This study investigates the changes in the morphology of portlandite (Ca(OH)₂) particles formed under different ion conditions. Experimental methods, including scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and laser diffraction, were used to analyze the particle shapes and sizes. Atomistic simulations, employing classical energy minimization and molecular dynamics, were also conducted to understand the surface energies and equilibrium morphologies of portlandite in vacuum and water. Key findings include: 1. **Morphology Changes**: - **Chloride and Nitrate**: Faceted particles with a regular shape, similar in size (2.65-3.72 μm). - **Sulfate**: Hexagonal platelet morphology, with a higher aspect ratio (3.16). - **Silicate**: Large, irregularly shaped agglomerates (10 μm). 2. **Surface Energies**: - **Vacuum**: [00.1] surface energy is very low, while [20.3] surface energy is high. - **Water**: All surface energies are slightly lowered, with the [20.3] surface becoming part of the equilibrium morphology due to stabilization by water. 3. **Atomistic Simulations**: - The force field used was validated for crystallographic unit cell parameters and elastic moduli. - The water description was accurate, reproducing the phase diagram and radial distribution function. - The [20.3] surface energy in vacuum was significantly higher than in water, explaining its appearance in most particles. 4. **Conclusion**: - The presence of different ions significantly affects the morphology and surface energies of portlandite particles. - Further simulations are needed to understand the mechanisms behind these changes, particularly the influence of chloride, nitrate, and sulfate ions. This research provides insights into the factors controlling the morphology of portlandite, which is crucial for understanding the durability and properties of cementitious systems.This study investigates the changes in the morphology of portlandite (Ca(OH)₂) particles formed under different ion conditions. Experimental methods, including scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and laser diffraction, were used to analyze the particle shapes and sizes. Atomistic simulations, employing classical energy minimization and molecular dynamics, were also conducted to understand the surface energies and equilibrium morphologies of portlandite in vacuum and water. Key findings include: 1. **Morphology Changes**: - **Chloride and Nitrate**: Faceted particles with a regular shape, similar in size (2.65-3.72 μm). - **Sulfate**: Hexagonal platelet morphology, with a higher aspect ratio (3.16). - **Silicate**: Large, irregularly shaped agglomerates (10 μm). 2. **Surface Energies**: - **Vacuum**: [00.1] surface energy is very low, while [20.3] surface energy is high. - **Water**: All surface energies are slightly lowered, with the [20.3] surface becoming part of the equilibrium morphology due to stabilization by water. 3. **Atomistic Simulations**: - The force field used was validated for crystallographic unit cell parameters and elastic moduli. - The water description was accurate, reproducing the phase diagram and radial distribution function. - The [20.3] surface energy in vacuum was significantly higher than in water, explaining its appearance in most particles. 4. **Conclusion**: - The presence of different ions significantly affects the morphology and surface energies of portlandite particles. - Further simulations are needed to understand the mechanisms behind these changes, particularly the influence of chloride, nitrate, and sulfate ions. This research provides insights into the factors controlling the morphology of portlandite, which is crucial for understanding the durability and properties of cementitious systems.