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Characterisation of Iron Oxide Black
Addtime: 2017/09/01 Read:4672 Font size: Large Small
Iron oxide black (E 172, synonymous CI Pigment Black 11, triiron-tetraoxide, black iron oxide, ferrous ferric oxide, magnetite, Colour Index 77499) is identical to the active substance iron(II,III) oxide (International Union of Pure and Applied Chemistry (IUPAC) name, Chemical Abstracts Service (CAS) number 1317-61-9, molecular formula FeO·Fe2O3, molecular weight 231.55).
Iron oxide black is produced via chemical synthesis using iron oxide yellow (FeO(OH)) or iron oxide red (Fe2O3) and/or iron(II) sulfate as starting chemicals which are converted/reacted in the presence of pure oxygen and caustic soda (precipitation process).
Iron oxide black is a black powder with a relative and apparent density of approximately 4.6 kg/L and 0.7 kg/L, respectively. It is insoluble in water and organic solvents, and soluble in mineral acids.
A typical composition of the additive is the following: iron(II,III) oxide 98.4%, sodium sulfate 0.2%, water 0.4%, aluminium oxide 0.5% and magnesium oxide 0.5%.
Five batches of iron oxide black were analysed for the specified contents.12 They all complied with the specifications (iron oxide black expressed as iron: 68.5–70.9%; water-soluble salts: 0.09–0.13%; arsenic: < 1 mg/kg; cadmium: < 1 mg/kg; chromium: 25–58 mg/kg; copper: 6–31 mg/kg; lead: ≤ 4 mg/kg; mercury: < 0.2 mg/kg; nickel: 57–117 mg/kg; and zinc: 32–65 mg/kg).
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