With a usual bulb glass, an experiment has been carried out on the approach of specific volume to an equilibrium value for several samples which were pre-treated under various conditions, i. e. by quenching, annealing and stabilization. An electric self-controlled furnace is used for the heat treatment and the density at 20°C is measured by means of the sink method by using an aqueous solution of potassium iodide and mercuric red.
After treated for a sufficient time at a constant temperature in the transformation range, the density of the sample approaches to an equilibrium value from which and characteristic orientations of structural units seem to exist at respective temperatures within the range. From the curves of dV/dt vs. V, where V and t mean specific volume and time respectively, it is found that:
(i) The shape of relaxation curve is not always determined from the direction of approach towards the equilibrium state.
(ii) At the same holding temperature, the rate, dV/dt, is not the same even for the samples of the same specific volume if they are differently pre-treated. The non-equilibrium state during stabilizing process of glass is presumed to depend on the thermal history of the sample.
(iii) Samples, which are incompletely annealed and are kept at a constant temperature different from that of the annealing, undergo a rapid dilatation followed by a gradual contraction. This volume change is thought to have been caused by the combined effect of varied binding conditions among the structural units and the difference in structural orien-tations between the initial and final states.
As for the structural unit that contributes to the volume relaxation, a chain of solid clusters of Si-O
4 groups, for example, is reasonably conceived.
抄録全体を表示