Contents

Preface

In the quantitative determination of new structures, micro-/nano-crystalline materials pose significant challenges in the field of materials, chemical and bio-chemical crystallography. The different properties of materials are structuredependent. Traditionally, X-ray crystallography has been used for the analysis of these materials. Electron crystallography offers an alternative approach in the study of very small crystals that are a million times smaller than those needed for X-ray diffraction. Under certain conditions, electron crystallography has some advantages over X-ray crystallography: it is possible to record single crystal information from individual micro-/nano crystals and sometimes it helps in the resolution of overlapped reflections in X-ray powder data. This is possible due to the greater scattering cross section of matter for electrons than X-rays. The defects in crystals can be studied using high resolution electron microscopy images. In recent years, electron diffraction has been widely applied for determining the structure of unknown crystals. With the introduction of advanced methodologies, important methods for crystal structural analysis in the field of electron crystallography have been discovered. There are two methods that are developed for collection of complete three-dimensional electron diffraction data: the rotation electron diffraction (RED) and automated electron diffraction tomography (ADT). Large numbers of crystal structures have been solved using the RED method. These include the most complex zeolites ever solved, open-framework compounds and quasicrystal approximants, such as the

Chapter 1 is related to the introduction about the electron crystallography. In Chapter 2, electron diffraction, high resolution transmission and scanning transmission electron microscope imaging in materials research, especially in the study of nano-science, are presented. In Chapter 3, a comprehensive review and comparison of different methods used for generating the empires are presented. The focus is given to the 'cut and project method', which can be generalized to calculate empires for any quasicrystals. In Chapter 4, the structure analysis of complex pseudo-decagonal (PD) quasicrystal approximants PD2 and PD1 using the RED method have been discussed. PD2 and PD1 are built of characteristic 2 nm wheel clusters with 5-fold rotational symmetry. In Chapter 5, the crystallographic structure evolution of stainless steels during rolling, piercing and plasma nitriding is described and the mechanism of microstructure evolution during metal forming

and materials processing is presented. The EBSD (Electron Back Scattering Diffraction) technique is employed for the crystallographic analysis. In Chapter 6, the experimental and theoretical charge-density analysis has been performed to understand the topological and electrostatic properties of the 1-10 phenanthroline hydrate molecule. In Chapter 7, a study on the interaction of dislocation-dopant ions during plastic deformation by strain-rate cycling tests has been presented and

We wish to express our sincere appreciation to IntechOpen for giving us the opportunity to publish a book on the topic of electron crystallography. We would

pseudo-decagonal approximants.

discussed.


**5. Conclusions**

A test of the combined injection of tracers (organic and ionic) and helium-saturated water was done in April 2019 to assess and optimize the concept of injecting water saturated with hydrogen, planned for later, and monitoring its physicochemical properties.

The test has confirmed the technical feasibility, under field conditions, of saturating a significant quantity of water with a low-solubility gas and injecting it in a controlled manner into a shallow aquifer.

It was possible to properly monitor the propagation of the dissolved gas plume in the aquifer with the means of analysis used. Helium could be detected up to 20 m downstream of the injection well by mass spectrometer analysis of the gas mixture obtained through partial degassing of water samples by mechanical agitation.

Among the five tracers used, uranine and lithium were shown to be the most effective. The first is a colored fluorescent organic tracer, easily and continuously detectable in situ but affected in this specific hydrogeological context (fine matrix and fissure porosity) by a certain retardation factor with respect to the propagation of the water. The second is a colorless ionic tracer, not affected by such a retardation factor, but not detectable in situ. To obtain a cleaner signal, the tracer mass used will be ten times higher when injecting the water saturated with hydrogen.

The temporal modeling of the post-injection evolution of these two tracers reveals, as a function of the distance from the injection well, two distinct hydrodynamic regimes linked to the existence of a multiple porosity, of both matrix and fissure type. These elements will be essential in understanding the transport of the hydrogen plume during the next injection simulation.

The preparation and the conditions of injection of the tracer tank and hydrogen-saturated water tank have been modified to take the results obtained into account: doubling of the number of bubbling outlets in the 5 m3 tank bubbling device, establishment of a latency period between the two injections, reduction of the flow rate of the second tank.

Finally, the protocol of monitoring has also been modified: the establishment of specific monitoring of the PZ2BIS piezometer with continuous in situ recordings of a maximum of data, adaptation of the sampling schedule to the specificity of each piezometer and increase in the overall monitoring time.

Thus, the adoption of all of these improvements will permit proper execution of the main experiment of injecting hydrogen-saturated water and carrying out the associated monitoring, which will also be preferentially done during periods of high water.

**Author Contributions:** Conceptualization, methodology, and validation, P.G., E.L., S.L., and Z.P.; analysis, S.L., P.G., Z.P., E.L., P.d.D., and N.J.; writing—original draft preparation, S.L., P.G., and Z.P.; writing—review and editing, S.L., P.G., Z.P., E.L., P.d.D., and N.J.; supervision, P.G. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the French Scientific Interest Group GEODENERGIES in the framework of the ROSTOCK-H project (Risks and Opportunities of the Geological Storage of Hydrogen in Salt Caverns in France and Europe).

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.