JPH06249829A - Measuring device for metal oxide solubility in molten salt - Google Patents

Abstract

PURPOSE:To measure the quantity of the matal oxides molten in a molten salt in a molten salt environment at high temperature through the electrochemical method for a long period, by immersing a Pt electrode and an Ag electrode having a protecting pipe in a molten salt, and measuring the electric potential between both the electrodes. CONSTITUTION:A Pt electrode and an Ag electrode 3 having a protecting pipe 1 are immersed in a molten salt, and the electric potential between both the electrode pipes is measured. The protecting pipe 1 is made of Al2O3.SiO2 containing Y2O3 and/or ZrO2, and the inside is charged with Na2SO4-Ag2SO4 powder 2, and an Ag wire 3 is embedded into the powder. The Ag electrode 3 is fixed in the protecting pipe 1 by a piston 8 and an O ring 9 so that the position does not change, and further led outside a sensor holder 5, penetrating through a seal plug 10, and applied with the electric contact. The sensor holder 5 is installed through the cover 4 of a container for accommodating the molten salt having a high temperature, and in order to prevent the rise of the temperature of the electrode holder body, a water-cooled chamber 6 is provided.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a sensor for electrochemically measuring the amount of a metal oxide dissolved in a molten salt.

[0002]

2. Description of the Related Art When a metal material is covered with a molten salt film of Na ₂ SO ₄ or Na ₂ CO ₃ in a high temperature gas environment, it may be significantly damaged by high temperature corrosion. This phenomenon has been observed in high temperature combustion parts such as a boiler tube for thermal power generation, a gas turbine rotor blade part, and a waste incineration boiler tube. In particular, in a refuse incineration boiler, the combustion temperature is raised from the conventional temperature of 400 ° C. to 500 ° C. in order to improve the combustion efficiency, and high temperature corrosion occurs in the materials used conventionally.

Recently, the maximum temperature has been set to around 700 ° C. in order to improve the combustion efficiency, and the corrosive environment is becoming more severe. This high temperature corrosion problem is difficult to reproduce, and research has only limited to measuring the weight change by immersing the material in a molten salt environment for a long time.
However, in the mankind's mission to develop new materials, it is difficult to develop new materials without clarifying the mechanism by which high temperature corrosion occurs.

Usually, the corrosion resistance of a material is ensured by a metal oxide film formed on the surface, and when this oxide is dissolved and its thickness is reduced, or when it is locally destroyed, it leads to severe corrosion. Therefore, from the viewpoint of ensuring corrosion resistance, it is important to monitor the solubility of oxides formed on the material surface and to grasp the soundness of the oxides. However, there is no established means for measuring the amount of metal oxide dissolved in molten salt, and so far, for example, Journ published in 1962.
al of Electrochemical Soci
It was estimated from equilibrium calculations as disclosed in ety magazine, vol. 109, page 525. Since such a calculation handles an ideal system, there is a point that it does not match the actual molten salt corrosion, and actual measurement has been required. However, in actual measurement, an apparatus that can be used in a high temperature molten salt environment of 400 ° C. or higher, particularly a sensor that can be stably used for a long time in a solubility measuring apparatus, did not exist from the viewpoint of chemical stability and life.

[0005]

The object of the present invention is to electrochemically measure the amount of the metal oxide dissolved in the molten salt in the molten salt environment of high temperature as described above. .

[0006]

MEANS FOR SOLVING THE PROBLEMS The gist of the present invention is as follows: (1) A metal in a molten salt in which a Pt electrode and an Ag electrode having a protective tube are immersed in the molten salt and the potential between the electrodes is measured. Oxide solubility measuring device. (2). The protective tube described in (1) is Y ₂ O ₃ and ZrO _2.
One or containing two or consists _{Al 2 O 3 · SiO 2,} Na 2 SO 4 powder and Ag ₂ SO ₄ molten salt in the metal oxide, characterized in that it is filled with powder Solubility measuring apparatus.

(3). The protective tube described in (2) is 7 in mol%.
% Or more and 14% or less of Y ₂ O ₃ and more than 2% to 7% or less of ZrO ₂ and the balance is substantially A.
A device for measuring the solubility of metal oxides in a molten salt, which comprises l ₂ O ₃ .SiO ₂ . (4). (2) The protective tube has a mol% of more than 14% to 21%.
% Or less Y ₂ O ₃ and more than 7% to 12% or less ZrO ₂
1 or 2 of the above, with the balance being substantially Al ₂ O ₃
A device for measuring the solubility of metal oxides in a molten salt, which is made of SiO ₂ . (5). The protective tube described in (2) is more than 21% by mol% to 27%.
% Or less Y ₂ O ₃ and more than 12% to 17% or less ZrO
It contains one or two _2, the balance being substantially Al ₂ O
It is a device for measuring the solubility of metal oxides in a molten salt, which is characterized by comprising ₃ · SiO ₂ .

[0008]

The present invention will be described in detail below. First, an outline of the structure of the solubility measuring sensor according to the present invention will be described with reference to FIG. The Na ₂ SO ₄ —Ag ₂ SO ₄ powder 2 of the present invention is filled inside the protective tube 1 of the present invention, and the Ag wire 3 is embedded in the powder. The Ag electrode is fixed by a piston 8 and an O-ring 9 so that the position of the Ag electrode does not change in the protection tube, and further penetrates the seal plug 10 to be guided to the outside of the sensor holder 5 to be electrically contacted. The seal plug 10 includes a nut 12 and a ring 13.
The main body of the protection tube is fixed by the above-mentioned method, and the fluctuation of the position of the protection tube body is suppressed. The sensor holder 5 is installed via a lid 4 of a container for containing a high temperature molten salt, and has a water cooling chamber 6 in order to avoid the temperature of the main body of the electrode holder from becoming high. The water cooling chamber is fixed by a stopper plate 7. An electric potential is obtained by immersing the protective tube of the solubility sensor configured as described above in a high temperature molten salt.

The inventors of the present invention have made possible a sensor that enables electrochemical measurement of solubility in a molten salt environment based on many experimental results regarding a stable and reliable solubility sensor in molten salt. Got The reason why the constituent material of the electrode is limited in the present invention is as follows. Al ₂ O ₃
Since SiO ₂ allows Na ⁺ to pass therethrough as an electric conductor, it combines with oxygen present in the molten salt to become Na ₂ O. This Na
_{Since 2} O is in equilibrium with O ^{2 −} existing as an ion in the molten salt, it thermodynamically shows the activity of oxygen.

Y ₂ O ₃ is chemically stable in the molten salt and has the effect of stabilizing Al ₂ O ₃ .SiO ₂ . 40
In a molten salt at 0 ° C. or higher and lower than 500 ° C., the effect does not appear unless it is added in an amount of more than 7% in terms of mol%, and the effect remains unchanged even if added in an amount of more than 14 mol%. 500 ° C or higher 600
The effect does not appear unless it is added in an amount of more than 14% by mol% in the molten salt of less than ° C, and the effect is not changed even if it is added in an amount of more than 21 mol%. Further, in the molten salt at 600 ° C. or higher, the effect does not appear unless it is added in an amount of more than 21% by mol%, and the effect is not changed even if it is added in an amount of more than 27 mol%.

ZrO ₂ was used as a protective tube because it is chemically stable up to a high temperature range, is easily available, and is relatively easy to handle. In a molten salt of 400 ° C. or more and less than 500 ° C., the effect does not appear unless it is added in an amount of more than 2% in terms of mol%, and the effect does not change even if it is added in an amount of more than 7 mol%.
7% in mol% in molten salt above 500 ° C and below 600 ° C
If it is not added in excess of 12 mol%, the effect does not appear, and even if added in excess of 12 mol%, the effect does not change. 600 ° C
In the above molten salt, the effect does not appear unless it is added in an amount of more than 12% by mol%, and even if it is added in an amount of more than 17 mol%, the effect is saturated and remains unchanged. Therefore, by appropriately selecting the composition of the protective tube according to the measurement temperature, economical and effective measurement can be performed.

[0012]

EXAMPLES Protections with the compositions according to the invention shown in Tables 1 to 3
We made a solubility sensor using a tube and measured it as shown in Fig. 2.
Compose the path, Cr₂O₃Mixed with Na₂SO_Four-A
g ₂SO_Four-CaCO₃Immerse in molten salt for 336 hours
Perform a potential measurement with a potentiometer 16 across
It was From the obtained potential value, the Nernst of
The formula was used to convert to solubility in molten salt. Dissolution reaction: M_mO_n= MM²⁺+ NO^2- Potential difference: E = (RT / zF) ln [a (M²⁺) ・ PO
^2-] Here, E is the measured potential difference, R is the gas constant, and T is the temperature.
Degree, F is the Faraday constant, a (M²⁺) Is the dissolved metal acid
Value corresponding to the concentration of compound, PO^2-Oxygen ion in molten salt
It is the activity of

FIGS. 3 to 5 are examples of the results of measuring the amount of oxygen, showing a steady value from 2 days after the start of measurement and showing a stable amount of dissolution over a long period of time. The measurement results obtained by the sensors equipped with the protective tubes having the compositions shown in Tables 1 to 3 are all shown in FIG.
It showed a stable oxygen content similar to the potential change shown in FIG.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

[Table 3]

[0017]

INDUSTRIAL APPLICABILITY The present invention provides a sensor for electrochemically measuring the amount of metal oxide dissolved in a molten salt environment, in which the potential corresponding to the amount of metal oxide dissolved in the molten salt is maintained for a long period of time. This makes it possible to measure and enables corrosion monitoring in a molten salt environment, which greatly contributes to the detection of the degree of material deterioration.

[Brief description of drawings]

FIG. 1 is a sectional view showing the structure of a solubility sensor,

FIG. 2 is a circuit diagram of potential measurement,

FIG. 3 is a diagram showing a time-dependent change in measured solubility at 400 ° C.

FIG. 4 is a diagram showing the time-dependent change in the measured solubility at 500 ° C.

FIG. 5 is a graph showing the time-dependent change in the measured solubility at 600 ° C.

[Explanation of symbols] 1 Protective tube 2 Na ₂ SO ₄ · Ag ₂ SO ₄ powder 3 Pt electrode 4 Container lid plate 5 Sensor holder 6 Water cooling chamber 7 Stopper 8 Piston 9 O-ring 10 Seal plug 11 Nut 12 Ring 13 Coating material 14 Pt wire 15 Oxygen sensor 16 Potentiometer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroyuki Ogawa 20-1 Shintomi, Futtsu City, Chiba Shin Nippon Steel Co., Ltd. Technology Development Division

Claims (5)

[Claims] 1. A having a Pt electrode and a protective tube in molten salt
An apparatus for measuring the solubility of a metal oxide in a molten salt, which comprises immersing a g electrode and measuring an electric potential between both electrodes. 2. A protection tube according to claim 1, wherein contains one or two Y ₂ O ₃ and ZrO ₂ Al ₂ O ₃ · Si
An apparatus for measuring the solubility of metal oxides in a molten salt, which comprises O ₂ and is filled with Na ₂ SO ₄ powder and Ag ₂ SO ₄ powder. 3. The protective tube according to claim 2, wherein the mol% is more than 7% to 14% of Y ₂ O ₃ and more than 2% to 7% of Zr.
Containing one or two O _2, balance substantially Al ₂
A device for measuring the solubility of a metal oxide in a molten salt, which is composed of O ₃ · SiO ₂ . 4. The protective tube according to claim 2 is 14% in mol%.
Super ~ 21% or less Y ₂O₃And over 7% to 12% or less
ZrO₂1 or 2 of the above, with the balance being substantially A
l₂O₃・ SiO₂In molten salt characterized by comprising
Metal oxide solubility measuring device. 5. The protection tube according to claim 2 is 21% in mol%.
Super ~ 27% or less Y ₂O₃And over 12% to 17% or less
ZrO₂Containing one or two of the above, with the balance being substantially
Al₂O₃・ SiO₂Molten salt characterized by comprising
Medium metal oxide solubility measuring device.