Magnox magnesium alloy fuel cladding has been safely wet stored in cooling ponds for long periods of time. Under long-term storage conditions it has been observed that exposure to certain types of pre-treatment produces a far more corrosion resistant surface compared to alloy specimens alloy which have not received the same type of pre-conditioning. However, there is currently a lack of understanding regarding the origin of this apparent improved passivity compared to materials not exposed to the same conditions. The main aim of this project is to identify how the various passivated Magnox surfaces differ in regard to corrosion initiation behaviour compared to those which are not.
Specimens will be pre-treated to simulate storage conditions which lead to enhanced passivity of the magnesium alloy. These pre-treated specimens will then be analysed using a variety of methods which will include DC electrochemistry and electrochemical impedance spectroscopy (EIS). Once an understanding of how pre-treatments may benefit the alloy, further work will investigate the initiation, propagation and extent of corrosion using in-situ techniques. Swansea University’s own in-house scanning vibrating electrode technique (SVET) will be used to map the surface for areas of localised corrosion. A SVET time-lapse imaging approach may also be used to give visual information, complementing the surface current density maps. Scanning Kelvin probe (SKP) will provide information on the Volta potentials allowing different pre-treatments to be compared for materials with artificial defects present, such as a scribe. Focussed ion beam scanning electron microscopy (FIB-SEM), present within the advanced imaging of materials (AIM) facility at Swansea, will allow cross sectional post corrosion imaging to be undertaken for the alloy to allow a better understanding of how corrosion propagates within pre-treated and control specimens.
The combination of the techniques listed above will a lead to a more detailed understanding of the fundamental mechanisms behind pre-treatments, passivity and corrosion in Magnox magnesium alloy.
To achieve insight into (a) which pre-treatments have passivated the alloy and had a beneficial impact in retarding corrosion, and (b) an understanding of the passivation mechanism behind the pre-treatment.
1. Pre-treatment of magnox alloy:
· Control specimen
· Storage in NaOH
· Storage in fluoride containing solution
· Variation in temperature
· Presence of blast furnace slag concrete in pond
The above environments will be used to simulate storage conditions which may lead to passivation of the magnesium alloy.
2. Immersion in a pond storage conditions and accelerated testing. Pre-treated magnesium alloys specimens, if passivated, will have a lower corrosion rate than non-treated specimens; therefore accelerated corrosion will need to take place. This may be undertaken either by artificial defect, polarisation or increased electrolyte temperature.
· DC/EIS electrochemistry to gain an understanding of the corrosion performance of the alloy
· SVET time lapse imaging to understand locations in which corrosion initiates and the respective current density at those sites
· SKP to identify corrosion under the passive film, or at an artificial defect
· FIB-SEM to identify areas where corrosion has initiated and if corrosion propagation differs for pre-treated and non-treated magnesium alloy
Materials Engineering preferred, but other physical sciences accepted (Engineering, Physics, Chemistry) with previous experience with some of the techniques mentioned above
and a basic understanding of corrosion or how materials may degrade is desirable. Ideally the candidate is keen to publish research and present at conferences.
Sponsoring Company The National Nuclear Laboratory (NNL)
Candidates should hold an Engineering or Physical Sciences degree with a minimum classification level of 2:1 or equivalent relevant experience.
Our funders require applicants to also meet the following eligibility criteria:
Further information regarding eligibility criteria can be found at: http://www.materials-academy.co.uk/eligibility
The Athena SWAN Charter recognises work undertaken by institutions to advance gender equality. The College of Engineering is an Athena SWAN bronze award holder and is committed to addressing unequal gender representation.Funding
The studentship covers the full cost of UK/EU tuition fees, plus a tax free stipend of £12,500 p.a.Closing Date 28 February 2018