## 3 Results and Discussion
### Discussion of the PXRD and DSC-TG/MS Results  
The results of the PXRD-measurements with the Rietveld method and the DSC-TG/MS/IR-measurements were collected and plotted in three diagrams (Figures 7-9). The quantity of the phases wollastonite (black squares), amorphous (blue triangles), calcite (magenta circles) and aragonite (green circles) were determined by the Rietveld method. The red circles symbolized the sum of calcite and aragonite and therefore the content of carbonate in the sample detected by PXRD. The amount of CaCO\({}_{3}\) determined by TG measurements were shown by cyan circles. In Figure 7, the carbonation of wollastonite at 296 K is shown with seven different reaction times. To show the good reproducibility several experiments were performed two times (Figure 7). At 296 K, the reaction was not completed after 144 h. The content of calcite (magenta circles), the amount of CaCO\({}_{3}\) determined by TG measurements (cyan circles) and of the amorphous content (blue triangles) in the sample increased exponentially while the content of wollastonite (black squares) decreased similarly. No further aragonite (green circles) was formed (Figure 7). At 323 K, a high degree of conversion (>90%) was already achieved after 48 h (Figure 8). The content of calcite (magenta circles), aragonite (green circles), the amount of CaCO\({}_{3}\) determined by TG measurements (cyan circles) and the amorphous content (blue triangles) increased exponentially, while the content of wollastonite (black squares) decreased exponentially in an analog manner. At 24 h, the contents of calcite and aragonite almost reached the same amount (~20 wt %), while at the beginning of the experiment the content of calcite was higher (Figure 8, grey circles marked by arrows). Figure 6: Result of the DSC-TG/MS measurement of carbonated (at 2 MPa and 333 K for 24 h) wollastonite (initial weight 15.2 mg). Measurement from 296 K to 1273 K with heating rate of 10 K/min. The weight loss (wt %) is represented by the black line, the DSC-signal (mW) by the blue line. The green line shows the mass flow (A) for H\({}_{2}\)O, and the magenta line the mass flow (A) for CO\({}_{2}\). Figure 8: Carbonation of wollastonite at 323 K (50 \({}^{\circ}\)C), 2 MPa and aqueous conditions (H\({}_{2}\)O). The quantity of the phases wollastonite (black squares), amorphous (blue triangles), calcite (magenta circles) and aragonite (green circles) were determined by the Rietveld method. The red circles symbolize the sum of calcite and aragonite and therefore the content of carbonate in the sample detected by PXRD. The amount of CaCO\({}_{3}\) determined by TG measurements are symbolized by cyan circles. The ellipsoids with arrows depict the symbols, at which aragonite and calcite exhibite nearly the same amount. Figure 7: Carbonation of wollastonite at 296 K (23 \({}^{\circ}\)C, ambient), 2 MPa and aqueous conditions (H\({}_{2}\)O). The quantity of the phases wollastonite (black squares), amorphous (blue triangles), calcite (magenta circles) and aragonite (green circles) were determined by the Rietveld method. The red circles symbolize the sum of calcite and aragonite and therefore the content of carbonate in the sample detected by PXRD. The amount of CaCO\({}_{3}\) determined by TG measurements are symbolized by cyan circles. At 333 K, the conversion was nearly completed already after 24 h (Figure 9). The contents of calcite (magenta circles), aragonite (green circles) and the total amount of CaCO\({}_{3}\) determined by TG measurements (cyan circles) and the amorphous content (blue triangles) increased exponentially, while the content of wollastonite (black squares) decreased exponentially. At 12 h the contents of calcite and aragonite almost reached the same amount (\(\sim\)20 wt %) whereas at the beginning (6 h and 18 h) of the experiment the content of calcite was higher (Figure 9, grey circles marked by arrows). At each investigated temperature (296 K, 323 K, 333 K), an exponentially decrease of wollastonite was observed.