Hydrogen reduction method of α-iron oxide
High-purity micronized α-Fe2O3 is loaded into a tray, and the powder layer should not be too thick. After placing the disk into the reaction tube, high-purity nitrogen is passed in to completely replace the air. Then hydrogen gas saturated with water is slowly fed through the gas wash bottle. A heating temperature of 300-400°C (e.g. 330°C) is appropriate. After the reaction is confirmed (usually 1~3h) and cooled, the hydrogen is stopped and the sample is removed after replacement with nitrogen. Insufficient amount of water vapor, too high heating temperature or excessive reduction will generate FeO, so care must be taken. The amount of water vapor can be increased by increasing the temperature of the gas wash bottle (40-60°C is suitable). Needle-shaped α-FeO(OH) as the starting material is heated and dehydrated to obtain α-Fe2O3. α-Fe2O3 can be used to produce needle-shaped ferric tetroxide particles. The black audio tape is used as the tape recording medium for this kind of ferric tetroxide.
Addition method
Ferrous sulfate is produced by reacting iron filings with sulfuric acid, and then adding caustic soda and iron oxide at 95-105°C for an additional reaction to produce the ferric oxide, which is filtered, dried and crushed to produce ferric oxide black.
Slow oxidation method of ferrous hydroxide
The aqueous solution containing ferrous hydroxide precipitate is heated above 70°C and slow oxidation is carried out to obtain ferric oxide powder consisting of fairly uniform ortho-octahedral or cubic single crystal particles with a prism length of about 0.2 μm. Air bubbles can also be transported as a means of oxidation. Oxidizing agents like KNO3 can also be used.
Harber method
The Harber method adds 220g of 20% ammonia to 2.2L of FeSO4-7H2O aqueous solution, boils it under cut-off conditions (you can use a round-bottom flask equipped with a capillary tube), and adds a concentrated aqueous solution containing 25.5g of KNO3 to the boiling, and if you are skilled, you can obtain a chemically calculated composition of Fe3.00O4.00 of ferric tetroxide.
Alkali addition method
The solution of ferrous sulfate is oxidized by adding alkali or the solution of iron salt and ferrous salt is mixed in a certain ratio and precipitated by adding alkali.
