## 4 Discussion
The calculated corrosion rate showed a reduction with increasing time, in agreement with other studies [71; 72; 73; 74]. [PERSON] et al. [75] reviewed the corrosion rates of four different in situ experiments, the FEBEX in situ experiment being one of them. A range of corrosion rates between 6 and 11 \(\upmu\)m/year were calculated for this experiment, conducted for 18 years at 70 \({}^{\circ}\)C, using carbon steel and FEBEX bentonite. In the present research at 100 \({}^{\circ}\)C and over the short term, compared to the FEBEX in situ experiment, the final corrosion rate was nearly in the same range or even lower but within the same order of magnitude as observed after 18 years. The Mg-saturated bentonite could enhance passivation, which will presumably be confirmed by ongoing longer-term experiments. Taking into account the mineralogical observations, a scheme showing the reaction products at the steel-bentonite interface after at the three experimental times (1, 6 and 22 months) is presented in Figure 10. This scheme is based on those presented by [PERSON] et al. [75] and [PERSON] et al. [73]. [PERSON] et al. [75] studied corrosion in eight bentonite pre-saturated with Aspo groundwater heated to 130 \({}^{\circ}\)C in the ABM2 in situ experiment. [PERSON] et al. [73] studied the steel-bentonite interactions in the FEBEX in situ experiment, in which carbon steel, in contact with FEBEX bentonite, was heated at 100 \({}^{\circ}\)C for 18 years. The proposed scheme tries to visualize the different mineral phases detected after 1, 6 (presumably under unsaturated water vapor migration conditions) and 22 months (under water saturated conditions at the end of the experiment). The alteration thicknesses are not presented at scale but indicate the transformation of some phases into others. The increase of siderite with time as well as the presence of Fe\({}^{2+}\)-silicates in a wider region after 22 months than after 1 and 6 months were observed by XRD. Although each zone is represented by solid colors, a mixture of minerals was observed at the interfaces of each zone. Figure 10: Proposed mineral phase evolution scheme for steel–FEBEX-Mg interface after 1, 6 and 22 months. Mag: magnetite; Mgh: maghemite; Hem: hematite; Sd: siderite; GR: green rust; Ank: ankerite; Lpc: lepidocrocite; using similar scheme and colors as in [PERSON] et al. [73]. Determinations on the iron redox state in bentonite, analyzed after 22 months of reaction, showed an increase of Fe\({}^{2+}\) and Fe\({}^{3+}\) near the steel interface (<2 mm), presumably affecting a larger thickness compared to less humid and earlier times (1 and 6 months under the same conditions). Magnetite formed as the main steel corrosion mineral, as observed in several water-saturated environments under reducing conditions (i.e., [PERSON] et al. [76]). The determination of redox potential in the clay-metal-iron interface in a transient oxic to anoxic state is complex and ambiguous as many Fe\({}^{3+}\) and Fe\({}^{2+}\) minerals are involved and present in small quantities, making them difficult to identify. [PERSON] et al. [77] established the presence of magnetite/magnetite-coupled minerals mainly controlling the Fe\({}^{2+}\) redox solution equilibrium at pH 6.5-8.5, exhibiting more negative potential than the corresponding lepidocrocite and hematite at progressively less negative potentials. The expansion of the reducing front towards the bentonite may have led to the presence of these Fe\({}^{3+}\) iron oxides in regions relatively far (up to 2 mm) from the interface where Fe\({}^{3+}\) predominated. The potential intercalation of Fe\({}^{2+}\) ions as hydroxide in a chloritic structure added complexity and probably further enhanced the transport of Fe\({}^{2+}\) to the clay material. [PERSON] et al. [18] mostly identified the iron in the zone closest to the heater as Fe\({}^{3+}\), which was consistent with the detection of hematite, magnetite, maghemite and lepidocrotic in this zone.