Known for its heat resistance and physical durability, borosilicate glass is useful in many applications mostly involved with temperature changes. The material owes its strength and resistance to its unique combination of silica, boric oxide, among various other oxides. The presence of boron oxide to replace some of the oxide components enhances the binding forces within the glass material.
Borosilicate glass properties
Low thermal expansion
With a thermal expansion coefficient of at least 3.2 x 10-6 1/K, pure borosilicate glass is significantly more resistant to temperature changes where other types of glass may become warped or deformed.
Its strength in thermal shock exposure makes the material suitable for laboratory heating and cookware. This characteristically low thermal expansion allows the material to maintain its integrity, even when transferred from a cold region (such as a refrigerator) to a hot area (like an oven) in seconds.
Modifications in the amount of its components may increase the thermal expansion coefficient to 7.38 x 10-6 1/K, but it is still much more resistant than ordinary soda-lime glass.
Other thermal properties of borosilicate glass include the following:
- Annealing temperature = 470 - 640°C
- Vicat softening temperature = 460 - 840°C
- Transition temperature = 440 - 560°C
High material strength
Compared to similar glassware, borosilicate glass can withstand blunt force impact better. It has a Shear modulus of 2650 – 27000 MPa and Knoop hardness of 400 – 480 at 20°C.
Borosilicate glass can withstand corrosion and breaking when exposed to acidic environments.
Production and processing
This special type of glass is produced from melting the following substances (with corresponding approximate composition): silica sand (59.5%), boric oxide (21.5%), potassium oxide (14.4%), zinc oxide (2.3%), and trace amounts of calcium oxide and aluminium oxide.
Other variants – such as in cases wherein borosilicate glass is used as cookware – may change the silica composition to as high as 81%, depending on its intended use.
The melting process requires an exceedingly higher temperature than traditional glass production, owing to the material’s high transition temperature of up to 560°C.
Once the substrate has been produced, borosilicate glass may be processed in a number of ways depending on the application for the material. This glass material may be moulded or drawn into tubes, and processed into custom shapes and sizes.
Applications of borosilicate glass
Borosilicate glass has become useful in a wide variety of industries and applications, because of its physical and chemical properties.
Borosilicate glass is popular as a base material for laboratory glassware, mainly because of the material’s chemical and thermal stability. Most of the modern beakers, flasks, and other glass receptacles designed for laboratory use are made of borosilicate glass.
Medical glass tubings
Some syringes and vials used for intravenous administration of drugs are made of borosilicate glass. The material is mostly chemically inert when in contact with most liquid medication products.
Cookware and kitchen implements
Owing to its remarkable thermal resistance, this glass material has found its way into kitchenware, particularly for cooking and baking. Popular cookware brands make use of borosilicate glass for baking dishes and glass cooking pots.
In addition, because of its low thermal expansion, this glass material is used for measuring cups and similar receptacles. Graduations labelled on the glass containers retain their accuracy because the material won’t warp when exposed to high temperatures.
Due to the stability of borosilicate glass, it is a good material in fabricating slides and lenses for microscopes, telescopes, and other optical devices. Addition of doping agents may change the glass characteristics, such as optical absorption spectra.
Lighting equipment requires glass receptacles and membranes that can withstand intense heat, and this is where borosilicate glass is extremely useful. Devices that use this glass type include HID lamps, modern high-powered flashlights, and studio spotlights.
Recent studies involve modifications in the chemical composition of borosilicate glass, through the addition of doping chemicals. Alteration in the photoluminescence spectra of the material is poised to become useful for solid state display, W-LED, and similar applications.