G. McAdam

Silica exposed-core microstructured optical fibers

We report the fabrication of silica microstructured optical fibers with the core exposed along the whole length, and characterize the stability of these new fibers when exposed to some typical sensing and storage environments. We show the fiber loss to be the best achieved to date for exposed-core fibers, while the deterioration in the transmission properties is up to ∼2 orders of magnitude better than for the previously reported exposed-core fibers produced in soft glass. This opens up new opportunities for optical fiber sensors requiring long term and/or harsh environmental applications while providing real time analysis anywhere along the fibers length.

Enhanced cerium migration in ceria-stabilised zirconia

Abstract The metal components inside jet engines which are exposed to hot combustion gases often must be thermally insulated with thermal barrier coatings. Most thermal barrier coatings consist of a porous zirconia layer deposited over a NiCoCrAlY layer. However, the zirconia layer can spall during thermal cycling unless it is stabilised to prevent the zirconia changing between its tetragonal and monoclinic phases. We have studied thermal barrier coatings in which the zirconia was stabilised by alloying with 2.5 wt.% yttria and 25 wt.% ceria. The spatial distributions of the cerium in the zirconia layer before and after heat treatment were studied using electron microscopy (back-scattered electron imaging and X-ray analysis). The different phases present were identified by X-ray diffraction. We found that the cerium distribution in the newly-formed zirconia layer was essentially uniform. However, heating at 1200 °C could cause the formation of ceriumrich zones provided the coating was not separated from the NiCoCrAlY layer and the substrate before heating. This implied an interaction between the zirconia and the underlying metal. Experiments in the presence of oxygen getters and experiments in vacuum both suggest that cerium migration in ceria-stabilised zirconia is enhanced at high temperatures (1100 °C) under reducing conditions.

Novel polymer functionalization method for exposed-core optical fiber

We report on a one step functionalization process for optical fiber sensing applications in which a thin film (∼50 nm) polymer doped with sensor molecules is applied to a silica exposed-core fiber. The method removes the need for surface attachment of functional groups, while integrating the polymer, silica and sensor molecule elements to create a distributed sensor capable of detecting an analyte of interest anywhere along the fiber’s length. We also show that the thin film coating serves a protective function, reducing deterioration in the transmission properties of the silica exposed-core fiber, but increasing loss.

Influence of laser surface melting on the microstructure and corrosion behaviour of ZE41 magnesium alloy

In the present study, surface melting of a magnesium alloy, ZE41 (4%-Zn, 1%-RE) is performed by an Nd:YAG laser (operating in a continuous wave mode). The degree of microstructural refinement and the depth of the laser melted zone is a strong function of laser processing parameters (laser power, beam diameter, scan rate). The corrosion properties of the laser treated and untreated zone is investigated by potentiodynamic polarization method. The microstructural changes on the surface due to laser surface melting were analysed by optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy to understand their effect on the corrosion behaviour of ZE41.

Optical Fibres for Distributed Corrosion Sensing - Architecture and Characterisation

This paper summarises recent work conducted on the development of exposed core microstructured optical fibres for distributed corrosion sensing. Most recently, exposed-core fibres have been fabricated in silica glass, which is known to be reliable under a range of processing and service environments. We characterise the stability of these new silica fibres when exposed to some typical sensing and storage environments. We show the background loss to be the best achieved to date for exposed-core fibres, while the transmission properties are up to ~2 orders of magnitude better than for the previously reported exposed-core fibres produced in soft glass. This provides a more robust fibre platform for corrosion sensing conditions and opens up new opportunities for distributed optical fibre sensors requiring long-term application in harsh environments.

Fiber optic approach for detecting corrosion

Corrosion is a multi-billion dollar problem faced by industry. The ability to monitor the hidden metallic structure of an aircraft for corrosion could result in greater availability of existing aircraft fleets. Silica exposed-core microstructured optical fiber sensors are inherently suited towards this application, as they are extremely lightweight, robust, and suitable both for distributed measurements and for embedding in otherwise inaccessible corrosion-prone areas. By functionalizing the fiber with chemosensors sensitive to corrosion by-products, we demonstrate in-situ kinetic measurements of accelerated corrosion in simulated aluminum aircraft joints.

Influence of Laser Processing Parameters on Microstructure and Corrosion of Laser Surface Melted ZE41 Magnesium Alloy

In the present study, surface melting of a magnesium alloy, ZE41, was performed with an Nd:YAG laser, using different laser parameters (scan rate and beam type). The microstructure of the laser treated and untreated specimens were characterised by optical and scanning electron microscopy. The degree of microstructural refinement and melt depth was found to be a function of the laser scan rate. Electrochemical characterisation of the different laser treated specimens along with the untreated alloy was performed using electrochemical impedance spectroscopy. The laser treated specimens and untreated alloy showed similar corrosion resistance.