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Long term steels corrosion : physico-chemical properties of ferrous hydroxysalts
No full textCette étude a porté sur différents hydroxysels ferreux, formés en milieu carbonaté ou sulfaté. Ces composés sont connus pour le rôle important qu’ils jouent lors des processus de corrosion à long terme des aciers en milieux naturels (sols, milieu marin). La chukanovite, hydroxycarbonate ferreux de composition Fe2(OH)2CO3, a été particulièrement étudiée. Son enthalpie libre standard de formation a ainsi pu être déterminée à partir d’une étude détaillée des conditions d’équilibre avec l’hydroxyde de Fe(II), réalisée sur des suspensions aqueuses vieillies jusqu’à 6 mois. Cette détermination a permis de tracer des diagrammes d’équilibre potentiel-pH du fer incluant la chukanovite et mettant en évidence son domaine de stabilité thermodynamique. Par comparaison avec des diagrammes similaires incluant la sidérite FeCO3, il a été possible de montrer que la chukanovite était métastable (à 25°C) par rapport à la sidérite. Nous avons également étudié les mécanismes de transformation de la chukanovite pour différentes conditions d’oxydation, en utilisant notamment le peroxyde d’hydrogène pour accélérer la cinétique de la réaction. Les résultats obtenus montrent, qu’à 25°C, la chukanovite se transforme en lépidocrocite et/ou goethite sans passer par un composé intermédiaire Fe(II,III) de type rouille verte. La goethite est favorisée par une augmentation du pH (excès de carbonate par exemple). Une oxydation violente par le peroxyde d’hydrogène conduit à la formation d’un oxycarbonate de Fe(III), structurellement très proche de la chukanovite. Enfin, deux hydroxysulfates ferreux ont été mis en évidence et caractérisés par diffraction des rayons X et spectroscopie Infrarouge. Ces composés n’ont cependant pas pu être obtenus seuls, mais toujours ensembles, et/ou avec Fe(OH)2, voire un 3ème hydroxysulfate ferreux. Une étude des processus d’oxydation a permis de révéler que tous ces composés se transformaient dans un premier temps en rouille verte sulfatée.This study deals with various ferrous hydroxysalts formed in carbonated or sulphated environments. These compounds are known to play an important role during the long term corrosion processes of carbon steel in natural media (soils, seawater). Chukanovite, the Fe(II) hydroxycarbonate with composition Fe2(OH)2CO3, was studied more particularly. Its standard Gibbs free energy of formation could be determined via the detailed study of the equilibrium conditions with Fe(II) hydroxide, performed with aqueous suspensions aged up to 6 months. Potential-pH equilibrium diagrams of iron could then be drawn including chukanovite and highlighting its domain of stability. A comparison with diagrams drawn with siderite FeCO3 revealed that chukanovite was metastable (at 25°C) with respect to siderite. The mechanisms of transformation of chukanovite were also studied for various conditions of oxidation. Hydrogen peroxide was for instance used to accelerate the reaction. The obtained results show that the oxidation of chukanovite leads, at 25°C, to lepidocrocite and/or goethite without the formation of an intermediate Fe(II,III) green rust-like compound. Goethite is favored by an increase of pH (i.e. excess of carbonate). The violent oxidation by hydrogen peroxide leads to a Fe(III) oxycarbonate structurally similar to chukanovite. Finally, two Fe(II) hydroxysulphates could be identified and characterised by X-ray diffraction and infrared spectroscopy. These compounds could not however be obtained alone, but always together, and/or with Fe(OH)2 or maybe a third Fe(II) hydroxysulphate. The study of their oxidation process revealed that all these compounds were first transformed to sulfated green rust
Corrosion des aciers à long terme : propriétés physico-chimiques des hydroxysels ferreux
No full textThis study deals with various ferrous hydroxysalts formed in carbonated or sulphated environments. These compounds are known to play an important role during the long term corrosion processes of carbon steel in natural media (soils, seawater). Chukanovite, the Fe(II) hydroxycarbonate with composition Fe2(OH)2CO3, was studied more particularly. Its standard Gibbs free energy of formation could be determined via the detailed study of the equilibrium conditions with Fe(II) hydroxide, performed with aqueous suspensions aged up to 6 months. Potential-pH equilibrium diagrams of iron could then be drawn including chukanovite and highlighting its domain of stability. A comparison with diagrams drawn with siderite FeCO3 revealed that chukanovite was metastable (at 25°C) with respect to siderite. The mechanisms of transformation of chukanovite were also studied for various conditions of oxidation. Hydrogen peroxide was for instance used to accelerate the reaction. The obtained results show that the oxidation of chukanovite leads, at 25°C, to lepidocrocite and/or goethite without the formation of an intermediate Fe(II,III) green rust-like compound. Goethite is favored by an increase of pH (i.e. excess of carbonate). The violent oxidation by hydrogen peroxide leads to a Fe(III) oxycarbonate structurally similar to chukanovite. Finally, two Fe(II) hydroxysulphates could be identified and characterised by X-ray diffraction and infrared spectroscopy. These compounds could not however be obtained alone, but always together, and/or with Fe(OH)2 or maybe a third Fe(II) hydroxysulphate. The study of their oxidation process revealed that all these compounds were first transformed to sulfated green rust.Cette étude a porté sur différents hydroxysels ferreux, formés en milieu carbonaté ou sulfaté. Ces composés sont connus pour le rôle important qu’ils jouent lors des processus de corrosion à long terme des aciers en milieux naturels (sols, milieu marin). La chukanovite, hydroxycarbonate ferreux de composition Fe2(OH)2CO3, a été particulièrement étudiée. Son enthalpie libre standard de formation a ainsi pu être déterminée à partir d’une étude détaillée des conditions d’équilibre avec l’hydroxyde de Fe(II), réalisée sur des suspensions aqueuses vieillies jusqu’à 6 mois. Cette détermination a permis de tracer des diagrammes d’équilibre potentiel-pH du fer incluant la chukanovite et mettant en évidence son domaine de stabilité thermodynamique. Par comparaison avec des diagrammes similaires incluant la sidérite FeCO3, il a été possible de montrer que la chukanovite était métastable (à 25°C) par rapport à la sidérite. Nous avons également étudié les mécanismes de transformation de la chukanovite pour différentes conditions d’oxydation, en utilisant notamment le peroxyde d’hydrogène pour accélérer la cinétique de la réaction. Les résultats obtenus montrent, qu’à 25°C, la chukanovite se transforme en lépidocrocite et/ou goethite sans passer par un composé intermédiaire Fe(II,III) de type rouille verte. La goethite est favorisée par une augmentation du pH (excès de carbonate par exemple). Une oxydation violente par le peroxyde d’hydrogène conduit à la formation d’un oxycarbonate de Fe(III), structurellement très proche de la chukanovite. Enfin, deux hydroxysulfates ferreux ont été mis en évidence et caractérisés par diffraction des rayons X et spectroscopie Infrarouge. Ces composés n’ont cependant pas pu être obtenus seuls, mais toujours ensembles, et/ou avec Fe(OH)2, voire un 3ème hydroxysulfate ferreux. Une étude des processus d’oxydation a permis de révéler que tous ces composés se transformaient dans un premier temps en rouille verte sulfatée
Corrosion des aciers à long terme : propriétés physico-chimiques des hydroxysels ferreux
No full textThis study deals with various ferrous hydroxysalts formed in carbonated or sulphated environments. These compounds are known to play an important role during the long term corrosion processes of carbon steel in natural media (soils, seawater). Chukanovite, the Fe(II) hydroxycarbonate with composition Fe2(OH)2CO3, was studied more particularly. Its standard Gibbs free energy of formation could be determined via the detailed study of the equilibrium conditions with Fe(II) hydroxide, performed with aqueous suspensions aged up to 6 months. Potential-pH equilibrium diagrams of iron could then be drawn including chukanovite and highlighting its domain of stability. A comparison with diagrams drawn with siderite FeCO3 revealed that chukanovite was metastable (at 25°C) with respect to siderite. The mechanisms of transformation of chukanovite were also studied for various conditions of oxidation. Hydrogen peroxide was for instance used to accelerate the reaction. The obtained results show that the oxidation of chukanovite leads, at 25°C, to lepidocrocite and/or goethite without the formation of an intermediate Fe(II,III) green rust-like compound. Goethite is favored by an increase of pH (i.e. excess of carbonate). The violent oxidation by hydrogen peroxide leads to a Fe(III) oxycarbonate structurally similar to chukanovite. Finally, two Fe(II) hydroxysulphates could be identified and characterised by X-ray diffraction and infrared spectroscopy. These compounds could not however be obtained alone, but always together, and/or with Fe(OH)2 or maybe a third Fe(II) hydroxysulphate. The study of their oxidation process revealed that all these compounds were first transformed to sulfated green rust.Cette étude a porté sur différents hydroxysels ferreux, formés en milieu carbonaté ou sulfaté. Ces composés sont connus pour le rôle important qu’ils jouent lors des processus de corrosion à long terme des aciers en milieux naturels (sols, milieu marin). La chukanovite, hydroxycarbonate ferreux de composition Fe2(OH)2CO3, a été particulièrement étudiée. Son enthalpie libre standard de formation a ainsi pu être déterminée à partir d’une étude détaillée des conditions d’équilibre avec l’hydroxyde de Fe(II), réalisée sur des suspensions aqueuses vieillies jusqu’à 6 mois. Cette détermination a permis de tracer des diagrammes d’équilibre potentiel-pH du fer incluant la chukanovite et mettant en évidence son domaine de stabilité thermodynamique. Par comparaison avec des diagrammes similaires incluant la sidérite FeCO3, il a été possible de montrer que la chukanovite était métastable (à 25°C) par rapport à la sidérite. Nous avons également étudié les mécanismes de transformation de la chukanovite pour différentes conditions d’oxydation, en utilisant notamment le peroxyde d’hydrogène pour accélérer la cinétique de la réaction. Les résultats obtenus montrent, qu’à 25°C, la chukanovite se transforme en lépidocrocite et/ou goethite sans passer par un composé intermédiaire Fe(II,III) de type rouille verte. La goethite est favorisée par une augmentation du pH (excès de carbonate par exemple). Une oxydation violente par le peroxyde d’hydrogène conduit à la formation d’un oxycarbonate de Fe(III), structurellement très proche de la chukanovite. Enfin, deux hydroxysulfates ferreux ont été mis en évidence et caractérisés par diffraction des rayons X et spectroscopie Infrarouge. Ces composés n’ont cependant pas pu être obtenus seuls, mais toujours ensembles, et/ou avec Fe(OH)2, voire un 3ème hydroxysulfate ferreux. Une étude des processus d’oxydation a permis de révéler que tous ces composés se transformaient dans un premier temps en rouille verte sulfatée
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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