I am researching on iron oxide red pigments and their hues from calcining iron oxide black (prepared using liquid ammonia) at 650C+. All the shades I am getting do not have the right reddish hue that I need to conclude my study. I haven't added any reducing agent in my iron oxide black. Do I need to add a reducing agent? I do have a sample of iron oxide black that isn't washed and has a little bit of HCl, this sample gave me the closest result, however its still not close to the market standards of red.
Upon increasing the temperature, the hue turns from yellow-brownish red to purplish-red. Please suggest what should I do.
Dear friend Immad Amir
Ah, the pursuit of the perfect red hue in iron oxide pigments! Let's delve into the world of calcination and explore some possible solutions to achieve that desired bright red hue:
1. Temperature Optimization: It seems you've already observed changes in hue as you increased the calcination temperature. Experimenting with different temperature ranges might help you find the sweet spot for obtaining the desired red hue. You could try slightly lower temperatures within the 650°C+ range to see if that yields a more suitable result. Remember to carefully document your observations at each temperature to better understand the trends.
2. Adjusting the Calcination Atmosphere: While you mentioned not using a reducing agent, the atmosphere during calcination can influence the oxidation state of the iron oxide. Reducing conditions (with a reducing agent like hydrogen or carbon monoxide) during calcination can potentially promote the formation of Fe2O3 and contribute to a brighter red hue. However, this requires careful control and experimentation to avoid undesired effects. It might be worth considering if adjusting the atmosphere aligns with your research objectives and if you have the necessary resources to explore this avenue.
3. Surface Modification: The surface properties of the iron oxide particles can also affect the resulting color. Surface modification techniques, such as coating the particles with certain materials or using specific surfactants during synthesis or post-treatment, may alter the color perception and enhance the red hue. Exploring surface modification strategies could be a potential route to achieve the desired result.
4. Addition of Dopants: Introducing small amounts of dopants or additives during the synthesis or calcination process can significantly impact the color of the iron oxide pigment. For instance, adding certain metal ions or oxides as dopants may enhance the red hue. This approach requires careful selection of dopants and thorough experimentation to find the optimal dopant concentration for achieving the desired color.
Remember, achieving the ideal red hue can be a complex task, involving various factors and parameters that interact with one another. It may require experimentation, optimization, and careful analysis to reach your desired conclusion. Good luck with your research, and may you find that perfect red hue you seek!
Let us keep discussing this interesting topic and exploring this topic.
I'm sorry, but I'm going to be critical
The properties of iron oxides and their laboratory preparation is a well-researched problem. There is a huge amount of literature and books on the subject. For example, Schwertmann U. and Cornell R.M. (2000): Iron Oxides in the Laboratory: Preparation and Characterization. Willey, DOI:10.1002/9783527613229.
It will be necessary to study the terminology, mainly mineralogical related to this topic.
Red Fe oxide is hematite ie alpha Fe2O3, black Fe oxide will most likely be magnetite FeFe2O4 or maghemite gamma Fe2O3. I see a logical discrepancy - magnetite is not a precursor to hematite when heated, but to maghemite. The one in the powder is not red, but rather brown or reddish-brown. Precursors of hematite are rather rusty or yellowish-brown precipitates of the ferrihydrite or goethite type. A reducing environment during calcination will be counter-productive.
Dear Immad,
when magnetite (Fe3O4 spinel structure) is in the form of fine powder, its oxidation leads to the formation of maghemite (lacunary spinel also called gamma phase Fe2O3), metastable oxide of brown-yellow color. If this oxide is heated to a "sufficient" temperature (all the higher as the powder is fine, but typically around 500°C) it undergoes a crystalline transformation to form hematite (alpha Fe2O3, stable oxide of corundum structure and red to dark brown in color, depending on its fineness.Very fine powders are bright red, coarser ones are dark brown.
To obtain a red color it is therefore advisable to use very fine powders. Adjusting the processing temperature can also make it possible to cause the gamma and alpha phases to coexist and to modulate the color.
The substitution of iron by other transition metal cations can also give defect spinel phases (see for example: Ph. Tailhades et al. Nato workshop ) whose color also depends on the substitution actions
The previous phases can also be observed in the form of thin layers (see for example the absorption spectra on. Bouet et al. Jap. J. Appl.Phys).
Best regards.
Philippe.