Platinum Metals Review - Volume 53, Issue 3, 2009

A novel palladium-promoted zeolite material with a significant ethylene adsorption capacity at room temperature is described. It was characterised by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and transmission electron microscopy (TEM) to show palladium particles dispersed over the support. Initial measurements of the ethylene adsorption capacity were conducted with a synthetic gas stream at a higher ethylene concentration than would normally be encountered in fruit/vegetable storage, in order to obtain an accelerated testing protocol. Further laboratory-based trials on fruit samples show that the palladium-promoted zeolite material can be effective as an ethylene scavenger to prolong the shelf-life of fresh fruits.

Thermodynamic properties of diatomic molecules containing platinum (PtH, PtC, PtN and PtO) have been calculated using spectroscopic data and partition function theory. Values of the Gibbs energy (G), enthalpy (H), entropy (S) and specific heat capacity at constant pressure (CP) are presented for each species in the temperature range from 100 K to 3000 K. To obtain the most accurate data, anharmonicity, nonrigidity and stretching effects have been incorporated in the calculations. The variation of these properties with temperature is also discussed in terms of different modes of molecular motion.

Defect structure and its relationship with deformation behaviour at room temperature of iridium, the sole refractory face centred cubic (f.c.c.) metal, are discussed. Small angle boundaries and pile-ups of curvilinear dislocation segments are the main features of dislocation structure in polycrystalline iridium at room temperature, while homogeneously distributed rectilinear dislocation segments were the main element of defect structure of iridium single crystals at the same conditions. Small angle boundaries and pile-ups of curvilinear dislocation segments are formed in iridium single crystals under mechanical treatment at elevated temperatures (≥ 800°C) only. The evolution of defect structure in polycrystalline iridium and other f.c.c. metals under room temperature deformation occurs by the same process: accumulation of dislocations in the matrix leads to the appearance of both new sub-grains and new grains up to the fine grain (nanocrystalline) structure. Neither single straight dislocations nor their pile-ups are observed in iridium at room temperature if small angle boundaries have been formed. This feature may be considered as the reason why polycrystalline iridium demonstrates advanced necking (high localised plasticity) and small total elongation.

Under the Platinum Development Initiative, platinum-based alloys were being developed for high-temperature and special applications for good corrosion and oxidation resistance. Work on ternary alloys had previously identified that the best of these systems for both mechanical properties and oxidation resistance were Pt86:Al10:Cr4 and Pt86:Al10:Ru4 (1), although the maximum precipitate volume fraction was only ∼ 40% as opposed to ∼ 70% achieved in nickel-based super alloys. Since Pt86:Al10:Cr4 and Pt86:Al10:Ru4 gave the best results, a range of quaternary alloys were also made, using these compositions as a basis. The optimum composition was found to be around Pt80:Al14:Cr3:Ru3. Subsequently, further additions were made to the quaternary alloys to change selected properties.