Glass is an amorphous solid, lacking the ordered structure of crystals. Its amorphous structure allows for transparency and malleability for diverse applications. Glassmaking originated around 3500 BCE in Mesopotamia or Egypt. Over time, manipulating its composition has led to many glass types for specific purposes.
Everyday and Common Glass
Soda-lime glass is the most prevalent type (about 90% of manufactured glass). Its composition includes silica (70-74%), sodium oxide (15%), and calcium oxide (9%). Soda acts as a flux, lowering silica’s melting temperature, while lime enhances chemical durability and stability. This glass is inexpensive, chemically stable, and easily workable, ideal for mass production.
Suitable for common items like windowpanes, bottles, jars, and drinking glasses. While it has moderate chemical resistance and softens at 700°C, it can be repeatedly remelted and recycled without degradation.
Aluminosilicate glass incorporates aluminum oxide (20-40% alumina) and silica. This enhances its strength, scratch resistance, and thermal durability compared to soda-lime glass. It can withstand higher temperatures, with a softening point exceeding 920°C and a working temperature up to 600°C.
Its improved properties make it preferred for durability applications. It is commonly found in smartphone screens, oven doors, and specialized architectural glass. It is also used in gauge and sight glass, aerospace components, and electronics for electrical insulation and chemical resistance.
High-Performance and Specialized Glass
Borosilicate glass, known for thermal properties, contains silica and boron trioxide. Its low coefficient of thermal expansion makes it thermal shock resistant. It can withstand rapid temperature changes without fracturing, and remains stable for continuous use up to 450°C.
Beyond thermal resilience, borosilicate glass exhibits chemical durability and optical clarity. These characteristics make it suitable for laboratory glassware, bakeware, and pharmaceutical packaging. It is also used in specialized lighting and electronic components for temperature stability and chemical inertness.
Fused silica glass is known for its high purity, primarily silicon dioxide. Its near-pure composition results in high temperature resistance, with a deformation temperature up to 1700°C, allowing use up to 1000°C. It possesses a low thermal expansion coefficient and resistance to thermal shock.
Fused silica glass offers transparency across a broad spectrum, including UV, and is chemically inert. It is used in fiber optics, telecommunications, semiconductor manufacturing, and high-temperature lamp envelopes. It is also used in precision optical components and environments requiring chemical resistance.
Advanced and Designer Glass
Lead glass, often referred to as crystal, is distinguished by the inclusion of lead oxide (often at least 24% by weight). This increases its refractive index, creating sparkle and optical dispersion. Lead also makes the glass softer and heavier, allowing intricate cutting and engraving, and produces a ringing sound when tapped.
Its optical properties and workability make it suitable for decorative crystalware, chandeliers, and ornamental objects. Beyond aesthetics, lead glass is also used in specialized optical lenses and for radiation shielding in medical and research, as it absorbs X-rays and gamma radiation.
Glass-ceramics are a class of materials formed as glass then heat-treated for controlled crystallization. This results in a microstructure of glassy and crystalline phases, combining glass fabrication ease with ceramic properties. They exhibit high thermal shock resistance, low thermal expansion, strength, and non-porous characteristics.
These materials are valued for their durability and thermal stability. Common applications include cooktops, ovenware, and industrial components for temperature fluctuations. They are also employed in biomedical devices like dental restorations and bone substitutes, and in advanced electronics and aerospace components for their tailored properties.