Investigating Iron Alloy Phase Changes Using High Temperature In Situ SEM Techniques.

This research utilises a novel heat stage combined with a Zeiss scanning electron microscope to investigate phase changes in iron alloys at temperatures up to 800 ℃ using SE and EBSD imaging. Carbon steel samples with starting structures of ferrite/pearlite were transformed into austenite using the commercial heat treatment process whilst imaging within the SEM. This process facilitates capturing both grain and phase transformation in real time allowing better insight into the microstructural evolution and overall phase change kinetics of this heat treatment. The technique for imaging uses a combination of localised EBSD high temperature imaging combined with the development of high temperature thermal-etching SE imaging technique. The SE thermal etching technique, as verified by EBSD images, enables tracking of a statistically significant number of grains (>100) and identification of individual phases. As well as being applied to carbon steel as shown here, the technique is part of a larger study on high temperature in situ SEM techniques and could be applied to a variety of alloys to study complex phase transformations.

The Functionally Grading Elastic and Viscoelastic Properties of the Body Region of the Knee Meniscus.

The knee meniscus is a highly porous structure which exhibits a grading architecture through the depth of the tissue. The superficial layers on both femoral and tibial sides are constituted by a fine mesh of randomly distributed collagen fibers while the internal layer is constituted by a network of collagen channels of a mean size of 22.14 [Formula: see text]m aligned at a [Formula: see text] inclination with respect to the vertical. Horizontal dog-bone samples extracted from different depths of the tissue were mechanically tested in uniaxial tension to examine the variation of elastic and viscoelastic properties across the meniscus. The tests show that a random alignment of the collagen fibers in the superficial layers leads to stiffer mechanical responses (E = 105 and 189 MPa) in comparison to the internal regions (E = 34 MPa). All regions exhibit two modes of relaxation at a constant strain ([Formula: see text] to 7.7 s, [Formula: see text] = 49.9 to 59.7 s).

On the diatomite-based nanostructure-preserving material synthesis for energy applications.

The present article overviews the current state-of-the-art and future prospects for the use of diatomaceous earth (DE) in the continuously expanding sector of energy science and technology. An eco-friendly direct source of silica and the production of silicon, diatomaceous earth possesses a desirable nano- to micro-structure that offers inherent advantages for optimum performance in existing and new applications in electrochemistry, catalysis, optoelectronics, and biomedical engineering. Silica, silicon and silicon-based materials have proven useful for energy harvesting and storage applications. However, they often encounter setbacks to their commercialization due to the limited capability for the production of materials possessing fascinating microstructures to deliver optimum performance. Despite many current research trends focusing on the means to create the required nano- to micro-structures, the high cost and complex, potentially environmentally harmful chemical synthesis techniques remain a considerable challenge. The present review examines the advances made using diatomaceous earth as a source of silica, silicon-based materials and templates for energy related applications. The main synthesis routes aimed at preserving the highly desirable naturally formed neat nanostructure of diatomaceous earth are assessed in this review that culminates with the discussion of recently developed pathways to achieving the best properties. The trend analysis establishes a clear roadmap for diatomaceous earth as a source material of choice for current and future energy applications.

An investigation into experimental in situ scanning electron microscope (SEM) imaging at high temperature.

This paper presents an investigation into high temperature imaging of metals through the use of a novel heat stage for in situ Scanning Electron Microscopy (SEM). The results obtained demonstrate the benefits and challenges of SEM imaging at elevated temperatures of up to 850 °C using Secondary Electron (SE) and Electron Backscatter Diffraction (EBSD) detectors. The data collected using the heat stage demonstrate good beam, vacuum, and detector stability at high temperatures without the need for shielding or detector modification owing to the heat stage geometry. SE imaging highlighted one possible application: carrying out thermal etching, a process in which surface grooves form along a material's grain boundaries during heating in situ. The data suggest that using the heat stage to perform imaging during the process gives a more accurate representation of a material's microstructure at temperature than examining the thermally etched specimen after cooling. This study also highlights some of the challenges of high temperature in situ EBSD imaging in both steel and nickel at a variety of temperatures and time scales. In particular, the data demonstrate the effect of surface roughness on EBSD imaging and how microstructural changes during heating may affect this. Additionally, the ease with which a material can be imaged using EBSD at temperature may be affected by the material's magnetic properties. For the first time, it is shown that at temperatures close to the Curie temperature of ferromagnetic materials, in this case Nickel, there is a loss of EBSD image quality. Quality was regained when temperatures were further increased. Despite these challenges, good quality EBSD scans were produced, further highlighting the benefits of in situ testing for providing information on grain boundaries, orientations, and phase change at elevated temperatures.

Novel microscopy-based approaches to study the film formation mechanism and associated mechanical response in polymer lattices.

In this paper, we present the results from novel microscopy-based approaches aimed at providing further insight into the mechanism of film formation and associated mechanical response in polymer lattices. Firstly, a 'simple' methodology, combining the use of variable pressure scanning electron microscopy and a recently introduced enhanced coolstage (-50 to +50°C), was successfully developed and not only used to study dynamic processes, e.g. different stages of latex film formation, but also for high-resolution imaging of 'freeze-dried' structures. By using the enhanced freeze-drying capability of the system, it was also possible to preserve the structure and features of the studied system with minimum shrinkage and distortion and in the case of polymer lattices at a desired stage of film formation. Moreover, specimens can then be readily imaged, without the need of conductive coatings and at much lower chamber gas pressures, thus minimizing the beam skirting effects and allowing higher resolutions to be achieved. The second and final part of our study consider the mechanical response of the studied latex dried under different conditions, with the particular emphasis on the effects of drying rate [% relative humidity (RH)]. Atomic force microscopy force distance curve measurements revealed that while the %RH did not have an effect on the structures formed, it did have an effect on the adhesive properties of the studied system. It is strongly believed that the methodologies developed and used here can be applied to other material systems, including biologicals and pharmaceuticals.

Cracking of drying latex films: an ESEM experiment.

In this study environmental scanning electron microscopy was used to observe the cracking of drying latex films below their glass-transition temperature. By controlling the relative humidity so that it decreases linearly with time, a critical level of humidity at which cracking occurs can be determined and this is measured as a function of film thickness. It was found that the cracking humidity decreases with increases in film thickness for thicknesses in the range of 30 to 100 mum and then remains almost unchanged. A scaling argument can be used to fit the data very well and indicates that cracking occurs as soon as the entire film is consolidated into close packing.

A new tensile stage for in situ electron microscopy examination of the mechanical properties of "superelastic" specimens.

We have developed a novel tensile stage that can be used for in situ electron microscopy examination of the mechanical properties of "superelastic" materials. In our stage, one of the specimen clamps is replaced by a cylindrical roller, which when driven by a motor can easily stretch ("roll on") any specimen irrespective of its plastic properties. We have used the so-called Roll-o-meter in the study of the tensile behavior of two different film formed latex formulations, here referred to as standard and novel. We find that the values of the tensile strength and extension to break of the studied systems, measured by using the Roll-o-meter, are similar to those measured by a Hounsfield tensile testing machine outside the microscope chamber. Further, in situ environmental scanning electron microscopy examination of the deformation and failure of the lattices revealed that the standard specimens exhibit a more ductile behavior, compared to the novel ones.