High-pressure high-temperature stability of hcp-Ir Os1− (x = 0.50 and 0.55) alloys

Abstract

Hcp-Ir 0.55 Os 0.45 and hcp-Ir 0.50 Os 0.50 alloys were synthesised by thermal decomposition of single-source precursors in hydrogen atmosphere. Both alloys correspond to a miscibility gap in the Ir─Os binary phase diagram and therefore are metastable at ambient conditions. An in situ powder X-ray diffraction has been used for a monitoring a formation of hcp-Ir 0.55 Os 0.45 alloy from (NH 4) 2 [Ir 0.55 Os 0.45 Cl 6 ] precursor. A crystalline intermediate compound and nanodimentional metallic particles with a large concentration of defects has been found as key intermediates in the thermal decomposition process in hydrogen flow. High-temperature stability of titled hcp-structured alloys has been investigated upon compression up to 11 GPa using a multi-anvil press and up to 80 GPa using laser-heated diamond-anvil cells to obtain a phase separation into fcc+hcp mixture. Compressibility curves at room temperature as well as thermal expansion at ambient pressure and under compression up to 80 GPa were collected to obtain thermal expansion coefficients and bulk moduli. hcp-Ir 0.55 Os 0.45 alloy shows bulk moduli B 0 =395 GPa. Thermal expansion coefficients were estimated as α = 1.6•10-5 K-1 at ambient pressure and α = 0.3•10-5 K-1 at 80 GPa. Obtained high-pressure high-temperature data allowed us to construct the first model for pressure-dependent Ir─Os phase diagram.

Microwave-Assisted Synthesis of Classically Immiscible Ag–Ir Alloy Nanoparticle Catalysts

“…Heterogeneously, Ir is employed in NO reduction, in CO and ammonia oxidation, in water splitting, in hydrazine decomposition, and in the hydrogenation of aldehydes and nitrobenzenes, for which Ir shows unrivalled selectivity. Metallic Ir is one of the most corrosion- and oxidation-resistant metals known, whose alloys with Os and Pt display extreme mechanical hardness . For related reasons, the synthesis of size- and shape-controlled IrNPs is particularly problematic: its high melting point and resistance to surface etching limits the size to which IrNPs can be grown.…”

Ir–Re binary alloys under extreme conditions and their electrocatalytic activity in methanol oxidation

“…Nevertheless, their alloys have seldom been studied. Only Ir-Os alloys were tested under high-pressure high-temperature conditions in situ up to 140 GPa and 3000°C [10][11], and the Ir-Re system has been investigated under high-temperature high-pressure up to 9 GPa and 2000°C ex situ using a belt press [12][13][14][15][16]. High-temperature highpressure studies may lead to a deeper understanding of the stability of ultra-hard ultraincompressible alloys upon extreme conditions and eventually be exploited as tools for the construction of realistic pressure-dependent phase diagrams.…”

Modification of Lu's (2005) high pressure model for improved high pressure/high temperature extrapolations. Part II: Modeling of osmium–platinum system at high pressure/high temperature

“…In general, along compression the two-phase domain should shift towards the metal with larger atomic volume [4]. Such trend has been confirmed for Ir-Os and Ir-Re binary alloys, where metals have close atomic volumes and significantly different compressibility (Ir-Os binary alloys) or different atomic volumes and nearly identical compressibility (Ir-Re binary alloys) [5][6][7][8]. Os-Pt system represents significant differences in atomic volumes and compressibility and shows that upon compression the two-phase field becomes more narrow with pressure [9].…”

“…These two latter applications require not only the knowledge of the phase diagram but also its modifications at ultra high hydrostatic pressure above 100 GPa. From the experimental point of view, several platinoid systems at high pressure have already been studied up to 140 GPa at room temperature and upon heating above 3000 °C [5][6][7][8]. Os-Pt system has been also studied up to 50 GPa and 2300 °C [9].…”