Continuous Thermogravimetry under Cyclic Conditions

Thermogravimetry during cyclic oxidation of metallic alloys is described. A methodology is given in order to determine the Net Mass Gain, the GrossMass Gain, the total mass of spalled oxide, the rate of metal consumption and the average oxide scale thickness as a function of the number of cycles. The fraction of oxide scale which spalls at each cycle can be also calculated, and the parabolic constant can be estimated at each cycle. Two examples are given: the cyclic oxidation of a NiAl single crystal in flowing oxygen at 1150xC, and the cyclic oxidation of alloy P91 at 800xC in laboratory air. Advantages and disadvantages of this technique are discussed in regards to classical interrupted tests in crucibles. Thermogravimetry during cyclic oxidation appears to be a powerful tool in order to model and quantify the cyclic oxidation test which is of great interest in order to qualify the resistance of materials to oxidation in conditions close to their actual use, but a specific aspparatus need to be developed in order to obtain data in an efficient and economical manner. A new apparatus designed for this purpose is described briefly

Numerical simulation of cyclic oxidation kinetics with automatic fitting of experimental data

This paper proposes a model, based on a Monte Carlo method, to assess cyclic oxidation tests. The numerical code fits automatically the experimental net mass change curves. Oxidation kinetics are identified as well as the relationship between spalling and local oxide thickness or time. The modelling is applied to cyclic oxidation of NiPtAl single crystals at 1150 °C in dry air

Pairing correlations in a trapped one-dimensional Fermi gas

We use a BCS-type variational wavefunction to study attractively-interacting quasi one-dimensional (1D) fermionic atomic gases, motivated by cold-atom experiments that access the 1D regime using an anisotropic harmonic trapping potential (with trapping frequencies $\omega_x = \omega_y \gg \omega_z$) that confines the gas to a cigar-shaped geometry. To handle the presence of the trap along the $z$-direction, we construct our variational wavefunction from the harmonic oscillator Hermite functions that are the eigenstates of the single-particle problem. Using an analytic determination of the effective interaction among harmonic oscillator states along with a numerical solution of the resulting variational equations, we make specific experimental predictions for how pairing correlations would be revealed in experimental probes like the local density and the momentum correlation function.Comment: 8 pages, 6 figures. Published in Phys. Rev.

Shaping immigrant and ethnic heritage in North America: ethnic organizations and the documentary heritage

This article will explore some of the issues that immigrant and ethnic groups have dealt with when tackling the task of archiving – gathering and preserving the documents that tell the group’s story – and that of history- or memory-building through archives, a process I will refer to, for the sake of convenience, as ethnic archiving. The paper will trace the process of ethnic archiving through the case study of three specific groups–Finnish, German and Jewish communities in the United States–in the period preceding and following the ethnic “revival” of the 1960s. These groups were chosen because they illustrate the evolution of ethnic archiving among immigrant groups that arrived in the United States before the 1920s and the adoption of restrictive immigration laws. The similarities and differences these groups display are visible in the groups’ negotiations of, and answers to, the following questions: Who should be responsible for archiving? What should be the purpose of archiving and of the transmission of migration heritage? What should be archived and transmitted? These questions have broad implications for the shaping of history and memory.Cet article explore les questions auxquelles les groupes ethniques et immigrés ont été confrontés lorsqu’ils ont cherché à constituer leurs archives – à rassembler et préserver les documents qui permettent de retracer leur histoire – et à construire leur histoire et leur mémoire collective à travers ces archives. Cet article s’intéresse à trois groupes ethniques – Finlandais, Allemands et Juifs – dans la période qui précède et suit la résurgence ethnique des années 1960. Ces groupes ont été choisis parce qu’ils illustrent l’évolution des archives ethniques chez les communautés immigrées établies avant les années 1920 aux États-Unis. On peut identifier des similitudes et des différences entre ces groupes dans la façon dont ils ont abordé les questions suivantes : qui est responsable de la constitution des archives ? Quel doit être le but de ces archives et de la transmission du patrimoine migratoire ? Quels documents et quels aspects doivent être préservés et transmis ? De la réponse à ces questions dépendent l’histoire et la mémoire collective de ces groupes et de la nation américaine.Este artículo explora las cuestiones a las cuales se confrontaron los grupos étnicos cuando buscaron constituir sus archivos - reunir y preservar los documentos que permiten trazar su historia - y constituir su historia y su memoria colectiva a través de estos archivos. Este artículo se interesa a tres grupos étnicos – finlandeses, alemanes y judíos – durante el periodo que precede et sigue la resurgencia étnica de la década de los 60. Estos grupos han sido escogidos porque ilustran la evolución de los archivos étnicos de las comunidades de inmigrantes radicadas en los Estados Unidos antes de los años 1920. Entre estos grupos se puede identificar las similitudes y diferencias de la manera en que ellos abordaron los cuestionamientos siguientes : ¿ quién es responsable de la constitución de los archivos ? ¿ Cuál debe ser el objetivo de estos archivos y de la transmisión del patrimonio migratorio ? ¿ Qué documentos y que aspectos deben ser preservados y transmitidos ? De la respuesta a estos cuestionamientos dependen la historia y la memoria colectiva de estos grupos y de la nación americana

Low Temperature Oxidation of pure Iron : Growth kinetics and scale Morphologies

Isothermal oxidation of pure iron has been performed in air at atmospheric pressure between 260°C and 500°C. Growth kinetics are accurately analysed and scale morphologies are investigated by SEM and TEM observations. The calculation of the variations of the parabolic rate constant kp with scale thickness allows a better understanding of scale growth mechanisms involved at this intermediate temperature range, which have been poorly investigated up to now. These results are discussed with the objective of long term behaviour for long term interim storage of some nuclear waste containers

Numerical Model for Oxide Scale Growth with Explicit Treatment of Vacancy Fluxes

In the framework of research on behaviour of nuclear waste containers, to evaluate the effects of possible evolution of experimental conditions, as well as evolution of parameters controlling oxidation rate during long-term interim storage, a numerical model has been developed in order to take into account non-stationary states. To anticipate effects like cold working of the metal on the scale growth kinetics and risks of scale detachment by over saturation of vacancies at the metal/oxide interface in the course of scale growth, the model is based on the calculation of chemical species, but also vacancies profiles evolution in the oxide and the metal following a simple time integration. An original numerical treatment is proposed to easily describe elimination of vacancies by introducing sink strength in the metal. The first calculations are presented and discussed

High-temperature oxidation kinetics of NiAl single crystal and oxide spallation as a function of crystallographic orientation

Isothermal and cyclic high-temperature oxidation of NiAl single crystal samples are presented. Oxidations have been carried out at 900, 1050, 1100 and 1150 ◦C on (1 0 0) and (1 1 0) oriented surface. Continuous thermogravimetry in cyclic conditions allows isothermal oxidation kinetics and spalling at each cycle to be followed. Oxidation kinetics are compared between (1 0 0) surface and (1 1 0) surface. (1 0 0) oriented surfaces appeared to oxidize slightly faster than (1 1 0) oriented surfaces. Experimental results of cyclic oxidation are compared to simulated results using a previously published statistical model. Spalling increases when the average oxide scale thickness increases with the number of cycles. Longer tests are necessary to study this evolution during the ’steady-state’ but no critical oxide thickness was found