Flux
Definition and meaning of Flux in chemistry.
Flux is a substance added to an ore, metal, or ceramic mixture to promote fusion by reacting with and removing oxide or silicate impurities, thereby lowering the melting point of the material being processed.
In more detail
During smelting, flux reacts with unwanted gangue minerals to form a low-melting, low-density slag that separates from and floats above the molten metal, allowing easy removal. In soldering and brazing, flux instead strips oxide films from metal surfaces and shields them from further oxidation, letting molten solder wet and bond properly. The choice of flux depends on the impurity involved: a basic flux (like lime) reacts with acidic silica gangue, while an acidic flux (like silica) is used against basic oxide gangue.
Key facts
| Field | Inorganic Chemistry |
|---|---|
| Common flux | Limestone, CaCO3 |
| Function | Removes oxide/silicate impurities as slag |
| Used in | Smelting, soldering, glassmaking |
In blast furnace iron production, limestone (CaCO3) is added as a flux; it decomposes to calcium oxide (CaO), which combines with silica (SiO2) impurities in the ore to form calcium silicate (CaSiO3) slag that floats on the molten iron and is drawn off separately.
Frequently asked questions
What is the difference between a flux and a slag?
Flux is the material added to promote fusion and remove impurities; slag is the fused, glassy waste byproduct formed when the flux reacts with those impurities.
Why does adding flux lower the melting point of a mixture?
The flux and impurities form a eutectic mixture, which melts at a lower temperature than either component would alone, so less energy is needed to keep the material molten.