Iron Oxide Series Pigment Development Overview and Related Applications (2)

In the presence of α-Fe2O3 crystal nucleus and ferrous sulfate, ferrous sulfate is oxidized with air, and the generated ferric oxide is deposited on the crystal nucleus. Simultaneously, the generated sulfuric acid is neutralized with ammonia, and ferrous sulfate and ammonia are continuously added dropwise. The nucleus grows and forms iron red.

The chemical reaction formula is as follows:

Seed preparation: FeSO4+2NH3·H2O=Fe(OH)2↓+(NH4)2SO4

2Fe(OH)2+1/2O2=2γ-FeOOH+H2O

Seed conversion: 2γ-FeOOH → α-Fe2O3 + H2O

Two-step oxidation: 2FeSO4+1/2O2+2H2O=Fe2O3↓+2H2SO4

H2SO4+2NH3=(NH4)2SO4

1.2.2. Ammonia iron yellow

Ammonia is used to neutralize the ferrous sulfate solution to a pH of 5-6. After neutralization, there is still a certain amount of ferrous sulfate in the system. The air is oxidized at room temperature to obtain iron yellow seeds. Two-step oxidation is performed in the presence of seed crystals. The two-step oxidation process is similar to that of ammonia ferric red and is not repeated here.

The chemical reaction formula is as follows:

Seed preparation: FeSO4+2NH3·H2O=Fe(OH)2↓+(NH4)2SO4

2Fe(OH)2+1/2O2=Fe2O3·H2O+H2O

Two-step oxidation: 2FeSO4+1/2O2+3H2O=Fe2O3·H2O↓+2H2SO4

H2SO4+2NH3=(NH4)2SO4

1.3. Ferrous Hydroxide Gel Oxidation Process for Production of Iron Black

The basic substance (NaOH, NH3, etc.) is used to neutralize ferrous sulfate to generate ferrous hydroxide, and air is used to oxidize ferrous hydroxide to grow seeds spontaneously during the oxidation process, and then the particles are controlled to grow uniformly by changing the process conditions. Tiny and well-distributed iron black with high tinting power.

This method has mature production technology, and the coloring power of the product is already at the leading level in the world. The focus of future research is to improve the application performance so that the comprehensive performance of the product can reach the world level. 1.3.1. Granular iron black for aqueous systems

The main purpose of iron black is still as a building material. In Europe and the United States, the use of iron oxide for construction materials requires no dust, which requires granulation of the iron oxide. If the iron black is made into a pellet shape, it will be difficult to disperse and affect the performance, and the granulation aid must be added. Granulation aids must meet three conditions: 1 does not affect the performance of the system applied iron black; 2 make iron black in the case of dry particles have a certain degree of hardness; 3 so that the iron black particles in the aqueous system can be quickly dispersed. Granulation aids consist of a wetting dispersant and a binder.

1.3.2. Ultrafine Iron Black for Oil System

The iron black was ultrafinely pulverized with a jet mill, and the aggregates were broken up to a fineness of 5 μm or less. The auxiliaries must also be added before the gas stream is crushed, otherwise the particles will re-aggregate to the desired fineness. Iron black can also be used for different purposes by changing the type of additive.

1.3.3. Heat Resistant Iron Black

Due to the unstable nature of divalent iron in iron black, it is oxidized to trivalent iron at a temperature greater than 140°C to make iron black red.