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 (H3O+) in the structure through the process of ion-exchange.
[3] The same logic applies in pharmaceutical glass items such as vials that are intended to hold medicinal products.
This action helps to avoid undesired changes in pH or ionic strength of the solution, which not only inhibits eventual attack of the glass as previously described, but can also be important in maintaining the efficacy or stability of sensitive product formulations.
A rapid ion-exchange reaction proceeds that depletes the inside surface of alkali, and is performed when the glass is at high temperature, usually on the order of 500–650 °C or greater.
The latter is left behind as water-soluble crystalline deposits, or bloom, on the glass surface that must be rinsed away prior to filling.
These materials are introduced inside the container after forming and decompose into gases in the annealing lehr, where the resulting sulfur-containing gas mixture carries out the dealkalization reaction.
This method is purportedly safer than flooding the annealing lehr since the unreacted components in the gas mixture will tend not to escape to the atmosphere, but rather react with each other and recreate the original salt in the container that can later be rinsed away.
[6] Treatment with fluorine-containing compounds is typically accomplished through the injection of a fluorinated gas mixture (e.g. 1,1-difluoroethane mixed with air) into bottles at high temperatures.
The mixture gently combusts inside the bottle, creating an extremely small dose of hydrofluoric acid that reacts with the glass surface and serves to dealkalize it.
standing for internal treatment) as Ball Corporation held the patent and developed the first commercially available system implementing this process.