326 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1962 



Figure 3. — Schematic two dimensional representation according to Warren of the structure 

 of soda-sihcate glass. The silicons are here shown to be bonded to only three oxygens. 



As the molten glass cools, tlie network becomes more and more rigid 

 until, usually at 400° to 600° C, it is completely solid. The plasma, 

 however, usually does not "freeze" at such a high temperature as the 

 network, so that at temperatures where the glass is completely rigid, 

 diffusion and chemical reaction can still occur among the modifier 

 ions. At still lower temperatures, but still above room temperature, 

 the plasma also freezes so that no translational motion of molecules or 

 ions can occur. At room temperature, high-energy ionizing radiation 

 can produce electronic transitions, but not molecular rearrangements. 



We can see then that the simplest glasses, except for one-component 

 glasses like plain fused silica, are molecular two-phase systems al- 

 though they are amorphous by any macroscopic or microscopic 

 observation. In more complex glasses such as the alkali borosilicates, 

 two interpenetrating polymer networks can be present, one containing 

 mostly silica, the other mostly boric oxide. At low temperatures 

 these two networks tend to separate into really discrete phases, so 

 that submicroscopic channels or droplets of alkali borate glass are 

 present in a silica matrix. This behavior is the basis of high-silica 

 glass, which is made by heat treating a special alkali borosilicate 



