# The Role of Brownmillerite in Preparation of High-Belite Sulfoaluminate Cement Clinker
## 3 Results and Discussion
### Sintering of HBSC Clinker Containing Brownmillerite
#### 3.2.3 Mineral Composition  
The mineral composition of HBSC linker containing brownmillerite sintering at 1330 \({}^{\circ}\)C for 30 min was analyzed by qualitative XRD (QXRD). QXRD patterns are shown in Figure 4. The corresponding mineral compositions calculated through QXRD are listed in Table 9. The main minerals in HBSC clinker containing brownmillerite were C\({}_{4}\)A\({}_{3}\)S, C\({}_{2}\)S, brownmillerite, gelhentic (C\({}_{2}\)AS), perovskite and C\({}_{3}\)A. As shown in Table 9, C\({}_{4}\)A\({}_{3}\)S and brownmillerite were slightly higher and much lower, respectively, than the theoretical mineral compositions shown in Table 2. It has been reported that either Fe\({}^{3+}\) or Al\({}^{3+}\) could occupy al\({}^{3+}\) position in C\({}_{4}\)A\({}_{3}\)S structures to form a C\({}_{4}\)A\({}_{3-x}\)F\({}_{x}\)S solid solution. The replacement amount of Fe\({}^{3+}\) could range from 2% to 10% or even higher [15; 16; 17; 18; 26; 27; 28]. Substitution of Fe\({}^{3+}\) for Al\({}^{3+}\) in C\({}_{4}\)A\({}_{3}\)S led to a lower content of actually generated brownmillerite than the theoretical calculation value. Meanwhile, some Al\({}^{3+}\) existed in the form of C\({}_{3}\)A (Table 9). Overall, the C\({}_{4}\)A\({}_{3}\)S increased to more than the theoretical mineral composition with the increase in the designed brownmillerite content in HBSC clinker; that is, brownmillerite promoted the formation of C\({}_{4}\)A\({}_{3}\)S, and also had a specific stabilizing effect for C\({}_{4}\)A\({}_{3}\)S. The content of C\({}_{2}\)S differed little from the theoretical content, as shown in Tables 2 and 9. However, \(\beta\)-C\({}_{2}\)S content tended to decrease with the increase in designed brownmillerite content, while \(\gamma\)-C\({}_{2}\)S content showed an increasing trend. Fe\({}_{2}\)O\({}_{3}\) can interact with \(\beta\)-C\({}_{2}\)S to form an unstable solid solution, further reduced to FeO in a reductive atmosphere to form CaO-FeO-SiO\({}_{2}\) (CFS), thus destroying \(\beta\)-C\({}_{2}\)S lattices [30; 31]. As is well  
Figure 3: Petrographic images of HBSC linker **(a)** GF-1 \(\times\) 400, **(b)** GF-2 \(\times\) 400, **(c)** GF-3 \(\times\) 400, **(d)** GF-4 \(\times\) 400, and **(e)** GF-5 \(\times\) 400.  
known, \(\gamma\)-C\({}_{2}\)S has poor hydration activity, and the increase in \(\gamma\)-C\({}_{2}\)S with the increase in designed brownmillerite content indicated that brownmillerite destroyed the \(\beta\)-C\({}_{2}\)S lattice and might affect the hydration of HBSC.  
Figure 4: QXRD patterns of HBSC linker containing brownmillerite (**a**) GF-1, Rwp = 5.80%, (**b**) GF-2, Rwp = 5.88%, (**c**) GF-3, Rwp = 5.90%, (**d**) GF-4, Rwp = 6.07%, and (**e**) GF-5, Rwp = 6.22%.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**C\({}_{4}\)A\({}_{3}\)S**} & \multicolumn{6}{c}{**C\({}_{2}\)S**} & \multirow{2}{*}{**C\({}_{2}\)AS**} & \multirow{2}{*}{**C\({}_{3}\)A**} & \multicolumn{6}{c}{**Brownmillerite**} \\ \cline{3-3} \cline{5-12}  & & \(\alpha\) & \(\beta\) & \(\gamma\) & \(\Sigma\) & & **C\({}_{4}\)AF** & **C\({}_{2}\)F** & **CF** & \(\Sigma\) \\ \hline GF-1 & 29.13 & 4.39 & 44.19 & 4.41 & 52.99 & 2.49 & 3.08 & 4.74 & 1.99 & 0.93 & 7.66 \\ GF-2 & 25.64 & 3.49 & 42.78 & 4.66 & 50.93 & 2.41 & 3.85 & 8.49 & 2.62 & 0.69 & 11.80 \\ GF-3 & 23.55 & 3.31 & 42.21 & 5.13 & 50.65 & 2.32 & 2.97 & 10.78 & 2.01 & 0.79 & 13.58 \\ GF-4 & 17.60 & 3.48 & 41.18 & 5.31 & 49.97 & 2.93 & 3.41 & 16.05 & 2.09 & 1.02 & 19.16 \\ GF-5 & 13.94 & 3.37 & 39.59 & 5.78 & 48.74 & 2.47 & 3.37 & 17.83 & 1.20 & 1.99 & 21.02 \\ \hline \hline \end{tabular}
\end{table}
Table 9: Main mineral composition of HBSC linker through QXRD patterns (wt%).