Table Of ContentSmall Particles Technology
Small Particles Technology
Jan-Erik Otterstedt
Chalmers University of Technology
Gothenburg, Sweden
and
Dale A. Brandreth
Widener University
Chester, Pennsylvania
Springer Science+Business Media, LLC
Library of Congress Cataloging in Publication Data
Otterstad, 13n Erik.
Small particles technology / Jan-Erik Otterstedt and Dale A. Brandreth.
p. cm.
Includes bibliographical references and index.
ISBN 978-1-4419-3301-0 ISBN 978-1-4757-6523-6 (eBook)
DOI 10.1007/978-1-4757-6523-6
1. Particles. 2. Metallic oxides. 3. Silica. 4. Surface chemistry. 5. Colloids. 6. Catalysts. I.
Brandreth, Dale A. II. Title.
TA418.78.088 1998 98-41315
620'.43-DC21 CIP
ISBN 978-1-4419-3301-0
© 1998 Springer Science+Business Media New York
Originally published by Plenum Press, New York in 1998
Softcover reprint of Ihe hardcover 1s i edition 1998
http://www.plenum.com
10987654321
AII rights reserved
No part 01 this book may be reproduced, stored in a data retrieval system, or
transmitted in any lorm or by any means, electronic, mechanical, photocopying,
microlilming, recording, or otherwise, without written permission Irom the Publisher
To the memory of
Ralph lIer
Preface
It is difficult to imagine modem technology without small particles, 1-1000
nm in size, because virtually every industry depends in some way on the use of
such materials. Catalysts, printing inks, paper, dyes and pigments, many
medicinal products, adsorbents, thickening agents, some adhesives, clays, and
hundreds of other diverse products are based on or involve small particles in a
very fundamental way. In some cases finely divided materials occur naturally or
are merely a convenient form for using a material.
In most cases small particles play a special role in technology because in
effect they constitute a different state of matter because of the basic fact that the
surface of a material is different from the interior by virtue of the unsaturated
bonding interactions of the outermost layers of atoms at the surface of a solid.
Whereas in a macroscale particle these differences are often insignificant, as the
surface area per unit mass becomes larger by a factor of as much as 109, physical
and chemical effects such as adsorption become so pronounced as to make the
finely divided form of the bulk material into essentially a different material
usually one that has no macroscale counterpart.
The creation of finely divided forms of different materials depends a great
deal on the material itself. Grinding will produce a certain fraction of very small
particles, but economic, technical, and safety factors frequently make that
primeval method of little use, particularly when the desired size is less than about
10 ~m (10,000 nm). In addition in some materials such as catalysts, the specific
surface is greatly increased by the presence of pores, which are not created by
grinding.
For the past twelve years one of the authors has given a course in Small
Particles Technology to senior engineering students and graduate students at
Chalmers University of Technology in Gothenburg, Sweden, where this subject
has also been a very active and successful area of research in the Department of
Engineering Chemistry at that university.
The authors, who both graduated from the Department of Chemical
Engineering at the University of Toronto in Canada, and who were also
colleagues at E. I. Du Pont & Company in Wilmington, Delaware, agreed that it
would be worthwhile to expand the course in Small Particles Technology to a
book that would seek to be a useful compendium of facts and ideas to those
working in research, development, and manufacturing involving aspects of small
particles technology.
The goal of our book is, therefore, to present the chemical, and also to
some extent, the physical principles of methods for making small particles of
various materials, especially metal oxides, and to describe the particle surface and
methods for modifying it. We also want to demonstrate how small particle
technology can be used in various technical applications and how to make
technically important materials.
VII
VIII PREFACE
In particular, we want to bring out the possibility of tailoring materials to
meet special needs and standards of performance that small particles technology
offers. Pigments, for instance, are small particles whose performance depends on
their size and shape. In many cases pigments are made by grinding or milling
coarser particles to a finer size-procedures that do not guarantee uniformity of
particle size or shape.
Ceramics are made of small particles that also have been obtained by
grinding coarser particles. The high performance of ceramics, especially high
tech ceramics in demanding applications, depends critically on the quality of the
small particles, e.g., their size and shape, that make up the starting material.
Small particles with carefully controlled size, shape, and surface characteristics
can be made by the methods of small particles technology as described in this
book.
Thus we have devoted attention to descriptions of typical preparation
methods for the most important types of small particles. As it turns out, particles
in the colloidal range of, say, 10 to 1000 nm, are not easy to handle in the dry
state and in many cases are not easy to prepare in the dry state, so that in this
book the emphasis is on preparations in the wet state, which frequently is a
convenient state in which to ship and use the product, for instance, pigments.
The majority of important heterogeneous catalysts have a porous structure,
the surface of which is either catalytically active or has been made so by
depositing catalytically active substances on it. Small particles, 5-1000 nm, in
different packing configurations, make up the structure. Catalytically active
materials, e.g., noble metals, deposited on the porous structure are present in the
form of very small particles, 1-10 nm. We believe that if one can make small
particles of various materials, e.g., zeolites, silica, alumina, titania, zirconia, and
other metal oxides, in different sizes and shapes, and can chemically modify the
surface of such particles, one has an excellent tool for developing not only new
and improved catalysts, but also porous materials for other technically important
applications.
In this book we have sought to examine small particles technology by
dividing the topic into a consideration of the principal types of materials of
importance to industry. Thus, in the first part of this book, silica in its various
forms, alumina and other metal oxides, carbon, and various metals in finely
divided forms, are considered with regard to their special properties and types,
after which, in the second part, applications in specific industries such as
papermaking are considered.
In so doing, of course, we inevitably neglect some materials and
applications that may well deserve more consideration were it practical to double
the book's size. As with all such choices, the experiences, knowledge, and
interests of the authors are key factors in determining what is included. On the
other hand, we believe that many of the methods and techniques described in
particular applications can be generalized to include neglected or new uses.
Although some more basic, theoretical material is used, we have not sought
to make this a partial text in surface chemistry and physics, for there are many
PREFACE IX
excellent texts available to fill that need. We will mention Adamson: Physical
Chemistry of Surfaces (1983); Fridrikhsberg: A Course in Colloid Chemistry
(1986); Prutton: Introduction to Surface Physics (1994); Hiemenz: Principles oj
Colloid and Surface Chemistry (1977); and Evans and Wennerstrom: The
Colloidal Domain (1994).
Special mention should also be made of the two books by Ralph Iler on the
chemistry of silica: The Chemistry of Silica (1979), The Colloid Chemistry of
Silica and Silicates (1955), and the book by Brinker and Scherer: Sol-Gel Science
(1990).
In his earlier book Iler assembled and correlated information on the
behavior of silica and silicates in the colloidal state so as to present a coherent
picture of such phenomena as solubility, formation, and behavior of colloidal
particles of silica and surface chemistry of the solid phase.
In Her's second book (1979), which he first intended to be an updated
edition of his first book but which became the definitive book on silica chemistry,
he presented a complete and coherent account of the chemistry of amorphous
silica, including soluble silica and silicate precursors of soluble silica,
polymerization of poly silicic acids, colloidal sols and gels, and the surface
chemistry of silica.
In the last three areas there is some overlap among Ralph Iler's two books
and our book, but we have reviewed, condensed, and updated material in those
areas, and also included results of our own work. Furthermore, we describe
fewer technical applications, but cover each application in considerably more
depth and detail.
In their book Sol-Gel Science, Brinker and Scherer state that their goal is
to present the physical and chemical principles of the sol-gel process in a manner
suitable for graduate students and practitioners in that field. They define sol-gel
rather broadly as the preparation of ceramic materials by preparation of a sol,
gelation of the sol, and removal of the solvent. The sol may be produced from
inorganic or organic precursors and may consist of dense oxide particles or
polymeric clusters. Their emphasis is on the science rather than the technology.
There is some overlap between Brinker and Scherer's book and this book's
Chapter 3 dealing with hydrolysis of metal ions, but we have tried to minimize it.
In addition to stating what this book is about, perhaps it is worthwhile
stating some of the topics which are not included, despite their obvious
importance. We have not included biomedical, safety, toxicological, natural
phenomena, and environmental aspects of fine particles except in passing mention
for three main reasons: 1) we interpret the word "technology" in the title to mean
industrial technology aimed at creating small particles, and using them in
industrial processes; 2) each of these topics is highly specialized and very diverse
with a profuse literature of its own, generally outside areas where we can claim
much experience; 3) we have restricted ourselves to solid particles, because
aerosols with liquid droplets are an essentially different field.
Conventional photography too, in terms of both its enormous commercial
and general significance, has its roots in small particles technology, but we
x
PREFACE
consider it to be too specialized, beyond fundamental considerations treated in
several chapters here, to be able to do justice to it.
This is not to say that there are not areas of common interest and overlap.
In many applications of small particles one may be concerned with the behavior
of such particles in settling, or in other transport modes, i.e., the mechanics of
small particles. That subject is a much studied area of vast importance in
atmospheric science and biomedical applications, but it already has been very
thoroughly covered in the literature, most especially in a survey by the Russian
scientist, N. A. Fuchs, in a classic work, The Mechanics of Aerosols (1989).
Chemical engineers have long been interested in the transport properties of
gases and liquids in pores such as those found in solid catalysts and have
developed a very wide literature covering both the theoretical and experimental
sides of that topic. Those areas too we neglect here as being too tangential.
Currently, with the impressive number of new analytical tools for
exploring surfaces, considerable progress is being made in understanding the
details of processes such as catalysis occurring at solid surfaces. Here we have
occasionally made brief mention of some results based on these modem methods,
but again the constraints of space make it necessary for interested readers to look
at some of the references for more details.
It is the future of small particles technology that we find the most
intriguing. Exciting developments abound. For example, nanotechnology-the
creation of devices on the super-microscale-is rapidly emerging as an area with
enormous implications in medical science, computers, communications, and
control devices, to name but a few possibilities. Small particles technology must
inevitably play a role in the materials used and as a limitation of the sort already
accepted in microchip computer manufacturing, where miniaturization depends
on controlling the size of small particle contamination. Other new areas, e.g., in
catalysts and zeolites, are mentioned throughout this book.
As Kingery pointed out, high-tech ceramics have an enormous leverage
derived from their criticality to the effective functioning of a whole range of
devices to which our world's culture is dedicated. "Companies or nations that do
not remain at the forefront of ceramic developments will find it impossible to
remain at the forefront of the device developments that will playa dominant role
in the future of our materials culture. "-Kingery (1988). As we show in Chapter
10, high-tech ceramics are an integral part of small particles technology.
We believe that our approach to small particles technology has some unique
features and hope that this book will stimulate further interest in the field and
will contribute to the understanding of properties of materials and the
development of new materials needed to enhance the quality of our lives in
maintaining a high standard of living while protecting our environment.
Jan-Erik Otterstedt, Bohus, Sweden
Dale Brandreth, Hockessin, Delaware, USA
PREFACE XI
References
Adamson, A., Physical Chemistry of SUlfaces, 4th ed., John Wiley, NY
(1983).
Brinker, C. J., and Scherer, G. W.: Sol-Gel Science, Academic Press, NY (1990).
Evans, D. F., and Wennerstrom, H.: The Colloidal Domain, VCH, NY
(1994).
Fridrikhsberg, D. A., A Course in Colloid Chemistry, Mir Publishers, Moscow
(1986).
Fuchs, N. A., The Mechanics of Aerosols, Dover Publications, NY, (1989).
Hiemenz, P. c., Principles of Colloid and Surface Chemistry, Marcel
Dekker, NY (1977).
Iler, R. K., The Colloid Chemistry of Silica and Silicates, Cornell University
Press, NY (1955).
Iler, R. K., The Chemistry of Silica, John Wiley, NY (1979).
Kingery, W. D., The Materials Revolution, ed. T. Forester, The MIT Press,
Cambridge, 315 (1988)
Prutton, M.,Introduction to Surface Physics, Oxford University Press,
(1994).
Acknowledgment
The authors acknowledge their indebtedness to the many people who made
the publication of this book possible.
We appreciate the helpful discussions with Dr. Horacio Bergna, Dr.
William O. Roberts, and Dr. Paul C. Yates, our former colleagues at E. I. Du
Pont & Company, and also with Dr. Randol Carroll and his staff at The PQ
Corporation in Valley Forge, PA. We are particularly grateful to Dr. John
Bugosh, who not only followed the progress of the book, but also provided the
information on hydrolysis and formation of fibrous particles of alumina in
Chapter 3.
The contributions from the work of IngMari Axelsson, Lars Eriksson,
Lennart Evaldsson, Borje Gevert, Peter Greenwood, Lars Lowendahl, Anders
Persson, Brian Schoeman, Magnus Skoglundh, Johan Sterte, Anders Torncrona,
Zhong-Shu Ying, and Yan-Min Zhu, former graduate students and associates of
one of the authors in the Department of Engineering Chemistry at Chalmers
University of Technology, have been crucial and are gratefully acknowledged.
Our very great appreciation goes to Mary Mattsson, who did many of the
drawings and performed many experiments on colloidal silica and silicates, the
results of which have heightened the value of important parts of the information
in this book.
We are in the greatest debt to Elisabeth Hawami, who patiently and
efficiently sent out, collected, and organized the several hundred copyright
permission requests. This book would not have been finished without the help and
support of Elisabeth.
We also gratefully acknowledge the help of Amelia McNamara, Mary
Curioli, Meri Zeltser, and their staffs at Plenum Publishing Corporation for their
help, patience, and forebearance in what has turned out to be a far greater task
than the authors ever could have envisioned.
XIII
