JPH0687049B2 - Sensor probe with solid reference material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a solid reference material used for measuring the concentration of hydrogen or water vapor in exhaust gas discharged from a boiler, a sintering furnace, an automobile or the like. More particularly, the present invention relates to a sensor probe provided with a solid reference material that uses a solid reference material as a reference for galvanic electromotive force.

[Prior Art] Measuring the concentration of hydrogen and water vapor in high temperature exhaust gas is
It is indispensable for accurately obtaining the combustion efficiency of boilers, combustion furnaces, automobile engines, etc. Therefore, there is a demand for the development of a highly reliable hydrogen and water vapor concentration measuring device that operates stably in high-temperature exhaust gas.

Therefore, conventionally, there has been proposed a hydrogen or water vapor sensor which uses a proton conductive solid electrolyte made of a perovskite type oxide such as strontium oxide and cerium oxide (SrCeO ₃ ) as a sensor element (JP-A-58-5).
0458,60-263853,61-2064,61-3054,61-14566).
This solid electrolyte has proton conductivity at a temperature of 400 ° C. or higher, a senna element made of this solid electrolyte is formed in a closed type, and the inner surface and the outer surface thereof are covered with a porous inner electrode and outer electrode, respectively. It is configured to wear. Then, a reference gas that serves as a reference for the Galauvani electromotive force, that is, a gas containing hydrogen or water vapor of a predetermined concentration is enclosed in this sensor element.

When a sensor probe for measuring the concentration of hydrogen or water vapor using this perovskite-type proton conductive solid electrolyte is inserted into the gas to be measured, the inner surface becomes different due to the difference in hydrogen or water vapor concentration between the reference gas and the gas to be measured. An electromotive force is generated between the electrode and the outer surface electrode. Then, by detecting this electromotive force, the concentration of hydrogen or water vapor in the gas to be measured can be measured.

However, since the above-mentioned conventional technique uses a gas containing a predetermined concentration of hydrogen or water vapor as a reference substance,
There are the following problems.

When the solid electrolyte, the gas introduction pipe, or the like is damaged, the reference gas leaks into the measurement atmosphere, and the measurement becomes impossible or a measurement error occurs. Further, in this case, the leaked reference gas pollutes the measurement atmosphere.

In order to supply the reference gas to the probe and circulate it, a gas circulator or the like is required, and a compact device cannot be obtained.

Therefore, the present inventors have developed a solid reference material that exhibits a stable hydrogen activity at high temperatures, and have proposed using this solid reference material for a hydrogen or water vapor sensor (Japanese Patent Laid-Open No. 63-269053).

[Problems to be Solved by the Invention] However, in the above-described hydrogen or water vapor sensor, it is difficult to completely seal between the reference gas or solid reference substance and the measurement atmosphere because the entire sensor is exposed to high temperature. There is a drawback. That is, a seal material that seals between the reference gas or solid reference substance and the measurement atmosphere is required to have high heat resistance. Therefore, conventionally, a glass O-ring, a ceramic sealing material or the like has been used as a sealing material for sealing between the reference gas or the solid reference material and the measurement atmosphere. However, when using these sealing materials,
A crack is likely to occur in the sensor element or the seal material due to the difference in the coefficient of thermal expansion between the seal material and the sensor element. Therefore,
It is difficult to seal the reference gas or solid reference substance and the measurement atmosphere for a long period of time. In addition, in order to avoid cracks in the sensor element and the sealing material, it is necessary to take care so that the temperature change becomes slow when heating the sensor probe to the operating temperature and cooling it to room temperature after use. Yes, it is complicated.

The present invention has been made in view of such problems,
The occurrence of cracks in the sensor element and sealing material can be suppressed, the heating time when the sensor is used and the cooling time after use can be shortened, and the solid reference substance can be sufficiently sealed from the gas to be measured for a long period of time. It is an object of the present invention to provide a sensor probe provided with a solid reference substance capable of achieving the above.

[Means for Solving the Problems] A sensor probe provided with a solid reference material according to the present invention is
A one-end closed sensor element formed of a perovskite-type proton conductive solid electrolyte, a sleeve externally fitted to the closed end side portion of the sensor element and fixed to the outer surface of the sensor element, and the sleeve and the sensor element. A solid reference material filled between the two and serving as a reference for galvanic electromotive force, a reference electrode formed on the outer surface of the sensor element in contact with the solid reference material, and a measurement formed on the inner surface of the sensor element. It is characterized by having a pole, a seal portion provided at the open end of the sensor element, and an introducing member for introducing the gas to be measured into the sensor element.

It is preferable that a flange is provided on an outer surface of the open end side portion of the sensor element, and the open end of the sensor element is closed by a seal portion having a sealing material sandwiched between both sides of the flange. .

[Operation] In the present invention, the solid reference substance is arranged outside the one-end closed type sensor element, and the gas to be measured is introduced into the sensor element through the introduction part. As described above, in the present invention, it is not necessary to expose the entire sensor to a high temperature atmosphere in order to measure the concentration of hydrogen or water vapor by introducing the gas to be measured into the sensor, and to raise only the closed end side of the sensor element. It may be heated to a predetermined temperature for power measurement. By doing so, the mounting portion of the sleeve to the sensor element and the open end side portion of the sensor element have a relatively low temperature, the thermal expansion and thermal shock of the sensor element are suppressed, and the sensor element and the sealing material. It is possible to avoid the occurrence of cracks. Therefore, the sensor heating time at the start of use and the sensor cooling time after use can be shortened.

In this case, if a flange is provided on the open end side portion of the sensor element, the flange is sandwiched from both sides by the seal portion via a sealing material such as silicon rubber or a heat resistant gasket, so that the inside of the sensor element is covered. Leakage of measurement gas can be easily prevented. If the temperature of the flange portion is 200 ° C. or lower, silicon rubber can be used as the sealing material, and the risk of cracks in the sealing material can be significantly reduced. For this reason, the size of the sensor element and the position and shape of the heating furnace that heats the sensor are properly selected so that the temperature of the open end side of the sensor element when using the sensor is 200 ° C or less, and this sensor is used. It is preferable that a flange is provided at the end of the element and the open end of the sensor element is closed by using silicon rubber as a sealing material at the flange.

The proton conductive solid electrolyte is Ca, Sr and B.
at least one element selected from the group consisting of a
As a component, at least one element selected from the group consisting of Ce, Zr, Ti and Hf is used as a B component, and Yb, Y, Sc, Zn, Nd, Mg, I
When M component is at least one element selected from the group consisting of n, Sm, Dy, Eu, Ho, Gd, Tm, Ca and La, the general formula
It is a perovskite complex oxide represented by AB _1-x M _X O _3-Y . However, both X and Y are numerical values in the range of 0 to 0.5.

Examples of such perovskite-type composite oxides include SrCe _0.95 Yb _0.05 O _3-Y , BaCe _0.9 Nd _0.1 O _3-Y and CaZr _0.9 I
n _0.1 O _3-Y etc.

EXAMPLES Examples of the present invention will be specifically described below with reference to the accompanying drawings.

FIG. 1 is a sectional view showing a sensor probe according to an embodiment of the present invention. The sensor element 1 has a tubular shape with one end closed, and the outer peripheral surface of the open end projects outward and the collar 1a
Is provided. A reference electrode 3 and a measurement electrode 4 are formed on the outer circumference and the inner surface of the closed end portion of the sensor probe 1 by depositing a porous material.

A cylindrical sleeve 5 is externally fitted to approximately half of the sensor element 1 on the closed end side, and the closed end of the sensor element 1 is arranged substantially at the center inside the sleeve 5. The end of the sleeve 5 on the side of the sensor element 1 is fixed to the outer peripheral surface of the sensor element 1 at a substantially central position by a ceramic adhesive 6.
The other end is sealed by the ceramic sealing portion 8. The sleeve 5 is filled with the fixed reference substance 2 from the other end side thereof to the vicinity of the ceramic sealing portion 8, and further, the alumina powder 7 is filled on the solid reference substance 2, and these solid reference substances are filled. 2 and alumina powder 7 are sealed in the sleeve 5 by the ceramic sealing portion 8.

On the outer peripheral surface of the sensor element 1, a strip-shaped printed lead wiring 9a is formed along the longitudinal direction from the reference electrode 3 to substantially the center of the sensor element 1 in the longitudinal direction. Also, at the end of the printed lead wiring 9a on the central side of the sensor element 1, a lead is provided.
10a is connected, whereby the reference electrode 3 is led to an external measuring device (not shown) via the printed lead wiring 9a and the lead 10a.

On the outer peripheral surface of the open end side portion of the sensor element 1, basically cylindrical metal holders 11a and 11b are externally fitted, and these holders 11a and 11b are arranged on the collar 1a so as to sandwich the collar 1a from both sides. It is fixed. O-rings 15 made of heat-resistant rubber are interposed between the holders 11a, 11b and the collar 1a, respectively.
The O-ring 15 hermetically seals the both.

Further, an introducing pipe 13 is inserted into the sensor element 1 through a lower end opening 12 of a holder 11b, and the introducing pipe 13 has a tip portion thereof slightly separated from an inner surface of the closed end of the sensor element 1. It is arranged concentrically inside. This introduction pipe 13
Is to introduce the gas to be measured into the sensor element 1,
An opening 12 of the holder 11b is fixed between the introduction pipe 13 and the inner surface of the holder 11b so that gas can flow therethrough. A pattern lead wiring 9b is formed on the introduction tube 13 along the longitudinal direction thereof, and the end of the wiring 9b on the tip end side of the introduction tube is connected to the measurement electrode 4. Further, a lead 10b is connected to an end portion of the wiring 9b on the proximal end side of the introduction tube, whereby the measurement electrode 4 is connected to the pattern lead wiring 9b and the lead 10b.
It is electrically led to the external measuring device via b.

Sensor element 1 is SrCe _0.95 Yb _0.05 O _3-Y , CaZr _0.9 In
It is molded with a proton conductive solid electrolyte consisting of a perovskite type complex oxide such as _0.1 O _3-Y , BaCe _0.95 Y _0.05 O _3-Y .

The reference electrode 3 and the measurement electrode 4 are formed by baking a porous material such as Pt, Ni or an oxide conductor.

Further, as the solid reference substance 2, for example, there is a mixture of cerium sulfate and an alkali carbonate mixed with Ni powder, or hydroxyapatite.

In the sensor probe configured as described above, the tip of the sensor element 1 on which the reference electrode 3 and the measurement electrode 4 are arranged is the electric furnace 14
It is inserted into the electric furnace 14 so as to be in the center of the heating area of the.

Next, the operation of the sensor probe according to the present embodiment will be described.

The gas to be measured is supplied into the sensor element 1 formed of a solid electrolyte through the introduction pipe 13, and the closed end portion of the sensor element 1 in which the reference electrode 3 and the measurement electrode 4 are arranged is fixed by the electric furnace 14. Heat to the electromotive force measurement temperature. Then, between the inner surface of the solid electrolyte contacting the measurement gas containing hydrogen or water vapor and the outer surface of the solid electrolyte contacting the solid reference substance 2, the concentration of hydrogen or water vapor in the measurement gas and the solid reference substance Due to the difference between the reference concentrations of 2, the protons migrate. A galvanic electromotive force is generated between the measurement electrode 3 and the reference electrode 4 due to the movement of the protons. By detecting this electromotive force via the leads 10a and 10b, the hydrogen or water vapor concentration of the gas to be measured can be detected. The gas to be measured is discharged to the outside of the sensor element 1 through the opening 12, and the gas to be measured is continuously supplied to the inside of the sensor element 1 through the introduction pipe 13. As a result, the hydrogen concentration or the water vapor concentration of the measurement gas can be continuously measured.

In this case, in this embodiment, the electric furnace 14 mainly heats the closed end of the sensor element 1 when the sensor is used.
Then, the mounting portion (adhesive 6) of the sleeve 5 and the collar 1a
Is located outside the heating zone of the electric furnace 14 and is therefore maintained at a relatively low temperature. As a result, thermal expansion of the sensor element 1 at the mounting portion of the sleeve 5 and the open end of the sensor element 1 is suppressed, and cracks in the sensor element 1 and the sealing material (O-ring 15) can be avoided. If the temperature of the collar 1a of the sensor element 1 is 200 ° C. or lower when using the sensor, the O-ring 15 made of silicon rubber can be used. This significantly reduces cracking of the O-ring 15.

Next, the result of the heat cycle test in which the hydrogen concentration in the argon gas was repeatedly measured a plurality of times using the sensor probe according to the present embodiment described above will be described.

Measurement of Hydrogen Concentration A sensor probe having the structure shown in FIG. 1 was used. The sensor element 1 of this sensor probe is SrCe _0.95 Yb _0.05 O _3-Y , Ca
It is formed of a perovskite-type proton conductive solid electrolyte having a composition such as Zr _0.9 In _0.1 O _3-Y or BaCe _0.95 Y _0.05 O _3-Y .

After the porous electrodes (reference electrode 3 and measurement electrode 4) made of Pt, Ni or an oxide conductor are baked on the inner surface and the outer surface of the sensor element 1, the sleeve made of ceramic or metal is formed on the outer side of the sensor element 1. 5 was fixed with a ceramic adhesive 6. Then, the inside of the sleeve 5 is filled with a solid reference substance 2 such as a mixture of mixed salt of cerium sulfate and alkali carbonate and Ni powder, or hydroxyapatite, and the alumina powder 7 is added on top of the solid reference substance 2. After filling with, the upper end portion of the sleeve 5 was sealed with a ceramic sealing portion 8.

Further, the reference electrode 3 outside the sensor element 1 and the sensor element 1
In order to seal the measuring electrode 4 inside the
The flange 1a of the above was sandwiched between the metal holders 11a and 11b via the two heat resistant rubber O-rings 15 and sealed.

The hydrogen concentration in the Sargon gas was measured using the apparatus thus configured. That is, the tip of the sensor probe was heated from room temperature to 700 ° C., and the relationship between the hydrogen concentration in argon gas and the electromotive force of the sensor probe was investigated. afterwards,
The sensor probe was cooled to room temperature. Then, this heating and cooling (heat cycle) was repeated 50 times, and changes in the electromotive force characteristics of the sensor probe were investigated.

FIG. 2 is a graph showing the electromotive force characteristics of the sensor probe when the heat cycle is repeated once, twice and 50 times, with the horizontal axis representing hydrogen concentration and the vertical axis representing electromotive force. As is clear from FIG. 2, the electromotive force characteristics of the sensor probe according to this example did not change even after 50 heat cycles. From this, it is clear that the sensor probe according to the present embodiment is excellent in airtightness of the solid reference material and has high reliability.

As described above, according to the present invention, the solid reference substance is arranged outside the sensor element and the gas to be measured is introduced inside the sensor element. Therefore, when measuring the hydrogen or water vapor concentration, the sensor element is It suffices to heat only the closed end of. Therefore, the seal portion and the sleeve mounting portion that close the open end of the sensor element can be provided at a relatively low temperature portion. Therefore, even if the heat cycle is repeated, the generation of cracks in the sensor element and the sealing material can be avoided. Further, it is possible to shorten the heating time of the sensor element at the start of use of the sensor and the cooling time after use. Furthermore, the maintenance of the sensor is facilitated, and a small and highly reliable sensor probe can be obtained.

[Brief description of drawings]

FIG. 1 is a sensor probe provided with a solid reference material according to an embodiment of the present invention, and FIG. 2 is a graph showing the result of the heat cycle test. 1; Sensor element, 1a; Tsuba, 2; Solid reference material, 3; Reference electrode, 4;
Measurement electrode, 5; Sleeve, 6; Adhesive, 7; Alumina powder, 8; Ceramic sealing part, 9a, 9b; Pattern lead wiring, 10a, 10b; Lead, 11a, 11b; Holder, 12; Opening part, 13 ; Introduction tube, 14; Electric furnace, 15; O-ring

Claims (5)

[Claims] 1. A one-end closed sensor element formed of a perovskite-type proton conductive solid electrolyte, a sleeve externally fitted to a closed end side portion of the sensor element and fixed to an outer surface of the sensor element, and this sleeve. And a solid reference material serving as a reference for galvanic electromotive force between the sensor element, a reference electrode formed on the outer surface of the sensor element in contact with the solid reference material, and an inner surface of the sensor element. A sensor provided with a solid reference substance, comprising: a measuring electrode formed on the substrate; a seal portion provided at the open end of the sensor element; and an introducing member for introducing a gas to be measured into the sensor element. probe. 2. A flange is provided on an outer surface of the open end side portion of the sensor element, and the seal portion has a seal material sandwiched between both sides of the flange, whereby the flange is formed. The sensor probe provided with the solid reference substance according to claim 1, wherein an open end side portion of the sensor element is closed. 3. The sensor probe having a solid reference material according to claim 2, wherein the sealing material is made of silicone rubber. 4. The perovskite type proton conductive solid electrolyte is a composite oxide of strontium and cerium,
The main component is any one selected from the group consisting of a complex oxide of barium and cerium and a complex oxide of calcium and zirconium. Sensor probe with solid reference material of. 5. The perovskite-type proton conductive solid electrolyte contains at least one element selected from the group consisting of indium, scandium, ytterbium, magnesium, bismuth, aluminum, gallium, yttrium and neodymium. A sensor probe comprising the solid reference material according to claim 4.