Wikipedia
Dealkalization is a process of surface modification applicable to glasses containing alkali ions, wherein a thin surface layer is created that has a lower concentration of alkali ions than is present in the underlying, bulk glass. This change in surface composition commonly alters the observed properties of the surface, most notably enhancing corrosion resistance.
Many commercial glass products such as containers are made of soda-lime glass, and therefore have a substantial percentage of sodium ions in their internal structure. Since sodium is an alkali element, its selective removal from the surface results in a dealkalized surface. A classic example of dealkalization is the treatment of glass containers, where a special process is used to create a dealkalized inside surface that is more resistant to interactions with liquid products put inside the container. However, the term dealkalization may also be generally applied to any process where a glass surface forms a thin surface layer that is depleted of alkali ions relative to the bulk. A common example is the initial stages of glass corrosion or weathering, where alkali ions are leached from the surface region by interactions with water, forming a dealkalized surface layer.
A dealkalized surface may have either no alkali remaining or may just have less than the bulk. In silicate glasses, dealkalized surfaces are also often considered “silica-rich” since the selective removal of alkali ions can be thought to leave behind a surface composed primarily of silica (SiO). To be precise, dealkalization does not generally involve the outright removal of alkali from the glass, but rather its replacement with protons (H) or hydronium ions (HO) in the structure through the process of ion-exchange.