When people hear the word flux, they usually think of constant change or flowing water. In chemistry, flux plays a very specific and active role in purifying materials. During the intense smelting process, raw metal ores contain unwanted rocky minerals called gangue.
The chemical flux reacts directly with these stubborn oxide or silicate impurities. This chemical reaction creates a new fused byproduct called slag. Slag has a much lower melting point and a very low density.
The liquid slag floats cleanly on top of the heavier molten metal inside the furnace. Factory workers can then easily skim the liquid slag away to leave pure liquid metal behind. Flux also plays a critical role in delicate soldering and brazing.
In these applications, the flux chemically strips away tough oxide films from the metal surfaces. It also shields the hot exposed metal from oxygen in the surrounding air. This protection allows the molten solder to flow smoothly and create a strong physical bond.
Chemists must carefully choose specific fluxes based on the exact impurities present. They use a basic flux like lime to react with acidic impurities. They use an acidic flux like silica to neutralize basic rocky impurities.