Platinum Metals Review - Volume 49, Issue 1, 2005

Pure platinum is too soft to be used for jewellery and scratches easily. Alloying platinum increases its hardness significantly. However, platinum alloys used in jewellery do need to be easy to work and thus the alloy should be sufficiently soft, but not so soft that their wear resistance is low. A good compromise would be to work with a soft alloy during jewellery manufacture, then harden the alloy so the final finished properties were improved. In order to identify platinum alloys suitable for hardening, platinum with different alloying additions was studied. Platinum alloys with additions of less than 7 wt.% of Ag, Au, Cu, Co, Cr, Fe, Ga, Ge, In, Mg, Mn, Mo, Ni, Si, Sn, Ta, Ti, V, W or Zr were examined, and the merits of each system were assessed for commercial viability. The platinum-titanium system was deemed to show the most promise.

The thermal conductivity of platinum alloys with a f.c.c. single phase was comprehensively surveyed by the laser flash method. Thermal conductivity is predominantly determined by alloy composition and temperature and is little affected by work hardening. An addition of solute clearly decreases the thermal conductivity of Pt, and the conductivity-composition relationship is characterised by a sharp maximum at pure Pt. The Wiedemann-Franz relationship that holds for Pt alloys suggests that the electron is the dominant carrier of thermal conduction. An empirical rule is proposed that the thermal conductivity of a Pt alloy decreases significantly as the position in the Periodic Table of the solute element becomes horizontally more distant from Pt (for the B-subgroup). The thermal conductivity of Pt alloys increases with increasing temperature in the range 300 to 1100 K. The temperature coefficient of thermal conductivity was found to be inversely correlated with the thermal conductivity.

Work presented at the Fourth International Symposium on Proton Conducting Membrane Fuel Cells is reviewed here. For these fuel cells to become commercially successful there are a number of challenges to be met. For instance, the polymer electrolyte membrane fuel cell needs more active catalysts and cheaper, more durable, membranes. In addition, an improved understanding of the deterioration mechanisms of the membrane electrode assemblies is required. New work on all these aspects is described here. Work on direct methanol fuel cells is also reported, focusing on more effective anode catalysts and new proton conducting membrane materials with reduced permeability to methanol.

This paper describes a class of ruthenium indenylidene complexes which constitute robust and efficient pre-catalysts for olefin metathesis reactions, specifically ring-closing metathesis of substituted linear dienes, acyclic diene metathesis of α, ω-dienes, enyne metathesis and ring-opening metathesis polymerisation of cycloolefins. They readily allow reactions not promoted by many prior ruthenium catalysts, such as the synthesis of tri- and tetrasubstituted cycloalkenes as well as ring-closing metathesis involving highly substituted dienes. The activity and stability of these pre-catalysts can be finely tuned by adjusting both steric and electronic effects in the metal coordination sphere through an appropriate selection of ancillary ligands. Due to their accessibility, enhanced activity and good stability, this class of ruthenium complexes gratifyingly extends the scope and utility of the currently used metathesis catalysts.

Brazil does not have working platinum mines, nor even large reserves of the platinum metals, but there is platinum in Brazil. In this paper, four massifs (mafic/ultramafic complexes) in eastern Brazil, in the states of Minas Gerais and Ceará, where platinum is found will be described. Three of these massifs contain concentrations of platinum group minerals or platinum group elements, and gold, associated with the chromitite rock found there. In the fourth massif, in Minas Gerais State, the platinum group elements are found in alluvial deposits at the Bom Sucesso occurrence. This placer is currently being studied.