Boron Trioxide (B₂O₃)

Formula: B2O3

Melting point: 450ºC

Density: 2.55 g/cc (common form)

Solubility: Slowly in water. Poor chemical resistance.

B₂O₃ is a boron oxide known since the 19th century, but rarely used in isolation due to its slightly soluble nature and fragility. Its true importance lies as an essential component in technical and specialty glass, particularly in the manufacture of borosilicates. The glass industry systematically incorporated it beginning in the early 20th century, after it was discovered that its addition significantly improved the mechanical and thermal properties of silica-based glasses.

Pure boron trioxide occurs as a glassy, ​​amorphous solid, white in appearance and hard in texture, with an irregular structure that gives it properties different from those of quartz crystals (SiO₂). Despite its partial solubility in water, its combined use with other oxides transforms it into a stable and chemically inert component. When fused with silica and other metallic additives, it forms three-dimensional glass networks that are extremely resistant to thermal shock and chemical attack.

The typical B₂O₃ content in borosilicate glasses ranges between 8% and 15% by mass. In these materials, boron trioxide dissolves in the silica matrix along with oxides such as Na₂O, CaO, and Fe₂O₃, generating a homogeneous and stable glassy structure. The presence of B₂O₃ improves toughness and hardness without compromising corrosion resistance, as the resulting network is virtually insoluble.

Boron trioxide is not typically used pure, but it is the basis of borosilicate glass, widely used in applications requiring high thermal resistance and chemical stability. This type of glass is common in laboratories, kitchen utensils subjected to extreme temperatures, high-performance lighting systems, and industrial components exposed to aggressive environments.

Furthermore, B₂O₃ is used in the formulation of ceramic glazes, specialty optical fibers, and glasses for the electronics industry, where its presence helps control thermal expansion and improve the durability of materials.

Boron trioxide remains a strategic material for glass engineering. Although in its pure form it has limited chemical resistance, its role as a network modifier in borosilicates makes it an indispensable component for the manufacture of high-quality technical glasses. Its incorporation allows the production of lightweight, hard, and durable materials, with applications ranging from domestic use to advanced science and the aerospace industry.