Large glass structures have become a signature of modern architecture, creating a sense of space and minimalism, whilst absorbing the sun’s rays to naturally heat and light structures. Advances in the ways we produce glass have revolutionised the way we use it, resulting in varieties with specific properties for use everywhere.
Toughened and tempered glass are processed by controlled thermal or chemical treatments to increase their strength. This is achieved by cooling the exterior of the glass more quickly than the interior, producing a large amount of compressive and tensile stress throughout the glass to make it stronger both physically and thermally.
The quicker the cooling process, the stronger the glass; tempered glass is cooled more rapidly and is usually around four to six times the strength of standard glass, whereas toughened or heat-strengthened glass is cooled more slowly, and is up to twice the strength.
Owing to its increased thermal resistance, tempered glass is often used for cooking and baking purposes. It is also a common building material as it is able to withstand more pressure and therefore less likely to cause injury. Furthermore, high compressive and tensile stress also means that if the glass it broken, it will crumble into small chunks rather than large jagged pieces, again reducing the risk of injury. Phone boxes, skylights, sliding doors and car windows all make use of tempered glass.
The main disadvantage of toughened or tempered glass is that it must be cut to size before the tempering process begins and cannot be reworked afterwards. This is because the stresses throughout the glass are balanced, making it more susceptible to breaking entirely should enough pressure be placed on it, especially at its perimeter where the tensile stress is particularly high. This can be a security concern as any exposed edges of the glass are weak points by which entry can be gained, for example, store fronts or vehicles.
Glass can be further treated by a lamination process, in which an adhesive film is placed inside the glass, meaning that should it break, the pieces it crumbles into are contained. This is useful for any application in which human impact is possible, such as wind-shields. It is also commonly used in refrigerator and freezer doors, where broken glass might otherwise contaminate food.
Glass comes in many varieties, for use in high stress environments such as aquariums as well as lower stress applications like car windows and bus stops, therefore its properties should be considered in line with the nature of its intended use.