JPS60189832A - Preparation of alkaline-earth carbonate - Google Patents

Abstract

PURPOSE:To obtain alkaline-earth carbonate which has needle crystal and is capable of controlling crystal grain size by dissolving salt containing ammonium ions in an alkaline-earth nitrate solution and thereafter allowing it to react with a carbonate solution. CONSTITUTION:A given amount of salt containing ammonium ions such as ammonium nitrate is mingled to dissolve in three kinds of soluble alkaline-earth nitrate solution composed of Ba, Sr and Ca. The mingled solution is heated while being stirred, and a soluble carbonate solution such as ammonium carbonate is added to react and subsequently crystal maturation is carried out. At this time, when an additive amount of ammonium salt is increased, crystal grains size is enlarged. By this method, it is possible to effectively obtain alkaline-earth carbonate in the state of needle crystal suitable for an oxide-coated cathode for an electron that.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for producing an alkaline earth carbonate, and more particularly to a method for producing an alkaline earth carbonate for use in a bride cathode for an electron tube.

[Technical background of the invention and its problems]

Current oxide cathodes for electron tubes are made by thermally decomposing alkaline earth carbonates in vacuum to form oxides.

Therefore, the properties of alkaline earth carbonates are extremely important.
It is related to various characteristics as an electron tube.

That is, the initial emission, the yield rate of the coating by thermal decomposition, the peeling off of the coating, and the emission life fj:, etc. Of course, the properties of these as a cathode are also influenced by the conditions for conversion to an oxide, but the conditions at this time are controlled by elements other than the cathode, and the controllable range is usually extremely narrow. Furthermore, the properties of the carbonate have a large effect on the construction of the cathode. That is, the viscosity of the coating liquid, the density of the coating layer, the roughness of the surface, etc.

Therefore, many studies have been carried out on the production conditions and properties of alkaline earth carbonates, and the relationship between the composition ratio of alkaline earth carbonates and the concentration has also been elucidated. .

There are various methods for producing alkaline earth carbonates, but all of them are based on the reaction between alkaline earth metal ions and carbonate ions in an aqueous solution. As the alkaline earth metal ion, nitrate is mainly used, and as the carbonate ion, sodium carbonate or ammonium carbonate is mainly used. Also, as a solution having good vc electron emission characteristics, a mixed solution of three types of soluble alkaline earth nitrates is often used, in which the alkaline earth nitrate contains the largest amount of barium, and the amount of strontium and calcium decreases in that order.

A general method for producing alkaline earth carbonates is to stir an alkaline earth nitrate solution, such as Pariu A 33wt%, strontium 4Q wt%, Calc 94, while heating, and then heat the alkaline earth nitrate solution to the same temperature. A sodium carbonate solution is added at a predetermined addition rate to precipitate alkaline earth carbonates. Then, after this reaction is finished, washing with hot water is repeated to remove impurities.
Finally, there is a method of dehydrating and drying to obtain alkaline earth carbonate powder.

The crystal shape and grain size of the alkaline earth carbonate thus obtained are affected by the concentration of the reaction solution, reaction temperature, carbonate addition rate, and stirring during the reaction, and various crystals may be obtained. However, it is difficult to change only the crystal grain size while keeping the crystal shape the same by changing the reaction conditions as described above. The crystal shape of the alkaline earth carbonate used in the oxide cathode depends on the coating characteristics of the cathode. In other words, it is said that an acicular crystal shape is advantageous due to adhesion and porosity within the cathode coating layer, and cracks in the coating layer due to shrinkage after thermal decomposition, and this acicular crystal shape is often used. has been done.

However, alkaline earth carbonates with needle-like crystal shapes and fine crystal grains are desired for electron tubes that require various electron tube characteristics, smoothness of the coating surface, high density coating layer, etc. .

Even under the current reaction conditions for alkaline earth carbonates, it is possible to create a reaction condition in which the acicular crystal shape is almost the same and only the crystal grain size is changed, but this reaction condition makes the reaction rate very thin. It is not necessary for mass production and is not economical. Therefore, there is a need for a method for producing alkaline earth carbonates that is highly economical and that controls only the particle size of the crystals in the acicular crystalline state required for various electron tubes.

[Purpose of the invention]

The present invention was made in view of the above-mentioned problems and demands, and it is possible to obtain an acicular crystalline state that is advantageous for various electron tube cathode characteristics, and to control the crystal grain size required for each electron tube cathode. The present invention aims to provide a possible method for producing alkaline earth carbonates.

[Summary of the invention]

Next, an embodiment of the method for producing an alkaline earth carbonate of the present invention will be described.

First, a solution of barium, strontium, calciramrahilirum 53 wt%, strontium 4Q wt%, and calcium 7 wt% as alkaline earth nitrates was dissolved in nitric acid at a concentration of about 0.52 mol/l. Further, a salt such as ammonium nitrate in an amount of O to 10% by weight based on the weight of calcium nitrate is added and dissolved.

Next, heat this solution to about 87°0 while stirring.Next, for example, heat an ammonium carbonate solution with a concentration of 1.1 mol/l to about 87°0, and add this ammonium carbonate solution to an alkaline earth nitrate solution. The alkaline earth nitrate solution was heated to the same temperature as the alkaline earth nitrate solution, that is, the reaction temperature of 87°, and added to the alkaline earth nitrate solution at the same rate as the alkaline earth nitrate solution, allowing both solutions to fully react, and the reaction solution was stirred even after the reaction was completed. This continues for about 30 minutes to ripen the crystals.

Next, precipitated alkaline earth carbonates (Ba, Sr
.

Oa) 00s is allowed to stand still, the supernatant liquid is discharged, hot water washing is repeated until impurities are removed, and finally, water is dehydrated by a method such as centrifugal dehydration.

When the crystal shape of the alkaline earth carbonate obtained by such a production method was compared with the amount of ammonium nitrate with zero additive using electron micrographs, it was found that as the amount of ammonium nitrate was increased, the crystal grain size maintained an acicular crystal shape. However, it was confirmed that the amount of ammonium nitrate added was due to the promotion of grain size growth.

≠The dark curve (1) shows the relationship between the amount of ammonium nitrate added to the alkaline earth carbonate produced in this example and the average particle size of the crystals produced by the reaction, measured using a sedimentation type particle size distribution measuring device.

From this figure, it can be seen that according to the production method of the present invention, the average particle size becomes coarser as the amount of ammonium nitrate added increases.
It can be seen that the results show the same tendency as the results from the machine gun photographs.

Although the effect of ammonium ions on crystal grain size is not clear at present, it has become clear that they have the effect of promoting crystal growth.

In the above embodiments, the amount of ammonium nitrate added was based on Cal/Rum nitrate, but it is not limited to this, and it goes without saying that the same effect can be obtained by mixing it into the nitrate solution.

In addition, although the explanation was made using ammonium nitrate in the examples, the carbonate Ral V- uses ammonium salts other than salts that require bad writing for the cathode, and is water-soluble and stable ammonium salts with a decomposition temperature of 100°C or higher. Needless to say, similar results can be obtained.

〔Effect of the invention〕

As mentioned above, according to the method for producing alkaline earth carbonates of the present invention, the crystal grain size individually required for various electron tubes can be controlled while maintaining the acicular crystal state that is said to be advantageous for electron tube characteristics. In addition, the highest yield can be achieved by using ammonium ions, which can be precipitated under economical reaction conditions, and whose characteristics are not bad even if they are mixed into the electron tube @ electrode to the extent of impurities. There is no need to worry about deterioration of characteristics.

[Brief explanation of drawings]

The figure is a curve diagram showing the relationship between the amount of ammonium nitrate added and the average particle size. 1...Curve showing the relationship between the amount of ammonium nitrate added and the average particle size Agent Patent attorney Inoue - Male

Claims (2)

[Claims] (1) Three types of soluble alkaline earth nitrate solutions consisting of barium, strontium, and calcium are reacted with a soluble carbonate solution to produce a composite carbonate powder of barium, strontium, and calcium. At this time, a predetermined amount of salts containing ammonium ions having the effect of promoting crystal growth is mixed and dissolved in the soluble alkaline earth nitrate bath solution, and then reacted with the soluble carbonate solution to form the barium and strontium. / A method for producing an alkaline earth carbonate, characterized in that the crystal shape of the alkaline earth carbonate powder consisting of thium and calcium is made to be the same and the crystal grain size is variable. (2) The solution according to claim 1, wherein the predetermined amount is 1% or less (does not include O).