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Studies have been made on the conditions of the formation of multicomponent glasses assuming that the one to one correspondence between the glassy state and the glass structure does hold good. This idea is strongly supported by the experimental results of the glass formation range of the systems of borate, silicate, germanate, tellurite glasses, etc.The conditions of glass formation may be divided into two groups, namely, one puts stress on the geometry of the structure, and the other on the strength of chemical bonds. The former is represented by Zachariasen's rule, and the latter by the mixed bond, and electronegativity theories etc. However, the author pointed out that the conditions regarding the bond strength are implied by those of geometry being necessary for giving glassy state.According to the picture of glass structure consisting of network and modifier ions Zachriasen's rules are to be applied to the network. The important point in this rule is that the valency of the ion of the network is equal to its coordination number, i.e. Z/S (electrostatic valency)=1. For multicomponent glasses this condition is to be extended as follows:(1) A cation whose valency is less than the coordinate number, an intermediate ion, may join in the network to take the office of a network former if the condition Z/S=1 is satisfied by making up the difference with the positive charge of an attached modifier.(2) In order to form glass at least one dimentional continuity should exist in the structure. In addition oxygen polyhedra should share corners, and the central ion of the polyhedra should be small.These conditions of glass formation are supported strongly by the experimental survey of the area of glass formation covering many polycomponent glasses.Furthermore, the glass forming range involving b-subgroup ions as Pb may be explained by the idea that Pb-ion itself helps the formation of network of four coordinated Pb.On the other hand, glass formation range changes by the influence of modifier ions. It was concluded from geometrical calculation that the radius of a modifier ion being most suitable to the network atom is 6 coordination. It the network is formed by four coordinated ions the most suitable radius ratio is Rm/Rn=2, where Rm and Rn are respectively the radii of modifier and network ions.
社団法人日本セラミックス協会の論文
1959-11-01

著者

今岡稔
東京大学生産技術研究所

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