JP2878603B2 - Sensor for measuring dissolved amount of hydrogen 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 for measuring the amount of dissolved hydrogen in molten metal, which measures the concentration of hydrogen in the molten metal using a solid electrolyte member having proton conductivity.

[0002]

2. Description of the Related Art Conventionally, there are the following methods for measuring the hydrogen concentration in a molten metal.

Initial Bubble Method First, a molten metal is sampled, and the molten metal is placed in a measurement room having a built-in heater. Thereafter, the pressure in the measurement chamber is reduced, and the amount of hydrogen is calculated from the temperature and the pressure in the measurement chamber when bubbles are first generated from the surface of the molten metal.

Vacuum Solidification Method The sampled molten metal is solidified under reduced pressure, the state of bubbles in the sample after solidification is observed, compared with the specific gravity of a standard sample, and the amount of hydrogen gas is determined from the state of bubbles in the cross section of the sample.

Partial pressure equilibrium method A small amount of inert gas is injected into a molten metal and circulated. When the hydrogen gas diffuses into the inert gas and reaches an equilibrium state, the inert gas is recovered and the thermal conductivity is measured. The hydrogen concentration in the inert gas is analyzed by a type detector, gas chromatograph, mass spectrometer, or the like, and the hydrogen concentration in the molten metal is determined from the analysis result and the temperature of the molten metal.

Vacuum extraction method A sample obtained by sampling a molten metal, rapidly cooling and solidifying the sample is heated in a vacuum, and the amount of hydrogen gas released from the sample is measured by a thermal conductivity detector, a gas chromatograph, and a mass spectrometer. Alternatively, the amount is determined using an infrared analyzer or the like.

However, these conventional methods for measuring the hydrogen concentration in molten metal have the disadvantage that the measurement takes a long time, the measurement accuracy is poor, or an expensive measuring device is required. Neither is suitable for measuring the amount of hydrogen dissolved at the actual casting site.

As a measuring method developed to solve these problems, there is a gas concentration cell type hydrogen sensor using a proton conductive solid electrolyte. In this type of sensor, a reference electrode made of a porous conductor and a reference substance which comes into contact with this reference electrode and serves as a reference for electromotive force of a concentration cell are arranged on one surface side of a member made of a solid electrolyte having proton conductivity. The measurement electrode provided on the other surface is brought into contact with the molten metal, and the molten metal is generated from the electromotive force generated by the difference in hydrogen activity between the hydrogen partial pressure on the reference electrode side and the hydrogen concentration in the molten metal. It detects the hydrogen concentration inside. This sensor has the advantages that it can directly measure the hydrogen concentration in the molten metal, has a high response speed, and can obtain high accuracy.

[0009]

However, the sensor using the above-mentioned conventional proton conductive solid electrolyte is
When used for a long time, there is a problem that the measurement electrode reacts with a component in the molten metal due to contact with the molten metal, and it becomes impossible to measure the hydrogen concentration. In addition, when a large amount of flux or the like is used in the molten metal processing, there is a problem that the measurement electrode is corroded in a short time and the sensor does not operate.

The present invention has been made in view of the above problems, and it is possible to prevent corrosion of an electrode due to a molten metal and a molten metal processing flux, thereby extending the life of a sensor and dissolving hydrogen in the molten metal for a long time. It is an object of the present invention to provide a sensor for measuring the amount of dissolved hydrogen in molten metal which can stably measure the amount of hydrogen.

[0011]

According to the present invention, there is provided a sensor for measuring the amount of hydrogen dissolved in a molten metal according to the present invention, comprising a solid electrolyte member formed of a solid electrolyte material having proton conductivity, and a solid electrolyte member provided on the solid electrolyte member. A reference electrode and a measurement electrode, a reference substance for giving a reference of electromotive force of the concentration cell to the reference electrode, an insulating sleeve fixed to the solid electrolyte member to form a space connected to the measurement electrode, and the space A first filling layer composed of ceramic powder or fiber filled on the measurement electrode side, and a conductive powder or fiber filled on an end of the space on the side opposite to the measurement electrode. And a second filling layer that is configured and electrically connected to the measurement electrode.

[0012]

In the present invention, an insulating sleeve is fixed to a solid electrolyte member, and a first filling layer and a second filling layer are provided in a space formed by the insulating sleeve and connected to a measurement electrode.
Is provided. The first packed layer is made of ceramic powder or fiber such as alumina, zirconia, magnesia and silicon carbide,
Since the second filling layer is made of powder or fiber of carbon or metal, these filling layers have air permeability. That is, in the hydrogen dissolved amount measurement sensor according to the present invention, the space inside the sleeve is a gas chamber,
This gas chamber is interposed between the measuring electrode and the molten metal to
It prevents the body electrolyte member and the molten metal from coming into direct contact. This can prevent the reaction between the measurement electrode and the molten metal and the corrosion of the measurement electrode due to flux or the like.

In the sensor according to the present invention, the sleeve side is immersed in the molten metal during measurement. Then, the second filling layer comes into contact with the molten metal, and the molten metal and the measuring electrode are electrically connected via the second filling layer. Therefore, the molten metal has the same potential as the measuring electrode. For example, by immersing the conductive member in the molten metal and measuring the potential difference between the conductive member and the reference electrode, the electromotive force of the gas concentration cell is measured. Can be measured.

At this time, it is conceivable that the molten metal invades the second filling layer. However, in the present invention,
The first filling layer arranged on the measurement electrode side is made of ceramic powder or fiber. Since the ceramic powder or fiber has a large ability to prevent the intrusion of molten metal, the first filling layer is melted in the first filling layer. It is possible to reliably prevent metal from entering. Thereby, the molten metal does not come into direct contact with the measuring electrode. Therefore, the filling layer needs to have a two-layer structure of a first filling layer composed of ceramic powder or fiber and a second filling layer composed of conductive powder or fiber. .

[0015]

Next, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a cross-sectional view showing a sensor for measuring the amount of dissolved hydrogen in molten metal according to a first embodiment of the present invention. The solid electrolyte member 1 is made of CaZr _0.9 In _0.1 O _3-x
(However, x is 0 to _0.05 ), SrCe _0.95 Yb _0.05 O
_3-x and BaCe _0.9 Nd _0.1 O _3-x are formed in a tubular shape whose one end is closed by ceramic or glass having a composition having proton conductivity, such as BaCe _0.9 Nd _0.1 O _3-x, and the inner surface and the outer surface of the solid electrolyte member 1 As the measurement pole and the reference pole respectively
For example, porous electrodes 2a and 2b made of Pt, Ni, an oxide conductor, or the like are formed by baking.

A ceramic pipe 4 is fitted to the closed end of the solid electrolyte member 1, and the pipe 4 and the solid electrolyte member 1 are joined by an inorganic adhesive. The joint between the solid electrolyte member 1 and the pipe 4 is hermetically sealed with a glass sealing material 6.
The glass sealing material 6 is a dense glass whose coefficient of thermal expansion is close to the coefficient of thermal expansion of the solid electrolyte member 1 in the temperature range of 300 to 1000 ° C., which is the operating temperature range of the sensor, and whose pour point is higher than the operating temperature of the sensor. It is preferably a sealing material.

The glass sealing material 6 is coated with a coating material 7 made of ceramics. This coating material 7 is for preventing the reaction between the glass sealing material 6 and the molten metal.

A metal pipe 9 made of stainless steel is inserted into the inside of the ceramic pipe 4, and the tip of the metal pipe 9 is joined to the porous electrode 2b. The solid electrolyte member 1 is connected via the metal pipe 9.
Then, a reference gas 8 whose hydrogen gas partial pressure is adjusted to be constant is supplied as a reference substance. Also, this metal pipe 9
It also acts as a lead for the porous electrode 2b.

On the other hand, a ceramic sleeve 3 is fitted on the open end side of the solid electrolyte member 1. An extraction electrode 2c electrically connected to the porous electrode 2a is provided near the end of the solid electrolyte member 1 on the inner surface of the sleeve 3. Further, at least one type of ceramic powder selected from the group consisting of alumina, zirconia, magnesia and silicon carbide is filled as a first filling layer 12 inside the solid electrolyte member 1.
A conductive fiber made of carbon or metal is filled as a second filling layer 13 between the end on the open end side and the tip of the sleeve 3. The second filling layer 13 is electrically connected to the porous electrode 2a via the extraction electrode 2c.

In the sensor for measuring the amount of dissolved hydrogen according to the present embodiment, the sleeve 3 is immersed in the molten metal. In this case,
The filling layers 12 and 13 in the sleeve 3 can prevent the molten metal from entering the sleeve 3, and the inside of the sleeve 3 serves as a gas chamber to prevent direct contact between the molten metal and the solid electrolyte member 1. Can be prevented. Further, the porous electrode 2a serving as the measurement electrode is electrically connected to the molten metal via the extraction electrode 2c and the second filling layer 13.

Next, a gas containing a predetermined concentration of hydrogen or water vapor is supplied as a reference gas 8 to the porous electrode 2b side of the solid electrolyte member 1 through a metal pipe 9. Then, an electromotive force is generated between the porous electrodes 2 a and 2 b on both sides of the solid electrolyte member 1 due to the difference in the hydrogen activity between the molten metal and the reference gas 8. By measuring this electromotive force, the hydrogen concentration in the molten metal is measured. This measurement principle is performed by measuring the electromotive force of a gas concentration cell using a proton conductive solid electrolyte substance.

A gas concentration cell type hydrogen sensor using a solid electrolyte exhibiting proton conductivity operates stably at a high temperature and shows an electromotive force close to the theoretical value given by the following equation (1).

[0023]

E = (RT / 2F) ln [P _H1 (1) / P _H2 (2)] where E is electromotive force (V), R is gas constant, F is Faraday constant, T is absolute temperature, P _H1 (1) and P _H2 (2) are hydrogen partial pressures on the measurement electrode side and 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 follows the Sieverts rule of Equation 2 below.

[0025]

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 molten metal.

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.

In general, the hydrogen concentration in a molten metal depends on the hydrogen partial pressure in the gas phase in contact with the molten metal and the temperature of the molten metal. The dependence of the hydrogen partial pressure and the temperature of the molten metal depends on the Sievert rule and Henry's law. (Henry) rules. For this reason, the hydrogen concentration S can be expressed by the following equation (3).

[0028]

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

Then, the sleeve 3 side of the sensor shown in FIG. 1 is immersed in the molten metal, and the hydrogen concentration in the molten metal is measured. That is, from the electromotive force generated between the reference electrode and the measurement electrode, the hydrogen partial pressure P _H2 is obtained by using the above-described equation (1), and this hydrogen partial pressure is substituted into the equation (3) to obtain the hydrogen concentration S in the molten metal. Can be requested.

For example, a carbon rod is inserted into the molten metal, the potential difference between the carbon rod and the metal pipe 9 is measured, and the amount of hydrogen dissolved in the molten metal is detected based on the result. be able to.

In this case, in this embodiment, a ceramic sleeve 3 is fitted to the solid electrolyte member 1 and the molten metal and the porous electrode serving as a measuring electrode are filled by the filling layers 12 and 13 in the sleeve 3. Since direct contact with 2a can be prevented, deterioration and corrosion of the porous electrode 2a due to molten metal or flux can be suppressed. Therefore, the sensor for measuring the amount of dissolved hydrogen according to the present embodiment has a long sensor life and can measure the amount of dissolved hydrogen in the molten metal over a long period of time. It is conceivable that molten metal may enter the second filling layer 13 during use. However, even if the molten metal enters the second filling layer 13, the first filling layer 12 may be formed of ceramic powder. Because of its high ability to prevent the intrusion of molten metal,
Of the molten metal can be reliably prevented from entering the filled layer 13 of the first embodiment.

FIG. 2 is a sectional view showing a sensor for measuring the amount of dissolved hydrogen in molten metal according to a second embodiment of the present invention. This embodiment is different from the first embodiment in that a solid reference material 18 is used as a reference material, and other configurations are basically the same as those in the first embodiment. Are denoted by the same reference numerals, and their detailed description is omitted.

In this embodiment, the inside of the ceramic pipe 4 fitted to the closed end side of the solid electrolyte member 1 is
As the solid reference material 18, for example, a mixture of aluminum phosphate and an electronic conductive oxide or a mixture of a metal and a metal hydride is charged. These substances have the property that the hydrogen or steam activity is always kept constant. At the end of the pipe 4 on the side opposite to the solid electrolyte member 1, alumina cement 11 and ceramic filler 1
4 are filled in this order from the outside, and the solid reference material 1
8 is hermetically sealed by the alumina cement 11 and the filler 14. Incidentally, the lead 1 0 are electrically connected to the porous electrode 2b is a reference electrode, a solid reference material 1
8, the filler 14 and the alumina cement 15 are inserted and led out. In this embodiment, the same effects as in the first embodiment can be obtained.

A description will now be given of the result of actually manufacturing the sensor for measuring the amount of dissolved hydrogen in molten metal according to the first embodiment of the present invention and examining the initial response characteristics thereof.

First, CaZr _0.9 In _0.1 O _{3- x} which is a perovskite-type proton conductive oxide (where x is 0 to 0)
0.05), a tubular solid electrolyte member 1 having one end closed was formed. Then, porous Pt electrodes 2a and 2b were baked at a temperature of 900 ° C. on the inner and outer surfaces of the solid electrolyte member 1 as a measurement electrode and a reference electrode, respectively.

Next, a pipe 4 made of alumina (having an outer diameter of 6.5 mm and an inner diameter of 4.0 mm) was placed on the closed end side of the solid electrolyte member 1.
5 mm and a length of 500 mm) were fixed using an alumina ceramic adhesive, and the bonded portion was hermetically sealed with a glass sealing material 6. Further, the gas sealing material 6
Was coated with an alumina ceramic coating material 7. Further, an alumina sleeve 3 was fitted and fixed to the open end side of the solid electrolyte member 1. Then, on the inner surface of the sleeve 3, an extraction electrode 2c electrically contacting the porous electrode 2a was formed.

Thereafter, about 1
A filler 12 containing graphite powder in a percentage by weight and the balance being alumina powder was filled. In this case, the filling rate of the filler 12 was set to 75% in order to reduce the gas volume in the space inside the sleeve. Further, the graphite powder is heated by the heat of the molten metal when measuring the amount of dissolved hydrogen, reacts with the oxygen present in the sleeve 3 to quickly remove the oxygen, thereby shortening the initial response time of the sensor. There is.

Next, the solid electrolyte member 1 in the sleeve 3
A carbon fiber was filled as the conductive fiber 13 between the open end of the sleeve 3 and the tip of the sleeve 3. Also, a stainless steel pipe 9 is inserted inside the alumina pipe 4, and the tip of the pipe 9 is connected to the porous electrode 2b.
And was fixed in electrical contact.

In this way, four sensors having the same structure according to the embodiment were manufactured, and these sensors were inserted into an aluminum alloy having a temperature of 700 ° C. dissolved in a graphite crucible, and the electromotive force response of the sensors was measured. It was measured. At the time of measurement, an argon gas containing 1% by volume of hydrogen was introduced into the reference electrode side through a stainless steel pipe 9. Further, the hydrogen concentration in the molten metal was adjusted by changing the gaseous hydrogen gas concentration on the aluminum alloy dissolved in the graphite crucible. Furthermore, by inserting a carbon rod into the molten metal and measuring the potential difference between the carbon rod and the stainless steel pipe 9, the electromotive force between the reference electrode and the measurement electrode of the solid electrolyte member 1 is measured. A measurement was made. The temperature in the molten metal was measured with a chromel-alumel thermocouple (K thermocouple). Then, the sensor life was examined.

For comparison, four conventional sensors for measuring the amount of dissolved hydrogen of the type in which the measuring electrode was brought into direct contact with the molten metal were manufactured, and the sensor life was examined in the same manner as in the examples. The results are shown in Table 1 below.

[0041]

[Table 1]

As is clear from Table 1, Conventional Examples 1 to
The sensor life of each of the sensors of Example 4 is as short as 13 hours or less, whereas the sensor life of each of the sensors of Examples 1 to 4 is 65 hours or more, and the sensor life is extremely long as compared with the conventional example. Was.

In each of the above embodiments, a case was described in which a ceramic pipe was previously attached to the solid electrolyte member. However, the ceramic pipe was fixed to the solid electrolyte member with an inorganic adhesive during use. Is also good. In this case, as a sealing material for sealing the joint between the solid electrolyte member and the ceramic pipe, a dense glass sealing material whose softening point is equal to or lower than the operating temperature of the sensor and whose pour point is equal to or higher than the operating temperature of the sensor is used. It is preferred to use.

[0044]

As described above, the sensor for measuring the amount of dissolved hydrogen in molten metal according to the present invention has an insulating sleeve, and a ceramic powder or fiber is placed in the space connected to the measuring electrode inside the sleeve. And the second filling layer made of conductive powder or fiber and electrically connected to the measuring electrode, so that the measuring electrode directly contacts the molten metal. Can be prevented, and the reaction between the molten metal and the measuring electrode and the flux
Corrosion of measuring Teikyoku can be suppressed that. Therefore, the sensor for measuring the amount of dissolved hydrogen according to the present invention has an effect that the amount of dissolved hydrogen in the molten metal can be stably measured over a long period of time.

[Brief description of the drawings]

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

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1: Solid electrolyte member 2a, 2b; Porous electrode 3: Sleeve 4: Ceramic pipe 6; Glass sealing material 7; Coating material 8; Reference gas 9; Metal pipe 12;

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01N 27/406 G01N 27/416

Claims (3)

(57) [Claims] 1. A solid electrolyte member formed of a solid electrolyte material having proton conductivity, a reference electrode and a measurement electrode provided on the solid electrolyte member, and a reference of an electromotive force of the concentration cell with respect to the reference electrode. And a first insulating material that is fixed to the solid electrolyte member to form a space connected to the measurement electrode, and a ceramic powder or fiber filled on the measurement electrode side of the space. And a second electrically conductive powder or fiber filled at the end of the space opposite to the measurement electrode and electrically connected to the measurement electrode.
A sensor for measuring the amount of dissolved hydrogen in molten metal, comprising: 2. A solid electrolyte member formed in a tubular shape, one end of which is closed by a solid electrolyte material having proton conductivity; a reference electrode provided on an outer surface of the solid electrolyte member; A reference substance that provides a reference for the electromotive force of the concentration cell, a measurement electrode provided on the inner surface of the solid electrolyte member, and an open end side of the solid electrolyte member are fitted to form a space connected to the measurement electrode. An insulating sleeve;
A first filling layer made of ceramic powder or fiber filled on the measurement electrode side of the space, and a powder having conductivity filled at an end of the space on the side opposite to the measurement electrode or A sensor for measuring the amount of dissolved hydrogen in molten metal, comprising: a second filling layer made of fiber and electrically connected to the measurement electrode. 3. The ceramic powder or fiber is at least one selected from the group consisting of alumina, zirconia, magnesia and silicon carbide, and the conductive powder or fiber is any one of carbon and metal. 2. The method as claimed in claim 1, wherein said one side comprises one side.
Or the sensor for measuring the amount of dissolved hydrogen in molten metal according to 2.