渝东南两套富有机质页岩的孔隙结构特征——来自FIB-SEM的新启示

使用聚焦离子束扫描电镜(FIB-SEM)对渝东南地区下寒武统牛蹄塘组和上奥陶统五峰组—下志留统龙马溪组2套富有机质页岩的孔隙结构进行了系统观察,并对页岩纳米级有机质孔隙进行了三维重构和孔隙结构参数定量分析。研究发现,五峰组—龙马溪组页岩内层间微裂隙、矿物粒内孔、矿物粒间孔和有机质孔隙均较为发育。其中,有机质孔隙呈蜂窝状均匀发育,孔隙半径集中在3~100 nm,孔隙连通性较好,FIB-SEM三维重构计算有机质孔隙度在9.13%~18.42%之间,岩石总孔隙度中有机质孔隙度的贡献受控于TOC含量;牛蹄塘组页岩内溶蚀孔和粒间孔较为发育,有机质孔隙发育不均匀,孔隙呈扁平状或针孔状,孔隙半径集中在3~25 nm,孔隙连通性较差,有机质孔隙度在1.59%以下,有机质孔隙度对岩石总孔隙度的贡献与TOC含量关系较小,页岩的总孔隙度主要来自于矿物基质孔。FIB-SEM揭示了2套页岩有机质孔隙结构存在较大差异。     

基于FIB-SEM双束系统的纳尺度真空间隙电学特性原位实验装置

纳米尺度真空电气击穿与绝缘特性研究是高电压与绝缘技术领域的前沿课题.一方面,随着微纳尺度加工技术的不断发展,电气部件和电子器件的特征物理尺寸已经逐步降低到微米、纳米甚至是分子原子尺度,并且在军事和民用领域得到越来越广泛的应用;另一方面,传统的放电击穿理论和绝缘性能评价方法无法用来解释和预估微纳尺度的放电特性和绝缘水平.因此,本文基于聚焦离子束和扫描电子显微镜(FIB-SEM)双束系统,借助纳米压电位移技术和微弱电流测量技术,建立了纳尺度真空间隙电学特性的原位研究系统.该系统不仅能够进行微纳尺度(曲率半径为15 nm~10μm)金属电极的原位加工,材料组成成分的定量分析,而且可以实现纳尺度真空间隙(>20 nm)的放电特性研究,为纳尺度击穿规律和绝缘特性的实验研究提供了有力的支撑.     

基于FIB-SEM制备尖晶石微米颗粒的球差校正透射电镜样品

针对尖晶石微米颗粒材料,利用聚焦离子束扫描电镜双束系统(FIB-SEM),在传统透射电镜样品制备方法的基础上进行技术性改进,成功制备了高质量的球差校正透射电镜样品。并利用球差校正透射电镜成功观察到了尖晶石颗粒的截面原子结构,为更深入地研究尖晶石材料的结构和性能奠定了基础。     

基于卷积神经网络的岩心FIB-SEM图像分割算法

岩心聚焦离子束扫描电镜(FIB-SEM)图像存在灰度分布不均及孔隙内局部高亮等现象,采用传统图像分割算法所得孔隙分割精度较低,而基于轮廓的分割算法需对孔隙进行人工标记,操作繁琐且无法精确提取孔隙。提出一种利用卷积神经网络的端到端岩心FIB-SEM图像分割算法。结合光流法与分水岭分割图像标注法构建岩心FIB-SEM数据集,联合ResNet50残差网络、通道和空间注意力机制提取特征信息,采用改进的特征金字塔注意力模块提取多尺度特征,利用亚像素卷积模块经上采样获取更精细的孔隙边缘并恢复为原始分辨率。实验结果表明,与阈值分割算法和基于主动轮廓的岩心FIB-SEM分割算法相比,该算法分割精度更高且无需人工操作,其平均像素精度和平均交并比分别达到90.00%和85.81%。     

Characterization of 3D pore nanostructure and stress-dependent permeability of organic-rich shales in northern Guizhou Depression,China

The three-dimensional (3D) pore structures and permeability of shale are critical for forecasting gas production capacity and guiding pressure differential control in practical reservoir extraction. However, few investigations have analyzed the effects of microscopic organic matter (OM) morphology and 3D pore nanostructures on the stress sensitivity, which are precisely the most unique and controlling factors of reservoir quality in shales. In this study, ultra-high nanoscale-resolution imaging experiments, i.e. focused ion beam-scanning electron microscopy (FIB-SEMs), were conducted on two organic-rich shale samples from Longmaxi and Wufeng Formations in northern Guizhou Depression, China. Pore morphology, porosity of 3D pore nanostructures, pore size distribution, and connectivity of the six selected regions of interest (including clump-shaped OMs, interstitial OMs, framboidal pyrite, and microfractures) were qualitatively and quantitatively characterized. Pulse decay permeability (PDP) measurement was used to investigate the variation patterns of stress-dependent permeability and stress sensitivity of shales under different confining pressures and pore pressures, and the results were then used to calculate the Biot coefficients for the two shale formations. The results showed that the samples have high OM porosity and 85% of the OM pores have the radius of less than 40 nm. The OM morphology and pore structure characteristics of the Longmaxi and Wufeng Formations were distinctly different. In particular, the OM in the Wufeng Formation samples developed some OM pores with radius larger than 500 nm, which significantly improved the connectivity. The macroscopic permeability strongly depends on the permeability of OM pores. The stress sensitivity of permeability of Wufeng Formation was significantly lower than that of Longmaxi Formation, due to the differences in OM morphology and pore structures. The Biot coefficients of 0.729 and 0.697 were obtained for the Longmaxi and Wufeng Formations, respectively.     

Fusion of Mitochondria to 3-D Networks,Autophagy and Increased Organelle Contacts are Important Subcellular Hallmarks during Cold Stress in Plants

Low temperature stress has a severe impact on the distribution, physiology, and survival of plants in their natural habitats. While numerous studies have focused on the physiological and molecular adjustments to low temperatures, this study provides evidence that cold induced physiological responses coincide with distinct ultrastructural alterations. Three plants from different evolutionary levels and habitats were investigated: The freshwater alga Micrasterias denticulata, the aquatic plant Lemna sp., and the nival plant Ranunculus glacialis. Ultrastructural alterations during low temperature stress were determined by the employment of 2-D transmission electron microscopy and 3-D reconstructions from focused ion beam–scanning electron microscopic series. With decreasing temperatures, increasing numbers of organelle contacts and particularly the fusion of mitochondria to 3-dimensional networks were observed. We assume that the increase or at least maintenance of respiration during low temperature stress is likely to be based on these mitochondrial interconnections. Moreover, it is shown that autophagy and degeneration processes accompany freezing stress in Lemna and R. glacialis. This might be an essential mechanism to recycle damaged cytoplasmic constituents to maintain the cellular metabolism during freezing stress.     

Microstructural analyses of artificial ageing in 5 commercially and non-commercially available Zirconia dental implants

ObjectivesThe presentin vitro study evaluated the effect of LTD (Low Temperature Degradation) on microstructural properties, phase transformation and micro-crack formation of 5 commercially and non-commercially available Zirconia dental implant systems.MethodsAccelerated ageing at 134 °C and 2 bar pressure for 30 h was completed. Focused Ion Beam-Scanning Electron Microscopy (FIB/SEM), X-ray diffraction (XRD) and cathodoluminescence quantified phase transformation and micro-crack formation.ResultsTransformation of the tetragonal grains towards the monoclinic symmetry was observed in all systems. The highest depth was measured in non-commercial TAV dental with the largest grain size (8.7 μm). A micro-cracked layer was associated with the transformation zone. The ageing-related micro-crack formation was parallel to the surface for all groups and was deepest for the non-commercial TAV dental with the largest grain size (7.4 μm).ConclusionLTD following in vitro ageing using an autoclave was minimal for all implant systems investigated.     

Formation of corrosion pockets in FeNiCrAl at high temperatures investigated by 3D FIB-SEM tomography

A recently published study of high temperature nitridation of iron chromium aluminum alloys (FeCrAl) at 900°C in N₂–H₂ has redundantly shown the formation of locally confined corrosion pockets reaching several microns into the alloy. These nitrided pockets form underneath chromia islands laterally surrounded by the otherwise protective alumina scale. Chromia renders a nitrogen-permeable defect under the given conditions and the presence of aluminum in the alloy. In light of these findings on FeCrAl, a focused ion beam–scanning electron microscope tomography study has been undertaken on an equally nitrided FeNiCrAl sample to characterize its nitridation corrosion features chemically and morphologically. The alloy is strengthened by a high number of chromium carbide precipitates, which are also preferential chromia formation sites. Besides the confirmation of the complete encapsulation of the corrosion pocket from the alloy by a closed and dense aluminum nitride rim, very large voids have been found in the said pockets. Furthermore, metallic particles comprising nickel and iron are deposited on top of the outer oxide scale above such void regions.     

聚集离子束扫描电镜(FIB-SEM)在页岩纳米级孔隙结构研究中的应用

页岩中大量发育的纳米级孔隙组成了页岩气储集的主要空间。聚集离子束扫描电镜(FIB-SEM)通过对页岩样品的连续切割和成像,能够在纳米尺度上三维重建页岩的空间分布。依据不同岩石组分灰度值的差异,可以将页岩内的孔隙、有机质、黄铁矿等分割提取出来,不仅可以三维展示其空间分布形态,还可以对孔隙的分布特征和孔隙度等参数进行定量计算。聚集离子束扫描电镜在页岩纳米孔隙中的应用,将给页岩微观结构的深入研究提供新的研究手段。     

Understanding sintering characteristics of ZnO nanoparticles by FIB-SEM three-dimensional analysis

In this study, we utilize three-dimensional (3D) reconstruction by focused ion beam (FIB) cutting and SEM imaging to understand the evolution of pore volume, pore-solid interfacial area, pore shape, pore connectivity, and pore number during the two-step sintering of ZnO nanoparticles. After the first-step sintering, the density is 75% and all the pores are connected. During the second-step sintering, the decrease of pore volume leads to the segmentation of pores and formation of closed pores. The shape of closed pores is irregular. The pore number first increases with the formation of closed pores, and then decreases due to the disappearance of small pores. The pore-solid interfacial area keeps decreasing during sintering. FIB-SEM 3D reconstruction offers an opportunity to directly and quantitatively observe the pore evolution and understand the sintering process at nanoscale.