Nano-scale 3D reconstruction of C-S-H-phases using modern FIB/SEM technology

Abstract

Demonstration of the application of FIB/SEM on hydrated alite

Full text

Bauhaus-Universität Weimar
Professur Werkstoffe des Bauens
Contact
Nano-scale 3D reconstruction of C-S-H-phases
using modern FIB/SEM technology
Florian Kleiner, Christiane Rößler, Horst-Michael Ludwig
Introduction
Modern Scanning Electron Microscopes (SEM) allow high-
resolution imaging of the nano- to microstructure of building
materials like cement and concrete. Until now, the structural
exploration has mainly been carried out on fractured or polished
2D surfaces. While this approach was able to unveil many
details like the shape of C-S-H-phases, it was not possible to
create a digital 3D reproduction of those shapes.
Experimental challenges
The Focused Ion Beam (FIB) technology is already widely
adopted in the semiconductor industry, cell biology and to
analyse the pore structure of battery materials, oil shales and
clay material [1, 2]. It utilizes a gallium ion beam to cut layer by
layer of a material volume and then using the various SEM
detectors to image and analyse the revealed surface. This allows
to reconstruct a detailed 3D-volume of many materials. While
some approaches to image several cubic micrometer small
volumes of hydrated alite already exist [3], none of these
approaches were able to deliver a detailed 3D-volume of the C-
S-H-needle structure (Figure 1) due to the sensitivity of the
material to the electron and ion beam. Using low voltages for
the electron beam is key to obtain undisturbed images.
Furthermore, for those relatively porous specimens, a resin
intrusion is essential to avoid artifacts caused by the pore
background.
The preparation site for a typical FIB process is shown in Figure
2. The electron beam scannes the surface to be evaluated at an
angle of 52°. Since the region of interest (ROI) remains
connected to the bulk material, a shadowing effect can be
observerd (Figure 3). While this effect may be corrected in some
degree by image manipulation, the degrading signal quality
bevcomes an issue using less sesitive detectors like EDS-
detectors. Furthermore, charging artefacts become an issue in
the progession of the imaging process, since the material is non-
conductive. Therefore, the ROI-cube will be lifted out of the
bulk material as visualized in Figure 5. This leads to an improved
image quality (Figure 4).
The resulting image stack
is easyly segmentable as
demonstrated in Figure 6
and can be
reconstructed as a voxel
based or an
triangulated model.
This 3D-volume can
be further processed
so that quantification
of solids and pores at
nanoscale dimension
is possible.
Results
The 2D images (Figures 4 and 6) and the respective
reconstructions (Figures 7 to 9) show, that it is possible to
obtain a close-to-native 3D-representation of the nano-
structure of hydrated alite pastes. It was possible to obtain a
voxel resolution down to 4 x 4 x 10 nm as shown in Figure 1.
Results of 3D data analysis will be compared with conventional
2D analysis. The obtained pore connectivity in 2D and 3D
analysis will we discussed.
Figure 8: Voxel based 3D-
reconstructions of the needle structures
of C-S-H phases in hydrated alite.
[1] J. Goral, I. Walton. M. Andrew, M. Deo, Fuel 2019, 258 (DOI: 10.1016/j.fuel.2019.116049)
[2] S. Gaboreau, J.-C. Robinet, D. Prêt, Microporous and Mesoporous
Materials 2016, 224 (DOI: 10.1016/j.micromeso.2015.11.035)
[3] Y Zhao, X. Liu, B. Chen, F. Yang, Y, Zhang, P. Wang, I. Robinson,
Materials 2019, 12 (DOI: 10.3390/ma12121882)
Figure 1: Fractured surface of 28 days
hydrated alite overgrown with needle
shaped C-S-H phases. (SE, 2 kV)
Figure 2: Typical FIB-Preparation site.
The cube is 10 x 10 µm and will be cut to
10 nm slices. (Ion-Image, 30 kV)
Bauhaus-University Weimar
F. A. Finger Institute for Building Material Science
Coudraystraße 11A
99423 Weimar
florian.kleiner@uni-weimar.de
christiane.rossler@uni-weimar.de
References
Figure 6: Segmentation of the C-S-H phases of an example FIB-slice.
Figure 4: ROI-cube of hydrated alite,
welded to a copper grid (A). (B) alite,
(C) C-S-H, (D) CH, (E) resin. (SE, 2 kV)
Figure 5: Liftout of the ROI-cube (A) with a needle (B). The cube will be welded to
a copper grid (C) using a platin deposition system (D), (SE, 2 kV)
Figure 3: Fractured surface of 28 days
hydrated alite overgrown with needle
shaped C-S-H phases.
Figure 9: Triangulated surface of the
needle structures of C-S-H phases in
hydrated alite.
Figure 7: 3D-reconstruction of pores (solid, grey)
within dense inner C-S-H (semi-transparent, red) of a
28d hydrated alite specimen (3.7x3.3x0.74 µm³).
link to
presentation / talk
https://youtu.be/fgJw6lUKkPM