Joint Academic Research Programme for Defence
Microfluidic devices for structural health monitoring: Part 2
A.
1
Cranny ,
N.
1
Harris ,
A.
1
Lewis ,
2
Neodo ,
S.
M.
2
Nie ,
K.
3
Stokes ,
J.
2
Wharton
and R.
2
Wood
1School
of Electronics and Computer Science, University of Southampton, Southampton, Hampshire, SO17 1BJ, UK
2nCATS, School of Engineering Sciences, University of Southampton, Southampton, Hampshire, SO17 1BJ, UK
3Defence Science and Technology Laboratory, Porton Down, Salisbury, Wiltshire, SP4 0JQ, UK
Sensors
Corrosion Database
Research 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.
● We have established a capillary electrophoresis methodology to simultaneously detect up to six metal cations that
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
● 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:
800
700
600
0.5 mM
1.1 mM
1.8 mM
2.5 mM
1 : Fe  3 e
3.4 mM
5.4 mM
2 : Cu  2 Cl
7.0 mM
2
3 : CuCl
10.0 mM
4 : Fe

 e
 e
 e


- In-depth understanding of the evolution of localised corrosion solution chemistry;
3

 CuCl
 Cu
 Fe
2

2
 2 Cl
- Identification of key corrosion makers for corrosion monitoring.

● The evolution of corrosion solution chemistry is being correlated with the material degradation process, thus
3
establishing a library of characteristic ‘fingerprints’ that categorise the state of corrosion and define the timing for
maintenance or mitigation actions.
400
300
3
100
Insulation
 Fe
500
200
Open window
2

2

Crevice Forming Test Structures
4
1
0
-900
-700
-500
1. Block structure
-300
-100
100
300
500
700
900
E vs Ag/AgCl (3.5M KCl), mV
AgPd
layer
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.
Substrate
Gold or
platinum
Solderable
end contact
.
2. Boron-doped diamond (BDD) electrodes:
Access holes for
extracting samples
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.
Boron atom substituted at
vacancy in carbon lattice
● Direct determination of Ni2+ in a reagentless process
0.90
0.00
0.80
-0.05
0.70
2
-0.15
-0.20
1 mM
-0.1
5 mM
10 mM
-0.2
-0.25
100 mM
-0.3
0
50
Conc / mM
100
35 uM
40 uM
45 uM
50 uM
55 uM
60 uM
65 uM
70 uM
75 uM
0.25
0.50
0.20
0.40
0.30
Electrolyte
level
Silicone seal
around 3 sides
Polyurethane base
1000
0
0
50
100
150
200
250
300
350
400
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.
Metal sample
PMMA crevice
former
0.15
1
0.10
Ni
2
 e

 Ni
Isometric view
3
2
3
0.00
0.10
Titanium bolt, nut
and washers
20
30
40
50
60
70
80
Conc / uM
4
0.00
-700
-500
-300
-100
100
300
500
700
900
450
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.
Sectional view
0.05
0.20
150 mM
150
30 uM
0.60
30 mM
50 mM
-0.30
-900
j / mA cm-2
0.0
j Peak / mA cm -2
j / mA cm-2
-0.10
j Peak / mA cm -2
 Fe
1500
Crevice
Isometric view
Crystalline structure of boron-doped diamond electrode.

Nickel ion
Immersion time in 3.5% NaCl (Days)
● Good response to Cu2+, Cu+, Fe3+ and Fe2+
 e
Aluminium ion
500
Metal sample
Based on our research, we have observed:
3
Ferric ion
2000
Allows direct sampling of crevice solution at different
depths from crevice entrance, which are then analysed
using capillary electrophoresis.
Nylon bolts
Fe
Cupric ion
Concentration (ppm)
Current, uA
(304, 316, 430, 430S17)
are representative of corrosion products from a wide variety of structural metals and alloys.
0
200
400
600
800
1000
1200
1400
E vs Ag/AgCl (3.5M KCl), mV
E vs Ag/AgCl (3.5M KCl), mV
Reduction of Fe3+ to Fe2+ in background of 3.5% NaCl
using differential pulse voltammetry.
Oxidation of Ni2+ to Ni3+ in background of 3.5% NaCl
using differential pulse voltammetry.
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.
Sectional view