Glass Network Formation and the Covalency Factor

JSGT 1947 V31 T114-T121

The various expressions which have been derived to determine whether an element acts as a network-former in glass, or as a stabiliser or modifier are discussed. On the basis of the author's theory of glass structure, in which such atoms as sodium are considered as playing a more or less important part in the maintenance of the continuous network, a covalency factor (ϕ) is assigned to the various elements. It is emphasised that very strong bonds tend to produce regular crystalline atomic arrangements, and that normally weak bonds may be constrained by the rest of the structure to have some additional covalent character. The arbitrary classification of elements into glass formers, stabilisers or intermediates, and modifiers cannot be supported.

H. Cole