Pugnetti Michele, Zhou Yi, Biedermann Andrea R
Institute of Geological Sciences, University of Bern, Baltzerstrasse 1+3, 3012 Bern, Switzerland.
Transp Porous Media. 2022;144(2):367-400. doi: 10.1007/s11242-022-01809-0. Epub 2022 Jul 2.
Magnetic pore fabrics (MPF) are an efficient way to characterize pore space anisotropy, i.e., the average pore shape and orientation. They are determined by impregnating rocks with ferrofluid and then measuring their magnetic anisotropy. Obtaining even impregnation of the entire pore space is key for reliable results, and a major challenge in MPF studies. Here, impregnation efficiency and its spatial variability are systematically tested for natural (wood, rock) and synthetic (gel) samples, using oil- and water-based ferrofluids, and comparing various impregnation methods: percolation, standard vacuum impregnation, flowthrough vacuum impregnation, immersion, diffusion, and diffusion assisted by magnetic forcing. Seemingly best impregnation was achieved by standard vacuum impregnation and oil-based ferrofluid (76%), and percolation (53%) on rock samples; however, sub-sampling revealed inhomogeneous distribution of the fluid within the samples. Flowthrough vacuum impregnation yielded slightly lower bulk impregnation efficiencies, but more homogeneous distribution of the fluid. Magnetically assisted diffusion led to faster impregnation in gel samples, but appeared to be hindered in rocks by particle aggregation. This suggests that processes other than the mechanical transport of nanoparticles in the pore space need to be taken into account, including potential interactions between the ferrofluid and rock, particle aggregation and filtering. Our results indicate that bulk measurements are not sufficient to assess impregnation efficiency. Since spatial variation of impregnation efficiency may affect MPF orientation, degree and shape, impregnation efficiency should be tested on sub-samples prior to MPF interpretation.
The online version contains supplementary material available at 10.1007/s11242-022-01809-0.
磁孔织物（MPF）是表征孔隙空间各向异性（即平均孔隙形状和方向）的有效方法。它们通过用铁磁流体浸渍岩石，然后测量其磁各向异性来确定。实现整个孔隙空间的均匀浸渍是获得可靠结果的关键，也是MPF研究中的一项重大挑战。在这里，使用油基和水基铁磁流体，对天然（木材、岩石）和合成（凝胶）样品的浸渍效率及其空间变异性进行了系统测试，并比较了各种浸渍方法：渗滤、标准真空浸渍、流通真空浸渍、浸泡、扩散以及磁强迫辅助扩散。标准真空浸渍和油基铁磁流体（76%）以及岩石样品上的渗滤（53%）似乎实现了最佳浸渍效果；然而，子采样显示样品内流体分布不均匀。流通真空浸渍的整体浸渍效率略低，但流体分布更均匀。磁辅助扩散使凝胶样品中的浸渍速度更快，但在岩石中似乎因颗粒聚集而受阻。这表明除了孔隙空间中纳米颗粒的机械传输过程外，还需要考虑其他过程，包括铁磁流体与岩石之间的潜在相互作用、颗粒聚集和过滤。我们的结果表明，整体测量不足以评估浸渍效率。由于浸渍效率的空间变化可能会影响MPF的方向、程度和形状，因此在进行MPF解释之前，应在子样品上测试浸渍效率。
在线版本包含可在10.1007/s11242-022-01809-0获取的补充材料。
