As a decisive factor in the formation of a glassy phase from a silicate or borate melt on cooling, the crit. rate of cooling (vcr) was studied for the system Na2O 0-50 mole-B2O3 by the systematic measurement of the cooling rate conditions controlling crystn. from the melt on cooling, or from glass by heating. The WELCH thermocouple heating device (cf. Gossink, 1970) was used by which the beginning of crystn. during cooling and heating could be obsd., and thus the vcr was calcd. for 1 mg samples. The log of vcr as a function of the Na2O concn. in the binary mixts. coincides when plotted on the temp.-mole fraction projection of the phase diagram with the max. of congruent fusion-crystn. equil. for the stoichiometric ratios Na2O:B2O3 = 1:1; 1:2; 1:4; the min. of the log vcr curve coincided with the compn. of binary eutectica with 30 and 34 mole Na2O. There is a min. for the peritectic equil. for the 1:3 compn. The temp. of the first indication of crystn. in the melt on cooling (Tcm), and in the glass on heating (Tcg) were detd. at a rate of +-1 Deg/sec. The interval between Tcm and Tcg indicates the presence of easily crystallizing compns., and crit. temp. ranges which must be passed as rapidly as possible to avoid devitrification
|Publication status||Published - 1972|
Baeten, M. H. C., Stein, H. N., & Stevels, J. M. (1972). La relation entre la vitesse critique de refroidissement et le diagramme de phases dans le système B2O3-Na2O. Silicates Industriels, 37(2), 33-36.