Influence of the composition and viscosity of volcanic ashes on their adhesion within gas turbine aeroengines
Influence of the composition and viscosity of volcanic ashes on their adhesion within gas turbine aeroengines
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DOI：
10.1016/j.actamat.2016.02.011
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发表时间：
2016-05
期刊：
影响因子：
9.4
通讯作者：
J. Dean;C. Taltavull;T. Clyne
中科院分区：
文献类型：
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作者：
J. Dean;C. Taltavull;T. Clyne
本文介绍了四种类型的（冰岛）火山灰（VA）的粘附特性的实验研究。首先，将粉末（0.5 -50 μm）注入到改进的真空等离子喷涂装置中，并测量粘附到基底的颗粒的分数质量。其次，将每种灰的大的（约60 mm）致密颗粒加热并投射在基底上，通过高速摄影监测其撞击响应。四种灰分分为两组，一组具有高Si含量（>20%），另一组含有较少的Si，但含有较高水平的低价阳离子（如Ca、Mg和Fe）。玻璃化转变温度都相对较低（650-750 °C），有利于燃气轮机表面上的颗粒粘附。所有的灰往往粘附，特别是与较高的气体温度和冲击速度。然而，这一趋势是更大的两个灰具有高水平的低价阳离子。高速摄影证实这是由于这两种灰具有低得多的粘度（在高应变速率下）。这种行为不能仅仅根据Tgor玻璃含量值来预测。然而，这些阳离子作为“网络改性剂”在硅基玻璃，影响熔体粘度急剧下降，因此推论的危险，具体VA可能是可能的，从简单的组成分析。在任何情况下，对任何特定喷发期间产生的VA进行采样（可能是通过无人机）和分析，而不是仅仅依赖于对大气灰分水平的远程测量，这显然很重要。
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 ofTgor 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.