Density Phenomena in the Transformation Range of a Borosilicate Crown Glass

Abstract

The effect of heat‐treatment in the transformation range on the density of a borosilicate crown glass was studied by the method of quenched samples. An empirical equation is presented which satisfactorily represents the approach of the density to its equilibrium value at three temperatures. The density‐temperature relation in the special case of cooling at a constant rate is discussed theoretically and experimentally. It is shown that if the initial temperature is sufficiently high, the density‐temperature relations for different cooling rates are identical except for a displacement along the equilibrium density‐temperature line by an amount proportional to the logarithm of the cooling rate. The final density reached after cooling through the entire transformation range is also shown to depend linearly on the logarithm of the rate. The implications of these results are discussed.