Refinement (glass)
Under purification refers to the expulsion of bubbles from the finished molten glass . Bubbles are a glass flaw . The basic principle is that the small bubbles are carried along by larger bubbles that rise faster. Small bubbles do not rise quickly enough in the viscous glass mass, so that, in addition to increased temperature and stirring, further support measures are necessary in order to accomplish this in an economical period of time.
This is usually done by adding refining agents in batches . Sulfur refining with sodium sulphate with the release of SO 2 and O 2 is of industrial importance . High melting point glasses, e.g. B. Borosilicate glasses are refined with NaCl, which is volatile at high refining temperatures due to its vapor pressure. Alkali-free refractory glasses, e.g. B. for LCD displays, use SnO 2 . The arsenic clarification was historically significant and is only used today for special optical glasses .
In addition to chemical refining, the proportion of bubbles can be reduced by bubbling , i.e. blowing in gases. Tests are also carried out with ultrasound (bubbles combine on the standing waves) and negative pressure (bubbles rise faster). The refining is generally supported by lowering the viscosity of the glass melt when the temperature is increased.
Individual evidence
- ^ Crawford, G. (2005). “Flexible Flat Panel Displays,” p.42. John Wiley & Son
- ↑ http://www.schott.com/d/advanced_optics/a803a4c7-ca14-4a0c-9ca9-3fffee42666f/1.0/schott-laser-munich-workshop-optisches-glas-elösungen-mai-2013.pdf , page 10 ( Accessed January 19, 2018)