*3.2. X-ray Diffraction (XRD)*

#### 3.2.1. XRD of the Investigated Samples after Treatment at Temperature 1000 ◦C for 2 h

X-ray diffraction analysis of the studied glass–ceramic samples G10–G80 after heat treatment at a temperature of 1000 ◦C for 2 h is shown in Figure 3. The main crystalline minerals developed are β-wollastonite (CaSiO3) (JSPDS No.27-1064), parawollastonite (CaSiO3) (JCPDS No.27-88), diopside (CaMgSi2O6) (JCPDS No.22-534), anorthite (CaAl2Si2O8) (JCPDS No.12-301) and cordierite (Mg2Al4Si5O18) (JCPDS No.13-294). Concerning samples G10 and G20, it is obvious that β- wollastonite (CaSiO3) is the only monomineralic phase formed, characterized by the following lines 3.296, 3.807, 3.489, and 3.076 Å. While for samples G30 and G40, the β-wollastonite transferred into parawollastonite, characterized by lines 2.97, 3.318, and 2.699 Å with the formation of the diopside phases, which is characterized by the following lines 2.972, 3.182, and 2.503 Å. Whereas in glass–ceramic samples Nos (G50–G70), the parawollastonite transforms into anorthite, characterized by the following lines 3.202, 4.036, 3.739, and 2.501 Å. In sample G80, the low-cordierite phase formed, which is characterized by the following lines, 8.412, 3.128, 3.366, and 3.015 Å with an anorthite phase. Samples G10 and G20 show the formation of β-wollastonite only; this is consistent with Table 2, where the percentage of wollastonite ranges from 90 to 80 % in samples G10 and G20, respectively. It also agrees with many publications, such as Shaker et al. [27] and Khater et al. [28,29], who explained that β-wollastonite is formed at low temperatures and is unstable and then transformed into parawollastonite. Samples G30 and G40 show the formation of parawollastonite and diopside. This shows that β-wollastonite (CaSiO3) is converted to parawollastonite, which agrees with Shaker et al. [27]. In samples G50, G60, and G70, the formation of diopside and anorthite is attributed to the aluminum elements present in cordierite with wollastonite, which help form the anorthite mineral while the magnesium and silica elements present in

cordierite help in the formation of diopside. Sample G80 contains both minerals cordierite and anorthite, indicating the reach of a stage close to equilibrium phases.

**Figure 3.** X-ray diffraction patterns of the investigated samples based on by-pass cement dust after heat-treatment at 1000 ◦C for 2 h.
