Oxides and oxide films

BOOK REVIEWS Colloid Formation and Growth : A Chemical Kinetics Approach. By JULIA~ HErCKL~N. Academic Press, New York, 1976. 132 pp. $14.50. In this book the formation and growth of colloids are treated kinetically. This purely kinetic approach is of particular importance at the present time because of its implication in environmental sciences. Frequently kinetic factors are considerably more important than arguments based purely upon thermodynamics in determining the nature of the phases formed in many condensation reactions. The book has a strong mathematical flavor and will therefore be somewhat limited in its appeal to environmental scientists even at the aimed-for graduate level. However, in a number of cases approximate formulae are developed which are relatively easy to use. Thus simplified solutions are presented for procedures such as the calculation of the average speed at which molecules are removed at the wall in a steady state treatment, and the calculation of steady state supersaturations. Rigorous treatments are given for processes such as homogeneous and heterogeneous nucleation, condensation, vaporization, coagulation, and gravitational settling. Considerable attention is given to the evaluation of parameters for the calculation of rate coefficients and extensive numerical tables have been compiled to aid in the use of the formulae presented. These include the relative rates of volume and wall removal of particles during condensation reactions, gas kinetic collision rate coefficients as a function of particle radius, and steady state supersaturations. As is to be expected, this monograph focuses on the extensive studies which have been made by the author over the past several years. Although as a consequence it is somewhat limited in its coverage, it is authoritatively written in an easy and rather informal style. Its chapters, indeed, constitute a series of essays on first-order physical loss processes, bimolecular coalescence, the thermodynamics of vaporization and disintegration, homogeneous and heterogeneous nucleation, and accommodation coefficients. A major problem in treating nucleation and condensation processes is the appropriateness of using macroscopic physical quantities to describe the behavior of very small particles. A particularly interesting feature of this book is the special attention which it gives to deviations from the theory which occur with very small clusters, i.e., less than 30 molecules.

The book is well produced and illustrated, with few errors discernible to this reviewer. Although the mathematical treatments which are presented will necessarily restrict the appeal of this book, it will be of considerable value to those actively interested in the kinetics of particle formation and growth, and as a graduate course text. G. H. ~NTANCOLLAS Department of Ckeraistry State University of New York at Buffalo Buffalo, New York 14214 Oxides and Oxide Films, Volume III. Edited by JOHN W. DIGGLE AND ASRO~: K. VUm Marcel Dekker, New York, 1975. 333 pp. $33.50. This third volume in a series is dedicated to John Diggle, who died while the book was in preparation. I t contains two articles: "Space Charge Effects on Anodic Film Formation," by A. T. Fromhold, Jr., of Auburn University (271 pp.), and "Chemisorption Phenomena on Oxides: The Dependence of Chemisorption on the Microscopic Properties of Zinc Oxide," by Peter Mark and Shih-Chia Chang of Princeton University (41 pp.). Neither article bears any relation to the other. Fromhold writes in a clear, logical, and sequential manner. There are 104 figures and 17 tables presented either as aids in carrying the reader along or as computer-derived data from the equations developed. Four details are treated in appendixes. At appropriate places throughout the text, summary statements are given that describe the important consequences of the mathematical development. The final summary statement reads as follows: "Under constantpotential conditions, space charge severely retards the growth rate and gives rise to growth curves which have a marked limiting-thickness character." The basis for the mathematical equations developed is the concept of thermally activated h o p p i n g of charged particles over discrete energy barriers. The equations developed are utilized to calculate defect density, total charge from one boundary to a certain location in the film, electric field at different positions, and electrostatic potential at different positions, all at different total film thicknesses and different particle currents. Reasonable values are used for the defect density at metal/oxide and oxide/solution interfaces,

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Journal of Colloid and Interface Science, Vol. 59. No. 2, April 1977 ISSN 0021-9797

Copyright ~ 1977 by Academic Press. Inc. All rights of reproduction in any form reserved.

BOOK REVIEWS activation energy for diffusion, temperature, attempt frequency, lattice parameter, valence of diffusing species, and relative dielectric constant. Similar calculations are then made for anodic films on iron, 10, 20, 40, 80, and 160 monolayers thick, using the following set of parameters: defect density at iron/ oxide surface = 1012/cm2; defect density at oxide/ solution interface = 101°/cm2; activation energy for diffusion = 0.5 eV; 300°K; attempt frequency = 1013/ sec; lattice parameter = 3.2 A; valence of diffusing species = --2; relative dielectric constant = 6. Equations are developed for the rate of anodization when a large space charge is present in the film and numerical plots are presented for applied forces of 100, 200, 300, 400, and 500 volts. Extensive comparisons are made with the prior treatments of Verwey, Cabrera and Mott, and Dewald. The article by Mark and Chang is concerned with an understanding of the surface properties of ZnO as they relate to catalysis and electrophotography. The research utilized single-crystal material but the authors show a continuous awareness of the fact that the application of the results is to high-area ZnO. Information about the surface crystallography of ZnO is summarized and the evidence is strong that the nonpolar faces such as (1150) and (10i0) tend to approach the ideal structure, whereas the polar faces such as the (0001) and (0001) have a nonidealized structure. Chemisorption properties as a function of surface crystallography are determined by making LEED and AES studies, subjecting the sample to a corona discharge, followed by further studies of the surface structure and composition. Data are summarized on surfaces prepared by ion bombardment and annealing, chemical polishing, chemical etching, and cleavage. The major conclusion of the work is the following: "The relationship between chemisorptive activity and these microscopic surface properties is attributed to the fact that such features provide electrostatic potential energy, derived from the partial bonding ionicity of all oxide material, that can be responsible for a chemical shift of free-space adsorbate energy levels into energy ranges of the adsorbent band structure, where charge exchange between the adsorbent and the adsorbate is energetically possible." The article by Fromhold should become a classic, particularly if novel experimental tests of the equations can be developed. Some of the work summarized by Mark and Chang has been published, or will be published, in journals and ownership of the book for their article alone is less compelling. HENRY LEIDHEISER, JR. Center for Surface and Coatings Research Lehigh University, Bethlehem, Pennsylvania 18015

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Equilibrium in Solutions + Surface and Colloid Chemistry. A Commonweaith Fund Book. By GEORGE SCATCHARD. Harvard University Press, Cambridge, Mass., 1975. xxxv + 306 pp. $30.00. This single volume contains two previously unpublished works by the late George Scatchard, Professor of Physical Chemistry at the Massachusetts Institute of Technology for many years. They represent the notes used by the author for, respectively, his graduate course in the equilibrium thermodynamics of solutions and his senior level undergraduate course in surface and colloid chemistry. The typed manuscripts of both texts were corrected by the author prior to his death in 1973. I t also contains a sympathetic introduction by I. Herbert Scheinberg, presently a Professor of Medicine at Albert Einstein College of Medicine and one of the author's associates in the late 1940s; an autobiographical note including a commentary on all his published works; a complete chronological bibliography of his publications; and satisfactory indexes. The publication was enabled by a grant-in-aid from the Commonwealth Fund and its cooperative arrangement with the Harvard University Press. In the Introduction Professor Walter H. Stockmayer, one of the author's colleagues, is quoted concerning the reason for publishing these two distinctly historical items at this late date: "Publication of any text 20 years after its last revision implies that it is unique and in some measure timeless. These two Scatchard texts are judged to pass this test." Unique they certainly are in the sense that they represent the logical, compressed, somewhat dogmatic, and highly mathematical style characteristic of most of Scatchard's publications. They are timeless only in the sense that the basic principles of the fields covered are timeless. "Equilibrium in Solutions" covers ideal and speciesideal gases; physical models of real gases; gas mixtures; liquid mixtures, including measurement of their chemical potentials; and electrolyte solutions, including ion atmosphere and electrostatic potential, and their free energies and chemical potentials. The Appendix includes a list of symbols, the analytical expression of experimental results, a brief review of general thermodynamics, and the classification of molecules according to types of forces present in them. It is a treatise by a theoretician of the "desk calculator" era who did not often visit his laboratory. Thus, a great deal of his mathematical approach is that empirical type involving high-order curve fitting and series expansions. The relatively few references are given as footnotes. None of the extensive statistical mechanical developments of the past two decades are included. Even with these drawbacks, some workers in the field of solutions of electrolytes, including those of proteins, may find something of value

Journal of Colloid and Interface Science, Vol. 59, No. 2, April 1977