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Formation mechanisms of (meta)stable 3d-metal nitrides via in situ neutron diffraction

Mardi 24 février 2015 14:00 - Duree : 1 heure
Lieu : ILL4, Seminar Room, 71 avenue des Martyrs - Grenoble

Orateur : Marc WIDENMEYER (Universität Stuttgart - Institut für Materialwissenschaft)

Considering the overwhelming technical importance of nitrides, like for example in the industrial steel hardening process or as materials for light emitting diodes (GaN), astonishing little information about their formation process and the involved intermediate phases is available. In situ neutron diffraction is ideally suited to achieve the required information, due to the large coherent nuclear scattering power of nitrogen and the tolerance towards complex sample environments. The multiple material requirements needed for a successful investigation of solid-gas-reactions including production of gaseous by-products as well as use of corrosive gaseous ammonia and hydrogen with high diffusivity on a neutron diffractometer enforced the development of special sample containers and environments. Two different construction types were developed and permanently improved : i) A sapphire single crystal cell for lower reaction temperatures up to 600 °C allowing in combination with a contact less laser heating system a low and unstructured measurement background. ii) A silica glass cell for higher reaction temperatures up to 1000 °C, which can be operated either with the laser heating system or in a classical high-temperature resistance furnace.

The developed experimental setups can be easily adapted to different neutron diffractometers like D20 or SPODI (FRM-II). In situ investigations were applied to 3d-metal nitrides of the elements vanadium to copper. To achieve a complete understanding of the reaction process observed the combination with additional in situ methods especially Thermal Analysis such as thermogravimetry, differential thermal analysis and exhaust gas analysis are required.

The systems V–N, Cr–N, Fe–N and Cu–N with view on reactions of various starting materials with ammonia will be discussed.

Contact : dubouloz@ill.fr

Discipline évènement : (Physique)
Entité organisatrice : (ILL)
Nature évènement : (Séminaire)
Evènement répétitif : (General ILL Seminar - College 5A)
Site de l'évènement : Polygone scientifique

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