How can salt (NaCl) ever possibly form sodium silicate in the process of salt glazing (pottery)? isn’t the bond in salt way to strong for something like that to happen?
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Heat.
The heat breaks the bonds and allows new ones to form. Salt glazing requires around 900°C to work. Cone 6 -10 if I remember rightly. Throw in a reducing atmosphere and you have the ingredients to break those bonds and form new ones.
In salt glazing, it’s not the salt itself but the extreme heat of pottery kilns that causes a reaction. The heat breaks down the salt (NaCl), releasing sodium (Na) and chlorine (Cl). The sodium then reacts with silicates in the pottery to form sodium silicate, creating a glassy glaze. So, it’s not about the strength of the salt bond, but the high temperature that makes this happen.
The bond strength is relative to the environment and the concentration of molecules in question. If it’s really hard for a molecule to make a bond but that molecule is highly concentrated, eventually it’ll bond.
The bonding between sodium and chloride ions comes from their strong attraction. It is not a covalent bond and so doesn’t pair up specific atoms except to make sure the charges balance. It’s going to attract any two sodium ions equally as long as they’re both the same distance away.
If you introduced a solution of potassium iodide at the surface, the potassium ions would fill the same purpose as the sodium ions and so easily swap place. No bonds are breaking – the iodide ions are present in the outside solution to serve the same purpose as the chloride ions in the solid.
No bond is too strong if you throw enough energy at it. That’s why the process involves a kiln at extremely high temperatures. Even diamonds will burn in a hot enough flame.
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