JPH05132311A - Production of sol of ceric oxide - Google Patents

Abstract

PURPOSE:To obtain a transparent and stable sol of ceric oxide by a simple process economically and advantageously by reacting cerous carbonate with an oxidizing agent to form a gel of ceric oxide and flocculating the ceric oxide with an acid. CONSTITUTION:Finely granulated cerous carbonate is slurried with water to prepare about 5-20wt.% calculated as CeO2 slurry. Then the slurry is reacted with about 1-10 equivalents oxidizing agent (e.g. hydrogen peroxide) under heating to form a gel slurry of ceric oxide. Then the prepared gel slurry of ceric oxide is treated with an acid (e.g. hydrochloric acid), deflocculated under heating to give a sol of ceric oxide. The prepared sol of ceric oxide is suitably used for various kinds of ultraviolet absorption uses taking advantage of its transparency or for uses of an abradant utilizing its uniformity of fineness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing cerium oxide sol, which provides cerium oxide sol useful as an industrial material used as an ultraviolet absorber, an abrasive, a catalyst, a ceramic raw material, etc. And a novel method for producing the ceric oxide sol.

[0002]

2. Description of the Related Art Conventionally, powdered ceric oxide has been produced mainly by a thermal decomposition method of ceric oxalate. However, the powdery cerium oxide is naturally insoluble in water and other solvents, so that it was difficult to apply it to the use as an ultraviolet absorber that requires transparency, for example. Further, in order to improve the transparency, it has been studied to obtain cerium oxide which is as fine as possible, but the improvement is naturally limited because it is a powder.

In order to solve such a problem, a technique for providing ceric oxide in the form of a colloidal dispersion, that is, a sol has been developed in recent years. For example, JP-A-62-38235,
JP-A-62-275021 and JP-A-1-197316 disclose methods for producing the cerium oxide sol.

In these conventional production methods, a solution of ceric nitrate is heated to destabilize it to precipitate ceric oxide containing nitrate radicals and redispersed in water to obtain a sol. This is a method of partially neutralizing an aqueous solution of cerium nitrate with a basic aqueous solution to obtain a sol, but none of these methods is industrially advantageous, and the obtained sol is not satisfactory in terms of quality.

That is, according to the method of (1), the aqueous solution of ceric nitrate as the raw material is subjected to electrolytic oxidation of ceric nitrate,
Alternatively, it must be obtained by allowing nitric acid to act on the cerium oxide hydrate obtained from the solution of the cerium salt, and then the aqueous solution is thermally hydrolyzed for a long time, and the formed precipitate is separated by solid-liquid separation. Therefore, this method cannot be said to be an industrially advantageous method because it has to undergo a complicated process of re-dispersing the same in water. Further, there is a problem that nitrate radicals in the raw material are wastefully discarded as nitrate ions in solid-liquid separation.

Further, according to the method (1), there is the same problem that cerium nitrate is used as a raw material, and when the aqueous ammonia is used as the basic aqueous solution, the obtained sol is obtained. There is a problem that ammonium nitrate is contained in the solution as a large amount of impurities. Furthermore,
In JP-A-1-197316, a sol obtained by these methods is used, which is once precipitated with a salt of a monovalent weak acid, and the precipitate is redispersed in water. Although a method for obtaining the above has been proposed, this method is advantageous in producing a sol stabilized with an acid other than nitric acid, but the process becomes more complicated, and there are many by-product impurities industrially. Is a disadvantage.

As described above, all of the conventionally known methods for producing cerium oxide sol require complicated steps, and as a result, it is difficult to obtain a sol of stable quality. At present, it is not always an advantageous method for economic reasons.

[0008]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention The inventors of the present invention have conducted extensive studies as to a method for obtaining a stable cerium oxide sol which is economically advantageous by a simple process and is high in quality. It was found that a cerium oxide sol can be easily and stably obtained by a method of producing a sol from a gel obtained by reacting cerium with an oxidizing agent, and completed the present invention based on such findings. It is something that has come to be.

[0009]

Means for Solving the Problems That is, the present invention is characterized by reacting cerium carbonate with an oxidant to form a cerium oxide gel, and then peptizing this with an acid. The present invention relates to a method for producing a cerium sol.

[0010]

The operation of the cerium oxide sol of the present invention will be described in more detail below. In the method for producing a ceric oxide sol of the present invention, first, as a first step, ceric carbonate is reacted with an oxidizing agent to obtain a ceric oxide gel. Cerium carbonate is a powder insoluble in water, but this reaction oxidizes trivalent cerium to tetravalent,
A cerium oxide gel is formed after the reaction. Conventionally,
As a method of obtaining cerium oxide, a method of obtaining cerium carbonate by a reaction using an oxidizing agent is not known, and as a result of various studies conducted by the present inventors, the following findings were obtained. Got

First, it is desirable to use a powder of cerium carbonate as a raw material which is as fine as possible, and commercially available cerium carbonate which is generally available has a particle diameter of about several tens of μm. When this product is used, it is preferable to use it after pulverizing it to 10 μm or less. Examples of the oxidizing agent include hydrogen peroxide, ozone, azides such as sodium azide, persulfates such as ammonium persulfate, dichromates such as potassium dichromate, and fluorine. However, among these oxides, it is most desirable to use hydrogen peroxide or ozone because salts are not by-produced by the reaction. That is, this by-product salt requires a separate removal operation in the latter stage, and if it remains in the finally obtained sol solution, it causes a problem as an impurity.

Next, regarding the use ratio of cerium carbonate and oxidizer, the stoichiometry of the reaction varies depending on the particle size of cerium carbonate used and the type of oxidizer used. The formula is represented by the following formula Ce ₂ (CO ₃ ) ₃ + XO → 2CeO ₂ + 3CO ₂ + X (however, XO represents an oxidant), and the oxidant is usually about 1 to cerium carbonate. It suffices to use them so that the ratio is up to 10 equivalents. In particular, when hydrogen peroxide is used as an oxidant, the reaction equivalent is approximately 1 to 20 due to the self-decomposing property of hydrogen peroxide.
It is preferable to use it in an equivalent range.

Cerium carbonate is insoluble in water, and this powder is slurried with water for use in the reaction. The concentration at that time is about 5 to 20% by weight as CeO ₂ . The temperature during the reaction is not particularly limited, but is generally
The reaction temperature is 20 to 100 ° C. Generally, the higher the reaction temperature, the shorter the reaction time.However, when hydrogen peroxide is used, the start temperature of the reaction is 40
It is desirable to carry out the reaction at a temperature of not higher than 0 ° C. and then gradually raise the temperature to carry out the reaction.

The reaction between cerium carbonate and the oxidizing agent is most preferably completed, but even if the reaction is not completed, unreacted in the gel after the deflocculating step with an acid in the latter stage. Cerium carbonate can be separated and removed as a cerium salt by using a means such as ultrafiltration.

Thus, the cerium carbonate is reacted with the oxidizing agent, and the gel produced by the reaction is then deflocculated by the acid in the next step. The types of acids used are inorganic acids such as hydrochloric acid, nitric acid, perchloric acid, formic acid, acetic acid,
Organic acids such as lactic acid can be used alone or in combination.

The amount of these acids used varies depending on the type of acid used and cannot be generally stated. However, when a strong acid such as hydrochloric acid is used, the amount thereof may be relatively small, and a weak acid such as acetic acid is used. In that case, the amount becomes large and the cerium oxide gel is peptized to form a transparent sol. The amount is 1 mol of CeO ₂ concentration of the gel,
The range is approximately 0.2 to 5.0 mol.

If the amount of this acid used is insufficient,
Peptization of the ceric oxide gel does not proceed sufficiently, and if the amount of the acid used is too large, the ceric oxide gel is completely decomposed, which is not preferable because it forms a salt of cerium. The yield of the sol obtained is low.

Regarding the conditions for peptization with this acid, the reaction temperature is preferably about 50 ° C. or higher, preferably about 90 ° C., and the reaction time is 0.1 to 1
It's 0 hours. Further, the concentration of the ceric oxide gel is not particularly limited, and the reaction is usually carried out at 1 to 15% by weight as CeO ₂ , but it is efficient to carry out the reaction at a concentration as high as possible. A cerium oxide sol can be obtained by the method of the present invention described above.

[0019]

The present invention will be further described below with reference to examples of the present invention, but the present invention is not limited thereto. still,
In the examples, all percentages are by weight unless otherwise specified.

Example 1 Cerous carbonate (CeO ₂ 32.7)
%, Particle size 5-10μ) to 1000g, water 2139g and hydrogen peroxide water
131 g of (H ₂ O ₂ 34.5%) were added. After stirring this at room temperature for 1 hour, the liquid was heated to a temperature of 93 ° C., and the reaction was carried out while stirring for 1 hour.

After the reaction, the product became a yellowish white gel slurry and the cerium concentration was CeO ₂ 11.4%. The slurry was dried at 60 ° C., and the X-ray diffraction of the obtained powder was measured. As a result, the d values of the main peaks were 3.12, 1.91, and 1.6, respectively.
It is 3 angstroms and its crystal form is ceric oxide (Cerium oxide).
ianite).

Next, to 1000 g of this cerium oxide gel slurry, 1239 g of water and 41 g of hydrochloric acid (HCl 35.4%) were added, and the mixture was heated at 90 ° C. for 1.5 hours to carry out peptization treatment to oxidize it. A second cerium sol was obtained. As a result of analyzing this sol, it was CeO ₂ 5.2% and HCl 0.66%, and it was a transparent sol liquid with no precipitation and was extremely stable.
There was no change even if left for one month.

Example 2 Cerous carbonate (CeO ₂ 51.3)
%, Particle size 50-70 μ), and 2420 g of water was added to form a slurry, which was wet-milled for 2 hours using a vibrating ball mill (ball diameter 10 mm). After wet grinding, the particle size of cerium carbonate became 3 to 6μ. Next, to 1000 g of this pulverized slurry, ozone-containing air (O ₃ 1.1%) generated by an ozonizer was blown at a flow rate of 200 L / hr for 25 hours at room temperature to carry out a reaction to obtain a gel slurry of ceric oxide. ..

To this gel slurry, 500 g of water and 52 g of acetic acid were added, and deflocculation treatment was performed while heating at a temperature of 97 ° C. for 6 hours to obtain a cerium oxide sol. As a result of analyzing this sol, it was CeO ₂ 10.3%, acetic acid 3.6%, it was a transparent and extremely stable sol liquid without sediment, and there was no change even if this sol liquid was left for 1 month. It was

(Example 3) To 1000 g of cerium carbonate used in Example 1, 4709 g of water, 521 g of ammonium persulfate and 310 g of aqueous ammonia (NH ₃ 26.3%) were added. While stirring this, a reaction was carried out at a temperature of 70 ° C. for 2 hours. In this reaction, the use of aqueous ammonia is intended to neutralize sulfuric acid, which is a decomposition product of ammonium persulfate, and prevent the formation of water-soluble cerium salt. After completion of the reaction, the product was filtered and washed, and washed until ammonium ion and sulfate ion were not observed in the filtrate. The obtained wet cake was suspended in water to obtain 4671 g of a gel slurry of CeO ₂ 7.0% cerium oxide.

Next, 1000 g of this slurry was added to nitric acid (HNO ₃ 6
7.4%) was added thereto, and the mixture was heated at a temperature of 85 ° C. for 1 hour for peptization treatment to obtain a cerium oxide sol. As a result of analyzing this sol, it was CeO ₂ 7.1% and HNO ₃ 2.1%, and it was a transparent sol liquid.

Example 4 To 1000 g of cerium carbonate used in Example 2, water and hydrogen peroxide solution (H ₂ O ₂ 34.5%) were added at the ratios shown in Table 1, and the mixture was kept at room temperature. After stirring for 6 hours, the liquid was heated to a temperature of 93 ° C., and the reaction was carried out for 1 hour while stirring. After the reaction, the gel slurry of cerium oxide obtained was diluted with water until the concentration became CeO ₂ 2.0%, and then 461 g of hydrochloric acid (HCl 35.4%) was added thereto, and the temperature was 90 ° C for 2 hours. A cerium oxide sol was obtained by heating and peptizing treatment.

The solization rate of cerium in the sol thus obtained was determined. The method is ultrafiltration of each cerium oxide sol (using an ultrafiltration membrane with a molecular weight cut-off of 10,000), the concentration of Ce ³⁺ contained in the ultrafiltrate is measured, and cerium sol is formed according to the following formula. The rate was calculated. Solation rate (%) = (1- (Ce ³⁺ concentration in ultrafiltrate / sol in sol
CeO ₂ concentration × 172/140)) × 100 The results are shown in Table 1.

[0029]

[Table 1]

All these sol solutions were extremely stable and transparent. In addition, the sol obtained under the No. 1 production conditions in Table 1 was subsequently subjected to ultrafiltration,
The concentration of the sol solution was concentrated to CeO ₂ 30%, and the concentrated solution of this sol was also a stable and transparent sol.

[0031]

The method for producing a ceric oxide sol of the present invention has a simple production process and is a very economically advantageous method. Further, the simple manufacturing process makes it easy to obtain a sol of stable quality.

Therefore, the cerium oxide sol obtained by this method is a stable sol solution composed of extremely fine colloidal particles, and in particular, it is used for various ultraviolet absorbing applications utilizing the transparency peculiar to the sol, and the uniform sol peculiar to the sol. It is expected to be used in various fields such as abrasives, catalysts, ceramic raw materials that make use of fineness, and it will create new applications as cerium oxide-based materials.

Claims (2)

[Claims] 1. A method for producing a cerium oxide sol, which comprises reacting cerium carbonate with an oxidizing agent to form a cerium oxide gel and then peptizing the cerium oxide gel with an acid. 2. The method for producing a ceric oxide sol according to claim 1, wherein the oxidizing agent is hydrogen peroxide or ozone.