Iron Oxides

Chemical properties

Iron oxides occur as yellow, red, black, or brown powder. The color depends on the particle size and shape, and crystal structure.

Production Methods

Three main manufacturing processes are currently applied for iron oxide pigments:
(a) Solid-state reactions (red, black and brown): calcination of black or yellow iron oxides to red iron oxide; thermal decomposition of ferrous sulfate.
(b) Precipitation process (red, orange, yellow and black): treatment of ferrous sulfate solutions with alkali and oxidation. The Penniman–Zoph process uses ferrous sulfate, alkali, iron powder and air or oxygen.
(c) Laux process or aniline process (red, yellow, and black): reduction of nitrobenzene to aniline with iron.

Pharmaceutical Applications

Iron oxides are widely used in cosmetics, foods, and pharmaceutical applications as colorants and UV absorbers. As inorganic colorants they are becoming of increasing importance as a result of the limitations affecting some synthetic organic dyestuffs. However, iron oxides also have restrictions in some countries on the quantities that may be consumed, and technically their use is restricted because of their limited color range and their abrasiveness.

Safety

Iron oxides are widely used in cosmetics, foods, and oral and topical pharmaceutical applications. They are generally regarded as nontoxic and nonirritant excipients. The use of iron oxide colorants is limited in some countries, such as the USA, to a maximum ingestion of 5 mg of elemental iron per day.
LD50 (mouse, IP): 5.4 g/kg
LD50 (rat, IP): 5.5 g/kg

Storage

Iron oxides should be stored in well-closed containers in a cool, dry place.

Incompatibilities

Iron oxides have been reported to make hard gelatin capsules brittle at higher temperatures when the residual moisture is 11–12%. This factor affects the use of iron oxides for coloring hard gelatin capsules, and will limit the amount that can be incorporated into the gelatin material.

Regulatory Status

Accepted for use as a food additive in Europe. Included in nonparenteral medicines licensed in many countries including Japan, UK, and USA.