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06.02.2019

Tru Vue blog: Instrumental Methods in Electrochemistry Summer School

Back in the summer, Charles Stable ACR was fortunate enough to receive funding from TruVue to attend the Instrumental Methods in Electrochemistry Summer School at Southampton University. 

National Museums Scotland (NMS) Artefact conservation have been applying electrochemical techniques cleaning and removal of active corrosion of mainly silver and silver gilt objects and also for many years creating electrotype replicas. To support this work NMS have acquired a Potentiostat to develop and test electrochemical techniques applied to objects and also the effects using different electrolytes and their behaviour and reaction with objects. This TruVue Grant enabled me to attend a week of immersive study aimed to help to improve my own knowledge of electrochemical techniques and application of Potentiostatic instrumental techniques to investigate and develop lab treatments of a broader range of metals an alloys.

The Summer School in Instrumental Methods of Electrochemistry run by Southampton university comprised of a combination of morning lectures and afternoon practical laboratory demonstrations and also provided formal and informal opportunities for discussion of topics related to the interests of the participants.

The course has been organised almost yearly since 1969 , the Summer School and the Southampton Chemistry faculty has a strong international reputation. In this particular year there were over 40 attendees coming as far as Australia and South Africa. Electrochemistry has a broad range of applications and this was in evident by the range of specialisms represented on the course ranging from medical applications, battery and fuel cell development to corrosion science. The majority of delegates were working in either academic institutions at doctorate or post-doctorate level or in research and development for large companies, so the course was very much targeted for this type of audience, and I think a unique experience for them to have a conservator enrol on the course.

The Summer school was fully supported by with lecture notes and books and hands-on practical sessions. The early lectures will cover core material while the remainder will address specific electrochemical techniques.

The lectures introduced both fundamental electrochemistry and electrochemical techniques. Examples of the use of each technique to obtain kinetic and/or thermodynamic parameters are given and how complications can arise which may effect interpretation of results, modern methods of data handling and analysis as well as the selection of appropriate techniques for particular investigations were discussed.

The practical sessions offer each participant the occasion to carry out five experiments to reinforce the lectures and many opportunities for informal discussion. The experiments illustrate the electrochemical techniques and their application to the study of systems of practical interest.

The practical experiments I selected for the week were Cyclic Voltammetry, AC Impedance Spectroscopy and Metal deposition.

Cyclic Voltammetry (CV) is a fundamental technique used in extensively in electrochemistry, the basis of this in experimental terms is to create  a 3 electrode cell  these are the , the working electrode , a reference electrode that has a known potential to measure against the response of the working electrode and the counter-electrode through which a current is passed. In cyclic voltammetry, the voltage of the working electrode is controlled with a Potentiostat , the potential can be stepped up in in a negative or positive direction and at different rates, the response of the current to the change of potential can be observed in real time graph plot of potential against current. Different stages and processes of electrochemical reaction can be observed such as reduction and oxidation reactions and evolution of hydrogen. The electrochemical activity of the working electrode and activity of species in the electrolyte can be observed and was demonstrated in the experiments that we undertook. From a conservation viewpoint, the Working electrode is the object or metal we are proposing to treat, and we are looking mainly to reduce a corrosion. In the practical demonstrations and experiments we were using Working electrodes with precisely defined, standard physical characteristics , generally these were polished glassy carbon discs of known diameter and roughness. The effect of the surface area of the working electrode has a fundamental effect on the migration of electrons in the electro-chemical reaction and in having these known the rate of reactions and the quantities of product produced can be empirically calculated. For the CV experiments we undertook there was a lot of careful cleaning preparation and polishing of the glassy carbon Working electrodes to enable them to work at their optimum, which is something that cannot be done with an artefact being treated.

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Fig 1 Typical 3 electrode experimental cell set up and the results of Cyclic Voltametry using a potentiostat

Impedance Spectroscopy has been recently utilised and reported on in Conservation as a technique to evaluate the effectiveness of protective coatings on metals and the also evaluate the permeability of consolidants in stone, the technique  is widely used by corrosion scientists so I was very intrigued to understand the fundamentals of this technique. In the demonstration of evaluation of Materials using AC impedance spectroscopy it was shown how materials depending on their construction and morphology behave like resistors or capacitors and so the techniques use a certain amount of theoretical and practical modelling using circuit board arrangements determine and characterise the behaviour of a surface or substrate. Impedance spectroscopy experiment came before the lecture scheduled for the topic, this made understanding of the concepts discussed during the experiment session quite challenging personally to understand, the theory behind the modelling became clearer after the lectures.

Metal deposition had direct relevance to the electrotyping work we have undertaken at NMS one issue with producing a quality electrotype is that defects that occur in the precipitation and deposition of a metal on conductive mould during the electrolyte process. One such effect is the deposition of a coarse metal grain structure. In the experimental session we used a "Hull" cell to deposit lead on a surface , the Hull cell positions the working electrode plate is positioned on a 45 degree angle to the counter-electrode plate which means there is increasing distance between the 2 plates and so effect that  distance has on the current density ,rate of deposition and grain structure can be observed . As part of the experiment we were able to observe the metal deposition of lead under a Scanning Electron Microscope

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Fig 2 : Left Hull Cell set up in practical demonstration right SEM imaging of granular deposition of lead on the electrode

With all the examples of the practical sessions the experiments were very well designed, and the elements of components such as the surface area and the material of the working electrode Known and well defined, this  is key to accurately determining reaction rates and the influence thermo-dynamics in the electro-chemical reactions. The challenge for myself is how to apply this theory to real objects where characterisation of the material in terms of surface area , morphology and composition can be challenging to determine. In talking to fellow attendees and tutors on the course about the type of objects I treated they described my work as an “Industrial “ application, the experimental cells created in the lab conditions were contained within 200 –500ml glassware vessels.

Electrochemistry is a very complex subject and the Summer school was taught at an advanced level,  has given me a great insight into aspects of the techniques that I had not considered before and has had an immediate impact on how I would approach this work in future. In the level of teaching there was a big step in level from what I had been taught in my early years of training as a conservator , so  this was a very challenging few days for me understand all of the of the concepts involved. In learning about new techniques such EIS I would like to development techniques that are applicable and relevant to current issues across the range of NMS collections , eg monitoring corrosion rates of our aircraft collection and long term display of silver collections. In my continuing development now being introduced to these concepts I need to continue reading more literature in terms of conservation related applications. We also need to be able engage with specialists in this field , going on this course has enabled me to make some contacts in this area.

I am extremely grateful to TruVue and the Institute of Conservation for the financial support which enabled me to attend this course.

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Image: Creative Commons w/ attribution to Andrew Balet

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