Marine corrosion performance of copper alloy UNS C69100

Tungum alloy (UNS C69100) is an aluminium-nickel-silicon brass (chemical composition: 81-84% Cu, 0.70-1.20 Al, 0.8-1.40 Ni, 0.80-1.30 Si, with the remainder Zn) and is reported to have a good corrosion performance in marine environments (fully wetted, splash zone and atmospheric conditions). In order to gain an in-depth understanding of the marine corrosion performance of this alloy, electrochemical test methods including open-circuit potential, electrochemical impedance spectroscopy, potentiodynamic polarization, and zero-resistance ammetry were used for corrosion investigation of UNS C69100 in a 3.5 wt.% sodium chloride aqueous testing solution, in combination with optical microscopy and scanning electron microscopy. The corrosion properties of UNS C69100 obtained by electrochemical methods are also compared to six other alloys: UNS S31603, UNS S31254, UNS S32750, UNS N04400, UNS N08904 and UNS C36000. Galvanic coupling behaviour of UNS C69100 against these six alloys in a 3.5% NaCl solution for 30 days immersion are also reported in this paper

Lifetime performance characteristics of screen-printed potentiometric Ag/AgCl chloride sensors

Ag/AgCl chloride sensors were fabricated using thick-film technology. A number of different formulations were prepared and chloride responses were investigated over time. Near Nernstian, identical responses were observed over the first 160 days with an average chloride sensitivity of -51.8 ± 0.4 mV per decade change in chloride concentration (pCl), irrespective of paste formulation. After 6- months continuous immersion in tap water, pastes formulated with a glass binder began to exhibit a loss in sensitivity whilst those formulated from a commercial thickfilm dielectric paste remained functional for the best part of a year. The difference is attributed to the inclusion of proprietary additives in the commercial paste aiding adhesion and minimising AgCl leaching

Screen-printed platinum electrodes for measuring crevice corrosion: Nickel aluminium bronze as an example

Screen-printed platinum electrodes were used to monitor crevice corrosion processes. The electrodes, printed on an inert alumina substrate, formed the bottom of an artificial crevice when mechanically clamped to a rectangular block of nickel-aluminium bronze (NAB). Cyclic differential pulse voltammetry was used to detect corrosion products over time whilst the assembly was immersed in a 3.5% by weight aqueous solution of sodium chloride. Cupric (Cu2+), ferric (Fe3+) and ferrous (Fe2+) ions were detected with evolution profiles indicative of selective phase corrosion

Screen-printed platinum electrodes for the detection of cupric and ferric ions in high chloride backgrounds

Screen-printed platinum electrodes developed for use in corrosion monitoring applications have been used to detect cupric and ferric ions both individually and as mixtures in a background of 3.5% by weight sodium chloride and in the presence of dissolved oxygen. In single species detection linear responses for the Fe3+/Fe2+ couple were observed over the concentration range 0.3 to 100mM. By contrast, the small size of the working electrode caused a current limiting response for cupric ions over the same concentration range. In mixtures of these ions, the sensors show good differentiation and are able to separate the individual metal ion responses

Rapid manufacture of integrated self-powered sensing systems using additive manufacturing for critical structure health monitoring

In this project, the feasibility of rapid manufacturing of integrated corrosion monitoring sensing systems within critical engineering structural components using advanced AM technologies has been demonstrated with an exemplar model structure of crevice corrosion monitoring with integrated carbon-based electrochemical sensors. Corrosion performance of all five different materials model crevice former structures built using different AM technologies have been investigated for the first time in a 3.5% NaCl test solution, and the tests results provide the guidelines for the selection of appropriate AM technologies for rapid manufacturing engineering structures in corrosive environment applications. The model crevice corrosion monitoring structure and the rapid manufacturing approaches achieved in this project also provide proof of the concept for design and rapid manufacturing of functionalised engineering components with self-powered embedded structural health monitoring devices

Screen-printed potentiometric Ag/AgCl chloride sensors: Lifetime performance and their use in soil salt measurements

Silver – silver chloride electrodes (Ag/AgCl) for the detection of chloride ions were fabricated using thick-film technology. Five different formulations were prepared and chloride responses were investigated over time. Almost identical and near Nernstian responses were observed over the first 162 days with an average chloride sensitivity for all formulations of -51.12 mV ± 0.45 mV per decade change in chloride concentration compared with a value of -50.59 mV ± 0.01 mV over 388 days for the best two formulations. After 6-months continuous immersion in tap water, pastes formulated with a glass binder began to exhibit a loss in sensitivity whilst those formulated from a commercial thick-film dielectric paste remained functional for the best part of a year. This difference in lifetime performance is attributed to the inclusion of proprietary additives in the commercial paste aiding adhesion and minimising AgCl leaching. The mechanical and chemical robustness of these electrodes has been demonstrated through their ability to detect changing levels of chloride when immersed in soil columns. This particular capacity will make them an invaluable tool in the fields of hydrology, agricultural science, soil science and environmental science

A Closed-loop, Non-linear, Miniaturised Capillary Electrophoresis System Enabled by Control of Electroosmotic Flow

The miniaturisation of capillary electrophoresis (CE) systems makes separation of ionic species with similar electrophoretic mobilities challenging. We report on a novel closed-loop system that does not rely on migration time to identify ionic species unlike many conventional CE systems. To aid miniaturisation our method requires the sample undergoing separation to travel back and forth along the short channel multiple times. For each consecutive cycle the sample becomes increasingly separated until it is deemed sufficiently separated such that it can be reliably identified by any appropriate detection system. As the sample approaches either of the channel ends, contactless conductivity detectors detect the presence of the sample and trigger the modification of the electroosmotic flow (EOF) to reverse the direction of flow in the channel. After sufficient separation the identification is performed in-channel using, in our case, an electrochemical detection scheme. Incorporation of a closed-loop control system means that unpredictable variation in migration time does not present an issue for ionic species identification. This new method of non-linear CE is demonstrated in a microfluidic channel formed in PDMS (polydimethylsiloxane), reversibly sealed to a glass wafer on which metal electrodes are patterned in gold. The sample movement in both directions along the channel occurs without affecting the electrophoretic separation already achieved during each cycle by changing the EOF in magnitude and direction. The EOF is changed by modifying the zeta-potential along the channel wall through the application of a voltage on a zeta-potential modification (ZPM) electrode placed close to the channel surface. Depending on the magnitude and polarity of the voltage applied to the ZPM electrode our experiments have shown the ability to increase, decrease or reverse the EOF

Novel fabrication method for rapid creation of channels using PDMS for microfluidic networks on planar substrates

A novel and simple method for the rapid fabrication of microfluidic networks is presented. A silicone elastomer (PDMS - poly(dimethylsiloxane)) is cured around formers, which are then removed post-cure, resulting in a microstructure suitable for fluidic applications. The limiting factors in the fabrication method are in the materials and tools used for the development of the formers. If the methods used cannot produce a structure of accurate dimensions then the microstructure formed will be limited. For creating very narrow fluidic channels, the material used needs to be strong so that even with narrow dimensions it can be removed without damage but the use of sacrificial materials has been investigated as this overcomes this requirement. The principle of the technique is demonstrated with an unusual material (caramelised sugar – which can be easily dissolved in water) to fabricate channels with diameters down to 16μm

Review on the development of truly portable and in-situ capillary electrophoresis systems

Capillary electrophoresis (CE) is a technique which uses an electric field to separate a mixed sample into its constituents. Portable CE systems enable this powerful analysis technique to be used in the field. Many of the challenges for portable systems are similar to those of autonomous in-situ analysis and therefore portable systems may be considered a stepping stone towards autonomous in-situ analysis. CE is widely used for biological and chemical analysis and example applications include: water quality analysis; drug development and quality control; proteomics and DNA analysis; counter-terrorism (explosive material identification) and corrosion monitoring. The technique is often limited to laboratory use, since it requires large electric fields, sensitive detection systems and fluidic control systems. All of these place restrictions in terms of: size, weight, cost, choice of operating solutions, choice of fabrication materials, electrical power and lifetime. In this review we bring together and critique the work by researchers addressing these issues. We emphasize the importance of a holistic approach for portable and in-situ CE systems and discuss all the aspects of the design. We identify gaps in the literature which require attention for the realization of both truly portable and in-situ CE systems

An Investigation into Separation Enhancement Methods for Miniaturised Planar Capillary Electrophoresis Devices

Large structures such as buildings, ships and aircraft often contain numerous components which are exposed to a failure risk due to corrosion processes. Aside from the extra cost of repair and replacement, there are also potential health and safety issues which need to be addressed. Corrosion detection is not a new concept and there exists a variety of methods to detect and evaluate corrosion. The analysis method that is the focus of this work is capillary electrophoresis (CE); commonly used for a number of biological and chemical processes, such as drug, food and water quality analysis, DNA and protein separation and so on. An alternative method to high pressure (or performance) liquid chromatography (HPLC), CE boasts high analysis speeds as well as low limits of detection. Both are of crucial advantage for use in a pharmaceutical market; however the application of CE for in-situ or portable corrosion monitoring has not been investigated in great depth