Effect Of Annealing On The Density Of Borosodium Glasses

Glasses made from calcined borax (2B2O3.Na2O) and boron anhydride or sodium carbonate were melted at 1100C under atmospheric pressure in a Pt crucible. After the density was determined (in xylene), the glasses were annealed at a temperature at least 50C higher than their respective transformation points and left for a week at this temperature; they were then cooled slowly (at a rate of 0.8/hr). This treatment did not modify the density; equilibrium was attained in all cases. Curves show the behaviour of the different glasses and the increase in the specific volume as a function of the alkali content.