Markus Wegmann

Three-dimensional analysis of porous BaTiO3 ceramics using FIB nanotomography

Three‐dimensional (3D) data represent the basis for reliable quantification of complex microstructures. Therefore, the development of high‐resolution tomography techniques is of major importance for many materials science disciplines. In this paper, we present a novel serial sectioning procedure for 3D analysis using a dual‐beam FIB (focused ion beam). A very narrow and reproducible spacing between the individual imaging planes is achieved by using drift correction algorithms in the automated slicing procedure. The spacing between the planes is nearly of the same magnitude as the pixel resolution on scanning electron microscopy images. Consequently, the acquired stack of images can be transformed directly into a 3D data volume with a voxel resolution of 6 × 7 × 17 nm. To demonstrate the capabilities of FIB nanotomography, a BaTiO3 ceramic with a high volume fraction of fine porosity was investigated using the method as a basis for computational microstructure analysis and the results compared with conventional physical measurements. Significant differences between the particle size distributions as measured by nanotomography and laser granulometry indicate that the latter analysis is skewed by particle agglomeration/aggregation in the raw powder and by uncertainties related to calculation assumptions. Significant differences are also observed between the results from mercury intrusion porosimetry (MIP) and 3D pore space analysis. There is strong evidence that the ink‐bottle effect leads to an overestimation of the frequency of small pores in MIP. FIB nanotomography thus reveals quantitative information of structural features smaller than 100 nm in size which cannot be acquired easily by other methods.

Cryo-FIB-nanotomography for quantitative analysis of particle structures in cement suspensions.

Cryo‐FIB‐nanotomography is a novel high‐resolution 3D‐microscopy technique, which opens new possibilities for the quantitative microstructural analysis of complex suspensions. In this paper, we describe the microstructural changes associated with dissolution and precipitation processes occurring in a fresh cement paste, which has high alumina and sulphate contents. During the first 6 min, precipitation of ettringite leads to a general decrease of the particle size distribution. In the unhydrated cement paste almost no particles smaller than 500 nm are present, whereas after 6 min this size class already represents 9 vol%. The precipitation of ettringite also leads to a significant increase of the particle number density from 0.294*109/mm3 at t0min to 20.55*109/mm3 at t6min. Correspondingly the surface area increases from 0.75 m2/g at t0min to 2.13 m2/g at t6min. The small ettringite particles tend to form agglomerates, which strongly influence the rheological properties. The particular strength of cryo‐FIB‐nt is the potential to quantify particle structures in suspension and thereby also to describe higher‐order topological features such as the particle–particle interfaces, which is important for the study of agglomeration processes.

Electronically functional fibre technology development for ambient intelligence

Most of everyday clothing consists of textile fibres woven together to produce a fabric. Their primary purpose is structural and aesthetic. Fibres can have added functionality by the integration of computing power into the material that forms them. The purpose of the “fibre computing” concept is to integrate this new dimension of functionality into fibres, thus turning everyday objects into intelligent artefacts. The objective is to make large flexible integrated systems for wearable applications and high-tech-textile products by building functional fibres with single crystal silicon transistors at its core. The concept of wearable computing opens entirely new possibilities in areas such as medical monitoring and telemedicine, sports and athletics, entertainment and expressive musical/dance performance (Gemperle 1998). It offers the potential of harnessing a very high degree of applicable functional processing power for the user in a particularly convenient manner through the placement of non-invasive sensors around the body. However, a key barrier to this are the challenges associated with the unobtrusive deployment of effective sensors. Even current state of the art (VivoMetrics), in integrating electronics into wearable systems comprises of previously packaged integrated electronic components, interconnected with each other by means of conductive fibres and enclosed by protective material/casing. An approach more conducive to everyday living, which would enable this technology to recede even further into the background is required. The solution is the development of a novel technology for creating intelligent fibres.