Delphine Neff: preserving our heritage and securing our nuclear future through the study of metal corrosion

Delphine Neff is a Director of Research at the Nanosciences and Innovation for Materials, Biomedicine and Energy Laboratory (NIMBE - Univ. Paris-Saclay, CEA, CNRS), which is a part of the Archaeomaterials and Alteration Prediction Laboratory (LAPA). She specialises in the study of the long-term corrosion of archaeological metals, in the dual context of the nuclear industry and heritage.

After graduating in Materials Engineering from Polytech Orléans in 1999, Delphine Neff developed a passion for the study of materials in a historical context. In 2000, she pursued this path by completing a DEA (“Diplôme d'études approfondies”, now equivalent to a Master's degree) in physical measurements applied to archaeology at the Université de Bordeaux Montaigne. "Ancient materials are objects in touch with history, I like the idea of establishing some kind of link with them when I study them." Her interest in the interaction of materials with their environment naturally led her to the study of corrosion, a phenomenon that affects metals. As part of this course, she completed an internship at the NIMBE laboratory (at the time known as the Pierre Süe laboratory), where she worked on understanding production processes in ancient metals.

Safe storage of radioactive waste

In 2003, Delphine Neff defended her thesis at NIMBE, funded by the French National Radioactive Waste Management Agency (Andra). The thesis focused on understanding how corrosion affected the ferrous materials used as containers for radioactive waste packages, as they should be designed to last 2,000 years. "Gathering data on the weathering of materials on ferrous archaeological objects is important for dimensioning and predicting the lifespan of containers, in order to guarantee the safety of waste storage over this period." In this context, Delphine Neff studied some 50 archaeological objects, such as nails, from six different archaeological sites. She cut these objects, set them in resin and analysed the structure of the mineralogical phases that made up the layers of corrosion products. Her goal was to trace the evolution of physiochemical corrosion mechanisms over the long term. "Thanks to the data obtained on archaeological objects, it is possible to use these ancient objects as analogues, in other words to transpose the understanding of long-term corrosion mechanisms to current technical devices, in order to predict their behaviour."

Mastery of a wide range of techniques

In order to gain international experience and further her scientific production, Delphine Neff spent ten months in India, at the Indian Institute of Technology in Kanpur. "I learned a lot about human relations and the integration of cultural differences, both professionally and personally." When she came back to France in 2004, she spent two years as a post-doctoral researcher at the From Molecules to Nano-objects: Responsiveness, Interactions and Spectroscopy laboratory (MONARIS - CNRS, Sorbonne Univ.), then called the Laboratory of Dynamics, Interactions and Reactivity (LADIR). Here was where she perfected her Raman spectroscopy skills. "It's a technique for identifying phases in corrosion that I still use a lot today." This approach relies on the interaction of a laser with the sample to obtain a characteristic spectrum of the crystalline phases present in the material, a signature of the minerals that make up a layer of corrosion products. The area probed is micrometric, making it possible to carry out mapping mode acquisitions in the thickness of corrosion products observed in a cross-section. "For example, in the corrosion of ferrous materials, we observed that the phases formed varied according to the different environments in which they had corroded." Delphine Neff also used a combination of complementary techniques to carry out multi-scale analyses of the chemical composition and crystalline structure of samples. Each technique provided complementary information on material properties, in order to reach a deeper understanding of their behaviour.

Towards new research horizons

In 2006, Delphine Neff returned to NIMBE for her final year as a post-doctoral fellow, during which she continued her work on archaeological analogues, although this time it was for a new material: glass. "I studied slag, the glassy waste from blast furnace production in the steel industry."  At the end of that same year, she obtained a position as a research engineer in the laboratory, and took advantage of the opportunity to diversify the corrosion environments and materials she studied. Whether ferrous or cuprous, terrestrial, underwater or atmospheric, she diversified her areas of expertise. "I also broadened the scope of my studies, moving from the nuclear context to projects involving the conservation of heritage objects. My goal was to preserve their integrity." To achieve this, she started collaborating with various different heritage players, in particular the research laboratories of the French Ministry of Culture. "For example, I studied the corrosion of metals in the cathedrals of Amiens, Bourges and Metz, to examine the long-term performance of the existing chains. I also examined iron bars from underwater Roman shipwrecks to help optimise stabilisation treatments that preserve their original surface during restoration work."

From the laboratory to industry

Almost ten years ago now, Delphine Neff and her team began a fruitful partnership with the SME A-Corros, which specialises in corrosion diagnostics and the restoration of historical objects of various different sizes. "This collaboration was really motivating, as it provided me with an application horizon and an opportunity to test our solutions in real-life conditions. What works in the laboratory doesn't always work in the same way in the field, or on the same scale." And when it comes to fieldwork, thanks to the know-how she has developed over the years in the nuclear field, Delphine Neff is now able to characterise samples from cores taken in an industrial context (that of waste storage in Andra's underground laboratory). "These are corrosion features similar to archaeological systems, which present the same type of complexity."

Promising future research projects

In 2012, Neff obtained her authorisation to direct research and became director of research in the laboratory where she still works today. As she's never short of ideas, she has numerous plans for the coming years to advance the frontiers of understanding corrosion in materials. One of them is the launch of a programme for archaeological copper analogues. "In France, storage containers are made of steel, but internationally, in Sweden, Finland, Canada and Switzerland, copper is preferred. So I'm currently in the process of setting up a research programme for this material." Within the framework of heritage conservation, Delphine Neff is currently developing a programme to protect copper objects by inhibiting corrosion with the use of eco-compatible organic products.