Britannica Sources used in this answer

Why can mixtures of calcium oxide and aluminum oxide form glass more easily than either pure material?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

How to properly care for contact lenses — amorphous solid Learn about the chemistry of contact lenses and why it is important to keep them clean.

In the binary system of calcium oxide (CaO) and aluminum oxide (Al₂O₃), neither pure material readily forms a glass on its own. However, mixtures of these two oxides form glass much more easily because the freezing point of the system exhibits a deep minimum near the middle of the composition range.1

In physics, the tendency of a liquid to form an amorphous solid depends on its ability to be cooled from its freezing temperature ( $T_{f}$ ) to the glass transition temperature ( $T_{g}$ ) without crystallizing. When a system has a lower freezing point, the temperature interval during which the liquid is at risk of crystallization is significantly reduced, making it much easier to quench the liquid into a glass phase. This phenomenon is a common characteristic in many binary systems, and it is a primary reason why many practical oxide glasses are composed of complex chemical mixtures rather than pure substances.1