3D reconstruction of porous materials through FIB-SEM

Introduction

FIB-SEM tomography of porous materials can resolve meso and macropores, and characterize the interactions between them. 

Understanding these features provides essential information about the formation mechanism and the transport properties of such materials. 

Many examples are directly relevant to industrial use, where the study of transport properties is essential to facilitate the recovery of oil and gas contained in reservoir rocks. 

FIB-tomography can provide such 3D data down to nanometre-scale resolution within a representative volume. [1]

Concept of 3D acquisition in FIB-SEM

The one particular technique available on the FIB-SEM is referred to as Serial Sectioning Tomography, which is the creation of 3D datasets with nanoscale resolution within a representative volume from the specimen, this can be applied to a large variety of materials. [2]

Example 1

Diatomite also referred to as diatomaceous earth, is a fragile rock that consists of loosely bound fossilized unicellular diatom algae. As a consequence, this material has high porosity and thus high permeability, high surface area, and low density.

These properties make this material particularly interesting as a heavy metal adsorbant for contaminant removal and for catalysis e.g., for the generation of phenol, as a catalytic substrate. 

All these processes are dependent on the interconnectivity of the porosity and accessibility of the surface area, thus 3D visualization can provide a wealth of information about how gases and liquids can permeate these materials.

Example 2

Olivine is a useful input material for a lot of different industrial processes including the neutralization of highly acidic fluids and industrial carbon dioxide sequestration. Amorphous silica can be produced through the experimental reaction of olivine with an acidic solution. 

The formation and properties of newly precipitated material on olivine surfaces will control further reactivity as it will mediate the ability of reactive fluid species to access the reacting interface. The reaction of olivine produced an amorphous silica pseudomorph around the original olivine grain that appeared to be layered from 2D imaging and 3D reconstruction. The layering in reacted silica shows a discrete separation with high porosity. [3]

Challenge of Segmentation

The most challenging aspect of using FIB-SEM tomography on porous materials is the data processing, in order to produce representative reconstructions. 

As the porosity and pore size distribution are unknown prior to analysis, it makes the accuracy of the segmentation procedure of the internal microstructures difficult to evaluate. 

There is no benchmark of the precision of the segmentation, which is influenced by artefacts introduced by negative interactions between the beams and the material into the slice images during 3D acquisition. 

The final result is therefore dependent on the instrument operator. This information is fed directly into further analysis of pores, pore network verification (connectivity), and area and volume calculation; in addition, different segmentation procedures have a direct impact on the final results. [1]

Please contact Dr Yang Liu for further enquiries

References

  • [1] Liu Y, King H, van Huis M, Drury M & Plümper O 2016 'Nano-Tomography of Porous Geological Materials Using Focused Ion Beam-Scanning Electron Microscopy'. Minerals 6, (4) 104-104, DOI
  • [2] Holzer, L.; Indutnyi, F.; Gasser, P.H.; Münch, B.; Wegmann, M. Three-dimensional analysis of porous BaTiO3 ceramics using FIB nanotomography. J. Microsc. 2004, 216, 84–95. DOI
  • [3] King, H.E.; Plümper, O.; Geisler, T.; Putnis, A. Experimental investigations into the silicification of olivine: Implications for the reaction mechanism and acid neutralization. Am. Mineral. 2011, 96, 1503–1511. DOI