Tempered glass is two or more times stronger than standard annealed glass. This type of glass is used in buildings and products where regular glass could be dangerous. Two types of tempered glass are heat treated glass and chemically strengthened glass.
Standard annealed glass is heated to 680 degrees and immediately undergoes a cooling process. The glass is exposed to cold air which causes the outer surface to freeze while the interior is still hot liquid. This process makes the glass stronger than annealed glass. By design, heat-treated tempered glass breaks into many small blunt pieces.
Chemically Treated Glass
Chemically treated glass is soaked in dissolved potassium salts at about 380 degrees. While it is not common to use this type of glass for windows, chemically strengthened glass is utilized in applications where a strong, thin glass is needed. On impact, this glass breaks into large pieces.
Heat-strengthened glass is used in high-traffic areas that require safety precautions. Building codes usually require this type of glass to be used in the construction of entrances and windows. Sliding doors, shower doors, skylights and coffee maker carafes are also made from heat-strengthened tempered glass.
Chemically treated tempered glass is used in military design because of its visibility qualities. It is also used in the production of protective covers and retail scanners.