Basic Information
Iron oxide yellow, also known as iron yellow, is an iron oxide containing water of crystallization.

Iron oxide yellow
Formula: Fe2O3·H2O
Molecular Weight: 177.71
CAS No.： 51274-00-1
Physical Properties
1. Fe2O3, ≥86%; 2. Residue (320 mesh), ≤0.5%; 3. Water-soluble salt, ≤0.5%; 4. Moisture, ≤1%; 5. Oil absorption, 25-35%; 6. pH value: 3.5-7.
Properties: Powder with a color ranging from lemon yellow to brown. Relative density of 2.44 to 3.60. Melting point of 350 to 400°C. Insoluble in water and alcohol, soluble in acid. Fine powder with a crystal structure of iron oxide hydrate. Due to different production methods and operating conditions, the degree of hydration varies, resulting in significant differences in crystal structure and physical properties. Excellent in color strength, covering power, lightfastness, acid resistance, alkali resistance, and heat resistance. Decomposes to release crystalline water at over 150°C, turning into red. Inhalation of dust can cause pneumoconiosis, with an allowable maximum concentration in air of 5 mg/m².
Quality Indicators
Indicator Name: First-class Quality; Passing Quality
Iron (based on dry Fe2O3) mass fraction/% ≥ 86.0 80.0
Water-soluble material/% ≤ 0.5 1.0
"105"C Volatiles/% ≤ 1.0 1.5
Acidity/Alkalinity of Water Extract/mL 20 1 60
Aqueous suspension pH value 4～6 4~6
Oil absorption (g/100g) 25~35 25～35
Method
Method One: Ferrous Sulfate Oxidation Method The reaction of sulfuric acid with iron scrap generates ferrous sulfate. Add sodium hydroxide and introduce air to oxidize to prepare the crystalline nucleus. Then, add ferrous sulfate and iron scrap to the suspension of crystalline nuclei, heat the solution and introduce air to oxidize. After pressing, washing, drying, and grinding, the iron oxide yellow is obtained.
Fe + H2SO4 → FeSO4 + H2↑
FeSO4 + 2NaOH → Fe(OH)2 + Na2SO4
4Fe(OH)2 + O2 → 4FeOOH + 2H2O
H2SO4 + Fe + 7H2O → FeSO4·7H2O + H2↑
FeSO4·7H2O + O2 → 2Fe2O3·H2O↓ + 4H2SO4 + 2H2O Reaction conditions: Add 74g iron scrap to 1000ml 15% sulfuric acid and react until the iron scrap disappears, generating about 200g/L ferrous sulfate solution. Add enough 30% sodium hydroxide to the above-obtained ferrous sulfate solution, continuously stir to convert 40% of the iron into ferrous hydroxide [Fe(OH)2], and pass air at 30-35℃ to oxidize Fe to Fe to form nuclei. Then add 90g/L iron scrap to the solution, making 7g/L nuclei and 40g/L ferrous sulfate, continue to heat to 85℃, and oxidize 64h at a speed of 600L/h by blowing air, then filter, wash, dry, and grind to obtain iron oxide yellow containing water.
Method Two: Oxidation of Aromatic Nitro Compounds Can Simultaneously Produce Aromatic Amine Compounds. The Reaction Equation Is As Follows:
Fe + H2O + R-NO2 → Fe2O3·H2O + R-NH2
The reaction conditions are as follows: add 560 parts of water, 36.5 parts of 32% hydrochloric acid, 160 parts of iron powder, and 10 parts of aluminum powder to the reaction kettle. Add 1460 parts of a water solution containing 253 parts of 5-nitro-8-nitro-naphthalene sulfonic acid and 8-nitro-naphthalene sulfonic acid to the reaction kettle within 16-24 hours, with a pH value of 6 for the naphthalene sulfonic acid aqueous solution and a temperature of 80-85°C. The temperature in the reaction kettle is 95-100°C, with a pH value of 6-6.5, and the reaction lasts for 2 hours under these conditions. Add 8 parts of 25% ammonia water, and further react for 4 hours. Filter, and wash the filter cake with 560 parts of water three times. Mix the washed filter cake with 1000 parts of water, heat at 95-100°C, add 45 parts of 32% hydrochloric acid, stir for 2 hours, filter, and wash the filter cake with water until no acid is detected, and dry to obtain 160 parts of iron oxide yellow pigment, while also obtaining amino naphthalene sulfonic acid, with a yield of 96%.
Usage
1、Iron oxide yellow pigment is used as a pigment or dye in precast concrete and construction products materials, directly mixed into cement for application. Various indoor and outdoor colored concrete surfaces, such as walls, floors, ceilings, pillars, porches, roads, parking lots, steps, stations, etc.; various building ceramics and glass ceramics, such as tiles, floor tiles, roof tiles, inlaid panels, terrazzo, mosaics, artificial marble, etc.
2. Iron oxide yellow pigment is suitable for various types of coating and protective materials, including water-based interior and exterior wall paints, powder coatings, etc.; It can also be used in oil-based paints, including oxides, alkyd, amino, and various primers and top coats; It can also be used in toy paints, decorative paints, furniture paints, electroplating paints, and magnet paints.
3. Iron oxide yellow pigment is suitable for coloring plastics, such as thermosetting plastics and thermoplastic plastics, as well as for coloring rubber products, such as automobile inner tubes, aircraft inner tubes, and bicycle inner tubes, etc.
4. Widely used in the construction industry for the coloring of artificial marble and terrazzo. It is also an ingredient in watercolors, oils, paints, and rubber. It is used as an intermediate for iron oxide pigments, such as in the production of iron oxide red and iron black.
In addition, iron oxide yellow pigment can also be used for coloring various cosmetics, paper, and leather.