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THE CONSTITUTION OF GLASS *
Author(s) -
MOREY GEORGE W.
Publication year - 1934
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1934.tb19332.x
Subject(s) - thermodynamics , phase diagram , glass transition , crystallization , silicate , discontinuity (linguistics) , viscosity , classification of discontinuities , mineralogy , atmospheric temperature range , materials science , alkali metal , chemistry , phase (matter) , composite material , physics , polymer , mathematics , organic chemistry , mathematical analysis
Glass is to be regarded as a liquid which has a viscosity so great as to be practically rigid; and the glasses of commerce are all solutions undercooled far below their normal crystallizing temperatures. Nothing more is known regarding the constitution of these highly concentrated solutions than is known about the constitution of other concentrated solutions. The phase‐equilibrium diagram gives no information as to the compounds present in the liquid phase, for there is no known correlation between the properties of a homogeneous system and those of the heterogeneous system formed from it on crystallization. Evidence based on the rate of volatilization of alkali from alkali‐silicate glasses does not indicate compound formation. The discontinuous change of properties of a glass in the “annealing range” has been considered by some to be evidence that the glassy state is a fourth state of matter separated from the liquid state by this transition temperature; by others, as indicating that above this discontinuity the material is a liquid, below it, a brittle solid. These views are unsound, because they are based on measurements of physical properties made with changing temperature when those properties themselves not only change with temperature but also require at each temperature considerable time to reach their equilibrium value. When the measurements are made on glasses which have been held at constant temperature long enough for the equilibrium value of the property to be attained, no discontinuities are observed and there is no justification for calling glass a fourth state of matter or for separating a “brittle” from a “viscous” temperature range. Arguments, based on the variation of physical properties with composition in which it is considered that such variation is represented not by a continuous curve but by a series of straight lines determined by the composition of hypothetical compounds, are shown to be theoretically improbable and not in accord with the facts. Recent speculations on the constitution of glass based on X‐ray evidence and recent studies of glass by means of X‐rays indicate that the glassy state is distinguished by a random nonrepeating atomic network. This conclusion is in harmony with the view that glass is an undercooled liquid representing a solution in which definite compounds can not be identified.