Читать книгу Encyclopedia of Glass Science, Technology, History, and Culture - Группа авторов - Страница 253

The degree of polymerization of the aluminosilicate network affects most glass and melt properties. Melt polymerization can be expressed as the proportion of nonbridging oxygen (NBO) per tetrahedrally coordinated cations (T), NBO/T. The NBO/T can be calculated from the chemical composition of a glass and melt, provided that types and proportions of network‐forming cations are known. Then, NBO/T = (2·O–4·T)/T, where T and O are atomic proportions of tetrahedral cations and oxygen, respectively, and T is given a formal charge of 4 can be readily calculated.

The principal network‐formers (tetrahedral cations) in complex glasses and melts are Si⁴⁺ and Al³⁺. These will be discussed first.