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Molten Salt Discussion Group Summer Research Meeting 2015
Final Programme & Abstracts
Department of Materials Science and Metallurgy, University of Cambridge
3-5 August 2015
Authors’ Abstracts Abstracts presented on the following pages are compiled by the MSDG for distribution amongst attendees of the 201r MSDG Summer Research Meeting and are based on the submitted versions received from the Authors who are responsible for issues related to the scientific correctness and copyright. This booklet is also available from the MSDG’s website.
MSDG Summer 2015 Research Meeting Programme MONDAY AUGUST 3RD 11:30-12:30 Registration and assembly at Fitzwilliam College 12:30-12:50 Group walk (20 minutes) to the Department of Materials Science and Metallurgy 12:50-13:50 Lunch at the Department of Materials Science and Metallurgy 13:50-14:00 Chairman’s welcome by Professor George Z Chen 14:00-14:45 Invited Lecture
Some unique properties of ionic liquid/water mixtures
Hiroyuki Ohno1,2 1 Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588 Japan 2 Functional Ionic Liquid Laboratories (FILL), Graduate School of Engineering, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588 Japan Contact E-mail: [email protected]
14:45-16:15 Technical Sessions 1 Chair Dr Anna Croft 14:45-15:15 Effects of impurities on the current efficiency in aluminium electrolysis
Geir Martin Haarberg Department of Materials Science and Engineering, Norwegian University of Science and Technology,Trondheim, NO-7491, Norway Contact E-mail: [email protected]
15:15-15:45 Control of metal corrosion in molten salt nuclear reactors with sacrificial zirconium
Ian R. Scott1 1 Moltex Energy LLP, 6th Floor Remo House, 310-312 Regent St., LondonW1B 3BS Contact E-mail: [email protected]
15:45-16:30 Tea break and Poster Session No. 1 16:30-17:00 Technical Sessions 2 Chair Dr Trevor R Griffiths 16:30-17:00 Uranium Metal Production by Direct Electrodeoxidation of Uranium Dioxide in
Molten Salts
D. Sri Maha Vishnu1,2,3,a, K.S. Mohandas3 and K. Nagarajan3 1 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge , CB3 OFS, UK 2 with National Chair of Materials Science and Metallurgy, University of Nizwa, Nizwa, 613, Sultanate of Oman 3 Chemistry Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, 603102, India. a Contact E-mail: [email protected]
17:00 Walk back to Fitzwilliam College
18:00 – 19:00 Dinner at Fitzwilliam College TUESDAY AUGUST 4TH 07:45-08:30 Breakfast at Fitzwilliam College for over-night residents. 08:30- 08:50 Walk to the Department of Materials Science and Metallurgy 09:00-11:30 Technical Sessions 3 Chair Dr Stuart Mucklejohn 09:00-09:30 Probing Reactions in Ionic Liquids: Experiment meets Theory
Sinead T. Keaveney1,2, Hon Man Yau1,2, Jason B. Harper1 & Anna K. Croft2 1 Department of Chemistry, University of New South Wales, Sydney, 2052, Australia 2 Department of Chemical and Environmental Engineering, University of Nottingham, Nottingham NG7 2RD, UK Contact E-mail: [email protected]
09:30-10:00 The International Current Situation Concerning Molten Salt Nuclear Reactors and
the Results of a Government Sponsored UK Feasibility Study
Trevor R. Griffiths1, Rory O’Sullivan2 & Jasper Tomlinson2
1 Energy Process Developments, 58 High Ash Avenues, Leeds, LS17 8RF, UK) 2 Energy Process Developments, 185 New Kent Road, London, SE1 4AG, UK
10:00-10:30 PuCl3 – ZnCl2 Phase Diagram
Robert Watson AWE plc, Aldermastion, Reading RG7 4PR, UK Contact E-mail: [email protected]
10:30-11:00 Role of Carbon Materials in the Front and Back End of Metallic Fuel Cycle
Jagadeesh Sure1,2,3,a, D. Sri Maha Vishnu1,2,3,b 1 Corrosion and Chemistry Groups, Indira Gandhi Centre for Atomic Research, Kalpakkam, India 2 With National Chair of Materials Science and Metallurgy, University of Nizwa, Sultanate of Oman 3 Presently at Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, UK. Contact E-mail: a [email protected]; b [email protected]
11:00-11:30 Coffee break and Poster Session 2 11:30-13:00 Technical Session 4: Chair Dr Robert Watson 11:30-12:00 Towards Understanding Reactivity in Ionic Liquids
Richard M. Fogarty1, Robert G. Palgrave2, Richard A. Bourne3,Thomas W. Chamberlain4, Nick A. Besley4, Josephina Werner,5 Gunnar Öhrwall,5 Olle Björneholm,5 Patricia A. Hunt1, Kevin R. J. Lovelock1 1 Department of Chemistry, Imperial College London 2 Department of Chemistry, University College London 3 School of Chemistry, University of Leeds
4 Department of Chemistry, University of Nottingham 5 Department of Physics and Astronomy, Uppsala University Contact E-mail: [email protected]
12:00-12:30 Electrochemical Production of High Purity Tantalum by the FFC Cambridge Process
Greg Doughty1, James Deane1, Ian Mellor1. 1 Metalysis Ltd. Unit 2, Farfield Park, Manvers Way, Wath-Upon-Dearne, Rotherham S63 5DB Contact E-mail: [email protected]
12:30-13:00 Molten salt preparation of graphene and its potential applications
Ali Reza Kamali &Derek J. Fray Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB3 0FS, UK Email:[email protected]
13:00-14:00 Lunch at the Department of Materials Science and Metallurgy 14:00-15:30 Technical Session 5: Chair Professor Geir Martin Haarberg 14:00-14:30 Fission gas composition in the Stable Salt Reactor
Ian R. Scott1 1 Moltex Energy LLP, 6th Floor Remo House, 310-312 Regent St., LondonW1B 3BS Contact E-mail: [email protected]
14:30-15:00 Solid State Extraction and Consolidation of Titanium Alloys Direct from Synthetic
Rutile
Lyndsey L Benson1, Ian Mellor2 & Martin Jackson1 1 Department of Materials Science and Engineering, The University of Sheffield, Sir Robert Hadfield building, Mappin Street, Sheffield, S1 3JD, United Kingdom 2Metalysis Ltd, Unit 2 - Farfield Park, Manvers Way, Wath-upon-Dearne, Rotherham, S63 5DB, UKContact E-mail: [email protected]
15:00-15:30 Further progress in black silicon for solar photovoltaics
P. R. Coxon1, E. Juzeliunas1,2 & D. J. Fray1 1 Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge, CB3 0FS, UK 2 Campus Rectorate, Klaipėda University, Herkaus Manto str. 84, LT-92294 Klaipėda, Lithuania Contact E-mail: [email protected]
15:30-16:00 Tea break and Poster Session 3. 16:00-17:00 Technical Session 6: Chair Dr Andrew Doherty 16:00-16:30 Investigating nano-segregation and structuring in the bulk-phase and surface of ionic
liquid mixtures
Lucía D'Andrea1, Duncan W. Bruce1, Christopher P. Cabry1, John M. Slattery1,
Matthew L. Costen2, Kenneth G. McKendrick2, Simon M. Purcell2, María A. Tesa-
Serrate2, Brooks Marshall3, Timothy K. Minton3, Eric Smoll3, George C. Schatz4, José N. Canongia Lopes5,6, Karina Shimizu5,6 & Sarah Rogers7 1Department of Chemistry, University of York, Heslington, York YO10 5DD, UK 2Institute of Chemical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK 3Department of Chemistry and Biochemistry, MSU, Montana 59717, USA 4Department of Chemistry, Northwestern University, Illinois 60208-3113, USA 5Centro de Química Estrutural, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal 6ITQB, Universidade Nova de Lisboa, Avenida República, 2780-157 Oeiras, Portugal 7ISIS, Science & Technology Facilities Council, Rutherford Appleton Laboratory, UK [email protected]
16:30-17:00 Effects of Process Conditions on the Fluidised Cathode Electrochemical Reduction of
Tungsten Oxide in Molten LiCl-KCl
R. Abdulaziz, L.D. Brown, D. Inman, P.R. Shearing, D. J. L. Brett 1 Electrochemical Innovation Lab, Department of Chemical Engineering, University College London, Torrington Place, London, WC1E 7JE, United Kingdom Contact E-mail: [email protected]
17:00 Walk back to Fitzwilliam College 19:00-19:30 Pimms’s at Fitzwilliam College 19:30-21:00 Banquet at Fitzwilliam College: After dinner speech by Barry Snelson MBE. 21:00 Close of meeting. WEDNESDAY AUGUST 5th 08:00- Breakfast at Fitzwilliam College for over-night residents and departure.
LECTURES
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Effects of impurities on the current efficiency in aluminium electrolysis
Geir Martin Haarberg
Department of Materials Science and Engineering, Norwegian University of Science and Technology, Trondheim, NO-7491, Norway
Contact E-mail: [email protected] Aluminium is produced by electrolysis in molten NaF-AlF3-Al2O3 at ~955oC [1]. The current efficiency with respect to aluminium can be as high as 96 % in modern Hall-Heroult cells. The cell reaction is:
( ) ( ) ( ) ( )2 3 21 3 3 diss + C s = Al l + gAl O CO2 4 4
In a typical industrial cell the current densities are about 0.8 A/cm2. Aluminium dissolves in the molten electrolyte, which is a general phenomenon taking place when a metal is in contact with a molten salt containing the metal cation or other species of the metal. In molten cryolite based electrolytes dissolved Na must be considered in addition to dissolved Al. The dissolved metals react with the anode product CO2 in the so-called back reaction: which takes place outside the diffusion layer near the cathode. The back reaction is the main reason for loss in current efficiency. The rate of the back reaction depends on the rate of diffusion of dissolved metals near the cathode, which is related to the metal solubility and the diffusion layer thickness. Impurities of metals that are more noble than aluminium tend to codeposit at the cathode. The most important metals of this kind are iron and silicon. Dissolved impurity species of elements such as phosphorus may have a larger impact on the loss in current efficiency due to cyclic redox reactions occurring at repeatedly both electrodes. Sulfur originating in the carbon anode is quantitatively the most important impurity element in the process. The effect of sulfur on the current efficiency is not clear. In this study it was found that additions of sulfate to the electrolyte caused a significant loss in current efficiency. Future raw materials, mainly alumina and anode carbon, may contain higher impurity levels which may affect the current efficiency and the metal quality. Therefore, more fundamental studies of the behaviour of impurities must be carried out. References [1] J. Thonstad, P. Fellner, G.M. Haarberg, J. Hives, H. Kvande, Å. Sterten: "Aluminium Electrolysis. Fundamentals of the Hall-Heroult Process", Aluminium-Verlag, Düsseldorf (2001)
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Iron (III) Oxide Solubility in Alkaline Melts
Yaroslav V. Fedorov & Igor N. Skryptun
Institute of General and Inorganic Chemistry of National Academy of Sciences of Ukraine, 32/34 Palladin Ave, Kiev. 03680, Ukraine
e-mail: [email protected] Molten salts, and particularly molten alkali hydroxides and their mixture with alkali chlorides are well known as good reaction media for performing selective solubilisation or precipitation in chemical reactions, and have already been proposed as a promising route for the treatment of raw materials and subsequent recovery of valuable metals by electrowinning. In this work iron (III) oxide solubility in alkali hydroxides melts has been investigated in wide temperature range. The solubility of Fe2O3 has been determined by the method of isothermal saturation [1, 2] at temperature 673 – 823 K. The obtained results have been present in Fig. 1.
Obtained data indicate that the solubility of iron (III) oxide increases with rising temperature. As known the liquidus line for saturated solution of Fe2O3 is described by the next equation:
( )( )
( )R
OFeHTd
ad fussat
OFe 32
1ln
32
oΔ−= , (1)
where ( )32OFeH fusoΔ is the enthalpy of
fusion for Fe2O3, satOFea
32 is activity of Fe2O3 in
the melt using pure liquid iron (III) oxide as standard state. In our case the experimental data on the solubility were obtained and fitted well the equation of a straight line TBAC −=ln , where C is the mole fraction of Fe2O3 in molten solution and A and B are constants. Using the method of least squares (R =0.95) the next equations were obtained
TC 680566.2ln −= for melt-solvent NaOH, TC 478783.0ln −= for melt-
solvent KOH and TC 953008.7ln −= for melt-solvent 0.5NaOH–0.5KOH. Also found that in series melts NaOH–KOH–05.NaOH–0.5KOH the solubility of Fe2O3 increases. Thus these data indicate that the solubility of iron (III) depended by the temperature and nature of the solvent. References [1] I.N. Skriptun, O.G. Zarubitskii, Russian J. Inorg. Chem., 45, 1457, (2000). [2] I.N. Skryptun ECS Transactions, 33 (7) 303–309 (2010), doi: 10.1149/1.3484788.
Fig. 1. The solubility of iron (III) oxide in alkaline melts vs temperature. 1 – NaOH; 2 – KOH; 3 – 0.5NaOH–0.5KOH.
Uranium Metal Production by Direct Electrodeoxidation of Uranium Dioxide in Molten Salts
D. Sri Maha Vishnu1,2,3,a, K.S. Mohandas3 and K. Nagarajan3 1 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge , CB3 OFS, UK
2 with National Chair of Materials Science and Metallurgy, University of Nizwa, Nizwa, 613, Sultanate of Oman 3 Chemistry Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, 603102, India.
a Contact E-mail: [email protected] Direct Oxide Electrochemical Reduction (DOER) of metal oxides to the corresponding metals in
molten salts [1] is attracting wide attention due to its potential for commercialisation for production of various metals including actinides. Nuclear energy is one of the potential options for meeting the ever increasing demand for electricity and countries such as USA, Russia, France, Japan, UK and India have been operating nuclear reactors. Metallic fuels (e.g., U-19Pu-10Zr) are preferred as fuels in fast breeder nuclear reactors [2]. Obviously, the DOER process is of interest in nuclear technology in the context of (i) production of actinide metals (e.g., U and Pu) towards preparation of metal fuels and (ii) pyrochemical reprocessing of spent oxide fuels in which the spent oxide fuel is first converted into an alloy by DOER process and then subjected it to molten salt electrorefining process for further processing. Since U metal (or oxide) is the major component of the metallic (or the spent oxide) fuel, investigations were carried out on the electrochemical reduction of UO2 pellets to U in molten CaCl2 and CaCl2-NaCl and LiCl-KCl-CaCl2 salts with graphite as the anode. The mechanism and the factors influencing the electro-reduction of UO2 pellets were studied.
High temperature of operation in case of CaCl2 melt (1173 K) led to preferential surface metallisation whereas the bulk remained unreduced due to the sintering of U metal at the surface. Due to the incomplete reduction of UO2 pellets in CaCl2 melt, CaCl2-48mol% NaCl was employed as the electrolyte at 923 K. The low temperature allowed the electro-reduced U metal to remain porous (Fig. 1) and thus to extend the reduction to the bulk parts of the dense pellet. Experiments carried out for intermediate time periods showed that the reduction of UO2 to U occurred without the formation of any intermediate CaxUOy compounds or sub-oxides of U and hence is a one step process. The electro-deoxidation of solid UO2 in the melt was enhanced by increase in the duration of electrolysis and applied voltage. Increase in the open porosity of UO2 pellets does make the deoxidation faster, but the bulk reduction of even highly porous pellets became difficult when thickness of the electrode was high. Although the reduction was enhanced when the temperature increased to 1023 K, further increase in temperature to 1173 K led to the inhibition of the bulk reduction due to sintering of U metal particles on the surface of the pellet. The results obtained also indicated that the consumption of graphite anodes was significantly less in the melt compared to that of CaCl2 melt employed at 1173 K. Low melting LiCl-KCl-CaCl2 eutectic (50.5:44.2:5.3 mol%) was electrochemically characterised by cyclic voltammetry for its use as electrolyte for the electrochemical reduction of UO2. At lower temperatures the cathodic limit was the deposition of Ca2+ ions (T<773 K). Employing this fact electro-generated calcium induced reduction of UO2 to U was carried out in the melt at much lower temperature (673 K).
Fig. 1. SEM of (a) UO2 before and (b) U after electrolysis at 3.3 V in CaCl2-48mol.%NaCl at 923 K. References [1] G.Z. Chen, D.J. Fray & T.W. Farthing, Nature, 407, p.261-264 (2000). [2] K.S. Mohandas, Trans. Inst. Min Metall. C, 122, p.195-212 (2013).
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The International Current Situation Concerning Molten Salt Nuclear Reactors and the Results of a Government Sponsored UK Feasibility Study
Trevor R. Griffiths1, Rory O’Sullivan2 & Jasper Tomlinson2
1 Energy Process Developments, 58 High Ash Avenues, Leeds, LS17 8RF, UK) 2 Energy Process Developments, 185 New Kent Road, London, SE1 4AG, UK
The advantages of molten salt nuclear reactors, MSRs, in which the core is a liquid at high temperature, are generally not well understood or appreciated by the UK nuclear industry, where the only experience is with PWR/BWR. The molten salt based design has not been in use in the UK though an early competition by the US Atomic Energy Commission had 80 designs submitted and of the five winners, four were water-based, and are still used today. The fifth one was the Molten Salt Reactor, declared the best design, was submitted and then built by the Oak Ridge National Laboratory, Tennessee, where it was operated successfully and safely for ten years. The Cold War in the 1950 - 60s meant that plutonium was required by the military but because the molten salt reactor, MSR, did not produce any, the MSR design was a sidelined, despite its several significant advantages. Today, in a (generally) non-proliferation atmosphere, there is an excess of plutonium and this can be fuel for molten salt reactors. There are over 30 advantages listed for MSRs over solid fuel-in-water reactors in the present literature and selected advantages will be discussed. Energy Process Developments have undertaken a Government funded (by TSB, now Innovate UK) feasibility study of the optimum design(s), based on the latest technology from around the world, for a subsequent test-bed or pilot design. Our Report is now complete. Places and groups visited included and with whom discussions were held were:
Moltex – Stable Salt Reactor (SSR) (UK-based) Seaborg Technologies – Seaborg Waste Burner (SWaB) in Copenhagen FLIBE Energy – Liquid Fluoride Thorium Reactor (LFTR) in Canada Martingale Inc. (ThorCon) in Florida, USA Terrestrial Energy (IMSR) in Canada Transatomic Power Reactor (TAP) in Cambridge, Massachussetts
Our preferred design, and our reasoning, will be revealed at this conference.
Basic Molten Salt Reactor Design
PuCl3 – ZnCl2 Phase Diagram Robert Watson
AWE plc, Aldermastion, Reading RG7 4PR, UK Contact E-mail: [email protected]
A two stage oxidation – reduction process (Pyroredox Process) has been proposed to recover plutonium from high impurity metallic residues, Eqn 1 and 2. [1] Impurities with chlorides less stable than ZnCl2 will not be oxidised and will remain in the zinc phase.
2Pu + 3ZnCl2 2PuCl3 + 3Zn (Eqn 1) 2PuCl3 + 3Ca 2Pu + 3CaCl2 (Eqn 2)
The high vapour pressure of zinc chloride can be reduced by having it in combination with potassium chloride. While the binary phase diagrams of potassium chloride with zinc chloride and plutonium chloride are known, there is no published data on the plutonium chloride – zinc chloride system. Knowledge of this binary systems would allow the ternary system to be calculated and any phases likely to affect the reaction pathway could be identified. Experimental determination of the PuCl3 – ZnCl2 system shows a eutectic at 4.5±0.5 mol% PuCl3 at 318.5±0.5°C , Figure 1. Phase behaviour at high ZnCl2 concentrations is uncertain. A solid state transition was observed at 314.5±2°C at PuCl3 concentrations up to 15mol%.
Figure 1. Experimental phase transition temperatures PuCl3 – ZnCl2 system
for PuCl3 concentrations > 5mol%.
The reported binary phase diagrams of ZnCl2 with UCl4 [2], CeCl3 [3]and SmCl3 [4] are simple eutectics with a low melting point eutectic at high ZnCl2 concentrations. References 1. Chemistry of the Actinide and Transactinide Elements’ 3rd Ed. Eds. L.Morss, N.Edelstein & J.Fuger
Vol 2, p872 Springer (2006) ISBN 978-1-4020-3555-5. 2. W.Gawel & J.Terpilowski, Roczniki Chemii, 51, p.2099-104 (1977). 3. G.Perry & C.Hawthorn, Thermochimica Acta, 211, p. 323 (1992). 4. Y.Zhang, R.Gao & Y.Fu, Thermochimica Acta, 275, p.295-300 (1996).
© British Crown Owned Copyright 2015/AWE
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Role of Carbon Materials in the Front and Back End of Metallic Fuel Cycle Jagadeesh Sure1,2,3,a, D. Sri Maha Vishnu1,2,3,b
1 Corrosion and Chemistry Groups, Indira Gandhi Centre for Atomic Research, Kalpakkam, India 2 With National Chair of Materials Science and Metallurgy, University of Nizwa, Sultanate of Oman
3 Presently at Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, UK Contact E-mail: a [email protected]; b [email protected]
Fast Breeder Reactor with closed metallic fuel cycle is an inevitable technology option to the energy security for India [1]. For making metallic fuels (ex. U-Pu-Zr) directly from a mixture of the corresponding oxides by electrode-oxidation process (FFC Cambridge process) through molten chloride medium, graphite has been proposed to be used as anode material. The spent metallic fuels will be reprocessed through pyrochemical route involving eutectic mixture of LiCl–KCl molten salt as the electrolyte medium. Carbon based materials are proposed as candidates for the fabrication of containers (crucibles/liners) and electrodes in pyrochemical reprocessing. For understanding all these requirements, the corrosion behaviour of carbon materials in molten salt as an electrode and crucible applications have been investigated. Selection of materials is one of the critical issues in molten salt based technologies in the context of nuclear energy. High density graphite (HDG) rods have been selected as electrode materials for direct electrochemical de-oxidation of solid oxides (Nb2O5 and UO2) in molten chloride medium. Corrosion behaviour of HDG as anode in the electrochemical de-oxidation of Nb2O5 pellet electrodes in molten CaCl2 at 1173 K was studied. The degradation of the graphite anodes, recovered from the electro-de-oxidation cells at predetermined intervals of time (2, 9, 22, 26, 35, 44 and 56 h) during the long-duration electrolysis, was determined by mass loss measurements and the morphological changes by scanning electron microscopy (SEM) imaging [2]. After gaining confidence on electrochemnical reduction studies on Nb2O5 cathode using HDG anode; the electro-reduction of the UO2 pellets under different experimental conditions in CaCl2-48 mol% NaCl melt was studied in the temperature range 923–1173 K by mass loss of the electrode. Unlike in pure CaCl2 melt at 1173 K, the consumption of graphite anode and the carbon contamination of the melt were found to be minimum in CaCl2-NaCl melt [3]. The corrosion behaviour of the carbon materials viz. low density graphite (LDG), HDG, glassy carbon (GC) and pyrolytic graphite (PyG) in molten LiCl-KCl salt at 873 K was investigated and the morphological changes in the samples induced by molten LiCl–KCl salt after continuous exposure to 2000 h has been evaluated at micrometer scale using SEM, atomic force microscopy, X-ray diffraction and Raman spectroscopy [4]. The possible mechanism by which surface degradation of carbon materials occurred in molten salt has been discussed. Owing to its availability and economic viability, HDG is considered as one of the structural materials for salt purification system and as cathode processor crucible. The performance of HDG in molten LiCl-KCl salt clearly indicated that ceramic coatings are desirable on HDG crucibles in order to protect them from corrosion attack by salt and molten uranium and to extend their service life and mechanical integrity at high operating temperatures. The partially stabilized zirconia (PSZ) coated HDG samples were exposed to molten LiCl-KCl salt for 2000 h at 873 K and compatibility test with molten uranium at 1623 K for 20 min under ultra high pure argon atmosphere [5,6]. The results of the present investigation on the corrosion behaviour of PSZ coatings in molten salt gave the confidence for developing PSZ coating on engineering scale HDG crucibles by plasma spray process. References [1] Baldev Raj, Energy Procedia, 7, 186-198 (2011). [2] D. Sri Maha Vishnu, Jaagadeesh Sure, K.S. Mohandas, Carbon, 93, p.782-792 (2015). [3] D. Sri Maha Vishnu, N. Sanil, G. Panneerselvam, R. Sudha, K. S. Mohandas, and K. Nagarajan, J. Elec. Soc., 16, D394-D402
(2013). [4] Jagadeesh Sure, A.R. Shankar, S. Ramya, C. Mallika, U. Kamachi Mudali, Carbon, 67, p.643-655 (2014). [5] Jagadeesh Sure, A.R. Shankar, S. Ramya, U. Kamachi Mudali, Ceram. Inter., 38, p. 2803-28112 (2012) & Ceram. Inter.,40,
6509-6523 (2014).
Towards Understanding Reactivity in Ionic Liquids Richard M. Fogarty1, Robert G. Palgrave2, Richard A. Bourne3, Thomas W. Chamberlain4, Nick A.
Besley4, Josephina Werner,5 Gunnar Öhrwall,5 Olle Björneholm,5 Patricia A. Hunt1, Kevin R. J. Lovelock1
1 Department of Chemistry, Imperial College London 2 Department of Chemistry, University College London
3 School of Chemistry, University of Leeds 4 Department of Chemistry, University of Nottingham
5 Department of Physics and Astronomy, Uppsala University Contact E-mail: [email protected]
The vast majority of chemical reactions occur in liquids. The valence and conduction bands play a vital role in controlling liquid phase reactivity: thermal stability, solute-solvent interactions, electrochemical reactivity, and surface-ionic liquid interactions. The identity and energy of the frontier orbitals, i.e. the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), is most important, particularly whether the HOMO and LUMO are from the solute or the solvent. For ionic liquid-based systems, the valence band is regularly calculated, but experimental data is extremely scarce.[1]
X-ray spectroscopy is regularly used to study the valence and conduction bands of solids. Ionic liquids are sufficiently involatile that standard apparatus can be used to study the liquid phase at room temperature.[1-3] Studying the valence bands of volatile liquids, e.g. water-ionic liquid mixtures, is far more challenging, and a liquid microjet is usually used.[4] We used X-ray photoelectron spectroscopy (XPS), resonant Auger electron spectroscopy (RAES) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy to probe the electronic structure of both neat ionic liquids and solutes in ionic liquids. Experiments were carried out on a lab-based XPS apparatus, and a range of synchrotron beamlines. We compared our experimental results to DFT and time-dependent DFT calculations for a range of systems.
The HOMO was usually from the anion, but for two ionic liquids there was competition between the cation and the anion to be the HOMO. Excellent agreement was found between the experimental and calculated HOMOs and LUMOs for seven neat ionic liquids, including a range of cations and anions. For calculations, the system size was found to be particularly important. The HOMO energy for [C4C1Im][SCN]-water mixtures was found to vary with the concentration, and was significantly smaller for the mixtures compared to neat water (Figure 1). Lastly, metal ion complex speciation in ionic liquids was probed, and found to relate to the valence band structure. These results have significant implications for reactivity of ionic liquid-based systems. References 1. K. R. J. Lovelock, I. J. Villar-Garcia, F. Maier, H. P. Steinrück and P. Licence, Chem. Rev., 2010, 110,
5158-5190. 2. K. R. J. Lovelock and P. Licence, in Ionic Liquids UnCOILed: Critical Expert Overviews, eds. K. R.
Seddon and N. V. Plechkova, Wiley, Oxford, 2012, ch. 8, pp. 251-282. 3. S. Kuwabata, T. Tsuda and T. Torimoto, J. Phys. Chem. Lett., 2010, 1, 3177-3188. 4. B. Winter and M. Faubel, Chem. Rev., 2006, 106, 1176-1211.
Figure 1. EHOMO for [C4C1Im][SCN]x(H2O)1-x when x = 0.00, 0.03, 0.10, 0.25 and 1.00.
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Molten salt preparation of graphene and its potential applications
Ali Reza Kamali &Derek J. Fray Department of Materials Science and Metallurgy, University of Cambridge,
Cambridge CB3 0FS, UK Email:[email protected]
Carbon nanostructures include fullerenes, carbon nanotubes, nanofibres and graphene. In recent years graphene has received widespread attention owing to its extraordinary physical, mechanical and chemical properties which make it a promising candidate for many applications. However, unfortunately, most of the available methods for producing graphene suffer from one or more disadvantages such as a low rate of production [1], the low quality of graphene product [2-4] and the use of hazardous organic solvents [5]. Hence, currently, there is no process available that can economically produce large amounts of graphene. Molten salts offer an opportunity to solve these problems: The intercalation of hydrogen into the interlayer space of graphite crystallites at the graphite electrodes immersed in molten LiCl in a moist argon gas flow leads to the formation of high quality graphene nanosheets in a high yield [6]. The graphene nanosheets produced possessed a lateral size of several hundred nanometers and a hexagonal structure of graphene. This process is anticipated to be a simple and efficient method for the large-scale production of graphene nanomaterials. The possible applications of the graphene product in energy storage systems and composites are presented.
TEM micrograph of the graphene nanosheets produced in molten salt and a typical electron diffraction pattern recorded at a flat edge of a graphene sheet.
[1] T. Mori, et al., Relat. Mater. 17, p. 1513 (2008). [2] V. Nicolosi et al., Science, 340, p. 1226419 (2013). [3] D. R. Dreyer et al.,Chem. Soc. Rev., 39, p. 228 (2010). [4]Y. Hong, Z. Wang & X. Jin, Sci. Rep., 3, p.3439 (2013). [5] K. R. Paton et al., Nat. Mater., 13, p.624 (2014). [6] A.R. Kamali & D.J. Fray, Nanoscale, 7, p.11310 (2015).
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Solid State Extraction and Consolidation of Titanium Alloys Direct from Synthetic Rutile
Lyndsey L Benson1, Ian Mellor2 & Martin Jackson1
1 Department of Materials Science and Engineering, The University of Sheffield, Sir Robert Hadfield building, Mappin
Street, Sheffield, S1 3JD, United Kingdom 2Metalysis Ltd, Unit 2 - Farfield Park, Manvers Way, Wath-upon-Dearne, Rotherham, S63 5DB, UK
Contact E-mail: [email protected] With recent developments within the titanium industry, it is clear that a step-change is needed to significantly drive down the cost of titanium. Substantial effort has gone into reducing both the cost of extraction, as well as the cost of fabrication. Facilitating further expense reductions, direct reduction of synthetic rutile derived from beach sands, could have a significant role to play within the evolution of low cost titanium powder. In this presentation, synthetic rutile powder has been successfully reduced via the FFC (Fray Farthing Chen) process and characterised throughout the reduction process using a wide range of techniques. Downstream solid state processing experiments have also been conducted and the resulting microstructures have been analysed.
Fig 1: Secondary electron image of a partially reduced synthetic rutile illustrating calcium ditatanate needles.
Further progress in black silicon for solar photovoltaics
P. R. Coxon1, E. Juzeliunas1,2 & D. J. Fray1 1 Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge,
CB3 0FS, UK 2 Campus Rectorate, Klaipėda University, Herkaus Manto str. 84, LT-92294 Klaipėda, Lithuania
Contact E-mail: [email protected] Black silicon (b-Si) is an actively growing research area in renewable energy materials. Its highly porous and dense nanostructure makes it particularly attractive as a highly-absorbent anti-reflection coating (ARC) to boost the performance of crystalline silicon solar cells by suppressing optical losses caused by reflection at the front face. [1] Conventional ARCs based on silicon nitride coatings, though common, suffer a significant drawback since their anti-reflection performance is limited to specific range of incident angles and wavelengths. Black silicon offers a low cost and efficient replacement for ARC coatings. By texturizing the wafer surface with random structures, off-normal optical scattering is increased, raising the average path length of the light in the c-Si absorbing layer, which leads to a stronger absorption of the light. We employ a low-cost route of b-Si production to introduce a dense silicon surface texture based on the electrochemical reduction of silica layers through the FFC-Cambridge process. Here we present further results in our research to produce a low-cost and sustainable antireflection coating for solar cells. By carefully engineering the electrolysis conditions and employing thin (50nm) coating of TiO2 we are able to bring reflection down to <0.1% from over 3%, firmly placing b-Si in the family of ultrablack absorbers for photon management in solar cells. This compares well with < 2% reflectance offered by b-Si produced via reactive ion etching (RIE) and at a significant cost advantage (~ $25/wafer by RIE against $9/wafer by FFC.) References [1] X. Liu, P. R. Coxon, M. Peters, B. Hoex, J. M. Cole & D. J. Fray, Energy Environ. Sci.,7, 3223-3263 (2014)
Investigating nano-segregation and structuring in the bulk-phase and surface of ionic liquid mixtures
Lucía D'Andrea1, Duncan W. Bruce1, Christopher P. Cabry1, John M. Slattery1, Matthew L. Costen2, Kenneth G. McKendrick2, Simon M. Purcell2, María A. Tesa-Serrate2, Brooks Marshall3, Timothy K.
Minton3, Eric Smoll3, George C. Schatz4, José N. Canongia Lopes5,6, Karina Shimizu5,6 & Sarah Rogers7
1Department of Chemistry, University of York, Heslington, York YO10 5DD, UK 2Institute of Chemical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK
3Department of Chemistry and Biochemistry, MSU, Montana 59717, USA 4Department of Chemistry, Northwestern University, Illinois 60208-3113, USA
5Centro de Química Estrutural, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal 6ITQB, Universidade Nova de Lisboa, Avenida República, 2780-157 Oeiras, Portugal 7ISIS, Science & Technology Facilities Council, Rutherford Appleton Laboratory, UK
[email protected] An understanding of the chemical composition and molecular arrangement of ions in the bulk and at the gas-liquid and vacuum-liquid interfaces is of fundamental interest for IL-based applications. However, the identification of the molecules present in the near-surface region and whether there is enhancement of certain ions (or parts of ions) with respect to the bulk composition is a non-trivial challenge. Numerous experimental and theoretical techniques have been employed so far to probe the surface structure of ILs.[1] Our own investigations on pure ILs have demonstrated that detailed reactive and inelastic scattering dynamics of super- and hyperthermal oxygen atoms on IL surfaces can give valuable information that is complementary to that provided by other studies.[2, 3, 4] IL mixtures are seen as a possible approach to improve target properties of ILs while maintaining their favourable characteristics. However, more research in this area is necessary to understand the structure and dynamics of these systems and to realise the goal of rationally designed tunability. While data on the physical properties, structure and dynamics of pure ionic liquids are now becoming available widely, data for ionic liquid mixtures are still limited.[5, 6] In an effort to overcome this limitation and obtain a fundamental understanding of the bulk and interface structuring of binary IL mixtures, a combination of conductivity, viscosity, small-angle neutron scattering (SANS), small-angle X-Ray scattering (SAXS) measurements and reactive-oxygen scattering experiments were carried out. In this contribution, surface enrichment effects in mixtures of imidazolium-based will be discussed. References [1] K.R.J. Lovelock, Phys. Chem. Chem. Phys., 14, p.5071-5089 (2012). [2] B. Wu, J. Zhang, T.K. Minton, K.G. McKendrick, J.M. Slattery, S. Yockel & G.C. Schatz, J. Phys. Chem. C, 114, p.4015-4027 (2010). [3] C. Waring, P.A.J. Bagot, J.M. Slattery, M.L. Costen & K.G. McKendrick, J. Phys. Chem. Lett., 1, p.429-433 (2010) [4] C. Waring, P.A.J. Bagot, J.M. Slattery, M.L. Costen & K.G. McKendrick, J. Phys. Chem. A, 14, p.4896-4904 (2010). [5] H. Niedermeyer, J.P. Hallett, I.J. Villar-García, P.A. Hunt & T. Welton, Chem. Soc. Rev., 41, p.7780-7802 (2012). [6] M.T. Clough, C.R. Crick, J. Gräsvik, P.A. Hunt, H. Niedermeyer, T. Welton & O.P. Whitaker, Chem. Sci., 6, p.1101-1114 (2015).
Effects of Process Conditions on the Fluidised Cathode Electrochemical Reduction of Tungsten Oxide in Molten LiCl-KCl
R. Abdulaziz, L.D. Brown, D. Inman, P.R. Shearing, D. J. L. Brett
1 Electrochemical Innovation Lab, Department of Chemical Engineering, University College London, Torrington
Place, London, WC1E 7JE, United Kingdom Contact E-mail: [email protected]
The direct electrochemical reduction of titanium oxide to titanium metal has been evinced by the FFC Cambridge process. [1] Numerous studied have been carried out to assess the performance and applicability of the process to the reduction of titanium, other refractory metals and metal alloys. However, there are some limitations to the FFC Cambridge process. For example, at least in the case of titanium, the current efficiency is quite low (10-40% to achieve 0.3% oxygen content in the final titanium product). [2] There are two main reasons that hinder the reduction process: oxide product build-up in the electrolyte close to the surface and within the pores of the precursor, resulting in anomalous electro-migration of the oxygen vacancies, creating a barrier to the reduction process; and limited diffusion of the electrolyte within the precursor porous matrix. [3] Thus, innovative new designs of the process are needed. The fluidised cathode process [4] offers a solution to these problems. Figure 1 is a schematic of the electrolytic cell used. The process is potentially applicable to the range of metals and molten salts systems and has been exemplified for the reduction of WO3 in LiCl-KCl eutectic. However, there is still much to be investigated to establish a full understanding and optimise the process. This paper discusses experimental findings of the effects the fluidisation rate and the metal oxide-salt ratio have on the fluidised cathode applied to the Li-K-W-O-Cl system.
Figure 1. Electrolytic cell for the reduction of WO3 particles using a fluidised cathode. [4] References [1] G. Z. Chen, D. J. Fray and T. W. Farthing, Nature, 407(6802), 361 (2000). [2] C. Schwandt, D. T. L. Alexander and D. J. Fray, Electrochim. Acta, 54(14), 3819 (2009). [3] E. Krasicka-Cydzik, ECS Trans., 50(11), 39 (2013). [4] R. Abdulaziz, L. D. Brown, D. Inman, S. Simons, P. R. Shearing and D. J. L. Brett, Electrochem. Commun., 41(0), 44 (2014).
POSTERS
Electrochemical Reduction of Metal Oxide Powders
S. M. Wilcock1 and A. M. Parkes1
1 AWE, Aldermaston, Reading, RG7 4PR, UK Contact E-mail: [email protected]
The ability to electrochemically reduce sintered pellets of metal oxides in molten salts has been established for some time now. Processes such as this are potentially of great interest to AWE as they offer the prospect of regenerating plutonium metal from oxide without the waste production associated with purely chemical processes. Unlike most currently published work the focus of our research has been to develop a method for processing oxide in powder form as avoiding the sintering stage will reduce the time the worker is exposed to radiological dose. Initial work into this area at AWE showed a good deal of promise [1] but refining the process proved a challenge. Recently, however, the problems faced have shown signs of being surmounted and the development of a robust system appears tantalisingly possible. The work presented here covers efforts in the non-active labs at AWE to develop a reliable process for the reduction of oxide powders to metal products. Consideration of process requirements such as salt reuse and inert anode necessity are examined with the result being the development of new experimental cell designs.
Picture: Diagram of a novel cell design for electrochemical reduction of oxide powder. References [1] Jones A H, ‘Electrochemical Reduction of Titanium Oxide, Cerium Oxide and Plutonium Oxide Powders’, MSc Thesis, University of Cambridge (2010)
© British Crown Owned Copyright 2015/AWE
In situ extractions of butanol from fermentation broths using ionic liquids
Angela L Tether,1 Stephen Hall,1 James Nicolle,2 Anna Croft,1 and Gill Stephens 1
University of Nottingham, Dept. of Engineering, Biorenewables & Bioprocessing Research Group, Coates Building, Coates Road, University Park, Nottingham, NG7 2R2
Green Biologics Ltd., 45A Western Avenue, Milton Park , Abingdon , Oxfordshire , OX14 4RU Contact E-mail: [email protected]
A collaborative project has been initiated between the Biorenewables and Bioprocessing group at the University of Nottingham and Green Biologics Ltd. The HIPHOP (High Productivity Homofermentative Process for Butanol) project will use optimised fermentation techniques and Ionic Liquids to solve common problems associated with the ABE fermentation process. Butanol is quickly gaining a foothold in the bio-based fuel and fine chemical markets. Along with being a plausible alternative to ethanol as a biofuel, butanol is also used in coatings, paints, resins, inks, varnishes, natural and artificial flavourings, perfumes, as solvent for antibiotics and vitamins, and can be converted to building blocks for polymers and plastics. Butanol can be produced using the ABE (Acetone, Butanol, Ethanol) fermentation process, where non-pathogenic bacteria (Clostridium species) use sugars which can be obtained from non-food crops or biomass waste products to produce acetone, butanol and ethanol as metabolic end products. Various ionic liquids are being explored as improved solvents for the extraction of butanol in situ to mitigate product toxicity to cells and decrease the energy cost of product recovery. Initial toxicity studies conducted with ionic liquids and Clostridium strains are promising as is the extraction of butanol using model and spent fermentation broths.
Calcium Reduction of Spent Electrorefining Salt
Clare Stawarz, Robert Watson
AWE plc, Aldermaston, Reading, RG7 4PR, UK Contact E-mail: [email protected]
Spent Electrorefining (ER) salt from the pyrochemical processing of plutonium at AWE is currently stored on site awaiting a suitable recovery route. Restrictions on the materials storage and disposal mean reprocessing is required to find a more suitable storage form and recover the plutonium metal. A Calcium Reduction process is currently being developed at AWE to treat spent ER salt residues. The process aims to reduce the Pu3+ species in the spent salts to plutonium metal via the addition of calcium metal. The product is a consolidated plutonium button and salt residues that contain considerably lower levels of plutonium than before processing. In total, six experiments have been carried out at AWE to demonstrate calcium reduction as a potential plutonium recovery process. Of the six experiments carried out; three experiments were on spent ER salt with no crucible fragments and three on spent ER salt containing crucible fragments. Alongside the experiments carried out on the two different salt feeds, varying levels of calcium were used in different runs to identify a suitable excess amount of calcium for the process. Initial findings from AWE experiments show a high removal of plutonium in both types of spent ER salt, with or without crucible fragments. The product metal in most cases has formed a consolidated button which sometimes contains un-reacted calcium metal. The salt after assay and initial analysis has shown to contain very low levels of plutonium.
Figure 1: Photograph of the spent ER salt containing ceramic fragments after the calcium reduction process. This experiment used 30 % excess calcium. Two phases can be seen in the salt block. The white upper layer is
expected to contain almost no plutonium. The darker layer is expected to be plutonium rich where partial reduction of the plutonium occurred. The bottom surface is the consolidated metal button.
© British Crown Owned Copyright 2015/AWE
Liquid-Crystalline Ionic Liquids as Reaction Media
Christopher P. Cabry, Yanan Gao, John M. Slattery,* Duncan W. Bruce*
Department of Chemistry, University of York, UK
*E-mail: [email protected], [email protected] Liquid-crystalline ionic liquids (LC-ILs) are exciting as novel, ordered reaction media owing to their short- and long-range structural anisotropy. [1] Performing reactions in ordered liquid-crystalline media could offer control over reaction kinetics and/or regioselectivity as the mesogenic medium exerts steric and electronic demands upon the system. [2] This contribution will discuss two different reactions, namely a Claisen and an aza-Claisen rearrangement, which have been performed in a range of ILs and LC-ILs. As the anisotropic nature of the LC-ILs leads to challenges in following the reactions, in order to monitor kinetic parameters, the continued development of a facile way to collect such data in situ is presented. Thus it was found that one system shows a liquid-crystalline effect on the kinetics of the rearrangement, whereas in the other no such effect is seen. These differences can be rationalised by considering the location of the substrate within the LC-IL matrix. In addition to studies of reactivity, the preparation and mesophase behavior of a novel series of liquid-crystalline stilbazolium salts, which are related to the dicationic LC-ILs prepared previously in the group, are also presented, Figure 1. [3] The potential of these new LC-ILs as reaction solvents is discussed.
Figure 1: Structure of the stilbazolium salt based LC-ILs References [1] K. Binnemans, Chem. Rev., 2005, 105, 4148 [2] R. G. Weiss, Tetrahedron, 1988, 44, 3413 [3] Y. Gao, J. M. Slattery and D. W. Bruce, New J. Chem., 2011, 35, 291
Electrochemical Oxidation of Lignin in an Ionic Liquid
Majd Eshtaya1, Gill Stephens1, George Z. Chen1, 2 and Anna Croft1
1Department of Chemical and Environmental Engineering, University of Nottingham, Nottingham, United Kingdom
2Faculty of Science & Engineering, University of Nottingham Ningbo China, Ningbo, P. R. China Contact E-mail: [email protected]
Lignin is the second most abundant natural polymer and might serve as a sustainable resource for aromatic derivatives for the chemicals industry after being depolymerized [1, 2]. In this work, the mediator, 2,2’-azino-bis(3-ethylbenthiazoline-6-sulfonic acid) diammonium salt (ABTS), has been evaluated by means of cyclic voltammetry for enhancing the oxidation of the non-phenolic lignin model compound (veratryl alcohol) and three types of lignin (organosolv, Kraft and lignosulfonate) in an ionic liquid (1-ethyl-3-methylimidazolium ethyl sulfate, [C2mim] [C2SO4]). Addition of veratryl alcohol and organosolv lignin could increase the second oxidation peak of ABTS, indicating that ABTS mediated oxidation of the two added molecules at high potentials in [C2mim] [C2SO4], as both electrolyte and solvent. Furthermore, cyclic voltammetry was applied as a quick and efficient way to explore the impact of water in the ABTS-mediated oxidation of lignosulfonate lignin. Higher catalytic efficiencies of ABTS were observed for lignosulfonate solutions either in sodium acetate buffer or when [C2mim] [C2SO4] (15 v/v%) was present in the buffer solution whilst there was no change found in the catalytic efficiency of ABTS in [C2mim] [C2SO4]- lignosulfonate mixtures relative to ABTS alone. We are currently analysing the reaction products by gas chromatography–mass spectrometry (GC-MS) and gel permeation chromatography (GPC) to identify the nature of the chemical transformations.
Figure: Valorisation of lignin using electrochemical process References: [1] Bourbonnais, R., Leech, D., & Paice, M. G. (1998). Biochimica et Biophysica Acta (BBA) - General
Subjects, 1379(3), 381-390. [2] Harwardt, N., Stripling, N., Roth, S., Liu, H., Schwaneberg, U., & Spiess, A. C. (2014). RSC Advances,
4(33), 17097-17104.
Application of Ionic Liquids as Solvents for Chemical Analysis
Mohamed Rafiq Sulaiman1,2, Tom Welton1
1Department of Chemistry, Imperial College London, South Kensington Campus, London SW7 2AZ, UK. 2 Department of Chemistry Malaysia, Ministry of Science, Technology & Innovation (MOSTI), Jalan Sultan, 46661
Petaling Jaya, Malaysia. [email protected]
The main focus of this research is to investigate extraction methods using ILs as the extraction
solvents for target chemicals in environmental samples. This research will focus on the modification of existing ILs and the synthesis of novel functionalised ILs that are suitable for the isolation of selected chemicals. Replacing organic solvents with ionic liquids will produce safer analytical protocols which can be used by any chemical testing laboratory. Protocols to analyse ionic liquid solutions containing target chemicals has been developed by Headspace-Gas Chromatography/Mass Spectrometry (HS-GC/MS). Headspace injection methodology is the approach of choice due to the capability of obtaining a sample quickly and without contamination of the GC, when analysing volatile organic compounds. References [1] Welton, T., Room-Temperature Ionic Liquids: Solvents for Synthesis and Catalysis. 2, Chem. Rev.,
1999, 99 (8), pp 2071–2084. [2] S. U. Mokhtar, et al., Direct ionic liquid extractant injection for volatile chemical analysis – a gas
chromatography sampling technique, Green Chem., 2015, 17, 573.
Study on The Electrochemical Reduction of CeO2 to Ce in molten LiCl-KCl eutectic
C.Knox1, L.D.Brown1, R.Abdulaziz1, P.R.Shearing1, D.J.L.Brett1, A. H.Jones2
1 Electrochemical Innovation Laboratory, Dept. Chemical Engineering, UCL, London, WC1E 7JE
2 AWE Aldermaston, Reading, Berkshire, RG7 4PR
This work presents the initial research carried out on the electrochemical reduction of cerium (IV) oxide to metallic cerium in LiCl-KCl molten salt eutectic at 723K. The reduction process originated both from the FFC Cambridge1 (direct mechanism) and Ono and Suzuki2 (indirect mechanism) processes which successfully reduced titanium (IV) oxide to titanium in a molten chloride salt. This reduction reaction can be used in the reprocessing step of the nuclear fuel cycle and it is now the focus in research to make this possible on a commercial scale. Cerium (IV) oxide is a useful material in the nuclear industry due to the similarities in its chemical, thermodynamic, and electrochemical properties to plutonium (IV) oxide.3 The purpose for using it as a chemical surrogate is to reduce exposure time to radiation and cost; it is also more readily available. Two cathode designs were employed in this study: a metallic cavity electrode (MCE) and a pellet electrode. Cyclic voltammetric analysis was carried out on both to determine ceria’s reduction potential and its possible reaction mechanism. The advantage of using the MCE technique is the reduced IR drop which occurs and the fast electrode kinetics. Pellets have both a larger IR drop and slower electrode kinetics due to diffusion limitation; however their flexibility in design and their recovery after the reaction has taken place (unlike in MCE’s where there is a chance that the powder will fall out) allows them to be practically useful in experiments. It was found that the reduction potentials of the MCE and pellet electrode were -2.1V and -2.03V respectively. Despite the slight variation, both were due to ceria reduction. Predominance diagrams were produced to thermodynamically predict the stable species present at various pO2- and electrode potential values. This thermodynamic prediction helped confirm that the reduction potential was in fact due to ceria. The presence of a reduction peak whilst avoiding the deposition potential of lithium suggests that the reduction process proceeds through a direct means whereby the ceria is electrochemically reduced. This differs from Claux et.al’s work in CaCl2-KCl at 1023K who suggests that the ceria was reduced chemically with calcium.4
References [1]- G.Z. Chen, D.J. Fray, T.W. Farthing, Direct electrochemical reduction of titanium dioxide to titanium in molten calcium chloride, Nature, 407 (2000) 361-364. [2]- K. Ono, R. Suzuki, A new concept for producing Ti sponge: Calciothermic reduction, JOM, 54 (2002) 59-61. [3] – Kolman, David G., et al. "An assessment of the validity of cerium oxide as a surrogate for plutonium oxide gallium removal studies." (1999). [4]- B. Claux, J. Serp, J. Fouletier, Electrochemical reduction of cerium oxide into metal, Electrochimica Acta, 56 (2011) 2771-2780.
List of Delegates. Professor Hiro Ohno [email protected] Professor Barry Snelson
Dr Rory O’Sullivan Energy Process Developments Ltd. [email protected]
Dr Greg Doughty Metalysis Ltd [email protected]
Dr Trevor Griffiths Energy Process Developments [email protected]
Dr Olga Kuzmina Imperial College London [email protected]
Dr Alistair Parkes AWE plc [email protected] miss Clare Stawarz AWE [email protected] Dr Robert Watson AWE plc [email protected] Dr Steven Wilcock AWE [email protected] Dr Ian R. Scott Moltex Energy [email protected]
Dr Stuart Mucklejohn Ceravision Limited [email protected]
Dr. Angela Tether University of Nottingham [email protected]
Dr JAGADEESH SURE
University of Cambridge & University of Nizwa [email protected]
Dr. D. Sri Maha Vishnu
University of Cambridge & University of Nizwa [email protected]
Prof. George Chen University of Nottingham [email protected]
Miss Happiness Ijije University of Nottingham [email protected]
Miss Lyndsey University Of Sheffield [email protected]
Ms Rema Abdulaziz University College London [email protected]
Miss Chloe Knox UCL [email protected]
Dr Anna Croft University of Nottingham [email protected]
Dr Andrew Doherty Queen's University [email protected]
Prof Geir Martin Haarberg
Norwegian University of Science and Technology [email protected]
Dr Paul Coxon University of Cambridge [email protected]
Dr Kevin Lovelock Imperial College London [email protected]
Professor Ian Metcalfe Newcastle University [email protected]
Professor Derek Fray University of Cambridge [email protected]
Nur Liyana Ismail Imperial College [email protected]
Christopher Cabry York University [email protected]
Majid Eshtaya Nottingham University [email protected]
Mohamed Rafiq Sulaiman Imperial College [email protected]
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