Influence of the composition and viscosity of volcanic ashes on their adhesion within gas turbine aeroengines
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Dean, J., Taltavull, C., & Clyne, B. (2016). Influence of the composition and viscosity of volcanic ashes on their adhesion within gas turbine aeroengines. Acta Materialia, 109 8-16. https://doi.org/10.1016/j.actamat.2016.02.011
This paper presents experimental investigations into adhesion characteristics of four types of (Icelandic) volcanic ash (VA). Firstly, powder (∼5–50 μm) was injected into a modified vacuum plasma spray set-up and the fractional mass of particles that adhered to a substrate was measured. Secondly, large (∼6 mm), dense pellets of each ash were heated and projected at a substrate, with their impact response monitored via high speed photography. The four ashes fall into two groups of two, one with high Si content (>20%) and the other containing less Si, but higher levels of lower valence cations (such as Ca, Mg & Fe). The glass transition temperatures were all relatively low (∼650–750 °C), favouring particle adhesion on surfaces in gas turbines. All of the ashes tended to adhere, especially with higher gas temperatures and impingement velocities. However, this tendency was much greater for the two ashes with high levels of the lower valence cations. The high speed photography confirmed that this was due to these two ashes having much lower viscosities (at high strain rates). This behaviour could not have been predicted solely on the basis of Tg or glass content values. However, these cations act as “network-modifiers” in silica-based glasses, effecting sharp reductions in melt viscosity, so inferences about the danger of specific VA may be possible from simple compositional analysis. In any event, it's clearly important for VA being generated during any particular eruption to be sampled (presumably by drones) and analysed, rather than relying solely on remote measurement of atmospheric ash levels.
gas turbines, volcanic ash, viscosity, composition, deposition
This work forms part of a research programme funded by EPSRC (EP/K027530/1). In conjunction with this project, a consortium of partners has been set up under the PROVIDA ("PROtection against Volcanic ash Induced Damage in Aeroengines") banner and information about its operation is available at http://www.ccg.msm.cam.ac.uk/initiatives/provida. The invaluable assistance of Kevin Roberts (Materials Department in Cambridge) with operation of the plasma spray facility is gratefully acknowledged. The authors are also grateful to Mr. Max Burley, of the Materials Science Department in Cambridge, for helpful contributions to the high speed photography and gas gun work, and to Dr. Margaret Hartley, of the University of Manchester, for kindly collecting the ashes during field trips to Iceland (funded by EasyJet) and also for extensive and valuable discussions related to the science of the specific eruptions concerned, and more generally concerning the complex relationships between geological and rheological characteristics of volcanic magma and ash. In compliance with EPSRC requirements, raw data in the form of selected video files are available at www.ccg.msm.cam.ac.uk/publications/resources, and are also accessible via the University repository at http://www.data.cam.ac.uk/repository.
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External DOI: https://doi.org/10.1016/j.actamat.2016.02.011
This record's URL: https://www.repository.cam.ac.uk/handle/1810/253856