General Introduction

Clays, Clay Minerals, and Clay Science

F. Bergayaa and G. Lagalyb,    aCRMD, CNRS-Université d’Orléans, Orléans Cedex 2, France,    bInstitut für Anorganische Chemie, Christian-Albrechts-Universität zu Kiel, Kiel, Germany

Abstract

Clays and clay minerals are recognized as the materials of the twenty-first century. Chapter 1 provides a general introduction into clay science, illustrates the classification of the clay minerals (planar and non-planar 1:1 and 2:1 clay minerals), shows the idealized formulae of some representative clay minerals, lists the current names of clays, and reports the important properties of clay minerals. As yet, there is no uniform nomenclature in clay science, a unifying terminology is proposed that should be acceptable to all disciplines, users, and producers. This mainly concerns the terms “clay and clay mineral“, “associated minerals and associated phases“, “particles and aggregates“, “swelling“, and “delamination and “exfoliation“. Finally, in addition to belonging to the class of silicates, three alternative concepts of clay minerals are proposed to extend the benefit to a wider scientific audience.

Keywords

Aggregates; Associated phases; Clay; Clay mineral; Classification; Delamination; Exfoliation; Formulae; Inorganic polymer; Names of clays; Names of clay minerals; Particles; Porous layered (hydr)oxides; Properties; Salts with 2D polyanion; Swelling

The authors believe that clays and clay minerals, either as such or after modification, will be recognized as the materials of the twenty-first century because they are abundant, inexpensive, and environment friendly. With that in view, this Handbook of Clay Science has assembled core information on the varied and diverse aspects that make up the discipline of clay science, ranging from the fundamental structure and surface properties of clays and clay minerals to their industrial and environmental applications.

Clay has been known to, and used by, humans since antiquity. Indeed, clay was implicated in the prebiotic synthesis of biomolecules and the very origins of life on earth. Clay has also become indispensable to modern living. It is the material of many kinds of ceramics, such as porcelain, bricks, tiles, and sanitary ware, as well as an essential constituent of plastics, paints, paper, rubber, and cosmetics. Clay is non-polluting and can be used as a de-polluting agent. Of great importance for the near future is the potential of some clays to be dispersed as nanometre-size unit particles in a polymer phase, forming nanocomposite materials with superior properties. The diversity of structures and properties of clays and clay minerals and their wide-ranging applications make it difficult to compile a comprehensive reference text on clay science.

1.1 Aim and Scope

If the general knowledge about clay and its use have ancient roots, the scientific study of clay (i.e. ‘clay science’) is a relatively recent discipline, dating back only to the mid-1930s, following on the emergence and general acceptance of the ‘clay mineral concept’. According to this concept, clays are essentially composed of micro-crystalline particles of a small group of minerals, referred to as the clay minerals (Grim, 1968). Since then, clay science or ‘argillology’ (Konta, 2000) has become an autonomous, multi-faceted discipline.

Since people who work with clay come from diverse backgrounds and have diverse interests, there are probably as many concepts and views of clay as there are clay mineral species. It is not surprising, therefore, that clay scientists have varied trainings, including geology, mineralogy, chemistry, physics, and biology, and hold different perspectives. The multi-disciplinary nature of clay science is indicated by the scope, contents, and multi-authorship of this handbook. It is also reflected in the wide range and variety of scientific journals where papers on clays and clay minerals are published. At the same time, individuals or groups who investigate and use clay—whether they be in academe or industry—often fail to realize that they share a common interest, or worse, are ignorant of one another’s existence. Similarly, information about clay is dispersed in many scientific conferences and symposia whose themes (e.g. nanotechnology, rheology, and heterogeneous catalysis) often make no reference to the experimental material used. Indeed, the word ‘clay’ in many publications is often subsumed into such terms as ‘microporous solid’ or ‘layered material’. This is probably because, for many people, clay is associated with soil (dirt) and mud. By the same token, clay science is not generally considered to be intellectually challenging. If clay science features at all in the syllabus or curriculum of a university degree course, the focus is usually on the mineralogy of clay, while its colloidal and physico-chemical aspects are glanced over, if not ignored. The teaching of clay science also varies from school to school within a given country, and from one country to another.

The first two textbooks by Grim, Clay Mineralogy and Applied Clay Mineralogy, were published some 5–6 decades ago (Grim, 1953, 1962, 1968). Since then, a great deal of information on clays and clay minerals has accumulated. Also, many advanced analytical and instrumental techniques have been developed, as well as novel industrial and environmental applications. A number of books on particular aspects are available (e.g. Weaver and Pollard, 1973; Farmer, 1974; Theng, 1974, 1979, 2012; van Olphen, 1977; Brindley and Brown, 1980; Chamley, 1989; Wilson, 1994; Velde, 1995; Moore and Reynolds, 1997). The first general reference text, however, in the English language was published by Bergaya et al. (2006). The second edition of this Handbook of Clay Science is now being published in two volumes.

The Handbook of Clay Science aims to provide up-to-date information on the fundamental structural and surface properties of clay minerals, their industrial and environmental applications as well as analytical techniques, and the teaching and history of clay science. The book is intended to be a critical review and not just a compilation of the published literature. To our knowledge, this holistic multi-disciplinary approach does not exist in any other clay book. Here, we describe some generally held concepts and working definitions of clay and clay minerals that might be acceptable to most disciplines and practitioners of clay science.

This handbook will therefore provide a point of first entry into the clay science literature for research scientists, university teachers, postgraduate students, and industrial chemists, as well as people in agriculture, environmental engineering, industry, and waste disposal, who need to know about clays and clay minerals. This book will also be useful to commercial users of clays.

1.2 Clay

There is, as yet, no uniform nomenclature for clay and clay material. Nonetheless, we do not seek a consensus1 about the meaning of the terms ‘clay’, ‘clays’, and ‘clay minerals’ (Table 1.1). Indeed, the quest for a unifying terminology that is acceptable to all disciplines, users, and producers would be a fruitless exercise. Rather, here we aim to highlight the common meaning of these terms and the impact of these materials on our actual daily life, together with their potential for the ever-growing number of practical applications (Kühnel, 1990; Murray, 1999).