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Why is borax used as a flux in welding and soldering?

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A labeled diagram of the periodic table entry for boron shows its atomic number 5, symbol B, electron configuration, atomic weight range, and classification as a solid, weakly acidic, other nonmetal with a rhombohedral crystal structure at room temperature. — boron Properties of boron.

Borax is used as a flux in welding and soldering primarily because of its ability to dissolve metallic oxides.12

In these processes, a flux serves several critical functions:
* Removal of oxide films: It cleans the metal surfaces by dissolving the oxide layers that naturally form on them.3
* Promotion of wetting: By removing these impurities, the flux allows the solder or filler metal to flow and adhere properly to the base material.3
* Prevention of reoxidation: It acts as a protective barrier, preventing the formation of new oxides on the metal surfaces while they are being heated.3

Because of these properties, borax acts as an effective solvent for metal-oxide slags, ensuring a clean, strong bond between the materials being joined.2