Table Of ContentStudies in Inorganic Chemistry
Other titles in this series
1. Phosphine, Arsine and Stibine Complexes of the Transition Elements
by C.A. McAuliffe and W. Levason
2. Phosphorus: An Outline of its Chemistry, Biochemistry and Technology (Second Edition)
byD.E.C.Corbridge
3. Solid State Chemistry 1982
edited by R. Metselaar, H.J.M. Heijligers and J. Schoonman
4. Gas Hydrates
by E. Berecz and M. Balla-Achs
5. Sulfur: Its Significance for Chemistry, for the Geo-, Bio-, and Cosmosphere and
Technology
edited by A. Müllerand Β. Krebs
6. Phosphorus: An Outline of its Chemistry, Biochemistry and Technology (Third Edition)
byD.E.C.Corbridge
7. Inorganic High Pressure Chemistry: Kinetics and Mechanisms
edited by R. van Eldik
8. Graphite Fluorides
by N. Watanabe, T. Nakajima and H. Touhara
9. Selected Topics in High Temperature Chemistry: Defect Chemistry of Solids
edited by 0. Johannesen and A.G. Andersen
10. Phosphorus: An Outline of its Chemistry, Biochemistry and Technology (Fourth Edition)
byD.E.C.Corbridge
11. Chemistry of the Platinum Group Metals
edited by F.R. Hartley
12. Luminescence and the Solid State
byR.C. Ropp
13. Transition Metal Nuclear Magnetic Resonance
edited by P.S. Pregosin
14. Chemistry of Inorganic Ring Systems
edited byR.Steudel
Studies in Inorganic Chemistry 15
Inorganic Polymeric Glasses
R.C. Ropp
138 Mountain Avenue, Warren, Ν J 07059-5260, U.S.A.
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Amsterdam — London — New York — Tokyo 1992
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ν
PREFACE
This manuscript describes experimental work accomplished over the past
twenty years which has led to a new method of preparing hydrolysis-stable
non-silicate glasses. It elucidates the rules of preparation required to produce
such molecularly-polymerized glasses from carefully prepared inorganic
molecular monomers. This domain has not been known or described
heretofore. Essentially, only silicate-based glasses have been known to be
stable, whereas non-silicate glasses of the prior art have not been believed
able to possess such properties. For example, earlier work had only achieved
phosphate glasses that dissolved in boiling water within a few hours. Hence,
such glasses have not found widespread usage in industry. The new phosphate
glasses described herein exhibit stabilities better than many of the silicate
glasses. For example, the nuclear-waste glass exhibits absolutely no
measurable loss in boiling water, something entirely foreign to the zinc
borosilicate glasses developed for nuclear waste encapsulation here in the
U.S. by Battelle-Northwest. Even the other silicate version being used in
France for encapsulation of high level nuclear waste cannot compare.
The exceptional stability of these new glasses is achieved by selecting an
inorganic compound capable of being polymerized, and then causing it to
polymerize in a proper manner, in the absence of "chain-stoppers". It will
become apparent that, to obtain glasses equal or superior in hydrolysis
stability to silicate-based systems, one must employ molecular polymerization
in situ, starting from carefully prepared precursors of exact stoichiometric
proportion. Only when this approach is used does one obtain stable non-
silicate glasses.
I have enjoyed preparing this manuscript and hope that you will find reading
it both profitable and enjoyable.
Dr. R.C. Ropp - December, 1991
vii
This work is dedicated to my wife Francisca
Margarita, who has staunchly supported my efforts
and me during these past 39 years.
xiii
IMTIRODÜCTIIOM
The history of glassmaking extends as far back as 7000 years in antiquity.
When we think of glass, we usually mean silicate-based glass - that is, glass
made from sand (S1O2) and other ingredients. To make glass, man has
learned to mix sand, limestone and soda-ash, heat the mixture to form a melt,
and then to cast the melt into a mold to form a glass article. Although non-
silicate glasses have been known for many years, none have been observed to
exhibit hydrolytic stability in boiling water even close to that of silicate-based
glasses. In some cases, the non-silicate glass article was found to become
completely dissolved in hot water in just a few hours. Yet, the method of
mixing oxides together to form the melt, to form the glass, has persisted
throughout the history of glass-making.
The stability of silicate-based glass undoubtedly lies in the fact that the
structural basis of silicate-glass is predicated upon a random three-
4
dimensional network of S1O4 - tetrahedra. However, it is equally apparent that
3
non-silicate glass-formers, such as PO4 - , cannot form a three-dimensional
network, but only a two-dimensional chain. Yet, the methods of preparing
such glasses have continued to follow those rules set up for preparing "glass",
ie- silicate-based glass. It will be come clear from this manuscript that the
rules of formation for non-silicate glass compositions differ considerably from
those determined most efficacious for silicate-based glasses. Nevertheless, all
prior glass investigators and experts, when preparing non-silicate based
glasses, have continued to follow rules determined most effective for making
silicate glasses.
In this monograph, I have set forth the rules and requirements for preparing
stable non-silicate glass compositions, which are not attacked by the
hydrolytic action of boiling water.
Essentially, one starts with a molecular compound capable of being
polymerized and holds the melt for a time sufficient to complete the
polymerization process, so as to produce chain-lengths capable of
withstanding hydrolytic erosion. When this is done properly, one obtains a
stable glass, capable of withstanding the hydrolytic action of boiling water for
xiv
extended periods of time. Additionally, such a glass does not exhibit internal
diffusion mechanisms, because of its polymeric character.
These effects are elucidated within the manuscript and methods of avoidance
of specific pitfalls, to obtain inorganic glasses having hydrolytic stability to
boiling water better than many silicate-based glasses, are described in detail.
Although polymerized phosphates are used as examples for the most part, the
rules and descriptions given are applicable to all other non-silicate glass
compositions as well. These include: borates, sulfates, germanates and other
glasses of molecular proportion.
Chapter 1 gives a short history of glass-making. Chapter 2 presents a short
description of prior work on phosphate-based glasses while Chapter 3
elucidates the experimental work leading to a description of the "Rules for
Preparing Stable Non-Silicate Based Glasses". In Chapter 4, we investigate
some of the properties of polymeric phosphate glasses, including some
anomalous results. These embody the impurity phase-segregation factor,
effects of polymerization on glass points, multiple-expansion coefficients,
"heat of softening", anomalous strain-relief and recrystallization effects, and
methods required to obtain optical-quality glass. In Chapter 5, some of the
potential uses for phosphate-based polymeric glasses are outlined, including
that of a high-level radioactive waste encapsulation glass which exhibits
absolutely no losses due to hydrolytic etching when held in boiling water for
96 hours.
1
CHAPTER 1
INTRODUCTION TO SILICATE GLASS TECHNOLOGY
1.1 GLASS AND ANTIQUITY
GLASS is one of man's most useful and versatile materials. It is also one of
the oldest. Obsidian, a glass formed by volcanic action, had widespread usage
during the Stone Age because it was easily flaked to form sharp cutting edges
for arrowheads, spearheads, knives and the like. Its use has been documented
in East Africa as early as 150,000 years ago and it was used at least to the end
of the Stone Age in the New World, about 1500 years ago. Indeed, obsidian
has been known as the "Dating Stone" (1) because of the ease to which it
lends itself in age determination. Wherever prehistoric peoples and volcanic
glass occurred together in nature, humans made use of this natural product as
a raw material for manufacture of tools. This has become evident from the
widespread discovery of detritus, in the form of worked- fragments and
shards, found in the vicinity of present- day deposits of eruptive rocks in
many parts of the world.
Obsidian varies in appearance from nearly clear colorless to pinkish or even
gray-green, brown, red, and black. Its usefulness as a tool- making material
derives from the ease with which it furnishes the sharp edges required for
cutting or scraping. Obsidian is readily flaked by percussion and pressure
methods similar to those used for working flint. However, the edges
produced are much sharper than any other material, except perhaps that of
worked metals.
The obsidian dating method depends upon the fact that, while the glass
originally formed contains about 0.1 to 0.3% water by weight, water from the
atmosphere continues to slowly diffuse into the body of the glass over a long
period of time. Obsidian itself is a complex silicate containing about twelve
major components, including silica. Depth of penetration of the water is a
measure of how long it has been since the surface of obsidian was created, or
2
when the stone was last chipped or cracked. If one removes an edge of glass
from a given obsidian artifact and views it under magnification in polarized
light, the edge that has been penetrated by water has a higher refractive
index than that of the pristine glass. This allows one to observe an interface
between the hydrated part and the non-hydrated part, seen in the
microscope as a thin line. The uptake of water also changes the volume of the
affected glass, and causes a mechanical strain which renders it visible as a
bright band under polarized light due to an effect called strain- birefringence.
The thickness of the rind may vary from 1.0 micron (0.00004 inches) to
more than 50 microns. Dates have been established as far back as 200,000
years, and have been authenticated, in many cases, by radioactive Krypton/
Argon studies. It is thus clear that man (Homo Sapiens) has used natural glass
from dates close to that of his origination.
Perhaps the earliest known artificial glass is the glaze found on stone beads
of the Barbarian Age (12,000 B.C.). The oldest known articles made
completely from glass have been dated to about 7000 B.C. There is a tale that
glass manufacture was discovered in antiquity by sailors who were
transporting large blocks of soda-ash to a distant port. They happened to land
on a beach and used the blocks as a wind- screen for a bonfire. The heat of
the fire caused the combination of sand and soda-ash to form a melt. This,
when cooled, produced a hard product similar to obsidian. Thus, artificial
glassmaking was born.
"Modern" glassmaking began in Egypt about 3500 years ago. This took the
form of fibers, flattened plates, dishes and utensils, and bottles of varied
shapes. Glass fibers were used as early as 1500 B.C. after the discovery that
glass could be drawn into fine filaments from a melt. It was also discovered
that additions of manganese, nickel, cobalt, copper, iron, and chromium
could be used to produce "colored" glasses. In the Egyptian XVIIIth Dynasty,
glassmakers created small vases for cosmetics by attaching either a small clay
form or a bag filled with sand to a stick. Rotating this form in molten glass
resulted in a small vase of the desired shape. Coarse fibers of colored glass
were then heated and pressed into the external walls of the vessel to make
decorative patterns. Similar decoration, using colored glass fibers, was used
in the Rhineland of Middle Europe during the Roman Empire to make glass
dishes, cups and bottles, i.e.- up until about 100 A.D.
3
However, the production of "flat" glass posed a seemingly insurmountable
obstacle for nearly 2000 years. Somewhere around 200 A.D., the invention of
the glass-blowing pipe in Syria permitted glassmakers to produce a
forerunner of flat glass. Glass was blown into a large cylindrical shape, then
cut and either "spun" or ironed flat before it hardened. The first colorless
glass had been made about 100 years earlier by adding manganous oxide to
the melt. Although attempts to manufacture acceptable flat glass went on for
centuries, it was not until the 1600's that the first plate glass was produced in
France by cutting and grinding. Until the late eighteenth century, flat glass
was an expensive handmade luxury. Crown spinning, that is- formation of a
blown bulb of hot glass which was cut and then spun to form a flat disc of
glass, was the predominant method of making flat glass in this era. And it is
only in recent times that man has learned how to make plate glass by a "float"
method. This will be described in more detail below.
During the past 3000 years, man has learned how to make controlled melts of
glass. Glass technology has advanced slowly, with more progress in the past
80 years than in all the preceding years that glassmaking had existed. This
process began in the 1800's with the Industrial Revolution and the
establishment of scientific research in Industry. Systematic studies of many
thousands of compositions, the development of special manufacturing
techniques, and the discovery of processes for attaining new and unusual
properties, forms, and uses, have made glass an extremely versatile material.
At present, about 700 different glass compositions are in use which have been
fabricated into tens of thousands of different articles for varied uses.
Noteworthy among these modern developments are:
1. Air tempering to improve strength (some standard- temper products
are strong enough to withstand severe abuse such as use as a hammer to
drive nails).
2. Chemical tempering has produced glasses with strengths of more
than 100,000 psi. in tensile strength.
3. Photosensitive glasses which reversibly darken and fade in
response to light intensity exposure.
