PhD: Dynamic forging of magnesium-based alloys for solid-state hydrogen storage (M/F)

Job Description

Thesis Subject

Hydrogen is a promising energy carrier in the context of the energy transition. The solid-state storage of hydrogen in the form of reversible metal hydrides enables a higher volumetric storage density to be achieved compared to compressed gas or liquid at cryogenic temperatures, whilst offering a significant reduction in energy costs and an enhanced safety, as the absorption takes place at pressures of only a few tens of bars.

Magnesium, an abundant and reasonably priced metal, reacts with hydrogen to form a hydride (MgH₂) which possesses remarkable mass and volumetric storage capacities (7.6 wt. % and 110 g/L). The development of magnesium-based storage systems therefore represents a major challenge for the hydrogen sector. However, the excessive thermodynamic stability of the MgH₂ phase and the slow hydrogen sorption kinetics limit its use.

The mechanical grinding of MgH₂ powders in the presence of additives acting as catalysts is known to be highly effective in improving reaction kinetics. However, this process results in pyrophoric powders, of which handling is barely compatible with large-scale production. Several processes for nanostructuring magnesium via severe plastic deformation (SPD) have also proven effective in improving reaction kinetics. These processes enable the production of solid materials that are non-flammable in contact with air. However, although they enable the production of 'model materials', these processes have little industrial potential as the volumes of material produced are very low.

Over the past few years at the Institut Néel, we have developed a forging process for magnesium alloys and demonstrated that very different sorption properties can be achieved, depending on the conditions applied. A systematic and in-depth study of the microstructure, conducted in close collaboration with LEM3, has enabled to establish correlations between the measured sorption properties and the microstructures developed. Easily scalable to large-scale production, forging offers advantages in terms of both safety and production costs, and has a significant potential for practical applications. The process optimized at the Néel Institute involved samples weighing only around ten grams and used a minimally instrumented 'drop-forging' apparatus. Therefore, in order to conduct both qualitative and quantitative studies, the use of a fully instrumented rapid mechanical loading system is necessary. The Hopkinson bar apparatus, developed by the Rapid Contact Thermomechanics team (LEM3), allows precise control of the deformation conditions applied via the projectile (stress, velocity, temperature).
The aim of the thesis will be to study novel, highly-deformed microstructures produced using this forging process under dynamic conditions. This setup will make it possible to distinguish between effects linked to the effective stress level and those caused by the heating generated during ultra-rapid deformation. The results obtained will also enable the formulation of mechanical behaviour laws that can be integrated into theoretical models and the establishment of a relationship between the plastic deformation energy and the state of the stressed specimen.
The Mg- and Ni-based composites will first be synthesized at the Néel Institute. The synthesis conditions for the composites (initial composition, annealing temperature, etc.) and the forging conditions will be adjusted based on observations regarding microstructure and hydrogen sorption properties. The impact of the microstructure on hydrogen sorption kinetics will thus be systematically studied, in order to better understand the influence of various microstructural parameters on the mechanisms involved in hydrogen sorption reactions.

Furthermore, to understand the specific characteristics of dynamic forging tests compared with more conventional methods of slow but very severe deformation, such as SPD, a comparative analysis will be carried out as part of an existing collaboration with the Japanese team led by Prof. K. Edalati (Kyushu University, Japan), which is specialized in HPT (High Pressure Torsion) deformation for energy applications.
Ultimately, this study as a whole will enable the optimisation of forging conditions, in view of the industrialisation of the process.

The PhD student will be required to:
- optimise the sample preparation process (composition, heat treatment, etc.),
- occasionally take part in tests on the hyperdeformation platform at LEM3 in Metz,
- analyse the mechanical properties of materials in order to derive behaviour laws,
- carry out detailed characterization of the microstructure of alloys before and after deformation, and its evolution after several cycles of hydrogen absorption/desorption (SEM, EBSD, TEM, etc.),
- measure hydrogen sorption kinetics and the thermodynamic properties of hydrides with a view to establishing correlations between the developed microstructure and sorption properties,
- participate in in situ diffraction experiments at large-scale facilities (ILL and/or ESRF) to deepen the understanding of sorption mechanisms.

Required profile and skills:
The candidate must hold a Master's degree or an engineering degree in mechanical engineering or materials science. A solid understanding of continuum mechanics and materials science (X-ray diffraction, microstructural analysis) is essential. The project will be supervised by the Néel Institute in Grenoble in partnership with LEM3 in Metz. We are therefore looking for a serious and motivated student, capable of working in a collaborative environment. As the subject spans several fields and involves multiple characterization techniques (experience in experimental work is desirable), a rigorous approach and the ability to communicate effectively in writing and orally (in French and English) are expected.

Your Work Environment

The PhD research work will be carried out as part of the ANR ADyCT project (Dynamic Activation of Magnesium-based Composites for Hydrogen Storage), which involves three partners (the Néel Institute in Grenoble, LEM3 in Metz and IJL in Nancy).

- PhD supervisors (Néel Institute) : Patricia de Rango and Aude Bailly
- Co-supervisors : Laetitia Laversenne (Néel), Roxane Massion, Sylvain Philippon, Julien Vincent, Marc Novelli and Thierry Grosdidier (LEM3).


The Institut NEEL, UPR 2940 CNRS, is one of the largest French national research institutes for fundamental research in condensed matter physics enriched by interdisciplinary activities at the interfaces with chemistry, engineering and biology. The laboratory is related to the CNRS Physique. It is located in the heart of a unique scientific, industrial and cultural environment. It is part of one of Europe's biggest high-tech environment in micro- and nanoelectronics, right next to the French Alpes.
The Institut NEEL is a CNRS laboratory. CNRS is a public, scientific and technological organisation.
The core mandate is to identify, carry out ou have carried out, either alone or with partners, all research that advances science or contributes to the country's economic, social, and cultural progress. Internationally recognised for the excellence of its scientific research, the CNRS is a reference in the world of research and development, as well as for the general public.

Compensation and benefits

Compensation

2300 € gross monthly

Annual leave and RTT

44 jours

Remote Working practice and compensation

Pratique et indemnisation du TT

Transport

Prise en charge à 75% du coût et forfait mobilité durable jusqu’à 300€

About the offer

About the CNRS

The CNRS is a major player in fundamental research on a global scale. The CNRS is the only French organization active in all scientific fields. Its unique position as a multi-specialist allows it to bring together different disciplines to address the most important challenges of the contemporary world, in connection with the actors of change.

CNRS

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