Showing papers in "Platinum Metals Review in 2005"

Potential Applications of Fission Platinoids in Industry

Abstract: Amounts of fission-generated platinoids, as recovered from high-level liquid radioactive wastes, could considerably supplement amounts of metals claimed from natural sources. Of particular interest are fission palladium and rhodium, which can be decontaminated from other fission products to a non-hazardous level. What remains is intrinsic radioactivity which is weak in fission palladium, and which in fission rhodium decays to an acceptable level after 30 years. The intrinsic radioactivity should not play a negative role when fission platinoids are applied to nuclear technology. Some non-nuclear applications of fission platinoids may be possible, if irradiation and contamination of personnel as well as uncontrolled release of the platinoids, are avoided.

Ruthenium-Catalysed Asymmetric Reduction of Ketones

Abstract: ketones is a reaction of particular importance to the pharmaceutical industry. In the 1980s, research by Professor Ryoji Noyori’s group at Nagoya University in Japan, on BINAP-ruthenium catalysts opened the way to the efficient asymmetric hydrogenation of C=O groups (3). They found that BINAP-ruthenium catalysts were useful for the hydrogenation of functionalised ketones (such as β-ketoesters, β-amino-ketones and β-hydroxyketones) that possessed secondary binding groups capable of coordinating the substrate to the reactive ruthenium metal centre in the form of 5and 6-membered chelates. The chelates were believed to be necessary for high enantioselectivity. In the mid 1990s, Noyori’s group developed a ‘second generation’ of catalysts. These are based on a ruthenium metal centre bearing a chiral diphosphine and a chiral diamine ligand, see Figure 1 (4). In the presence of a base (such as t-BuOK) the asymmetric hydrogenation of a wide range of unfunctionalised ketones now became possible, without the previous need to have a secondary binding group on the substrate. Mechanistic studies then confirmed that the catalytic reaction was taking place without the direct coordination of the substrate to the metal centre (5). In effect, the catalyst is acting as a ‘bifunctional’ scaffold for anchoring the substrate and transferring the hydride, see Figure 1. Hydrogenation of the ketone is taking place within the external coordination sphere of the catalyst. Using this catalyst, an enormous array of chiral secondary alcohols could be prepared – for the first time – with extremely high stereoselectivity and turnover number (TON = moles of substrate/moles of catalyst). For instance, a TON of up to 1 million is achievable on model substrates, such as aryl ketones. Aromatic, heteroaromatic and unsaturated ketones could be reduced with excellent productivity and enantioselectivity; however, aliphatic ketones were reduced, but only with moderate selectivity.

The Hardening of Platinum Alloys for Potential Jewellery Application

Abstract: 60) to be used for fabricating jewellery, so alloying additions are made to increase the hardness. Platinum jewellery alloys usually have platinum contents of 90 wt.% and higher. The most common alloys are hallmarked as 950 platinum (95 wt.%). Unlike carat gold (Au) jewellery alloys, where relatively large additions can be made (to alter the properties of the alloy such as its hardness or colour): for instance 18 ct gold contains 25 wt.% of alloying additions, the 950 platinum alloy hallmarking, only allows alloying additions of up to 5 wt.% (to alter properties, such as increase its hardness). Several platinum jewellery alloys are available, and usage depends on national preference and hallmarking regulations. Typical alloying elements include copper (Cu), palladium (Pd), cobalt (Co), gallium (Ga) and indium (In). Cu is often added and creates a general-purpose alloy which casts well and is easy to work. Adding Co results in a very good casting alloy, while additions of Ga or In produce alloys with good springiness. Other popular alloying additions are iridium (Ir) and ruthenium (Ru). Pd can be added to platinum, but while this alloy has a good surface finish, softness limits its use. Examples of hardening platinum by alloying additions are shown in Figure 1 (1, 2). There has been much work on hardening platinum by alloying and this is demonstrated in several patents. Citizen Watch Co. holds a patent for an alloy of 85–95 wt.% Pt, 1.5–6.5 wt.% Si with the balance being one or more of Pd, Cu, Ir, Rh, Au, Ag, Ni and Co (3). This company also patented a Pt-Fe-Cu-Pd alloy (85–90 wt.% Pt, 2.5–3.5 wt.% Fe, 7.5–12.5 wt.% Cu and 0–4 wt.% Pd) (4). A patent on hard Pt alloys for jewellery application states the hard, high-purity Pt alloy contains 10–100 ppm Ce with a minimum Pt content of 99 wt.% (5). Another patent is concerned with maintaining the high purity of platinum while increasing its hardness by minor additions (0.01 to 1 wt.%) of titanium or a rare earth metal. No age hardening was reported (6). Hard, but still workable, platinum alloys have been reported with good abrasion resistance. These were achieved by modifying a surface layer to induce hardening (7, 8). An intermetallic layer of platinum, containing especially aluminium and chromium, developed on the surface. One patent

The Thermodynamic Properties of Platinum

Abstract: 141 Platinum has a face centred cubic structure with a lattice parameter at 20oC of 0.39236 nm and a density of 21.45 × 10 kg m (1). In the present paper the variation of the thermodynamic values of the specific heat at constant pressure, enthalpy, entropy and Gibbs free energy with temperature have been revised in the condensed phases and gaseous phase at a 1 bar standard state pressure. The vapour pressure data was calculated from the selected heat of sublimation of 565 kJ mol as shown in Table I and from the nett Gibbs free energy between the condensed and gaseous phases. Values for these properties are reassessed in the light of revised data.

Ruthenium Complexes Bearing N-Heterocyclic Carbene (NHC) Ligands

Abstract: A review of recently published aspects on ruthenium complexes with nucleophilic N-heterocyclic carbene (NHC) ligands is presented here, in continuation of a paper published in the July issue of this Journal, that covered initial work and subsequent main developments in this chemistry. In Part II selected applications of these complexes as pre-catalysts in metathesis reactions are highlighted. Particular attention is paid to metathesis in room temperature ionic liquids as the solvents, asymmetric catalysis, and in situ generated, very active catalytic systems based on NHC-platinum group metals. Most NHC-platinum group metal complexes are useful as highly active and selective pre-catalysts for fundamental chemical transformations.

Thermal conductivities of platinum alloys at high temperatures

Abstract: 21 The advantage of using platinum (Pt) in industrial applications is due to its unique properties, such as its catalytic activity, high melting point (1), ductility (2, 3) and chemical inertness over a wide range of temperatures (4, 5). Platinum has been used for biomedical components, specialty chemicals, fuel cells and for pollution control catalysts, such as in automobile exhausts, as well as for jewellery, thermocouples and the cathodic protection of ships’ hulls (3). One typical application of platinum is in electronics devices, with thick film conductors being among the major products (6). Alloying elements, selected from the platinum group metals and noble metals, are usually employed to help develop higher strength or to protect a surface against deleterious service conditions (3). However, the addition of an alloying element may degrade the conductivity. Until now, the data available on the conduction properties of platinum alloys have been limited (7–12). This present investigation will survey the parameters of thermal conductivity in various platinum alloys at high temperatures. First, the composition dependence of thermal conductivity will be investigated and the results will be ordered according to the Periodic Table; second, the effect of work hardening will be investigated; and third, the temperature dependence of thermal conductivity will be surveyed.

Diesel Engines: Design and Emissions

Abstract: 119 The “Diesel Particulates and NOx Emissions” course (1) is one of an ongoing series of professional development courses established about 20 years ago by Gordon E. Andrews, now Professor of Combustion Engineering at the University of Leeds, who identified a need for education in this field. The course was held at the Weeton Hall Hotel and Conference Centre, Leeds from Monday 23 to Friday 27 May; this series of courses is held both in the U.K. and the U.S.A. Lectures were given by Professors Andrews and David B. Kittelson (University of Minnesota) (2), and representatives of major industrial organisations and consultants involved in research into diesel technology. The thirty-nine attendees from industry and universities in the U.K., Europe and Asia. were mostly practitioners from a variety of backgrounds linked with diesel engines.

Ruthenium Catalyst for Treatment of Water Containing Concentrated Organic Waste

Abstract: The catalytic wet oxidation process (CWOP) is a promising technique for the treatment of highly concentrated organic wastewater that is difficult to degrade biochemically. This technique is based on the wet air oxidation (WAO) method of treating industrial effluent – in use for many years. WAO is a thermal liquid-phase process whereby organic substances in highly concentrated wastewater are oxidised by air at high temperatures and pressures, for long periods of time. Removal of ammonic nitrogen and cyanide is, however, difficult. The CWOP aims to improve on the disadvantages of the WAO method. Tests were conducted to find the best catalysts. Catalyst CWO-11 reduced the severity of the reaction required and improved the chemical oxygen demand and the total nitrogen conversion of organic wastewater.

Casting platinum jewellery alloys The effects of composition on microstructure

Abstract: each being marketed according to applications for which it is suitable. For instance, platinum-5 wt.% iridium has high work hardening and is suitable for making clasps, wire and the like, while softer platinum-5% palladium is used for fine casting and delicate settings (1). Two commercially available, general purpose alloys, platinum-5% copper (Pt5%Cu) and platinum-5% ruthenium (Pt-5%Ru), are in common use by manufacturing platinum jewellers. Jewellers who work with these two alloys report some significant differences between them. This paper will examine the differences in these alloys and reasons for their preferential use. We will look for factors affecting their different characteristics, and how working conditions can be manipulated to optimise the performance of each alloy in jewellery manufacture. Differences between these alloys, experienced during handworking and casting, are summarised in Table I.

Iridium/Carbon Films Prepared by MOCVD

Abstract: gas sensors because of their unique physical and chemical properties, such as their inertness, good oxidation resistance, electrical conductivity and catalytic performance. However, due to sluggish charge transfer reactions at the sensing electrode interface at low temperature (less than 500oC) (1), a gas sensor constructed with traditional Pt electrodes and ZrO2 electrolyte needs to be heated to a higher temperature to obtain sufficient voltage output and a shorter response time. In order to improve the properties of these sensors, Ir cluster films have been prepared by MOCVD (metalorganic chemical vapour deposition) and investigated (2–8). This paper reports on the composition, structure and electrochemical properties of some Ir/C films. Experimental Procedure A schematic diagram of a horizontal hot-wall MOCVD apparatus is shown in Figure 1. The precursor for the Ir/C films was 500 mg of iridium tris-acetylacetonate, (CH3COCHCOCH3)3Ir, Ir(acac)3. Oxygen and argon were used as the reactant and transmission gases, respectively. The substrates were quartz (10 mm × 10 mm × 1 mm thick) and YSZ (yttria stabilised zirconia): 6 mol % Y2O3, (10 mm Φ × 2 mm thick). The temperature of the precursor (Tsor) was kept at 190oC. The total gas pressure in the chamber was fixed at 500 Pa, with argon flow maintained at 50 ml min. The precursor was placed in a small quartz boat in the MOCVD apparatus. The deposition temperature (Tdep) was varied from 450 to 650oC, for a deposition time of 60 minutes. The flow of oxygen (FO2)

Platinum Group Minerals in Eastern Brazil GEOLOGY AND OCCURRENCES IN CHROMITITE AND PLACERS

Abstract: The platinum group metals occur in specific areas of the world: mainly South Africa, Russia, Canada and the U.S.A. Geological occurrences of platinum group elements (PGEs) (and sometimes gold (Au)) are usually associated with Ni-Co-Cu sulfide deposits formed in layered igneous intrusions. The platinum group minerals (PGMs) are associated with the more mafic parts of the layered magma deposit, and PGEs are found in chromite crystals which are a major component of chromitite rock. The PGMs occur in the chromitite matrix, in chlorite and serpentine minerals, and around the borders of the chromite crystals (1). The distribution of PGEs in chromitite is consistent with crystallisation being caused by metamorphic events. PGEs also occur in alluvial, placer deposits (2).

Casting platinum jewellery alloys

Abstract: Comparisons are made between platinum-copper and platinum-ruthenium alloys used for jewellery to evaluate the effects of casting variables. The effects of flask temperatures, investments, and centrifugal speeds on microstructure, percentage fill, and porosity were examined over a range of temperatures. Optimum conditions and materials for successful casting of high quality platinum jewellery alloys, using a Hot Platinum induction melting and casting machine, are described. Suitable choice of investment materials and rotational speeds produced good grid fills with Pt-5%Cu and Pt-5%Ru alloys. Metal porosity was more difficult to control, due to the inherently chaotic nature of the casting process, but casting into a relatively cool mould minimised the probability of bad porosity for both alloys. Pt-5%Ru was found to be successful as a casting alloy when used with induction melting technology. It displayed superior uniformity, hardness and colour, compared with cast Pt-5%Cu alloy.

Modern Palladium Catalysis

Abstract: 77 This book is intended as an update to the original title “Palladium Reagents and Catalysts – Innovations in Organic Synthesis” written by the same author and published by Wiley in 1995 (1). It is to be used in conjunction with the original review to “cover the whole of organopalladium chemistry, from the past to the present” (mid2003). The book gives a detailed overview of the main recent advances in organopalladium chemistry from a synthetic organic chemist’s view point. The book is organised by types of organic reactions that are catalysed or effected by organopalladium reagents. The first chapter comprises a very concise and useful summary of the basic chemistry of organopalladium catalysis. This is followed by separate chapters on each type of synthetic reaction. The first types of reaction to be considered are oxidative reactions with Pd(II) compounds. As the author states in his introduction, ‘oxidative’ normally refers to a reaction of Pd where the oxidation state of the metal is increased. This chapter, however, refers to oxidation in the classical organic sense, for example, the conversion of an alkene to an aldehyde catalysed by a Pd(II) compound. The narrative begins with the first major example of this reaction, the Wacker process, and proceeds to more specific and recent examples. This chapter is detailed and includes some important chemistry contributed by the author himself. This is obviously an area close to his heart!