JP2530076B2 - Sensor probe for measuring the amount of dissolved hydrogen in molten metal and method of using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensor probe for measuring the amount of dissolved hydrogen for measuring the hydrogen concentration in molten metal, and a method of using the sensor probe.

[0002]

2. Description of the Related Art As a method for measuring the hydrogen concentration in a molten metal, an initial bubble method for calculating the amount of hydrogen gas from the pressure when a bubble is first generated on the surface of a sample under reduced pressure and the temperature of the sample, Observation of the state of bubbles in a sample solidified under reduced pressure, comparison with the specific gravity of a standard sample and the reduced pressure solidification method for measuring the amount of hydrogen gas from the state of bubbles in the sample cross section, as well as injecting a small amount of gas into the melt, Is circulated in the molten metal and then recovered, and when the hydrogen gas diffuses into this gas and becomes in an equilibrium state, there is a telegas method or the like in which the hydrogen gas in the exhaust gas is analyzed by a gas chromatography method.

However, these methods have problems that measurement time is too long, accuracy is low, equipment is large, and measurement is very costly when used at an actual casting site. .

The inventors of the present application have proposed a solid electrolyte SrCe _0.95 Yb _0.05 O _3-x which exhibits proton conductivity at high temperatures.
A hydrogen sensor of galvanic cell type is constructed by using and the hydrogen concentration in the molten metal is measured from the electromotive force generated by the hydrogen activity difference between the hydrogen partial pressure on the reference electrode side of the sensor and the hydrogen concentration in the molten metal. Suggesting a way to do it. This method has the advantages that the measurement cost is low, the measurement can be performed in a short time, and the change in the hydrogen concentration in the molten metal can be continuously measured as an electromotive force.

[0005]

However, in a molten metal, particularly in a metal having an extremely low equilibrium oxygen partial pressure, such as aluminum, the solid electrolyte is reduced, and an insulating oxide is formed on the interface between the solid electrolyte and the molten metal. A material film is formed,
It is difficult to measure for a long time. That is, when measuring the hydrogen concentration in the molten metal using the proton-conductive solid electrolyte, if the sensor probe is directly immersed in the molten metal, the interface between the molten metal and the solid electrolyte at a sensor operating temperature of 400 to 1100 ° C. An insulating oxide film is formed on the
This makes measurement of hydrogen concentration impossible.

The present invention has been made in view of such a problem, and in order to prevent reduction of a solid electrolyte in a portion constituting a sensor element, an electromotive force measuring portion of the sensor element is directly immersed in a molten metal. It is an object of the present invention to provide a sensor probe for measuring the amount of dissolved hydrogen in molten metal which can measure the concentration of hydrogen in molten metal without the need.

[0007]

A sensor probe for measuring the amount of dissolved hydrogen in molten metal according to the present invention comprises a perovskite-type proton-conducting solid electrolyte element with one closed end and an open end side of this element. A sleeve for external fitting and holding, a reference electrode composed of a porous electrode formed on the outer surface of the element, a measurement electrode composed of a porous electrode formed on the inner surface of the element, the reference electrode and the measurement electrode And a solid reference material which is placed in contact with the reference electrode and serves as a reference for galvanic electromotive force.

The sensor probe for measuring the amount of hydrogen dissolved in the molten metal is arranged by immersing the open end side end of the element in the molten metal, and sealing the inside of the element in contact with the molten metal surface. The amount of hydrogen dissolved in the molten metal is measured by forming the space.

The perovskite-type proton conductive solid electrolyte is SrCe _0.95 Yb _0.05 O _3-x , BaCe _0.9
It has a composition such as Nb _0.1 O _3-x and CaZr _0.9 In _0.1 O _3-x . The cup-shaped sensor holder is formed of a dense, gas-impermeable, ceramic material. Further, when the sealing material is subjected to a sealing treatment before use of the sensor, the solid electrolyte, for example, SrCe _0.95 Yb _0.05
O _3-x , CaZr _0.9 , In _0.1 O _3-x and BaCe _0.95
Sensor operating temperature range of 300 to 1100 ° C such as Y _0.05 O _3-x
Coefficient of thermal expansion between 8.5 × 10 ^{-6 and} 9.8 × 10 ^-6
Thermal expansion coefficient close to (/ ° C) 8.0 × 10 ^{-6 to} 10.0 ×
Use a dense glass sealing material having a temperature of 10 ^-6 (/ ° C) and a pour point above the sensor usage temperature, or if you seal when using the sensor, have a softening temperature below the usage temperature and use It is preferable to use a dense glass sealing material having a pour point above the temperature.

[0010]

In the present invention, first, the open end of the sensor element is immersed in the molten metal. Thereby, the sealed space in contact with the molten metal is confined in the sensor element. Then, the amount of hydrogen gas that comes out from the molten metal into the gas in this space is measured as the hydrogen partial pressure in the gas in the space.
This measurement principle is performed by measuring the electromotive force of a galvanic cell using a proton conductive solid electrolyte. In this manner, the hydrogen concentration in the high-temperature portion near the surface of the molten metal is measured with the sensor probe for measuring the amount of dissolved hydrogen, and the hydrogen concentration in the space when the hydrogen concentration in the space reaches the equilibrium value is measured. The hydrogen concentration can be determined. In the present invention, the open end of the sensor element made of a solid electrolyte is immersed in molten metal. However, this immersion part is a part of the sensor element, and unlike the conventional case where the entire solid electrolyte and the measurement electrode are immersed in the molten metal, the electromotive force measurement part is not immersed.
For this reason, since no insulating oxide film is generated in this portion, there is no problem in the measurement operation.

A hydrogen concentration cell type hydrogen sensor using a solid electrolyte exhibiting proton conductivity operates stably at high temperatures and exhibits an electromotive force close to the theoretical value given by the following mathematical formula 1.

[0012]

E = (RT / 2F) ln [P _H2 (1) / P _H2 (2)]

Where E is an electromotive force (V), R is a gas constant,
F is Faraday constant, T is absolute temperature, P _H2 (1) and P _H2
(2) is the hydrogen partial pressure on the molten metal in the closed space and the hydrogen partial pressure of the reference gas, respectively.

An equilibrium relationship is established between the hydrogen concentration in the molten metal and the hydrogen partial pressure on the molten metal.
Follow the rules of erts.

[0015]

[Equation 2] S = K (P _H2 ) ^1/2

Where S is the equilibrium solubility of hydrogen, K is a constant,
P _H2 is the hydrogen partial pressure on the melt.

As can be seen from Equation 2, if the hydrogen partial pressure in the gas phase in contact with the molten metal can be measured, the concentration of hydrogen dissolved in the molten metal can be determined.

Generally, the hydrogen concentration in the molten metal depends on the hydrogen partial pressure and the melt temperature in the vapor phase in contact with the melt, and the dependence of the hydrogen partial pressure and the melt temperature follows the Sieverts rule and the Henry rule. For this reason, the hydrogen concentration S can be expressed by the following equation (3).

[0019]

LogS = A− (B / T) + (１ ／) log (P _H2 ) where A and B are constants depending on the metal composition.

Therefore, a sensor probe having a shape as shown in FIG. 1 is assembled, and the end of the sensor element is immersed in the molten metal to form a space occupied by the gas phase in contact with the molten metal in the Tamman tubular electrolyte sensor element. The partial pressure of the hydrogen gas released from the molten metal into the gas phase is measured using the sensor probe for measuring the amount of dissolved hydrogen of the present invention. From the electromotive force generated between the reference electrode and the measurement electrode of the sensor probe, the hydrogen partial pressure P _H2 is obtained by using the above-described equation (1), and the hydrogen partial pressure is substituted into the equation (3), whereby hydrogen in the molten metal is obtained. The concentration S can be determined.

As described above, according to the present invention, the hydrogen concentration in the molten metal can be measured for a long time without directly contacting the portion where the sensor element measuring electrode made of the solid electrolyte is provided with the molten metal.

[0022]

Embodiments of the present invention will now be specifically described with reference to the accompanying drawings.

FIG. 1 is a sectional view showing a sensor probe for measuring the amount of dissolved hydrogen according to a first embodiment of the present invention.

The sensor element 1 is a perovskite type proton conductive solid electrolyte (for example, SrCe _0.95 Yb _0.05 O).
_3-x , CaZr _0.9 In _0.1 O _3-x , BaCe _0.95 Y _0.05 O
_3-x, etc.) having a closed shape at one end, and the reference electrode 2 and the measurement electrode 3 made of porous material such as Pt, Ni, or an oxide conductor are formed on the outer surface and the inner surface of the sensor element 1 by baking. Has been formed.

A sleeve-shaped holder 8 made of dense ceramics (for example, alumina, mullite, or silicon nitride) is fitted on the sensor element 1. The sensor element 1 is arranged in the holder 8 such that the end portion on the open end side slightly projects from the tip portion of the holder 8, and the holder 8 and the sensor element 1 are connected to each other by the glass sealing material 7 at the tip portion of the holder 8. It is fixed to. The reference electrode 2 is airtightly separated from the outside air and the atmosphere of the measurement electrode 3 by the glass sealing material 7.

The sensor element 1 is provided on the outer surface of the holder 8.
A lead 9 made of a conductive paste is formed so as to be electrically connected to the measuring electrode 3 extending slightly from the inner surface to the outer surface at the open end thereof. It is connected to an external processing device (not shown). On the other hand, one end of a ceramic insulating tube 4 for supporting a sensor is inserted in the upper half of the ceramic holder 8, and a lead wire such as a Pt wire or a Ni wire is inserted into the center hole of the insulating tube 4. 5 is inserted. This lead wire 5 is Pt
Alternatively, it is electrically connected to the porous reference electrode 2 by a conductive paste 6 such as Ni, and the reference electrode 2 is led to an external processing device via a lead wire 5. The insulating tube 4 is fixed to the holder 8 by the glass sealing material 10, and the gap between the insulating tube 4 and the holder 8 is sealed from the outside by the glass sealing material 10.

A space between the sensor element 1 and the ceramic insulating tube 4 in the holder 8 is filled with a solid reference substance 11, which serves as a reference for galvanic electromotive force, in contact with the reference electrode 2. Examples of the solid reference substance 11 include hydroxyapatite and aluminum phosphate (JP-A-63-269053).

Next, the operation of the sensor probe thus configured will be described. The lower end portion of the sensor element 1 made of a proton conductive solid reference substance is immersed in a molten metal (not shown), and a space surrounded by the molten metal surface of the sensor element 1, the holder 8 and the molten metal 19 is formed in the sensor element 1. Form. The sensor element 1 is only partially immersed in the molten metal 19 at its end, and most of its measuring electrode 3 is located in the space.

Then, the hydrogen dissolved in the molten metal becomes in equilibrium with the hydrogen gas in the space surrounded by the sensor element 1 and the molten metal 19 (see FIG. 3), and the hydrogen solubility S in the molten metal becomes
And the hydrogen partial pressure P _H2 in the space establishes the relationship represented by the above-described Expression 3. Therefore, the hydrogen partial pressure P _H2 in this space is measured by the sensor element 1 using the galvanic electromotive force. That is, the electromotive force E generated between the reference electrode 2 that comes into contact with the solid reference substance 11 that serves as the reference of the galvanic electromotive force and the measurement electrode 3 that comes into contact with the gas in the space is detected,
From this electromotive force, the hydrogen partial pressure P on the molten metal is calculated according to Equation 1 above.
_{Find H2} . Then, from the hydrogen partial pressure P _H2 , the hydrogen solubility S in the molten metal is calculated by the above-mentioned formula 3. In this way, the solubility of hydrogen in the molten metal is measured by the measuring electrode 3 of the sensor element 1.
Can be measured without immersing the forming part of the, i.e., the electromotive force measuring part in the molten metal. Therefore, the erosion of the sensor element 1 by the molten metal is avoided, and the hydrogen dissolution amount can be measured for a long time.

Next, the results obtained by manufacturing the sensor probe of the embodiment shown in FIG. 1 and conducting a measurement test of the amount of hydrogen dissolved in the molten metal will be described. First, a platinum porous electrode was baked at a temperature of 900 ° C. on the inner and outer surfaces of the one-end closed sensor element 1 made of CaZr _0.9 ln _0.1 O _3−x which is a perovskite type proton conductive solid electrolyte. Thereafter, fitted around the alumina holder 8 to the sensor element 1, powdered glass sealing material 7 _{(composition; Na 2 O 3 · B 2} O 3 · SiO 2, the thermal expansion coefficient: 9.5 × 10 ^-6, the softening point; 695 ° C, pour point: 88
The holder 8 and the element 1 were fixed at 0 ° C. Next, in the holder 8, AlPO was used as the solid reference material 11.
₄ and La _0.4 Sr _0.6 CoO _3−x mixed powder was filled, and Pt was added.
At the tip of the alumina insulating tube 4 passing through the lead wire 5, Pt
The paste 6 was applied and inserted into the holder 8, and the insulating tube 4 was fixed to the holder 8 with the powder glass sealing material 10. Then, the lead wire 5 and the reference electrode 2 were electrically connected by the Pt paste 6 at the tip of the insulating tube 4. The thus-assembled one was heated in an electric furnace to fuse the powder glass sealing materials 7 and 10.

Next, using this sensor probe, as shown in FIG. 2, the amount of hydrogen dissolved in the molten aluminum 31 melted in the graphite crucible 30 was measured. Sensor element 1
Has a hydrogen concentration of 1%. The hydrogen gas partial pressure on the aluminum melt 31 is obtained by mixing a mixed gas obtained by setting various amounts of these gases from the gas mixer 35 connected to the Ar gas source 37 and the hydrogen gas source 36 into the crucible 30. Was adjusted. Then, the hydrogen concentration in the molten metal was controlled to various values by being placed under these various hydrogen partial pressure atmospheres, and the electromotive force of the sensor element 1 was measured under the conditions. The measured values of the molten metal temperature and electromotive force are the recorder 33
Recorded. The molten metal in the crucible 30 was heated by the heater 34 and maintained at a predetermined temperature.

In order to estimate the accuracy of the measured value of the sensor probe of this embodiment, the hydrogen concentration in the molten aluminum 31 is Telega using the gas chromatography analyzer 38.
It was measured by the s (telegas method) method. In this case, nitrogen gas is blown into the melt from the nitrogen gas source 40, and the nitrogen gas is bubbled and circulated in the melt so that the hydrogen concentration in the atmosphere nitrogen gas on the surface of the melt balances with the hydrogen concentration in the melt. The hydrogen concentration in the nitrogen gas at the time when the temperature reached was led to a gas chromatograph analyzer 38, and the hydrogen concentration was measured by the gas chromatograph analyzer 38. The temperature of the molten metal 31 to be measured was measured by the K thermocouple 32. In addition, the temperature of the molten metal was 700-800 degreeC. The telegas method is known as a method capable of measuring the hydrogen concentration in a molten metal with high accuracy.

FIG. 3 is a graph showing the hydrogen concentration measured by the telegas method on the horizontal axis and the electromotive force of the sensor element on the vertical axis, and the measured value is indicated by ◯. However, this data is obtained when a 99% by weight pure aluminum melt is heated to 750 ° C. As shown in FIG. 3, there is a very good correlation between the hydrogen concentration in the molten metal measured by the telegas method and the electromotive force of the sensor element. The same relationship can be obtained under other temperature conditions.

FIG. 4 is a graph comparing the measured values of hydrogen concentration in the molten metal obtained by the telegas method on the horizontal axis and the measured values of hydrogen concentration measured using the sensor element of this embodiment on the vertical axis. Is. As is apparent from FIG. 4, the value obtained by the telegas method and the value measured using the sensor according to the present invention were in very good agreement. Therefore, it can be seen that the accuracy of the measurement value of the sensor probe of this embodiment is extremely high.

[0035]

According to the present invention, by immersing a part of the sensor element of the sensor probe in the molten metal (molten metal),
The concentration of hydrogen dissolved in the melt can be measured, and since the electromotive force measuring portion of the sensor element of the sensor probe does not contact the melt, continuous measurement over a long period of time is possible. Also, the hydrogen concentration in the molten metal can be measured simply by measuring the electromotive force of the sensor element of the sensor probe,
The measuring device can be downsized, and the operability is improved when it is used in the actual casting process. Further, since there is no need to circulate gas unlike the telegas method, the running cost required for measurement can be reduced. Therefore, according to the present invention, it is possible to provide an apparatus for measuring the concentration of hydrogen in molten metal that is small, has high measurement accuracy, and has high reliability.

Further, in the case of the telegas method, which has been conventionally considered to have excellent measurement accuracy, it cannot be used in the case where the flow of the molten metal is fast as in the degassing process. However, since the sensor probe according to the present invention can measure the hydrogen concentration without any problem even if the molten metal has a flow, the object to be measured is significantly expanded, and the present invention is a technical field requiring the hydrogen concentration measurement. Is extremely useful.

[Brief description of drawings]

FIG. 1 is a cross-sectional view illustrating a sensor probe for measuring the amount of dissolved hydrogen according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing an apparatus for testing the measurement accuracy of the sensor probe of this embodiment.

FIG. 3 is a graph showing the relationship between the hydrogen concentration measurement value by the telegas method and the electromotive force of the sensor element of this example.

FIG. 4 is a graph showing a relationship between a measured hydrogen concentration by the telegas method and an electromotive force of the sensor element of the present embodiment.

[Explanation of symbols]

 1; Sensor element 2; Reference electrode 3; Measuring electrode 4; Ceramic insulating tube 5; Lead wire 6, 9; Conductive paste 7, 10; Powder glass seal 8; Ceramic holder

Claims (2)

(57) [Claims] 1. A one-end-closed element made of a perovskite-type proton conductive solid electrolyte, a sleeve for externally fitting and holding the open end side of the element, and a porous electrode formed on the outer surface of the element. A reference electrode consisting of, a measurement electrode consisting of a porous electrode formed on the inner surface of the element, a sealant separating the reference electrode and the measurement electrode, a galvanic electromotive force arranged in contact with the reference electrode A sensor probe for measuring the amount of dissolved hydrogen in a molten metal, which has a solid reference material as a reference. 2. The sensor probe for measuring the amount of dissolved hydrogen according to claim 1, wherein the open end side end portion of the element is immersed in molten metal and disposed, and the molten metal level inside the element. A method of using a sensor probe for measuring the amount of dissolved hydrogen, which comprises forming a closed space in contact with a substrate.