JPH035323A - Manufacturing method of fine bismuth oxide - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing fine bismuth oxide, which is optimal as dibismuth tetroxide for coating on the surface of a shadow mask in a cathode ray tube.

[Conventional technology]

One of the uses of bismuth oxide is for coating the surface of shadow masks used in cathode ray tubes. This is intended to prevent distortion of the shadow mask by reflecting electron beams hitting the shadow mask and preventing heat generation.

The common method for applying bismuth oxide to a shadow mask is to suspend the bismuth oxide in water, adjust the viscosity by adding water glass, etc., then spray it onto the shadow mask, dry it, and then bake it. .

For this reason, in order to prevent uneven coating and clogging of the spray, and to obtain a dense film by baking, the average particle size is 0.2 μm.
The following fine bismuth oxide with slow sedimentation rate is required.

[Problem to be solved by the invention]

Current bismuth oxide is not necessarily sufficient to meet the above requirements. In other words, conventional bismuth oxide is obtained by hydrolyzing bismuth nitrate with a concentrated alkaline solution, or by thermally decomposing bismuth salts such as bismuth oxycarbonate and bismuth hydroxide. If this method is followed, only columnar crystals with an average particle size of 5 to 10 μm can be obtained, and in the latter method, the particle size of bismuth salt such as bismuth oxycarbonate or bismuth hydroxide, which is a raw material, is 1 to 10 μm. 5μI,
Even if it is baked, only about 0.5 to 1 μI can be obtained. For this reason, it has to be crushed in order to be used as a shadow mask, but even if the materials obtained by these methods are crushed with a ball mill, etc., they will not become smaller than 0.5 μm, resulting in uneven coating and clogging of the spray. Such problems cannot be resolved.

The object of the present invention is to provide fine bismuth oxide having an average particle size of 0.2 μm or less and a slow sedimentation rate.

[Means to solve the problem]

In order to solve the above problems, the method for producing bismuth oxide of the present invention includes adding one or two persulfates to a nitric acid solution containing trivalent bismuth ions in an amount of 1 to 3 equivalents based on the amount of bismuth in the nitric acid solution. The mixture was stirred for 1 to 6 hours while maintaining the pH at 8 or higher, and the solid was separated and dried. It is characterized in that bismuth oxide is obtained by baking at 350 to 500°C in the coexistence of bismuth.

[For production]

The method of the present invention hydrolyzes bismuth nitrate, wet-oxidizes the obtained bismuth oxynitrate to obtain dibismuth tetroxide, and roasts this to obtain trivalent bismuth oxide.
Since bismuth tetroxide obtained as an intermediate is extremely fine, bismuth oxide with an average particle size of 0.2 μm or less can be obtained.

In the present invention, a nitric acid solution containing trivalent bismuth ions is used as a raw material because dissolving bismuth nitrate causes partial hydrolysis. This is because it remains as an unreacted component in the bismuth tetroxide produced, and coarse bismuth oxide particles are produced by roasting. Therefore, the amount of nitric acid may be as long as it can prevent hydrolysis of bismuth.

Persulfates that can be used in the present invention are sodium persulfate, potassium persulfate and ammonium persulfate. Persulfate may be added after the pH is adjusted and bismuth oxynitrate is produced, but at this time the liquid temperature is high and self-decomposition of persulfate is likely to occur, resulting in the need for an excess of persulfate. Therefore, add it before raising the temperature (
This is desirable. If bismuth oxynitrate is roasted unreacted, coarse bismuth oxide will be included in the resulting product, so the amount of persulfate added must be equal to or greater than that of bismuth nitrate. However, since addition of an excessive amount of persulfate deteriorates economic efficiency, it is desirable to limit the amount to 3 equivalents or less.

The reason why the liquid temperature is set to 40° C. or higher is to complete the production of bismuth oxynitrate and to complete the oxidation. In addition, the temperature is set at 80°C or lower to prevent the agglomeration and growth of particles of bismuth oxynitrate and the tetravalent bismuth salt that is generated, and to prevent excessive self-analysis of persulfate. This is to ensure safety.

The reason for setting the pH to 8 or higher is to precipitate bismuth nitrate as bismuth oxynitrate, and usable alkalis include caustic alkali, alkali carbonate, ammonia, and the like. By the way, as mentioned above, bismuth oxynitrate is relatively stable, and even after adding it to water to make a slurry, adding persulfate, adjusting the pH, and heating it, the oxidation rate is said to be extremely slow. The freshly produced bismuth oxynitrate has high reactivity, and if oxidized as it is without solid-liquid separation, it can be oxidized to bismuth tetroxide in a reaction of one hour or more. Even if the oxidation time of bismuth oxynitrate is made too long, there will be no noticeable effect and the economic efficiency will only deteriorate. Therefore, the reaction time needs to be 1 to 6 hours, preferably 1 to 4 hours.

The bismuth tetroxide thus obtained is separated into solid and liquid and then dried.

Dried bismuth tetroxide is roasted and reductively decomposed into bismuth oxide, but if the roasting temperature is too low, the reductive decomposition is insufficient and dibismuth tetroxide is mixed into the product, which may cause problems when used as a shadow mask. Shorten the life of the cathode ray tube. Also, if the firing temperature is high, sintering will occur. For this reason, it is necessary to set the roasting temperature to 350 to 500°C.

[Example 1] 200 g of Wako Pure Chemical's reagent-grade bismuth nitrate/natural water salt was dissolved in 11 10% nitric acid solution, and KzSzO1171,
After 1 g was added and dissolved, the temperature was raised and when the temperature reached 60°C, a solution obtained by dissolving 131 g of NaOH in 11 water was added, and the mixture was reacted for 2 hours at a liquid temperature of 80°C. Note that the pH at this time was approximately 12.

The produced dibismuth tetroxide was filtered out and the valve was washed four times. After washing, air dry at 100℃, 97.8
g BitOn was obtained. Next, this was heated at 400℃ for 2
After aerated roasting for an hour, 95.4 g of βBi2O3 was obtained. The particle size of this bismuth oxide was measured by the Fisher method and was found to be 0.1 μm on average.

[Example 2] 200 g of reagent-grade bismuth nitrate/natural water salt manufactured by Wako Pure Chemical Industries, Ltd. was dissolved in 11 10% nitric acid solution, and KtS, OH23, 4
After the solution was dissolved, the temperature was raised to 60°C, and when the temperature reached 60°C, a solution obtained by dissolving 131g of NaOH in 11 water was added, and the mixture was reacted for 4 hours at a liquid temperature of 60°C. In addition, p at this time
H was about 12.

The produced dibismuth tetroxide was filtered out and the valve was washed four times. After washing, air dry at 80℃, 96.0
g of Bi2O2 was obtained. This was then aerated at 450°C for 2 hours and 93.6 g of β-Bi20. I got it.

The particle size of this bismuth oxide was measured by the Fisher method and was found to be 0.1 μm on average.

[Example 3] 200 g of reagent-grade bismuth nitrate/natural water salt manufactured by Wako Pure Chemical Industries, Ltd. was dissolved in 11 10% nitric acid solution, and K2S20°71,1
After the solution was dissolved, the temperature was raised to 60°C, and when the temperature reached 60°C, a solution obtained by dissolving 171g of NaCOx in 11 parts of water was added, and the mixture was reacted at a liquid temperature of 80°C for 4 hours. Note that p)I at this time was about 12.

The produced dibismuth tetroxide was filtered out and the valve was washed four times. After washing, air dry at 80℃, 98.2
g of Bi204 was obtained. This was then aerated at 400° C. for 1 hour and treated with 95.8 g of β-Bi, 0.5 g of I got it. The particle size of this bismuth oxide was measured by the Fisher method and was found to be 0.1 μm on average.

〔Effect of the invention〕

According to the method of the present invention, fine izO+ is used as an intermediate.
By using this method, extremely fine bismuth oxide having an average particle size of 0.2 μm or less can be easily obtained.

Claims (1)

[Claims] One or more persulfates in an amount of 1 to 3 equivalents based on the amount of bismuth in the nitric acid solution are added to a nitric acid solution containing trivalent bismuth ions, the liquid temperature is adjusted to 40 to 80°C, and the pH is adjusted. 8 or higher for 1 to 6 hours to obtain dibismuth tetroxide, which is separated into solid and liquid, dried, and then roasted at 350 to 500°C in the presence of oxygen to obtain bismuth oxide. A method for producing fine bismuth oxide, characterized by: