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Flux (metallurgy)
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<p>In <a href="/facts/Metallurgy/1SANyxX4">metallurgy</a>, a flux is a chemical <a href="/facts/Redox/Pyd5RVcj">reducing</a> agent, flowing agent, or purifying agent. Fluxes may have more than one function at a time. They are used in both <a href="/facts/Extractive_metallurgy/TkszJ19Y">extractive metallurgy</a> and <a href="/facts/Metalworking/eAT0Pvz2">metal joining</a>. </p><p>Some of the earliest known fluxes were <a href="/facts/Sodium_carbonate/P6RHvIoK">sodium carbonate</a>, <a href="/facts/Potash/4e2vBL9L">potash</a>, <a href="/facts/Charcoal/tpYGBHTn">charcoal</a>, <a href="/facts/Coke_(fuel)/vD8xjd0m">coke</a>, <a href="/facts/Borax/IQrXRJ3N">borax</a>, <a href="/facts/Lime_(material)/uMcVXGBM">lime</a>, <a href="/facts/Lead(II)_sulfide/IXauvWYq">lead sulfide</a> and certain minerals containing <a href="/facts/Phosphorus/27xCeIqs">phosphorus</a>. Iron ore was also used as a flux in the <a href="/facts/Smelting/Ghdvhlga">smelting</a> of copper. These agents served various functions, the simplest being a reducing agent, which prevented <a href="/facts/Oxides/DXtoVe1C">oxides</a> from forming on the surface of the molten metal, while others absorbed <a href="/facts/Impurities/FfPvIRoB">impurities</a> into <a href="/facts/Slag/LD3qEAlV">slag</a>, which could be scraped off molten metal. </p><p>Fluxes are also used in <a href="/facts/Foundry/Hww9Nrmr">foundries</a> for removing impurities from molten <a href="/facts/Nonferrous_metal/lY7X8rAY">nonferrous metals</a> such as <a href="/facts/Aluminium/7wmR8jYE">aluminium</a>, or for adding desirable trace elements such as <a href="/facts/Titanium/53ArnDoy">titanium</a>. </p><p>As reducing agents, fluxes facilitate <a href="/facts/Soldering/fod6dLHD">soldering</a>, <a href="/facts/Brazing/JBgswMLw">brazing</a>, and <a href="/facts/Welding/6EJ62mYV">welding</a> by removing <a href="/facts/Oxidation/Pyd5RVcj">oxidation</a> from the metals to be joined. In some applications molten flux also serves as a heat-transfer medium, facilitating heating of the joint by the soldering tool. </p>