Maqueda et al. [28] calculated theoretical curves under
linear heating rate conditions by means of the Runge–Kutta
algorithm included in the Mathcad software. However, the
process of calculation is rather complicated. The theoretical
curves were also determined by a graphical method [29,
30]. Figure 3 shows the DTA curve for the crystallization
peak of Nd2Si2O7 at h = 10 K/min, besides the crystallization
fraction, x (crystallized at a given temperature T)
given by x = AT/A, where A is the total area of the exothermic
peak between the temperatures, Ti (the onset of
crystallization) and Tf (the full crystallization), and AT is
the area between Ti and T.