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PhD subjects

Dernière mise à jour : 20-01-2018

2 sujets IRAMIS

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• Ultra-divided matter, Physical sciences for materials

 

Curvature-induced charge separation in oxide semiconductor nanotubes: towards photocatalysis

SL-DRF-18-0439

Research field : Ultra-divided matter, Physical sciences for materials
Location :

Service Nanosciences et Innovation pour les Materiaux, la Biomédecine et l'Energie (NIMBE)

Laboratoire Interdisciplinaire sur l'Organisation Nanométrique et Supramoléculaire (LIONS)

Saclay

Contact :

Sophie LE CAER

Antoine THILL

Starting date : 01-10-2018

Contact :

Sophie LE CAER

CNRS - DRF/IRAMIS/NIMBE/LIONS

01 69 08 15 58

Thesis supervisor :

Antoine THILL

CEA - DSM/IRAMIS/NIMBE/LIONS

01 69 08 99 82

Personal web page : http://iramis.cea.fr/Pisp/antoine.thill/thill_fr.html

Laboratory link : http://iramis.cea.fr/nimbe/lions/

Imogolite are natural nanotubes having a well-defined very high curvature. It is possible to produce large quantities of synthetic version of this nanomaterial thanks to the PRODIGE pilot at NIMBE. It has been recently predicted by DFT calculation that the strong curvature of the imogolite wall induces a surface density of dipole at the imogolite wall. Such radially symmetric polarization is in favour of electron/hole charge separation during photo-induced events.

In this PhD project, we propose to investigate the existence of such polarization and quantify its magnitude. Different complementary experimental strategies are proposed to reach this goal for both native and hybrid imogolite nanotubes. Iron doping of the tubes will also be tested to modulate the band gap of the nanotubes.

Intermediate amorphous states during precipitation of cerium oxalate: towards a new nucleation model

SL-DRF-18-0111

Research field : Ultra-divided matter, Physical sciences for materials
Location :

Service Nanosciences et Innovation pour les Materiaux, la Biomédecine et l'Energie (NIMBE)

Laboratoire Interdisciplinaire sur l'Organisation Nanométrique et Supramoléculaire (LIONS)

Saclay

Contact :

Sophie CHARTON

David CARRIÈRE

Starting date : 01-11-2018

Contact :

Sophie CHARTON

CEA - DEN/DMRC

+33 (0)4.66.79.62.29

Thesis supervisor :

David CARRIÈRE

CEA - DSM/IRAMIS/NIMBE

0169085489

Personal web page : http://iramis.cea.fr/Pisp/68/david.carriere.html

Laboratory link : http://iramis.cea.fr/nimbe/lions/index.php

The formation of crystals by liquid reaction takes place in the many natural and artificial processes, and in particular in reactive crystallization processes. The control of the kinetics of the formation, the size and the morphology of the precipitates is still very challenging. Size control of precipitated powder is also an important issue of nuclear fuel treatment, where plutonium is precipitated as oxalate, before being converted into the oxide used in the manufacture of MOX.

The reference theory for predicting rate of crystal formation, used in process modeling, is the classical theory of nucleation (CNT), which is based on the thermodynamic description of the liquid-vapor equilibrium proposed by Gibbs in 1876. But this model sometimes dramatically fails because it ignores all the disordered intermediate states possibly achieved between the initial solution and the final crystal: clusters, liquid-liquid phase separations, amorphous particles or networks, etc. In particular, such amorphous intermediate states were observed in the precipitation of cerium oxalate, one of the reference simulating systems for plutonium, suggesting a two-stage nucleation process in contradiction with the CNT.

The general objective of this thesis is to characterize the intermediate states of the nucleation of cerium oxalate and their impact on the predictions of classical theory. As a close collaboration between CEA Marcoule and CEA Saclay, this thesis will combine techniques known to be able to tackle this difficult problem: X-ray scattering in laboratory and synchrotron facilities (SAXS/WAXS), microfluidics, thermodynamic and kinetic models.

 

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