SensorsResearch effort has focused on electrochemical sensors with two different technologies being investigated. These will be integrated into custom holders positioned within the measurement zone of the microfluidic ion separator.

1. Screen-printed platinum and gold electrodes:

● Good response to Cu2+, Cu+, Fe3+, Fe2+

● Cheap, mass-producible

● Multitude of electrode geometries available

● Generally printed on alumina substrates

● Can be directly printed on to some stainless steels

(304, 316, 430, 430S17)

2. Boron-doped diamond (BDD) electrodes:

BDD electrodes are widely used in electroanalysis due to their outstanding properties. Their chemical-physical characteristics result in a sensitive response to a number of chemical species.

Based on our research, we have observed:

● Good response to Cu2+, Cu+, Fe3+ and Fe2+

● Direct determination of Ni2+ in a reagentless process

Joint Academic Research Programme for Defence

Microfluidic devices for structural health monitoring: Part 2A. Cranny1, N. Harris1, A. Lewis1, S. Neodo2, M. Nie2, K. Stokes3, J. Wharton2 and R. Wood2

1School of Electronics and Computer Science, University of Southampton, Southampton, Hampshire, SO17 1BJ, UK2nCATS, School of Engineering Sciences, University of Southampton, Southampton, Hampshire, SO17 1BJ, UK

3Defence Science and Technology Laboratory, Porton Down, Salisbury, Wiltshire, SP4 0JQ, UK

Corrosion Database● We have established a capillary electrophoresis methodology to simultaneously detect up to six metal cations that are representative of corrosion products from a wide variety of structural metals and alloys.

● By applying this methodology to crevice solution samples, a crevice corrosion solution chemistry database is being developed for a variety of alloys used in marine environments, providing:

- In-depth understanding of the evolution of localised corrosion solution chemistry;

- Identification of key corrosion makers for corrosion monitoring.

● The evolution of corrosion solution chemistry is being correlated with the material degradation process, thus establishing a library of characteristic ‘fingerprints’ that categorise the state of corrosion and define the timing for maintenance or mitigation actions.

Evolving metal ion concentration profiles in the crevice of a sample of nickel-aluminium bronze (NAB) as it corrodes in 3.5% NaCl over a period in excess of 1 year.

Left: Schematic of single screen-printed electrode. Above: Oxidation of equal concentrations of Cu2+ and Fe3+ at a platinum screen-printed electrode in 3.5% NaCl using differential pulse voltammetry.

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E vs Ag/AgCl (3.5M KCl), mV

Cu

rre

nt,

uA

0.5 mM 1.1 mM

1.8 mM 2.5 mM

3.4 mM 5.4 mM

7.0 mM 10.0 mM

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2

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FeeFe:4

Cl2CueCuCl:3

CuCleCl2Cu:2

Fee3Fe:1

Boron atom substituted at vacancy in carbon lattice

Crystalline structure of boron-doped diamond electrode.

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Immersion time in 3.5% NaCl (Days)

Co

nc

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tra

tio

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pp

m)

Cupric ion

Ferric ion

Aluminium ion

Nickel ion

Crevice Forming Test Structures1. Block structure

Allows direct sampling of crevice solution at different depths from crevice entrance, which are then analysed using capillary electrophoresis.

2. Cortest structure

A large number of identical assemblies are immersed in a corrosive electrolyte solution. At predefined times, single samples are removed and frozen prior to disassembly. Upon thawing, residual solutions are collected from various locations of the corroded metal surface for CE analysis.

Images of cast lean duplex stainless steel CLD 21 with Cortest crevice corrosion testing in 3.5% NaCl for 28 days. (1) outside crevice (2) trench (3) crevice, no attack (4) crevice, severe attack.

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Isometric view

Sectional view

Metal sample

Titanium bolt, nut and washers

PMMA crevice former

Sectional viewIsometric view

Metal sample

Polyurethane baseSilicone sealaround 3 sides

Access holes for extracting samples

Electrolytelevel

Crevice

Nylon bolts

AgPdlayer

Insulation

Gold orplatinum

Substrate

Open window

Solderableend contact

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E vs Ag/AgCl (3.5M KCl), mV

j / m

A c

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150 mM-0.3

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j Pea

k /

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-2

Reduction of Fe3+ to Fe2+ in background of 3.5% NaCl using differential pulse voltammetry.

23 FeeFe

Oxidation of Ni2+ to Ni3+ in background of 3.5% NaClusing differential pulse voltammetry.

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E vs Ag/AgCl (3.5M KCl), mV

j / m

A c

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40 uM 45 uM

50 uM 55 uM

60 uM 65 uM

70 uM 75 uM

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32 NieNi