Beck G.,Research Institute for Precious Metals and Metals Chemistry |
Janek J.,Justus Liebig University
Solid State Ionics | Year: 2012
Platinum and Palladium films were prepared on (111) orientated yttrium-stabilised zirconia (YSZ) by pulsed laser deposition (PLD). Afterwards, the Pt/YSZ and Pd/YSZ systems were annealed and/or electrically polarised. The polarisation was performed in the manner that oxygen was alternatingly built-out and built-in (= cyclovoltammetry experiment) at and within the metal films. The as-deposited, annealed and polarised films, respectively, were characterised by EBSD, SEM, X-ray pattern and pole figure measurements. In addition, the X-ray patterns were measured in situ during annealing and during polarisation. The as-deposited metal films were nearly single crystalline, but with twins of a size between 100 nm and 300 nm as defects. These twins disappear completely during annealing in platinum films on perfect (111) orientated YSZ single crystals and holes are built instead. Whereas-at least a small fraction of-twins remains in films on twin-rich YSZ(111) substrates. Nevertheless, during polarisation these twins also disappear completely, probably due to formation and cracking of oxygen bubbles at twin positions within the metal films. Palladium films behave similarly, but they show stronger de-wetting phenomenon during annealing. They are also oxidised during annealing at an oxygen partial pressure [= p(O 2)] above 1·10 - 3 mbar at temperatures between 500 °C and 700°C or even at this low p(O 2) after some hours at 500°C. During polarisation they are even oxidised at 400°C at p(O 2) > 1·10 - 3 mbar. © 2012 Elsevier B.V. All rights reserved.
Freudenberger R.,Research Institute for Precious Metals and Metals Chemistry
Galvanotechnik | Year: 2011
Scanning the literature on precious metals in 2009 reveals that the emphasis is overwhelmingly on the Platinum Group metals, in particular platinum and palladium. The activity in development of palladium-based solutions is presumably due to its cost advantage as compared with gold and has resulted in significant improvements in the industrial uses of palladium alloy electrolytes. Cost pressures are also evident in respect of platinum electrodeposition of catalysts where catalysts based on platinum combined with non-noble metals continue to find new applications.
Balzer M.,Research Institute for Precious Metals and Metals Chemistry
Thin Solid Films | Year: 2014
Coatings deposited by Physical Vapour Deposition techniques have been characterised for decades for their corrosion protection capabilities. The coating microstructure has often been stated to be the key factor. Improvements, mostly based on electrochemical corrosion measurements, often did not prove true when verified by neutral salt spray test. The pitting corrosion then observed has usually been explained by the presence of growth defects. With the Large Area High Resolution mapping a method has recently been developed which allows localizing and characterising the growth defects responsible for pitting corrosion attacks. It is based on scanning the topography of the entire surface (several cm2) of lab sized coated samples with a lateral resolution in sub-μm range by confocal microscopy. Using this method on the same sample before and after a corrosion test enables to trace back the corrosion pits to their responsible growth defects. Furthermore reliable defect statistics, defect maps and Cartesian coordinates for each individual defect are available. The method is introduced in detail including issues that had to be solved like dust particles being present on the sample surfaces during the scan. Finally results for TiN coatings deposited by dc magnetron sputtering are presented. These results indicate that large as well as very small growth defects are the only reason for pitting corrosion attacks on the investigated samples. A corrosion relevance of different defect sizes is determined and correlations between the defect concentration and the appearance of the samples after the neutral salt spray test are presented. © 2014 Elsevier B.V. All rights reserved.
Klotz U.E.,Research Institute for Precious Metals and Metals Chemistry
Gold Bulletin | Year: 2010
Blue and purple gold alloys form in the alloying systems of gold with gallium/indium and aluminium respectively and are known to be very brittle and to possess low corrosion resistance. Taking into account these drawbacks this paper describes the results of a European funded research project. The properties of the blue and purple gold alloys and coatings such as corrosion resistance, metal release rates, hardness and colour and the influence of alloying additions on these properties are presented and discussed. Surface engineering techniques and investment casting were used for manufacturing of jewellery items with selectively coated coloured surface. Coatings of AuGa 2 and AuIn 2 blue gold alloys were applied on 18kt gold and Sterling silver jewellery by electroplating, laser/torch cladding or dipping into liquid gallium. The suitability of blue gold coatings for jewellery purposes will be discussed in the light of reliability and feasibility. The work consists of two parts. Part I describes properties and surface processing techniques while Part II deals with investment casting and related alloy design of coloured gold alloys.
Fenker M.,Research Institute for Precious Metals and Metals Chemistry
Galvanotechnik | Year: 2012
Pulsed sputtering processes have long been used for the deposition of insulating layers in vacuum coating systems. HiPIMS is a new generation pulsed sputtering process using extremely heavy duty pulses. This results in a high degree of ionisation of the sputtered particles in the plasma, thereby improving the coating properties. In addition to the many advantages of this process (improved adhesion, higher density of coating, increased wear resistance), it also has certain drawbacks (e.g. lower deposition rate). As well as an introduction to HiPIMS technology, its scope and limitations are also discussed.