Dissolved gases in glass by unknow

Author:unknow
Language: eng
Format: epub
Tags: Glass manufacture -- Chemistry
Publisher: Urbana, University of Illinois

the ability of the glass to adsorb gases from the atmosphere, the latter being an entirely independent process.

The evidence for his second conclusion not being available, its exact significance is not entirely clear. The fact that the atmospheric gases seem able to diffuse througji quartz glass at comparatively low temperatures renders it not improbable* that a similar behavior might be exhibited by some of the ordinary commercial glasses under some circumstances, although doubtless to a considerably less extent.

22. The Influence of Dissolved Gases upon the Properties and Behavior of Glass. —Evolution of dissolved gas in the form of bubbles tends to occur whenever the pressure, on glass, while in a fluid condition, is decreased. Such a decrease in pressure will occur during the manufacturing operation whenever there is a marked fall in the barometer, and it would be interesting to know whether there is any record of troubles with "seedy" glass accompanying periods of barometric depression.

A condition of reduced pressure with a consequent evolution of bubbles of gas also results from the strains set up by the contraction of the glass itself. If the outside of a mass of glass be allowed to solidify while the interior is still in a fluid condition, it is evident that the gradual solidification of the remaining glass must bring about a tension upon the still fluid portions; and this decrease in pressure will cause them to evolve their dissolved gases, with the consequent formation of a mass of bubbles in those portions of the glass which remain longest in the fluid condition. Some interesting examples of the formation of seed from this cause have been described by Williams, t

Still another instance of the occurrence of reduced pressure during manufacturing operations is met with in cases where the glass is "gathered" by suction, as in the case of the Owens machine. If the glass when it reaches the gathering machine is supersaturated with dissolved gases, the operation of gathering will evidently result in the formation of seed, some of which will not disappear again when the suction is released. If the glass at the moment of gathering is

* Of. Le Chatelier, "La Silice et les Silicates," p. 94, Hermann et Fils, Paris 1914; Mayer, E. C., "Leakage of Gases through Quartz Tubes," Phys. Rev., Vol. 4, 283 (1915),

t Williams, A. E., "Observations on the Formation of Seed in Optical Glass Melts," Jour. Amer. Ceramic Soc., Vol. I, 134 (1918).

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