JPS5938170B2 - Manufacturing method of fine chromium oxide - Google Patents

Description

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

Generally, chromium oxide is used as a green pigment or as an abrasive.
It is also a useful industrial raw material widely used in the ceramic industry.

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 tends to have a uniform particle size and crystal shape, but depending on the precipitation conditions of chromium hydroxide, it becomes thick (which affects the properties and prevents hydration). The operation and process are very complicated because 95 objects are removed.

On the other hand, the latter is a so-called dry method, and this method is often used industrially.

When chromic anhydride is heated, it decomposes into chromium oxide as shown in the following formula (% formula %) (1), and the chromium oxide obtained by this 7JD thermal calcination is crushed and classified to produce a product.

However, the chromium oxide obtained by this method has large particles and is in the form of agglomerated powders or agglomerates. Since it has a high abrasive force as it is used as a material, the more you seek to reduce the particle size through pulverization, the more foreign matter from the pulverizer and the wear of the pulverizer become severe, so there is a limit to the amount of pulverization that can be done.

Therefore, the disadvantages of chromium oxide can be removed by direct thermal decomposition of chromic anhydride (as shown in the following formula (%) (2)). .

The feature of this method is that when ammonium dichromate is heated, it self-combusts, which eliminates the need to use mechanical methods. You can get what you want.

- However, this method has a lower NH4)2 value than the direct method.
In order to handle the Cr 20□ crystals, additional operational steps such as reaction of chromic anhydride and ammonia, cooling, crystallization and separation, and drying are required, so the manufacturing cost is inevitably very high.

Further, although the chromium oxide produced by this method has some degree of freedom in controlling the firing temperature, the characteristics of the chromium oxide are fixed and there is a drawback that it cannot be produced in a grade that meets the requirements.

In addition, as another method, there is a method in which dichromate is roasted 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, as a method for producing fine chromium oxide, the applicant has developed a method for producing fine chromium oxide by adding 800 to
A method of thermal decomposition at a firing temperature of 1200°C
15040) and a two-step thermal decomposition method (Japanese Patent Application Laid-Open No. 1983-4498) in which ammonia of a specific molar ratio is present in chromic anhydride.

All of these are chromium oxides with a high crystal ratio that have developed crystals with a specific surface area of 0.4 to 4 rlt/f at most.

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.

Looking at the use of chromium oxide in the ceramic industry, the conventional crystal-developed coarse particles are often unsuitable due to their inert reactivity with other ceramic materials.Furthermore, from the standpoint of energy consumption, manufacturers If you look at both the users and the users, this means that there is a lot of waste.

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 inventor has 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, an alkali agent is applied to an aqueous trivalent chromium salt solution to generate chromium hydroxide, and the hydroxide obtained after separation by filtration is heated at a temperature of about 450° C. or lower in the presence of salts. The present invention relates to a method for producing fine chromium oxide, which is characterized by washing the fired product with water.

In the present invention, the trivalent chromium salt to be applied is not particularly limited, but typical examples include chromium sulfate, basic chromium sulfate, chromium nitrate, chromium chloride, and chromium alum. It may be a species or a mixture of two or more species.

Moreover, there is no problem even if winter aluminum components are mixed in these.

An alkali agent is applied to the above chromium salt aqueous solution to precipitate chromium hydroxide.

As the alkaline agent, aqueous ammonia, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, etc. are used.

In this case, the conditions for precipitation of chromium hydroxide are such that the pH is in the range of 5 to 9 (and the temperature does not need to be particularly limited, ranging from room temperature to 100°C).

Within the above range, a hydroxide with good filterability is produced.

This is because when the pH is about 5 or less, hydroxide is insufficiently produced or no hydroxide is produced, whereas when the pH is about 9 or more, the alkali is wasted, which is economically unfavorable.

In addition, in the reaction, a method of simultaneously injecting a trivalent chromium salt aqueous solution and an alkali agent aqueous solution at a constant pH, a method of gradually adding an alkali agent to a trivalent chromium salt aqueous solution until a predetermined pH is reached, or vice versa. Although there is a method of adding, there is no need to specifically limit it in the present invention.

After chromium hydroxide is produced and precipitated in this way, it is not necessary to perform solid-liquid separation and wash the separated and collected precipitate (which may be dried) (because the by-product salts have been adsorbed). Heat treated in its original state.

In this case, the heat treatment is performed at a high temperature (even about 450°C, preferably 40°C).
It is necessary to perform heating in a low temperature range down to 0°C, with the lower limit being about 150°C or higher.

The reason for this is of course related to the firing time, but the temperature is about 400°C.
In the above cases, the chromium oxide produced by dehydration crystallizes and the growth of particles becomes remarkable.This tendency becomes especially noticeable at temperatures above about 450°C, resulting in the formation of active chromium oxide with a large surface area. On the other hand, below about 1509C, dehydration is insufficient and the firing time becomes very long (and at the same time, conversion to chromium oxide is not achieved).

Furthermore, there is a tendency for the removal of contaminated salts to be insufficient in the subsequent water washing treatment.

For example, FIG. 1 shows chromium oxide according to the present invention, which is extremely fine and has no crystal growth.

The chromium oxide shown in FIG. 2 has a hexagonal crystal shape of about 0.1 μm.

The former was heated at 350°C and the latter at 500°C, but a significant difference appears.

The resulting fired product converted to chromium oxide is washed with water to remove the contaminant salts produced as a by-product in the previous step, and then dried and pulverized to produce a product.

As described above, in the present invention, in the heating process, the hydroxide is not washed with water, but is washed with water after heating while salts coexist. .

During heating, the coexistence of salts generally has a greater effect on crystal growth and particle growth of chromium oxide particles, but
Under the firing conditions of the present invention, there is almost no effect (and relatively pure, fine, active chromium oxide can be easily produced.

The chromium oxide according to the present invention has a conventional hexagonal crystal type (unlike a developed crystal type, conventional chromium oxide is a chromium oxide with low crystallinity or nearly amorphous).
BS (National Bureau of S.
When compared with X-ray diffraction under the same conditions as the standard Coranta Hiroshi (standards), the intensity ratio of the diffraction line between the 113 plane of corundum and the 04 plane of chromium oxide is gO04, but the chromium oxide obtained by the present invention has a 0.2
It has the following low crystallinity.

On the other hand, the particles of conventional chromium oxide are coarse and hard, and it is extremely difficult to finely grind them to the point where they can be used as an abrasive itself. Although difficult to obtain in reality, the chromium oxide of the present invention has a large specific surface area (approximately 107Tl''/g to 400Tl''/g).
m7 y (7) Fine particles in the range.

Such chromium oxides would of course be very suitable as active and reactive chromium oxides, especially in ceramic material applications.

This will be further explained below in Examples.

Example 1 Chromium Meishun 25 aqueous solution 51 was placed in a 10/2 reactor and heated to 80°C, and a 5 molar potassium hydroxide aqueous solution heated to about 80'C with stirring was added until the pH of the reaction solution was 6. The solution is left to cool for about 1 hour until it reaches 0, and is then dropped to form a chromium hydroxide precipitate.

After that, stirring was continued at 80'C for about 3 hours.

It is then filtered to separate the solid and liquid and dried at 110°C.

The dried product is placed in a Matsufuru furnace and heated at 320°C for 4 hours.

Immediately thereafter, it was washed with water to remove contaminant salts such as potassium sulfate, and then filtered, dried, and pulverized using conventional methods to obtain a product.

The chromium oxide obtained as described above has a dark greenish-gray color.
It's very minute.

The specific surface area determined by the BET method was 56rrl'7y.

Moreover, the crystallinity was so low that chromium oxide could barely be identified by X-ray diffraction.

Example 2 Basic chromium sulfate (Cr20325.7% basicity 33
．． 2%) 30% aqueous solution and 25% sodium hydroxide aqueous solution were each heated to about 75°C, and the reaction temperature was adjusted to 75°C and pH to 6.2 to 6.4 in a 101 reactor equipped with a stirrer. Add at the same time.

The reactants are drawn off continuously at a flow rate of 10//h.

Note that the amount of raw materials charged is adjusted so that the average residence time in the reactor is about 1 hour.

The reaction product was continuously separated into solid and liquid, and the wet cake was directly transferred to a rotary kiln (diameter 20011M, length 2500M).
tnm) at 350°C.

Next, the baked product is washed with water to remove impurities such as sodium sulfate, and is then filtered, dried, and pulverized by conventional methods to obtain a product.

The chromium oxide thus obtained was extremely fine and had a specific surface area of 63 g/f by the BET method.

Example 3 Aqueous solution of 50% chromium chloride and 50% was placed in a 1001 reactor and heated to 60°C, and 28% ammonia water was added over about 2 hours until the pH reached 5.7 to complete the reaction. .

Thereafter, stirring was continued for about 2 hours to mature the chromium hydroxide precipitate, and the mixture was then filtered to separate the ammonium chloride solution.

Place the obtained cake as it is in a Matsufuru furnace and heat it to 180°C.
Heat for 8 hours to form chromium oxide.

The material taken out from the Matsufuru furnace is washed with water, filtered, dried, and crushed into products.

The chromium oxide obtained in this way is very fine and has a BE
The specific surface area by T method was 83rrtyyy.

Comparative Example 1 The reaction product of Example 2 was taken out and washed with water and tested for filterability.

First, a certain amount of the reactant is put into a test filter, and the time until it can be filtered is measured, and this is considered as the first time.

Next, add fresh water in the same amount as Part F to the cake and stir for 1 hour to disperse.

Place this in a test filter, measure the time, consider this as the second time, and calculate the ratio with the first time.

When this was repeated until SO;-gana(), the following data was obtained.

The more salt there is, the longer the washing time will be, requiring a large amount of washing water and time.

On the other hand, when the fired product of Example 2 was taken out and washed with water to remove the contaminant salts, the precipitated eluate became smaller and it became possible to perform decantation.

Therefore, most of S;- can be removed by three decantations.

As can be seen from the above results, it can be seen that it is more efficient to wash with water after forming an oxide than to wash with water using a hydroxide.

Comparative Example 2 In Example 2, chromium oxide was produced by changing the heating temperature, and the characteristics of the resulting product were measured, and the following results were obtained.

[Brief explanation of drawings]

FIG. 1 is a photograph of chromium oxide of Example 2, and FIG. 2 is a photograph of Comparative Example 1.

Claims (1)

[Claims] 1. A trivalent chromium salt aqueous solution is treated with an alkaline agent to generate chromium hydroxide, and the hydroxide obtained after separation by filtration is heated at a temperature of 450°C or less in the coexistence of salts, and the fired product is washed with water. A method for producing fine chromium oxide.