Electrochemical corrosion rates of Cu and Cu-Ni alloys have been measured in oxygenated 0.5M NaCI and in synthetic seawater using the Tafel extrapolation procedure. In addition, Cu corrosion has been measured with the linear polarization procedure. A rotating disk electrode system was used in the measurements with rotation rate varying from 500 to 6000 rpm. The corrosion characteristics of Cu and 90Cu-10Ni alloy in the two media, and 70Cu-30Ni alloy in 0.5M NaCI have been found to be similar. For these systems, the variation of corrosion current, corrosion potential, and anodic partial current with rotation rate of the electrode could be explained in terms of a convective diffusion controlled corrosion mechanism incorporating the generation of a soluble copper complex on the electrode surface. The 70-30 alloy in synthetic seawater behaved differently. Corrosion current, corrosion potential, and the anodic partial current were all constant with rotation rate, indicating a surface kinetic-controlled corrosion mechanism.Cu + 2CI -=CuCl2 -+ e kc (1)

Fibre Bragg gratings, used as stress sensing elements, show a temperature dependence of their stress response, which is mainly characterized by Young's modulus of the fibre material. The temperature dependence of the stress response of a fibre Bragg grating over a range from −38 • C to +110 • C has been measured. The stress sensitivity decreases linearly by 1.22 × 10 −4 K −1 over this range which is nearly identical to the increase of Young's modulus of fused silica over this range implying that it is predominantly Young's modulus which defines and characterizes this thermal dependence. Significantly, bare and re-coated fibres show a markedly different behaviour below 0 • C due to the glass transition temperature of the jacket material.

Palladium and its alloys show a high and selective affinity for hydrogen, resulting in a volume expansion. Fibre Bragg gratings attached to palladium elements are used to monitor the resultant strain from the hydrogen uptake. The technique is aimed at low concentration hydrogen monitoring to a few hundred ppm, where H2 is the result of ageing of polymer materials. We demonstrate a sensor exhibiting 10 ppm sensitivity and report on observed cross sensitivity to environmental conditions.

Electrochemical corrosion rates of 70Cu-30Ni alloy have been measured in oxygenated 0.5M NaCI and in synthetic seawater by the Tafel extrapolation procedure using a rotating disk electrode system. The rotation rate was varied from 500 to 6000 rpm. A log-log plot of the corrosion current vs rotation rate was linear, with a slope of 1/6 for the alloy in 0.5M NaCI; the corrosion potential for the same system became more negative at a rate of approximately -20 mV/dec of rotation. The anodic partial currents at potentials close to the corrosion potential in 0.5M NaCI increased linearly with the square root of the rotation rate. Corrosion current and corrosion potential as well as the anodic partial current for the alloy in synthetic seawater remain unchanged with rotation rate. The anodic Tafel slopes were 60 and 90 mV in 0.5M NaCI and synthetic seawater, respectively. The cathodic Tafel slope was 200 mV for both systems.Two separate corrosion mechanisms for the alloy in two electrolytes have been recognized. In 0.5M NaCI, the corrosion proceeds through the formation of a soluble CuC1 2 -complex. In synthetic seawater, the corrosion proceeds through a surface kinetic process, possibly because of the formation of Cu 2 0 and Cu2(OH)3 CI on the surface. The cathodic reduction of oxygen is probably the same in both systems.

A novel dual-fibre Bragg grating sensor structure is described, incorporating integrated mechanical stress amplification and temperature compensation by common mode rejection. Stress amplification allows the measurement of very low actuator forces, such as generated by small cross section bellows, for operation as a barometric pressure sensor. We demonstrate a pressure sensor range of 800-1100 hPa and a resolution of 0.1 hPa.

We describe the development of a fibre optic system using absolute distance interferometry for application to long-term monitoring of component positions. Initially we demonstrate the operation of a single probe in air with a distance resolution of 8 nm and an absolute displacement accuracy of 0.08% over relatively short baselines of up to a few mm. The technique is then developed to measure distance through a transparent polymer. Our in situ method utilizes a dual probe arrangement to measure optical path length and refractive index simultaneously.

Sensors based on optical fibre materials will be required to tolerate a restrictive combination of physical and environmental parameters for several remote monitoring applications at AWE. These include changes in atmospheric pressure, temperature, humidity, vibration, shock and acceleration, with the sensors being required to operate reliably for periods of up to 30 years with minimal intervention for maintenance. In addition, it is necessary that the sensors can function in the presence of ionising radiation. The sensors are being developed for a number of challenging in-situ physical and chemical measurements. These include remote gas composition analysis, monitoring shape change in compliant materials and the movement of metallic and polymeric components using sensors based on fibre Bragg gratings and interferometric techniques. Reliability issues include the long-term mechanical and optical performance of standard and novel glasses, optical fibres and cables, connectors, couplers, optical switches and Bragg gratings. The durability of materials used in the construction of fibre optic sensing components also requires to be assessed in addition to the epoxy and metallic coatings used to bond these components to a variety of material substrates.

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