JP2741543B2 - Sized chromium oxide and its production method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing fine and sized chromium oxide, and more particularly, an oxidized oxide useful for fine abrasives such as abrasives for magnetic tapes and pigments. It is intended to provide chrome.

[Conventional technology]

Conventionally, chromium oxide has been industrially manufactured for various uses such as pigments, abrasives and refractory materials by the following various methods.

A method in which an aqueous solution of a trivalent chromium salt is neutralized with an alkali agent to form chromium hydroxide, which is fired at a high temperature.

A method in which a reducing agent such as carbon, sulfur or SO ₂ or H ₂ S gas is allowed to act on alkali dichromate, followed by heating and firing, followed by washing with water and separation.

The above is called the so-called wet method.
JP-B-59-38170, JP-B-59-35843, JP-B-62
It is disclosed in Japanese Patent No. 50410 and the like.

A method of thermally decomposing chromic anhydride or ammonium bichromate.

This method is called a so-called dry method and is the most typical method as an industrial production method. In this method, it is known that a nitrogen-containing compound is present as an improvement method for obtaining a pigment having a large specific surface area and excellent pigment properties (Japanese Patent Publication No. 15040/1979 and Japanese Patent Publication No. 55-23213).

As the above-mentioned modified method, there is known a method of adding an acid and a nitrogen-containing compound to an alkali dichromate or ammonium dichromate and thermally decomposing (JP-A-51-108697, JP-A-52-8999). And JP-B-58-1047).

Furthermore, chromium oxide is classified into sized chromium oxide by dry centrifugation under warm air (Japanese Patent Application Laid-Open No. 60-260426), or fine chromium oxide having a substantially spherical particle diameter of 0.03 to 0.3 microns is obtained. It is also known to use an abrasive (Japanese Patent Application Laid-Open No. 63-45125).

[Problems to be solved by the invention]

Recently, chromium oxide has been required to have more functionality unlike conventional chromium oxides, and it has become impossible to follow chromium oxides with conventional particle characteristics.

That is, chromium oxide requires a heating step due to its production method, but the particles of chromium oxide generated at this stage have a strong tendency to adhere and agglomerate with each other, so that the average particle size is 1 μm.
m and its particle size distribution is sharp, and it is difficult to obtain chromium oxide particles that are nearly monodisperse.
Apparent particles are much larger than single crystal particles.

Such a tendency is not a problem limited to chromium oxide in general, but is a phenomenon generally observed as the particles become finer.However, in the case of chromium oxide which inevitably takes a firing step, sintering between particles also occurs. Therefore, it has been considered extremely difficult to form a material close to monodispersion.

Therefore, usually, a means is employed in which the produced chromium oxide is subjected to strong grinding and classification operations to select and recover only a portion close to a desired particle size.

The present invention relates to a chromium oxide having a specific particle state having an average particle size of 2 μm or less, particularly 1 μm or less and a sharp particle size distribution close to monodispersion, which cannot be obtained by the above-mentioned conventional technology. Therefore, it is an object of the present invention to provide a production method for obtaining such chromium oxide without obviating the above-mentioned problems and without requiring additional steps such as special pulverization and classification.

[Means for solving the problem]

That is, the present invention provides an aqueous solution of a raw material preparation containing a hexavalent chromium compound, an alkali salt and a nitrogen-containing compound.
After spray drying or spray pyrolysis at 0 ° C or less, 800-1200
The present invention relates to a method for producing sized chromium oxide, characterized by firing at a temperature of ° C and then washing the fired product with water.

 Hereinafter, the present invention will be described in detail.

One of the features of the chromium oxide according to the present invention is that it is substantially spherical as described above.

Here, the term "substantially spherical" means that the primary particles of chromium oxide have a continuous and smooth curved surface having no convex portion, and for example, a ridge or the like constituted by a crystal plane is not clearly recognized. Say.

Such spherical shape of the chromium oxide particles can be confirmed by observation with an electron microscope (SEM) as shown in FIG.

Such a shape feature, together with an appropriate particle size, can provide a function applicable to pigments and precision polishing.

Next, the chromium oxide according to the present invention has an average particle of 0.1-2.
The second feature is that the value is in the range of μm and the n value in the rosin-Ranmler diagram is 3 or more.

The particle size distribution in the present invention is represented by a value obtained by an electron microscopic method or a light scattering type particle size measuring method, and the average particle diameter means a 50% representative diameter (R50) of the cumulative value, particularly 0.1%. It is preferably in the range of 1.0 to 1.0 μm.

In addition, the particle size distribution was determined by Rosin-Rammr.
er) formula R (Dp) = 100exp (-bDp n) [R (Dp) particle size
The weight distribution of particles larger than Dp, b and n are constants], it can be said that the larger the n value, the sharper the particle distribution, but the chromium oxide according to the present invention may have 3 or more. It is a feature.

Furthermore, chromium oxide having such particle properties is substantially monodisperse particles, has very good dispersibility, and is different from the conventional cohesive modified chromium.

Such chromium oxide can be manufactured industrially by the above-mentioned characteristic operation.

First, examples of the hexavalent chromium compound serving as a raw material include chromic anhydride, alkali dichromate, ammonium dichromate, alkali chromate, and the like. Alkali, alkali sulfate and the like can be mentioned.

As the nitrogen-containing compound, ammonia, ammonium salt, nitrate, urea, guanidine and the like can be used.

In addition, each of the above materials may be used alone or in combination of two or more.

Therefore, as is clear from the above, a hexavalent chromium compound,
It is not always necessary to use the alkali salt and the nitrogen-containing compound individually, but it is only necessary that the raw material preparation eventually contains the three components in a predetermined amount.

However, such a raw material formulation containing hexavalent chromium must be formulated so as to generate chromium oxide and neutral salts when calcined as described below.

The reason is that hexavalent chromium remains in the calcined product when the raw materials are mixed to produce salts showing alkalinity after the calcining, which results in a decrease in chromium oxide yield.

In addition, the quantitative ratio of salts used as starting materials is in the range of 20 to 120 mol% with respect to chromium oxide (Cr ₂ O ₃ ), in which the amount of neutral alkali salt by-produced in the fired product is generated. Especially
It is preferable that the content be 30 to 100 mol%. If the amount of the by-produced neutral alkali salt is less than 20 mol%, the resulting chromium oxide particles grow insufficiently and have a nonuniform particle size distribution. On the other hand, if the content exceeds 120 mol%, the entire fired product becomes a molten state and adheres to the firing furnace wall, making it difficult to discharge from the furnace. Characteristics cannot be obtained.

For the same reason, the nitrogen-containing compound to Cr ₂ O ₃ 80 to 120
A mole% range is preferred.

In the present invention, it is important to perform either the operation of spray drying or spray decomposition on the aqueous solution of the raw material mixture, and these differ only in the hot atmosphere at the time of spraying. Spray drying is carried out by using a so-called desired spray drier to instantaneously evaporate and remove water by bringing a mist-like aqueous solution into contact with hot air to obtain a fine and uniform dry powder. This operation itself is well known in the field of chemistry.

The spray decomposition of the mixed salt aqueous solution is performed by spraying at a high temperature of about 300 ° C. or more, and a finer and higher uniform decomposition product than the former dry powder can be obtained. Such operations are also
For example, it can also be obtained by directly spraying an aqueous solution into a rotary kiln heated to a high temperature of 0 ° C. or higher. This spray decomposition method allows instantaneous evaporation and removal of water and heat decomposition of the raw material, and a fine and uniform decomposition product powder can be obtained.

The powder of the spray-dried product or the decomposition product obtained in this manner is calcined in a rotary kiln, shuttle kiln, or other furnace at a temperature of 800 to 1200 ° C. for 0.5 to 3 hours, and the calcined product is washed with water to obtain a secondary product. The desired chromium oxide is obtained by removing biological salts as much as possible and drying.

Although crushing may be performed if necessary, it is not an indispensable operation in the present invention.

(Operation)

The chromium oxide according to the present invention has substantially spherical and sized fine particles having good dispersibility.

Such chromium oxide is obtained by subjecting an aqueous solution of a raw material mixture of hexavalent chromium, an alkali salt and a nitrogen-containing compound to a spray treatment in a heated atmosphere, so that fine powder having good fluidity becomes a nucleus, and each particle is formed. By completely pyrolyzing under uniform firing conditions, gas generation of oxygen gas, nitrogen gas, water, etc. and chromium oxide crystallization promotion due to the presence of alkali salt are performed for each uniform particle, so that it has the above characteristics. It is believed that chromium oxide is obtained.

〔Example〕

 Hereinafter, the present invention will be described based on examples.

Example 1 chromic anhydride: a (CrO ₃ 99.7%) 100 parts by weight were dissolved in 100 parts by weight of water, sodium sulfate _{(Na 2 SO 4: 98wt%} ) 72 parts by weight of aqueous ammonia (NH _3: 28wt%) 61 The aqueous solution prepared by adding parts by weight was spray-dried at a temperature of 140 ° C. The obtained dry powder was spherical with an average particle size of 5 μm, and as a result of chemical analysis, it was confirmed that the powder was a highly uniform and fluid powder having no segregation of the raw materials.

Next, 30 g of the dry powder placed in an alumina crucible (100 cc) was fired in an electric furnace controlled at 1100 ° C. for 1 hour, and cooled naturally.

The calcined product was washed with water to remove by-product sodium sulfate, and dried to obtain 11 g of chromium oxide.

Observation of the obtained chromium oxide with an electron microscope (SEM) confirmed that the particles were substantially spherical and well-ordered as shown in FIG. 1, and the particle size distribution was measured.
0 = 0.4 μm Rosin-Rammler equation: Finely divided chromium oxide having n = 3.1. Further, when the BET specific surface area was determined, it was 2.9 m ² / g.

Example 2 double chromate sodium: the _{(Na 2 Cr 2 O 7 ·} 2H 2 O 99.5%) 50 parts by weight were dissolved in 250 parts by weight of water, sulfuric acid _{(H 2 SO 4: 98%} ) 16.7 parts by weight of urea [( NH ₂ ) ₂ CO: 98%] 10.2 parts by weight were added and completely dissolved, and the aqueous solution of the raw material mixture obtained was spray-treated in a hot atmosphere at a temperature of 400 ° C. to perform spray decomposition.

The obtained powder was brown and uniform fine particles having good fluidity. Next, this fine powder was fired in an electric furnace at 1100 ° C. for 1 hour in the same manner as in Example 1, then cooled and washed with water to remove as much sodium sulfate by-product as possible, and dried to obtain chromium oxide.

When the particle characteristics of the chromium oxide were measured in the same manner as in Example 1, the following results were obtained.

SEM: substantially spherical Average particle diameter (R50): 0.3 μm n-value of rosin-Rammler equation: 3.3 BET specific surface area: 3.84 m ² / g Comparative Example 1 The aqueous solution prepared in Example 1 was evaporated to dryness at 120 ° C. I let it. The obtained solid was pulverized, baked at 1100 ° C. for 1 hour (same as in Example 1), washed with water and dried to obtain chromium oxide.

When the particle characteristics of the obtained chromium oxide were examined, the following results were obtained.

SEM: Heterogeneous particles having high cohesiveness (Fig. 2) Average particle size (R50): 0.5 µm Rosin-Rammler n value: 1.5 BET specific surface area: 2.30 m ² / g [Effect of the Invention] Oxidation according to the invention Chromium is substantially spherical and has a rosin-Rammler n-valued particle size of 3 or more and sized particles.

Such chromium oxides are useful as precision abrasives or pigments for magnetic recording media.

On the other hand, according to the production method of the present invention, chromic anhydride, bichromate or the like is used as a chromium source in a relatively simple step, and by firing at a relatively low temperature, as described above, the fine and sharp particle size distribution is obtained. It is possible to obtain chromium oxide in a particle state.

[Brief description of the drawings]

FIG. 1 is an electron micrograph (15,000 times) showing the particle structure of chromium oxide as one of the embodiments of the present invention, and FIG. 2 is an electron micrograph (15000) showing the particle structure of chromium oxide as a comparative example. Times).

Claims (1)

(57) [Claims] An aqueous solution of a raw material preparation containing a hexavalent chromium compound, an alkali salt and a nitrogen-containing compound is spray-dried or pyrolyzed at 400 ° C. or less, and then calcined at a temperature of 800 to 1200 ° C. A method for producing sized chromium oxide, wherein the calcined product is washed with water.