JPH0720082A - Sensor probe for measuring amount of hydrogen dissolution in melted metal - Google Patents

Abstract

PURPOSE:To provide a sensor probe which can be miniaturized and a hydrogen concentration measurement method which can measure hydrogen concentration over a long period of time by preventing the reduction in solid electrolyte constituting a sensor element and accurately measuring the hydrogen concentration in the melted metal without dipping the sensor element directly into molten metal. CONSTITUTION:A measurement electrode 3 consisting of a porous electrode is formed on the inner surface of a sensor element 1 whose one edge is blocked consisting of perovskite type proton conductive solid electrolyte and a reference electrode 2 consisting of a porous electrode is formed on the outer surface of the sensor element 1. Silicon carbide porous filter 10 is engaged to the open edge part of the sensor element 1 and a part containing the filter 10 is dipped into molten metal while supplying a reference gas to the outer surface of the sensor element 1, thus forming a space with a hydrogen gas concentration which is balanced with the hydrogen concentration in a melted metal and measuring the hydrogen gas concentration from galvanic electromotive force.

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]

According to a first aspect of the present invention, there is provided a sensor probe for measuring the amount of dissolved hydrogen in a molten metal according to the present invention, which comprises a perovskite-type proton-conducting solid electrolyte and a closed end element, and A measuring electrode composed of a formed porous electrode, a reference electrode composed of a porous electrode formed on the outer surface of the element, a sealant separating the reference electrode and the measuring electrode, and a reference of galvanic electromotive force. A means for bringing a reference substance into contact with the reference electrode; a support for supporting the element with its open end side facing outward; and a porous filter fitted into the open end of the element to prevent molten metal from entering. It is characterized by having.

A sensor probe for measuring the amount of hydrogen dissolved in a second molten metal according to the present invention comprises a perovskite-type proton conductive solid electrolyte element with one closed end and a porous electrode formed on the inner surface of the element. A reference electrode composed of a reference electrode, a measurement electrode composed of a porous electrode formed on the outer surface of the element, a sealant separating the reference electrode and the measurement electrode, and a reference substance serving as a reference of galvanic electromotive force. A sleeve that is fitted to the element so as to project from the closed end of the element, and a porous filter that is fitted to the end of the portion of the sleeve that projects from the element to prevent the intrusion of molten metal. It is characterized by

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 made 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 filter fitted into the open end of the sensor element or the protruding side end of the sleeve is formed of a material that does not allow molten metal to pass through but allows gas to pass through. As such a material, there is a silicon carbide material having poor wettability with molten metal. It is preferable that the wettability with the molten metal is poor because the molten metal rarely adheres to the porous filter and penetrates into the porous filter. As described above, in order to reliably prevent the invasion of the molten metal, the porous filter has a pore diameter of 30.
It is preferable to use a porous material having a size of μm or less.

[0011]

In the present invention, when the porous filter is fitted to the open end of the sensor element, the porous filter is fitted to the inside of the sensor element, and the porous filter is fitted to the end of the sleeve. A space is formed in a portion of the sleeve that projects from the sensor element. Therefore, the portion including the porous filter is immersed in the molten metal. The filter is impermeable to molten metal and permeable to gas. Therefore, the molten metal does not enter the space inside the sensor element or the space inside the sleeve, and the hydrogen gas partial pressure in this space is in equilibrium with the hydrogen concentration in the molten metal. Therefore, the amount of hydrogen gas in the space is measured as the hydrogen partial pressure in the gas in the space. This measurement principle is carried out by measuring the electromotive force of a galvanic cell using a proton conductive solid electrolyte. In this way
This 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 in the molten metal is calculated from the hydrogen concentration when the hydrogen concentration in this space reaches an equilibrium value. 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.

[0013]

[Equation 1] E = (RT / 2F) ln [P _H2 (1) / P _H2 (2)] where E is an electromotive force (V), R is a gas constant, and F is Faraday.
A constant, T is the absolute temperature, and P _H2 (1) and P _H2 (2) are 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 outer surface and the inner surface of the sensor element 1 by baking. Has been formed.

A portion of the sensor element 1 on the closed end side is externally fitted to a ceramic insulating tube 4 for holding the sensor element, and the sensor element 1 has a portion on the open end side thereof slightly protruding from the ceramic insulating tube 4. In this state, it is fixed to the ceramic insulating tube 4 by the glass sealing material 5 and is hermetically sealed. As a result, most of the outer peripheral surface of the sensor element 1 is covered with the insulating tube 4 and the glass sealing material 5. A pipe 6 made of a dense ceramic (for example, alumina, mullite, or silicon nitride) for introducing a reference gas (gas having a constant hydrogen concentration) is inserted into the ceramic insulating tube 4. A lead wire 8 such as a Pt wire or a Ni wire is inserted in the pipe 6. The lead wire 8 is electrically connected to the reference electrode 2 on the outer surface of the sensor element 1 by a metal paste 7 such as Pt or Ni.

Then, the reference gas is supplied to the reference electrode 2 through the passage in the pipe 6 which is the inner pipe concentrically arranged in the ceramic insulating pipe 4, and the insulating pipe 4 which is the outer pipe and the inner pipe The reference gas is used as the reference electrode 2 through the gap between the pipe 6 and the pipe 6.
Is discharged from around. 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 inner 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.

A silicon carbide (SiC) -based filter 10 is fitted to the end of the sensor element 1 on the open end side, and serves as a plug at the end of the sensor element 1. Then, the filter 10 is attached to the sensor element 1 with the ceramic adhesive 11.
It is fixed to. The filter 1 is a porous member composed of pores having an average pore diameter of 30 μm or less.

Next, the operation of the sensor probe thus constructed will be described. First, a portion including the silicon carbide filter 10 is immersed in a molten metal (not shown), and a part of a space formed by the filter 10 inside the sensor element 1 is located below the molten metal surface. Position it. As a result, the filter 10 prevents the molten metal from entering the space, and the space contacts the molten metal through the filter 10,
The measuring pole 3 of the sensor element 1 contacts the gas in this space.

Then, the hydrogen dissolved in the molten metal is in equilibrium with the hydrogen gas in the space inside the sensor element 1,
The relationship represented by the above mathematical formula 3 is established between the hydrogen solubility S in the molten metal and the hydrogen partial pressure P _H2 in the space. Therefore,
The hydrogen partial pressure P _H2 in this space is measured by the sensor element 1 using 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 reference gas on the outer surface of the sensor element 1 is detected. The hydrogen partial pressure P _H2 on the melt is determined. 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 hydrogen solubility in the molten metal can be measured without bringing the sensor element 1 into contact with the molten metal. For this reason,
Corrosion of the sensor element 1 by the molten metal is avoided, and the amount of dissolved hydrogen can be measured for a long time.

Next, a second embodiment of the present invention will be described with reference to FIG.

The sensor element 21 is a perovskite type proton conductive solid electrolyte (eg, 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 sensor element 21 has a reference electrode 22 and a measurement electrode 23, which are made of a porous material such as Pt, Ni, or an oxide conductor, on the inner and outer surfaces thereof.
Are formed by baking.

One end of a ceramic insulating tube 24 for holding the sensor element is inserted in the upper half of the sensor element 21, and the sensor element 21 and the ceramic insulating tube 24 are fixed by a ceramic adhesive 27. A lead wire 25 such as a Pt wire or a Ni wire is inserted into the center hole of the insulating tube 24. The lead wire 25 is electrically connected to the reference electrode 22 on the inner surface of the sensor element 21 by a metal paste 26 such as Pt or Ni.

The space enclosed by the insulating tube 24 in the sensor element 21 is filled with the solid reference substance 12, which serves as a reference for galvanic electromotive force, in contact with the reference electrode 22. Examples of the solid reference substance 12 include hydroxyapatite and aluminum phosphate (Japanese Patent Laid-Open No. 63-269053).

A ceramic sleeve 28 having both ends opened is fitted on the sensor element 21. The upper end of the sleeve 28 is flush with the upper end of the sensor element 21, and the sleeve 2
The lower end of 8 projects slightly below the lower end of the sensor element 21. A glass sealing material 29 is arranged on the upper ends of the sleeve 28 and the sensor element 21.
8 and the upper end of the sensor element 21 and the outer peripheral surface of the ceramic insulating tube 24 are hermetically sealed. A conductive paste 13 is applied to the lower inner surface and outer surface of the sleeve 28, and the conductive paste 13 is applied to the sensor element 2.
The measurement electrode 23 on the outer surface of No. 1 is electrically connected. As a result, the measuring electrode 23 is led to the external signal processing device via the conductive paste 13.

A silicon carbide porous ceramic filter 14 is fitted in the lower end opening of the sleeve 28. This filter 14 is the filter 10 of the first embodiment.
In the same manner as the above, silicon carbide (SiC
Quality) porous material and has an average pore diameter of 30 μm in order to surely prevent the permeation of the molten metal.

Next, the operation of the sensor probe thus constructed will be described. First, the sleeve 28 and the filter 14 are immersed in a molten metal (not shown), and the sleeve 2
8, the space surrounded by the sensor element 21 and the filter 14 is located below the surface of the molten metal. As a result, the space comes into contact with the molten metal via the filter 14. Then, the measuring electrode 23 of the sensor element 21 comes into contact with this space.

Then, the hydrogen dissolved in the molten metal is in equilibrium with the hydrogen gas in the space, and between the hydrogen solubility S in the molten metal and the hydrogen partial pressure P _H2 in the space, The relationship shown in 3 is established. Therefore, in the same manner as in the first embodiment, the hydrogen partial pressure P _H2 in this space is measured by the sensor element 21 using the galvanic electromotive force. However, the reference of the galvanic cell is the solid reference substance 12 that contacts the reference electrode 22 in the sensor element 21. 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. For this reason,
Corrosion of the sensor element 21 by the molten metal is avoided, and the amount of dissolved hydrogen can be measured for a long time.

In the method of using the sensor probe of each of the above embodiments, it is not necessary to deeply immerse the sensor element 1 or the sleeve 28 in the molten metal. Porous filter 10,1
4 may be completely immersed in the molten metal, and the sensor probe may be immersed to such an extent that the space contacting the measuring electrodes 3 and 23 does not communicate with the outside through the filters 10 and 14.

Next, description will be made on the results of the test of measuring the amount of dissolved hydrogen in the molten metal after manufacturing the sensor probe of the embodiment shown in FIG. 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 21 made of CaZr _0.9 ln _0.1 O _3−x which is a perovskite type proton conductive solid electrolyte.

Next, AlPO ₄ was used as the solid reference substance 12.
And a mixed powder of La _0.4 Sr _0.6 CoO _9-x are filled, and Pt is added.
The alumina insulating tube 24 passing through the lead wire 25 was coated with Pt paste 26 at its tip, inserted into the sensor element 21, and fixed with a ceramic adhesive 27. Then, an alumina sleeve 28 having a length of 10 mm protruding from the tip of the sensor element 21 is externally fitted to the sensor element 21, and together with the alumina insulating tube 24, a powder glass sealing material 29 (composition: N
a ₂ O ₃ · B ₂ O ₃ · SiO ₂ , coefficient of thermal expansion: 9.5 × 10
^-6 , softening point: 695 ° C, pour point: 880 ° C), and sealing was performed. Further, a silicon carbide based porous filter 14 having an average pore diameter of 15 μm is fitted to the tip of the sleeve 28, and the ceramic adhesive 15 is applied to the opening of the sensor element 21.
Fixed by. The thus assembled one is heated in an electric furnace (heating / cooling rate: 5 ° C / min, 850 ° C: 1 ° C).
After holding for 0 minutes), the powdered glass sealing material 29 was fused and the ceramic adhesives 15 and 27 were solidified.

Next, using this sensor probe, as shown in FIG. 3, the amount of hydrogen dissolved in the molten aluminum 31 melted in the graphite crucible 30 was measured. 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 was controlled to various values by being placed under these various hydrogen partial pressure atmospheres, and the electromotive force of the sensor element 21 was measured under the conditions. 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 is heated by the heater 34.
And maintained at a predetermined temperature. In order to estimate the accuracy of the measured values of the sensor probe of this example, the hydrogen concentration in the molten aluminum 31 was measured by the Telegas (telegas method) using the gas chromatography analyzer 38. 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. Further, the temperature of the melt 31 to be measured is K
It was measured with a thermocouple 32. The temperature of the molten metal is 700
It was ~ 800 ° C. The telegas method is known as a method capable of measuring the hydrogen concentration in a molten metal with high accuracy.

FIG. 4 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. 4, 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. 5 is a graph comparing the measured values of the hydrogen concentration in the molten metal obtained by the telegas method on the horizontal axis and the measured values of the hydrogen concentration measured using the sensor element of this embodiment on the vertical axis. Is. As is apparent from FIG. 5, the values obtained by the telegas method and the values 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.

[0043]

According to the present invention, the concentration of hydrogen dissolved in the molten metal (molten metal) can be measured simply by immersing the sensor probe in the molten metal (molten metal). Since it 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 sectional view showing a sensor probe for measuring the amount of dissolved hydrogen according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing a sensor probe for measuring the amount of dissolved hydrogen according to a second embodiment of the present invention.

FIG. 3 is a schematic diagram showing an apparatus for testing the measurement accuracy of the sensor probe of this embodiment.

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.

FIG. 5 is a graph showing the relationship between the hydrogen concentration measured value by the telegas method and the hydrogen concentration measured value by the sensor element of the present embodiment.

[Explanation of symbols]

 1, 21; Sensor element 2, 22; Reference electrode 3, 23; Measuring electrode 4, 24; Ceramic insulating tube 5, 29; Glass seal material 8, 25; Lead wire 10, 14; SiC porous filter 11, 15 , 27; Ceramic adhesives

Claims (4)

[Claims] 1. A one-end closed type element made of a perovskite type proton conductive solid electrolyte, a measuring electrode made of a porous electrode formed on the inner surface of the element, and a porous electrode formed on the outer surface of the element. A reference electrode, a sealant separating the reference electrode and the measurement electrode, a means for bringing a reference substance that serves as a reference of galvanic electromotive force into contact with the reference electrode, and the element with its open end side facing outward. A support to support,
A sensor probe for measuring the amount of hydrogen dissolved in a molten metal, comprising: a porous filter fitted into the open end of the element to prevent the molten metal from entering. 2. A one-end closed element made of a perovskite-type proton conductive solid electrolyte, a reference electrode made of a porous electrode formed on the inner surface of the element, and a porous electrode formed on the outer surface of the element. A measuring electrode, a sealing material separating the reference electrode and the measuring electrode, a means for bringing a reference substance that serves as a reference of galvanic electromotive force into contact with the reference electrode, and an element externally fitted to the element so as to project from its closed end. A sensor probe for measuring the amount of hydrogen dissolved in a molten metal, comprising: a sleeve; and a porous filter fitted into an end of a portion of the sleeve protruding from the element to prevent the molten metal from entering. 3. The sensor probe for measuring the amount of hydrogen dissolved in molten metal according to claim 1, wherein the means for bringing the reference material into contact with the reference electrode is a standard gas or a solid reference material. . 4. The porous filter has an average pore diameter of 30.
The sensor probe for measuring the amount of hydrogen dissolved in a molten metal according to any one of claims 1 to 3, wherein the sensor probe is a silicon carbide material having a diameter of not more than µm.