Table Of ContentFundamental
Phenomena
in the
Materials Sciences
Volume 3
Surface Phenomena
Fundamental
Phenomena
in the
Materials Sciences
Volume 3
Surface Phenomena
Proceedings of the Third Symposium on
Fundamental Phenomena
in the Materials Sciences
Held January 25-26, 1965, at Boston, Mass.
Edited by
L. J. Bonis
Ilikon Corporation
Natick, Massachusetts
P. L. de Bruyn
Department of Metallurgy
Massachusetts Institute of Technology
Cambridge, Massachusetts
and
J. J. Duga
Battelle Memorial Institute
Columbus, Ohio
9:>
PLENUM PRESS· NEW YORK ·1966
ISBN 978-1-4684-8708-4 ISBN 978-1-4684-8706-0 (eBook)
DOl 10.1007/978-1-4684-8706-0
Library of Congress Catalog Card No. 64-20752
© 1966 Plenum Press
Softcover reprint oft he hardcover 1s t edition 1966
A Division of Plenum Publishing Corporation
227 West 17 Street, New York, N. Y. 10011
All rights reserved
No part of this publication may be reproduced in any
form without written permission from the publisher
Foreword
This volume explores in detail the four interrelated branches of the
study of surface phenomena-surface thermodynamics, nucleation,
diffusion, and fine-particles technology-providing an unusual and
comprehensive body of knowledge that will be of interest and practical
value to both materials researchers and practising engineers.
The growing awareness-since the advent of the space age-among
solid-state physicists, metallurgists, ceramists, chemical engineers, and
mechanical engineers of the need for a broad interdisciplinary under
standing of the fundamental phenomena common to all matedals has
led in recent years to the development of a new field of scientific
investigation, Materials Science. To help promote interest in and con
tributions to this new technology, annual symposia on "Fundamental
Phenomena in the Materials Sciences" have been organized by the Ilikon
Corporation. The first symposium, reported in Volume 1 of this series,
was held in Boston, Massachusetts, on February 1 and 2, 1963;
sintering and plastic deformation were the main topics of discussion.
The second meeting, also held in Boston, on January 27 and 28, 1964,
was exclusively concerned with the general interdisciplinary problems
related to surface phenomena, that is, all of those physical and chemical
areas that are pertinent to the surface of a solid, or to the interface
between a solid and a gas, a solid and a liquid, or a solid and a solid.
Ten noted researchers, from major universities and industrial organiza
tions, presented papers that dealt with the principles of surface physics
and surface chemistry. Surface phenomena were treated, therefore, in
a broad sense, with emphasis on structures, electronic configurations,
and properties of clean real surfaces, rather than on the generic bases
of specific material types.
Although unique and broadly rewarding, that second meeting
barely "scratched the surface" of what all the participants at the
meeting recognized to be a truly fundamental materials technology
subject. It was decided, therefore, to continue these surface phenomena
investigations at a third meeting. The papers presented at that
conference, held January 25 and 26, 1965, in Boston, together with
v
vi Foreword
the panel discussions as they occurred, are presented in this
volume.
In the first chapter, P. L. de Bruyn (Massachusetts Institute of Tech
nology) reviews Gibbs' classical thermodynamics treatment of surfaces
and interfaces,giving particular attention to Gibbs' concept of a dividing
surface. In this context of the classical thermodynamics equations, the
author proceeds in his discussion to point out that, in most thermo
dynamic treatments of multiphases, it is assumed that, when the main
interest is in the bulk properties, the surface may be completely ignored.
Next, he suggests that for the study of the interface between two juxta
posed contiguous phases it is convenient to introduce a mathematical
"dividing" surface, with respect to which all "excess" surface properties
may be defined. This dividing surface and the surface properties
defined by it, however, must take into account the fact that there is a
definite gradient in properties in the vicinity of any interface. Following
a discussion of the implications of this gradient, the author defines
and discusses surface tension, arguing that it is always directly propor
tional to the pressure differences across the interface boundary.
In the second chapter, E. W. Hart (General Electric Research
Laboratory) continues the consideration of surface tension by describing
the results of the application of the recently developed thermodynamic
theory for equilibrium in homogeneous systems to the problem of the
surface tension of the interface between two fluid phases. He states that
the results of the experimentation were inconsistent with earlier con
clusions regarding both the concept of surface tension and the existence
of minimum surface tension, proving rather that the surface tension
of a planar interface was given solely by the difference of two quantities
that are characteristic of the two homogeneous bulk phases.
The subject of nucleation is introduced in the third chapter by
K. C. Russell (Massachusetts Institute of Technology), who points
out that at the present time there is a I-to-7 order-of-magnitude
difference between the experimentally determined and the theoretically
predicted behavior of homogeneous nucleation and, furthermore, that
the best this situation can be improved is by about one order of magni
tude-unless more sophisticated techniques are employed. He describes
such techniques as those that would focus attention on those additional
energy and entropy characteristics that may be meaningful.
In the next chapter, J. P. Hirth and K. L. Moazed (Ohio State
University) describe different nucleation mechanisms related to deposi
tion onto substrates. They demonstrate how through a minimization
Foreword vii
of the free energy of formation it is possible to determine, in order,
the critical nucleus size above which crystal growth can be expected
to begin, the volume density of the critical-size nucleus, and the
observable nucleation rate. Following this enumeration, the authors
describe mechanisms that are dependent principally on the temperature
of the substrate. In this chapter they also discuss surface imperfections
and the phenomenon of epitaxy.
F. P. Price (General Electric Research Laboratory) discusses, in
the fifth chapter, the nucleation and growth of single-crystal organic
polymers, presenting evidence that classical nucleation theory applies
equally well to polymer crystals and low-molecular-weight materials.
He shows that the thermal history of organic solids controls the size
of crystalline spherulites and that for polychlorotrifluoroethylene there
is correlation between spherulite size and fatigue life.
In the sixth chapter, P. G. Shewmon (Carnegie Institute of
Technology) introduces the subject of surface diffusion by examining
the experimental techniques used to determine the surface diffusion
coefficient Ds . Then he argues that surface diffusion rather than volume
is the major factor in the process of fine powder sintering. He describes
recent computer studies in support of this minority opinion.
Consideration of the relation of surface diffusion to the sintering
process is continued in the seventh chapter, where C. E. Birchenall
and J. M. Williams (University of Delaware) express the view that any
consideration of surface diffusion must take into account the additional
factors of surface impurity size and distribution, crystalline anisotropies,
divacancy migration through the surface, the long mean free paths at
high temperatures, and the chemical effects that "pin" atoms to the
adsorbed species. They discuss these factors in some detail and then
proceed to comment on the sintering process itself, expressing the
opinion-contrary to the usual-that neck size is more important
than particle size.
In the eighth chapter, after commenting on the formation of surface
point defects on ionic crystals, authors C. Y. Li and J. M. Blakely
(Cornell University) question the legitimacy of utilizing the bulk
dielectric constant in the neighborhood of a surface, pointing out that
a correction in this constant would make it more difficult to create a
surface pair, for any such correction would result in an increase of
the polarization component of the removal energy.
In the discussion of surface-initiated failures in structural materials
presented in the ninth chapter, I. R. Kramer (Martin Company) points
viii Foreword
out that the surface of any material has a significant effect on the
mechanical behavior of the material and that, in fact, suitable changes
in the surface can result in the altering of all of the usual mechanical
properties of the material-tensile behavior, fatigue, creep, and stress
rupture.
Ultrafine particles in gases is the subject of the final chapter.
One of the principal suggestions in this broad, comprehensive discus
sion by J. Turkevich (Princeton University) is that the formation as
well as the texture of these particles are the result of a degree of
"memory" residing in an organized aggregate of the materials. Another
suggestion is that in the growth of these particles there are none of
the growth-promoting driving forces found in crystallites and that
these particles are so nearly perfect that the "growth sites" associated
with dislocations do not exist. In addition to these ideas, the author
describes in detail some of the problems associated with the formation
of these ultrafine particles.
Great efforts were put into trying to preserve the flavor of the
meeting in this book, examples of which are shown in the two sections
where selected discussions are presented.
It is not without pride that we view the ever-mounting interest
in these meetings, viewed not only from the number of people attending
(because of this, attendance is now limited to "by invitation only"),
but also from the high caliber of the participants.
L. J. Bonis
Contents
Some Aspects of Classical Surface Thermodynamics
P. L. de Bruyn, Massachusetts Institute of Technology.
Modern Theory of Fluid Surface Tension
Edward W. Hart, General Electric Research Laboratory. 37
Nucleation in Homogeneous Vapors
K. C. Russell, Massachusetts Institute of Technology. 43
Nucleation Processes in Deposition onto Substrates
J. P. Hirth and K. L. Moazed, Ohio State University. 63
Nucleation and Condensation in Polymer Systems
Fraser P. Price, General Electric Research Laboratory. 85
Panel Discussion: Session I. . . . . . . . . 105
Surface Self-Diffusion at High Temperatures
P. G. Shewmon, Carnegie Institute of Technology. 111
Self-Diffusion on Nearly Pure Metallic Surfaces
C. E. Birchenall and J. M. Williams, University of Delaware 133
Defects Near Ionic Crystal Surfaces
Che-Yu Li and J. M. Blakely, Cornell University. 153
Effect of Surfaces on Mechanical Behavior of Metals
1. R. Kramer, Martin Company. 171
Ultrafine Particles in the Gas Phase
John Turkevich, Princeton University. 195
Panel Discussion: Session II. 213
Index .......... . 223
ix
Some Aspects of
Classical Surface Thermodynamics
P. L. de Bruyn
Department of Metallurgy
Massachusetts Institute of Technology
Cambridge, Massachusetts
INTRODUCTION
The special contribution of matter lying in and around phase
boundaries to the total energy of heterogeneous systems is normally
ignored in thermodynamic treatises. This neglect implies that the
density of energy of a given phase remains uniform up to a mathematical
surface separating it from contiguous phases. However, because of the
finite, although short, range of action of atomic forces, the assumed
sharp phase boundaries should actually be replaced by an interphasal
region of finite thickness across which the density of energy or of any
other thermodynamic property changes much less abruptly. It is
reasonable to expect the normal thickness of this transition region
to be of the order of a few molecular diameters; unless the system has
a relatively high surface to volume ratio, as would be the case in
colloidal systems, the additional contribution of the "surface" atoms
to the total energy content may justifiably be ignored.
However, a solid or liquid surface, no matter how small in extent,
will be the seat of special physical and chemical phenomena because
those atoms or molecules which terminate the condensed phase are
subjected to unsymmetrical forces. Adsorption from the gaseous or
liquid phase onto solid surfaces, wetting and spreading of liquids on
solids, and capillarity are examples of industrially important surface
phenomena. Surfaces also play an important, although not dominant,
role in such physical and chemical processes as phase transformations,
nucleation and growth, electrode reactions, sintering, and electron
emission-to name but a few. The colloid chemist has long been
aware of the role of surfaces in colloidal phenomena because he has
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