# Damage Characteristics of Thermally Deteriorated Carbonate Rocks: A Review
## 2 Thermal Dilatancy and Alteration in Rock Fabric
### Reasons behind the Thermal Expansion
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Mineral Type** & **Major Developments** & **Reference** \\ \hline Calcite & The kinetic parameters were obtained from a new method that avoids the Arrhenius equation. & [41] \\ \hline Dolomite & Thermo-mechanical damage was examined under intensive grinding using X-ray diffraction and thermal analysis. & [42] \\ \hline Calcite & The solid-state transformation was evaluated using thermogravimetric analysis, evolved gas analysis-mass spectrometry, and high-temperature XRD. & [43] \\ \hline Dolomite & The thermal decomposition mechanism was explained in detail using thermogravimetry and X-ray powder diffraction. & [33] \\ \hline Dolomite & Thermal expansion and decomposition behavior were investigated using thermogravimetric analysis, differential thermal analysis, XRD, and scanning electron microscopy. & [29] \\ \hline Dolomite & Stoichiometric ordered and disordered single crytal dolomite was studied using X-ray diffraction under high pressure and temperature conditions. & [44] \\ \hline Dolomite & Investigation of kinetics of isothermal and non-isothermal decompositions. & [25] \\ \hline Calcite & A simulated model was presented that effectively predicted the conversion time curve and described the calcination-carbonation cycle after performing thermogravimetric analysis. & [45] \\ \hline Dolomite & Differential scanning calorimetry and thermogravimetric analysis based on non-isothermal calcination carried out under varying CO\({}_{2}\)-air environments. & [46] \\ \hline Calcite & Thermo-physical decomposition was studied under equilibrium dynamic simulation. & [47] \\ \hline Calcite & Parameters including unit cell volume alteration, thermal expansion, variations along lattice axis, and thermal strains were studied using high-temperature X-ray powder diffraction. & [26] \\ \hline Calcite & Thermal decomposition analysis was performed to validate improved reaction kinetic equation based on the pore structure model. & [48] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: \(Cont.\)no distortion [52; 53]. The possible reason for such trends in these carbonate minerals is the thermal expansion between the oxygen atoms of octahedra at the basal edge and lateral edge. Furthermore, the Ca-octahedron of calcite shows less anisotropic thermal expansion. However, the thermal expansion in Mg-octahedron of dolomite displays more anisotropic character relative to magnesite [54]. Figure 1 illustrates the thermal effect on the interatomic distances of Ca-O and Mg-O in calcite, dolomite, and magnesite. As concerns the thermal dislocation of the carbonate group in dolomite, it is intermediate between the calcite and magnesite. In calcite, the displacement of the carbonate group is the result of rotational disorder, which is the rotary oscillation about the three-fold axis [55]. In the case of dolomite and magnesite, the influence of the Mg-O bond confines the motion of the oxygen atoms. Therefore, the dislocation of the carbonate group in both dolomite and magnesite is less relative to that in calcite [56]. However, in magnesite, it is further less just because of the slight tilting of the basal plane. The displacement of the carbonate group contributes a minimum in the thermal deterioration of carbonate rocks. Previous studies show that, in calcite, the change in orientation of the carbonate group even at elevated temperature (i.e., 600 \({}^{\circ}\)C) is \(<\)0.5\({}^{\circ}\) as compared to its ambient conditions [49]. In dolomite, the adjacent layers share corners with different octahedra. In other words, the carbonate group makes the bond with unlike cations that further restrict its motion. This signifies that rotation of the carbonate group is not a decisive factor in the thermal deterioration of carbonate rocks. The thermal expansion of calcium and magnesium octahedral systems considerably affects the thermal damage of the carbonate rocks.