Borosilicate Vs. Tempered Glass

Test tubes are made of borosilicate glass

Different types of specialized glass have unique properties that are desired in different situations. Borosilicate glass is very crack-resistant glass that is perhaps most commonly found in laboratory glassware. Tempered glass is glass that has been treated to make it stronger and safer; it is quite common and is found in many places, including safety glass windows and doors.

Untreated Glass

Regular glass is a very useful substance, but among its limitations are its tendency to shatter into razor-sharp pieces on impact, its tendency to crack upon experiencing sudden changes in temperature (thermal shock), and its low structural strength. Tempered glass and borosilicate glass are special glasses that are made to improve the performance of the material in one or more of these areas.

Borosilicate Glass

This special glass is especially resistant to thermal shock, but is also stronger and more durable than regular glass. The trademarked laboratory glassware Pyrex is an example of this type of glass. Borosilicate glass is made by replacing the calcium carbonate component of regular glass with boric oxide.

Tempered Glass

Tempered glass is regular glass that has been treated with a thermal or chemical process to make it stronger and more heat-resistant. If broken, it breaks into many small squared-off fragments, making it safer to use in applications such as the side and back windows of passenger vehicles and the glass doors and windows of buildings.

Differences

Borosilicate glass has superior thermal shock resistance and a lower thermal expansion factor, which is useful in some special optical uses such as instrument lenses. Tempered glass is better for use in passenger vehicles, as its physical characteristics make it less likely to form shards upon breaking; it also cannot be cut or physically altered once tempered.

Similarities

Both types of glass are stronger and more resistant to thermal shock than regular glass.

References

• Solstice Glass: What is Borosilicate Glass?
• "General Chemistry, 2nd ed.;" John W. Hill, Ralph H. Petrucci; 1999
• Corning, Inc.: Corning, Pyrex and Telescopes

Resources

• Duran Group: Duran [Borosilicate Glass] Properties
• Rayotek Scientific, Inc.: Choosing the Right Material