24 research outputs found
Theory of a quodon gas. With application to precipitation kinetics in solids under irradiation
Rate theory of the radiation-induced precipitation in solids is modified with
account of non-equilibrium fluctuations driven by the gas of lattice solitons
(a.k.a. quodons) produced by irradiation. According to quantitative
estimations, a steady-state density of the quodon gas under sufficiently
intense irradiation can be as high as the density of phonon gas. The quodon gas
may be a powerful driver of the chemical reaction rates under irradiation, the
strength of which exponentially increases with irradiation flux and may be
comparable with strength of the phonon gas that exponentially increases with
temperature. The modified rate theory is applied to modelling of copper
precipitation in FeCu binary alloys under electron irradiation. In contrast to
the classical rate theory, which disagrees strongly with experimental data on
all precipitation parameters, the modified rate theory describes quite well
both the evolution of precipitates and the matrix concentration of copper
measured by different methodsComment: V. Dubinko, R. Shapovalov, Theory of a quodon gas. With application
to precipitation kinetics in solids under irradiation. (Springer
International Publishing, Switzerland, 2014
Nonmonotonic inelastic tunneling spectra due to surface spin excitations in ferromagnetic junctions
The paper addresses inelastic spin-flip tunneling accompanied by surface spin
excitations (magnons) in ferromagnetic junctions. The inelastic tunneling
current is proportional to the magnon density of states which is
energy-independent for the surface waves and, for this reason, cannot account
for the bias-voltage dependence of the observed inelastic tunneling spectra.
This paper shows that the bias-voltage dependence of the tunneling spectra can
arise from the tunneling matrix elements of the electron-magnon interaction.
These matrix elements are derived from the Coulomb exchange interaction using
the itinerant-electron model of magnon-assisted tunneling. The results for the
inelastic tunneling spectra, based on the nonequilibrium Green's function
calculations, are presented for both parallel and antiparallel magnetizations
in the ferromagnetic leads.Comment: 9 pages, 4 figures, version as publishe
Mineralogy and microporous structure of rocks from a natural CO2 reservoir
Different experimental approaches have been combined to reconstruct the mineral association and microporous structure of rocks from a natural CO2 reservoir.
The fluid reservoir (Caprese Reservoir), was discovered while drilling PSS1 (Pieve Santo Stefano 1) wellbore in San Cassiano Basin (Eastern Tuscany, Central Italy, and consists of sedimentary rocks (Burano Fm.) interbedded with altered volcanic rocks, its depth being about 3,300 m with respect to the land surface. At 3,700 m depth fluid pressure and temperature are 700 bar and 120 \ub0C respectively, with a density for the supercritical CO2\u2013rich fluid of 840 Kg\ub7m-3.
The study was conducted on the volcanic rocks altered by CO2 from the PSS1 wellbore drillcores and on some volcanic rocks unaffected by the presence of CO2. Lastly, rocks from the Burano Formation, unavailable from PSS1, have been sampled on outcrop.
Focus is on rocks samples corresponding to the depth 3,864-3,871 m with respect to PSS1 log, which have been investigated with SEM-EDS and XRD for mineralogical characterization. Moreover, Small Angle Neutron Scattering (SANS) experiments at LLB (Saclay, France) served for microporous structure investigation of PSS1 rocks, and other volcanic rocks from Eastern Alps (IG1) and the Albani Hills (IG2 and IG3) unaffected by CO2, as well as Burano Formation rocks from outcrop
Texture analysis of oxide dispersion strengthened (ODS) Fe alloys by X-ray and neutron diffraction
The ferritic ODS alloys studied were obtained by mechanical alloying. This strengthening method is very
attractive, in particular for nuclear applications. In order to ensure the alloy a good compromise
between mechanical resistance and ductility at high temperatures, it is necessary to control the
microstructure and in particular the evolution during the recrystallization. First, a preliminary study,
performed by X ray diffraction and optical microscopy, shows several grain growth mechanisms ; in
particular, the âabnormalâ grain growth mechanism which conducts to a large grain size [1], [2]. After
annealing (3600s at 1470C), the 30% cold-worked (swaging) alloys exhibit an heterogeneous
microstructure with a large grains size (~200 to 500 m) in the heart and near the surface of
the material when the intermediate zone is inhabited by small grains (~1 m). Fora higher
cold-work level (60%), large size grains are only present in the periphery of the material. On account
of the large grain size and strong heterogeneity of the microstructure, texture analysis using laboratory
x-ray beam in not well adapted and so we have decided to use neutron beam. The neutron diffraction texture
analysis has been performed at the Laboratoire LĂ©on Brillouin on the 6T1 diffractometer on 2
different rods of the alloy (corresponding to the reduction ratios of 30% and 60%). Specific samples
have been machined to characterise separately the zones with a different microstructure.
After deformation, the alloys exhibit a typical -fibre texture
whatever the
area of the sample and the reduction ratio. After recrystallization, a very inhomogeneous texture is
evidenced through the thickness of the sample, in particular for the rod deformed with a reduction ratio
of 30% : in the heart and in the periphery of the rod, a âsingle-crystalâ type texture is observed;
the a fibre remains for the intermediate diameter of the rod.
For the rod cold rolled with a reduction ratio of 60%, the $\alpha$-fibre keeps on the heart
of the material and as in the precedent case, a âsingle-crystalâ type texture is observed near the
surface of the sample. EBSD measurements have been performed to explicit at a local scale this behaviour
and in order to furnish some input data for the simulation of static recrystallization.Les aciers ferritiques avec dispersion d'oxydes étudiés sont obtenus par métallurgie des poudres,
ce qui leur confÚre une résistance mécanique accrue à haute température notamment pour des applications
nucléaires. La difficulté pour l'utilisation de tels alliages réside dans la maßtrise de leur
microstructure au cours de l'Ă©laboration en particulier durant la recristallisation. Une premiĂšre
étude en diffraction des rayons-x et en métallographie optique a permis de révéler différents
mĂ©canismes de croissance du grain lors de la recristallisation, notamment une croissance âanormaleâ
conduisant Ă une taille de grain trĂšs importante [t], [2]. AprĂšs recuit (3600s Ă 1470$^{\circ}$C),
précédé par un écrouissage de 30% sur des barres (par martelage) on voit apparaßtre une microstructure
hétérogÚne à gros grains (~200 à 500 $\mu$m) au coeur et en surface externe de la barre alors que
la zone intermédiaire est peuplée de grains fins ($\sim 1$
$\mu$m). Pour un écrouissage plus élevé (60%),
aprĂšs le mĂȘme recuit, on ne voit apparaĂźtre des gros grains qu'en pĂ©riphĂ©rie de la barre. Pour ce type
de microstructure fortement hétérogÚne et à gros grains, la diffraction des rayons-x pour l'analyse de
texture est mal adaptée, ce qui nous a conduit à utiliser la diffraction des neutrons sur le
diffractomÚtre 6TI du Laboratoire Léon Brillouin. Les deux matériaux, écrouis de 30% et 60%,
ont été analysés en réalisant des échantillons particuliers permettant d'étudier séparément le coeur
et la périphérie. AprÚs déformation, les deux échantillons présentent une texture de fibre $\alpha$
$\{ {\rm hkl} \} $
en tout point de la barre. AprĂšs recristallisation, on retrouve une texture trĂšs
hétérogÚne suivant le rayon de la barre, notamment aprÚs 30% : le coeur et la périphérie de la barre
prĂ©sentent une texture de type âmono-cristalâ, la zone intermĂ©diaire restant une fibre .
AprÚs écrouissage de 60%, on garde la fibre au coeur de la barre, la périphérie présentant,
comme pour l'Ă©crouissage prĂ©cĂ©dent, une texture de type âmono-cristalâ. Des analyses en EBSD ont
également été réalisées pour foumir des éléments de compréhension sur les mécanismes locaux de
recristallisation afin de simuler la recristallisation statique de ses alliages via une approche
numérique
Investigating a Chalcolithic gold bead from Mehrgarh (Balochistan). Hammering or casting process tracked by neutron diffraction texture analysis
International audienc
SANS study of the microstructural evolution of martensitic steels under thermal ageing and neutron irradiation
International audienceSANS technique has been used to study the microstructural evolution of martensitic steels containing 7-12% Cr, under thermal ageing and neutron irradiation. Some of the investigated alloys are industrial low activation martensitic (LAM) materials, where alloying elements have been substituted by elements with low radiological impact. For materials quenched from the austenitic phase, a direct correlation was found between the hardening and the number density of M2C precipitates induced by thermal ageing at 500 °C. Irradiation-accelerated spinodal decomposition of the B.C.C. ferrite was observed in alloys containing large (= 11%) chromium content
Analyse par diffraction des neutrons des déformations résiduelles dans un alliage de zirconium aprÚs un chargement thermomécanique
After a thermomechanical loading, it resides within a polycrystalline material an heterogeneous elastic
strain field resulting from accommodation of the plastic and/or thermal local deformations. X-rays or neutrons diffraction
makes it possible to quantify the average strain and their fluctuations within the diffracting volume (displacement and
broadening of the line profil). When measurements are taken in volume (neutrons in our case) on a massive sample containing
a large number of grains, they can be compared precisely with the results of homogenisation methods. Indeed, they are, as well
as diffraction, a statistical method to analysis local mechanical fields. Moreover, they give access not only to the average
mechanical fields by family of orientation (first order moment), but also to the heterogeneity of these fields (second order
moment) on the same family and thus by extension on a diffracting volume. We have the results obtained on Zircaloy-4 having
undergone a creep in traction at 400C, which validates the methodology of comparison between measurements and the
simulation carried out with a model of nonlinear homogenisation (self-coherent type affine in thermoelastoviscoplasticity) via
the âresidual strain mapâ.AprĂšs un chargement thermomĂ©canique, il rĂ©side au sein d'un matĂ©riau polycristallin un champ
de déformation élastique hétérogÚne issu de l'accommodation des déformations locales plastiques
et/ou thermiques. La diffraction des rayons X ou des neutrons permet de quantifier les déformations
moyennes et leurs fluctuations au sein du volume diffractant (déplacement et élargissement de la raie
de diffraction). Lorsque les mesures sont effectuées en volume (neutrons dans notre cas) sur un
Ă©chantillon massif contenant un grand nombre de grains, elles peuvent ĂȘtre comparĂ©es prĂ©cisĂ©ment
aux rĂ©sultats des mĂ©thodes d'homogĂ©nĂ©isation. En effet, ils sont, au mĂȘme titre que la diffraction,
une méthode statistique d'analyse des champs mécaniques locaux. De plus, ils donnent accÚs non
seulement aux champs mécaniques moyens par famille d'orientation (moment d'ordre 1), mais aussi
Ă l'hĂ©tĂ©rogĂ©nĂ©itĂ© de ces champs (moment d'ordre 2) sur la mĂȘme famille et donc
par extension sur un volume diffractant.
Nous prĂ©sentons les rĂ©sultats obtenus sur un Zircaloy-4 ayant subi un fluage en traction Ă
400C, qui valide la méthodologie de comparaison entre les mesures et la simulation
menée avec un modÚle d'homogénéisation non linéaire (type auto-cohérent affine en
thermoĂ© lastoviscoplasticitĂ©) via la âcarte de dĂ©formations rĂ©siduellesâ
Etude de la précipitation du cuivre sous irradiation électronique dans des alliages dilués à base de fer
The copper precipitation in dilute ferritic alloys ( FeCu et FeCuMn ) has been studied under electron irradiation in the 170-370°C temperature range. The matrix depletion at low fluence has been followed by in situ electrical resistivity measurements, the mean radius and the number density of precipitates have been measured at higher fluence by Small Angle Neutron Scattering. The copper precipitation is not affected by manganese at 300°C but is strongly inhibited at 215°C. It is shown that a simple radiation enhanced precipitation model can reproduce quit well the first stage of precipitation but fails in the pure coarsening regime