INTRODUCTION TO SOL-GEL PROCESSING THE KLUWER INTERNATIONAL SERIES in SOL-GEL PROCESSING: TECHNOLOGY AND APPLICATIONS Consulting Editor Lisa Klein Rutgers, the State University of New Jersey INTRODUCTION TO SOL-GEL PROCESSING by c. Alain Pierre Universite Claude-Bemard-Lyon 1 ~. " SPRINGER SCIENCE+BUSINESS MEDIA, LLC ISBN 978-0-7923-8121-1 ISBN 978-1-4615-5659-6 (eBook) DOl 10.1007/978-1-4615-5659-6 Library of Congress Cataloging-in-Publication Data A C.I.P. Catalogue record for this book is available from the Library of Congress. Copyright© 1998 by Springer Science+Business Media New York Originally published by Kluwer Academic Publishers in 1998 Softcover reprint of the hardcover 1st edition 1998 Second Printing 2002. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, mechanical, photo copying, recording, or otherwise, without the prior written permission of the publisher, Springer Science+B usiness Media, LLC Printed on acid-free paper. This printing is a digital duplication of the original edition. To Marie-Claude David and Valerie Kaolinite gel network. From K. Ma and A. Pierre -Unpublished photograph. TABLE OF CONTENT PREFACE ix 1 . GENERAL INTRODUCTION 1 l.l -Short history 1 1.2 -Sols, gels and gelation 2 1.3 -Outline of sol-gel processing 4 1.4 -Recent developments 6 1.5 -Advantages and limitations of sol-gel processing 6 1.6 -Organization of the book 8 1. 7 -References 8 2 ·THE CHEMISTRY OF PRECURSORS SOLUTIONS 11 2.1 -Introduction 11 2.2 - Solvents 12 2.3 -Basis of precursors transformations in solution 17 2.4 -Metal salts solutions 24 2.5 -A1koxides solutions 50 2.6 -Other precursors 70 2.7 -Precursors mixing 73 2.8 -Non-oxide solutions 80 2.9 -References 85 3 - COLLOIDAL PARTICLES AND SOLS 91 3.1 -Introduction 91 3.2 -Nucleation and growth of particles in a liquid medium 92 3.3 -Powders not synthesized in liquid medium 116 3.4 - Sols 119 3.5 -Other phenomena in sols 158 3.6 -References 163 4 • GELATION 169 4.1 -Introduction 169 4.2 -Gelation and percolation models 169 4.3 -Growth-gelation models 177 4.4 -Experimental study of gelation 186 4.5 -Gelation mechanisms of ceramic materials 190 4.6 -References 201 viii Table of Content 5 - GELS 205 5.1 -Introduction 205 5.2 -Structure and classification of gels 205 5.3 -Properties of wet gels 220 5.4 -Drying gels 234 5.5 -Properties of dry gels 244 5.6 -References 247 6 - NEW TYPES OF SOL-GEL DERIVED MATERIALS 251 6.1 -Introduction 251 6.2 -Hybrid organic inorganic materials 251 6.3 -Ordered mesoporous materials made with surfactants 258 6.4 -References 276 7 - PHASE TRANSFORMATIONS 279 7.1 -Introduction 279 7.2 -Chemical transformations at intermediate temperatures 279 7.3 -Topotactic crystallization 287 7.4 -Glass formation 293 7.5 -Crystallization by nucleation and growth 299 7.6 -Conversion of oxides to non-oxides 303 7.7 -References 305 8 - SINTERING SOL-GEL CERAMICS 309 8.1 -Introduction 309 8.2 -Possible texture evolution 310 8.3 -Atomic transport mechanisms operating during sintering 318 8.4 -Grain growth 325 8.5 -Interaction of pores with the sintering process 328 8.6 -Hot-pressing 342 8.7 -References 344 9 - APPLICATIONS OF SOL-GEL PROCESSING 347 9.1 -Introduction 347 9.2 -Applications in the sol or in the gel state 347 9.3 -Coatings and thin films 349 9.4 -Fibers 355 9.5 -Monoliths 357 9.6 -Filtration membranes 362 9.7 -Sol-gel catalysts 369 9.8 -Applications of hybrid organic inorganic materials 378 9.9 -References 380 APPENDIX 387 PREFACE BACKGROUND Sol-gel processing has been known for a long time; the first silica gels were made in 1845 by M. Ebelmen at the "Manufacture de Ceramiques de Sevres" in France. However this processing technique has known a very important development during the last two decades. Several series of international conferences have addressed this theme, in particular: "International Workshops on Glasses and Ceramics from Gels" and conferences on "Better Ceramics Through Chemistry", "Ultrastructure Processing of Ceramics, Glasses and Composites", "Sol-Gel Optics", "Hybrid Organic-Inorganic Materials", "Aerogels". This list does not include many specialized sessions in international conferences devoted to materials. Sol-gel processes have brought a new view in the domain of glass and ceramics fabrication and they have enlightened the importance of chemistry along the complete fabrication lines of materials, from initial chemical precursors to the final products. The basic idea is to progressively create an oxide network by polymerization reactions of chemical precursors dissolved in a liquid medium The importance of sol-gel processing and its complexity is such that it deserves books and excellent ones, in particular on "Sol-Gel Technology for Thin Films, Fibers, Preforms, Electronics and Specialty Shapes", edited by 1. Klein (Noyes, Park Ridge, N.Y.,1985) and on "Sol-Gel Science. The Physics and Chemistry of Sol-Gel Processes" by C.1. Brinker and G.W. Scherer (Academic Press, N.Y.,1990), have appeared. The latter book definitely constitutes an outstanding and complete reference on the subject which researchers are advised to consult first. Certainly, new informations on sol-gel have been discovered since its publication. However, the aim of the present book is different. SCOPE The subject needs now to be taught in universities, in courses on inorganic chemistry, surface science and ceramics processing or combinations of them and books less extensive on research developments than those quoted and more concise on the main basic theories, are needed. The present volume is an attempt in this direction. It is the exact content of lectures which were progressively developed and taught, both at undergraduate and graduate levels, first at the University of Bordeaux in 1987 in France. then at the University of Alberta in Edmonton. Canada and since 1995 at the University of Lyon in France. A first shorter version was published in 1992 in French by the printing company Septima. in Paris. x Preface The book is organized in such a way that each chapter actually corresponds to one of the main chronological order steps involved in sol-gel processing. The detailed developments in many sections are a consequence of the input of students. Other clarifications are certainly needed, as new ones appear necessary each year during the course of a teaching session and I would like to apologize for this to the readers. I will be very grateful to all users of this book if they could communicate their remarks and suggestions for further possible versions dedicated to teaching. ACKNOWLEDGMENTS This book would not have been written without the strong initial encouragement of my colleagues at the University of Bordeaux: J. Etoumeau, M. Onillon, J. Portier and B. Tanguy. I would like to sincerely thanks them, as well those who helped me at some stage, in particular E. Matijevic of Clarkson University, S. Sakka from the University of Kyoto and mainly J. Livage of the University of Paris-VI. I would like especially to express my deep gratitude to L. Klein, Professor at Rutgers University, for her support and reviewing a first draft of the manuscript. This book would not have existed without her help. The technical support of the Kluwer printing company was very helpful and I am very pleased to acknowledge their help. Challenging discussions with many students over quite a few years led to drastically modify the content of many sections. This book is in part their fruit, indirectly, and I am very thankful to them. One of the main contributors, on all the chemical aspects of sol-gel, was my own daughter Valerie, student in engineering chemistry at the French "Grande Ecole" "Chimie , Physique, Electronique", of the University of Lyon-I; I am very much indebted to her.