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The successful use in rocket engines of iridium as a barrier coating is an important area of high-temperature application. The Ir coating must be continuous and dense in order to protect the underlying material from corrosion and oxidation. The microstructure and morphology of the coating can be effectively controlled by varying the deposition conditions. The microstructure has an important influence on the physical and mechanical properties of the coating. A number of deposition processes, which have different conditions and requirements, have been employed to produce Ir coatings on various substrate materials. Part I of this paper presents the introduction and reviews the different deposition processes, while Part II will deal with texture and structure evolution, mechanical properties, growth mechanisms and applications of Ir coatings. The mechanisms of micropore formation after high-temperature treatment will also be investigated in some detail.
In the century since the first platinum gauze for nitric acid production was made by Johnson Matthey, the demand for nitric acid has increased considerably with its vast number of applications: from fertiliser production to mining explosives and gold extraction. Throughout the significant changes in the industry over the past 100 years, there has been continual development in Johnson Matthey’s gauze technology to meet the changing needs of customers: improving efficiency, increasing campaign length, reducing metal losses and reducing harmful nitrous oxide emissions. This article reviews the progress in gauze development over the past century and looks at recent developments.
Iridium as a barrier coating is an important area of high-temperature application. In Part I, the introduction was presented and the different deposition processes were reviewed (1). This paper, Part II, describes the texture and structure evolution, mechanical properties, growth mechanisms and applications of Ir coatings. The mechanisms of micropore formation after high-temperature treatment are also investigated in some detail.
A novel process for the recovery of platinum group metals (pgms) from ternary alloys using a hydrocarbonyl process is proposed. The hydrocarbonyl process involves treatment of a chloride solution of the pgms with carbon monoxide at ambient pressure. The results demonstrate that the process can provide high purity pgms from a ternary platinum-rhodium-palladium alloy such as that obtained from palladium-nickel catchment alloys used with platinum-rhodium gauzes during high temperature ammonia oxidation.
The thermodynamic properties were reviewed by the author in 1995. A new assessment of the enthalpy of fusion has led to a revision of the thermodynamic properties of the liquid phase and although the enthalpy of sublimation at 298.15 K is retained as 377 ± 4 kJ mol–1 the normal boiling point is revised to 3272 K at one atmosphere pressure.
Definitive equations are suggested to represent the variation with temperature of the densities and molar volumes of the liquid platinum group metals whilst the previously unknown initial slopes of the melting curves for iridium, rhodium and ruthenium are estimated. 1. Introduction Paradis et al. (1) summarised determinations of the densities of the liquid platinum group metals but a...
The properties and glass-forming ability (GFA) of platinum- and palladium-based bulk metallic glasses (BMGs) for jewellery were introduced in Part I of this two-part review (1). Here, we will describe methods for their processing, tarnishing and corrosion resistance and consider their prospects and future developments.
Barring the presence of significant amounts of impurities, an important cause of thermoelectric inhomogeneity and therefore calibration drift of platinum-rhodium thermocouples at high temperatures is the vaporisation and transport of the oxides of Pt and Rh, which causes local changes in wire composition. By examining the vapour pressures of Pt and Rh oxides and their temperature dependence, it is shown that at a given temperature there is an optimal wire composition at which evaporation of the oxides has no effect on the wire composition, provided the vapour does not leave the vicinity of the wire. This may also have applications for Pt-Rh heater elements.
Anisotropic and average intrinsic electrical resistivity measurements of ruthenium were evaluated from 10 K to 1600 K and average values above this temperature up to the melting point. For osmium average values were evaluated from 30 K to 273.15 K and anisotropic and average values above this temperature and up to 1600 K.
For the metals used in jewellery, high hardness and the associated scratch resistance are much sought after. Conventional crystalline alloys for jewellery are alloyed and extensively processed (thermally and mechanically) to improve hardness, but it is difficult to reach values beyond 300 HV. The advent of bulk metallic glasses (BMGs), based on precious metals and with hardness exceeding 300 HV in the as-cast state, is therefore of great interest for both jewellery and watchmaking. The non-crystalline structure of these materials not only gives high hardness, but also the opportunity to shape metals like plastics, via thermoplastic forming (TPF). For more traditional jewellery manufacture, BMGs also exhibit high-definition and near-net-shape casting. Gold-based alloys have long dominated the consideration of BMGs for jewellery as they can comply with 18 karat hallmarks. Although BMGs based on platinum or palladium possess excellent thermoplastic formability and are without known tarnishing problems, achieving useful glass-forming ability (GFA) within the more restrictive hallmarking standards typically used for jewellery (≥95 wt% platinum or palladium) is at best challenging. In this two-part review, platinum- and palladium-based BMGs are discussed, focusing on their potential application in jewellery and on the further research that is necessary.
Since the 2018 review (1) one new light isotope of mass 165 (2) and four new heavy isotopes of masses 209 to 212 (3) have been identified for platinum (Table I). The heavy isotopes are only identified as being ‘particle stable’ – that is resistant to proton or neutron decay but all are expected to decay by beta decay in which an electron and anti-electron neutrino are emitted when a...
The principal possibility of processing the industrial poor collective concentrates of platinum group metals (pgms) using a hydrocarbonyl technology with the selective concentration of pgms from poor multicomponent chloride and chloride-sulfate solutions with the subsequent production of pure pgms is shown.
Titanium-platinum (Ti50Pt50) (all compositions in at%) alloy exhibits thermoelastic martensitic phase transformation above 1000°C and has potential for high-temperature shape memory material applications. However, as has been previously reported, Ti50Pt50 alloy exhibited a negligible recovery ratio (0–11%) and low strength in martensite and especially in the austenite phase due to low critical stress for slip deformation. In order to improve the high-temperature strength and shape memory properties, the effects of partial substitution of Ti with other Group 4 elements such as zirconium and hafnium and the effect of partial substitution of Pt with other platinum group metals (pgms) such as iridium and ruthenium on the high-temperature mechanical and shape memory properties of Ti50Pt50 alloy were recently investigated. This paper reviews the transformation temperatures and high-temperature mechanical and shape memory properties of recently developed Ti site substituted (Ti,Zr)50Pt50, (Ti,Hf)50Pt50 and Pt site substituted Ti50(Pt,Ru)50 and Ti50(Pt,Ir)50 alloys for high-temperature (~800°C–1100°C) material applications.
Electrical resistivity values for both the solid and liquid phases of the platinum group metals (pgms) palladium and platinum are evaluated. In particular improved values are obtained for the liquid phases of these metals. Previous reviews on electrical resistivity which included evaluations for the pgms included those of Meaden (1), Bass (2), Savitskii et al. (3) and Binkele and Brunen (4) as well as individual reviews by Matula (5) on palladium and White (6) on platinum.
We review developments in the study of the stability of platinum-iridium standard weights, in particular the kilogram prototypes manufactured from alloy supplied by Johnson Matthey in the 1880s that still stand at the heart of the International System of Units (abbreviated SI from the French: Système international d’unités). The SI has long since moved on from length standards based on physical artefacts fabricated from this alloy, but the SI unit of mass is still defined in this way, as the mass of a real physical object. The stability of these reference masses has been a concern since the 1930s, with mass loss or gain at the surface being the principal concern. In recent years X-ray photoelectron spectroscopy (XPS) has been particularly valuable in elucidating the types of contamination present and the mechanism by which contamination takes place. While direct studies on the International Prototype Kilogram are understandably difficult, at Newcastle University we have examined the surfaces of six Pt mass standards also manufactured in the mid-19th century, using XPS to identify contamination chemically. XPS shows a significant quantity of mercury on the surfaces of all six. The most likely source of Hg vapour is the accidental breakage of thermometers and barometers, and the mechanism of contamination may be similar to the poisoning of platinum group metal (pgm) catalysts by Hg, an effect known for almost a century.
Having established that osmium is the densest metal at room temperature the question arises as to whether it is always the densest metal. It is shown here that at ambient pressure osmium is the densest metal at all temperatures, although there is an ambiguity below 150 K. At room temperature iridium becomes the densest metal above a pressure of 2.98 GPa, at which point the densities of the two metals are equal at 22,750 kg m–3.
The down-scaling of nanoelectronic devices to ever smaller dimensions and greater performance has pushed silicon-based devices to their physical limits. Much effort is currently being invested in research to examine the feasibility of replacing Si by a higher mobility semiconductor, such as germanium, in niche high-performance metal oxide semiconductor (MOS) devices. Before Ge can be adopted in industry, a suitable contact material for the active areas of a transistor must be identified. It is proposed that platinum group metal (pgm) germanides be used for this purpose, in a similar manner as metal silicides are used in Si technology. Implementation of Ge-based technology requires a thorough understanding of the solid-state interactions in metal/Ge systems in order to foresee and avoid problems that may be encountered during integration. We present a systematic study of the solid-state interactions in germanide systems of four of the pgms: iridium, platinum, palladium and rhodium. Our approach was essentially twofold. Firstly, conventional thin film couples were used to study the sequence of phase formation in the germanide systems. Conventional thin film couples were also used to identify and monitor the dominant diffusing species during the formation of some of the germanides as these can influence the thermal stability of a device. Secondly, we observed and analysed several aspects of the lateral diffusion reactions in these four systems, including activation energies and diffusion mechanisms. Lateral diffusion couples were prepared by the deposition of thick rectangular islands of one material on to thin films of another material. Rutherford backscattering spectrometry (RBS) and microprobe-Rutherford backscattering spectrometry (μRBS) were used to analyse several aspects of the thin film and lateral diffusion interactions respectively. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were also employed.
BIORECOVER brings together diverse expertise with the goal of developing a new sustainable and safe process, essentially based on biotechnology, for selective extraction of critical raw materials (CRMs), rare earth elements (REE), magnesium and platinum group metals (pgms). The four-year European Union (EU) H2020 project involves 14 international partners from mining, microbiology, chemistry, engineering, metallurgy, sustainable process development, as well as CRM end-users. Starting from relevant unexploited secondary and primary sources of CRMs, BIORECOVER will develop and integrate three stages for CRM extraction: (a) removal of major impurities present in raw materials; (b) mobilisation of CRMs through use of microorganisms; and (c) development of specific technologies for recovering metals with high selectivity and purity that meet the quality requirements for reuse. Downstream processes will be developed and recovered metals will be assessed by end-users. Modelling and integration of the modular stages and economic and environmental assessment will be done to develop the most effective and sustainable process. This short feature describes the aims and approach, project technologies and intended outputs of the BIORECOVER project.
Platinum-based knitted gauzes are the most efficient catalysts for the production of nitric oxide, as a precursor to the manufacture of nitric acid and caprolactam. Decades of research and optimisation have resulted in a greater understanding of ammonia oxidation kinetics and associated metal movement within these catalyst packs, along with the development of beneficial binary and ternary alloys. The design of a pack has evolved from the simple addition or removal of metal to modelling the optimal installed metal content and distribution. This review discusses the fundamental kinetics and in situ metal loss for ammonia oxidation catalysts in nitric acid applications and outlines how they can, in conjunction with prevailing platinum group metal (pgm) market conditions and plant key performance indicators (KPIs), influence the optimal catalyst design.
The thermodynamic properties were reviewed by the author in 1995. A new assessment of the enthalpy of fusion at 68.0 ± 1.7 kJ mol−1 leads to a revision of the thermodynamic properties of the liquid phase and although the enthalpy of sublimation at 298.15 K is retained as 788 ± 4 kJ mol−1 the normal boiling point is revised to 5565 K at one atmosphere pressure.