高温烘烤对纳林庙岩石磁性的影响实验研究

Experimental study on influence of high temperature baking on magnetic properties of Nalinmiao rock

磁异常是煤田火灾重要的地球物理特征,为研究高温烘烤过后岩石的磁性变化规律,对磁法在火区圈定应用的中提供有效指导,利用磁化率测定系统测定了纳林庙3-1煤顶板砂岩的磁化率,分别研究了温度、粒径以及磁场强度对样品磁化率的影响。结果表明:在25~600℃整体范围内烘烤形成的烧变岩的磁化率整体上随温度增高而增大,随外界磁感应强度变大而减小。烘烤温度小于400℃时,样品粒径越小磁化率越大;通过X射线衍射实验分析了高温烘烤对岩石成分与结构的影响,表明岩石高温烘烤的过程中,菱铁矿(FeCO3)被氧化成铁磁性物质磁铁矿(Fe3O4),这是烧变岩相对常温岩石磁性增强的主要原因。

Magnetic anomaly is an important geophysical feature of coal field fires. In order to study the magnetic change law of high-temperature heated rocks and provide effective guidance for the application of magnetic method in the delineation of fire zones, the susceptibility measurement system was used to determine the magnetic susceptibility of Nalinmiao 3-1 coal roof sandstone. The effects of temperature, particle size, and magnetic field strength on the magnetic susceptibility of the samples were studied. The results show that the magnetic susceptibility of the burnt rock in the whole range of 25 ℃ to 600 ℃ increases with the increase of temperature, and decreases with the increase of the external magnetic induction intensity. When the heated temperature is less than 400 ° C, the smaller the particle size of the sample, the greater the magnetic susceptibility;the effect of high temperature baking on the composition and structure of the rock is analyzed by X-ray diffraction experiments, indicating that during the high temperature baking of the rock, FeCO3 is oxidized into Fe3 O4, which is the main reason why burnt rock is more magnetic than normal rock.