What is the colour of Iron oxide?
What is the colour of Iron oxide?
Understanding Iron Oxide Pigments
Exploring Iron Oxide
Iron oxide pigments represent some of the most widely utilized colorants globally. They come primarily in three distinct hues: yellow (FeOOH), black (Fe3O4), and red (Fe2O3), but also appear as blends yielding orange, beige, and various brown tones.
The Historical Significance of Iron Oxide
The use of Iron Oxides dates back to prehistoric eras, predominantly showcasing red tones. Early humans utilized these pigments to express their existence in cave spaces, evidenced by animal drawings meant to ensure successful hunting. Findings of the earliest cave art can be traced to locations like the Saubia Mountains (Germany), Lascaux (France), and Altamira (Spain), dated between 40,000 and 10,000 BC, using iron oxide-laden clay for colors. As time progressed, the presence of Iron Oxide was notable in Neolithic ceramics, Renaissance artworks, and bricks in ancient civilizations. Although natural Iron Oxides continue to be in use today, synthetic variants have surged in popularity, delivering superior pigment characteristics. Their widespread application stems from their natural appearance and remarkable chemical, physical, and performance attributes, making them crucial for various purposes.
Essential Characteristics of Iron Oxide
Range: Iron Oxides
Sub-range: Red Iron Oxides ( GO series)
Color Index: Pigment Red 101/C.I. (Iron Oxide Red)
Basic Chemical Composition: Fe2O3
Dispersibility (*): Excellent
Hiding Power/Opacity (*): Excellent
Heat Fastness (*): 800ºC, 5 min
Light Fastness (*): Excellent
Weather Fastness (*): Excellent
Acid Fastness (*): Excellent
Alkali Fastness (*): Excellent
Cement Compatibility (*): Excellent
Solvent Fastness (*): Excellent
Metamerism (*): No
Applications: Food Contact Packaging / Toys / General Packaging / Electric and Electronic Equipment / Automotive / Construction / Fertilizers / Plant Protection Products / Industrial Applications / Artistic Supplies and Craft Products.
Production Methods for Iron Oxide
Utilizing the Laux Process
In the creation of black pigments, the reaction is as follows: 9 Fe + 4 C6H5NO2 + 4 H2O → 3 Fe3O4 + 4 C6H5NH2 For yellow pigments: 2 Fe + C6H5NO2 + 2 H2O → 2 FeO(OH) + C6H5NH2 And for red pigments: 2 Fe3O4 + ½ O2 → 3 Fe2O3 Originally, the Laux process was developed for manufacturing aniline (C6H5NH2) from nitrobenzene (C6H5NO2), but chemist Dr. Laux discovered that the iron oxide formed could serve as an exceptionally potent pigment for various applications.
Employing the Precipitation Process
The precipitation process involves oxidizing iron sulfate with atmospheric oxygen in an alkaline environment creating yellow iron oxide pigment (Bayferrox® Yellow 920): 2 FeSO4 + 4 NaOH + ½ O2 → 2 FeO(OH) + 2 Na2SO4 + H2O. This technique relies on yellow nucleus pigments to enhance quality.
The Penniman Process for Yellow Iron Oxide
In this method, iron scrap is converted to yellow iron oxide (Bayferrox® Yellow 920) in an acidic medium: 2 Fe + ½ O2 + 3 H2O → 2 FeO(OH) + 2 H2. Here, iron sulfate serves as a catalyst, and quality yellow pigments depend on the availability of yellow nuclei for optimal outcomes.
Eco-Friendly Attributes of Iron Oxides
Synthetic iron oxides in shades of red, yellow, orange, brown, and black are considered non-toxic, made from a minimum of 60% recycled industrial materials.
Applications of Iron Oxide Pigments
Iron oxide pigments are extensively applied across various industries due to their cost-effectiveness and durability, offering a multitude of benefits.