CC BY
7Наноматериалы и нанотехнологии в аэрокосмической отрасли
величина допирования x и температура T. Последняя задается через тип магнитного упорядочения -парамагнитный или ферромагнитный, что соответствует температурам выше и ниже температуры Кюри TC.
В области 0,2 < x < 0,3 результаты для дисперсионных соотношений качественно совпадают с результатами фотоэмиссионных ARPES-исследований. Од-
нако переход «металл-диэлектрик» в точке ТС при значениях параметров, вычисленных в первоприн-ципном ЬБЛ-подходе, получить невозможно.
Библиографическая ссылка
1. Вальков В. В., Овчинников С. Г. Квазичастицы в сильно коррелированных системах. Новосибирск : Изд-во СО РАН, 2001.
V. A. Gavrichkov, S. G. Ovchinnikov L. V. Kirensky Institute of Physics, Russian Academy of Science, Siberian Branch, Russia, Krasnoyarsk
L. E. Yakimov
Siberian State Aerospace University named after academician M. F. Reshetnev, Russia, Krasnoyarsk ELECTRONIC STRUCTURE OF MANGANITE MATERIALS
The generalized tight-binding method is used to obtain the quasiparticle dispersion in La1-xSrxMnO3 manganites. The Hamiltonian of the MnO6 cluster is exactly diagonalized. The inter-cluster interactions Hamiltonian is written using the basis of cluster eigen states. The dispersion equation is solved numerically. The calculated dispersion reproduces the quasiparticle dispersion from ARPES data.
© Гавричков В. А., Овчинников С. Г., Якимов Л. Е., 2010
ISBN 669.713.7
G. Gosmanova, I. Kraus Czech Technical University, Czech Republic, Prague
XRD ANALYSIS OF OXIDE LAYERS FORMED ON ZrlNb ALLOY AT 360 °C IN VVER ENVIRONMENT*
The contribution deals with properties of oxide layers arising on ZrlNb alloy during oxidation.
Corrosion properties of zirconium alloys are intensively investigated because of their main use as fuel claddings in primary circuits of nuclear reactors. However, the corrosion mechanism of zirconium alloys is still not quite understood. The characterization of the oxide properties such as macroscopic stresses c and microstructure and their changes through different stages of oxide growth may contribute to better understanding of corrosion mechanism. The investigation has been performed in cooperation with UJP PRAHA, Inc., where the corrosion behavior of Zr-based alloys in different environments has been studied in long-term tests. Tubular specimens from Kroll ZrlNb alloy (Russia) denoted 6 were oxidized at 360 °C in VVER imitating water with exposures varying from 105 to 357 days. The measurements were carried out on two types of oxide layers so-called "wet" and "dry". While the "dry" samples were dehydrated on air after corrosion exposure, the "wet" samples were permanently kept in water. It is known that ZrO2 is gradually hydrated forming hydrated oxide of a gel character when exposed to water. The gel represents a two-phase system forming a joint structure composed of solid and liquid components. It can be assumed that "wet" samples better correspond to the oxide state in-situ. Since X-rays cannot detect the
amorphous gel, the obtained characteristics are related only to the crystalline part, i.e., monoclinic ZrO2 of the hydrated layer. The measurements were performed on {10-4} planes of monoclinic ZrO2 using CoKa radiation. The „sum of the surface principal stresses" technique with a reference substance was used to the macroscopic stresses determination [1].
The recent XRD research was focused on the properties of gel-like oxide layers [2]. It was shown that: (a) the values of macroscopic stresses c in the crystalline part of hydrated layers increase in comparison with those of dry samples. The effect can be caused by the increase in the hydrated layer volume provided a mechanical stability stays in the oxide/metal system, (b) the values of crystallite size D in the crystalline part of hydrated layers decrease in comparison with those of dry samples. The effect can be caused by dissolution of the mosaic blocks boundaries. These findings can be illustrated using average values of investigated quantities, which were calculated for the corresponding range of exposures:
a W (MPa) -1085 D W (nm) 14 s W 0,0069
a D (MPa) -990 D D (nm) 16 s D 0,0072
Ra(D-W) 94 R D(D-W) 2 R s (D - W) 0,0003
A a 51 A D 1 A s 0,0002
*This research has been supported by MSMT grant No 6840770021.
Решетневские чтения
Average values of macroscopic stresses c crystallite size D and microdeformations e determined for hydrated (W) and dehydrated (D) oxide layers of alloy ZrlNb type 6 oxidized at 360 °C in the VVER environment. The differences R between D and W values and errors of measurement are tabled as well.
The present investigation indicates that exceptions occur from this observation. The above-mentioned relations between characteristics of wet and dry oxide layers are reversed after some exposures, i.e. cW < cD and DW > Dd. Moreover intensity diffracted from (10-4) plane decreased for hydrated layers at the same exposures. Graphs in the figure illustrate differences Rc (D-W) and RM (D-W) (A), corrosion kinetics (B) and courses of crystallite size D of oxide layers for "wet" and "dry" samples of alloy 6 exposed in VVER water. Exposures related to kinetics changes are highlighted.
The increase of crystallite size D in the hydrated layers (Fig. C) can be caused by stress induced recrystalliza-tion. On the assumption that the whole mass of the crystalline component remains the same, reorientation of crystallites should occur if the diffracted intensity decreases for hydrated layers (Fig. A). Such changes in microstructure are accompanied with a decrease of macroscopic stresses (Fig. A) and probably with the pores evaluation in oxide layers. Consequently, the changes in
oxidation process can be expected for both the steady state and temporary character. As can be seen from Fig. B, the changes of oxidation process correspond with above-mentioned observations. It should be noticed that transition from parabolic to quasi-linear kinetic was actually declared for alloy ZrlNb type 6 about the exposure 210 days (Tox ~ 3.5 ^m).
It can be concluded from the results of XRD analysis that the changes in oxidation process are related to the changes in microstructure of oxide layers such as stress-induced recrystallization together with reorientation of crystallites. This assumption is in good agreement with the diffusion model of corrosion. Other important physical factors (as tetragonal - monoclinic phase transformation) contribute to steady state kinetics changes as well.
References
1. Kraus I., Trofimov V. V. Rentgenova tenzometrie. Praha : Academia, 1988.
2. Influence of hydration on the XRD-determined characteristics of zirconium oxide layers [Electronic resource] / Gosmanova G. et al // Proc. of 17th Int. Met. Conf. Metal 2008. Cerveny zamek, Hradec nad Moravici, CR. 13.05-15.05.2008. CD-ROM. Ostrava : Tanger, 2008. P. 1-3.
EXP (days)
Differences R (D-W) between values of stresses a and integral intensity respectively (A), oxidation kinetics (B) and crystallite size D (C) obtained for dehydrated (D) and hydrated (W) oxide layers by means of X-ray measurements.
The exposures related to kinetics changes are depicted
Галина Гозманова, Иво Краус
Чешский технический университет, факультет ядерной физики и физической инженерии, Чешская Республика, Прага
ПОРОШКОВАЯ РЕНТГЕНОСТРУКТУРНАЯ КРИСТАЛЛОГРАФИЯ ОКСИДНЫХ СЛОЕВ, ОБРАЗОВАННЫХ НА СПЛАВЕ ZrlNb ПРИ ТЕМПЕРАТУРЕ 360°C В ВОДНОМ ЭНЕРГЕТИЧЕСКОМ РЕАКТОРЕ
В исследовании рассматриваются свойства оксидных слоев, возникающих на сплаве ZrlNb во время окисления.
© Gosmanova G., Kraus I., 2010
