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Calcium nitrate (Ca(NO₃)₂) has been suggested to inhibit steel corrosion. However, the effectiveness of corrosion inhibition offered by calcium nitrate in highly halide-enriched environments, for example, completion fluids, is not well known. To better understand this, the inhibition of corrosion of API P110 steel by Ca(NO₃)₂was studied using vertical scanning interferometry in solutions consisting of 10 mass % calcium chloride (CaCl₂) or 10 mass % calcium bromide (CaBr₂), for example, to simulate the contact of completion fluids with the steel sheath in downhole (oil and gas) applications. The evolution of the surface topography resulting from the initiation and growth of corrosion pits, and general corrosion was examined from the nano-scale to micron-scale using vertical scanning interferometry. Special focus was paid to quantify surface evolution in the presence of Ca(NO₃)₂. The results indicate that, at low concentrations (≈1 mass %), Ca(NO₃)₂successfully inhibited steel corrosion in the presence of both CaCl₂and CaBr₂. Statistical analysis of surface topography data reveals that such inhibition results from suppression of corrosion at fast corroding pitting sites. However, at higher concentrations, calcium nitrate’s effectiveness as a corrosion inhibitor is far less substantial. These results provide a means to rationalize surface topography evolution against the electrochemical origin of corrosion inhibition by NO₃⁻species, and provide guidance regarding the kinetics, and susceptibility to degradation of the steel sheath during exposure to halide-enriched completion fluids.

Synthetic hydrotalcites were produced by a co‐precipitation method. The hydrotalcites are represented by the general formula [M^II_(1‐x)M^III_(x)(OH)₂][Aⁿ⁻]_x/n·zH₂O, where M^IIis a divalent cation (eg, Mg²⁺or Ca²⁺), M^IIIis a trivalent cation (eg, Al³⁺) and Aⁿ⁻is the interlayer anion. Herein, M^II = Mg, and M^III = Al such that [Mg/Al] = [2, 3] (atomic units) and Aⁿ⁻, represents intercalant species including: OH⁻, SO₄²⁻and CO₃²⁻anions. The thermochemical data of each compound including their solubility constants (K_so), density and molar volume were quantified at T = 25 ± 0.5°C, andP = 1 bar. The solubilities of the synthetic hydrotalcites, irrespective of their divalent‐trivalent cation partitioning ratio, scaled as CO₃²⁻ < SO₄²⁻ < OH⁻; in order of decreasing solubility. The type of anion, very slightly, affected the solubility with less than ±1 log unit of variation for [Mg/Al] = 2, and ±2 log units of variation for [Mg/Al] = 3. The solubilities of these phases were strongly correlated with that of gibbsite (Al(OH)₃); such that activity of the [AlO₂⁻] species wassolubility determiningwith increasing pH. The tabulated thermodynamic data were used to construct solid‐solution models for phases encompassing both cation distribution ratios and to calculate stable phase equilibria relevant to alkali‐activated slag (AAS) systems for diverse activator compositions.