Passive and transpassive behaviour of Alloy 31 in a heavy brine LiBr solution

The passive and transpassive behaviour of Alloy 31, a highly alloyed austenitic stainless steel (UNS N08031), has been investigated in a LiBr heavy brine solution (400 g/l) at 25 °C using potentiostatic polarisation combined with electrochemical impedance spectroscopy and Mott-Schottky analysis. The passive film formed on Alloy 31 has been found to be p-type and/or n-type in electronic character, depending on the film formation potential. The thickness of the film formed at potentials within the passive region increases linearly with applied potential. The film formed at transpassive potentials is thinner and more conductive than the film formed within the passive region. These observations are consistent with the predictions of the Point Defect Model for passive and transpassive films on metals and alloys

Effect of temperature on passive film formation of UNS N08031 Cr-Ni alloy in phosphoric acid contaminated with different aggressive anions

tThe influence of temperature and the effect of aggressive anions on the electrochemical behaviour of UNSN08031 stainless steel in a contaminated phosphoric acid solution were evaluated. Stabilisation of thepassive film was studied by potentiodynamic polarisation curves, potentiostatic tests, electrochemicalimpedance spectroscopy (EIS) measurements, Mott Schottky analysis and X-ray photoelectron spec-troscopy (XPS). The stability of the passive film was found to decrease as temperature increases. The filmformed on the stainless steel surface was a n-type semiconductor and the XPS spectrum revealed thepresence of fluoride ions.Authors express their gratitude to the Ministry of Education of Spain (MHE2011-00202) for its financial support during the stay at University of Manchester, to MAEC of Spain (PCI Mediterraneo C/8196/07, C/018046/08, D/023608/09 and D/030177/10) and to the Generalitat Valenciana (GV/2011/093) for the financial support. The authors would also like to acknowledge the support of the School of Materials at the University of Manchester for providing analytical and technical support for the study.Escrivá Cerdán, C.; Blasco Tamarit, ME.; García García, DM.; García Antón, J.; Akid, R.; Walton, J. (2013). Effect of temperature on passive film formation of UNS N08031 Cr-Ni alloy in phosphoric acid contaminated with different aggressive anions. Electrochimica Acta. 111:552-561. https://doi.org/10.1016/j.electacta.2013.08.040S55256111

Physicochemical Characterization of Passive Films and Corrosion Layers by Differential Admittance and Photocurrent Spectroscopy

Two different electrochemical techniques, differential admittance and photocurrent spectroscopy, for the characterization of electronic and solid state properties of passive films and corrosion layers are described and critically evaluated. In order to get information on the electronic properties of passive film and corrosion layers as well as the necessary information to locate the characteristic energy levels of the passive film/electrolyte junction like: flat band potential (Ufb), conduction band edge (EC) or valence band edge (EV), a wide use of Mott-Schottky plots is usually reported in corrosion science and passivity studies. It has been shown, in several papers, that the use of simple M-S theory to get information on the electronic properties and energy levels location at the film/electrolyte interface can be seriously misleading and/or conflicting with the physical basis underlying the M-S theory. A critical appraisal of this approach to the study of very thin and thick anodic passive film grown on base-metals (Cr, Ni, Fe, SS etc..) or on valve metals (Ta, Nb, W etc..) is reported in this work, together with possible alternative approach to overcome some of the mentioned inconsistencies. At this aim the theory of amorphous semiconductor Schottky barrier, introduced several years ago in the study of passive film/electrolyte junction, is reviewed by taking into account some of the more recent results obtained by the present authors. Future developments of the theory appears necessary to get more exact quantitative information on the electronic properties of passive films, specially in the case of very thin film like those formed on base metals and their alloys. The second technique described in this chapter, devoted to the physico-chemical characterization of passive film and corrosion layers, is a more recent technique based on the analysis of the photo-electrochemical answer of passive film/electrolyte junction under illumination with photons having suitable energy. Such a technique usually referred to as Photocurrent Spectroscopy (PCS) has been developed on the basis of the large research effort carried out by several groups in the 1970’s and aimed to investigate the possible conversion of solar energy by means of electrochemical cells. In this work the fundamentals of semiconductor/electrolyte junctions under illumination will be highlighted both for crystalline and amorphous materials. The role of amorphous nature and film thickness on the photo-electrochemical answer of passive film/solution interface is reviewed as well the use of PCS for quantitative analysis of the film composition based on a semi-empirical correlation between optical band gap and difference of electronegativity of film constituents previously suggested by the present authors. In this frame the results of PCS studies on valve metal oxides and valve metal mixed oxides will be discussed in order to show the validity of the proposed method. The results of PCS studies aimed to get information on passive film composition and carried out by different authors on base metals (Fe, Cr, Ni) and their alloys, including stainless steel, will be also compared with compositional analysis carried out by well-established surface analysis techniques

Etude théorique et expérimentale de dispositifs à ondes élastiques de surface (O.E.S) à base des structures multicouches (ZnO/Quartz, AIN/Diamant et ZnO/AIN/Diamant)

Ce mémoire avait l'objectif de modéliser, réaliser et caractériser des dispositifs SAW à base de structures multicouches à savoir : ZnO/Quartz, AlN/Diamant et ZnO/AlN/Diamant, pour les applications capteurs et hautes fréquences. La première partie de ce mémoire a été consacrée à l'étude théorique de modélisation de structures multicouches de dispositifs SAW. Dans la deuxième partie de ce travail, nous avons présenté les procédés technologiques nécessaires pour la fabrication de ces dispositifs, ainsi nous avons également présenté les méthodes de caractérisation des principaux paramètres de ces dispositifs. Concernant La troisième partie, nous avons étudié les dépôts de films de diamant, d'oxyde de zinc et de nitrure d'aluminium. Nous avons également proposé une solution originale consistant à utiliser la face de nucléation du diamant auto-supporté qui présente une bonne qualité morphologique permettant d'assurer une bonne propagation des ondes élastiques. Dans la dernière partie, nous avons réalisé des capteurs SAW à base de structure ZnO/Quartz stables aux variations thermiques et présentant de bonnes sensibilités. Nous avons également réalisé des filtres SAW à base de structure AlN/diamant fonctionnant à haute fréquence tout en offrant de bonnes qualités de filtrage. Enfin, nous avons étudié et réalisé une structure originale, ZnO/AlN/Diamant, combinant un grand coefficient de couplage électromécanique et une grande vitesse de propagation.We investigate in this work the multilayer structures ZnO/Quartz, AlN/Diamond and ZnO/AlN/Diamond for designing SAW sensors and high frequency SAW filters. Beginning with a theoretical study that we have developed for modelling the SAW structures, we discuss then the technological processes used for preparing such devices and also the characterisation methods implemented to determine the device principal parameters. We describe subsequently an original method that we have established for SAW device design of the deposits on the diamond. The films are grown in this method on the unpolished nucleation side of the freestanding CVD diamond. These nucleation side have good morphological qualities which enhance the acoustic wave propagation. The ZnO/Quartz-based SAW sensors and AlN/Diamond-based SAW filters that we have designed are then presented and discussed as to their performances. While the sensors show a high sensibility and a low temperature coefficient, the filter can be operate at high frequencies without loosing its filtering capacity. Finally, a. new SAW device based on ZnO/AlN/Diamond combining high phase velocity and high electromechanical coupling coefficient has been investigated for GHz-band applications.NANCY1-SCD Sciences & Techniques (545782101) / SudocSudocFranceF