JPS603010B2 - Manufacturing method of fine chromium oxide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION An object of the present invention is to provide a novel method for producing fine chromium oxide with low crystallinity.

Generally, chromium oxide is a green pigment and is a useful industrial raw material widely used in abrasives and other ceramic fields. Conventionally, various methods have been known to produce this chromium oxide, but the methods that have been implemented industrially are mainly a method in which chromium hydroxide is heated and calcined at a high temperature, and a method in which chromium oxide is produced using chromic anhydride as a starting material. This is a method of manufacturing by thermally decomposing.

In the former case, chromium oxide obtained by the so-called wet method can easily be obtained with a uniform particle size and crystal shape, but the properties are greatly affected by the precipitation conditions of chromium hydroxide, and the hydroxide is The handling and operations are very complicated. On the other hand, the latter is the so-called dry method,
Industrially, this method is often used. When chromic anhydride is heated, the following formula 31 C et al 03 13' Phantom 2 ↑...
...It decomposes into chromium oxide as shown in [1'], and the chromium oxide obtained by heating and firing is crushed and classified to produce a product.

However, the chromium oxide produced by this method has large and tightly aggregated powder to agglomerate particles, so it is essential to pulverize it in the grinding process as described above. Since it has a large abrasive force and is used as a grinder, the more you seek to reduce particle size through pulverization, the more contamination of foreign matter from the pulverizer and the greater the wear of the pulverizer, so there is a limit to how much pulverization can be achieved.

Therefore, as a method to eliminate the drawbacks of chromium oxide by direct thermal decomposition of chromic anhydride, the following formula (N ratio) has been conventionally used:
2Cr207-Cr2031N2↑Jumisaki20↑……{2
A method of thermally decomposing ammonium dichromate crystals is known.

The feature of this method is that ammonium dichromate is heated, so there is no need to necessarily use a functional method, and it is powdered by an exothermic mountain reaction. You can obtain excellent products. However, compared to the direct method, this method requires additional operational steps such as reaction of chromic anhydride and ammonia, cooling, crystallization and separation, and drying in order to handle the crystals of 2Cr207 (N ratio), so the manufacturing cost is high. It is inevitable that the price will become very high. In addition, although there is some degree of freedom in producing chromium oxide using this method depending on how the firing temperature is controlled,
The disadvantage is that the properties of chromium oxide are fixed and it is not possible to produce grades that meet demands.

In addition, as another method, there is a method in which dichromate is ignited in the presence of a reducing agent, and then soluble salts are removed by washing with water.

In all of these methods, the final heating temperature depends on the application, but the final heating temperature is relatively high, and coarse particles of chromium oxide with high crystallinity can be obtained. Recently, the present applicant has developed a method for producing fine chromium oxide, in which anhydrous chromium oxide is thermally decomposed at a calcination temperature of 800 to 1200°C in the presence of a nitrogen-containing compound (Japanese Patent Publication No. 54-1504 Bikarasu) and anhydrous chromium oxide. By making ammonia exist in a specific molar ratio in chromic acid,
Two-step thermal decomposition method (Japanese Patent Application Laid-Open No. 52-4498
No.) was developed.

All of these are highly crystalline chromium oxides that have developed crystals with a specific surface area of 0.4 to 4. Furthermore, the present inventor has developed a method of producing chromium oxide by adding and blending a mineral acid and a nitrogen-containing oxide such as ammonia to sodium dichromate and firing the blend.

(Mochiseki Sho 54-180295) However, this method
It produces ordinary pigment-grade chromium oxide which is fired at a temperature of 0 to 1100°C, and the chromium oxide has a particle size of 0.5 to 3 grains with high crystallinity, and is the fine and active material of the present invention. It is different from chromium oxide, which has chromium oxide.

By the way, one of the main uses of chromium oxide is as a ceramic material, but in this case, it is rather exceptional that chromium oxide is used alone, and in many cases it is used as a material for forming spinel. It is used in combination with alumina bricks to improve slag resistance, or as a strength-enhancing material for refractory materials by reacting with other materials.

When looking at chromium oxide for use in the ceramic industry, coarse grains of the secondary crystal growth type are often unsuitable because of their inert reactivity with other ceramic materials.

Moreover, from the perspective of energy consumption, it is extremely wasteful for both manufacturers and users. When considering chromium oxide as a ceramic material, it has been pointed out that extremely fine and active chromium oxide is suitable, but in reality, such chromium oxide is not commercially available, and its production method is simple in principle. However, it is extremely difficult to establish industrial technology based on its characteristics and considering how to satisfy various demands. In view of the above facts, the present inventors have completed the present invention as a result of intensive research to produce a new type of chromium oxide suitable for ceramic materials. That is, in the present invention, approximately equivalent amounts of a mineral acid and a nitrogen-containing compound are added to and mixed with an alkali dichromate or/and an alkali chromate and its alkali, and then the mixture is heated at a temperature above its decomposition temperature and below 400°C. The present invention relates to a method for producing fine chromium oxide, which is characterized by carrying out thermal decomposition by controlling the temperature while venting to a temperature atmosphere, and then washing the obtained decomposed product with water.

First, as the raw material chromium, either alkali dichromate or alkali chromate or a mixture thereof is used, but in most cases sodium dichromate is used, and it may be either liquid or crystalline. On the other hand, hydric acid and nitrogen-containing compounds are used for such chromium salts. Key acids include sulfuric acid,
Hydrochloric acid or nitric acid, with sulfuric acid being most preferred. Suitable nitrogen-containing compounds include, for example, ammonia, ammonium salts, thiourea, urea and its derivatives, and guanidine salts. Examples of ammonium salts include ammonium carbonate, ammonium bicarbonate, ammonium nitrate, ammonium sulfate, ammonium chloride, ammonium chromate, ammonium dichromate, ammonium acetate, and ammonium oxalate. Examples of urea derivatives include ammonium carbamate, alkyl Examples include urea, methylol urea, and guanidine salts include guanidine nitrate, guanidine carbonate, aminoguanidine, and the like. These may be used alone or in combination. The mixing ratio of these raw materials is such that the inorganic acid is nearly equivalent to the alkali dichromate or the alkali chromate, and some range around this is allowed. If the amount of inorganic acid is excessive, acidic gas will be generated which will harm the environment, while if it is insufficient, the yield of chromium oxide will be reduced. In addition, the amount of nitrogen-containing compounds varies depending on the type, thermal decomposition conditions, and use of the target product, but in many cases, the amount of the chromium salt (
The amount is preferably 0.1 mol or more per 1 mol (in terms of CrQ). The reason for this is that if the amount of the nitrogen-containing compound is less than about 0.1 mole, the addition effect cannot be expected much and the effect of direct decomposition of the ring hydrochromic acid generated becomes large, whereas at the upper limit, it will be thermally decomposed. Therefore, there is no particular reason to limit it, but it is naturally limited solely for economic reasons, and in most cases, up to 5 mol is sufficient. However, in the case of ammonium salts of strong acids such as sulfuric acid, hydrochloric acid, or nitric acid among nitrogen-containing compounds, since these acids and ammonia are precursors of the ammonium salts, the amount of acid depends on the total amount of acid groups used. Just use it.

Therefore, depending on the amount of the ammonium salt used, it may not be necessary to mix the inorganic acid in a free state. These raw materials are mixed in the desired proportions. As a mixing method, it is best to mix in an aqueous solution state, and then evaporate to dryness and charge it into a kiln.

Of course, there is no need to limit the above method as long as uniformity can be obtained by other mixing methods. This mixture is pyrolyzed in a kiln under controlled temperature conditions. The ambient temperature is above the decomposition temperature of the mixture, but in a relatively low temperature range, often below about 400 pm. The decomposition temperature is in the range of approximately 200°C, and when the mixture reaches this temperature, it decomposes markedly together with the action of the nitrogen-containing compound, and exhibits a foaming state due to exothermic phenomenon, and then self-pulverizes into extremely fine particles. It's becoming more and more. This phenomenon is continuous and generates a lot of heat, so the temperature should be well controlled and fired at a relatively low temperature. Therefore, after the start of decomposition, there is no need to supply external heat at all; rather, it is controlled to prevent overheating, but the upper limit is about 400 m
It is best not to exceed ℃. Overheating at this time should be avoided because the particles of chromium oxide grow large from around 400°C and at the same time crystallization develops, making it impossible to obtain the desired fine chromium oxide with low crystallinity.
In this method, it is necessary to supply raw materials as quantitatively as possible in order to reduce rapid reactions, and also to control the temperature by blowing air into the furnace and to take out the fine particles that have been turned into powder out of the furnace. is collected by a filter like a bag filter.

In addition, examples of the reactor include a muffle furnace, a rotary kiln, an air inlet, a decomposition product outlet, a raw material supply port,
If necessary, a cylindrical reactor equipped with rotating blades may be used.

The decomposition products thus collected by thermal decomposition are washed with water to thoroughly remove the total salts, and then dried and pulverized to produce a product.

The chromium oxide according to the present invention is a chromium oxide with low crystallinity or nearly amorphous, unlike conventional well-developed hexagonal crystalline chromium oxide. The subordinate chromium oxide is a National Bureau of Standard.
When comparing the crystallinity with standard corundum (RDS) using X-ray diffraction under the same conditions, the degree of crystallinity is defined as the intensity ratio of the diffraction lines between every 11 milks of corundum and the 104 plane of chromium oxide. [Oath] is from Q4. Since this intensity ratio is meant to represent the degree of crystal development, if this is defined as the degree of crystallinity in the present invention, the chromium oxide according to the present invention has a crystallinity of 0.2 or less. It can be said that it is of low quality. On the other hand, the secondary chromium oxide is coarse and hard, and it is extremely difficult to pulverize it to the extent that it can be used as an abrasive in itself, and it is difficult to obtain a fine oxide in reality. However, the chromium oxide obtained according to the present invention has a specific surface area of at least 4 mm/h, and in most cases about 10 mm/h.
Another characteristic is that the particles are fine in the range of 300 m/m or more.

Such fine, low-crystalline chromium oxide is naturally active, and as a reactive chromium oxide it is particularly suitable as a ceramic material. It can be provided industrially advantageously without requiring. Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1 2 moles of 35% hydrochloric acid and 1 mole of guanidine are added to 1 mole of potassium chromate and mixed.

A self-serving plate is attached to the center of the heating section, which has a low diameter and a length of 50 m (heating part is 25 m), the lower part is open to let in air, and the upper part is a duct for taking out the grilled cod and a place for preparing raw materials. An electrically heated vertical furnace equipped with a heating pipe is used as a reactor, and the atmospheric temperature in the furnace is set to 220°C, and raw materials are quantitatively charged onto a perforated plate. The mixture is thermally decomposed and turned into fine particles, which are guided through a duct to a scrubber by wind power and collected.

Next, the bottle collection is further washed with water to remove potassium chloride and unreacted hexavalent chromium compounds, and the crude cake is dried and crushed to produce a product. The product was identified as chromium oxide by X-ray diffraction, but it was a greenish-gray color with low crystallinity of 0.08.

Further, the specific surface area measured by the BET method was 43 days, which was very fine, and the yield based on the raw material chromium was 97.4%.

Example 2 8 per mole of 50% solution of sodium dichromate dihydrate
A mixed raw material is prepared at a ratio of 1.05 moles of 5% sulfuric acid and 2 moles of urea.

Internal heating kiln (kerosene heating, diameter 200 ribs, length 2500
The reactor is used as a reactor to ignite the raw materials.

The atmospheric temperature in the furnace was maintained at 23.0 by adjusting the amount of raw material charge and the amount of air. The charged raw material mixture becomes powder and is blown away by wind power and collected by a scrubber. Next, the sintered product is purified by washing with water to remove impurities such as sodium sulfate and unreacted hexavalent chromium compounds, and is dried and pulverized to obtain a product.
Similar to Example 1, this product is a fine greenish-gray chromium oxide with low crystallinity, its specific surface area is 39〆/unit, and the yield from the raw material chromium is 1.5%. It was 5%.

Example 3 35 parts of 95% sulfuric acid and 11 parts of a 36% urea aqueous solution are thoroughly mixed with 100 parts of sodium dichromate dihydrate, and the mixture is concentrated until the moisture content becomes 8 to 18% to obtain a raw material.

An electrically heated cylindrical reactor with a diameter of 10 m and a depth of 20 m, equipped with a pipe for supplying raw materials, a duct for taking out the flammables, an air intake, and a rope impeller, is used to maintain the atmospheric temperature inside the furnace. Charge the raw materials while maintaining the temperature at 215°C.

The raw materials immediately react and turn into powder, which is taken out using wind power and constructed using a cyclone and bag filter. Next, “
The bottle was washed with water to remove impurities, purified, dried, and ground into a product. The chromium oxide thus obtained is extremely fine and has a specific surface area of 43 by BET method.
It was evening. Also, the yield from the raw material chromium is Satoshi.
It was 3%. Example 4 - For 5 parts of sodium dichromate dihydrate salt spot, 21 parts of ammonium chloride (equivalent as hydrochloric acid and equivalent as ammonium with respect to sodium dichromate) and 3 parts of water
Add Yuito, mix and crush to form a paste.

- The raw material prepared as described above is dropped into the own plate of the same reactor used in Example 1 and phosphorized.

The temperature inside the furnace was adjusted to 22 psi by controlling the amount of raw material charge or the amount of air. Goku decomposition products are taken out by wind, guided through a duct to a bag filter, and captured. Next, the grilled mackerel collected in the bag filter is washed with water to remove impurities such as sodium chloride and unreacted hexavalent chromium compounds, and then dried and crushed to produce a product.

This material was identified as chromium oxide with low crystallinity by X-ray diffraction, and its particles had a specific surface area of 4 by the BET method.
The product was as fine as 1.1 mm, and the yield based on the raw material chromium was 81%. Example 5 2 moles of ammonium nitrate crystals were added to 1 mole of a 30% aqueous solution of potassium flea chromate, mixed with heat, and the water was then evaporated to a concentration of 4 to 7%. The same reactor as in Example 3 was used for holding.

The reaction conditions are as follows: While maintaining the temperature of the reactor at 220:00, the raw materials are introduced little by little from the feed port. The raw materials immediately react, heat decompose, and turn into powder. This is pulled out from the outlet by wind power and collected by a cyclone and bag filter. The powder collected by the cyclone and bag filter was washed with water, dried and ground to form a product. The chromium oxide thus obtained is very fine particles with low crystallinity, and BET
The specific surface area determined by the method was 31〆/unit. Furthermore, among commercially available chromium oxides, those for use in fine pigments were measured by company A when measuring the specific surface area using the same BET method.
．． 9th / Company B...... 2.5th / Company C...... It was 2.8' evening.

Example 6 Sodium dichromate dihydrate 4.5[9, ammonium sulfate 1.2k9, 98% sulfuric acid 0.6kg (sulfuric acid equivalent to sodium dichromate, ammonia 60% of the equivalent)
A raw material mixture made into a paste by mixing at a ratio of
The internal atmosphere temperature is maintained at 235 degrees Celsius by heating with propane, adjusting the air volume, and the amount of charged raw materials.

After thermal decomposition, heating with propane is rarely done. The decomposed products that are washed and turned into powder are collected in a cyclone and bag filter by wind power. Next, this orange collection is purified by washing with water to remove impurities such as sodium sulfate and unreacted hexavalent chromium, and then filtered, dried, and crushed to obtain a product.

When experimenting with a feed rate of 8 kg/hour of raw materials, the BE of the product
Fine chromium oxide was obtained with a specific surface area of 28/unit by the T method. Comparative Example A reaction was carried out under the same conditions as in Example 2 without adding urea as a nitrogen compound.

Claims (1)

[Claims] 1. Addition and mixing of an alkali dichromate and/or an alkali chromate and a mineral acid and a nitrogen-containing compound in an amount equivalent to the alkali, and then the mixture is heated at a temperature above its decomposition temperature for 40 minutes.
A method for producing fine chromium oxide, which comprises thermally decomposing the chromium oxide by controlling the temperature while venting in an atmosphere at a temperature of 00° C. or lower, and then washing the obtained decomposed product with water. 2. The method for producing fine chromium oxide according to claim 1, wherein the mineral acid is hydrochloric acid, sulfuric acid, or nitric acid. 3. The method for producing fine chromium oxide according to claim 1, wherein the nitrogen-containing compound is a compound selected from ammonia, ammonium salts, urea, and guanidine salts. 4 Fine chromium oxide has a crystallinity [ICr_2O_3(
104)/IA1_2O_3(113)] is 0.2 or less and the specific surface area is 10 to 300 m^2/g, the method for producing fine chromium oxide according to claim 1.