Structures for Oxides Glasses

Experimental studies are being conducted to obtain the stmcture of glasses. The crystal structure can be determined accurately, whereas the glass structures cannot be determined precisely. Usually, the most common glasses are silicate, borate, aluminosilicate, phosphate and germinate. In this section, we discuss the structure of borate, silicate, and aluminosilicate glasses in detail which are within the scope of this book. 

The basic building block for silicate glasses is a silicon-oxygen tetrahedral. These tetrahedrals are linked to each other to form a 3-D network (Fig. 5.23). 

Let us take the general composition to be XA2O + (100 — x) Si02- Total oxygen content would be [x + (100 - x)2]. Every oxygen is shared by two tetrahedrons as shown in Fig. 5.23. For different oxygen sharings, we define as 

Usually, alkali oxide contributes in NBO. For the total oxygen to be shared between 04 and 03, we write 

04 shares 2 oxygens/tetrahedron and 03 shares 2.5 oxygen/tetrahedron, and hence we can write 

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