What Is Iron Fluoride?
Iron fluoride includes several compounds of iron, including iron(II) fluoride (FeF2), iron(II, III) fluoride, and iron(III) fluoride (FeF3), with iron(III) fluoride being the most commonly encountered. It is recognized as a skin corrosive and irritant under the GHS classification and is identified as a hazardous and toxic substance.
Uses of Iron Fluoride
Iron fluoride is utilized in ceramic and porcelain glazes, as a precursor for various catalysts, and in enhancing the corrosion resistance of metals like stainless steel through the formation of fluoride passive films. This application is particularly valuable in semiconductor manufacturing, where corrosive gases such as hydrogen chloride and hydrogen fluoride are prevalent.
Properties of Iron Fluoride
Anhydrous iron(III) fluoride appears as a white to green crystal or powder, with its hydrate form being pale pink. It boasts a melting point of over 1,000°C and exhibits insolubility in water but solubility in hydrofluoric acid upon heating. Known for its toxicity, iron(III) fluoride is a thermally robust antiferromagnetic solid with hygroscopic anhydrides and hydrates.
Structure of Iron Fluoride
Iron(III) fluoride, or iron trifluoride, features a molecular weight of 112.84 g/mol and a density of 3.52 g/cm3. It exists in α and β crystal forms, with the α-type forming at room temperature and the β-type at temperatures above 50°C. The α-type is unstable, transitioning to the β-type within days.
Other Information on Iron Fluoride
1. Synthesis of Iron(III) Fluoride
While pure iron(III) fluoride is not found as a mineral, a hydrated form known as topsøeite exists. It is synthesized by reacting iron chloride with hydrogen fluoride or by dissolving iron hydroxide in hydrofluoric acid and dehydrating the solution.
2. Properties of Iron(II) Fluoride
Iron(II) fluoride, a pale yellow crystal, transitions to iron(III) oxide upon heating in air. It exhibits slight water solubility and solubility in acids. Antiferromagnetic in nature, it forms through the reaction of iron with hydrogen fluoride and oxidizes in moist air to a hydrate of iron(III) fluoride.
3. Structure of Iron(II) Fluoride
Iron(II) fluoride, or iron bifluoride, with a molecular weight of 93.84 g/mol and a density of 4.09 g/cm3, forms light green tetrahydrate crystals that are insoluble in water but soluble in acid. Its octahydrate variant is used for passive fluoride coatings on steel, highlighting its toxicity.