JPH04181155A - Measuring sensor for oxygen partial pressure in molten salt - Google Patents

Abstract

PURPOSE:To measure an amount of oxygen in molten salt over a long period by filling a protection tube having specific composition with Pt powder, soaking a Pt line in the Pt powder, and electrically connecting a Pt electrode in molten salt outside the protection tube with a Pt electrode inside the protection tube to measure difference in potential generated between both Pt electrodes. CONSTITUTION:A protection tube 1 comprises such a material that contains, by mol%, 3 to 9% of CaO and one or two kinds of 5 to 12% of Y2O3 while the remaining comprises ZrO2. Pt powder 2 is fully put into the protection tube 1, and a Pt line 3 is buried in the Pt powder 2. This Pt electrode is fixed by a piston 8 and an O-ring 9 so that its position is not fluctuated in the protection tube 1, and further a seal plug 10 is put through to be led outside a sensor holder 5 so that electrical contact is given. By soaking the protection tube 1 in molten salt at high temperature, potential of a testing electrode can be obtained. By measuring difference in potential between a Pt electrode outside the protection tube and the Pt electrode in the protection tube, measurement over a long period is possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a sensor for electrochemically measuring the amount of oxygen remaining in a molten salt.

[Prior Art] When a metal material is covered with a film of molten salt such as Na2SO4 or Na2CO3 in a high-temperature gas environment, it may suffer significant damage called high-temperature corrosion. This phenomenon has been observed in high-temperature combustion parts such as boiler tubes for thermal power generation, gas turbine rotor blades, and boiler tubes for waste incineration. In particular, in boilers for waste incineration, the combustion temperature has been raised from the conventional 400°C to 500°C to improve combustion efficiency, causing high-temperature corrosion to occur with conventionally used materials. It is difficult to reproduce the phenomenon of this high-temperature corrosion problem, and research has been limited to measuring weight changes by immersing materials in a molten salt environment for a long time. However, in humanity's mission to develop new materials, it is difficult to develop new materials unless we clarify the mechanism by which high-temperature corrosion occurs.

Oxygen remaining in the molten salt is an important factor governing the corrosion mechanism, and the alkalinity of the environment is used as a quantitative indicator of the severity of the corrosive environment. However, there is no established method for measuring the amount of oxygen in molten salt, and until now, for example, the Journal of E published in 1962,
It was estimated from equilibrium calculations as disclosed in Electrochemical 5ociety, Volume 109, Page 525. Since such calculations treat an ideal system, there are points that do not match actual molten salt corrosion.
Actual measurements have been required. However, in actual measurement, 4
There has been no sensor that can be stably used in a device that can be used in a high-temperature melting environment of 00° C. or higher, especially in an oxygen concentration measuring device, due to concerns about chemical stability and longevity.

[Problems to be Solved by the Invention] The object of the present invention is to electrochemically measure the amount of oxygen remaining in a molten salt in a high-temperature molten salt environment as described above.

[Means for Solving the Problems] The gist of the present invention is that CaO is 3 to 9 mol %.
%, Y2O3 is 5 to 12% of one or two kinds, and the remainder is Zr02. A Pt powder is filled in a protective tube, and a Pt wire is immersed in the Pt powder, and a Pt main electrode in the molten salt outside the protective tube is formed. A sensor for measuring oxygen partial pressure in a molten salt, which measures the oxygen partial pressure in the molten salt by electrically connecting the Pt main electrode inside the protection tube and measuring the potential difference generated between both Pt electrodes. be.

[Effect] The present invention will be explained in detail below.

First, the outline of the structure of the oxygen amount measuring sensor according to the present invention will be explained based on FIG. A protective tube 1 according to the present invention is filled with Pt powder 2 according to the present invention, and a Pt wire 3 is embedded in the powder. It is fixed by a piston 8 and an O-ring 9 so that its position does not change within the Pt main electrode protection tube, and is guided to the outside of the sensor holder 5 through a seal plug 10 to provide electrical contact. The seal plug 10 is fixed by a nut 11 and a ring 12, and the position of the protection tube body is also suppressed from changing. The sensor holder 5 is installed through a lid 4 of a container containing high-temperature molten salt, and has a water cooling chamber 6 to prevent the main body of the electrode holder from becoming hot. The water cooling chamber is fixed by a stopper 7. The potential of the test electrode can be obtained by immersing the protective tube of the oxygen sensor configured as described above in a high-temperature molten salt.

The inventors of the present invention have obtained a sensor that makes it possible to electrochemically measure the amount of oxygen in a molten salt environment based on many experimental results regarding stable and reliable oxygen sensors in molten salt. . The reason why the constituent materials of the electrodes are limited in the present invention is as follows. ZrO2 was used as the protective tube because it is chemically stable in a high temperature range, easily available, and relatively easy to handle. In addition, by containing CaO, ZrO□ improves its chemical stability in the molten salt, making it easier for oxygen in the molten salt to diffuse into ZrO2. Y
2O3 is chemically stable in the molten salt and has the effect of stabilizing ZrO2. In a molten salt at 500° C. or lower, the effect will not appear unless it is added in an amount of 3 mol % or more, and the effect will not change even if it is added in an amount exceeding 9 mol %.

Y2O3 is chemically stable in the molten salt and has the effect of stabilizing ZrO2. In a molten salt at 500° C. or lower, the effect will not appear unless it is added in an amount of 5 mol % or more, and the effect will not change even if it is added in an amount exceeding 12 mol %. Y2O3
When combined with CaO, the effect of stabilizing ZrO□ is extremely large.

[Example] An oxygen sensor was manufactured using a protection tube having the composition of the present invention shown in Table 1, and a measurement circuit shown in FIG. 2 was constructed.
Potential measurements were performed with a potentiometer 16 immersed in molten Na2SO4 salt at 50° C. over a period of 336 hours.

The obtained potential value was converted into the amount of oxygen in the molten salt using the Ern5t equation shown by the following equation.

E = (RT/4F) 1nPoz (molten salt)
/Po2(air) where E is the measured potential difference, R is the gas constant, T is the temperature, F is the Faraday constant, and PO2 is the oxygen partial pressure in each environment.

FIG. 3 is an example of a diagram showing the oxygen amount measurement results, which showed a steady value from 3 minutes after the start of the measurement and a stable oxygen amount over a long period of time. All the measurement results using the sensor equipped with the protective tube having the composition shown in Table 1 showed stable oxygen amounts similar to the potential changes shown in FIG.

Table 1 [Effects of the Invention] The present invention provides a sensor that electrochemically measures the amount of dissolved oxygen in a molten salt environment, and the oxygen amount or potential in the molten salt can be measured over a long period of time. This will greatly contribute to the development of new materials by elucidating the internal corrosion mechanism.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the structure of the oxygen sensor, FIG. 2 is a circuit diagram for measuring potential, and FIG. 3 is a diagram showing changes over time in the amount of oxygen measured.

Claims (1)

[Claims] 1. CaO is 3-9% in mol%, Y_2O_3 is 5-1
A protective tube containing 2% of one or two types with the remainder being ZrO_2, a Pt powder filled in the protective tube, a Pt electrode immersed in the Pt powder, and a Pt electrode immersed in molten salt outside the protective tube. 1. A sensor for measuring oxygen partial pressure in a molten salt, characterized in that both Pt electrodes are electrically connected to measure the potential difference generated between the two Pt electrodes.