired range. The maximum surface temperatures of the FWPF graphite aeroshell of 1022–1131 K is well below the NASA specified limit of 1373 K. In addition, the total mass of the heat source assembly decreased by 19.6 kg, ∼43% saving compared to original design.

Mechanical and thermoelectric properties of iridium-ruthenium alloy grown by the micro-pulling-down method

Iridium, ruthenium, and iridium-ruthenium alloy wires were fabricated by the dewetting micro-pulling-down method, a type of unidirectional solidification method. The length of the grown Ir-20Ru reached 47 m. Furthermore, their mechanical and thermoelectric properties were investigated. The as-grown Ir-17.9Ru wire exhibited a tensile strength of approximately 765 MPa and a nominal fracture elongation of 21% at room temperature. After work-hardening by three cycles of winding and rewinding for a bending radius of 10 mm and annealing at 2273 K for 3 h, the tensile strength and fracture elongation of the Ir-Ru wire were 1061 MPa and 25%, respectively. From the electromotive force (EMF) characteristics of platinum obtained by integrating the Seebeck coefficient, the EMF characteristics from room temperature to ~ 2000 K of iridium, ruthenium, and Ir-17.9Ru were investigated. The EMF characteristics for several thermocouples using iridium, ruthenium, or Ir-17.9Ru as one of the pairs were estimated from the combination of the obtained EMF characteristics. Ir/Ir-17.9Ru showed similar EMF characteristics to Ir-40Rh/Ir.

In-situ oxidation of Palladium–Iridium nanoalloy anchored on Nitrogen-doped graphene as an efficient catalyst for methanol electrooxidation

Palladium (Pd)-based materials have been widely used as catalysts for the methanol oxidation reaction (MOR). Unfortunately, the catalytic activity was limited by structure, carbon monoxide intermediates (COads) tolerance and stability. It was currently difficult to be used in large-scale commercial production. Herein, to further improve their electrocatalytic activity, a facile oxidation method to achieve in-situ oxidation of palladium–iridium (PdIr) alloy on nitrogen-doped graphene (NGS) is used, which is named as Pd-Ir-O/NGS. The new catalyst exhibits remarkable MOR activity (1374.8 mA mg−1), COads tolerance (the onset oxidation potential reach 0.725 V) and stability (the current density retention rate after 500 cycles of cyclic voltammetry is 44.9%). As a catalyst for MOR, the Pd-Ir-O/NGS has more outstanding electrocatalytic performance compared with commercial Pd/C and other counterparts. The mechanism study shows that the excellent catalytic performance is attributed to (1) the synergistic electronic effect of Pd-Ir-O due to the introduction of Ir and O, (2) the insertion of O into PdIr alloy that kinetically accelerated the oxidation of poisoning methoxy intermediates and (3) the vital roles of unique three-dimensional (3D) structure of NGS with abundant nitrogen atoms. Our findings herald a new paradigm for the modification of palladium-based materials for MOR and provide an alternative design principle for novel 3D carbon-based material for various application.

Nickel Structures as a Template Strategy to Create Shaped Iridium Electrocatalysts for Electrochemical Water Splitting.

Low-cost, highly active, and highly stable catalysts are desired for the generation of hydrogen and oxygen using water electrolyzers. To enhance the kinetics of the oxygen evolution reaction in an acidic medium, it is of paramount importance to redesign iridium electrocatalysts into novel structures with organized morphology and high surface area. Here, we report on the designing of a well-defined and highly active hollow nanoframe based on iridium. The synthesis strategy was to control the shape of nickel nanostructures on which iridium nanoparticles will grow. After the growth of iridium on the surface, the next step was to etch the nickel core to form the NiIr hollow nanoframe. The etching procedure was found to be significant in controlling the hydroxide species on the iridium surface and by that affecting the performance. The catalytic performance of the NiIr hollow nanoframe was studied for oxygen evolution reaction and shows 29 times increased iridium mass activity compared to commercially available iridium-based catalysts. Our study provides novel insights to control the fabrication of iridium-shaped catalysts using 3d transition metal as a template and via a facile etching step to steer the formation of hydroxide species on the surface. These findings shall aid the community to finally create stable iridium alloys for polymer electrolyte membrane water electrolyzers, and the strategy is also useful for many other electrochemical devices such as batteries, fuel cells, sensors, and solar organic cells.

Facile fabrication of ultrafine nickel-iridium alloy nanoparticles/graphene hybrid with enhanced mass activity and stability for overall water splitting

• A facile and general method was developed for fabricating Ni-Ir alloy nanoparticles/graphene electrocatalysts. • The incorporation of Ir into metallic Ni lattice greatly improves the intrinsic activity for HER and OER. • The bifunctional catalyst shows much higher electrochemical performance than commercial 20 wt% Ir/C. Developing active and durable electrocatalysts for overall water splitting is desirable but challenging to realize sustainable hydrogen production. Here, we report a facile and general method to prepare ultrafine nickel (Ni)-iridium (Ir) alloy nanoparticles/graphene hybrids for overall water splitting. The optimized hybrid with 4.9 wt% Ir exhibits much higher catalytic activity and durability than commercial 20 wt% Ir/C for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Theoretical simulations reveal that the incorporation of Ir in metallic Ni lattice regulates hydrogen adsorption free energy to the optimum level, thus improving HER activity, while in situ generated amorphous Ir-Ni hydr(oxy)oxides around metallic Ni-Ir core have been demonstrated to be the active species under OER conditions, which switches OER rate-determining step to energy-favorable pathway. The overall water splitting electrolyzer assembled by the optimized electrocatalyst shows a low cell voltage of only 1.52 V and excellent stability to deliver a current density of 10 mA cm −2 . This work provides a powerful strategy toward general synthesis of ultrafine alloy nanoparticles for high-performance overall water splitting. Ultrafine nickel-iridium alloy nanoparticles/graphene hybrids serve as highly efficient bifunctional electrocatalysts for overall water splitting. The incorporation of Ir greatly improves the reaction kinetics for hydrogen evolution reaction and oxygen evolution reaction.

Microstructure and Isothermal Oxidation of Ir-Rh Spark Plug Electrodes.

High-temperature oxidation tests were performed on pure iridium, rhodium, and the iridium alloys, IrRh10, IrRh25, and IrRh40, at 1100 °C in a stable air environment for 60 h. The results of the oxidation were analyzed by X-ray photoelectron spectroscopy (XPS). Microstructural changes of the Ir–Rh alloys were characterized by scanning electron microscopy (SEM). XPS analysis results show that the main oxide of the Ir–Rh alloy in a 1100 °C environment was Rh2O3, and SEM analysis shows that the surfaces of the Ir–Rh alloys after oxidation formed both linear and ellipse-shaped corrosion pits, and had the same direction with the wire-drawing process. The oxidation behavior of Ir–Rh alloys, including the mass change, the reason for the mass loss, and the role of Rh in improving oxidation resistance performance, are discussed.

Research on rhenium–iridium alloy coating on microgroove molds in precision glass molding

There is an increasing demand for microgrooves in optical systems with a pitch at wave length level. Precision glass molding (PGM) is one of the most efficient methods for fabricating microgrooves on glass surface. Nickel–phosphorus (Ni–P) exhibits excellent cutting properties and is developed as the mold material for glass microgrooves. However, the phosphorus in Ni–P mold tends to diffuse into the glass during the PGM process at high temperatures, which may reduce the optical performance of the molded glass microgroove component. In addition, the atomic diffusion increases the interface friction coefficient between the glass and the mold, resulting in the decrease of molding accuracy of the microgroove array. To solve these problems, a rhenium–iridium (Re–Ir) alloy coating is deposited on the surface of the Ni–P microgroove mold by ion sputtering. In this paper, the surface roughness of the mold before and after coating with Re–Ir alloy coating is investigated. The mechanical properties of Ni–P and the Re–Ir alloy coating are obtained using a combination of finite element method (FEM) and experimental tests. The mold deformation after heating to the molding temperature is analyzed. The results show that the mechanical properties of the Ni–P mold surface can be strengthened after being plated with Re–Ir alloy coating, the Re–Ir coating isolates the diffusion of phosphorus from the Ni–P mold, and improve the forming accuracy of glass microgrooves.

The degradation of Pt/IrOx oxygen bifunctional catalysts

Platinum and iridium mixtures or alloys are the state-of-the-art bifunctional oxygen catalysts for unitized regenerative fuel cells (URFCs). Recently, we have shown that the degradation of these catalysts represents a serious challenge. In this work we explore the degradation mechanisms further by considering different catalysts and experimental conditions. For this, Pt/IrOx with varying Pt to Ir ratios are synthesized and their performances are evaluated. It is found that catalysts with higher Pt and Ir contents have higher oxygen reduction (ORR) and evolution reaction (OER) activities, respectively. The materials stability is investigated under a potential pulses protocol. Using on-line dissolution analysis, it is found that, besides the transient Pt dissolution identified in the previous works, continuous dissolution of Ir during the OER must be considered. The latter is assigned to a continuous formation of common OER and Ir dissolution intermediates. Further, identical location microscopy is employed to reveal the changes in the catalyst layer structure and morphology. It is shown that dissolution triggers significant particles agglomeration/coalescence, which are the main causes for the catalysts degradation. These processes must be attenuated for a feasible long-term application of Pt/IrOx materials as bifunctional oxygen catalyst.

Thermal analyses of heat source assembly for a dual loop, Turbo-Brayton Radioisotope power system

This paper presents the results of 3-D thermal analyses of the heat source assembly (HSA) for a dual-loop, Turbo-Brayton Radioisotope Power System (RPS) for generating in excess of 300 We. The HSA with 6 Step 2 General Purpose Heat Source (GPHS) modules, is thermally coupled to two Brayton loops, each with a 300 We Turbo-Brayton unit. Results show that with either vacuum or helium gas in all internal gaps and voids of the GPHS modules the temperatures of the 238PuO2 fuel pellets, the Iridium (Ir) alloy cladding, and the Fine Weave Pierced Fabric (FWPF) aeroshell are largely within safe margins. With vacuum in all internal gaps and voids, the highest aeroshell is 1271 K which is 102 K below the NASA specified maximum of 1373 K to limit potential heating of the Ir-alloy cladding during an unlikely reentry. The Ir alloy cladding temperature is ≥300 K above the suggested low limit of 1173 K, and ≥112 K below its recrystallization temperature of 1603 K. With helium gas in all internal gaps and voids, the highest surface temperature of the aeroshell is ≥145 K below 1373 K, while that of the Ir-alloy cladding is 80 K above the suggested minimum temperature (1173 K) to maintain ductility and 326 K below that for recrystallization and the onset of grain growth.

Excavated cubic platinum–iridium alloy nanocrystals with high-index facets as highly efficient electrocatalysts in N2 fixation to NH3

Excavated cubic Pt93Ir7 alloy nanocrystals enclosed by high-index {710} facets exhibit excellent electrocatalytic properties for the nitrogen reduction reaction (NRR) with a high faradaic efficiency (40.8%) and NH3 production rate (28 μg h-1 cm-2). The presence of Ir on the Pt stepped surface suppresses the hydrogen evolution reaction (HER) and accelerates the NRR.

Nanostructured Catalysts of Methanol Electrooxidation Based on Platinum–Ruthenium–Palladium and Platinum–Ruthenium–Iridium Alloys Derived from Coordination Compounds

Activities of the synthesized trimetallic catalysts PtRuPd/C and PtRuIr/C supported on highly dispersed carbon soot from solutions of coordination compounds of the corresponding metals are studied in the electrooxidation of methanol. According to the data of voltammetry, the Pt0.43Ru0.47Pd0.1/C and Pt0.44Ru0.46Ir0.1/C catalysts are not inferior to the commercial catalyst Pt0.5Ru0.5/C in specific characteristics, which is consistent with the data of structural studies and the electrochemical and power characteristics of the membrane electrode unit tested in the composition of a single methanol/air fuel cell.

Bimetallic palladium–iridium alloy nanoparticles as highly efficient and stable catalyst for the hydrogen evolution reaction

Addressed herein, a highly efficient, durable and uniformly dispersed activated carbon supported palladium–iridium nanomaterials (3.42 ± 0.34 nm) were reported for the first time as a catalyst in dimethylamine-borane dehydrogenation reaction at the room temperature. The activated carbon supported palladium-iridium nanosheet (Pd–Ir NPs) is obtained by a simple ultrasonic reduction method, and the fabricated nanocatalyst have been defined by Ultra-Violet-Visible (UV–VIS), Raman spectroscopy, X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy (TEM) and High-Resolution Transmission Electron Microscopy (HR-TEM). These newly prepared Pd–Ir nanocomposites were found to be highly efficient and stable for dehydrocoupling of dimethylamine borane. The catalytic activity of the Pd–Ir NPs was excellent by showing the one of the best catalytic activity with a very high turnover frequency (295.1 h−1) and low Ea value of 36.6 ± 2 kJ/mol for DMAB dehydrocoupling. Another important fact about the prepared catalyst is the reusability of the catalyst was very high and easily reused five times without any significant decrease in their catalytic performance. In the current work, the synthesize, characterization and the catalytic performance of the Pd–Ir nanoparticles for the dehydrogenation of the DMAB reaction will be discussed in detail.

Effect of Trace Levels of Si on Microstructure and Grain Boundary Segregation in DOP-26 Iridium Alloy

The thermodynamics and kinetics of Silicon (Si) segregation to grain boundaries in Iridium alloy DOP-26 with added trace levels of Si of 6, 11, 29, and 36 wppm was studied by Auger Electron Spectroscopy. The four alloys were annealed at 1500 or 1535 °C for 19 or 76 hours followed by cooling at three different rates. Si enrichment at the grain boundaries (GB) increased with increasing bulk Si content, with the grain boundary Si enrichment factors ranging from 62 to 344, depending on the bulk Si content and the cooling rate. Grain boundary Si contents increased with decreasing cooling rate in all alloys, indicating that Si GB segregation is influenced by both thermodynamic and kinetic factors in the alloys and temperature ranges of the study. A Langmuir-McLean isotherm-based model was successfully used to predict the temperature dependence of GB Si segregation in DOP-26 alloys with Si additions and estimate the temperature independent free energy of Si segregation to grain boundaries in DOP-26.