JPH07119729B2 - Sensor probe for measuring the amount of hydrogen dissolved in molten metal - 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.

[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 the problems that it takes too much measuring time to be used in an actual casting site, the accuracy is poor, the size of the apparatus becomes large, and the cost is very high. .

The inventors of the present application have so far developed 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 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 oxidation is caused at the interface between the solid electrolyte and the molten metal. A physical film is created,
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 the sensor operating temperature of 400 to 1100 ° C. An insulating oxide film is formed on the
This makes it impossible to measure the hydrogen concentration.

The present invention has been made in view of the above problems, and in order to prevent the reduction of the solid electrolyte constituting the sensor element, the hydrogen in the molten metal is not directly immersed in the sensor element but directly in the molten metal. An object of the present invention is to provide a sensor probe for measuring the amount of dissolved hydrogen in molten metal, which can measure the concentration.

[0007]

A sensor probe for measuring the amount of dissolved hydrogen in a molten metal according to the present invention is formed of a perovskite-type proton conductive solid electrolyte element having a closed end and an inner surface of the element. A reference electrode composed of a porous electrode, a measurement electrode composed of a porous electrode formed on the outer surface of the element, a sealing material separating the reference electrode and the measurement electrode, and a galvanic element arranged in contact with the reference electrode. The solid reference material, which is the reference for electromotive force, and the gas permeate but the molten metal
And a cap made of a porous ceramic which is made of a non-permeable porous ceramic and surrounds the element to form a space between the element and the element.

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 , CaZr _0.9 In _0.1 O _3-x, or the like. The cup-shaped sensor holder is formed of a gas-impermeable dense ceramic material. Further, when the sealing material is subjected to a sealing treatment before using the sensor, the sealing material may be, for example, SrCe _0.95 Yb _0.05.
O _3-x , CaZr _0.9 , In _0.1 O _3-x and BaCe _0.95
Y _0.05 O _3-x sensor operating temperature range 300 to 1100 ° C
Coefficient of thermal expansion between 8.5 × 10 ^{-6 and} 9.8 × 10 ^-6
Thermal expansion coefficient close to (/ ° C) 8.0 x 10 ^{-6 to} 10.0 x
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.

The porous ceramic cap is formed of a material that does not allow the permeation of molten metal but allows the passage of gas. As such a material, there is a silicon carbide material having poor wettability with molten metal. A material having poor wettability with the molten metal is preferable because the molten metal rarely adheres to the cap and penetrates into the cap.
Then, in order to surely prevent the invasion of the molten metal as described above, it is preferable to use a porous material having a pore diameter of 30 μm or less for the cap.

[0010]

In the present invention, the porous ceramic cap is immersed in the molten metal. As a result, a space is formed between the cap and the sensor element. The cap is impermeable to molten metal but permeable to gas. Therefore, the partial pressure of hydrogen gas in the space surrounded by the cap is in equilibrium with the hydrogen concentration in the molten metal. Therefore, the amount of hydrogen gas in the space surrounded by the cap is measured as the hydrogen partial pressure in the space gas. This measurement principle is carried out by measuring the electromotive force of a galvanic cell using a proton conductive solid electrolyte. In this way, the sensor probe for measuring the amount of dissolved hydrogen measures the hydrogen concentration in the high-temperature space that contacts the surface of the molten metal, and the hydrogen concentration when the hydrogen concentration in this space reaches the equilibrium value The hydrogen concentration in the metal can be determined.

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]

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

However, E is an electromotive force (V), R is a gas constant,
F is Faraday constant, T is absolute temperature, P _H2 (1), P
_H2 (2) is the hydrogen partial pressure on the measurement electrode side and the hydrogen partial pressure on the reference electrode side, respectively.

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

[0015]

## EQU2 ## S = K (P _H2 ) ^1/2 where S is the equilibrium solubility of hydrogen, K is a constant, and P _H2 is the partial pressure of hydrogen on the melt.

As can be seen from the 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 obtained.

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. Therefore, the hydrogen concentration S can be expressed by Equation 3 below.

[0018]

Equation 3] logS = A- (B / T) + (1/2) log (P H2) where, A and B are constants which depend on the composition of the metal.

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

As described above, according to the present invention, the hydrogen concentration in the molten metal can be measured for a long time without the sensor element made of the solid electrolyte coming into direct contact with the molten metal.

[0021]

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 the 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 inner surface and the outer surface of the sensor element 1 by baking. Has been formed.

One end of a ceramic insulating tube 4 for holding the sensor element is inserted in the upper half of the sensor element 1, and the sensor element 1 and the ceramic insulating tube 4 are bonded by a ceramic adhesive 7.
And are fixed. In the center hole of this insulating tube 4, P
A lead wire 5 such as a t wire or a Ni wire is inserted. The lead wire 5 is electrically connected to the reference electrode 2 on the inner surface of the sensor element 1 by a metal paste 6 such as Pt or Ni. A conductive paste 9 is applied to the outer surface of the insulating tube 4, and the conductive paste 9 is conducted to the measuring electrode 3 on the outer surface of the sensor element 1. As a result, the measuring electrode 3 is led out to the external signal processing device via the conductive paste 9.

The space enclosed by the insulating tube 4 in the sensor element 1 is filled with a solid reference substance 10 serving as a reference of galvanic electromotive force in contact with the reference electrode 2. Examples of the solid reference substance 10 include hydroxyapatite and aluminum phosphate (Japanese Patent Laid-Open No. 63-269053).

The silicon carbide-based porous ceramic cap 11 has a closed end shape, and the open end side of the cap 11 is externally fitted to the sensor element 1. A glass sealing material 8 is provided at the open end of the cap 11 and the open end of the sensor element 1, whereby the reference electrode 2, the measuring electrode 3 and the outside are hermetically sealed. Then, in a state where the cap 11 is fixed to the sensor element 1, an appropriate space is formed between the cap 11 and the outer surface of the sensor element 1 on the closed end side. This cap 11
Is formed of a silicon carbide (SiC) porous material that is difficult to wet with molten metal. As the porous material forming the cap 11, it is preferable to use one having a pore diameter of 30 μm in order to reliably prevent the permeation of the molten metal.

Next, the operation of the sensor probe thus constructed will be described. First, the silicon carbide porous cap 11 is immersed in a molten metal (not shown), and the space formed between the sensor element 1 and the cap 11 is positioned below the molten metal surface. As a result, the space surrounded by the cap 11, that is, the space between the cap 11 and the sensor element 1 contacts the molten metal via the cap 11. Then, the measuring electrode 3 of the sensor element 1 comes into contact with this space.

Then, the hydrogen dissolved in the molten metal becomes in equilibrium with the hydrogen gas in the space surrounded by the cap 11, and the hydrogen solubility S in the molten metal and the hydrogen partial pressure P in the space.
_The relationship expressed by the above-mentioned mathematical expression 3 is established between _H2 and _H2 . 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 measurement electrode 3 in contact with the gas in the space and the reference electrode 2 in contact with the solid reference material 10 in the sensor element 1 is detected, and from the electromotive force E, Then, the hydrogen partial pressure P _H2 on the molten metal is obtained in accordance with. And this hydrogen partial pressure P
_{From H2} , the solubility S of hydrogen in the molten metal is calculated by the above-mentioned formula 3. In this way, the hydrogen solubility in the molten metal can be measured without bringing the sensor element 1 into contact with the molten metal.
Therefore, the erosion of the sensor element 1 by the molten metal is avoided,
The amount of dissolved hydrogen can be measured over a long period of 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.

Next, AlPO _{4 is used} as the solid reference material 10.
And a mixed powder of La _0.4 Sr _0.6 CoO _9-x are filled, and Pt is added.
Insert the alumina insulation tube 4 through the lead wire 5 at the tip
The t paste 6 was applied, inserted into the sensor element 1, and fixed by the ceramic adhesive 7. Thereafter, a silicon carbide based porous ceramic cap 11 having an average pore diameter of 15 μm is covered so as to cover the entire sensor element 1, and the powdery glass sealing material 8 (composition: Na ₂ O ₃ ·.
Sealing was performed using B ₂ O ₃ .SiO ₂ , thermal expansion coefficient: 9.5 × 10 ⁻⁶ , softening point: 695 ° C., pour point: 880 ° C.). The thus assembled product is heated in an electric furnace (heating / cooling rate: 5 ° C / min, 850 ° C: 10 minutes)
Then, the powdery glass sealing material 8 was fused and the ceramic adhesive was solidified. Then using this sensor probe,
As shown in FIG. 2, the amount of hydrogen dissolved in the aluminum melt 31 melted in the graphite crucible 30 was measured. The reference gas of the sensor element 1 has a hydrogen concentration of 1%. The partial pressure of hydrogen gas on the molten aluminum 31 is the gas mixture 35 connected to the Ar gas source 37 and the hydrogen gas source 36, and the mixed gas obtained by setting various blending amounts of these gases in the crucible 30. It was adjusted by introducing Then, the hydrogen concentration in the molten metal is controlled to various values by placing it under various hydrogen partial pressure atmospheres, and the sensor element 1 (or 2) is controlled under the conditions.
The electromotive force of 0) was measured. The measured values of the molten metal temperature and the electromotive force were recorded in the recorder 33. The molten metal in the crucible 30 was heated by the heater 34 and kept at a predetermined temperature.

In order to estimate the accuracy of the measurement value of the sensor probe of this embodiment, the hydrogen concentration in the molten aluminum 31 was 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 molten metal from the nitrogen gas source 40, the nitrogen gas is bubbled in the molten metal and circulated, and the hydrogen concentration in the atmospheric nitrogen gas on the surface of the molten metal is balanced with the hydrogen concentration in the molten metal. The hydrogen concentration in the nitrogen gas when reaching the temperature was introduced into the gas chromatograph analysis device 38, and the hydrogen concentration was measured by the gas chromatography analysis device 38. The temperature of the molten metal 31 to be measured was measured by the K thermocouple 32. The temperature of the molten metal was 700 to 800 ° C. 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 for a case where 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 the present 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 is understood that the accuracy of the measurement value of the sensor probe of this example is extremely high.

[0034]

According to the present invention, the concentration of hydrogen dissolved in the molten metal (molten metal) can be measured simply by immersing the cap of the sensor probe in the molten metal (molten metal), and the sensor element of the sensor probe can be measured. Since it is protected by the cap and does not come into contact with the molten metal, continuous measurement over a long period of time is possible. In addition, since the hydrogen concentration in the molten metal can be measured simply by measuring the electromotive force of the sensor element of the sensor probe, it is possible to downsize the measuring device and improve the operability when it is used in the actual casting process. . Further, unlike the telegas method, it is not necessary to circulate the gas, so the running cost required for measurement can be reduced. Therefore, according to the present invention, it is possible to provide a device for measuring hydrogen concentration in molten metal that is small in size, 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 trouble even if there is a flow in the molten metal, the measurement target is remarkably expanded, and the present invention requires a hydrogen concentration measurement. Is extremely useful in

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing 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 the relationship between the hydrogen concentration measurement value by the telegas method and the electromotive force of the sensor element of this example.

[Explanation of symbols]

 1; Sensor element 2; Reference electrode 3; Measurement electrode 4; Ceramic insulating tube 5; Lead wire 7; Ceramic adhesive 8; Glass sealing material 10; Solid reference material

Claims (3)

[Claims] 1. A perovskite-type proton conductive solid electrolyte, which is a one-end closed type element, a reference electrode which is a porous electrode formed on the inner surface of the element, and a porous electrode which is formed on the outer surface of the element. A measuring electrode, a sealant separating the reference electrode and the measuring electrode, a solid reference substance that is placed in contact with the reference electrode and serves as a reference for galvanic electromotive force, and gas is permeable but molten metal is not permeable. Porous cell
A sensor probe for measuring the amount of hydrogen dissolved in a molten metal, comprising a porous ceramic cap that surrounds the element and forms a space between the element and the element. 2. The sensor probe for measuring the amount of hydrogen dissolved in a molten metal according to claim 1, wherein the porous ceramic cap is made of silicon carbide. 3. The sensor probe for hydrogen dissolution amount measurement according to claim 1, wherein the porous ceramic cap has a pore diameter of 30 μm or less.