*3.1. Differential Thermal Analysis (DTA)*

DTA of the studied glasses is explained in Figure 2. The curves resulting from the investigated glasses showed endothermic peaks in the temperatures ranging from 749 to 797 ◦C. The differential thermal analysis curves show that the endothermic peaks of the investigated glasses are wholly affected by the cordierite contents in the glass. As the cordierite content increases, the endothermic peak temperatures shift towards higher values. The endothermic and exothermic peaks of the investigated glasses for each glass composition are shown in Table 3. The DTA of the glasses G10 to G50 (Figure 2) are, to some extent, similar. They are characterized by a broad exothermic peak with a temperature ranging from 954 to 987 ◦C. While the other glasses, G60 to G80, have characterized sharp exothermic peaks recorded at temperatures ranging from 954 to 1018 ◦C, respectively.

**Figure 2.** Differential thermal analysis of the investigated glasses.


**Table 3.** Thermal expansion coefficient and phases developed of the investigated samples.

Where. B-woll. = B-wollastonite, Diop. = Diopside, parawoll. = Parawollastonite, An. = Anorthite, Cord. = Cordierite.

It should be said that the data recorded from DTA are considered to be the responsible guide for the heat treatment schedule of the investigated glasses.

The DTA curves show a slight dip in the range 749 to 797 ◦C most probably, as confirmed above, owing to the transition temperature of the glass (Tg) or corresponding approximately, following Devekey and Majumdar [25], to the temperature range named as Tg and Ts.

These endothermic agree to initial crystallization (precrystallization), where the glasscreating oxides begin to arrange themselves at this period in beginning structure groups appropriate for the subsequent crystallization El-Shennawi [26]. This thermal absorption span will be, however, considered as the nucleation range. Exothermic peaks result from glass devitrification with a corresponding release of thermal energy.
