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PREFACE I N D U S T R I A L U S E O F C O L L O I D A L S I L I C A S is growing steadily in both traditional areas and an ever-increasing number of novel areas. Colloidal silicas are found in fields as diverse as catalysis, metallurgy, electronics, glass, ceramics, paper and pulp technology, optics, elastomers, food, health care, and industrial chromatography. However, in spite of the apparent simplicity of silica s composition and structure, fundamental questions remain about the formation, constitution, and behavior of colloidal silica systems. As a result, a broad and fascinating area of study is open to scientists interested in fundamental aspects of silica chemistry and physics and to technologists looking for new uses of silica and for answers to practical problems. The work presented here includes both theoretical and experimental aspects of some of the most significant areas of colloidal silica science and technology. This book constitutes an update in the field since Ralph K. Her, the distinguished silica scientist, published the definitive book on silica chemistry in 1979. This new book includes the 11 plenary lectures presented at an international symposium honoring Her and 22 related research papers. To solve the lack of coherence typical of some publications emerging from scientific gatherings, the symposium organizers selected nine fundamental topics in the area of colloidal silica chemistry and then extended an open invitation to the world s most prominent silica scientists, asking for either an overview of the current state of knowledge in their field or an original paper representing current trends of research. More than 190 overview lectures and research papers were presented by some of the most outstanding silica scientists from the former Soviet Union, Europe, China, Japan, Australia, and New Zealand as well as Canada and the United States. Renowned authorities in the areas discussed at the symposium edited selected papers for publication in this book or in two special issues of Elsevier s international journal Colloids and Interfaces. This book offers a clear introduction to the science and technology of colloidal silica and will increase the reader s understanding of the most important problems in this area of science.
Acknowledgments The Ralph K. Her Memorial Symposium organizing committee is most grateful to the people and organizations that made the symposium and the publication of this book possible, especially the keynote speakers, the authors of papers presented at the symposium, the session chairpersons, the officers of the Division of Colloid and Surface Chemistry, and the staff of the American Chemical Society. xiii Bergna; The Colloid Chemistry of Silica Advances in Chemistry; American Chemical Society: Washington, DC, 1994.
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The committee also thanks the Cabot Corporation, DuPont, Degussa Corporation, Imperial Chemical Industries, Nalco Chemical Company, P Q Corporation, Sandia National Laboratory, and the former Soviet Academy of Sciences for their contributions to the symposium. I and the editors of the nine sections of this book wish to thank Janet S. Dodd, Cheryl Shanks, Cathy Buzzell-Martin, and Steven Powell of the A C S Books Department for their help and patience during the writing and editing of the manuscripts. We also appreciate the assistance of William B. Hambleton Jr., Donald Nickerson, and Carol Little of DuPont in various stages of the project. We give special thanks to Amelia V. Kahn, Executive Secretary, for her many contributions to the development of the symposium and the subsequent preparation of the papers for publication in this book. A special tribute goes to my good friend George Scherer for his kind support in the development of this book.
HORACIO E. BERGNA DuPont Wilmington, DE 19880-0262 March 6, 1993
Bergna; The Colloid Chemistry of Silica Advances in Chemistry; American Chemical Society: Washington, DC, 1994.
DEDICATION Κ . I L E R D E V O T E D M O S T O F H I S C A R E E R to exploratory and industrial research in the chemistry of colloidal materials. He is recognized worldwide for his unique contributions to a unified understanding of the colloidal chemistry of silica and silicates. His book The Chemistry of Silica, published in 1979, is the definitive book on silica chemistry and remains a primary source of reference in the field. Perhaps more than anybody else, Her helped advance the chemistry of colloidal silica from an art to a science; through the imagery he created to ex plain his ideas, he elevated this science to a fine art. Today his graphics are universally used to illustrate colloidal silica structure and behavior. Through his lectures, more than 30 papers, 101 U.S. patents, and more than 500 foreign counterparts, he has deeply influenced the thinking of silica chemists all over the world. At the end of World War II, when "colloidal silicic acid" was used on a very large scale in industry for water purification and as catalyst support, there was widespread disagreement as to its true chemical nature, the mechanism of its polymerization, its surface chemistry, and what determined its stabilization. Sols and gels were made by recipes and varied by empirical methods. Stability to ward gelation was generally unpredictable because mechanisms were only specu lative. In a series of investigations, publications, and patents, beginning in the early 1940s and continuing until his death, Her, his co-workers, and people working under his direction did much to clarify these uncertainties. They made signifi cant contributions toward the development of a clear and coherent picture of the polymerization, growth, aggregation, stabilization, physical properties, sur face chemistry, kinetics, and uses of silica sols and gels. This work was summarized and combined with an extensive and critical review of the literature in the lectures Her gave at Cornell University as George Fischer Baker Lecturer in chemistry. These series of lectures formed the basis for his first book, The Colloid Chemistry of Silica and Silicates, published by Cornell Press in 1955. Hers ideas were also expressed in chapters he wrote for other books and in the proceedings of conferences he attended as Alexander Memorial Lecturer at the Fourth Australian Conference on Colloids and Sur faces (1984) and as Keynote Awardee of the Second International Conference on Ultrastructure Processing of Ceramics, Glasses, and Composites held in Florida in 1985. Hers Keynote Award was given for a lifetime s contribution to
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R.ALPH
Adapted with permission from Colloids Surf. 1992, 63, ix.
xv Bergna; The Colloid Chemistry of Silica Advances in Chemistry; American Chemical Society: Washington, DC, 1994.
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Ralph K lier inorganic chemistry and for his pioneering work in the study of silica polymerization and colloidal chemistry. The work of Her and his co-workers led to the creation of new materials and industries. His studies of the surface chemistry of silica led to the invention of unique organophilic and hydrophobic silica products termed "estersils". Virtually a new industry was created when he rendered titania pigment particles in organic films and finishes photochemically inert by coating them with silica. In another area of surface chemistry, his discoveries of chromium complexes capable of forming a permanent and water-resistant bond between polyester resins and fiberglass was of great importance in establishing the current fiberglass-reinforced plastics industry. His recognition of the importance of having a bireactive molecule forming a permanent chemical bond with both surfaces to be joined, as exemplified by these chromium complexes, provided the model for many coupling agents that have subsequendy been developed. H e also discovered a water-soluble chromium composition, stearato chromic chloride, and demonstrated its use as a water repellent when applied to a surface and dried. This composition was used first in the paper industry, but applications have widened. Today stearato chromic chloride and related compoxvi Bergna; The Colloid Chemistry of Silica Advances in Chemistry; American Chemical Society: Washington, DC, 1994.
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sitions are used in many industries as water repellents, grease repellents, insolubilizing agents, and dispersing aids. Stearato chromic chloride is also used as a surface treatment to improve the finish and handling of the glass fibers going into textile uses. In an entirely different area of colloid chemistry, Her directed a research effort that led to the discovery and development of fibrillar colloidal alumina. He participated personally in this research program and also carried out studies of the sintering and transformation of phases in this colloidal alumina at high temperature, making observations on the mechanism of its conversion to alpha alumina. After 1952, as Manager of Exploratory Research at DuPont, Her led the way in applying colloid chemistry to the field of metallurgy. This work led directly to the development of T D Nickel, recognized as one of the outstanding developments of metallurgy. This new composition consists of a colloidal dispersion of thoria in nickel. It is many times stronger than nickel and retains useful strengths over longer periods at higher temperatures than the superalloys previously available. This development in metallurgy is equally considered an outstanding achievement in the field of colloids. Applying basic colloid techniques to the manufacture of microcrystalhne refractory solids, Her led a research group in the invention and development of several new compositions exhibiting a combination of strength and hardness previously unattained. The performance of Baxtron in cutting and forming tools for the metal-working industries was outstanding. A 1973 article in American Machinist, the 115-year-old magazine of manufacturing technology, said that Baxtron was a material that "cutting tools experts would include near the top of any list of significant developments of recent years". One of Her s accomplishments was the development of a new structure consisting of porous silica beads built up from colloidal silica particles. Use of this structure in liquid phase chromatography gready increased speed of operation and provided a first-order advance in the state of the art. Her was a member of the Chemistry Advisory Committee, Air Force Office of Scientific Research, from 1953 to 1955. He was on the advisory board of Journal of Colloid and Interface Science. Her died on November 9,1985. To all of those who had the privilege of knowing him and working with him, he will remain foremost an inspired teacher of unbounded generosity in sharing new observations and discoveries. His memory will remain with us as an example of unparalleled ethical standards and driving energy in the exploration and harnessing of nature to improve the quality of our lives. In May 1990, DuPont s Lavoisier Academy awarded the Lavoisier Medal for Technical Achievement to Her posthumously, and in September 1990, the DuPont Company opened a new research center in New Johnsonville, Tennessee, and named it after Ralph K. Her. xvii Bergna; The Colloid Chemistry of Silica Advances in Chemistry; American Chemical Society: Washington, DC, 1994.
