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The challenges of hydrogen and metals

Discussion meeting

Starts:

January
162017

09:00

Ends:

January
182017

17:00

Location

The Royal Society, London, 6-9 Carlton House Terrace, London, SW1Y 5AG

Overview

Scientific discussion meeting organised by Professor Anthony Paxton, Professor Michael Finnis and Professor Adrian Sutton FRS

Intergranular fracture surface of hydrogen-charged, annealed ultra high strength martensitic steel.

Hydrogen produced from renewable energy promises clean transport. The challenge is to defeat hydrogen's pernicious effects on metals deployed in its handling and storage. “Hydrogen embrittlement” is a major concern for the automotive, construction and energy sectors. This meeting will focus on the fundamental science underpinning the harmful effects of hydrogen on metals, from quantum mechanics to fracture mechanics.

Audio recordings of the speakers can be found below. A special issue of Philosophical Transactions of the Royal Society A will be published in due course.

Enquiries: Contact the Scientific Programmes team.

Event organisers

Select an organiser for more information

Schedule of talks

16 January

09:00-12:30

Political, economic and environmental concerns

3 talks Show detail Hide detail

09:00-09:50 Decarbonising the UK Gas Network – The H21 Project

Dan Sadler, Northern Gas Networks, UK

Abstract

The H21 Leeds City Gate project is a feasibility study developed by Northern Gas Networks (NGN). The project’s ambition is to establish if it is technically and economically possible to convert the existing natural gas supply in one of the largest UK cities (Leeds) to hydrogen.  It has addressed where and how the hydrogen would be produced, how supply and demand would be managed and what would be the overall costs for the conversion. This project could be used as a blue print for a potential UK wide incremental rollout of a hydrogen gas system to decarbonise heat.

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09:50-10:35 Clean energy and the hydrogen economy

Professor Nigel Brandon OBE FREng, Imperial College London

Abstract

In recent years, newfound interest in the hydrogen economy from both industry and academia has helped to shed light on its potential. Hydrogen can enable an energy revolution by providing much needed flexibility in renewable energy systems. As a clean energy carrier, hydrogen offers a range of benefits for simultaneously decarbonising the transport, residential, commercial and industrial sectors. Hydrogen is also shown to have synergies with other low carbon alternatives and can enable a more cost-effective transition to a de-carbonised and cleaner energy systems. This paper presents the opportunities for the use of hydrogen and fuel cells in each sector and identifies the benefits and challenges within the hydrogen supply chain for power-to-gas, power-to-power and gas-to-gas supply pathways. While, industry players have already started market introduction of hydrogen fuel cell systems, including fuel cell electric vehicles and micro-combined heat and power devices, the use of hydrogen at grid-scale requires the challenges of clean hydrogen production, bulk storage, and distribution to be resolved. Ultimately, greater government support, in partnership with industry and academia, is needed to realise hydrogen’s potential across all economic sectors.

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10:35-11:00 Coffee

11:00-11:45 Effect of material characteristics on hydrogen embrittlement failures of high strength steel fasteners

Professor Salim Brahimi, Industrial Fasteners Institute, USA

Abstract

High strength steel fasteners characterised by tensile strengths above 1 100 MPa are often used in critical applications where a failure can have catastrophic consequences. Preventing Hydrogen Embrittlement (HE) failure is a fundamental concern implicating the entire fastener supply chain. Research is typically conducted under idealised conditions that cannot be translated into know-how prescribed in fastener industry standards and practices. Additionally, inconsistencies and even contradictions in fastener industry standards have led to much confusion and many preventable or misdiagnosed fastener failures. The fact that HE is often mistakenly declared to be the root cause of failure as opposed to a mechanism of failure is a reflection of the confusion. HE susceptibility is a function of the material condition, which is comprehensively described by the metallurgical and mechanical properties. Material strength has a first order effect on HE susceptibility which increases significantly above 1 200 MPa and is characterised by a ductile-brittle transition.  For a given concentration of hydrogen and at equal strength, the critical strength above which the ductile-brittle transition begins can vary due to second order effects of chemistry, tempering temperature and sub-microstructure. Additionally, non-homogeneity of the metallurgical structure resulting from poorly controlled heat treatment, impurities and non-metallic inclusions can increase the susceptibility of steel in ways that are measurable but unpredictable. This is the root cause of many real-life failures, some cases of which will be examined in this talk.

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11:45-17:00

Hydrogen transport and trapping: from quantum effects to alloy design

4 talks Show detail Hide detail

11:45-12:15 The first principles approach: insights into hydrogen trapping by microstructures in steels

Dr Tilmann Hickel, Max-Planck-Institut für Eisenforschung GmbH, Germany

Abstract

Modern high strength steels contain a significant amount of precipitates and non-metallic inclusions. Their presence is often correlated to the sensitivity of the material to hydrogen embrittlement. The underlying assumption is that these particles strain the surrounding lattice and therewith promote the trapping of H in the interface. On the one hand, this increases the amount of diffusible and/or trapped H in the material. On the other hand, a resulting decohesion of the interfaces can yield crack initiation and therefore provides one of the possible mechanisms for hydrogen embrittlement. Experiments on H distribution based on atom probe tomography and of fracture surfaces (so-called fish-eyes) support these assumptions, but are typically not conclusive.

In the presented work, the first principles methods is therefore used to simulate the interaction of H with precipitates. To understand the impact of chemical and mechanical contributions to H solution enthalpies in the interfaces, the role of iron-based carbides (Fe3C and Fe3AlC1-x), and titanium-based precipitates are compared. For perfect and coherent interfaces the trapping energies are generally found to be small, but a noticeable impact on decohesion energies is confirmed. The presence of vacancies in the interface substantially increases the hydrogen trapping.

In the same way, the impact of misfit dislocations on H solubility has been considered in a semi-coherent approach. Different concepts to calculate the role of misfit dislocations are presented, using density functional theory (DFT) as well as tight-binding (TB) approaches. Such an extension of the H trapping investigation beyond the limited systems sizes accessible by DFT will form the last part of the presentation. The results obtained for precipitates with the H trapping at edge dislocations and grain boundaries will be compared. The insights can contribute to an optimization of microstructures such that their sensitivity to hydrogen embrittlement is reduced. 

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12:30-13:15 A kinetic Monte Carlo approach to diffusion controlled thermal desorption spectroscopy

Dr Jutta Rogal, Ruhr University Bochum, Germany

Abstract

Atomistic simulations of thermal desorption spectra (TDS) for effusion from bulk materials to characterize binding or trapping sites are a challenging task since large system sizes as well as extended time scales are required. A powerful tool to follow the dynamical evolution of an atomistic system on extended time scales are kinetic Monte Carlo (KMC) simulations. Combined with input data from electronic structure calculations KMC can e.g. provide detailed insight into the diffusion behaviour of hydrogen in iron for different microstructures. For diffusion controlled TDS of bulk samples KMC simulations can, however, become prohibitively expensive.

In this presentation a method is introduced where KMC is combined with an analytic approximation of superbasins within the framework of absorbing Markov chains. The approach is applied to the effusion of hydrogen from bcc iron, where the diffusion within bulk grains is coarse grained using absorbing Markov chains, which provide an exact solution of the dynamics within a superbasin. The analytic approximation to the superbasins is transferable with respect to grain size and elliptical shapes and can be applied in simulations with constant temperature as well as constant heating rate. The resulting TDS are in close agreement with direct KMC simulations, but the calculations are  computationally much more efficient. The presented approach is thus applicable to much larger system sizes and provides a first step towards an atomistic understanding of the influence of structural features on the position and shape of peaks in thermal desorption spectra.

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13:15-14:15 Lunch

14:15-15:00 The physics of hydrogen transport and trapping in metals

Professor Reiner Kirchheim, University of Göttingen, Germany

Abstract

Interstitial lattice diffusion in the presence of any distribution of trap concentration and energy is treated in the framework of statistical thermodynamics, reaction rate theory and kinetic Monte Carlo simulations. Consequences for hydrogen regarding electrochemical permeation measurements and thermal desorption spectroscopy are discussed. It will be shown that the “free” or “diffusible” hydrogen can be defined exactly via the chemical potential of hydrogen as the thermodynamic activity of hydrogen. For hydrogen the nature of traps stemming from lattice defects is discussed in detail. Among these vacancies and metal/oxide-interfaces provide the deepest traps.

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15:00-15:45 Isotopic tracing of hydrogen transport and trapping in nuclear materials

Dr Frantz Martin, CEA Saclay, France

Abstract

Some illustrations of the use of deuterium or tritium for isotopic tracing of hydrogen absorption, transport and trapping in nuclear materials are presented. Isotopic tracing of hydrogen has been shown to be successful for the determination of the boundaries conditions for hydrogen desorption or absorption in a material exposed to a hydrogen source. Also, the unique capabilities of isotopic tracing and related techniques to characterize H interactions with point defects and dislocations acting as moving traps has been demonstrated. Such transport mechanisms are considered to play a major role in some stress corrosion cracking and hydrogen embrittlement mechanisms.

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15:45-17:00 Tea and networking

17 January

09:00-14:00

Hydrogen in steels

5 talks Show detail Hide detail

09:00-09:45 Hydrogen related challenges for the steelmaker

Dr Richard Thiessen, Thyssenkrupp Steel Europe, Germany

Abstract

The modern steelmaker of advanced high-strength steels has always been challenged with the conflicting targets of increased strength while maintaining or improving ductility. These new steels help the transportation sector, including that of automotive, achieve goals of increased passenger safety and reduced emissions. With increasing tensile strengths, certain steels exhibited an increased sensitivity towards hydrogen embrittlement. Characterizing the material’s sensitivity in as-delivered condition has been developed and accepted (SEP1970), but the complexity of the stress-states that can induce an embrittlement together with the wide range of applications for high strength steels make the development of a standardized test for hydrogen embrittlement under in-service conditions extremely challenging. Some proposals for evaluating the material’s sensitivity give an advantage to materials with a low starting ductility. In spite of this, newly developed materials can have a higher original elongation while suffering only a moderate reduction in elongation due to hydrogen. This work presents a characterization of new materials and their sensitivity towards hydrogen embrittlement.

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09:45-10:30 Hydrogen embrittlement in structural steels

Professor Norman Fleck FRS, University of Cambridge, UK

Abstract

Hydrogen embrittlement reduces both the ductility and toughness of steels, and such degradation of performance is important in a range of applications from energy storage in transport (hydrogen tanks in automobiles) to the energy supply industry (such as subsea pipelines that are exposed to hydrogen as a consequence of cathodic protection measures).

In the first part of the presentation, it is argued that the reduction in strength and toughness by hydrogen is associated with the embrittlement of grain boundaries and other trapping sites for hydrogen.  Elementary kinetic theory suggests that embrittlement is associated with trap binding energies in the range -20 to -30 kJ/mol at room temperature.  In order to predict the reduction in macroscopic tensile strength due to the presence of hydrogen at grain boundaries, it is argued that the cohesive strength of the grain boundaries is reduced by hydrogen.  This can be modelled in two ways:

(i) macro-level:  no elevation in local tensile stress at the grain boundary and the presence of hydrogen reduces the macroscopic cohesive strength to the order of the yield strength;

(ii) meso-level:  a stress raising defect (such as a short crack) exists at the grain boundary such that the local stress level much exceeds the yield strength; the presence of hydrogen reduces the cohesive strength but it remains much above the yield strength.

In the second part of the talk, an analytical and numerical analysis is given of the electro-permeation test.  This test is commonly used to measure the diffusion behaviour of hydrogen in engineering steels (and other alloys).  There is no consensus in the literature on the values of trap binding energy and trap density for particular classes of trap, and this is in-part due to misinterpretation of permeation data, and by not varying the initial concentration of hydrogen over a sufficiently wide range.  Our analysis reveals regimes of behaviour, and the resulting permeation map can be used to obtain a clear and unique interpretation of the data.

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10:30-11:00 Coffee

11:00-11:45 Hydrogen embrittlement investigated by novel critical experiments

Tarlan Hajilou, Norwegian University of Science and Technology, Norway

Abstract

Among the experimental approaches to the hydrogen induced degradation, small scale testing has the capability to resolve the hydrogen interaction with microstructure and the crystal defects in the same length scale. However, small scale testing inquiries in situ examination to avoid hydrogen gradient or depletion on the testing materials. In this approach, in situ nanoindentation experiment capable of registering the onset of plasticity in a sub micro meter scale showed a reduction in dislocation nucleation energy in the presence of hydrogen. Going one step forward, in this study, we used the in situ electrochemical cantilever bending test method to probe the effect of hydrogen on the crack propagation in the micron sized notched beams. The experimantal setup is the integration of a miniaturized three electrode electrochemical cell inside a nanoindenter. This experimental method has the advantage of providing a complete overview of the plasticity and dislocations on the entire sample by post-mortem analyses. For this study Fe- 3wt% Si single and bi-crystal microcantilevers have been investigated. Mechanical behavior of the beams bent under hydrogen charging condition are compared with the air condition. The load-displacement curves reveal a continuous decrease in the flow stress for the cantilevers bent within the presence of hydrogen. Crack initiation and propagation are examined in the presence of hydrogen while the notch blunting occurs for the beams bent< in the air. Post-mortem cross-sectional EBSD analyses of the beams showed a localized plastic region for the hydrogen condition comparing with the air one.

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11:45-12:30 Hydrogen induced stress cracking in steels – examples of failures and numerical modelling

Dr Vigdis Olden, SINTEF Materials and Nanotechnology, Trondheim, Norway

Abstract

The occurrence of cracks in offshore structures and pipelines is an environmental and safety risk that should be eliminated. Hydrogen Induced Stress Cracking (HISC) has been a challenge in the Norwegian oil & gas industry since the late 1990s. The main sources of hydrogen are cathodic protection and to some extent also hydrogen from welding. Hydrogen induced stress cracking from cathodic protection is a result of interconnected mechanisms involving electrochemistry, diffusion, metallurgy and hydrogen degradation at different length scales from the nano- to the macro-scale.

Safe service requires predictive tools for assessing the structural integrity under CP conditions. For several years our group at SINTEF has worked with numerical models applying hydrogen informed cohesive zone elements to model HISC fracture as well as hydrogen-induced fracture in general.

Numerical simulation of hydrogen embrittlement requires a coupled approach; on one side, the models describing hydrogen transport must account for local mechanical fields, while on the other side, the effect of hydrogen on the accelerated material damage must be implemented into the model describing crack initiation and growth.

The talk will include examples of HISC fractures from the oil and gas industry as well as a review of numerical cohesive zone approaches for the prediction of hydrogen embrittlement.

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12:30-13:30 Lunch

13:45-14:30 Effects of hydrogen on fatigue crack growth in steel

Professor Hisao Matsunaga, Kyushu University, Japan

Abstract

In the context of the fatigue life design of components, particularly those destined for use in hydrogen refueling stations and fuel cell vehicles, it is important to understand the hydrogen-induced, fatigue crack growth (FCG) acceleration in steels. In the presentation, existing studies on the hydrogen-induced, FCG acceleration in various steels are first briefly reviewed, together with the acceleration mechanism and some of its influencing factors. The focus is then placed on the peculiar frequency dependence of the hydrogen-induced, FCG acceleration in steels. In a high-frequency regime (e.g., 10 ~ 0.1 Hz), the ratio of hydrogen-induced, FCG acceleration is seen to gradually increase with a decrease in test frequency, later reaching a peak. To justify the interpretation of the mechanism based on the hydrogen-enhanced successive fatigue crack growth (HESFCG) model, using both “internal” and “external” hydrogen, some critical experiments were performed on two types of material: Type 304 stainless steel and ductile cast iron.

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14:30-15:30 Tea

15:00-16:30

Mechanisms of hydrogen embrittlement in steels: panel discussion

1 talk Show detail Hide detail

Chairs

Professor Adrian Sutton FRS, Imperial College London, UK

15:30-17:00 Panellists

Professor Afrooz Barnoush, Norwegian University of Science and Technology, Norway
Professor David Dye, Imperial College London, UK
Professor Xavier Feaugas, Université de la Rochelle, France
Professor Hisao Matsunaga, Kyushu University, Japan
Professor Barbara Shollock, University of Warwick, UK

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16:30-18:15

Poster and drinks reception

18 January

09:00-11:45

Hydrogen effects in corrosion

3 talks Show detail Hide detail

09:00-09:45 High resolution imaging in corrosion studies

Professor Mary Ryan FREng, Imperial College London, UK

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09:45-10:30 Atomic level characterisation in corrosion studies

Professor Philippe Marcus, CNRS-Chimie ParisTech, France

Abstract

Various aspects related to the role of the surface structure and composition of  metals and alloys in corrosion processes will be presented, with emphasis on the essential topic of passivity and localised corrosion initiation.

After a short introduction on the surface science approach of corrosion, and a brief  review of the techniques used for high resolution characterization of  surface structure, chemical composition, and corrosion processes, the following aspects will be addressed:

- The metal-water interface: early stages of interaction studied in situ by Electrochemical Scanning Tunneling  Microscopy on metals (Cu, Ni, Ag).

- The reactivity of grain boundaries: localized dissolution at GBs

- The structure of oxide passive films on metals (Cu, Ni, Cr) and stainless steel

- The local electronic properties of passive films (investigated by Scanning Tunnelling Spectroscopy)

- Localised corrosion: its origin at the atomic scale

- The role of step edges at the exposed surface of oxide grains on the dissolution of the passive film

- Atomistic modeling of corrosion using DFT

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10:30-11:00 Coffee

11:00-11:45 Hydrogen embrittlement – the game changing factor on the applicability of Nickel alloys in oilfield technology

Dr Helmuth Sarmiento Klapper, Center for Materials Research - Baker Hughes, USA

Abstract

Precipitation hardenable (PH) Nickel (Ni) alloys are the most reliable engineering materials for demanding oilfield upstream and subsea applications. Despite their superior corrosion resistance and mechanical properties over a broad range of temperatures, the applicability of PH Ni alloys has been recently questioned due to their susceptibility to hydrogen embrittlement (HE) as confirmed in documented failures of components in upstream applications. While extensive work has been done in the last years to develop testing methodologies for benchmarking PH Ni based alloys in terms of their HE susceptibility little scientific attention has been put to achieve improved foundational knowledge about the role of microstructural particularities in these alloys on their mechanical behaviour in environments promoting hydrogen uptake. To elucidate the effect of gamma prime, gamma double-prime, and delta-phase in the microstructure of the oil patch PH Ni alloy 718 on its HE-susceptibility SSR tests under continuous hydrogen-charging were conducted on material after several different age hardening treatments. By correlating the obtained results with those from the microstructural and fractographic characterization, it was concluded that HE-susceptibility of oil patch alloy 718 is strongly influenced by the amount and size of these precipitates rather than on the strength level only. In addition, several HE mechanisms including Hydrogen Enhanced Decohesion (HEDE) and Hydrogen Enhanced Local Plasticity (HELP) were observed taking place on oil patch alloy 718 depending upon the characteristics of these phases when present in the microstructure.

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11:45-16:15

Hydrogen effects in non-ferrous alloys

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11:45-12:30 Hydrides and zirconium - a micromechanics story

Dr Ben Britton, Imperial College London, UK

Abstract

Zirconium is used as reactor fuel cladding materials in water based nuclear reactors. The oxidation of the Zr may result in both the ingress of hydrogen and the formation of hydrides. In this talk in-situ (X-ray and SEM) based micropillar experiments at both room temperature and ~reactor temperature to probe the behaviour Zr/Zr-hydrides at the micrometer lengthscale will be presented.

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12:30-13:30 Lunch

13:30-14:15 Hydrogen effects and hydride formation in Zr and Ti alloys

Professor Xavier Feaugas, Université de la Rochelle, France

Abstract

In this contribution, a survey was proposed of the possible implications of hydrogen on mechanical behaviour of Zr and Ti alloys with emphasis on the mechanisms of plasticity and strain hardening. Recent advances on the impact of oxygen and hydrogen on the activation volume show that oxygen content hinders the creep and that hydrogen partially screens this effect. Both aspects are discussed in term of looking-unlocking model of the screw dislocation mobility in prismatic slip. Additionally possible extension of this behaviour is suggested for the behaviour is suggested for the <c+a> pyramidal slip. The low hydrogen solubility leads in many cases to hydride precipitation. The nature of these phases depends the hydrogen content and can show crystallographic orientation relationships with the hexagonal compact structure of the alloys. Some advances on the thermal stability of these phases are illustrated and discussed in relation with the deepening of the misfit dislocations. Under tension loading, it is shown that hydrides enhance the hardening process in relation with internal stress due to strain incompatibilities between Zr and Ti matrix and hydride phases. Different plastic yielding processes of hydride were identified, which progressively reduce these strain incompatibilities.

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14:15-15:00 The role of hydrogen in stress corrosion cracking – a titanium alloy case study

Dr Tamara Chapman, Rolls-Royce plc, UK

Abstract

Ti6246 is a high strength heavily beta stabilised titanium alloy. It finds widespread use in the aerospace industry for critical rotating components, and in the appropriate environment may exhibit stress corrosion cracking. This presentation details a particular ‘hot salt’ stress corrosion mechanism that has unusual consequences for the certification and application space for titanium alloys. The utilisation of unusual combinations of advanced experimental techniques will be detailed in the context of the more traditional failure investigation / fractographic approach. The role of hydrogen in crack tip deformation will be reviewed in the context of the high temperature and high stress experienced in this case.

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15:00-15:30 Tea

15:30-16:15 Hydrogen in titanium and zirconium – an industrial perspective

Dr Dave Rugg, Rolls-Royce plc, UK

Abstract

Titanium has found widespread use in demanding applications dominated by the aerospace industry. Its strength to weight ratio, and critically, corrosion resistance make it well suited to highly stressed rotating components. Zirconium has more niche but no less critical application where its low neutron capture cross section and good corrosion resistance in hot water and steam make it well suited to reactor core use, including fuel cladding and structural applications. Hydrogen control during manufacture and subsequent in-service behaviour for titanium and zirconium alloys as a function of hydrogen content will be reviewed. This will include the potential for hydrogen ‘pick up’ in service for nuclear and aerospace sectors.  Empirically derived manufacturing methods and design / certification criteria will be detailed for pertinent material types and load regimes.

Much of our understanding about hydrogen in titanium and zirconium is inferred from macroscopic testing. Predictive capability for failure and the potentially subtle interplay between alloy chemistry, microstructure and hydrogen (location, mobility and degradation mechanisms) is therefore limited.  This paper will also review the current mechanistic understanding relating to hydrogen in high purity metals along with important alloy systems. The role of beta phase in hydrogen ‘pick-up’, trapping and transport will be discussed along with possible crack initiation mechanisms In addition, the scope for progress in this area over the next decade with respect to both developments in experimental techniques and physics based modelling capability will be discussed.

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16:15-17:00

Future directions panel discussion

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Chairs

Professor Anthony Paxton, Kings' College London, UK

16:15-17:00 Panellists

Yun Deng, Norwegian University of Science and Technology, Norway
Dr Tilmann Hickel, Max-Planck-Institut für Eisenforschung GmbH, Germany
Professor Mary Ryan FREng, Imperial College London, UK
Jon Saltmarsh, Department for Business, Energy and Industrial Strategy, UK

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