In conventional chemical tempering, potassium atoms are used to replace some of the sodium ions in the surface of the glass. Because the potassium atoms are larger, they crowd the other atoms and compress the glass's outer layer, making it stronger. Once flaws get through the surface, however, there's nothing to stop their spread. First, the process replaces sodium ions with potassium ions at the surface, just like the conventional process. Then sodium ions are put back on the surface, which pushes some of the surface potassium into a central layer.
Flaws can still form, but their growth is stopped by the subsurface barrier of potassium ions.
The new tempering method could put lighter and stronger glass in everything from eyeglasses to photocopying machines and electronic displays. All rights reserved.