Iron Oxide Pigment Development Overview and Related Applications (3)

Through special treatment, the heat resistance of iron black can be improved, so that iron black can be applied to some paints, plastics and other occasions that need to be processed and used at higher temperatures.

The most famous heat-resistant iron black is Bayer's 303T, which can withstand temperatures up to 220°C. To produce heat-resistant black iron, it is necessary to use iron black, which has a relatively large particle size and relatively stable thermal properties, and first coat it with a dense layer of aluminum and silicon, and then form a second organic material with good heat resistance. Layer coating, while improving its performance.

2. Transparent iron oxide pigment

Transparent iron oxide primary particle size of only a few tens of nanometers, when it is fully dispersed in a transparent medium to form a continuous film, the light will bypass the pigment particles diffraction phenomenon, so that the film has good transparency. The chemical structure of transparent iron oxide determines that it has good light resistance, weather resistance, acid resistance, alkali resistance, and solvent resistance. It also has strong UV absorption ability due to its very fine primary particle size, and its light resistance is even more. Excellent, BASF's transparent iron yellow, transparent iron orange, transparent iron red paint containing 1.7,1.3,0.9 grams per square meter, can absorb 99.5% of ultraviolet light. Transparent iron oxide can be used in limousine flash paint, hammer paint, wood coating colorant, imitation mahogany paint, cans inner wall paint, and architectural interior and exterior wall paints. It is also used for coloring inks and plastics. Transparent iron oxide, which strictly controls arsenic and heavy metals, can replace azo pigments, dyes, and other synthetic pigments that are banned from use, and are used as colorants for foods, medicines, and cosmetics.

Developed countries have started using transparent iron oxide pigments since the late 1970s. The main producers are Bath, Bayer, Hiltom-Davis Co., and Blaise Pigment. BlytheColours Ltd.) and France's Chappelle Co., etc., with their years of development, their application areas have expanded from the early limousine glitter paint to various fields.

At present, there are three main processes for producing transparent iron oxide, namely, air oxidation, carbonyl iron combustion, and sodium chlorate oxidation-transformation. The product particles produced by the air oxidation process are acicular with a ratio of length to short axis of 5 to 8; the carbonyl iron combustion method is unique to BASF. The product particles are amorphous and have a particle size of only a few nanometers; sodium chlorate is oxidized – The conversion method is mainly used in our country. The product particles are spindle-shaped, the ratio of length to short axis is 3~5, and the length of short axis is 10~20 nm.

2.1. Transparent iron yellow

I have published the paper "Preparation of Transparent Iron Oxide Yellow" and elaborated on the preparation principle and preparation method of transparent iron yellow. Sodium chlorate oxidation-transformation is briefly described here. The ferrous sulfate is oxidized with sodium chlorate to high-iron sulfate, colloidal iron hydroxide is generated by alkali neutralization of high-iron sulfate, and the amorphous iron hydroxide colloid is converted into α-FeOOH in the presence of iron skin, washed with water, and surface-treated. Then filtered, dried and pulverized to obtain transparent yellow pigment.

The chemical reaction formula is as follows:

Oxidation: 6FeSO4+NaClO3+3H2SO4=3Fe2(SO4)3+NaCl+3H2O

Precipitation: Fe2(SO4)3+6NaOH=2Fe(OH)3↓+3Na2SO4

Conversion: Fe(OH)3=α-FeOOH+H2O

2.2. Transparent Iron Red

Transparent iron yellow α-FeOOH is goethite, which has poor thermal stability. At temperatures higher than 177°C, it gradually loses its water of crystallization and causes changes in the phase of the material, which is converted into α-Fe2O3 hematite.

The transparent iron yellow was calcined and dehydrated at 300-350°C to obtain transparent iron red.