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Ph.D. (M/W) on TEM/NMR characterization of the reactivity of calcinated clays

This offer is available in the following languages:
Français - Anglais

Date Limite Candidature : vendredi 20 mai 2022

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General information

Reference : UMR6502-ANNGAI-001
Workplace : NANTES
Date of publication : Tuesday, May 10, 2022
Scientific Responsible name : Anne-Claire GAILLOT
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 3 October 2022
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly

Description of the thesis topic

In the context of natural resources saving, civil engineering and building companies are developing new cement using industrial secondary resources (slag, fly ashes) and mining products. In order to reduce the carbon impact, the cement industry is trying to partially replace Portland cement, which presents the best mechanical properties, by other materials from the alumino-silicate family, such as clays. Indeed, clay minerals represent a cheap and abundant resource that makes it promising in substitution to traditional clinker in cement.
Several studies allow to develop new formulations of low-carbon hybrid cement, from calcined clay treated with lime. But their optimization requires a better comprehension of the physico-chemical mechanisms during the calcination of these clays.

Work program:
The Ph.D. work will focus on the study of the physico-chemical reactions during the clay calcination, using multi-scale characterization techniques. It will include the chemical treatment of several clays (pure or as a mixture), such as palygorskite, smectite or kaolinite, in several chemical and thermal conditions. The pristine and after-treatment materials will thereafter be characterized by powder X-ray diffraction, to quantitatively follow the nature of the mineral phases, and by scanning and transmission electron microscopy (SEM-TEM) to study the morphological modifications of the clay phases. Complementary measurement of granulometry and specific surface (BET) will allow following the particle size evolution. The High-Angle Annular Dark Field imaging in scanning TEM mode (STEM-HEEDF) coupled to chemical mapping by Energy Dispersive X-ray spectroscopy (STEM-EDS) will then allow investigating the reactivity of the different clay phases, and the dissolution-recrystallization processes occurring during the calcination that are responsible for the pouzzolanic reactivity of these calcined materials. Finally, the modifications of the aluminum coordination (from VI to V then IV), that are thought to be one of the key points of these reactivity will be investigated by nuclear magnetic resonance (solid NMR), that is one of the major technique to follow this transformation. However, the information obtained by NMR remain averaged on all the coexisting clay minerals. A great part of the Ph.D. work will be dedicated on the development of the Electron Energy Loss Spectroscopy (EELS) at the Aluminum K (or L) edge to determine the chemical environment of aluminum at the clay particle scale, to better identify the nature of the reactive phases and their degree of reactivity.

The candidate, with an Engineer or Master degree, should have a large and solid background in solid chemistry, physics, materials or geomaterials domains, with knowledge on characterization techniques such as electron microscopies (SEM, TEM), and X-ray diffraction (XRD), and be curious and able to invest in an exploratory research topic. Good writing and communication skills in French or English are required.

Work Context

Ph.D. Director: Dimitri DENEELE
Principal Advisor: Anne-Claire GAILLOT
Doctoral school: ED-3M (Matière, Molécule et Matériaux)

The Ph.D. student will work at the Institut des Matériaux de Nantes Jean Rouxel (IMN - ~200 people), on the Lombarderie Campus (Michelet stop on the tramway Line 2), in the Engineering of Materials and Metallurgy (ID2M) group.
Website : https://www.cnrs-imn.fr/

The candidate will have the opportunity to work on last-generation instruments such as the Themis-Z FEG probe-corrected and monochromated TEM, equipped with an EELS spectrometer and of a ultra-sensitive electro-detection camera, as well as a large panel of other techniques for solis characterization (solid-NMR, SEM, XRD, BET, laser granulometry, TGA, …). He/she will work in collaboration with the group members and the research engineers in charge of the technical machines, and will evolve in a convivial atmosphere developed by the student SYRA association of the Institute.

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