The Role of Active Elements in the Oxidation Behaviour of High Temperature Metals and Alloys


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Brand new Book. Metals and alloys rely for their application at high temperature on the formation and retention of oxide scales, which act as a barrier between the metallic substrate and the reactive species in the environment such as 0, S, N, C, Cl, etc. This protection concept requires that the oxide grows slowly, develops a dense, uniform layer, is well adherent, has sufficient ductility to accom- modate plastic deformation of the substrate and is resistant to thermal cycling.

For many years it has been known that small concentrations of certain "active elements" such as Y and the rare earths, as well as carbon and sulphur, can exercise a significant influence upon the oxidation! An increasing number of experimental studies on this topic have been published recently.

However no generally accepted understanding with regard to the detailed mechanisms and the way in which alloy composition and structure, temperature and environmental conditions, etc. It therefore seemed to be an appropriate time to bring together a group of experts to review and evaluate the current state-of-the-art and to discuss various aspects of this important topic. Softcover reprint of the original 1st ed. Seller Inventory AAV New Book. Shipped from UK. Established seller since Seller Inventory LQ Seller Inventory LIE From: M. London, United Kingdom. Condition: good. Original Printed patent disbound with printed front blue wrapper present but not the back wrapper both often lacking in early patents About 27cm by 18cm some wear and tear due to the disbinding.

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Characteristics of Alloying Elements in Steel

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Seller Inventory ING Published by Springer Netherlands About this Item: Springer Netherlands, Condition: Brand New. In Stock. Seller Inventory x Published by Kiev About this Item: Kiev, Please feel free to request a detailed description. Short description : Directory. Naukova Dumka. Please contact us for details on condition of available copies of the book. SKUalb Language: Russian. Seller Inventory alb It was also found that upon subsequent removal of water from the gas phase the CO dissociation rate increased again. It is shown that the surface activity for CO dissociation should be a key factor for carbon uptake in certain applications and can be reduced by adsorbed water.

They also demonstrate that the partial dissociation of water into OH and H is faster than oxygen dissociation. The oxidation reactions and oxygen exchange mechanisms were studied by monitoring the concentration of consumed and evolved gases in a sealed volume with mass spectrometry. He demonstrated that very few of the molecules hitting the surface participate in oxidation and in oxygen exchange, which indicates that there are only a few active sites on the surface. An addition of 0.

This is most likely due to the fact that Y increases the O2 dissociation rate and, thereby, the surface concentration of atomic O. This could Fig.

Description

In i no O2 dissociation is needed. In ii and iii the adsorbed O can have two sources: the gas O2 and H2O or the oxide oxygen exchange with the oxide.


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  • In this type of eval- uation, an important question to resolve is whether 16,18O2 an intermediate in the formation of 18,18 O2. In any case, the surface-absorbed O in paths ii and iii must come from dissociation of O2 and H2O. An initial increase of 18,18O2 is due to path iii and the surface-adsorbed O comes from complete dissociation of H2O. O2 dissociation has a higher activation energy on diamonds than water, thus dissociation of water is favoured at low temperature and O2 dissociation at high temperatures []. Raynaud and Rapp [76] propose that the faster growth of whiskers in moist atmospheres is related to the generally faster dissociation of water molecules than for most other oxidant molecules.

    The observation of whisker formation, particularly at lower temperatures, is often associated with the presence of water vapour, for example, see also the work of Pieraggi et al. In conclusion, while a large amount of information exists about adsorption and disso- ciation processes derived from surface science studies at low temperatures room temper- ature or below , very little direct evidence exists about these processes at temperatures of interest to researchers concerned with high temperature corrosion.

    In general, it appears that dissociation of any gas molecule is favoured by defects in the surface, and thus the stoichiometric oxides such alumina may therefore be less active than, for example, FeO. There seems to be general agreement that relative acidity basicity of oxides controls the reaction with water vapour, where water vapour will react more strongly with more acidic oxides.

    However what is not clear is how to rank oxides. The commonly used method of PZC or IEP is believed to yield a good relative assessment while use of chemical shift mea- surements by XPS or heats of adsorption by calorimetry or gas chromatography yield bet- ter absolute values [93]. However Galerie et al. It was therefore concluded that, when competition occurs between these two oxides on the steel surface, at a crack tip or in an interfacial pore, haematite is favoured in the presence of water vapour, leading to nodule formation and catastrophic oxidation.

    The three main protective oxides will be considered, alumina, chromia and silica as well as the iron oxides and nickel oxide. The work of Kofstad [71,—], Norby [] and Atkinson et al. Dieckmann [] reviewed the trans- port of water in oxides but importantly also considered solution of water in oxides.

    Oxidation Metals Alloys - AbeBooks

    For stoichiometric oxides, Schottky defects occur when there are equivalent con- centrations of anion and cation defects, normally anion and cation vacancies, and Frenkel defects, which occur when an anion or cation lattice site is transferred to an interstitial site leaving a cation or anion vacancy anion Frenkel defects are also referred to as anti-Fren- kel defects. For materials with high concentrations of defects, these can become associated as clusters see, for example, discussion of the FeO defect structure in Section 5.

    Whereas simple defects can be treated as ideal solutions, this is not the case for clusters and thus the quantitative understanding of transport in these cases is more complex and in some cases still not fully understood. Kroger and Vink [] developed a helpful notation that is commonly used to describe these point defects and this is used in what follows. When a metal ion occupies a metal lattice site this is written MM, and likewise an oxygen ion on a normal oxygen site is writ- ten OO. Most oxides contain impurities, and these are written, for example in the case of iron in chromia, as FeCr or Fei if the iron ion occupies a chromium lattice or interstitial site, respectively.

    Charges on the site are written as net charges. At higher p H2O or p O2 protons may become the dominant defect, compensated for by defect electrons, me- tal vacancies, oxygen interstitials or acceptor dopants. In close packed structures such as the alumina and chromia, dissolution of molecular water would be less favoured. The concentration of protons is increased by acceptor doping and decreased by donor doping, so that it is possible to use acceptor dop- ing to enhance hydrogen transport in oxides, and conversely, to use donor doping to reduce it.

    Example of defect concentrations in M2O3 versus water vapour partial pressure at constant p O2 ; numbers along lines denote slopes, after Ref. This leads to a build up of stress and usually the scale buckles and eventually spalls. Hultquist et al. There remains some doubt about the intrinsic naturally occurring defects in a-Al2O3 although it is generally believed to have negligible non-stoichiometry [].

    Experimental and theoretical studies concerning the dominant intrinsic disorder are found to be incon- clusive, but where a preference is stated it is for Schottky disorder. Atkinson et al. The concentration of hydrogen in the oxide increases with an increase in the temperature used to saturate the oxide, the partial pressure of hydrogen used and the p O2 or p H2O. Proton conduction was observed by Kurita et al. Fuka- tsu et al. Norby and Kofstad [] also reported proton conduction in a polycrystalline sintered a-alumina under reducing conditions.

    This result is in general agreement with the results presented in Section 2. Chromia The extent of non-stoichiometry in chromia is very small, but unfortunately there are no reliable quantitative data. It is also proposed that segregation of the rare earth elements to the oxide grain boundary prevents grain growth and thus enhances oxide plasticity [71].

    Revealing internal flow behaviour in arc welding and additive manufacturing of metals

    They concluded that the oxide is an electronic conductor. For Ti-doped Cr2O3, the oxide is an n-type conductor at reduced oxygen activities and a p-type conductor at high oxygen activities. This is qualitatively the observed behaviour Fig. However Atkinson et al. They demonstrated that even at these relatively high doping levels a solid solution with negligi- ble change in unit cell volume was formed. The dependence of the electrical conductivity on the oxygen-activity is shown in Fig.

    The Role of Active Elements in the Oxidation Behaviour of High Temperature Metals and Alloys The Role of Active Elements in the Oxidation Behaviour of High Temperature Metals and Alloys
    The Role of Active Elements in the Oxidation Behaviour of High Temperature Metals and Alloys The Role of Active Elements in the Oxidation Behaviour of High Temperature Metals and Alloys
    The Role of Active Elements in the Oxidation Behaviour of High Temperature Metals and Alloys The Role of Active Elements in the Oxidation Behaviour of High Temperature Metals and Alloys
    The Role of Active Elements in the Oxidation Behaviour of High Temperature Metals and Alloys The Role of Active Elements in the Oxidation Behaviour of High Temperature Metals and Alloys
    The Role of Active Elements in the Oxidation Behaviour of High Temperature Metals and Alloys The Role of Active Elements in the Oxidation Behaviour of High Temperature Metals and Alloys
    The Role of Active Elements in the Oxidation Behaviour of High Temperature Metals and Alloys The Role of Active Elements in the Oxidation Behaviour of High Temperature Metals and Alloys
    The Role of Active Elements in the Oxidation Behaviour of High Temperature Metals and Alloys The Role of Active Elements in the Oxidation Behaviour of High Temperature Metals and Alloys
    The Role of Active Elements in the Oxidation Behaviour of High Temperature Metals and Alloys The Role of Active Elements in the Oxidation Behaviour of High Temperature Metals and Alloys

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