Chemically toughened glass (also "ion-exchanged toughened glass", "thermochemically modified glass") is a type of glass whose strength is increased due to chemical treatment. When destroyed, such glass still gives long sharp fragments, like ordinary glass, so lamination with a film is required if there are safety requirements. However, chemically toughened glass is usually six to eight times stronger than ordinary glass .

Description

The strength of glass is enhanced by surface treatment. ^{[1] The} glass is immersed in a bath containing potassium salt (usually potassium nitrate ) at 300 ° C. This allows potassium ions from the melt to replace sodium ions on the glass surface. ^[2]

Since potassium ions are larger than sodium ions, replacing the latter in the crystal lattice, they cause its deformation and compressive forces appear in the surface layer. The compressive forces in the surface of chemically treated glass can be up to 690 MPa.

The mechanism for increasing the strength of glass is due to the fact that the glass has great compressive strength and low tensile strength. Since compressive forces appear on both sides in the surface layer, this allows the glass to get a greater bend before tensile forces appear in it. The phenomenon is much similar to that used in construction when creating stressed concrete .

There is also a more complex two-stage chemical treatment process, when glass is pretreated in a bath with molten sodium nitrate at 450 ° C to saturate with sodium ions, which will be replaced by potassium ions in the next step (the number of replaced ions increases, which increases deformations and stresses on the surface).

Chemical tempering leads to an increase in strength similar to ordinary glass tempering . But this process does not use extreme temperature drops, which does not lead to deformation and warping, the appearance of optical defects, and allows you to process even thin-walled parts.

Also, unlike ordinary tempered glass, chemically tempered glass can be cut and processed after tempering without cracks and destruction, however, a place about 20 mm from the section loses its strength properties. Also, with deep scratches, the surrounding area also loses the strength acquired by chemical hardening.

Chemically toughened glass is used, for example, in the manufacture of lights for some fighters. Gorilla Glass is also a kind of chemically tempered glass.

See also

• Gorilla glass
• Strained glass