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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.
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