Platinum has only been known to Europe since the 16th century. This was impure platinum, found as grains of native metal in alluvial deposits and comprising mainly platinum alloyed with the other five platinum group metals. They were exploited by pre-Colombian native populations of Ecuador and Colombia. In more recent times, the use of platinum in jewellery dates from the late 19th or early 20th centuries, often as a basis for diamond (and other precious gemstone) jewellery. Early jewellery alloys tended to be based on the existing industrial alloys and comparatively little development of specific jewellery alloys was carried out. Its acceptance as a hallmarkable jewellery metal came in 1975 when, with wider availability of the metal, platinum was promoted as a high-value jewellery metal. Platinum jewellery started to grow in popularity, mainly at 950 and 900 fineness qualities. Since that time there has been alloy development specifically for jewellery application and tailored to the requirements of different manufacturing technologies. This review examines the evolution of platinum jewellery alloys over the past century against the challenges presented in developing improved alloys for jewellery application. There has been a substantial increase in alloy development over the past 30 years, particularly focused on improved investment (lost wax) casting alloys as well as better mechanical properties.

Introduction Platinum group metals (pgms) have widespread applications as functional materials in many different industries. The applications range from catalytic surfaces or particles, sensors, biomedical imaging or drug delivery systems and thermocouples up to jewellery items that we use for special moments of our life. The pgms are used as solid bulk materials, powders, thin films,...

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.

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.

Platinum-based alloys are being developed for high-temperature applications with the aim of replacing some of the currently used nickel-based superalloys (NBSAs) and benchmark alloy, PM2000. The platinum-based superalloys have a similar structure to the NBSAs and can potentially be used at higher temperatures and in more aggressive environments because platinum is more chemically inert and has a higher melting point. In this paper, the recent progress in research and development of platinum-based superalloys is overviewed. Firstly, the composition optimisation and structural design of platinum-base superalloys are introduced. The structural characteristics, mechanical properties, oxidation resistance and corrosion behaviour of platinum-aluminium ternary, quaternary and multiple superalloys are summarised. Finally, directions for further research and application of platinum-based superalloys are analysed and prospected.

Here, we report the frequency dependent ultrasonic attenuation of monometallic gold and bimetallic gold/platinum based aqueous nanofluids (NFs). The as-synthesised bimetallic NFs (BMNFs) revealed less resistance to ultrasonic waves compared to the monometallic NFs. Thermal conductivity of both NFs taken at different concentrations revealed substantial conductivity improvement when compared to the base fluid, although gold/platinum showed lesser improvement compared to gold. Characterisation of the as-synthesised nanoparticles (NPs) and fluids was carried out with X-ray diffraction (XRD), ultraviolet-visible (UV-vis) spectroscopy, transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). The distinct two-phase bimetallic nature of gold/platinum, its two plasmonic band optical absorption features and the spherical morphology of the particles were shown. The findings were correlated with the observed thermal and ultrasonic behaviour and proper rationalisation is provided. It was revealed that the comparatively lesser thermal conductivity of gold/platinum had direct implication on its attenuation property. The findings could have important repercussions in both industrial applications and in the mechanistic approach towards the field of ultrasonic attenuation in NFs.

It is known that platinum-rhodium thermocouples exhibit mass loss when in the presence of oxygen at high temperatures due to the formation of volatile oxides of platinum and rhodium. The mass losses of platinum, Pt-6%Rh and Pt-30%Rh wires, commonly used for thermocouples, were considered in this paper to characterise the mass loss of wires of the three compositions due to formation and evaporation of the oxides PtO₂ and RhO₂ under the conditions that would be seen by thermocouples used at high temperature. For the tests, the wires were placed in thin alumina tubes to emulate the thermocouple format, and the measurements were performed in air at a temperature of 1324°C, i.e. with oxygen partial pressure of 21.3 kPa. It was found that the mass loss of the three wires increases linearly with elapsed time, consistent with other investigations, up to an elapsed time of about 150 h, but after that, a marked acceleration of the mass loss is observed. Remarkably, previous high precision studies have shown that a crossover after about 150 h at 1324°C is also observed in the thermoelectric drift of a wide range of platinum-rhodium thermocouples, and the current results are compared with those studies. The mass loss was greatest for Pt-30%Rh, followed by Pt6%Rh, then platinum.

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.

Ruthenium tablets with mean grain size of ~4–5 μm were prepared by vacuum hot pressing (VHP), and tablets with maximum density of 12.2 g cm^–3 were obtained with sintering time of 2 h. X-ray diffraction (XRD) revealed that there was a texture change with sintering time. The microstructure of the ruthenium tablets was observed by electron backscatter diffraction (EBSD) and field emission scanning electron microscopy (FSEM). The microstructure evolution of ruthenium with sintering time is discussed.

Johnson Matthey is keen to encourage research into future applications of platinum group metals (pgms). As a global leader in sustainable technologies, our focus is on clean air, clean energy, healthcare and the efficient use of the planet’s natural resources – and on the fundamental properties of pgms on which these applications depend. Johnson Matthey’s commitment to progress in platinum...

Clustered together in the centre of the Periodic Table lie six remarkable elements, six metals without which the world would be a completely different place. Think about the food you eat, your computer, your car, your mobile phone or even the clothes you wear. At some stage during their production one or more of these six rare metals has been utilised, whether as a catalyst or perhaps in...

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.

Platinum-20% rhodium strengthened by oxides of zirconium and yttrium were prepared by solidification of platinum-rhodium-(zirconium)-yttrium powder which had been internally oxidised. After forging, rolling and annealing, 1 mm plates were obtained. Then the plates were mechanically ground to 50–70 μm from rolling-normal direction, followed by argon ion milling until a hole appeared on the centre of the foil to obtain samples which were characterised by transmission electron microscopy (TEM), combined with thermodynamic analysis. The existence of spherical ZrO₂ and Y₂O₃ particles was verified with platinum and rhodium present as pure metals at the same time. It was found that the deformation behaviour of ZrO₂ and Y₂O₃ particles was quite different during processing, where the former basically maintain their spherical shape and were bonded tightly to matrix, while the latter were compressed along normal direction and form two cracks on both sides of Y₂O₃ particles along the rolling direction. The differences in hardness and interface bonding properties of these two types of particles are supposed to be the main causes of different deformation behaviour during hot forging and cold rolling.

Deformation and fracture behaviour of cold drawing iridium wire under tension at room temperature is examined. High purity polycrystalline iridium was manufactured using pyrometallurgical technology. During the initial stage of cold rolling, iridium wire has its usual grain structure and exhibits brittle deformation behaviour: poor plasticity and brittle transgranular fracture (BTF). However, the wire begins demonstrating high plasticity including necking in spite of the brittle fracture mode when the lamellar structure has been formed in iridium during cold drawing.

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.

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.

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...

Platinum-rhodium gauzes are frequently used to catalyse the high temperature ammonia oxidation step for production of synthetic nitrogen-based fertilisers. The gauzes suffer from Pt loss in the form of platinum dioxide (PtO₂), due to the highly exothermic nature of the oxidation reaction. Industrially this is mitigated by installing one or more palladium-nickel catchment gauzes directly downstream of the combustion gauzes, to capture the lost Pt. The Pd-Ni catchment gauzes undergo severe structural modification during operation. In this study, we undertake a systematic study in a laboratory-scale furnace system to determine the role of each of the constituent gases O₂, H₂O and PtO₂ on the structural changes of the Pd-Ni gauzes. In addition, some samples are exposed to real industrial conditions in an ammonia combustion pilot plant reactor. Fresh and spent catchment gauzes are analysed by means of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TGA) and inductively coupled plasma mass spectroscopy/optical emission spectroscopy (ICP-MS/OES). By combining analysis of samples from furnace and pilot scale experiments, the main findings are that Pd-Ni gauzes undergo internal oxidation to nickel(II) oxide (NiO); which in the presence of steam results in Ni depletion and that PtO₂ vapour causes severe grain reconstruction. Furthermore, in laboratory-scale experiments no significant Pd loss is observed, which is in contrast to observations from the pilot plant where the samples are exposed to real post-ammonia oxidation conditions. Pd loss is likely attributed to some gas species contained in the real post-ammonia oxidation gas stream.

This paper provides a database of mechanical properties for most of the commercially available platinum alloys currently in use for jewellery purposes. The alloys were tested for mechanical properties through tensile and microhardness testing in the as-cast and hot isostatically pressed conditions. Microstructural characterisations were performed using scanning electron microscopy (SEM).