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Pyrex glass formula patent No. 1,304,623 - Page 3 Home > Insulators > Patents > Page 3 |
 1,304,623: 3 of 4 |
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Up: Patents |
Pyrex glass formula patent No. 1,304,623 - Page 3 Home > Insulators > Patents > Page 3 |
1,304,623: 3 of 4 |
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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 (except for compositions E) being between 60 and 70 per cent. of constituents other than the silica. It is possible to replace a part of the sodium oxid given in the formulæ 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 be taken up from the glass by substances undergoing analysis or treatment therein. 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 E, 15 to 1; while the second ratio for A, is 23 to 1; for B1, 21.4 to 1; for B2, 21.6 to 1; for C, 33 to 1; for D, 58 to 1; for E, 15.7 to 1; the molecular formulæ of the several compositions being as follows,--
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It will be noted that none of the oxids of the
second group of the periodic system (i.e. 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 desirable 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, which 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 (F/3) of 19. Its hardness, as defined above, is 800° C., and its stability also as defined above is .00015 grams. Its specific heat is .20. Using a factor for tensile strength comparable with the factors used by Winkelmann and Schott, its co-efficient of thermal endurance (F/3) is about 10. Having thus described our invention, what we claim, and desire to secure by Letters Patent is stated in the follow 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 not over 3 per cent. of the total, and the percentage of boric oxid to sodium oxid being 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 per cent. and not over 90 per cent. silica and containing alumina, boric oxid and alkali oxid, without oxids of the second group of the period 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. |