What is boric oxide responsible for in Type II glass?

• A. Chemical resistance or resistance to leaching
• B. Lower melting point than Type I
• C. Lower thermal expansion coefficient
• D. None of the above

Answer: (A)

The key idea here is chemical durability—how well the glass stands up to water and acids without leaching components. In Type II glass, boric oxide acts as a network-forming oxide that helps create a silicate-borate structure. This borate-containing network stabilizes the glass and reduces the rate at which water can attack the matrix, which slows down the diffusion of ions and minimizes leaching. In practical terms, adding boric oxide makes the glass more resistant to chemical attack, which is exactly what Type II glass is designed to achieve.

While boric oxide can influence properties like melting behavior and thermal expansion, the main role relevant to Type II glass is enhancing chemical resistance to leaching.