JPH06318432A - Manufacture of carbonate for electron tube cathode - Google Patents

Abstract

PURPOSE:To surely synthesize needle crystal carbonate having a length ratio of a longer axis to a shorter axis of crystals within a specific range, having uniform characterics as an electron tube cathode, and having an excellent emission life by setting the pH value of mixed solution of nitrate below in a specific value synthesizing reaction of the carbonate for the electron tube cathode. CONSTITUTION:Barium nitrate and strontium nitrate are dissolved in pure water to form mixed solution (A) of nitrate of the same specific concentration. Next, sodium carbonate is dissolved in pure water so as to form sodium carbonate solution (B) of a specific conceutration. The liquid (A) is agitated, and the liquid (B) is added gradually while liquid temperature is kept constant, so carbonate including barium and strontium is produced by (Ba, Sr)(No3)2+Na2 CO3 (Ba, Sr)CO3+2NaNO3. As the liquid (B) is added, a pH value increases from its initial value. When the pH value become 9, addition of the liquid (B) is stopped. In this method, needle crystal carbonate having a length ratio of a long axis to a short axis within a range of 4:1-20:1 is obtained.

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 a carbonate used as a cathode material for an electron tube used in a cathode ray tube or the like.

[0002]

2. Description of the Related Art Generally, a carbonate for an electron tube cathode is prepared by adding an aqueous solution of a binary mixture of barium nitrate and strontium nitrate or an aqueous solution of a ternary mixture obtained by adding calcium nitrate to the binary mixture to an aqueous solution of sodium carbonate or ammonium carbonate. (Ba, Sr) carbonate or (Ba, Sr, Ca) carbonate is precipitated and precipitated by mixing and reacting. The chemical reaction of this carbonate synthesis reaction is as follows.

(Ba, Sr) (NO ₃ ) ₂ + Na ₂ CO ₃ → (Ba, Sr) CO ₃ + 2NaNO ₃ (Ba, Sr) (NO ₃ ) ₂ + (NH ₄ ) ₂ CO ₃ → (Ba , Sr) CO ₃ + 2HNO ₃ +
2NH ₃ (Ba, Sr, Ca) (NO ₃ ) ₂ + Na ₂ CO ₃ → (Ba, Sr, Ca) CO ₃ + 2NaNO
₃ (Ba, Sr, Ca) (NO ₃ ) ₂ + (NH ₄ ) ₂ CO ₃ → (Ba, Sr, Ca) CO ₃ + 2N
The method using an aqueous solution of H ₃ + 2HNO ₃ sodium carbonate is called a soda precipitation method, and the method using an aqueous solution of ammonium carbonate is called an ammonium precipitation method.

Further, a large current density and a long life of the oxide cathode are strongly demanded in the process of increasing the size and definition of the CRT, and research and development are being advanced.
As an example, a method of dispersing and mixing a few% of scandium oxide, which is a rare earth oxide, in the above-mentioned carbonate has already been reported (M. Saito et al .: NTG Fachber, Vol. 95, No. 16).
5 pages, 1986). As still another example, an alkaline earth metal mixture carbonate containing barium as a main component obtained by coprecipitating and mixing indium hydroxide from an aqueous solution obtained by adding indium nitrate to an alkaline earth metal nitrate mixture aqueous solution containing barium as a main component. It has been reported to synthesize salts (Yukio Hara et al .: SID '90 Digest, 44th edition).
2 pages, 1990).

[0005]

When the shape of the precipitated crystal obtained by the soda precipitation method or ammonium precipitation method is enlarged and observed by a scanning electron microscope, various crystal shapes such as granular, rod-shaped and needle-shaped are recognized. It is generally empirically said that, as a crystal shape of a carbonate for an electron tube cathode, a needle-shaped large crystal has a large current density and a long life. However, in the conventional two types of precipitation methods, in order to precipitate and precipitate needle-like crystals, many parameters such as liquid temperature and solution concentration during the mixing reaction are controlled, but the reaction conditions are derived based on experience. It is the actual situation. For this reason, the crystals of carbonate produced often have irregular crystal sizes and change into granular, columnar, or acicular shapes. As a result, there is a large difference in the life characteristics of the cathode for an electron tube, and it has been desired to establish conditions for securely controlling the crystal size to deposit and precipitate needle-shaped crystals.

Further, regarding the method of adding an additive for increasing the current density and extending the life of the oxide cathode, in the method of adding scandium oxide, scandium oxide of the order of several% is uniformly dispersed and mixed. Therefore, it is difficult to mass-produce an electron tube cathode having uniform characteristics. On the other hand, the method of adding indium hydroxide has a problem that it is difficult to expect an effect for a long period of time because indium hydroxide decomposes during operation of the cathode for an electron tube.

[0007]

Means for Solving the Problems The present inventors have found the fact that acicular crystalline carbonate grows under the condition that the pH value of the solution during the mixing reaction is 9 or less, and based on this finding, completed the present invention.

That is, according to the method for producing a carbonate for an electron tube cathode of the present invention, an alkaline earth metal nitrate mixture aqueous solution containing barium as a main component and an aqueous solution containing carbonate ions are mixed and reacted to produce an alkali containing barium as a main component. In the reaction process of precipitating and precipitating the carbonate of the earth metal mixture, by setting the PH value of the mixed solution at the time of the mixing reaction to 9 or less, the length ratio of the major axis to the minor axis is 4: 1 to 20. It is to generate needle crystals in the range of 1 :.

In the method for producing a carbonate for an electron tube cathode according to the present invention, the rare earth metal ion is added to the alkaline earth metal nitrate mixture aqueous solution at 50 to 5000 pp.
Needle-like crystals in which the ratio of the length of the long axis to the length of the short axis is in the range of 10: 1 to 20: 1 by using a solution mixed with m% by weight and setting the PH value of the mixed solution to 9 or less. Is generated.

[0010]

According to the present invention, the P of the mixed solution during the mixing reaction is
By setting the H value to 9 or less, the crystal growth rate of carbonate is increased, and moreover, the crystal growth direction is limited, so that large needle-shaped crystals can be produced. further,
By using a solution prepared by mixing rare earth metal ions in an amount of 50 to 5000 ppm by weight with an alkaline earth metal nitrate mixture aqueous solution, it is possible to obtain a large-sized and uniform acicular crystal carbonate.

[0011]

【Example】

(Example 1) Barium nitrate and strontium nitrate are dissolved in pure water to prepare a nitrate mixed aqueous solution. The concentrations of barium nitrate and strontium nitrate in the mixed aqueous solution were
Both are the same 0.19 mol / l. Here, the pH value of this solution at a liquid temperature of 80 ° C. is measured and shows 6.3. This nitrate mixed solution is referred to as solution A. Then, sodium carbonate is dissolved in pure water to prepare a sodium carbonate aqueous solution.
The concentration of sodium carbonate is 2.2 mol / l. When the pH value of this aqueous sodium carbonate solution is measured, it shows 11.4 at a liquid temperature of 80 ° C. This solution is referred to as solution B. Solution A is stirred and solution B is gradually added while maintaining the solution temperature constant. At this time, the reaction represented by the formula (1) is established, and a carbonate containing barium and strontium is produced.

(Ba, Sr) (NO ₃ ) ₂ + Na ₂ CO ₃ → (Ba, Sr) CO ₃ + 2NaNO ₃ (1) The PH value of the A solution is the Since the value gradually increases from 6.3, the addition of solution B is stopped when the PH value reaches 9. When the alkaline earth metal carbonate produced by this method is magnified and observed by a scanning electron microscope, the ratio of the length of the major axis to the length of the minor axis in the size of 4 μm or more is in the range of 4: 1 to 20: 1. Needle-like crystals are seen.

Regarding the carbonates containing barium and strontium synthesized by such a method, the crystals formed by changing the upper limit of the PH value of solution A, which increases with the addition of solution B, between 7 and 11 When the relationship between the shape and the PH value was investigated, the results shown in FIG. 1 were obtained.

As is apparent from FIG. 1, the PH value of the liquid A is 9
In the following range, needle-like crystals are produced in which the length ratio of the major axis to the minor axis of the crystal is in the range of 4: 1 to 20: 1. However, when the PH value of the mixed solution exceeds 9 and the solution B is still added, many granular crystals having a length ratio of the major axis to the minor axis in the range of 1: 1 to 4: 1 are precipitated. Then, PH of liquid A
Using a carbonate containing barium and strontium obtained by variously changing the upper limit of the value, a cathode for an electron tube was manufactured by an ordinary method, a life test was performed at a current density of 0.8 A / cm ² , and the emission current When I examined the changes,
The results shown in FIG. 2 were obtained. In FIG. 2, curve A has a PH value of the mixed solution of 7, curve B has a PH value of 8,
Curve C shows the same PH value of 9, curve D shows the same PH value of 10, and curve E shows the same PH value of 11. As is clear from FIG. 2, the PH value of the mixed solution indicated by the curves A, B and C is 9
A carbonate crystal synthesized in the following range, that is, a crystal in which the length ratio of the major axis and the minor axis of the crystal is in the range of 4: 1 to 20: 1 is excellent in that emission reduction is small with respect to the life time. I understand. Therefore, in order to synthesize a large-sized acicular crystalline carbonate with less emission deterioration, the pH value of the reaction solution is 9 or less and the length ratio of the major axis to the minor axis of the crystal is 4: 1 to. It is necessary to produce crystals in the 20: 1 range.

In the examples of the present invention, the case where a nitrate mixed aqueous solution containing barium and strontium was used was shown. However, even when a nitrate mixed aqueous solution obtained by adding calcium nitrate to this solution was used, the pH value of the reaction solution was In the range of 9 or less, similar needle-like crystals having excellent emission life characteristics were obtained. Therefore, the alkaline earth metal nitrate mixture aqueous solution containing barium as a main component may be a binary system containing strontium or a ternary system containing strontium and calcium.

In the embodiment of the present invention, barium nitrate,
An example in which the concentrations of strontium nitrate and sodium carbonate are specified is shown. When the concentration of the solution changes, the particle size distribution changes, but the ratio of the length of the long axis to the short axis of the carbonate crystals is changed to 4: 1 to 20: 1. However, if the PH value is 9 or less, carbonate crystals in the range of 1: 1 to 4: 1 are not formed. Therefore, regardless of the solution concentration, it is sufficient to satisfy the condition that the pH value of the mixed solution during the carbonate synthesis reaction is 9 or less.

Example 2 Barium nitrate and strontium nitrate are dissolved in pure water to prepare a nitrate mixed solution. The concentrations of barium nitrate and strontium nitrate in the mixed solution are both 0.19 mol / l. Next, dysprosium oxide was dissolved in a 0.01 mol / l nitric acid solution,
Make a dysprosium nitrate solution. This dysprosium nitrate solution is added to a nitrate mixed solution containing barium and strontium to prepare a nitrate mixed solution containing barium, strontium and dysprosium. The mixing amount of dysprosium is 50 to 5000 ppm wt% with respect to the total weight of the carbonate to be synthesized. Here, when the pH value of this solution at a liquid temperature of 80 ° C. is measured, it is 4.5.
Indicates. This nitrate mixed solution containing a trace amount of dysprosium is referred to as liquid C. Subsequently, sodium hydrogen carbonate is dissolved in pure water to prepare an aqueous sodium hydrogen carbonate solution. The concentration of sodium hydrogen carbonate is 1.1 mol / l. When the pH value of this aqueous sodium hydrogen carbonate solution was measured, the liquid temperature was 80 ° C.
At the time of, it shows 8.5. This aqueous solution is referred to as liquid D. Solution C is stirred and solution D is added while keeping the solution temperature constant. At this time, the reaction represented by the chemical reaction formula (2) is established, and a carbonate containing barium, strontium and a trace amount of dysprosium is produced.

(Ba, Sr, Dy) (NO ₃ ) ₂ + 2NaHCO ₃ → (Ba, Sr, Dy) CO ₃ + 2NaNO ₃ + CO ₂ + H ₂ O (2) The PH value of the C liquid is The initial value of 4.5 was gradually increased with the addition of the D liquid, but no matter how much the D liquid was added, the PH value of the D liquid did not exceed the value of 8.5.
The condition that the H value is 9 or less is satisfied. When the alkaline earth metal carbonate produced by this method is enlarged and observed with a scanning electron microscope, the length ratio of the major axis to the minor axis of the crystal is 10: 1 to 2
It was recognized that they were acicular crystals in the range of 0: 1.

Regarding the carbonate containing barium, strontium and dysprosium in an amount of 50 to 5000 ppm by weight, which is synthesized by such a method, the upper limit of the PH value of the liquid C, which increases with the addition of the liquid D, is 6.5 to 8 The relationship between the shape of the formed crystal and the PH value was examined by changing the value between 0.5 and 0.5, and in any case, the length ratio of the major axis to the minor axis of the crystal was 10: 1 to 20: 1. A range of acicular crystals formed.

Further, regarding the carbonates containing barium, strontium and a trace amount of dysprosium synthesized by such a method, the shape of crystals synthesized by changing the content of dysprosium in the range of 0 to 5% by weight was investigated. However, the results shown in FIG. 3 were obtained. As is clear from FIG. 3, 50-5000 pp of dysprosium is added.
When it is contained in the range of m% by weight, needle-like crystals are produced in which the length ratio of the major axis to the minor axis of the crystal is in the range of 10: 1 to 20: 1. However, when added in excess of 5000 ppm by weight, the length ratio of the major axis to the minor axis of the crystal becomes 1: 1 to 4: 1.
A large number of granular crystals in the range of are generated.

Then, using a carbonate obtained by variously changing the amount of dysprosium added by such a synthesis method, a cathode for an electron tube was manufactured by an ordinary method, and the current density was 0.8 A / cm ² . When a life test was conducted and changes in the emission current were examined, the results shown in FIG. 4 were obtained. In FIG. 4, the curve F shows 1 ppm of dysprosium.
% By weight, curve G by 50 ppm by weight, curve H by 1000 ppm by weight, curve I by 5000 p
The content of pm wt% is shown. The curve J
Shows a conventional example. As is clear from FIG. 4, those of the examples of the present invention (curve G, H, I) containing dysprosium in the range of 50 to 5000 ppm by weight contained the conventional example (curve J) and 1 ppm by weight of dysprosium. It can be seen that compared with the comparative example (curve F), the decrease in emission is small and the life time is excellent. 5000p
When dysprosium is contained in an amount of more than pm% by weight, a large number of fine crystals having a length ratio of the major axis to the minor axis of the crystal in the range of 1: 1 to 4: 1 are produced. The life is shortened. Therefore, the content of dysprosium needs to be in the range of 50 to 5000 ppm wt% in order to obtain needle-like crystals with less emission reduction.

In the examples of the present invention, an example of using a nitrate mixed solution containing a trace amount of dysprosium in barium and strontium was shown. However, even if a nitrate mixed solution obtained by adding calcium nitrate to this solution is used,
The H value did not exceed 8.5, the PH value of 9 or less was satisfied, and the same needle-like crystals having excellent emission life characteristics were obtained. Therefore, the alkaline earth metal nitrate mixture solution containing barium as a main component may be either a binary system containing strontium or a ternary system containing strontium and calcium.

Even if another rare earth metal nitrate is contained in the range of 50 to 5000 ppm by weight in place of dysprosium, similar needle-like crystals can be obtained, and life test 5000
An excellent effect was observed in terms of emission deterioration after time.

In the embodiment of the present invention, barium nitrate,
An example in which the concentrations of strontium nitrate and sodium hydrogen carbonate are specified is shown. When the concentration of the solution changes, the particle size distribution changes, but the ratio of the long axis to the short axis of the carbonate crystals to be formed is changed to that the crystals are in the range of 10: 1 to 20: 1. However, as long as a trace amount of rare earth metal is added to the mixed solution and the pH value of the solution at the time of reaction is 9 or less, carbonate crystals in the range of 1: 1 to 10: 1 are not formed. Therefore, regardless of the solution concentration, it is sufficient to satisfy the condition that the PH value of the mixed solution during the carbonate synthesis reaction containing a trace amount of rare earth metal is 9 or less.

Example 3 Barium nitrate and strontium nitrate are dissolved in pure water to prepare a nitrate mixed solution. The concentrations of barium nitrate and strontium nitrate in the mixed solution are both 0.19 mol / l. Next, thallium oxide is dissolved in a 0.01 mol / l nitric acid solution to prepare a thallium nitrate solution. This thallium nitrate solution is added to a nitrate mixed solution containing barium and strontium to prepare a nitrate mixed solution containing barium, strontium and thallium. The amount of thallium mixed is 50 to 5000 ppm by weight based on the total weight of the carbonates synthesized. Here, when the pH value of this solution at a liquid temperature of 80 ° C. is measured, it shows 4.5. This nitrate mixed solution containing a trace amount of thallium is referred to as liquid E. Subsequently, ammonium carbonate (1: 1 mixture of ammonium hydrogen carbonate and ammonium carbamate) is dissolved in pure water to prepare an ammonium carbonate aqueous solution. The concentration of ammonium carbonate is 1.1 mol /
Let l. When the PH value of this ammonium carbonate aqueous solution is measured, it shows 8.4 when the liquid temperature is 80 ° C. This solution is designated as solution F. Solution E is stirred and solution F is added while keeping the solution temperature constant. At this time, the reaction represented by the formula (3) is established, and a carbonate containing barium, strontium and a trace amount of thallium is produced.

[0026] (Ba, Sr, Tl) ( NO 3) 2 + (NH 4) 2 CO 3 → (Ba, Sr, Tl) CO 3 + 2NH 3 + 2HNO 3 ...... (3) PH value of E liquid As the F liquid was added, the initial value was gradually increased from 4.5, but the PH value of the F liquid did not become 8.4 or more and the PH value of 9 or less was satisfied.
When the alkaline earth metal carbonate produced by this method is magnified and observed by a scanning electron microscope, the needle-like crystal having a ratio of the major axis to the minor axis of the crystal in the range of 10: 1 to 20: 1. It is recognized that it is crystallized.

Regarding barium, strontium, and carbonates containing 50 to 5000 ppm by weight of thallium synthesized by such a method, the upper limit of the PH value of the E liquid, which increases with the addition of the F liquid, is 6.5 to 8. When the relationship between the shape of the generated crystal and the PH value was investigated by changing the value between 4 and 4, the ratio of the major axis to the minor axis of the crystal was 10: 1 to 20: 1. A range of acicular crystals formed.

Further, regarding the barium, strontium, and carbonate containing a trace amount of thallium synthesized by such a method, the shape of crystals synthesized by varying the thallium content in the range of 0 to 5% by weight was investigated. However, the same result as in FIG. 3 was obtained. That is, 50 thallium
When the content is in the range of up to 5000 ppm by weight, needle-like crystals are produced in which the length ratio of the major axis to the minor axis of the crystal is in the range of 10: 1 to 20: 1. However, if it is added in an amount of more than 5000 ppm by weight, a large number of crystals, which are to be granular, having a ratio of the major axis to the minor axis of the crystal in the range of 1: 1 to 4: 1 are produced.

Then, using a carbonate obtained by variously changing the content of thallium by such a synthesis method, a cathode for an electron tube was manufactured by a usual method, and a current density of 0.8 A /
When the life test was conducted at cm ² and the change in emission current was examined, the results shown in FIG. 5 were obtained. In FIG. 5, curve K is 1 ppm by weight of thallium, curve L is also 50 ppm by weight, and curve M is also 1000 pp.
m wt% and the curve N are those containing 5000 ppm wt% respectively. The curve O shows a conventional example.
As is clear from FIG. 5, 50 to 5000 ppm of thallium
In the example of the present invention (curve L, M, N) contained in the range of wt%, the conventional example (curve O) and thallium are 1%.
It can be seen that, as compared with the comparative example (curve K) containing ppm ppm by weight, the emission time is less deteriorated and the life is excellent. When thallium is contained in an amount of more than 5000 ppm by weight, the length ratio of the major axis to the minor axis of the crystal is 1:
Since many fine crystals in the range of 1 to 4: 1 are generated, the life of the cathode for an electron tube is shortened. Therefore, the content of thallium must be in the range of 50 to 5000 ppm by weight in order to obtain needle-shaped crystals with less emission reduction.

In the examples of the present invention, an example of using a nitrate mixed solution containing barium, strontium and a trace amount of thallium was shown. Acicular crystals with excellent characteristics were obtained. Therefore, the alkaline earth metal nitrate mixture solution containing barium as a main component may be either a binary system containing strontium or a ternary system containing strontium and calcium.

Even if another rare earth metal nitrate is contained in the range of 50 to 5000 ppm by weight in place of thallium, the same needle-like crystals can be obtained, and the emission characteristics after a life test of 5000 hours are the same as those in FIG. Very good results were obtained.

In the embodiment of the present invention, barium nitrate,
An example in which the concentrations of strontium nitrate and ammonium carbonate are specified respectively is shown. When the concentration of the solution changes, the particle size distribution changes, but the ratio of the long axis to the short axis of the carbonate crystals to be formed is changed to that the crystals are in the range of 10: 1 to 20: 1. However, as long as a trace amount of rare earth metal is added to the mixed solution and the pH value of the solution at the time of reaction is 9 or less, carbonate crystals in the range of 1: 1 to 10: 1 are not formed. Therefore, it is not necessary to specify the solution concentration, and it is sufficient to satisfy the condition that the pH value of the mixed solution during the carbonate synthesis reaction containing a trace amount of rare earth metal is 9 or less.

In each of the above embodiments, the case where the sodium carbonate aqueous solution, the sodium hydrogen carbonate aqueous solution, and the ammonium carbonate aqueous solution are separately used as the carbonate ion-containing aqueous solution has been described. It suffices to use any one of the aqueous solutions containing P, and what is necessary is to satisfy the condition that the PH value of the reaction mixture solution is 9 or less.

[0034]

As described above, according to the method of the present invention, in the synthetic reaction of the carbonate for the electron tube cathode, by setting the PH value of the nitrate mixed solution to 9 or less, the major axis and the minor axis of the crystal can be reduced. It is possible to reliably synthesize acicular crystalline carbonate having good characteristics as an electron tube cathode having a length ratio of 4: 1 to 20: 1, and a rare earth metal in a nitrate mixed solution. By adding ions, it is possible to surely synthesize needle-shaped crystal carbonates having good emission characteristics, in which the length ratio of the major axis to the minor axis of the crystal is in the range of 10: 1 to 20: 1. Is. The electron tube cathode obtained by the method of the present invention has the excellent effects of uniform characteristics, large current density, and long life.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the upper limit of the PH value of a nitrate mixed solution at the time of carbonate synthesis in Example 1 of the present invention and the ratio of the major axis to the minor axis of the crystals formed.

FIG. 2 is a graph showing the relationship between the lifetime of the cathode for an electron tube and the emission current reduction rate in Example 1 of the present invention.

FIG. 3 is a graph showing the relationship between the content of dysprosium and the ratio of the major axis and the minor axis of the produced crystal in Example 2 of the present invention.

FIG. 4 is a graph showing the relationship between the lifetime of the cathode for an electron tube and the emission current reduction rate in Example 2 of the present invention.

FIG. 5 is a graph showing the relationship between the lifetime of the cathode for an electron tube and the emission current reduction rate in Example 3 of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mutsuo Masuda 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electronics Industrial Co., Ltd.

Claims (3)

[Claims] 1. A reaction process in which an aqueous solution of an alkaline earth metal nitrate mixture containing barium as a main component and an aqueous solution containing a carbonate ion are mixed and reacted to precipitate a carbonate of an alkaline earth metal mixture containing barium as a main component. In the above, by setting the PH value of the mixed solution at the time of the mixing reaction to 9 or less, the length ratio of the major axis to the minor axis of the crystal is 4: 1 to 20:
1. A method for producing a carbonate for an electron tube cathode, which comprises producing needle crystals in the range of 1. 2. Rare earth metal ions are added in an amount of 50 to 50 in an alkaline earth metal nitrate mixture aqueous solution containing barium as a main component.
In a reaction process in which a solution mixed with 00 ppm wt% and an aqueous solution containing carbonate ions are mixed and reacted to precipitate and precipitate a carbonate of an alkaline earth metal mixture containing barium as a main component, the pH of the mixed solution during the mixing reaction is By setting the value to 9 or less, the ratio of the lengths of the major axis and the minor axis of the crystal is 1
A method for producing a carbonate for an electron tube cathode, which comprises forming needle crystals in the range of 0: 1 to 20: 1. 3. The method for producing a carbonate for an electron tube cathode according to claim 1, wherein the aqueous solution containing carbonate ions is an aqueous solution of sodium carbonate, an aqueous solution of sodium hydrogen carbonate or an aqueous solution of ammonium carbonate.