Experimental and Theoretical Studies in Modern Mechanochemistry

Mechanochemistry is the branch of Chemistry focusing on the chemical reactivity of solid substances submitted to the application of mechanical forces under either elastic or plastic deformation conditions. A measure of its ancestral roots is given by the many citations to mechanochemical procedures in documents dating back to the Classical Roman Age. Quite noticeably, even then such learning was referred to as remarkably ancient. Other important tracks occasionally emerged during the Middle Age, when the so-called via caloris of Alchemists dreaming the transmutation of matter overwhelmed the slow comminution of powders in cold stone mortars. Yet, Mechanochemistry only apparently was sunk in oblivion. The ancient learning survived through the centuries, and was brought back to life by the insatiable curiosity of little and great scientists. After decades of continuous efforts, we are now aware that some of the most important properties of materials in high-technology applications are strongly influenced, or even controlled, by mechanochemical phenomena. The interplay between mechanical stress and chemical reactivity lies for example at the basis of the corrosion behavior as well as in metallic glasses and ceramics where local atomic strain plays a critical role in structural failure. At last, the entire field of Materials Science no longer ignores the fascinating properties of mechanochemical reactions. In contrast to their scientific and technological importance, our basic understanding of even the simplest mechanochemical processes is at best rudimentary. A deeper understanding and control of elementary processes in Mechanochemistry is therefore needed. To call attention on the considerable opportunities existing in this area of fundamental and applied research on materials, we highlight in this book a number of past achievements and promising recent developments in the field. It is today widely accepted that only a highly interdisciplinary approach holds the greatest promise to provide novel insight into the fundamental features of physical, chemical and mechanical processes in the various fields of Materials Science. The same is true for Mechanochemistry. As a whole, the “mechanochemical” community is as diverse as virtually any other in materials research, involving disciplines as disparate as fundamental Physics and Chemistry on the one hand, and Engineering, Physical Metallurgy and Physical Ceramics on the other. Yet, it is rare that this diverse pool of expertise is ever brought together in a focused attack on mechanochemical phenomena and properties. It is our hope that this volume could give the reader a sense of the rich and fertile common ground which already exists between the different disciplines, giving thus a contribution to bring these very different communities closer together. A central theme in much of the ongoing work on Mechanochemistry concerns the interrelation between the chemical properties and the underlying structure of materials. While for a number of scientific research subjects many suitable experimental techniques for the characterization and investigation of properties and processes have become available in recent years, Mechanochemistry still poses a major challenge. This is mostly due to the fact that in a general mechanochemical process only a small fraction of atoms is directly affected. It is precisely this inhomogeneity that undermines any effort to characterize in more detail the mechanochemical process. In organizing this book we soon realized that any attempt to cover a wide field of research such as Mechanochemistry would necessarily represent a highly selective endeavor. There are many ways of classifying the contributions offered by the different authors that can be in principle chosen. For example by distinguishing theoretical from experimental studies, microscopic from macroscopic investigations, or fundamental from applied research. The latter distinction appears to be particularly meaningful for two reasons. First, because the methodologies required for the investigations are fundamentally different. Second, because of the necessarily different aims of the works. Nevertheless, a clean-cut separation between fundamental and applied contributions is often difficult to find, thus the chosen classification of contributions may not be the most satisfactory one. Following the aforementioned distinction between fundamental and applied research, the first part of the book is devoted to contributions dealing with the fundamental features of Mechanochemistry, including thermodynamic as well as kinetic and atomistic studies. By contrast with the emphasis on fundamentals, the second part is instead dedicated to a variety of applications of mechanochemical methods devoted to the preparation of inorganic and organic materials and to the processing of minerals and wastes. The two parts of the book are opened by two introductory chapters. The former focuses on materials properties and chemical reactions under well-controlled and well-defined loading conditions, so introducing most of the fundamental concepts. The latter offers instead an overview of the reactivity enhancement promoted by the mechanical treatment in various apparatuses. We have greatly benefited from discussions with our colleagues at the University of Sassari and have received many useful suggestions from them as well as from all the contributors to this book. We would like to acknowledge the long-standing support we have received from all of our collaborators and students participating in formation programs. A special thank goes to Dr. Giuseppe Manai, for his continuous assistance and suggestions. We are indebted to Dr. Pietro De Martini, Banco di Sardegna, for his fundamental guide for fund raising. We are grateful to Prof. S. Rubino for his kind support and to Dr. Giovanna Tuveri, who followed our case at the Fondazione Banco di Sardegna. This work has been made possible by the funds kindly placed at our disposal by the Fondazione Banco di Sardegna. We wish to express here all of our deep gratitude to the Board of Directors. The University of Cagliari and the University of Sassari are as well acknowledged for the opportunity we had to use laboratories and facilities necessary to our study.