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To all whom it may concern: Be
it known that we, EUGENE C. SULLIVAN
and WILLIAM C. TAYLOR, both
citizens of the United States of America, and residents of Corning, New
York, have invented certain new and useful Improvements in Glasses, of
which the following is a specification. In
our prior application filed June 24, 1915, Sr. No. 36,136, we showed,
described and claimed a glass baking dish and compositions for a glass
suitable for fabrication into such dishes. The United States Patent
Office has required a division of such application between the claims on
the article and those on the composition and accordingly the present
application is filed. Glass
compositions A, B, C, D and E given herein are compositions even in the
prior application. Composition B2
given herein is specified because it is a composition which has been put
into extensive commercial use and because its physical properties have
been carefully and accurately determined. Our
invention has for its object to provide a new glass (that is to say a
substance containing Silica in combination with various bases and acids)
specially adapted for fabrication into pressed or blown ware intended
for culinary or laboratory uses. For these purposes it is desirable that the glass have the
following properties. (A)
A high co-efficient of thermal endurance, as hereinafter defined. (B)
High stability, that is to say, power to resist chemical attack. It is well known that certain glass making materials tend, when incorporated in the glass, to produce one or more of the desirable results, but in so doing, many of them also work against other desirable results, and in advance of an actual test, it cannot be predicted how a variation of the relative proportions of the different ingredients will affect certain of the named factors. This invention therefore consists in the selection of certain known glass making materials in such relative proportions as will result in a glass having the named properties combined in such manner as to adapt such glass for the purpose stated, and in a glass having certain desired properties. Generally
speaking, the present invention contemplates a glass for the purposes
stated, characterized by one or more of the following features,-- (1)
It is boro-silicate of high stability having a linear coefficient of
expansion less than .000004 and a high thermal conductivity (i.e. as
high as .0028). (2)
In it the molecular ratio of silica to base is greater than 13 to 1,
(tending to high stability (resistance to attack of reagents) and low
expansivity), while at the same time its hardness, (as measured in the
manner (3)
In it the molecular ratio of acid oxid or oxids to basic oxid or oxids
is not less than 15 to 1. (4)
It has a co-efficient of thermal endurance greater than 6. (5)
It has a stability better than .002 grams per 100 sq. cm. when measured
in the manner hereinafter stated. It
more specifically comprises a boro-silicate glass, in which no oxids of
the second group of the periodic system are present in quantities
sufficient to make them material constituents, containing over 75 per
cent of silica, and having a hardness of about 800 degrees C. As
examples of glass compositions falling within our invention, we give the
following,--
A. B1.
B2.
C. D.
E. SiO2
- -
70
80.6
80.9 90
85 90
B2O3-
- 20
13
12.9
6 12.5
5 Na2O
- - 4
4.4
4.4
3
1.5
-- Al2O3-
- 6
2
1.8
1
-- 2 Sh2O3-
- --
--
--
--
1
-- Li2O
- - --
--
--
--
-- 3
___ ____ ___
____ ___
___ Total
100 100
100 100
100 100 All of the glasses given above have the following
physical characteristics,- (1) A linear thermal expansivity less than .000004,
between 20 degrees C. and 300 degrees C., the coefficient of expansion
of glass (A) being .0000037; of B, .0000034; of B, .0000033; of C.,
.0000023, and of D, .0000022. (2) A relatively high coefficient of true internal heat
conductively, viz., .0028 calories per second per degree C. for each
square centimeter of plate 1 cm. thick, for glasses A, B, and B2,
and about .0030 for C. (3) Tenacity, modulus of elasticity density
and specific heat of such values that in connection with their
expansivity and conductivity the glasses have a high coefficient of
thermal endurance. This factor, which is the power to undergo sudden
cooling without fracture, is expressed by Winkelmann and Schott (Ann.
D. Phys. u. Chem. 51-730
(1894); also Hovestadt, Jena Glass, published by MacMillan
1902, p. 228), as follows;--
In
which- F
= coefficient of thermal endurance, P
= tensile strength, a
= the linear expansivity, E
= Young's modulus of elasticity, K
= heat conductivity, S
= density, c = specific heat. If
the cubic expansivity is used in the formula, instead of the linear
expansivity the result would be F/3 and these values of F/3 are used for
comparing glasses. The values of F/3 calculated by Winkelmann and Schott
for glasses of various composition range between 1.17 and 484. In
calculating F/3 Winkelmann and Schott use a figure for the tensile
strength which is undoubtedly too low, their tensile strength
determination having been made by a method which they themselves
recognized tended to give low results. Using
factors of tensile strength for our glasses, such as would be given by
them under the test methods of Winkelmann and Schott, the cubic
coefficient of thermal endurance (F/3) of all of our glass is greater
than 6. In specifying thermal endurance in our claims, we will base them
on such factors. Using the actual tensile strength of our glasses the
factor is still higher. (4)
High stability against chemical attack. As illustrative of this, it may
be stated that a glass of composition B2,
after being subjected to the solvent action of distilled water at 80
degrees C. for 48 hours (see for procedure, Walker, Journal of the
American Chemical Society, vol.27, p. 865, 1905) has only .0001 to
.0005 grams of matter dissolved per 100 sq. cm. exposed to the solvent
action, while all of the compositions here given have a stability better
than .OO2 grams per 100 sq. cm. (5) Good workability. This includes the ability to properly melt the
glass at the temperatures readily obtainable in ordinary glass
furnaces. It also includes the property of remaining amorphous, and of
being sufficiently plastic at a point below the furnace temperature to
permit its working in the ordinary manner by blowing, pressing, etc.
This latter property may be expressed numerically by the temperature on
the centigrade scale, at which a thread of the glass 1 mm. in diameter
and 23 cm. in length suspended vertically and heated through the upper 9
cm. elongates of its own weight at the rate of 1 mm. per minute. A glass
doing this at the temperature of 800 degrees C. is said to have a
hardness equal to, (or no greater than) 800 degrees C. Glasses A, B1,
and B2
have a hardness of about 800 degrees C., D of about 862 degrees C.,
while C and F have a hardness above 862 degrees C., and below 900
degrees C. (6)
The glasses are all colorless and are transparent. Chemically
the compositions above given are characterized,-- (7)
By high silica contents (i.e. not less than 70%).
This tends to low expansivity and good stability, but tends to
render the glass hard. It will be noted that in all of the above formulae the percentage of alumina is very low, as is desirable in order to reduce the hardness of the glass. Alumina has been heretofore used in sodium-boro-silicate glasses in larger percentages in order to obtain ability to resist chemical attack and prevent crystallization, but we find it possible to still achieve these desirable results while reducing the alumina contents, and to increase as stated, in a suitable mixture, the silica contents to 70 per cent or over, and that the expansion with such percentages is less than would be inferred from the hitherto known properties of silica. From our investigations we have discovered that with these high percentages of silica, the unit expansion factor of the silica is apparently less than the unit factor for less percentages of silica, or in other words that when the percentage of silica is made sufficiently great the factor by which its percentage is to be multiplied to obtain the thermal expansion due, to the silica is reduced. If the silica content is increased to above 84 per cent, which is thus rendered possible, while maintaining low expansion, the alumina contents may be decreased, say to one per cent, owing to the fact that with high silica contents suitably combined, but little alumina is required to give requisite resistance to chemical attack, and freedom from tendency to crystallize. In composition D, the antimony, and composition E, the lithia, serves to soften the glass without decreasing the resistance to chemical attack as would the amount |
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of soda or potash requisite to soften the glass to the same extent. Indeed
the alumina of compositions A, B1, B2,
C and E may be entirely dropped, being replaced by an equal amount of
silica. This, while effecting changes in the characteristics of the
glass, is within the scope of certain aspects of our invention and the
resultant glasses are useful, although not embodying desirable features
to the same extent as the compositions given. Thus if this change be
made in composition B1,
the resultant glass would be lower in expansivity, softer, less stable
and more inclined to crystallize than the glass of composition B1. (8)
In combining with the low expansivity due to the high silica contents,
and with good stability, good workability, this being due to the
compositions employed, in which a relatively high ratio of boric oxid to
alkali, is present, this ratio in none of the cases given, being less
than 2 to 1, the boric oxid (except for compositions B) being between 60
and 70 percent. of constituents other than the silica. It is possible to
replace a part of the sodium oxid given in the formula with potassium
oxid. To obtain the same
hardness, two parts of sodium oxid may be replaced by three parts of
potassium oxid, while for the same expansivity, five parts of sodium
oxid may be replaced by six parts of potassium oxid. In this
specification, the proportions of alkali will be stated in terms of
sodium oxid, it being understood that such alkali may be replaced by
potassium oxid in the proportions stated. It will be noted in glass E,
lithia forms the alkali. (9)
The relative simplicity of the compositions, all of the five given
containing four ingredients each, at least two of which are acid oxids
(silica and boric oxids), and a basic oxid (soda or lithia). Alumina and
the antimony oxid probably act as acids in the composition, and will for
purposes of description be so considered. This simplicity of composition
is of advantage in connection with chemical glass-ware by reducing the
number of elements which may It will be noted that in the compositions given, the
molecular ratios of silica to bases and of acidic oxids to basic oxids
are high. The first ratio for A is 18 to 1, for B, 18.9 to 1; for B2,
19 to 1; for C, 31 to 1; for D, 51 to 1; and for B, 15 to 1; while the
second ratio for A, is 23 to 1; for B1,
21.4
A.
B1.
B2.
C. D.
E. SiO2
- -
1.167 1.345
1.348 1.5
1.417 1.5
B2O3-
- .286 .186
.184 .0857
.179 .0714 Na2O
- - .0645 .071
.071 .0464 .0242
-- Al2O3-
- .06
.02 .018
.01
--
.02 Sh2O3-
- --
--
--
--
.0035 -- Li2O - - -- -- -- -- -- .01 It
Will be noted that none of the oxids of the second group of the periodic
system (e.g. lime and magnesia) are present, for while these oxids tend
to stability and good workability, they also tend to produce in such
compositions as these a cloudy and high expansion glass which it is
desired to avoid. Glass
B2
has gone into extensive commercial use in the manufacture of baking
dishes, and chemical ware, many thousands of which have been sold, and
has been tested by the Bureau of Standards, who find its linear
expansivity to be .0000033 its true internal heat conductivity to be
.0028, its density to be 2.246. Other
tests show its true tensile strength to be 16 kg. per sq. mm., its
Young's modulus to be 6530, giving a true coefficient of thermal
endurance Having thus described our invention, what we claim, and
desire to secure by Letters Patent is stated in the following claims, in
certain of which the term "acid" is used as indicating the
oxids of aluminum and antimony-- 1. A glass containing silica, alumina, boric oxid and
sodium oxid only, the silica being not under 70 per cent, and the
alumina being not over 3 per cent of the total, and the percentage of
boric oxid to sodium oxid being not less than two to one. 2. A glass containing silica, alumina, boric oxid and
sodium oxid, without oxids of the second group of the periodic system,
or the reducible oxids of lead or antimony, the silica being not under
70 per cent, and the alumina being not over 3 per cent of the total, and
the percentage of boric oxid to sodium oxid
not less than two to one. 3. A glass containing not under 70 per cent and not over
90 per cent silica and alumina, boric oxid and an alkali oxid, the boric
oxid being not less than 60 per cent or more than 70 per cent of the
combined alumina, boric oxid and alkali oxid contents. 4. A glass containing not under 70 percent
and not over 90 per cent silica and containing alumina, boric oxid and
alkali oxid, without oxids of the second group of the periodic system,
the boric oxid being not less than 60 per cent or more than 70 per cent
of the combined alumina, boric oxid and alkali oxid contents. 6.
A glass having the stability better than 0.002 grams per 100 sq. cm. and
a hardness no greater than 900 degrees C. and containing not under 76
per cent silica and also containing boric oxid, the boric oxid
comprising not less than 60 per cent of ingredients other than silica. 7.
A glass containing between 76 and 90 per cent silica, between 6 and 14
per cent boric oxid, and also containing sodium oxid and alumina. 8.
A glass containing silica, boric oxid and alkali, the boric oxid and
alkali forming not less than 6 per cent of the glass, the glass having
linear coefficient of expansion less than .0000036. 9.
A glass containing silica, boric oxid and alkali, the boric oxid and
alkali forming not less than 6 per cent of the glass, and the boric oxid
being to the alkali in the ratio of at least two to one, the glass
having a linear coefficient of expansion of less than .0000036. 10.
A glass containing silica, boric oxid and alkali without oxids of the
second group of the periodic system, or the reducible oxids of lead or
antimony, the boric oxid and alkali forming not less than 6 per cent of
the glass, the glass having linear coefficient of expansion of less than
.000004. 11.
A transparent glass containing over 70 percent silica, and having a
linear coefficient of expansion of less than .0000036 and a hardness not
greater than 800 degrees C. 12. A transparent glass containing more than 79 percent
silica and having a linear coefficient of expansion less than .000004,
and a hardness not greater than 850 degrees C. 13.
A glass having a hardness not greater than 850 degrees C.; a coefficient
of thermal endurance
(F/3) greater than six, and stability of 0.002 g. or better per
100 sq. cm. 14.
A glass having a hardness not greater than 850 C., a linear coefficient
of expansion of less than .0000036, and thermal coefficient of endurance
(F/3) greater than six. 15. A glass having linear expansivity less than
0.000004, stability better than 0.002 grams per 100 sq. cm. and hardness
not greater than 850 degrees C. 16.
A glass containing silica and boric oxid and having linear
expansivity less than 0.000004 and stability better than 0.002 grams per
100 sq. cm. 17.
A glass having hardness not greater than 820 degrees C. and linear
expansivity less than 0.0000036. 18.
A glass having a hardness not greater than 820 degrees C., a
linear expansivity less than 0.000004, and a stability better than 0.002
grams dissolved matter per 100 sq. cm. 19. A glass containing at least 76 percent silica and
containing at least one other acid oxid and a basic oxid, the molecular
ratio of the acid oxid contents except Such as are due to silica to the
basic oxid contents being at least two to one. 20. Glass containing at least 76 percent silica
containing at least one other acid oxid and a basic oxid, the percentage
ratio of the acid oxid contents except such as are due to silica to the
basic oxid contents being at least two to one. 21. A glass containing silica and not more than two other
acidic oxids, one of which may be alumina and only one basic oxid, the
molecular ratio of the acidic oxid contents, except such as are due to
silica and alumina, to the basic oxid contents being at least two to
one. 22.
A glass containing at least two acid constituents and only one basic
constituent, and having linear expansivity less than 0.000004. 23. A glass containing silica and not more than two other
acidic constituents and only one basic oxid constituent, and having
linear 24. A glass c9ntainlng between 76 percent and 85 percent
silica, over 9% of another acid oxid, and over 3% of a basic oxid. 25.
A glass containing over 76 percent silica and having linear expansivity
less than 0.O00004 and hardness not greater than 820 degrees C. In testimony whereof we have signed our names. EUGENE
C. SULLIVAN. WILLIAM C. TAYLOR. |
