Characterised by its exceptional resistance to high temperature and chemical exposure, aluminosilicate glass has become useful in numerous industrial, commercial, and personal applications.
This mineral-based material contains 57-60% silicon dioxide (SiO2) and 16-20% aluminium dioxide (Al2O3), along with small amounts of 5-7% lime (CaO), 6-12% magnesium oxide (MgO), boron trioxide (B2O3), among other cations.
Aluminosilicate glass properties
The following are some of the essential properties of aluminosilicate glass:
High strength and scratch resistance
Aluminosilicate glass is famous for making part of mobile devices, its properties are ideal to withstand scratches that are common on mobile devices.
The high alkali content in aluminosilicate glass makes the material intrinsically strong. The mechanical characteristics of this particular glass compound at 20 °C are as follows:
- Vickers Hardness = 480 – 670
- Knoop Hardness = 500 – 640
- Shear Modulus = 26000 – 31700 MPa
Resistance to high temperature
At an annealing temperature of up to 800°C and a Vicat softening temperature reaching up to 1010°C, aluminosilicate glass has relatively high thermal resistance compared to other similar glass materials. In fact, its temperature resistance is comparable to ceramics.
- Glass transition temperature = 620 - 790°C
- Thermal conductivity = 0.91 - 1.1 W/(m·K), at 20°C
High thermal expansion
Its coefficient of thermal expansion of 9.8x10-6 1/K (at 300°C) places the material on the same rank as materials used in electrodes. As a result, aluminosilicate glass may also be used as sealing material in hot systems and equipment.
Resistance to chemical degradation
The chemical durability of aluminosilicate glass has been confirmed in studies. The dissolution rate of this material is low at 10-4 g/(m2·day) under saturated conditions.
Production and processing
Aluminosilicate occurs in nature as zeolite, a microporous mineral that is commonly used for adsorption and as catalysts. However, due to the increasing demand for aluminosilicate glass, mass production of the material is necessary.
The manufacturing process of aluminosilicate glass is more complex than that of borosilicate glass, but its superior properties more than make up for the cost and effort in production.
The glass material may be processed into a wide range of products, mostly when combined with other compounds that enhance or augment its intrinsic properties:
- E-glass is formed when boric oxide is added to alkaline earth aluminosilicate glass. The result is a composite glass with higher electrical resistivity, refractive index, and density.
- Aluminoborosilicate glass is a modified version of borosilicate glass with some boron atoms replaced with aluminium.
- Gorilla glass is a brand of aluminosilicate glass that is chemically strengthened via an ion exchange process. During production, the glass is submerged in a 400°C molten potassium salt, from which the sodium atoms in the glass are displaced by potassium. The result is a glass with intensified surface strength, as well as resistance to cracks and scratches.
Applications of aluminosilicate glass
Glass screen for mobile devices
One of the most popular uses of aluminosilicate glass in recent times is in the mobile device industry due to their chemically-reinforced and shatter-resistant properties while maintaining the sleek appearance of glass over plastic. Advances in the manufacturing process have allowed the glass to be produced in thin sheets and act as an excellent conduit between our fingers and the device on touch screens.
High temperature systems
With its high temperature resistance, the material has become useful in several high-temperature applications:
- Halogen lamp glass receptacle: aluminosilicate glass has found a niche in glass bulbs and receptacles for halogen lamps.
- Thermometer tube for high temperature systems: Conventional glass may soften or weaken in extremely high liquids, and so using aluminosilicate glass as material for a thermometer may solve this issue.
- Ignition tubes: The material can withstand a significant amount of thermal shock in ignition systems.
- Cookware and utensils: Some kitchen utensils contain aluminosilicate glass, although not in its pure form due to cost considerations.