Sensors

1. 1 2 3 4 2 3 Open window 4 1 Insulation 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. Nylon bolts Access holes for extracting samples Substrate Crevice Gold or platinum Solderable end contact Metal sample Electrolyte level Silicone seal around 3 sides Polyurethane base Isometric view Sectional view Boron atom substituted at vacancy in carbon lattice Crystalline structure of boron-doped diamond electrode. Titanium bolt, nut and washers Metal sample PMMA crevice former Isometric view 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 Joint Academic Research Programme for Defence Microfluidic devices for structural health monitoring: Part 2 A. 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, 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 • 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. • 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) • 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. Crevice Forming Test Structures 1. Block structure Allows direct sampling of crevice solution at different depths from crevice entrance, which are then analysed using capillary electrophoresis. . • 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 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. 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.