Ferrophosphorus

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Ferrophosphorus is an iron–phosphorus alloy (a ferroalloy) that contains iron phosphides Fe2P and Fe3P. Its CAS number is 8049-19-2. Typical grades have about 18% or 25% phosphorus. It is a gray solid that melts around 1050–1100 °C and can release phosphine gas when it contacts water; very fine powder can be combustible.

What it’s used for
- In metallurgy: a phosphorus source for alloys, a deoxidizer, and a helper to move unwanted compounds into slag.
- Powder metallurgy steels: adds a small amount of phosphorus (about 0.45% by weight) to improve magnetic properties; higher amounts (up to ~0.8%) can help magnetism but require strict control to avoid phosphorus segregation and brittleness.
- Cast iron and steels: improves fluidity, wear resistance, machinability, and can slightly improve corrosion resistance in some steel alloys.
- Other uses: a construction aggregate for high-density concrete used in radiation shielding (usable with Portland or magnesia cement); reacts with sulfur or pyrite to make phosphorus pentasulfide; used to produce lithium iron phosphate (LiFePO4) for Li‑ion batteries.
- Coatings and paints: can replace zinc powder in some coatings due to good adhesion, anticorrosive properties, electrical and thermal conductivity, and wear resistance.
- Reducing agent: can be used to produce sodium or potassium from carbonate compounds.

How it’s made
- Ferrophosphorus is a byproduct of phosphorus production in submerged-arc furnaces from phosphate rocks (apatites), formed from iron oxide impurities.