Mica iron oxide is a class of iron oxide pigments, which is a pearlescent pigment. The following is a comprehensive introduction to the various preparation methods of micaceous iron oxide and related application methods.
1Preparation technology
1.1Machining method
 Natural micaceous iron oxide is generally produced by mechanical processing. The process is simple and easy to operate. However, the product has high impurity content and the purity is between 80% and 90%. There is no regular shape and the particle size distribution is uneven. Meet the requirements of some high-grade fine pigments.
1.2 molten salt high temperature complex oxidation method
The method uses waste iron scrap as raw material, chlorinates into anhydrous ferric chloride with chlorine gas, and then reacts with industrial salt to form a molten composite, and the molten composite is oxidized to micaceous iron oxide at a high temperature. The reaction is carried out in 3 steps:
Chlorination: 2Fe+3Cl22FeCl32FeCl3+Fe3FeCl22FeCl2+Cl22FeCl3
Complexation: FeCl3+NaClNaFeCl4FeCl2+NaClNaFeCl3
Oxidation: 2NaFeCl4+3/2O2-Fe2O3+2NaCl+3Cl2
2NaFeCl3+3/2O2-Fe2O3+2NaCl+2Cl2
The reactor is a cylindrical steel shell lined with refractory material. The reactor is filled with ceramic balls as a reaction support. During the reaction, porcelain balls, iron filings and industrial salt are mixed and placed in the reactor. In order to ensure product quality, the ceramic balls should be uniformly dispersed in the reactants. The ceramic ball can also serve as a gas distributor for the reaction.预 preheat the bottom of the filling material to about 700 °C, then pass a mixture of chlorine and air. The chlorine reacts with the preheated iron filings and industrial salt to form a reaction zone, forming a layer of NaFeCl4 on the surface of the ceramic ball. Film of NaFeCl3 (control film thickness greater than 150 um). The air is passed through to oxidize the NaFeCl4 and NaFeCl3 films into flaky iron oxide crystals and emit chlorine gas. The evolved chlorine gas moves over the reactor to form a new reaction zone, and the above steps are repeated until the reaction reaches the top. After the reaction is completed, the synthesized micaceous iron oxide is removed from the ceramic ball, collected in a filter, washed to a chloride-free state, dried, ground, and sieved to obtain a product. The reaction medium chlorine and NaCl can be recycled.
In the process, the thickness and the chip diameter of the product micaceous iron oxide are controlled by adjusting the size of the ceramic ball and the weight ratio of the iron raw material to the ceramic ball. The thickness can vary from 05 to 5um, and the film diameter varies from 1 to 100um, and the Fe2O3 content can reach about 97.5%. The reaction of this method is an exothermic reaction, so as long as the reaction is initiated by preheating, the reaction heat is reliably maintained at a later time, and thus the reaction temperature is maintained, so that the energy consumption is low.
1.3  water heat treatment method
1.3.1 FeSO4 direct oxidation method
The method synthesizes micaceous iron oxide by using titanium white by-product ferrous sulfate as raw material. The ferrous sulfate is dissolved in water at 60 ° C to prepare a saturated solution, and is oxidized to a hydrated iron sulfate slurry at this temperature, and then reacted with hydrated sodium hydroxide to form a hydrated iron hydroxide paste. Then, under the condition of 150 ° C or more and an excess of a base, hydrothermal treatment is carried out in an autoclave, that is, hexagonal crystal grains are crystallized. The product is then cooled down to 80 ° C and the NaOH in the raffinate can be reused after separation.
The oxidant used in hydrazine is sodium chlorate; the lowest temperature for hydrothermal treatment is 150 ° C. Below this temperature, hydrothermal crystallization cannot be carried out; the optimum temperature should be controlled at 180-220 ° C; the steam pressure is 1.0-2.3 MPa. The particle size of the product micaceous iron oxide is obviously affected by the concentration of sodium hydroxide in the reaction system. The larger the concentration of sodium hydroxide, the larger the particle size of the product. When the concentration of sodium hydroxide is varied from 5 to 14 mol/L, the particle size varies between 20 and 50 μm.
In order to obtain a larger particle size of micaceous iron oxide, Ado et al. in the United States added a crystal additive boric acid or borate to the slurry after oxidation of FeSO4 to promote the growth of crystal grains during hydrothermal crystallization. The size of micaceous iron oxide ranges from 30 to 100 um.
1.3.2 FeSO4 indirect oxidation method
In this method, FeSO4 is dissolved in water, and Na2CO3 is added to form a FeCO3 precipitate. The precipitate is washed and placed in an autoclave, an excess of alkali is added, the autoclave is sealed, oxygen is continuously supplied and maintained at a certain pressure, and the temperature is raised to a certain temperature to carry out oxidation reaction and crystallization, and then the temperature is raised to a certain temperature to carry out crystal aging. After cooling, it is filtered, washed, and dried to obtain micaceous iron oxide crystal grains. The temperature in the oxidation stage is usually controlled at 150 to 260 ° C for 4 to 7 hours. The crystallization temperature is controlled at 250~280 °C for 2~3h. This method can also use CaO as a precipitant for Fe2+, and SO2-4 in the reaction solution is precipitated as gypsum. After the reaction, it is separated from micaceous iron oxide by deposition, and this method uses oxygen as an oxidant. It will produce secondary pollutants, and NaOH can be recycled. Therefore, if the method can solve the pressure resistance problem of the equipment, it can be used as a solution for the large amount of by-product FeSO4 (1t titanium white by-product 3.5~4t ferrous sulfate). A way to get to the road.
粒径 The particle size of the product micaceous iron oxide can be controlled by controlling the concentration of NaOH in the reaction system and the pressure of oxygen. The NaOH concentration is usually controlled at 8~12mol/L, and the product obtained by adjusting the oxygen pressure has a particle size of 5~70um, a Fe2O3 content of 97%~98%, and a color of silver gray and purple.
1.3.3  magnetite oxidation method
In this method, iron ore, FeCl2 and other iron-containing raw materials and NaOH are placed in an autoclave, and the air in the kettle is replaced with N2, and the temperature is raised by stirring, and first, fine crystal grains of magnetite are formed. Then, it is cooled to 90 ° C and then the oxidizing agent NaClO3 is added, and the temperature is raised to a certain temperature to carry out hydrothermal oxidation reaction and crystallization, that is, hexagonal flaky crystal grains are precipitated. It is cooled to room temperature, filtered, washed, and dried to obtain micaceous iron oxide.
The particle size of micaceous iron oxide in this method is controlled by the concentration of the alkali solution in the hydrothermal reaction system, the temperature, and the heating rate of the system. Larger particle size micaceous iron oxide grains are obtained at higher lye concentrations, temperatures, and slower temperature ramp rates. It is also affected by the particle size of the fine crystallites of magnetite produced in the first step. To this end, to obtain the ideal size of micaceous iron oxide, the first to make the ideal fine crystal grains of magnetite. The product obtained by this method has a particle size of 1 to 50 um and a Fe2O3 content of 99.0%.
2 application of cerium oxide iron oxide
2.1  anti-rust pigment
Sericite iron oxide is mainly used as an anti-rust pigment. The sheet structure of micaceous iron oxide has excellent shielding properties. It also has the effect of reflecting external light, absorbing ultraviolet rays, and reducing the damage of ultraviolet rays to the paint film. Therefore, it is widely used as a rust preventive pigment for permanent steel buildings, such as bridges, towers, guardrails, vehicles, ship topcoats, and the like. The service life is up to 15a.
2.2  pearlescent pigment
Using the flaky nature of micaceous iron oxide, non-toxicity, gloss, stability to acids, bases, organic solvents and UV absorption, further development of various functional pigments and pearlescent pigments, such as cosmetics, printing Inks, sun cream, sun umbrellas, leather, food packaging and exterior architectural finishing materials. Some domestic manufacturers have already developed or are developing these products. Its price is expensive, and some are above 10,000 yuan/t, and the prospects are promising.
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