Method for Producing Refined Chromium Oxide Green , Pigment Green 17 , CI 77288
Method for Producing Refined Chromium Oxide Green , Pigment Green 17 , CI 77288
1) The Characteristics of Chromium Oxide Green.
Chrome oxide green, Hexagonal crystal family or amorphous dark green powder, with metallic luster. There are usually two shades: light olive green and deep olive green, with a metallic color. Relative density 5.21, melting point 2266 ℃, boiling point 4000 ℃. It has excellent heat resistance, can withstand a temperature of 1000 ℃ without discoloration, and has excellent acid and alkali resistance. The product has high purity, small particle size, uniform distribution, and extremely hard crystals. Extremely stable, even when hydrogen gas is introduced under red heat, there is no change. Soluble in heated Potassium bromate solution, slightly soluble in acids and bases, almost insoluble in water, ethanol and acetone.
2) The Application of Chromium Oxide Green Powder.
Chromium oxide green is mainly used for special steel smelting tapping holes, sliding plate openings, and large incinerators. It can be used for coloring ceramics and enamels, coloring rubber, preparing high-temperature resistant coatings, art pigments, and printing ink for paper currency and securities.
The color of chromium oxide green is similar to that of plant chlorophyll and can be used as camouflage paint, making it difficult to distinguish in infrared photography.
It is also widely used in metallurgy, making refractory materials, and grinding powders.
It can also be used as a catalyst for organic synthesis and is a good green pigment, used in fields such as green flooring, green glass, and colored cement.
3) Chromium oxide is used as a pigment and is called chromium oxide green.
There are many preparation processes, but there are mainly three commonly used methods: the preparation of chromium oxide from chromium oxide, the thermal decomposition method of ammonium sulfate sodium alum, and the direct thermal decomposition method of chromic anhydride.
3.1) Ammonium sulfate ton - sodium alum thermal decomposition method
This method is the basic method for producing chromium oxide in countries such as the United States, Britain, and Germany, and has become the production method with the largest output, best quality, and most varieties of chromium oxide in foreign countries. Its advantages are that the production process is simpler than that of the liquid phase reduction method, the cost is lower than that of the chromic anhydride decomposition method, the adaptability is wide (it can produce pigments, abrasives, refractories and metallurgical chromium oxide), it is suitable for large-scale production in Rotary kiln, and basically no harmful gas is produced in the production process. Therefore, it replaces the early thermal decomposition method of sodium alum and ammonium chloride. Almost all commercial chromium oxide is directly or indirectly produced from sodium alum, and its production accounts for approximately 20% of the consumption of sodium alum
The total production capacity of chromium oxide in various countries around the world is approximately 100,000 tons per year.
3.2) Direct thermal decomposition method of chromic anhydride.
Chromic anhydride thermal decomposition method: Chromic anhydride is thermally decomposed at 900 ℃ under high temperature conditions, and slightly cooled before being crushed to obtain the finished product. In recent years, the development of chromic oxide produced by this method in China has been very rapid. In 1999, the output of chromic oxide produced by chromic anhydride was about 13000 tons, which is twice as complex as the thermal decomposition process of chromic anhydride of metallurgical grade chromic oxide produced by Sodium chromate reduction in Tietai Gold Plant. As the temperature rises, chromic anhydride will decompose into four kinds of chromium oxides. As the chromic anhydride melts at about 200 ℃ and begins to decompose, oxygen and chromic oxide will be precipitated, so as the temperature rises, Chromium oxide crystals can gradually form and grow in the chromic anhydride melt. This method has less Crystallographic defect, can maintain many excellent properties of chromium oxide single crystal, and has high product quality, so it is widely used. Research has shown that Cr2O3 is already produced when the temperature rises to 470 ℃, and has been completely converted to Cr2O3 by 550V. However, during the experiment, it was found that the actual decomposition temperature was higher than this temperature. The reason is that during the decomposition process of Cr2O3, a Cr2O3 thin film is generated to coat the surface of the unconverted chromium oxide, while the melting point of Cr2O3 is very high (2266 ± 25) ℃, and the poor heat transfer hinders the further decomposition of the chromium oxide. To achieve this, a process of adding a small amount of water can be used to reduce the reaction temperature. On the one hand, Cr2O3 is highly soluble in water, and on the other hand, it can make the additive and Cr2O3 raw material mix evenly. The sample analysis results indicate that the mass fraction of Cr2O3 has reached over 99%. The reaction temperature and time also have a significant impact on the decomposition of chromic anhydride.
3.3) Preparation of Chromium(III) oxide from chromic oxide
Up to now, although there are many methods to produce Chromium(III) hydroxide from Chromium(III) sulfate solution through neutralization and separation, the Chromium(III) hydroxide generated is a fine colloidal substance, which is difficult to treat and has low purity. After long-term storage, it is insoluble in acid and alkali; In addition, if the neutralizer uses alkali metal hydroxides or carbonates, it will form insoluble or insoluble by-products, which limits the use of the neutralizer and limits the promotion of this method. In order to solve this problem, German patent 418050 proposed the following reaction method to produce Chromium(III) hydroxide:
But this method also has defects: the operation is complex, and iron is easy to mix with Chromium(III) hydroxide towel. Therefore, Chromium(III) hydroxide is prepared by neutralizing Chromium(III) chloride aqueous solution which is easy to use.
In addition, the water-soluble trivalent chromium salt is used to produce chromium oxide through Chromium(III) hydroxide or chromium hydroxide (CROOH); Using chromium containing waste to produce chromium oxide; Preparation of pigment grade chromium oxide from non pigment grade chromium oxide; Direct production of melt blown chromium oxide using aluminothermic or silicothermic methods.
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