JPS6276129A - Manufacture of electron-emitting substance for tubular bulb - Google Patents

Abstract

PURPOSE:To obtain an electron-emitting substance with superior electron emission which consists of a highly chemically active carbonate powder with small variation in particle size by blowing carbonic acid gas into an aqueous suspension of a powder of the hydroxide of an alkaline earth metal to deposit a micropowder of the carbonate of the alkaline earth metal. CONSTITUTION:A highly chemically active homogeneous powder of the carbonate of an alkaline earth metal with sufficiently small particle size is produced by blowing carbonic acid gas into an aqueous suspension of a powder of the hydroxide of an alkaline earth metal. Adding carbonate ions to a dilute aqueous solution of the hydroxide of an alkaline earth metal in discret amounts results in production of microcrystals of a carbonate. Since the solution is constantly agitated violently, crystals can not fuse each other resulting in dispersion of minute crystalline particles in the solution. Besides, since metallic ions are constantly supplied from the hydroxide powder, the concentration of metallic ions remains constant and crystallization conditions are maintained constant. Consequently, microcrystals with constant particle diameter are continuously formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for producing high-performance electron radioactive materials for use in various tubes such as neon lamps, fluorescent lamps, and cathode ray tubes.

[Technical background of the invention and its problems]

Neon lamps and fluorescent lamps are coated with an electron-emitting substance (activated substance) made of an alkaline earth metal oxide to facilitate electron emission from the electrodes.

Then, such an electron radioactive substance (activated substance) is produced by depositing a fine powder consisting of one or more types of alkaline earth metal carbonates on an electrode and firing it to convert the alkaline earth metal carbonates into oxides. Obtained by transmuting into.

Therefore, in order to obtain a highly active electron-emitting substance (activated substance), it is necessary that the particle size of the alkaline earth metal carbonate be as small as possible and that it be highly chemically active. Therefore, conventionally, an aqueous solution of nitrates such as barium, strontium, and calcium is neutralized with aqueous ammonia, and then an aqueous solution of sodium carbonate or ammonium carbonate is added to precipitate the alkaline earth metal as a carbonate. The material was washed and milled to obtain a fine powder, which was prepared into a suspension using the usual method and applied to the electrode.

This method was unsatisfactory because the particle size of the precipitated fine powder and its variations were unstable, and even after long-term milling, the properties remained inconsistent. Various attempts were made to improve the precipitation means, including concentration, pH, temperature, and stirring conditions, but no satisfactory results were obtained.

[Purpose of the invention]

The present invention provides a method for producing an electron radioactive material for tubes, in which the particle size of the alkaline earth metal carbonate for preparing the electron radioactive material is sufficiently small, the particle size is uniform, and the particle size is rich and exhibits good properties. The purpose is to

[Summary of the invention]

The present invention is carried out by blowing carbon dioxide gas into water in which alkaline earth metal hydroxide powder is suspended.

This is a method for obtaining carbonates of alkaline earth metals with sufficiently small particle size, uniformity, and high chemical activity.

[Embodiments of the invention]

The details of the invention are illustrated by the following examples.

First, barium hydroxide (Ba (OH), 8H20
) powder and strontium hydroxide (Sr(OH)2.81
120) Prepare powder.

Take it at a molar ratio of 1:1, mix it in pure water so that the total number of moles is 0.56/Q, and keep the liquid temperature at 50±5℃.
Keep stirring. At this time, the hydroxide in the liquid is in a suspended state. Therefore, carbon dioxide gas (CO2) is blown into the liquid while stirring. Then.

As the reaction progresses, the water becomes cloudy, resembling a white cloud. As the reaction progresses, the pH of the solution decreases to about 2
After hours, the pH reaches 6°5 and becomes stable. Therefore,
The fine carbonate powder precipitated in a cloud is filtered, milled, dispersed, and constituted into an electron-emissive material in the usual manner.

The above-mentioned precipitation reaction can be explained microscopically as follows. The solubility of alkaline earth metal hydroxide in water at 50°C is as follows. However, it is based on anhydrous equivalent.

Ba(OH), 11.61 g/100
g aqueous solution 5r(OH) 22.50 g / 100 g
Water fj liquid Ca (Oll), 0.097 g /
100 g aqueous solutionThe lower the temperature, the lower the solubility, and the higher the pH, the lower the solubility. Since the amount of the above-mentioned hydroxide mixed powder is much larger than this solubility value, most of it is dispersed in water in the same phase state, and is dissolved in water in an amount corresponding to the solubility. Moreover, the temperature of the liquid is kept constant without constant stirring during the reaction.

The concentration of the solution is constant. Furthermore, carbonate ions in water have a low concentration because their dissolution rate is slow and they are gradually converted into carbonates and consumed.

However, when carbonate ions are added little by little to a dilute aqueous solution of an alkaline earth metal hydroxide, the resulting carbonate crystals become extremely fine, and because they are continuously and vigorously stirred, the crystals become crystallized. They are unable to fuse with each other, and as a result, very thin crystalline particles are dispersed in the water. Moreover, since the metal ions are constantly supplied from the hydroxide powder, their concentration is constant and the crystal conditions do not change, so that microcrystals of a constant particle size are continuously formed. Furthermore, since the reaction solution is vigorously stirred, carbonate cannot precipitate on the surface of the hydroxide powder, so the hydroxide is always exposed and suspended in water, and the carbonate does not precipitate. There is no encapsulation, and the entire amount eventually reacts.

Therefore, theoretically, both the hydroxide ion concentration and the carbonate ion concentration should be constant during the reaction for the reasons mentioned above, but
In reality, these ions gradually decrease for various reasons, and the pH of the liquid gradually decreases accordingly. Then, as the amount of unreacted hydroxide decreases, the pH rapidly decreases and eventually approaches 6.5, which is the pH of carbonate ions. For these reasons, by controlling the liquid temperature and pH, the degree of one reaction and the crystal grain size can be controlled, and the end point of one reaction can be detected. This reaction theory applies equally to both the case of one kind of alkaline earth metal and the case of a mixture of three kinds of alkaline earth metals. The relationship between the progress of this reaction and PH is shown in FIG. In the figure, the horizontal axis shows the reaction progress time in minutes after the temperature was maintained at 50 ± 5°C and carbon dioxide gas was started being introduced while stirring, and the vertical axis shows PH.・The curve marked with - is for barium alone, and the curve marked with -〇- is for the equimolar ratio of barium and strontium, -×-
The marked curve shows the reaction curve when barium, strontium 11 and calcium are mixed in equimolar ratios. In the figure, the curves differ depending on the component, probably because the solubility differs depending on the component. The progress of the reaction can be controlled using this FIG.

The average particle size of the barium/strontium mixed carbonate of the above example thus obtained was 0.5 to 1 μm, which is much larger than the average particle size of conventional nitrates precipitated from 5 to 8 μm. It can be seen that it has become smaller. Moreover, as shown in FIG. 2, the particles of this example have the advantage of having a uniform particle size distribution.

The electron radioactive material made of the two-component carbonate thus obtained was deposited on the nickel electrode of a neon lamp, and the starting voltage and flicker occurrence rate were investigated.

As shown in FIG. 3, the starting voltage has very little variation and is of good quality. Furthermore, as shown in the following table, the flickering of light in this example is extremely low.

The reason why the product obtained by the method of this example is superior is considered to be that it can be uniformly deposited on the nickel electrode and has an excellent work function after activation.

Next, a method for manufacturing an electron radioactive material for fluorescent lamps will be described. In this method, the raw materials are barium hydroxide (Ba(Oll)-.8H,0), strontium hydroxide (Sr(OH)2.811□0) and calcium hydroxide (Ca(Oll), .81!, 0) in a molar ratio of L:L:1.This raw material is dispersed in water at a total mole ratio of 0.5 mol/Q, and the liquid temperature is adjusted to 50±5°C. While stirring vigorously, blow in carbon dioxide gas. After about 3 hours, the wash is then filtered, milled and constituted into an electron-emitting material in the usual manner.

This production method is also produced according to the above-mentioned reaction principle, and the obtained carbonate fine particles are small in particle size, uniform, and highly active. In this embodiment as well, the reaction rate and crystal grain size can be controlled by controlling the liquid temperature and pH during the reaction.

The average particle size of the three-component carbonate thus obtained was 0.
It can be seen that the average particle diameter of the particles precipitated from conventional nitrates at 3 to 0.7 microns is much smaller than the average particle size of 5 to 10 microns. Furthermore, as shown in FIG. 4, the particle size distribution is also uniform.

If a 20 W straight tube fluorescent lamp is constructed by applying the thus obtained three-component electron emissive material to a filament electrode, the starting voltage will be low and its variation will be small, as shown in FIG. this is.

This is thought to be due to the particle size of the carbonate, its small dispersion, and its high activity, resulting in an excellent work function after activation and a small dispersion.

Thus, the present invention can be applied to obtain carbonate from any one or more hydroxides of alkaline earth metals,
In either case, the particle size of the carbonate obtained and its variation are small and the activity is high.

Similarly, high performance can be obtained.

The alkaline earth metal hydroxide powder used in the method of the present invention may be obtained by any method.

In addition, in the present invention, the liquid may be stirred by vigorously blowing carbon dioxide gas instead of using mechanical stirring. Then,
The electron radioactive material obtained by the method of the present invention can be used as a cathode material for various discharge tubes as well as cathode ray tubes and X-ray tubes.

〔Effect of the invention〕

The method for producing an electron radioactive material for tubes of the present invention involves blowing carbon dioxide gas into water in which alkaline earth metal hydroxide powder is suspended to precipitate fine powder of alkaline earth carbonate. This method has the advantage that a carbonate powder with small variations in carbonate and high chemical activity can be obtained, and an electron-emitting substance with excellent electron-emitting properties can be produced.

[Brief explanation of drawings]

FIG. 1 is a graph showing changes in the pH of the reaction solution depending on the reaction time in the method for producing an electron radioactive material for tubes of the present invention;
FIG. 2 is a graph showing the particle size distribution of the carbonate fine powder obtained in the same manner, and FIG. 3 is a graph comparing the variation in characteristics of the neon lamp using the electron radioactive material according to this example with that of the conventional method. Fig. 4 is a graph showing the particle size distribution of carbonate fine powder according to another example, and Fig. 5 is a graph showing the variation in characteristics of a fluorescent lamp using an electron radioactive material according to another example, compared with that of a conventional method. It is a graph. Agent Patent Attorney Inoue-M/a-Ryo (μ) 2nd figure 茹萯孯 (V) 3rd figure (:l o () C) ro CJ O(:
) C) Sa Q to cheer〈God ℃N1 廼pier← Fukurogo Low Tsujiiji@Nono

Claims (1)

[Claims] Carbon dioxide gas is blown into water in which alkaline earth metal hydroxide powder is suspended to precipitate the alkaline earth metal carbonate fine powder, and the precipitated fine powder is used to obtain an electron radioactive substance. A method for producing an electron radioactive material for tubes, characterized in that: