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New Routes to Multicomponent Oxide Glasses.

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ANGEWANDTE CHEMIE
International E d i t i ~ n
VOLUME 1 0 . NUMBER 6
J U N E 1971
PAGES 363-434
New Routes to Multicomponent Oxide Glasses
By Helmut Dislich“]
Multicomponent oxide glasses can be produced not only by melting methods but also by hydrolysis
and condensation of alkoxide complexes with several metals. This requires temperatures only
up to the transformation range of the glass in question, usually 500600°C. The process does
not pass through the molten phase. It is possible to obtain glasses or polycrystalline substances,
depending on the composition. The method is particularly suitable for the production of thin,
transparent multicomponent oxide layers of almost any composition on substrates. Some of these
layers provide protection against climatic attack or against oxidation.
1. Introduction
It is generally known, though rarely mentioned, that glass
is the oldest thermoplastic. There is no reason to think of
the materials and methods of organic chemistry in connection with glass, since the ASTM definition of glass is
“an inorganic product of fusion, which has cooled to a
solid state without crystallizing”[’].
The concept of the “vitreous state” will not be discussed
here. The wisdom of including a production process
(melting) in the definition seems questionable, since the
definition then depends on the state of the art at the time
of its formation. It results from the fact that for 4OOO years,
glass has been produced almost exclusively by melting,
and from the technical importance that is attached to the
further development of the melting process and of fused
glasses. However, unfused glasses are also known. MackenzieIZ1has compiled an annotated list of unconventional
routes leading to glass (Table I).
The simplest method is hydrolysis ; Schroeder[’I prepared
vitreous layers of individual and mixed oxides (SiO,, TiO,,
and others) by hydrolysis and polycondensation of metal
alkoxides. However, single-oxide glasses are special cases,
and if one wishes to carry out investigations and to obtain
information about glass in general, the methods used must
also be suitable for the preparation of complicated multicomponent glasses such as occur in industry.
[*] Dr. H. Dislich
Organisch-Chemisches Laboratorium des Jenaer Glaswerkes
Schott und Gen.
65 Main& Postfach 2480 (Germany)
Angew. Chem. internat. Edit. 1 Vol. 10 (1971) 1 No. 6
The first step in this direction was made by the use of at
least one hydrolyzable metal compound in the preparation
of a multicomponent glass; this allowed the use of a lower
Table 1. Unconventional routes to glass (after 121).
-
.
Glass production in solid state:
(a) Shock-wave treatment
(b) Neutron bombardment
Glass production from the vapor phase:
(a) Direct methods, e. g. evaporation of crystalline A1,0,
and deposition of a noncrystalline A1,0, film, recently
also simultaneous evaporation of several individual
oxides, which deposit as a glass film 131
(b) Indirect methods, e. g. vapor-phase hydrolysis of SiCI,
to SO,.
(c) Preparation of multicomponent glass films by the
“Chemical Vapor Deposition” process [4].
Glass production from solution :
(a) Oxide films produced anodically from aqueous electrolytes
(b) Hydrolysis of e. g. metal alkoxides
melting temperatureI6I. Roy’s “gel method‘”71 ultimately
also aims in this direction. In this method, silica sols and
metal carbonates, hydroxides, nitrates, etc. are combined
to form gels, from which glasses are obtained below the
liquidus temperature but above the transformation temperature. No details are known, but layers of multicomponent glasses will presumably not be obtainable in this
way.
Multicomponent glasses have not so far been obtained at
temperatures not exceeding the transformation point. This
seems a desirable achievement, for the following reasons.
363
1. It would no longer be possible to describe the glass
structure merely as the structure of a supercooled melt,
as has been common until now, since no temperature
ranges in which crystallization occurs at a measurable rate
are traversed during cooling. Since the properties of a glass
are known to depend on its past history, glasses with novel
“histories” would be available for investigation.
with which we shall be concerned, must be regarded as a
structural unit of an “inorganic polymer”.
2. The axiom “glass is a product of fusion” would be re-
The search for heat-resistant plastics led to attempts to
use the principle of the Si-0 framework of the silicates,
but instead of the tetrafunctional group ( l ) ,which leads
to highly crosslinked products, the groups (2)-(4), whose
functionality can be read off directly, were incorporated.
The resulting successes of siliconechemistry are well known.
placed by Mackenzie’s definitioncz1:“Glass is a noncrystalline solid”, or by Krebs’: “Glass in the wider sense can
be defined as a solid with dense packing of the atoms, in
which crystalline arrangements do not extend beyond a
few interatomic distances”.
On the whole, attempts to extend the structural principles
of silicate chemistry farther into organosilicon chemistry
by transition to heteroorganopolysiloxanes e. g. of the type
(6)“ ( M = e . g. B, Al, Ti, Sn, Pb, P, As[*])have so far been
technically less successful. The investigations, which are
3. Preparation below the transformation temperature
would provide at least a possibility of obtaining glasses
that cannot be obtained at higher temperatures because
of an excessively strong’tendency to crystallize.
I
k
Since hydrolytic methods are well suited to the production
of layers, it would be possible to apply coatings of multicomponent glasses to substrates that are stable up to the
transformation temperature of the glass to be applied. This
is only very rarely possible by other methods.
Nothing much can be said at present about points 1 and 3.
Points 2 and 4 are in the forefront at present, and particularly the route by which multicomponent oxide glasses
and also crystalline multicomponent oxides can be prepared. This is where organic chemistry plays its part, for it
provides this route. There is much here that is old, insofar
as the starting materials are hydrolyzablemetal compounds,
particularly metal alkoxides, which can be readily degraded
to the metal oxide. The novelty is the advantage that is
taken of the strong tendency of alkoxides of various elements to react with one another. These reactions lead to
“alkoxo salts”, which are often very complicated, and which
are then degraded by hydrolysis and polycondensation to
multicomponent oxide glasses and crystalline multicomponent oxides.
2. Position and Statement of Problem
Let me first recall the old silicate-silicone comparison (the
contents of the followinglines are based on W Noll’s book[*’).
The smaller the number of organic residues R in Figure 1,
the more pronounced is the silicate character of the corresponding polymers; the type (I), which is the only one
R-Si-0-
R
I
R-Si-R
R
R
(4)
(5)
?
1
I
Fig. 1. Scheme of the silicon compounds. ( I ) : Structural unit of the
silicate network; (2)-(4) : structural units of the silicone polymers;
(5) : “pure” organosilicon compound.
364
R
R
- Si-0- M - 0 -
R
I
I
Si- 0-M- O- Si - (6)
k
B
/
0
\
0
\
Fig. 2. Section of the structure of a multicomponent glass. Silicon forms
a fourth bond to oxygen in the third dimension.
intended to yield polymers that can be processed at low
temperatures, have not yet been completed. Such polymers
are not highly crosslinked; the functionality of the monomers is limited by the incorporation of groups R. Polymers
of this type often have more or less irregular compositions,
and this makes the “starting material/end product” correlation very
Silicate glasses are highly crosslinked, but are nevertheless
thermoplastics. Their thermoplasticity, unlike that of
organic polymers, is due to the rupture of principal valences
in the network as a result of thermal motion at high processing temperatures. The structural groups in silicate
glasses correspond to type ( I ) above in the case of silicon,
and to the analogous type having the highest functionality
in the case of the other metals. Figure 2 shows a section from
the structure of a multicomponent glass containing some
of these groups.
The simplest case is silica glass, which can be preparedL5’
from esters of silicic acid by hydrolysis and polycondensation, formally in accordance with
p]
Shown with bivalent M for simplicity.
Angew. Chem. internat. Edit. 1 Vol. 10 (1971) 1 N o . 6
3. During the hydrolysis, condensation reactions take place
with formation of polyorganoxymetaloxanes, some of
which are polymeric, e.g. (9) and (10).
though the reaction undoubtedly proceeds via polyorganoxysiloxanes, and not via Si(OH),.
In the practical application of this "structural unit principle" for the production of multicomponent glasses and
crystalline multicomponent oxides, the metal alkoxides
provide a good source of monomeric structural units with
maximum functionality. The maximum functionality is a
necessary (but not sufficient)condition, since all the organic
groups must be split off to obtain pure oxide systems. This
is trivial in the case of a single metal alkoxide. When many
metal alkoxides are present together, the followingquestions
are of interest :
1. Can a multicomponent glass be prepared by the hydrolysis and polycondensation methods commonly used in
organosilicon chemistry without going through the molten
phase?
M (OR), + H,O
M(OH)(OR),- +ROH
(9)
M(OH)(OR),_ + M(OR), + (RO),_ MOM(OR),- +ROH
(10)
2M(OH(OR),_
--t (RO),
MOM(OR), - + H 2 0
(10)
+
The end product of the hydrolysis, after elimination of water
from OH groups by heating, is the metal oxide, which may
be regarded as a macromolecule built up from three-dimer.sionally linked metaloxane chains -M-0-M-0-.
Other reactions that sometimes complicate the situation,
but do not fundamentally change it, can be indicated briefly
by some typical examples (Fig. 3).
>B - O H
+ RO-Sit
>B -OH + H O - S i z
+ HO-Sif
>Al-OR
+
-
>B -0-Sig + R O H
-+
>Al-0-Sif
>B - 0 - S i c + H,O
+
ROH
2. Can crystalline multicomponent oxides be prepared in
the same way from the reactive metal alkoxides?
The first efforts were concerned with known multicomponent glasses and crystalline multicomponent oxides. This
has the advantage over the heteroorganopolysiloxanes (6)
that the end products can also be obtained by another
route, e. g. by melting, and it is therefore possible to compare
the properties of the products obtained by the known
method and by the new route.
.\
+ 3 ROH
3. Some Known Reactions of Metal Alkoxides
Fig. 3. Examples of crosslinking by metaloxane formation.
Metal alkoxides have been known for a long time, and
have been studied intensively and systematically during
the last twenty years, particularly by Bradley[''. ' I and
Mehrotra1lZ1,who cite hundreds of original articles in their
reviews["- '*I. Reference should also be made to"31.
These reactions of the metal alkoxides are particularly
important to the following discussion :
1. Many metal alkoxides react readily with one another
to form complex metal alkoxides, the "alkoxo salts". The
stability of these salts increases with the difference in the
electrochemical characters of the two metals. The complexes may be heteropolar, e. g. (7), or homopolar, e. g. (8).
Al(OR),
+ KOR
+
4. Preparation of Crystalline Multicomponent Oxides
Though we are interested mainly in glasses, we shall first
consider the crystalline multicomponent oxides, since the
reaction is much more straightforward, particularly in the
case of spinel, which has only two components. The preparations are carried out in a temperature range in which
the above reactions take place, i.e. up to about 500°C.
Reactions that take place in the melt, i. e. at much higher
temperatures, do not occur.
[Al(OR)d] K
4.1. Preparation of Magnesium-Aluminum Spinel
( 7)
Magnesium methoxide is allowed to react with aluminum
sec-butoxide in a molar ratio of 1:2 in alcohol. The magnesium aluminum alkoxide (11) is formed in solution [eq.
2 Al(OR),
+ Mg(OR),
( 1 ) y31.
+
OR
2. All metal alkoxides can be more or less readily hydrolyzed, as illustrated earlier for Si(OR),.
Angew. Chem. internal. Edit. / Vol. I0 (1971)
/ No. 6
( I ] ) , R = CH,. R' = CH(CH,),
365
The choice of the organic residues is a matter of purely
practical importance, since they are removed later in any
case.
Hard, glass-clear spinel layers can also be applied to
substrates by the method described in Section 7 (dipping
method).
On evaporation of the solvent in the presence of atmospheric moisture, hydrolysis occurs [eq. (2)].
5. Scope of the Method
Mg[Al(OR)(OR')3],
+ 8 HzO +
(11)
Mg[Al(OH),12+2ROH+2 R'OH
(2)
The resulting lumps of gel are then heated to 620°C to
induce the condensation, which undoubtedly also takes
place in part even at room temperature [eq. (3)].
(3)
4.2. Identification of the Magnesium-Aluminum Spinel
The small, hard, white lumps obtained were identified by
X-ray diffraction analysis as spinel (crystallite size 100 A).
The principal reflections of spinel appear (though they are
very broad) on heating at 250°C, and become more pronounced on heating at 400°C. The lattice constant at 20°C
is 8.084 A (literature value 8.080 A).
The product prepared by the alkoxide method at 620°C
absorbs water from the air on prolonged standing; this
water can be rapidly removed by reheating to 620°C. A
product heated to 1150°C no longer exhibits this water
absorption. The X-ray diffraction diagram also becomes
sharper. The crystallite size is then about 950 A. The polycrystalline material contains MgO and A1,0, in a ratio
of 1:1.08.
The spinel is thus formed at temperatures far below those
normally used for such syntheses. Whereas Mg and A1
alkoxides react with one another even at room temperature,
high temperatures are necessary for the normal reaction of
salts or oxides. We allowed Mg(NO,),. 6 H,O to react with
NH,Al(SO,),. 12 H,O, and found that spinel formation
started only above 850°C. According to Hiittig et uL."~],
the formation of the zinc-aluminum spinel also begins at
850°C, while the material consists entirely of spinel only
at 1150°C.
Bratton" uses lower temperatures.Al(OH), and Mg(OH),
are precipitated together at 100°C. Spinel is formed when
the precipitate is heated at 350-400"C (Fig. 4).
1.
[(Mg-A1) double-Hydroxide + Gibbsite]
1
1
Fig. 4. Preparationof spinel according to Bratton [15]. 1: Simultaneous
precipitation (100°C); 2: possible intermediate stage ( 3 5 U 0 0 ' C ) ;
3: crystallization of spinel (> 400°C).
The route oia the alkoxides seems more direct; no crystalline phases other than spinel are formed even at low
temperatures.
366
The formation of the spinel evidently depends on the prior
reaction of the components in accordance with eq. (I), so
that a sort of cocondensation occurs after hydrolysis instead of homocondensation. The latter possibility, which
appears, from literature data, to be more common~'61,
would
yield mixtures of single oxides instead of a homogeneous
multicomponent oxide. Part of the metal alkoxides may
naturally undergo condensation reactions with elimination
of alcohol even at room temperature, but this is of no
importance to the final result, since the reaction continues
via the polyorganoxymetaloxane stage (11). The temperatures mentioned are evidently necessary for the removal
of the last traces of water from hydroxyl groups bonded to
metal.
The process should be applicable to other elements if the
metal alkoxides react with one another, as they do in most
cases. For example, we have prepared eucryptite
[LiAl(SiO,)] in this way from lithium ethoxide, aluminum
sec-butoxide, and Si(OR),. After this work had been concluded Mazdiyasni, Dollof; and
reported the
preparation of BaTiO,, SrTiO,, and SrZrO, as polycrystalline material by a similar method ; this underlines the
scope of the method. (Investigations on a similar basis are
also being carried out at the ETH Zurich["].)
This therefore provides a relatively convenient route to
multicomponent oxides that are difficult or perhaps almost
impossible to obtain by other methods, and also offers the
possibility of obtaining substances of high purity. Very
pure metals may be used in the preparation of the metal
alkoxides, the alkoxides themselves or their reaction
products may be recrystallized, and even distilled in some
cases, and the reactions proceed under comparatively mild
conditions, so that contamination from the walls of the
vessel can be avoided. The method may also be of value
for doping.
Finally, there is practically no other method that allows the
preparation of thin layers of multicomponent oxides
having almost any desired composition on substrates (see
Section 7). The method is particularly elegant for this
purpose, since the action of atmospheric moisture (hydrolysis) and the removal of the condensation products water
and alcohol can be achieved without difficulty in the case
of thin layers (a few tenths of a pm). The preparative
difficulties in the production of polycrystalline material
are sometimes considerable, since the diffusion paths are
long and difficult to control, unlike those in thin layers.
This can lead, with rising temperatures, to pyrolysis with
separation of carbon before the hydrolytic removal of the
OR groups is complete. Though this does not interfere
with the necessary determination of the nature of the
material obtained, the product is not obtained in the pure
state. However, an improvement can generally be achieved
by the use of different experimental conditions, often established onIy by laborious trial and error.
Angew. Chem. internat. Edit. 1 Vol. 10 (1971)
/ No.6
5.2. Proof that the Product is a Borosilicate Glass
5.1. Preparation of Borosilicate Glass
Unlike the organic polymers, which are versatile in spite
of restriction to a few elements, the inorganic polymers,
i.e. the glasses, owe their versatility to the fact that their
composition can include practically any element from the
periodic system.
To prepare a multicomponent glass, the various components must be made to react with one another. In the
melting method, favorable conditions are provided by
heating the starting materials until they melt ; the various
components then react with one another, possibly with
elimination of gases such as CO,. The melt may then, for
example, be poured into a mold, where it cools and solidifies
to form a glass.
Since a multicomponent glass containing silica can be
regarded, on the basis of its structure (Fig. 2), as a crosslinked “polymultimetaloxanesiloxane”, it seemed interesting to us to look for a practical route that would also
justify this description.As in the spinel case, metal alkoxides
should combine here to form an alkoxo complex, which is
converted by hydrolysis and polycondensation via “polyorganoxymultimetaloxanesiloxanes” into the glass, which
contains no organoxy groups, and is in fact the “polymultimetaloxanesiloxane”.
To provide a better grasp, an example of a practical
procedure will now be described. A three-neck flask is
fitted with a stirrer and a reflux condenser, and the following ingredients are introduced in succession with stirring,
nitrogen being passed over the mixture at the same time:
50 g of ethanol (dry) 0.5 g of 2,4-pentanedione; 102 g of
Si(OCH,),, 5.3 g of Al(0-sec-C,H,),, 10.5 g of NaOCH,
(solution in methanol corresponding to 172 g of Na,O/l),
and 1.4 g of KOC,H, (solution in methanol corresponding
to 218 g of K,O/l). The precipitate formed on addition of
the aluminum sec-butoxide is brought into solution by
stirring and heating at 70°C. 11.2 g of H,BO, dissolved in
120 ml of boiling ethanol is then added. The precipitate
that forms dissolves within 5 minutes. The dark yellow solution contains about 160g of oxides (80.9% SiO,, 12.7%
B,O,, 3.6% Na,O, 2.2% A1,0,, 0.6% K,O) per liter.
+
The diluted solution containing 30 g of oxidefl is left open
to the air in a beaker. It sets to form a gelatinous mass,
which is then heated for 9 hours at 150°C. During this
Though the presence of clear, transparent fragments allows
little doubt as to the nature of the product, the properties
of a product prepared in this way must be compared with
those of a fused glass in order to provide rigorous proof
that a glass has in fact been formed in the region of the
transformation temperature, without fusion. A portion of
the glass-clear crumbs was therefore pressed into transparent plates at 630°C and 100 t (this can be achieved more
easily at 65&700”C), and another portion was fused at
1600°C. The investigations described below were carried
out on the crumbs, the molded plates, and the fused pieces,
and show that glass has in fact been formed (see Table 2).
Table 2. Chemicalcomposition of the borosilicate glass (valuesin wt.-%).
Glass
SiO, (%)
B,O, (%)
AL0, (%)
Na,O (%)
K,O (%)
5.91
4.97
2.62
2.62
3.92
3.67
0.66
0.67
~~
Unfused
Fused
86.85
87.99
The reason for the greatly reduced B,O, content in comparison with that in the original solution is that part of the
B,O, escapes as esters of boric acid. It should be remembered that I&l5% of the B,O, used in the melting method
can also escape with the flue gases.
The residual water content can be determined by IR spectroscopy (OH band at 2.9 pm).
Unfused glass contains 0.036% of H,O after a fragment
has been heated for 50 h at 550°C and pressed at 650°C.
If the same glass is heated for 4 h at 700°C under a high
vacuum before pressing, 0.029% of water can still be detected. Fused glass contains 0.023% of H,O (for comparison,
Duran 50, which is fused on a large scale, contains 0.033%
of H,O).
The water is thus very extensively removed during the
normal condensation at 550°C (followed by heating for a
short time at 650°C during pressing).
The residual carbon content of an unfused glass is 0.0002%,
which is surprisingly low in view of the fact that the glass
was made from alkoxides. The hydrolysis is thus practically
quantitative, despite the strong crosslinking.
The hydrolysis resistance of unfused glass in accordance
with DIN 12111 is 0.007 mg of Na,O/g of coarsely ground
glass (=hydrolytic class I), while that of fused glass is
0.005 mg of Na,O/g of coarsely ground glass (=hydrolytic
class 1). Physical and optical properties are shown in
Table 3.
Fig. 5. Preparation of a borosilicate glass from hydrolyzed alkoxides.
From left to right : starting solution, crumbs obtained by hydrolysis
at 2 0 T , crumbs obtained from these by heating at 550°C, glass obtained
from these on pressing at 2800 atm.
heating, it cracks and breaks up into small yellow crumbs,
which become colorless, glass-clear, and hard when heated
at 530°C. Small black impurities that sometimes form (see
above) are sorted out. This preparation route is illustrated
in Figure 5.
Angew. Chem. internat. Edit. j Vol. 10 (1971) j
No.6
The temperature function of viscosity was tested qualitatively by heating a fragment under constant load and observing it with the aid of a microscope. Deformation begins
at 675 “C.The temperature function of viscosity corresponds
to that of similar borosilicate glasses.
The agreement of the properties shows that the product
does not consist of single oxides or a number of two-component oxides, but of a homogeneous multicomponent
system, i. e. a borosilicate glass.
Let us now briefly compare the procedure for the hydrolytic condensation with that for the melting process. The
batch is replaced by a mixture of compounds that react
readily with one another. Homogenization is replaced by
367
dissolution in a common solvent. The reaction, which starts
only at high temperatures in the melting process, begins
here at room temperature (complex formation) and continues with the action of atmospheric moisture with hydrolytic elimination of alcohol, which is comparable to the
thermal elimination of CO, from a carbonate. The condensation reaction with elimination of water takes place
at the same time; this reaction requires temperatures up
to the transformation range of the glass. The pouring of a
fused glass into a mold is replaced by pressing of the glass
crumbs to form a transparent molding in the transformation
range.
Table 3. Physical and optical properties of the unfused and of the fused
glass.
Glass
Density
D,,
(g/cm3)
Transformation
of expansion temperature
(“C)
Unfused 2.28
32xlO-’
590
Fused
32x10-’
610
Glass
Unfused
Fused
2.27
Refractive
indexnd20
1.477
1.474
vd
65
66
Hardness to
scratching
scratches
window glass
and apparatus
glass 20
scratches
window glass
and apparatus
glass 20
X-ray diffraction analysis
contains no crystalline phases
contains no crystalline phases
This last step is obviously more difficult than a melting
process. Moreover, because of the simultaneous reaction
of five components, it is not so easy to explain the path as
in the case of the two-component system of spinel. Since
the initial and final states are known with certainty, we
could write a formal reaction equation, but we shall not
do so here. A first glimpse is provided by following the IR
spectrum of a film of borosilicate glass 0.5 pm thick on a
barium fluoride plate during its formation. After 30 min at
IOO’C, a pronounced metal-OH band is observed at 3 pm,
which is stronger after 30 min at 250°C. After 30 min at
530”C, the metal-OH groups have been consumed by
condensation, and can no longer be detected, at least in
this thin layer. A band at 3.4 pm is attributable to the CH,
and/or CH, vibration of the OR residues that have not yet
been removed (or of the free alcohol). It is present after
heating at 100°C, but has disappeared at 250°C, when
hydrolysis has progressed to an advanced state. The boric
acid band is situated at 7.2 pm and the Si-0 vibration at
9.4 pm. The characteristic of the curve corresponds to that
of a Duran 50 film (though the boric acid content of the
latter is considerably higher) and to that of a vapor-deposited layer of borosilicate glass.
6. Conclusions
According to all the observations reported, a multicomponent oxide glass can no longer be regarded exclusively
as an “inorganic product of fusion” (ASTM definition),
but can also be considered with equal right as a “multipolycondensation product” prepared by hydrolysis and polycondensation reactions from compounds containing metalOC groupings. Neither of these features is fundamentally
368
essential or necessary to the definition. It is important and
interesting, however, that practically no difference can be
detected between a fused and a condensed glass by the
investigation methods used. It may be possible, by more
refined methods, to find differences due to the past history
of the material, which could lead to further knowledge
about glasses.
An important point as far as the method is concerned is
that it is now possible to prepare a glass “from below”, i. e.
by approaching the glass state from a lower temperature.
It is therefore no longer necessary to pass through the temperature range of maximum crystallization rate. With this
release from the danger of crystallization during cooling,
it should now be possible to establish whether a given
composition that can be prepared by this method forms a
glass or a crystalline phase. The method may also be of use
in the study of phase separation phenomena.
7. Multicomponent Glass Layers on Substrates
It has only recently become possible to apply thin multicomponent glass layers to substrates by simultaneous vapor
deposition of individual oxides under vacuum[31. A
particularly important step is the development of special
“vapor deposition glasses”, with which homogeneous
glass layers suitable for technical use can be produced
directly[’91.Glass layers can also be applied by the chemical
vapor deposition process[4!
The process described can be used if the substrate does
not soften below the transformation temperature of the
glass to be applied. This is the simplest and above all the
most versatile method, since it allows the application of
coatings of multicomponent oxide layers having practically
any desired compositiontzo1.The methods by which substrates with relatively large surfaces can be coated with
oxide layers by dipping in organic solutions have been
described in detail by Schrueder[’ll. In analogy with these
methods, we dipped the substrates to be coated (metal,
glass, etc.) in the solution, removed it uniformly, and heated
it for a short time at a temperature not exceeding the transformation range of the layer-forming glass. Solid, hard
glass layers up to a few thousand Angstroms thick are
obtained.
The layer formation itself takes place effortlessly. This is
because the films are so thin that the diffusion of the water
required for hydrolysis and of the eliminated hydrolysis
products is greatly facilitated. For this reason we prepared
many multicomponent glasses in thin layers after the formation ofa glass had been proved for the borosilicate glass.
Examples are provided by experiments with solutions that
lead to the following glass compositions : borosilicate glass
layers (composition as described in Section 5.2), phosphate
silicate glass layers (containing SO2, A1,0,, P,O,, BaO,
B,O,, CaO, MgO), lead silicate glass layers (containing
SO,, PbO, Na,O), and alkali metal aluminosilicate glass
layers (containing SiO,, Na,O, A1,0,).
All these layers are transparent, hard, and amorphous to
x
Angew. Chem. internat. Edit. / Vol. 10 (1971) / No. 6
Even these few examples show the scope of the process.
A limitation exists with respect to the thickness of the
layers. Though some increase is possible by means of
additives in the solution or by multiple coating, it is difficult to obtain layers more than 0.5 pm thick; this is no
problem in the vapor deposition method. However, even
thin layers have technically useful properties. Thus metals
can be electrically insulated with multiple borosilicate
glass layers. The same layers also prevent or inhibit the
scaling of metals, e.g. of iron. Thus a coated sheet of iron
shows no scaling when heated for 3 hours at 800”C,
whereas an uncoated sheet of iron is completely scaled
under such severe conditions. The tarnishing of brass e. g .
at 530°C is also prevented, as is its corrosion. First exp e r i m e n t ~ ~indicate
’ ~ ~ that in the salt spray test and in the
condensation water test, white rust formation or corrosion
begins only after 1600 hours, and is then spontaneous. A
series of sensitive optical glasses can be very effectively
protected against climatic attack by phosphate silicate
glass layers (Fig. 6). This is important, since the concentration on certain optical properties in such glasses sometimes necessarily leads to poor stability to climatic conditions. It is also important here that the protective layers
should be very thin, as they may otherwise affect the optical
properties.
Attempts to convert this material into granular material
by heating at 620°C yields transparent crumbs together
with a few black components. The clear crumbs contain
no crystalline material. These crumbs are treated further
at 680°C and 830”C, in accordance with the temperature
program for the completely analogous glass-ceramic starting glass prepared from the melt. This gives h-quartz solid
solutions and nucleation phases containing Zr 0,. The
crystallization properties correspond to those of the fused
starting glass.
Another starting glass is prepared from a solution having
the following composition (converted to oxides): 62.00%
SiO,, 21.86% A1,0,, 6.16% ZnO, 2.82% Li,O, 1.77% TiO,,
1.77% ZrO,, 1.61% BaO, 1.11%MgO, 0.50% CaO, 0.40%
K,0[261. A second solution has the same composition,
except that it does not contain the nucleating agents. TiO,
and ZrO,. It seems interesting to compare the products
obtained from the two solutions. Clear layers can be
prepared from both solutions ; however, the crumbs obtained from both solutions are black. Differential thermal
analysis gives a crystallization signal for the substance
containing the nucleating agents, and none for the substance with no nucleating agent; this corresponds to the
behavior of the fused starting glass.
I am grateful to my assistant of many years’ standing, P. Hinz,
who carried out all the preparations. I have been greatly
assisted in the identification of the reaction products by many
colleagues at the Jenaer Glaswerke Schott u. Gen., Mainz,
by discussions and investigations. These, together with their
assistants, were Dr. Coenen, Dr. Dorr, Dr. Dutz, Dr. Geffcken,
Jenemunn, Kristen, Lindig, Dr. Mulfinger, Dr. Neuroth, Dr.
Petzold, Scheidler and Prof Schroder. I am very grateful to
Dr. Warnuch and Ing. Steinhofffor carrying out the Hifjicult
pressing experiments.
Received: March 17,1970 [A 817 I E ]
German version: Angew. Chem. 83,428 (1971)
Translated by Express Translation Service, London
Fig. 6. Protection of an optical glass against climatic attack by coating
with phosphate silicate glass. Top: uncoated (corrosion), bottom
(coated).
[I]
ASTM definitions appear in ASTM designation: C 1 6 2 4 6
[2] D . R. Secrist and J . D.Mackenzie, Modern Aspects Vitreous State3,
149 (1964).
8. Preparation of Starting Glasses for
Glass-Ceramics
[3] W Hiintein, Pavaux du IV‘ Congres International du Verre, Paris
1956, p. 419.
[4] W Kern, RCA-Rev. 29, 525 (1968).
[5] H . Schroeder, Optica Acta 9, 249 (1962).
[6] H . Schroder and G . Gliemeroth, French Pat. 1524490 (1967), Jenaer
Glass-ceramics contain finely dispersed crystalline phases
in a glass matrix. They are prepared by fusion of a starting
glass containing nucleating agents. A controllable partial
crystallization is then brought about by heat treatment.
Probably the best-known property of some glass-ceramics
of this type is their almost vanishingly small coefficient of
thermal expansion of O+ 1 x 10-7/”C[24!
Starting glasses for glass-ceramics have also been obtained
by the route described here. A solution of the alkoxides is
first prepared such that the composition, converted to the
oxides, corresponds to a Schott glass ceramic (61.4% SiO,,
21.6% A1,0,, 6.8% P,O,, 3.8% Li,O, 1.4% MgO, 0.5%
Na,O, 2.6% TiO,, 1.9% Zr0,1251).This solution, with a
total oxide content of 77g/l, is used to prepare hard, transparent layers by dipping and heating (58OoC, 30 min).
Angew. Chem. infernal.Edit. j Vol. 10 (1971) 1 N o . 6
Glaswerk Schott und Gen.
[7] R. Roy, J. Amer. Ceram. SOC.52, 344 (1969).
[8] W Noll: Chemie und Technologie der Silicone. 2. Edit. Verlag
Chemie, Weinheim 1968.
[9] H . Schmidbaur, Angew. Chem. 77,206 (1965); Angew. Chem. internat. Edit. 4, 201 (1965).
[lo] D. C . Bradley, Progr. Inorg. Chem. 2, 303 (1960).
[ll]
D. C . Bradley in F . G . A. Stone and W A. G. Graham: Inorganic
Polymers. Academic Press, NewYork 1962, p. 410; Coord. Chem. Rev. 2,
299 (1967).
[I21 R. C . Mehrotra, Inorg. Chim. Acta I, 99 (1967).
[I31 Houben- Weyf-Miiller: Methoden der organischen Chemie. Vol.
VI/2, SauerstoffverbindungenI, Part 2. Thieme-Verlag, Stuttgart 1963.
[I41 G. F. Hiittig, H . Wdrl, and H. H . Weitzer, Z. Anorg. Allg. Chem.
283, 207 (1956).
[I51 R. J . Bratton, Ceram. Bull. 48, 759 (1969).
[16] Houben- Weyl-Miiller: Methoden der organischen Chemie. Vol.
VIj2, SauerstoffverbindungenI, Part 2, p. 133. Thieme-Verlag,Stuttgart
1963.
369
[17] K . S. Mazdiyasni, R.7: Dollof, and J . S. Smith 11, J. Amer. Ceram.
Soc 52, 523 (1969);53, 91 (1970).
[18] Dr. G.Bayer, ETH Zurich, private communication.
1191 Aufdampfglas 8329 Schott-Datenblatt; H . D U t Z , H . 0.MuFnger,
andG. Krolla,Belg. Pat. 727217(1969);JenaerGlaswerkSchott undGen.
[20] H . Dislich, P . H i m , and R. Kaufmann, DAS 1941 191 (1969),
Jenaer Glaswerk Schott und Gen.
[213 H . Schroeder in G. Hass: Physics of Thin Films. Academic Press,
New York 1969, Vol. 5, p. 87.
[22] H . Dislich, Glastechn. Ber. 44, 1 (1969).
[23] Dr. H . L Oei, Metallgesellschaft Frankfurt/Main, private communication.
~ 2 4 1 Sack, Chem,-Ing,-Techn.37, 1154 (1965).
[25] J . Petzoldt, French Pat. 1583934 (196% Jenaer Glaswerk Schott
und Gen.
[26] W Sack, H . Scheidler, and J . Petzoldt, French Pat. 1562377(1968),
Jenaer Glaswerk Schott und Gen.
Nutmeg as a Narcotic
A Contributionto the Chemistry and Pharmacology of Nutmeg (Myristicafragrans)
By Dieter Abbo Kalbhen"]
The abuse of nutmeg for narcotic purposes has led to renewed chemical and pharmacological
interest in this drug. Several allylbenzene derivatives whose biological transformation products
have structures resembling mescaline and amphetamine have been identified as psychotropic
constituents. It is suggested that the intensity of the hallucinogenic action of these compounds
is due to the possibility of simulation of LSD-like structural elements.
1. Introduction
Nutmeg has a very checkered history as a medicine. Though
it was used in India and in the Arab countries as a spice
and as a remedy as early as the year 700 BC, this drug was
unknown to the Greeks and Romans, and it was only in
the Middle Ages that it was introduced into Europe by
Arab merchants and later by Portuguese.and Dutch traders.
The product, which came from the Moluccas in the East
Indies, was the monopoly of the Portuguese and Dutch for
a long time. It was not unfil 1843 that the British and
French managed to break this monopoly by growing
nutmeg trees on the islands of the Caribbean. Thus nutmegs
are now available both from the East Indies and from the
West Indies.
Like many other cooking spices, such as ctoves, pepper,
paprika, caraway, fennel, and aniseed, nutmeg was very
important to the ancient Indians and Arabs as a medicine,
and it is still found in the folk medicine of these countries.
Various nutmeg preparations were and are used as analgesics, stomachics, digestives, hypnotics, aphrodisiacs, and
amenorrhea1 agents. The European physicians of the
Middle Ages, who borrowed many recipes and treatments
from their Arab colleagues, prescribed nutmeg for an
equally wide range of indications.
Priv.-Doz. Dr. D. A. Kalbhen
Pharmakologisches Institut der Universitat
53 Bonn, Reuterstrasse 2 b (Germany)
370
Whereas the use of nutmeg as a spice has persisted to the
present day, its interest and importance in medicine has
declined in Europe since the beginning of the 18th century.
The end of the 19th century saw a brief return to popularity
in the wake of a rumor that nutmeg is an effective abortifacient. Several medical journals at this period reported a
high incidence of nutmeg poisoning in women.
Intoxication due to the benumbing and psychotropic
effects of nutmeg had been described even earlier. Thus the
famous Breslau physiologist Purkinje"' carried out an
experiment on himself; the symptoms that he described as
resulting from the ingestion of three ground nutmegs are
very similar to the effects of hashish. The excessive use of
nutmeg in folk medicine as a stomachic, as an abortifacient,
or in love potions leads in man to intoxication symptoms
that are manifested in outbreaks of sweat, desire to urinate,
headaches, nausea, disequilibrium, hysterical laughter,
hallucinations, and/or stupor.
Though the hallucinogenic action was described repeatedly
around the turn of the century, it was only after the second
world war that nutmeg came to be used as a narcotic, and
this use was mainly, if not exclusiveIy, confined to the USA.
This drug is used particularly by young people, students,
hippies, and convicts to attain an intoxicated state with
hallucinations. Since nutmeg is generally known as a spice,
can be bought anywhere, and has even been used in prison
kitchens, it is readily obtainable by the groups mentioned
above, and is welcomed by them as a substitute for controlAngew. Chem. internat. Edit. / Vol. 10 (1971) / No. 6
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