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In this paper we report on the performance as deuterium permeation barriers of sputtered amorphous, dense and not fully stoichiometric SiC coatings under relevant conditions for breeder blanket applications in fusion reactors. To do that, we investigate the following effects on permeation values: (i) thermal cycling at 450 °C, (ii) combined thermal cycling and e− irradiation (1.8 MeV up to a total dose of 1 MGy), as well as (iii) oxygen exposure at a temperature of 450 °C during e− irradiation. Data show that the permeation reduction factor (PRF) for the as-deposited SiC coated is ∼10 4, even at the predicted operation temperature for the breeder and it is slightly reduced either by thermal cycling without and during e− irradiation. However, the exposure to oxygen at 450 °C during e− irradiation leads to degradation of the coating and of its PRF of about three orders of magnitude. The origin of the coating degradation is discussed. We also study the D retention and desorption in SiC coatings that were implanted with D at energy of 7.5 keV prior to (as-deposited) and after being submitted to the treatments previously described. Secondary ion mass spectroscopy data show that thermal cycling, without and during e− irradiation, strongly increases the D retention in the coatings and leads to the appearance of D2 desorption peak at temperatures between ∼400-750 °C, whereas e-irradiation during thermal cycling does not significantly change the D retention but shifts to higher temperatures thisD2 desorption peak

Thin film solar cells based on Cu2ZnSn(S,Se)4 are very promising, because they contain earth-abundant elements and show high absorptivity. However, the performance of these solar cells needs to be improved in order to reach efficiencies as high as that reported for Cu(In,Ga)Se 2-based devices. This study investigates the potential of band-gap engineering of Cu2ZnSn1-xGexS 4 single crystals grown by chemical vapour transport as a function of the [Ge]/([Sn] + [Ge]) atomic ratio. The fundamental band gap E0 is found to change from 1.59 to 1.94 eV when the Ge content is increased from x = 0.1 to x = 0.5, as determined from spectroscopic ellipsometry measurements. This knowledge opens a route to enhancing the performance of kesterite-based photovoltaic devices by a Ge-graded absorber layer. Furthermore, the formation of GeO2 on the surface of the as-grown samples was detected by X-ray photoelectron spectroscopy, having an important impact on the effective optical response of the material. This should be also taken into account when designing photovoltaic solar cells. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The influence of initial surface conditions on the subsequent corrosion behaviour of AZ31 and AZ61 magnesium alloys in 0.6 M NaCl solution has been studied using electrochemical impedance spectroscopy. For obtaining the different surface conditions, some of the specimens were immersion tested with the surface in the as-received condition, while others were tested immediately after mechanical polishing, and part of the polished specimens after six months of exposure to the laboratory atmosphere. Considering the evolution of the high-frequency capacitive arc of the Nyquist diagram, whose diameter is related to the corrosion process, a clear effect of the initial surface conditions is observed only in the early stages of testing. This effect is especially significant for the freshly polished specimens

This paper studies the corrosion rate of magnesium alloys AZ31 and AZ61 exposed in humid air under continuous condensation conditions. The shape of the gravimetric curves for corrosion progress suggests that the process is controlled by factors related with the corrosion product layer growing on the metallic surface according to gravimetric results there is an initial period in which only a small part of the corroded metal is incorporated in the corrosion product layer, but after longer testing times the proportion of metal that comes to form part of this layer tends to increase very significantly

The purpose of this study has been to advance in knowledge of the chemical composition, structure and thickness of the thin native oxide film formed spontaneously in contact with the laboratory atmosphere on the surface of freshly polished commercial AZ31 and AZ61 alloys with a view to furthering the understanding of protection mechanisms. For comparative purposes, and to more fully describe the behaviour of the native oxide film, the external oxide films formed as a result of the manufacturing process (as-received condition) have been characterised. The technique applied in this research to study the thin oxide films (thickness of just a few nanometres) present on the surface of the alloys has basically been XPS (X-ray photoelectron spectroscopy) in combination with ion sputtering. Corrosion properties of the alloys were studied in 0.6 M NaCl by measuring charge transfer resistance values, which are deduced from EIS (electrochemical impedance spectroscopy) measurements after 1 h of exposure. Alloy AZ61 generally showed better corrosion resistance than AZ31, and the freshly polished alloys showed better corrosion resistance than the alloys in as-received condition. This is attributed to a combination of (1) higher thickness of the native oxide film on the AZ61 alloy and (2) greater uniformity of the oxide film in the polished condition. The formation of an additional oxide layer composed by a mixture of spinel (MgAl2O4) and MgO seems to diminish the protective properties of the passive layer on the surface of the alloys in as-received condition

The well-known radical and ion scavenger techniques of application in amorphous hydrogenated carbon film deposition studies are investigated in relation to the mechanism of tritium and deuterium co-deposition in carbon-dominated fusion devices. A particularly successful scheme results from the injection of nitrogen into methane/hydrogen plasmas for conditions close to those prevailing in the divertor region of present fusion devices. A complete suppression of the a-C: H film deposition has been achieved for N2/CH4 ratios close to one in methane (5%)/hydrogen DC plasma. The implications of these findings in the tritium retention control in future fusion reactors are addressed.© 2002 IOP Publishing Ltd

The effect of exposure to the UVCON (humidity and UV radiation) accelerated corrosion test of a poly(vinyl chloride) paint applied over cleaned, abraded, and pre-rusted mild steel substrates has been investigated from the interfacial chemistry and adhesion standpoints. The X-ray photoelectron spectroscopy (XPS) data reveal significant differences in the locus and mode of adhesion loss, which depend on the time of exposure and the initial presence of a rust layer on the mild steel. The adhesion values obtained with the pre-rusted mild steel were greater than those obtained with the cleaned and abraded mild steel before exposure. After 15 days of exposure, it was observed that changes in the interfacial surface composition of the PVC/cleaned and abraded mild steel systems might have important positive effects on the adhesion strength values. The XPS data suggest the oxidation of both interfacial surfaces incorporating polar C-O and C=O species, which would be expected to enhance the adhesion of paint to metal. In contrast, the PVC paint/pre-rusted mild steel system showed no change in adhesion values or interfacial surface composition over the entire period of exposure.