Platinum Metals Review - Volume 50, Issue 3, 2006

The semiconducting Magnus’salt derivatives [Pt(NH2eh)4][PtCl4] and [Pt(NH2dmoc)4][PtCl4], with eh = (R)-2-ethylhexyl and dmoc = (S)-3,7-dimethyloctyl, are compounds that exhibit a supramolecular structure comprising a backbone of linear arrays of platinum atoms. These compounds behave essentially like ordinary polymers. In this work they were processed into fibres by electrospinning from organic solvents such as toluene. X-ray diffraction patterns indicated that the platinum arrays in the fibres were oriented parallel to the axis of the fibres. Accordingly, the fibres show anisotropic optical and electrical properties. The electrical conductivities observed along the fibre axis were 2 × 10⁻⁵ S cm⁻¹ for [Pt(NH2dmoc)4][PtCl4] and 7 × 10⁻⁷ S cm⁻¹ for [Pt(NH2eh)4][PtCl4]. These exceeded the values for the respective bulk compounds by 2–3 orders of magnitude, in agreement with comparable observations in oriented semiconducting organic polymers.

Equations are given to represent the lattice parameter thermal expansion of platinum from 293.15 K to the melting point at 2041.3 K. This treatment is intended to supersede a combination of dilatometric equations with corrections for thermal vacancy effects.

This paper augments a series of articles on Russian roubles in this Journal (1–3) with a summary of recent research into the manufacturing history and materials characterisation of these coins. The results are not only significant for the identification of genuine roubles issued between 1828 and 1845, ‘Novodel’issues produced in the late 19th century, and outright forgeries of the 20th century, but offer a fascinating insight into the difficulties encountered at the time in the large-scale refining and processing of platinum metal. A range of instrumental methods have been used to elucidate the magnetic properties, chemical composition and low density of genuine roubles, and to reveal their complex internal structure. The resulting new insights into the historical practice of platinum metallurgy are unbiased by concerns about industrial espionage, state secrets, and professional rivalry.

The earliest authenticated scientific report of the occurrence of platinum in rocks from the Bushveld Complex, South Africa, appears to be that of William Bettel on 10th November 1906. Thereafter, prospecting of the chromite-rich rocks for platinum proved frustrating. It is argued that the resurgence of interest by Dr Hans Merensky in 1924 resulted from his realisation that newly panned platinum had a grain size different from that in the chromite layers and indicated a different source rock, which he promptly located as the Merensky Reef.

The background to a project in Brazil is described that has found promising concentrations of platinum group elements (PGEs) in phoscorite-carbonatite complexes. Further geochemical and mineralogical research is underway to determine their potential as ore deposits. The well-established industrial demand and current level of prices for the platinum group metals have encouraged the exploration of geological environments other than the layered maficultramafic intrusions that provide the bulk of platinum metals. Environments, such as the Ural-Alaskan Type Complexes (U-ATCs) and the associated placer deposits were for many years the only known sources of the PGEs. This paper attempts to show a connection between platiniferous dunite-pyroxenite pipes in the Ural Platinum Belt and those on the eastern margin of the Bushveld Complex, both being significant PGE producers in the past, and phoscoritecarbonatite pipe (PCP) complexes. PCP complexes may be a promising source of PGEs. Four Brazilian PCP complexes are sampled (Salitre, Tapira, Ipanema and Catalão) as well as the Phalaborwa PCP complex in South Africa.

The results from fast-pulse heating experiments (of duration 60 μs) performed on pure palladium are presented. Thermophysical properties derived include specific enthalpy, enthalpy of fusion, electrical resistivity, isobaric heat capacity, thermal conductivity and thermal diffusivity, over a range of temperatures from the melting transition up to some hundred degrees higher in the liquid state. Additionally, normal spectral emissivity at wavelength 684.5 nm is presented,