Hydroxidelaag

Hydroxidelaag, or hydroxide layer, is a thin film on a material surface that consists predominantly of metal hydroxides (for example M(OH)2 or M(OH)3) and forms when the surface is exposed to water, oxygen, and dissolved ions. Such layers often arise as corrosion products or as passive films that slow further degradation. The exact composition depends on the substrate and environment; iron can form Fe(OH)2 and Fe(OH)3, aluminum forms Al(OH)3, chromium can form Cr(OH)3, and other metals produce corresponding hydroxides.

Formation mechanisms include hydrolysis of metal ions released during oxidation and the precipitation of hydroxides when local pH increases near the surface due to chemical reactions or ion consumption. In aqueous environments, the presence of chlorides, carbonates, and sulfates can influence stability and protectiveness.

The role of a hydroxide layer in corrosion is dual. It can be protective by acting as a diffusion barrier to aggressive species, thereby slowing oxidation. Conversely, it can be porous or mechanically unstable, providing pathways for continued attack and leading to spall or pitting. The stability of these layers is affected by pH, temperature, ionic composition, mechanical stress, and the metal’s microstructure. Over time, hydroxide layers may transform into oxides or carbonate-containing films through dehydration or carbonation processes.

In cementitious systems, calcium hydroxide can form at interfaces and influence ion transport and durability. In engineering, understanding and controlling hydroxide-layer formation is important for passivation strategies, coatings, and corrosion management, as well as for electrochemical applications where the layer affects impedance and reaction kinetics.