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Formation of protective oxide scales is the main reason for the high oxidation resistance of TiAlN based coatings. Here the authors report on further improvement in the oxidation resistance of TiAlN by Ta alloying. An industrial-scale cathodic arc evaporation facility was used to deposit Ti–Al–Ta–N coatings from powder metallurgically produced Ti38Al57Ta5 targets. After oxidation in ambient air, a significantly reduced oxide layer thickness in comparison to unalloyed TiAlN reference material was observed. Energy-dispersive x-ray spectroscopy line scans and secondary ion mass spectroscopy depth profiling showed that the oxide scale consists of an Al-rich top layer without detectable amount of Ta and a Ti–Ta-rich sublayer. Transmission electron microscopy investigations revealed α-Al2O3, rutile-type TiO2, and anatase-type TiO2 as the scale forming oxides. Furthermore, the Ti–Ta-rich sublayer consists of a porous layer at the oxide-nitride interface but appears dense toward the Al-rich top layer. The improved oxidation resistance is explained by doping the TiO2 lattice by replacing Ti4+ with Ta5+ in the rutile lattice, which decreases the oxygen mass transport. This leads to reduced oxidation of Ti under formation of TiO2 at the oxide-nitride interface and is the reason for the excellent oxidation behavior of Ti–Al–Ta–N coatings.

Commercial copper wire and its polymer insulation cladding was investigated for the presence of three synthetic antioxidants (ADK STAB AO412S, Irganox 1010 and Irganox MD 1024) by three different mass spectrometric techniques including electrospray ionization-ion trap-mass spectrometry (ESI-IT-MS), matrix-assisted laser desorption/ionization reflectron time-of-flight (TOF) mass spectrometry (MALDI-RTOF-MS) and reflectron TOF secondary ion mass spectrometry (RTOF-SIMS). The samples were analyzed either directly without any treatment (RTOF-SIMS) or after a simple liquid/liquid extraction step (ESI-IT-MS, MALDI-RTOF-MS and RTOF-SIMS). Direct analysis of the copper wire itself or of the insulation cladding by RTOF-SIMS allowed the detection of at least two of the three antioxidants but at rather low sensitivity as molecular radical cations and with fairly strong fragmentation (due to the highly energetic ion beam of the primary ion gun). ESI-IT- and MALDI-RTOF-MS-generated abundant protonated and/or cationized molecules (ammoniated or sodiated) from the liquid/liquid extract. Only ESI-IT-MS allowed simultaneous detection of all three analytes in the extract of insulation claddings. The latter two so-called 'soft' desorption/ionization techniques exhibited intense fragmentation only by applying low-energy collision-induced dissociation (CID) tandem MS on a multistage ion trap-instrument and high-energy CID on a tandem TOF-instrument (TOF/RTOF), respectively. Strong differences in the fragmentation behavior of the three analytes could be observed between the different CID spectra obtained from either the IT-instrument (collision energy in the very low eV range) or the TOF/RTOF-instrument (collision energy 20 keV), but both delivered important structural information.

Silver-coated quartz crystal microbalance (QCM) disks were treated under different environmental conditions (including changes in parameters such as relative humidity (%RH) and SO(2)/H(2)S content) in atmospheres of synthetic air and pure N(2) for 24 h in a weathering chamber. The corroded surfaces were subjected to depth profiling by a time of flight (TOF) secondary ion mass spectrometry (SIMS) instrument, equipped with a Bi(+) analysis gun and Cs(+) sputter gun. The evaluation of the in-depth distribution of several elements and species provides evidence for the formation of a corrosion layer containing Ag(2)SO(3), even in the absence of oxidizing agents, such as H(2)O(2) or NO(2). Furthermore it could be elucidated that the thickness of the formed Ag(2)SO(3) layer does not depend on the SO(2) concentration but rather on the humidity and oxygen content of the ambient atmosphere. In weathering experiments in atmospheres composed of synthetic air, humidity, and H(2)S, the presence of different oxygen species (surface and bulk) and silver sulfide could be detected by TOF-SIMS depth profiling experiments. The obtained results for both acidifying gases are in good correlation with the corresponding tapping mode atomic force microscopy (TM-AFM) investigations and in situ QCM measurements.

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