JPS62153124A - Production of chromium oxide - Google Patents

Abstract

PURPOSE:To produce high-purity Cr2O4 having extremely fine particle size, by adding an alcohol to an aqueous solution of CrO3, separating produced Cr2O3 gel and drying, finely pulverizing and calcining the gel. CONSTITUTION:An aqueous solution of CrO3 containing 8wt% Cr component is prepared beforehand. 130g of ethyl alcohol is added little by little to the solution under agitation to effect the reaction of ethyl alcohol with CrO3 and produce amorphous Cr2O3 gel. The gel is aged for 8hr by heating at 98 deg.C, allowed to cool to rom temperature, filtered and dried to obtain about 300g of black Cr2O3 gel. The Cr2O3 gel is finely pulverized to <=1mum with a jet mill, attritor, ball mill, etc., charged in a muffle furnace and calcined at 500-1,000 deg.C for 3hr. Green Cr2O3 powder having particle diameter of 0.03-0.3mu and containing extremely small amount of impurities such as alkali metal, alkaline earth metal, heavy metals such as Fe, etc., can be produced without using pulverization process.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing chromium oxide, and more specifically, to a method for producing chromium oxide that is fine, has uniform particle size, and has good dispersibility. .

Chromium oxide has been commonly used as a green pigment, an abrasive material, and other refractory bricks for a long time, and has excellent chemical stability, heat resistance, and hardness, and is a useful industrial raw material.

[Prior art and its problems]

Conventionally, various methods have been known for producing chromium oxide, but the industrially practiced methods include a method in which chromic anhydride is used as a starting material and thermally decomposed, and a method in which chromium oxide is produced using pentavalent chromium salt. There is a method of producing chromium hydroxide by neutralizing an aqueous solution with an alkali and heating and baking the chromium hydroxide.

20rQ, →0rtOs +3/2o, ↑・・・・・・
(It decomposes into chromium oxide, and the chromium oxide obtained by heating and firing is crushed and classified to obtain the desired product.)

However, when producing chromium oxide using this method, due to the fact that the chromic acid anhydride first melts in the early stage of firing, the chromium oxide after firing has large particles and is in the form of tightly aggregated powder or lumps. A grinding process is essential.

In addition, because of mechanical crushing, it is impossible to reduce the particle size to less than 1 micron, and the particle size distribution is wide, so when used as a pigment or abrasive, problems due to coarse particles may occur.

On the other hand, the latter is a so-called wet method, and the chromium oxide obtained by this method tends to have a uniform particle size.

When a chromium chloride aqueous solution is neutralized by adding sodium hydroxide, chromium hydroxide is precipitated as shown in the following formula (% formula % (2)). When this cake is baked in an oxidizing atmosphere, it generates water and becomes chromium oxide as shown in the following formula: % formula % (31).

The chromium oxide obtained by this method is finer and has a more uniform particle size than the dry method, but since hydroxide is handled, the operations and steps of filtration and washing are very complicated.

Furthermore, in both methods, chromium oxide has a large abrasive power, as it is used as an abrasive, so the more you seek to reduce particle size through pulverization, the more contamination of foreign matter from the pulverizer and the wear of the pulverizer. There are limits.

As mentioned above, the method for producing chromium oxide is simple in principle, but it has not been possible to produce chromium oxide that is fine, has uniform particle size, has good dispersibility, and does not contain impurities, which is the modern requirement. .

The present inventors have completed the present invention as a result of extensive research in order to eliminate the above-mentioned drawbacks.

[Means for solving problems]

That is, the gist of the present invention is that when alcohol is added to an aqueous chromic acid anhydride solution, an amorphous chromium oxide gel as shown in the following formula 2 (% (4)) is produced.

This gel is used as a starting material, and this method is characterized by finely pulverizing and firing chromium oxide, which is characterized by fine grain size, uniform particle size, good dispersibility, and no contamination with impurities.

Next, the features of the present invention will be explained in detail by comparison with conventional methods.

First, chromium oxide gel is produced by adding alcohol to chromic anhydride, but compared to alkaline neutralization, no water washing is required. This is because the aldehyde adhering to the chromium gel is completely burned off and does not remain in the product chromium oxide because oxidation firing is performed at high temperature in the post-process.

This feature is a big difference considering that hydroxide filtration and cleaning are very sophisticated.

It goes without saying that the alcohol used is not particularly specified.

Next, 1. The greatest feature of this invention is that it is pulverized before firing. This pulverization is usually carried out until the particle size becomes 1 μm or less.

By firing this finely powdered chromium gel,
Chromium oxide is obtained, and this chromium gel is 500
Particle size can be controlled arbitrarily by firing at a temperature of 1000°C to 1000°C.

In other words, if fired at a low temperature, the grain size will become finer, and if fired at a higher temperature, the grain size will gradually increase. However, when the temperature exceeds 1000°C, it becomes difficult to control the particle size, and the particle size distribution tends to become uneven.

That is, at temperatures above 1000°C, the growth of particles is large and coarse particles may be formed in some areas.

The chromium oxide produced in this way is fine particles with a particle size of (LO3 ~ (13 microns) without pulverization, and each particle has a uniform shape and has good dispersibility. be.

Also, as mentioned later, chemical analysis revealed that it was alkaline.

Heavy metals such as alkaline earths and IPe have very low values.

〔Effect of the invention〕

The chromium oxide obtained by the present invention is a chromium oxide having a number of characteristics never seen before, and satisfies the requirements of the current state-of-the-art technical field. That is, since it is fine and has a uniform particle size, when used as a surface abrasive material for electronic materials, etc., the surface smoothness is improved by several steps. In addition, in paint-on type magnetic recording materials, the magnetic material itself is extremely finely divided, and if used as a lubricant, it will have the same fine 9 grain size, which is the characteristic of chromium oxide, and It is obvious that it is advantageous because of its good dispersibility.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 A chromic anhydride aqueous solution containing 8 wt% of chromium was placed in a commercially available 3t separable flask with a glass reflux device, and while stirring at 10 OR/M with a glass stirring rod,
The reaction was carried out by adding 150 g of ethyl alcohol at a rate of 19 per minute using a metering pump. At this time, the temperature was at room temperature before the reaction, but at the end of the addition of ethyl alcohol, the temperature was about 4.
The temperature had risen to 0°C.

This reaction solution was heated with a mantle heater while stirring,
It was aged for 8 hours at 98°C.

Next, the mixture was allowed to cool to room temperature, filtered, and dried to obtain approximately 3009, a black chromium oxide gel.

When we performed X-ray diffraction on this substance using an X-ray diffraction apparatus manufactured by Rigaku Denki, it was found that there were no peaks at all and the substance was amorphous.

Next, it was ground for 30 minutes in a tabletop ball mill, and the ground product was observed with an electron microscope (JΣM 1000XII, manufactured by JEOL Ltd.), and it was found that it was ground to 1 micron or less.

Next, it was charged into a Matsufuru furnace and fired at 700°C for 3 hours to obtain a final product.

This sample was first subjected to Xi diffraction using the above-mentioned apparatus, and AS
It was confirmed that it was a chromium oxide with good crystallinity when compared with the TM card A6-504C.

Further, chemical analysis revealed that there were very few impurities as shown in Table 1.

Next, B is said to represent the average size of fine particles.
When the specific surface area was measured using the ET method, it was 2h5rr? /
It was 9. This value and the true density of chromium oxide 5.219/
From d, assuming that this particle is a sphere, the difference between the particle diameter D (microns) and the specific surface area s (//9) is D=1.15/S.
According to this relationship, the average particle size of this chromium oxide was 1049 microns.

The biggest feature is the electron micrograph shown in Figure 1 (911 magnification).
, OO0 times), they are ultrafine particles with a uniform particle size of about t105 microns, and although they are ultrafine particles, they hardly aggregate and are made of chromium oxide with good dispersibility. there were. For comparison, two types of electron micrographs (magnification: 3α000 times) of commercially available chromium oxide powder are shown in Figures 2 and 3.

Table 1 Chemical analysis values (unit: ppm) Example 2 A chromic anhydride aqueous solution containing 8 wt% of chromium was placed in a glass-lined 50-ton reactor, and while stirring, it was pumped with ethyl alcohol every time using a 1.3009-ft constant ik pump. The reaction was carried out by adding 109 parts per minute.

While stirring the reaction solution, steam was passed through the jacket and heated, and the mixture was aged at 98° C. for 8 hours.

Next, the mixture was allowed to cool to room temperature, and the same procedure as in Example 1 was performed to obtain a pulverized chromium oxide gel of approximately 3 to 9 particles.

From this sample, 3009 pieces each were collected and 500°
The final product was obtained by firing at a temperature of C to 1000°C for 3 hours in a K-r 7 full furnace every 100°C.

Table 2 shows the results of measuring the specific surface area of each sample using the BIT method without any modification such as pulverization.

Further, the particle size was determined from the value of the specific surface area and the true density of chromium oxide, and the relationship with the firing temperature is shown in Figure 4.

As can be seen from Table 2 Firing Temperature and Specific Surface Area Diagram 4, by changing the firing temperature from the same intermediate product, ultrafine oxidation particles with uniform particle size, good dispersibility, and size that meets the requirements can be obtained. Chromium can be manufactured.

[Brief explanation of drawings]

Figure 1 is an electron micrograph (magnification: 9 Q, 000
Figures 2 and 3 are electron micrographs (at a magnification of 5 to 000) in place of drawings showing the crystalline state of commercially available chromium oxide for comparison. FIG. 4 is a diagram showing the relationship between firing temperature, specific surface area, and average particle size. In Figure 4, (1) shows the specific surface area, and (2) shows the average particle size. Patent applicant Toyo Soda Kogyo Co., Ltd. 4.~1

Claims (4)

[Claims] (1) A method for producing chromium oxide, which is characterized by adding alcohol to an aqueous chromic acid anhydride solution, filtering out the produced chromium oxide gel, drying, finely dispersing the product, and firing. (2) The method for producing chromium oxide according to claim (1), which comprises pulverizing and dispersing chromium oxide gel into particles of 1 micron or less using a jet mill, an attritor, or a ball mill, followed by firing. (3) The method for producing chromium oxide according to claim (1) or (2), wherein the firing temperature is 500°C to 1000°C. (4) The method for producing chromium oxide according to any one of claims (1) to (3), wherein the chromium oxide has a particle size of 0.03 to 0.3 microns.