Effect of cyclic loading at elevated temperatures on the magnetic susceptibility of a magnetite-bearing ore
Effect of cyclic loading at elevated temperatures on the magnetic susceptibility of a magnetite-bearing ore
复制标题
高温循环加载对含磁铁矿矿石磁化率的影响
DOI：
10.1093/gji/ggab400
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发表时间：
2021
影响因子：
2.8
通讯作者：
Kontny
中科院分区：
文献类型：
--
作者：
Dudzisz;Walter;Krumholz;Reznik;Kontny
在高温下的循环载荷既可以在构造或火山引起的地震中自然发生，也可以由于各种地质工程活动而人为引起。本研究的目的是测试是否可以通过磁性方法监测岩石中的机械疲劳。为此目的，研究了循环机械载荷（150 ± 30 MPa）对含磁铁矿矿石在不同温度（400和500 °C）和环境（空气和真空）下磁化率及其各向异性的影响。我们的研究表明，磁化率显着下降（高达23%），在空气条件下和真空（高达4%）内的第一个CA。1000个周期。进一步加载不会显著影响磁化率，磁化率随后保持或多或少恒定。在两种实验条件下，与400 °C相比，在500 °C下磁化率参数的降低更强。磁化率总是在加载的样品在室温下减压后测量，因此可以排除磁致伸缩作为这些变化的原因。装载样品的温度越高，磁铁矿氧化成赤铁矿的作用越明显。磁铁矿在环境条件下转变为赤铁矿是影响整体磁性的最重要机制。真空加载后磁化率的微弱变化可能是由于磁铁矿颗粒表面形成的晶内微裂纹引起的。这些表面变形结构伴随着磁畴的细化，这是通过磁力显微镜观察到的。大块磁性晶粒尺寸的修改也证实了磁滞参数，以及由增加的霍普金森峰比确定的磁化率测量居里点。磁各向异性和形状因子的程度只改变空气处理的样品，因此有关的赤铁矿的形成，而不是不可逆的韧性变形磁铁矿。我们的实验研究表明，循环加载可以显着改变岩石的磁性，由于矿物转化低于1000个周期，机械疲劳的第一阶段，这是岩石破坏的前兆，与这些转换密切相关。
Cyclic loading at elevated temperatures occurs either naturally during tectonic or volcanic-induced earthquakes or can be human-induced due to various geological engineering activities. The aim of this study is to test if mechanical fatigue in rocks can be monitored by magnetic methods. For this purpose, the effect of cyclic-mechanical loading (150 ± 30 MPa) on the magnetic susceptibility and its anisotropy of a magnetite-bearing ore with varying temperatures (400 and 500 °C) and environment (air and vacuum) was investigated. Our study shows that magnetic susceptibility decreases significantly (up to 23 per cent) under air conditions and in vacuum (up to 4 per cent) within the firstca. 1000 cycles. Further loading does not significantly affect the magnetic susceptibility which then remains more or less constant. The decrease of susceptibility parameters is stronger at 500 °C compared to 400 °C under both experimental conditions. Magnetic susceptibility was always measured after decompression of the loaded sample at room temperature so that magnetostriction can be excluded as a reason for these changes. The higher the temperature at which samples were loaded the more pronounced is the oxidation of magnetite to haematite. The transformation of magnetite into haematite under ambient conditions is the most important mechanism influencing bulk magnetic properties. The weak changes in magnetic susceptibility after vacuum loadings are probably caused by intragranular microcracks formed on the surface of magnetite grains. These surface deformation structures are accompanied by the refinement of magnetic domains, which is observed by magnetic force microscopy. Bulk magnetic grain size modifications are also confirmed by hysteresis parameters as well as by the increasing Hopkinson peak ratios determined from magnetic susceptibility measurements over Curie point. The degree of magnetic anisotropy and shape factor only change for the air-treated samples and are therefore related to the haematite formation and not to irreversible ductile deformation in magnetite. Our experimental study shows that cyclic loading can change significantly the magnetic properties of a rock due to mineral transformation below < 1000 cycles and that the first stages of mechanical fatigue, which are a precursor of the failure of rock, are closely associated with these transformations.