Role of vitrons in alkali silicate binary glasses

Abstract

Appli cations of v it ron t heo ry to analyses of properti es of R 20 s ili cate binary glasses indicate that change in slop e on t he property-composition curves m ay occ ur where t h ere are integral numbers of cation s p er dodecah edral cavity or cage of th e network. From geometrical consid eration s i t is found that 1 or 2 oxygens and 6 sodiums can be accommodated inside a cage, an d similar ly not more t h an 1 oxyge n a nd 4 potassiums can be inclosed in a cage.Data on ch emi cal attack and on solubility losses in water s ugges t for alkali s ilicate glasses a maximal a verage inclos u re of oxygen inside t he cavit ies at 16.7-mole p ercen t for K 20 , 23. 1 percen t for Na20, and probably 28.6 p ercent for Li 20 . T hese composit ions correspon d to 1, 1.5, an d 2 oxyge ns per cage. T hese co mposit ions m ark t he beginning deterioration of the net. poss ibl y because of non bridg in g oxygen. C hanges in rate of volatili zation occ ur at 28.6-, 37.5-, a nd 50 .0-per cent R ,O for potash , soda, and li t hi a sili cate glasses, res pectively. These crit ical co mposit ions are cons id ered t hose for which t he cavit ies in t he p;lasses are com p letely saturated wit h the modifi er oxides, R,O, and with additional cations, R .D etail ed analyses of cur ves of molar volume versus co mposition show th a t the critical points for oxide saturatio n arc evide nt and that ch a nges in slope may occur at other cri t ical compos ition s corresponding to in tegral numbers of cat ions per cage. It is found that t h e percentage of 16.7-percent N a 20 at hi gh temperatures and the sat ura t ion point of 37.5 perce n t at low temperatures are cri t ical in curves for specific (electri cal) resistance. The "deep-well " point at 16.7-perce n t Na20 critically separat es soda sili cate glasses t hat are very rea dily devitri fi ecl from those t hat contain more oxide modifi er a nd are more stable.

Selected properties of sodium silicate glasses and their structural significance

“…This shows that if there is a major structure change over the composition range tested it does not abruptly affect the electrical properties. This is in contrast to the structure theories of Huggxns (5) and Tilton(7). It also contradicts the results of Otto and Milberg (21) who found a break in the activation energy vs. composition curve at 25 mole % Na^O.C.…”

“…The electrical resistivity data of Seddon, Tippet, and Turner (8) has been interpreted in a different manner by Tilton (7). The electrical resistivities of sodium silicate glasses ranging from 7.9 to 40.0 mole % Na20 were determined at 50 hz.…”

Selected properties of sodium silicate glasses and their structural significance

“…This shows that if there is a major structure change over the composition range tested it does not abruptly affect the electrical properties. This is in contrast to the structure theories of Huggxns (5) and Tilton (7). It also contradicts the results of Otto and Milberg (21) who found a break in the activation energy vs.…”

“…The electrical resistivity data of Seddon, Tippet, and Turner (8) has been interpreted in a different manner by Tilton (7). He interprets the log p vs. composition curves as being composed of straight line segments with changes in slope at 16.7, 28.6, and 37.5 mole % Na20.…”

Vitrons as flow units in alkali silicate binary glasses

“… Two volume-changing processes found useful in studying the mechanism of viscous flow in glasses are: (a) stress-induced variation in fissuring near vitrons at their peripheries where the Si–O bonds are tensed and weakened, and (b) distention and modification of all silica network by added oxides. These idealized processes, readily derivable from the vitron concept of pentagonal ring structure in glass [ 1 ], 2 are sensitive to both temperature and composition and have previously been found useful [ 1 , 2 , 3 , 4 , 5 ] for understanding other properties of glasses. Viscous flow of vitrons as units in annealing ranges, and at higher processing temperatures for silica-rich glasses, is here viewed as permitted primarily by the breaking of tensed and weakened Si–O bonds in shell-like stressed tissues surrounding vitrons.…”