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Violet Iron Oxide: Precipitated Hematite Calcined at 1000-1100 °C (Nurdini et al. 2022)
Iron hydroxide is thrown down from hot ferric nitrate solution with ammonia, washed, dried and calcined. All of it ends as pure hematite, but the colour moves from bright red through dark red to purple as the calcining heat rises from 1000 °C, because the grains grow larger and more crystalline.
Result: pure violet to purple ferric oxide (hematite) after 4 hours at 1000-1100 °C.
Source: Nurdini et al., Heliyon 8 (2022) e10377, sections 2.2 and 4. Not given: batch size, how much ammonia, end pH, yield. Picture drawn by Youblob.
Intermediate
2 days
Instructions
1
1
Heat the ferric nitrate solution
Heat the ferric nitrate solution
Make a 0.05 M solution of ferric nitrate in distilled water and heat it to 80 °C.
Materials for this step:
Ferric Nitrate1 as requiredTools needed:
Distilled Water
Glass Beaker
Hot Plate
Thermometer2
2
Throw down the hydroxide with ammonia
Throw down the hydroxide with ammonia
Keeping it at 80 °C, add ammonia solution drop by drop while stirring well. Stir for 3 hours, then let it cool to room temperature: a red-brown precipitate forms. Not given: how much ammonia.
Tools needed:
Ammonia Solution - 25-28%
Dropping FunnelHot PlateThermometer3
3
Spin down, wash and dry
Spin down, wash and dry
Collect the precipitate in a centrifuge at 4000 rpm for 15 minutes, wash it with distilled water, and dry it at 110 °C for 24 hours.
Tools needed:
Benchtop CentrifugeDistilled Water
Drying Oven4
4
Calcine at 1000-1100 °C
Calcine at 1000-1100 °C
Calcine for 4 hours in air at 1000-1100 °C. Below 1000 °C it stays bright or dark red; from 1000 °C it turns purple. Grind the cooled oxide to a fine powder (they used an agate mortar).
Tools needed:
Muffle Furnace
Mortar and PestleMaterials
1- 1 as requiredPlaceholder
Tools Required
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