Platinum Metals Review - Volume 47, Issue 3, 2003

The molecular mechanisms of platinum cluster nucleation and growth in solution and on biopolymers have been investigated by means of first-principles molecular dynamics. In contrast with the classical picture where clusters nucleate by aggregation of metallic Pt(0) atoms, it was found that Pt-Pt bonds can form between dissolved Pt(II) complexes after only a single reduction step. Furthermore, small clusters were observed to grow by addition of unreduced [PtCl2(H2O)2] complexes, in agreement with an autocatalytic growth mechanism. Moreover, Pt(II) ions covalently bound to biopolymers were found to act as preferential nucleation sites for the formation of clusters. This is a consequence of the presence of heterocyclic donor ligands which both enhance the electron affinity of the metal nuclei and induce the formation of metal-metal bonds that are stronger than those obtained in solution. In fact, in metallisation experiments a clean and purely heterogeneous metallisation of single DNA molecules leading to thin and uniform Pt cluster chains extending over several microns was obtained.

The effects of cerium and ruthenium additions on the mechanical properties of Pt-15 Pd-3.5 Rh alloy (wt.%) at ambient and high temperature are examined. The mechanical properties of the alloy were improved by adding cerium (≤ wt.%) or ruthenium (≤ 0.5 wt.%) solute, with the cerium additions giving a better strengthening effect. Higher concentrations of cerium and ruthenium did not visibly increase the strength properties of the Pt-15Pd-3.5Rh alloy and even reduced some of the mechanical properties at high temperature. Increasing the palladium content in the Pt-Pd-Rh alloy could enhance the alloy strengths at room temperature but damaged the mechanical properties at high temperatures. Observations of the morphologies of fracture sections of alloy samples after creep-rupture tests at high temperature showed ductile fracture for alloys with lower contents of palladium, cerium or ruthenium and brittle fracture for alloys with higher contents ofpalladium, cerium or ruthenium. The different strengthening mechanisms of palladium, cerium and ruthenium additions to Pt-15Pd-3.5Rh alloy are discussed.

Several processes are reviewed for recovering fission platinoids from radioactive liquids and solid material that typically originate during the reprocessing of spent nuclear fuel by the Purex process. The liquids are radioactive high-level liquid waste and the solution obtained on dissolving the spent nuclear fuel in nitric acid (dissolver solution). The solid is the undissolved fuel residue (dissolver residue). The processes described here have been particularly developed to recover platinoids or, if aimed at the separation of actinides, platinoid recovery is included. Hydrometallurgical processes are predominantly based on solvent extraction, electrodeposition and ion exchange, and less frequently on precipitation and extraction chromatography. Pyrochemical processes are based on extraction or distillation.