JPH04110650A - Carbon-dioxide/oxygen sensor - Google Patents

Abstract

PURPOSE:To perform the measurement of the concentration of each gas in real time by operat ing an oxygen sensor element and a carbon dioxide gas sensor element under the state wherein the elements are heated to the same temperature, and measuring the concentration of oxygen gas and the concentration of carbon dioxide gas in gas to be detected which is made to flow into O<2-> conductive solid electrolyte. CONSTITUTION:A oxygen sensor element and a carbon dioxide sensor element are heated to the same temperature with a heater 9. When gas to be detected is made to flow into an O<2-> conductive solid electrolyte 1, the gas to be detected comes into contact with detecting electrodes 2 of the oxygen sensor element and a detecting electrode 6 of the carbon dioxide sensor element B at the same time. A reference electrode 3 of the oxygen sensor element is in contact with air. Therefore, in the oxygen sensor element, the sensor output corresponding to the ratio between the partial pressure of the oxygen in the air and the partial pressure of the oxygen gas in the gas to be detected is generated. The output is inputted into a signal processing circuit 13 through lead wires 2a and 3a. At the same time, in the carbon dioxide sensor element, the sensor output corresponding to the partial pressure of the carbon dioxide in the gas to be detected is generated and inputted into the circuit 13 through lead wires 5a and 6a. Thus, the concentration of the oxygen gas and the concentration of the carbon dioxide gas in the gas to be detected are measured.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention uses an oxygen ion conductive solid electrolyte and a sodium ion conductive solid electrolyte to simultaneously measure the oxygen concentration and carbon dioxide concentration in a sample gas. Regarding carbon dioxide gas/oxygen sensors that can be used.

(Prior art) In recent years, monitoring and control of the atmosphere in the fields of horticulture or medicine, measurement of oxygen deficient conditions during work in piping or tunnels, combustion management, and monitoring and control of the atmosphere in experiments related to biotechnology, etc. In this technical field, oxygen concentration and carbon dioxide concentration are measured. It is said that it is more effective to measure these gas concentrations at the same time than to measure each gas individually.

By the way, the conventional method for measuring the oxygen gas concentration in the test gas is to measure the electromotive force generated as the oxygen gas concentration changes in a concentration battery using an oxygen ion (0) conductive solid electrolyte. , a method for determining a change in electromotive force due to a change in oxygen dissolved in an electrolyte in a galvanic cell, a method for measuring a change in resistance of the metal oxide semiconductor due to a change in the amount of oxygen gas adsorbed to the metal oxide semiconductor, A known method is to measure the limit current value generated as a result of a change in oxygen gas concentration when a voltage is applied to an oxygen ion conductive solid electrolyte.

On the other hand, conventionally known methods for measuring the carbon dioxide concentration in a sample gas include a non-dispersive infrared absorption analysis method, a thermal conductivity calculation method, and a diaphragm type glass electrode method.

The following measuring instruments are currently provided on the market in order to measure the oxygen gas concentration and carbon dioxide gas concentration in the test gas by combining the individual measurement methods described above.

That is, 02 - a type in which a concentration battery type oxygen sensor using stabilized zirconia as a conductive solid electrolyte and a non-dispersive infrared absorption analysis type carbon dioxide sensor are connected in series and housed in one container. This is a carbon dioxide gas/oxygen sensor.

(Problem to be Solved by the Invention) However, since the above-mentioned type of carbon dioxide gas/oxygen sensor simply stores the conventional individual carbon dioxide sensor and oxygen sensor in one container, precisely,
It cannot be said that this sensor can measure carbon dioxide sludge concentration and oxygen sludge concentration in real time.

Moreover, this sensor, especially the carbon dioxide sensor, is expensive and large, and has insufficient accuracy, so there is a problem that it lacks versatility.

The present invention solves the above-mentioned problems and can measure carbon dioxide concentration and oxygen gas concentration in real time, and the measured values are highly stable and accurate, and are inexpensive and small in size. The purpose of the present invention is to provide a carbon dioxide/oxygen sensor that can be manufactured in a number of steps.

(Means for solving the problem) By the way, regarding the problem of manufacturing a small carbon dioxide gas sensor at low cost, Kazuki, Sasaki, Saito et al. A sensor has been proposed that is inserted into a sample gas to measure carbon dioxide concentration.

This carbon dioxide gas sensor uses sodium carbonate (
NaxCOs) and sodium ions (N
a”) Conductive solid electrolyte and Na as a standard substance,
Zr25ixPs-30,2 (X is 0≦X≦3
represents a number that satisfies the relationship. Usually, this solid electrolyte is N
It is called ASICON. ) is an all-solid-state sensor that measures changes in the concentration of carbon dioxide in the sample gas as changes in the electromotive force of a sodium concentration battery.

The above-mentioned carbon dioxide gas sensor has an operating principle based on Au (sensing electrode) l NazCOa l NAS I C
It can be expressed as a battery with a configuration of 0NAu (reference electrode), and its operating temperature is 300 to 750°C.

On the other hand, in the case of the aforementioned oxygen sensor using stabilized zirconia as the 02-conducting solid electrolyte, its normal operating temperature is in the range of 500-800°C.

Therefore, since the operating temperatures of this oxygen sensor and the carbon dioxide sensor mentioned above overlap with each other, by combining the two, it is possible to measure the carbon dioxide gas concentration and oxygen gas concentration in the sample dregs in real time. It can be made into a small and inexpensive carbon dioxide/oxygen sensor.

The carbon dioxide/oxygen sensor of the present invention was developed based on the above idea.

That is, the carbon dioxide/oxygen sensor of the present invention has a cylindrical
2-An oxygen sensor element comprising a conductive solid electrolyte and electrodes formed on the inner and outer wall surfaces of the 02-conductive solid electrolyte; 02-Na+a+ solid disposed inside the conductive solid electrolyte an electrolyte, a reference electrode formed on one end of the Na+a+ solid electrolyte in contact with the Na+a+ solid electrolyte, and a reference electrode formed on the other end of the Na+a+ solid electrolyte in contact with the Na+ conductive solid electrolyte. Alternatively, the sensing electrodes formed apart from each other and the Na+a+
A carbon dioxide gas sensor element comprising a conductive solid electrolyte and sodium carbonate bridging between the sensing electrodes; and a heating element surrounding the conductive solid electrolyte.

(Function) First, the oxygen sensor element constituting one of the carbon dioxide scum/oxygen sensors of the present invention is used in a heated state at a temperature of 500 to 800°C.

In this state, the oxygen partial pressure that gives a reference gas with a known oxygen gas concentration or a constant oxygen partial pressure to the electrode (reference electrode) formed in contact with the outer wall surface of the cylindrical 02-conductive solid electrolyte A reference substance is contacted, and a test gas with an unknown oxygen gas concentration is flowed inside the 02-conductive solid electrolyte, and it is applied to the other electrode (sensing electrode) formed by contacting the inner wall surface. When brought into contact, an electromotive force corresponding to the difference in oxygen gas concentration (partial pressure) is generated between the two electrodes. This electromotive force E° is expressed by the following equation.

E' = (RT/ 4 F Lj' n(P O'2
/ P O't) - (1) where, F: Faraday constant, R: gas constant, T: absolute temperature (K
), Po'2+ oxygen gas concentration (partial pressure) in the reference gas,
P O'2 represents the oxygen gas concentration (partial pressure) in the test gas.

Therefore, if the measurement temperature is constant and the oxygen gas concentration of the reference gas is known, the generated electromotive force E° becomes a function of the oxygen gas concentration (partial pressure) in the test gas.

Therefore, if the relationship between the electromotive force and the oxygen gas partial pressure is created in advance as a calibration curve, based on this calibration curve, when the test gas is flowed inside the 02-conductive solid electrolyte, this sensor element From the electromotive force shown, the partial pressure of oxygen gas in the test gas,
That is, the oxygen gas concentration can be known.

On the other hand, the carbon dioxide sensor element is used while being heated to a temperature of 300 to 7500C.

When a test gas containing carbon dioxide comes into contact with the sensor element heated to the above temperature, an electromotive force proportional to the carbon dioxide concentration (partial pressure) is generated between the detection electrode and the reference electrode. This electromotive crab E is expressed by the following formula % formula % F: Faraday constant, R: gas constant, T: absolute temperature (K
), ΔG01: chemical species i chemical species car model formation energy, aI
: Activity of one chemical species, Pl : Partial pressure of one chemical species, P*
It represents the atmospheric pressure for two people (1,01xl 05Pa).

Therefore, if the measurement temperature is kept constant and the activity of Na and 0 in the Na+aI solid electrolyte is kept constant, the electromotive force E generated between the image electrodes is a function of the partial pressure of carbon dioxide in the sample gas. . Therefore, if the relationship between the electromotive force and the partial pressure of carbon dioxide is created as a calibration curve in advance, then based on this calibration curve, the electromotive force that the sensor element will exhibit when inserted into the gas to be measured will be calculated based on this calibration curve. Partial pressure of carbon dioxide in the test gas from electric power,
In other words, it becomes possible to know the concentration.

The carbon dioxide/oxygen sensor of the present invention has the above-mentioned cylindrical 02
- The above carbon dioxide sensor element is arranged inside the conductive solid electrolyte, and O! - The conductive solid electrolyte is surrounded by a single heating element. Therefore, first, the oxygen sensor element and the carbon dioxide sensor element operate in a state where they are heated together to the same temperature by the heating element, and the oxygen gas concentration in the test gas flowing inside the conductive solid electrolyte. is measured by the oxygen sensor element based on equation (1),
At the same time, the carbon gas concentration in the test gas is measured by the carbon dioxide sensor element based on equation (2). That is, measurement of each gas concentration proceeds in real time.

(Embodiments) Hereinafter, each embodiment of the present invention will be described in detail based on the drawings.

FIG. 1 is a configuration diagram of the carbon dioxide/oxygen sensor A (the part surrounded by the broken line) and the entire electromotive force measurement system of the embodiment.

First, in sensor A, the oxygen sensor element is
A cylindrical 02-conductive solid electrolyte 1 having a
2 ~ Inner wall surface 1b and outer wall surface 1c of conductive solid electrolyte 1
Electrodes 2 and 3 are formed in such a way that they are in contact with each other and sandwich a conductive solid electrolyte l between them, and these electrodes 2
．． It consists of lead wires 2a and 3a drawn out from 3.

Here, the electrode 2 acts as a sensing electrode for oxygen gas,
The electrode 3 also acts as a reference electrode for oxygen gas.

02-A conductive solid electrolyte 1 has openings 1d and 1 at both ends.
One opening 1d is connected to a test gas supply source (not shown) via a flowmeter 11 and a pump 12, and the other opening 1e is open. Therefore, the test gas supplied from the supply source by the pump 12 is adjusted in flow rate by the flow meter 11, introduced into the hollow part 1a through the opening 1d, and then led out through the opening 1e.

0 mentioned above! - The conductive solid electrolyte is produced by rubber pressing a specified raw material powder into a cylindrical shape, sintering the resulting cylindrical molded body, and then processing this cylindrical sintered body using a processing machine such as a diamond cutter or lathe. It can be manufactured by cutting into the above shape using a .

Here, as the 02-conductive solid electrolyte, the following formula (MO
xh-, (RyOz)x (where M is Z r", T
h"Hf", represents a tetravalent cation of Ce'+, R is M
g2 +Ca", Sr", Ba", Co",
Divalent cations of Ni", Cu" or Fe", In"
, S03+, Y"Sm", Eu", Gd", Tb
”, Dy3+, Ho”Er”, Tm”, Yb”,
It represents a trivalent cation of Lu"+, and X is 0.05 to 0.
30, and y and Z represent the numbers that make (RyOz) electrically neutral).
B i20. )(RyOz)x (wherein, R is Mg2+
, Ca2+, Sr2+B a”, Co”, N i”
, Cu”, divalent cation of P b2+, Fe”
, In", 3 c3+, Y3+, Sm"Eu", G
d", Tb", Dy", Ho", E r"Tll1
3+, Yb3+, trivalent cation of Lu needle, or W6+
(X represents the number of 0.05 to 0 JOO, y and 2 represent the number that makes (RyOz) electrically neutral)
A compound represented by: can be used.

Each of the 02-conductive solid electrolytes described above has a slightly different internal impedance, so according to the operating principle described above, the electromotive force and response speed of each obtained sensor may also differ. .

However, in this regard, since each of the above-mentioned compounds exhibits high 02-conductivity, there is no problem in practical performance as a sensor.

02-A pair of electrodes 2.3 formed on the inner and outer wall surfaces 1b and 1c of the conductive solid electrolyte 1 are both porous gas diffusion electrodes.

These electrodes can also be formed by sputtering or vapor deposition, but due to the size and shape of the oxygen sensor, we applied a paste containing fine powder of the electrode material to both walls of the 02-conductive solid electrolyte. It is convenient and preferable to form the film by a paste coating pyrolysis method in which the film is then baked at a predetermined temperature. The material for these electrodes is platinum (platinum) because it is a material that does not dissolve oxygen and the constituent materials of the 02-conductive solid electrolyte even at high temperatures, and it is a material that has a catalytic effect on the dissociation reaction of oxygen. Pt) is preferred.

In addition, from the point of view of lowering the operating temperature of the oxygen sensor and increasing the response speed, it is possible to mix 02-conductive solid electrolyte powder into the electrode material powder, as disclosed in Japanese Patent Application Laid-Open No. 50-91389. If you use the paste made from
more effective.

By the way, when the carbon dioxide sensor element described below is heated to a temperature of 400°C or higher, Na2 constituting the sensor element
A portion of COs begins to thermally decompose into Na2O and Ce2.

If the electrode 2 (sensing electrode) of the oxygen sensor element is made of Pt as described above, a solid solution will be generated by the interaction of this Pt, Na from the aforementioned Na2O, and oxygen in the test gas. It is assumed that the Pt electrode 2 deteriorates as a result.

To solve this problem, we use a material that is generally known as an oxide electrode material and has a small difference in thermal expansion from stabilized zirconia, such as the following formula: La1-8S r
, M O3 (wherein M represents a cation such as Mn" or Co"Fe"+, and X represents a number of O≦X and 1.00), or a compound represented by the following formula: La , -z
sr, M', -, M", O, (where Ml is M n "
"F e" represents a cation such as Ca", Mg"+, M2 represents a cation such as Co", Cr", AC+, x, y are each 0≦x<1.00° This can be solved by using a compound represented by the following formula (representing a number of 0≦y≦1,00) as a material for the electrode 2.

Furthermore, even if the electrode 2 is a Pt electrode, as will be described later in other embodiments shown in FIGS. 5 and 6, between the electrode 2 of the oxygen sensor element and the carbon dioxide sensor element B, for example, By interposing the sensor cell 10 made of a heat-resistant material such as a quartz tube, reactions between Na, pt, and oxygen in the electrode 2 can be prevented.

In this oxygen sensor element, lead wires 2a and 3a are drawn out from electrode 2 and electrode 3, respectively, and display circuit 1
It is connected to the signal processing circuit 13 connected to 4. An electromotive force signal at the time of measuring the oxygen gas concentration is taken out from the lead wires 2a and 3a, processed by the signal processing circuit 13, and displayed on the display circuit 14.

These lead wires 2a and 3a are electrode 2 and electrode 3, respectively.
It is preferable that the electrode is made of the same material as the image electrode, and for example, it is preferably fixedly attached to the electrode using platinum paste or the like before or simultaneously with the formation of the picture electrode.

02-The carbon dioxide sensor element B installed in the conductive solid electrolyte 1 will be explained next.

Examples of the carbon dioxide sensor element B used are shown in FIGS. 2, 3, and 4. The carbon dioxide sensor element in Figure 2 is N
A reference electrode 5 and a sensing electrode 6 are formed at both ends of the a+ conductive solid electrolyte 4 in contact with the Na+ conductive solid electrolyte 4, and on the sensing electrode 6 side, this sensing electrode and the Na+
Both conductive solid electrolytes are coated with a film 7 of Na, CO,
It is of the type that is formed.

The carbon dioxide sensor element shown in FIG. 3 is of a type in which an Na+ conductive solid electrolyte 4 and a detection electrode 6 are separated from each other, and a film 7 of Na2COs is formed by bridging them.

In addition, the carbon dioxide sensor element shown in FIG. 4 is the sensor element of the type shown in FIG. , this 02-type is a type in which a reference electrode 5 is attached to a conductive solid electrolyte 8.

In each of these carbon dioxide sensor elements, lead wires 5a and 6a are drawn out from the reference electrode 5 and the detection electrode 6, respectively, and as shown in FIG. It is connected to a signal processing circuit 13 in the same way as the sensor element, and the electromotive force of the sensor is displayed on a display circuit 14.

In the case of these carbon dioxide gas sensor elements, the shape of the Na + conductive solid electrolyte 4 may be cylindrical, but may also be prismatic with a polygonal cross section, or may be a disk or a square plate. good.

The Na + conductive solid electrolyte 4 having such a shape is obtained by molding a predetermined raw material powder, sintering the obtained molded body, and then cutting the sintered body into the shape described above using a processing machine such as a diamond cutter or lathe. It can be manufactured by cutting.

As the Na+ conductive solid electrolyte, the above-mentioned NASIC
In addition to ON, for example, the following formula: Na2O x Aj? to
β-alumina represented by a (in the formula, X represents a number from 5 to 11); the following formula: Na++xMxA I I+-xo,
7 (wherein, M is M g2 +, Ca'', S r'', B
β”-alumina represented by a“CO””, Ni”, Cu2+ divalent cation, and X represents a number from 0 to 2);
M is F e”In 3 +, Sc3+, Y2+, Sm
", Eu", Gd"Tb3+, Dy3+, Ho3+
, E "3+, T [[13+, represents a trivalent cation of y b 2 + Lu3+, X represents a number from 0 to 2]": Compound represented by the following formula 2Nal+p□Z r, -8MxP30
u (wherein M is Mg", Ca", Sr"Ba",
Represents divalent cations of Co", N1", and Cu"+,
X represents the number of O~2); the following formula: N
aM S i+o 1t (wherein, M is Fe”1 n
3 +, SC", Y", Sm", Eu", Gd
"Tb3+, Dy3+, Ho3+, Er3+, Tm",
y b @ +L u” represents a trivalent cation, and X is O
~2), NMS-NAS I CO
Compound called N; following formula: Na5M Si+o
1t (wherein, M is Fe", In", SC",
Y″+, Sm”, Eu”Gd3+, Tb3+, Dy3
+, Ho3+, Er", Tm"Yb", represents a trivalent cation of Lu3+, X represents a number from 0 to 2); -Nap, Ai' 1.7Sio, 304
; Na3S CP 3012 can be used.

Also, JP-A-57-135714, JP-A-59-
The Na+ conductive solid electrolyte proposed in Publication No. 213609, European Patent Publication No. 0067274, etc.
Since Nap has high conductivity even at relatively low temperatures of 300 to 700°C, that is, its internal impedance is small, these can also be used as the Na + conductive solid electrolyte according to the present invention.

Here, since each of the Na+ conductive solid electrolytes described above has a slightly different Na+ concentration and internal impedance, according to the operating principle described above, the electromotive force and response speed of each obtained sensor will also differ. come. however,
In this regard, for example, regarding electromotive force,
By creating a unique calibration curve for each sensor in advance, differences in performance as a sensor can be eliminated, and in terms of response speed, all of the above-mentioned compounds have high N
Since it exhibits a+ conductivity, it does not impede its performance as a sensor in practice.

The reference electrode 5 and the detection electrode 6 formed at both ends of the Na+ conductive solid electrolyte 4 are both porous gas diffusion electrodes.

These electrodes can also be formed by sputtering or vapor deposition, but they can be formed by applying a paste containing fine powder of the electrode material to predetermined locations on the Na + conductive solid electrolyte, and then baking it at a predetermined temperature. Forming by a paste coating pyrolysis method called baking is preferred because it is simple. The material of the electrode used is
Gold (Au) is preferable because Na and oxygen do not form a solid solution even at high temperatures and change over time is less likely to occur.

A lead wire 5a attached to the reference electrode 5 and the detection electrode 6,
6 is preferably made of the same material as the reference electrode 5 and the detection electrode 6, and is preferably fixedly attached to these electrodes using gold paste or the like, for example, before or simultaneously with the formation of the picture electrode.

The film 7 of Na2CO, is made of an aqueous solution of Na2CO3 or N12.
Although an alcohol suspension of COa may be applied to bridge the 02-conductive solid electrolyte 4 and the sensing electrode 6 and then dried, the immobilization state of the Na2COa film 7 is ensured. In order to achieve this, it is preferable to form the layer by applying a NatCOa melt.

That is, NazCOs is heated to a temperature higher than its melting point (851°C) to melt it, and the portion of the Na'' conductive solid electrolyte 4 on the sensing electrode side is immersed in the melt, and then pulled up and the immersed portion is removed. At this time, Nat
Care must be taken to prevent the COa melt from coming into contact with the reference electrode 3.

In the carbon dioxide gas φ oxygen sensor A, the 0 of the oxygen sensor element
! - The outer periphery of the conductive solid electrolyte 1 is surrounded by a heating element 9.

The heating element 9 was prepared by winding a platinum wire around a tube made of a heat-resistant electrically insulating material such as alumina, zirconia, silicon nitride, or aluminum nitride, or by dispersing fine platinum powder in turpentine oil or the like. It can be manufactured by patterning the paste on the surface of the tube using a method such as screen printing and then baking the pattern. In addition to platinum, rhodium, platinum-rhodium alloy, tungsten, and nickel-chromium alloy can also be used as the material for the heating element. In addition, the above-mentioned baking is done outside of the law by masking the surface of the tube and applying vapor deposition, CV
The heating element 9 can also be formed by applying the D method, sputtering method, plasma spraying method, etc., or by electroless plating.

Lead wires 9 a and 9 b for heating elements are drawn from the heating element 9 , and these are connected to a power source 16 via a temperature control circuit 15 .

When the heating element is activated and the oxygen sensor element and carbon dioxide sensor element are heated to the same temperature, 0! - When the test gas flows into the conductive solid electrolyte 1, the test gas comes into contact with the electrode 2, which is the detection electrode of the oxygen sensor element, and the detection electrode 6 of the carbon dioxide sensor element B, almost simultaneously. and,
The electrode 3, which is the reference electrode of the oxygen sensor element, is in constant contact with air, for example.

Therefore, first, the oxygen sensor element produces a sensor output corresponding to the ratio of the oxygen partial pressure in the air (approximately 0.206) to the oxygen gas partial pressure in the test gas, and this produces a sensor output that corresponds to the
a and input to the signal processing circuit 13.

Further, at approximately the same time as the oxygen sensor element operates, the carbon dioxide sensor element also operates, producing a sensor output corresponding to the partial pressure of carbon dioxide in the test gas, which is taken out from the lead wires 5a and 6a and sent to the signal processing circuit 13. is input.

That is, the oxygen gas concentration and carbon dioxide gas concentration in the test gas are measured in real time.

FIG. 5 shows another embodiment.

The sensor of this embodiment is O! - A sensor cell I like a quartz tube with both ends open in the hollow part 1a of the conductive solid electrolyte
A carbon dioxide gas sensor element B is arranged in this sensor cell lO.

With this structure, the electrode 2 of the oxygen sensor element is p
Even if there is a main electrode, as mentioned above, Na2 generated from the carbon dioxide sensor element at an operating temperature of 400°C or higher
Since O is blocked by the sensor cell 10, a reaction between Na, PT, and oxygen on the Pt electrode 2 does not occur, and deterioration of the PT main electrode can be prevented.

FIG. 6 shows yet another embodiment.

In the sensor of this embodiment, a tubular sensor cell 10 is arranged in a hollow part 1a of a 02-conductive solid electrolyte, and a
It has a so-called double-tube structure in which an inlet for the gas to be detected into the sensor cell 10 is separately provided.

A part of the supplied gas to be detected flows from the opening 1d to the hollow part 1.
a, flows out from the opening 1e, and the oxygen gas concentration is measured by the oxygen sensor element, and the other part of the test gas flows into the cell from the opening 10a of the sensor cell IO and flows out from the opening 10b. During this process, the carbon dioxide concentration is measured by the carbon dioxide sensor element.

In the case of the sensor having this structure, as in the case of the embodiment shown in FIG. 5, even if the electrode 2 is a Pt electrode, its deterioration can be prevented.

(Example) Example 1 The carbon dioxide/oxygen sensor shown in FIG. 1 was manufactured as follows.

That is, first, the special grade reagent ythtrium oxide (YzO
a) The powder and zirconium oxide (ZrO□) powder, which is a special grade reagent, were weighed so that the molar ratio was 8:92, and then the two were mixed. The obtained mixed powder was placed in the air for 1
After heat treatment at 000° C. for 2 hours to cause a solid phase reaction and homogenization, the mixture was pulverized in a ball mill for 24 hours. The obtained powder was rubber press molded into a cylindrical shape at a pressure of 1 ton/crl, and the molded body was
Heat treatment was performed at ℃ for 2 hours. A sintered block of ittria-stabilized zirconia was obtained. This sintered block was processed using a diamond cutter and a lathe to form a cylinder 1 having an outer diameter of 8-1, an inner diameter of 6-1, and a length of 60 mm.

Surfaces 1 of the inner and outer walls of the longitudinal center of this cylinder 1
bX lc, platinum wire 2a with a diameter of 0.5 mm.

After applying platinum paste to a length of 10 mm with 3a attached thereto, the whole was heat-treated at 1100°C for 1 hour to form electrodes 2 and 3, respectively, to obtain an oxygen sensor element.

Next, 99.9% purity sodium phosphate (Na, P
O4) reagent (anhydrous) and zirconium silicate (ZrSi
O+) reagents were weighed so that the molar ratio was 1=2, and then both were mixed. The obtained mixed powder was heated to 1147°C for 4 hours.
After heat treatment for 8 hours to cause a solid phase reaction and homogenization, the mixture was pulverized in a ball mill for 24 hours. The obtained powder was rubber press molded at a pressure of 1 ton/ci, and then the molded product was heat-treated at 1247° C. for 12 hours. A sintered block of NASI CON was obtained.

This sintered block was processed using a diamond cutter and a lathe to form a cylinder 4 with a diameter of 2 mm and a length of 8 mm. Gold wires 5a, 6a with a diameter of 0.3L are attached to the outer periphery of both ends of this cylinder 4.
Further, gold paste was applied to the parts where the gold wire was wound, and then the whole was heat-treated at 700° C. for 1 hour to form a reference electrode 5 and a detection electrode 6.

Next, the detection electrode 6 side of the cylinder 4 was immersed in a melt made by melting anhydrous sodium carbonate, which is a special grade reagent, at a temperature of 860°C, and then pulled out and left to cool in the atmosphere to dissolve Na2CO.
A carbon dioxide sensor element as shown in FIG. 2 was manufactured by forming the film 7 of No. 3.

Next, a nickel-chromium alloy wire with a diameter of 0.8 mm was wound around the outer wall of an alumina tube with an outer diameter of 12 mm, an inner diameter of 10 mm, and a length of 40 mm, and multiple points of the alloy wire were bonded to the alumina tube with an alumina-based inorganic adhesive. After fixing, the entire outer surface was covered with alumina ceramic fiber to produce a cylindrical heating element IO.

The carbon dioxide sensor element B is inserted into the hollow part 1a of the oxygen sensor element described above, and after aligning the electrode 2 of the oxygen sensor element and the detection electrode 6 of the carbon dioxide sensor element, the element is inserted into the cylindrical heating element 10. Assembled a carbon dioxide gas/oxygen sensor.

This sensor was incorporated into the measurement system shown in FIG. 1, the operating temperature was maintained at 625°C by the temperature control circuit I5, and the flow meter 11 was adjusted to achieve a carbon dioxide concentration of 1100 pp and an oxygen gas concentration of 1.
A test gas of 8.0% (both nitrogen balance) was alternately introduced into the hollow portion 1a at a flow rate of 150 −/min.

Sensor outputs were obtained in real time from the oxygen sensor element and carbon dioxide sensor element. Calculate the concentration gradient (m/decade) of the sensor output from these values, and also calculate the theoretical concentration gradient under the above conditions obtained from equations (1) and (2) above, and calculate the above measured value. The ratio (%) was also calculated. The above results are shown in Table 1.

Table 1 () shows the ratio (%) to the theoretical concentration gradient. Example 2 Example 2 Except that the Na+ conductive solid electrolyte in the carbon dioxide gas sensor element was β-alumina produced by the following method. A carbon dioxide/oxygen sensor was manufactured in the same manner as in Example 1.

Anhydrous sodium carbonate of special reagent grade and aluminum hydroxide, also of special reagent grade, are converted to 1 in terms of Na2O:Aβ203.
・Weigh it so that it is 6 (molar ratio), mix both,
The resulting mixture was heat-treated at 800°C for 12 hours to cause a solid phase reaction and homogenized, and then heated in a ball mill for 2 hours.
Grinding treatment was carried out for 4 hours. 1 to
n/cr! The molded product was rubber press molded at a pressure of 1,297° C. for 12 hours to obtain a β-alumina block.

For this type of sensor, the generated electromotive force was measured under the same conditions as in Example 1, and the concentration gradient was determined. The results are shown in Table 2.

Table 2 () shows the ratio (%) to the theoretical concentration gradient. A carbon dioxide/oxygen sensor was manufactured in the same manner as in Example 1, except that the material was silver (Ag).

That is, first, the special grade reagent bismuth oxide (B1203
) powder and yttrium oxide (Y2O3) powder, which is a special grade reagent, were weighed so that the molar ratio was 75+25 (in terms of BLOa:Y2O3), and then the two were mixed. The obtained mixed powder was heat-treated in air at 700° C. for 3 hours to cause a solid phase reaction and homogenized, and then pulverized in a ball mill for 24 hours. The obtained powder is
After rubber press molding into a cylindrical shape at a pressure of ton/car, the molded product was heat-treated at 900° C. for 20 hours. A block of stabilized bismuth sintered body was obtained. This sintered block was processed using a diamond cutter and a lathe to create a tube with an outer diameter of 6 mm and an inner diameter of 6 mm.

Surfaces 1 of the inner and outer walls of the longitudinal center of this cylinder l
After coating silver base to a length of 10 mm with silver wires 2a and 3a of 0.5 mm in diameter attached to electrodes 2 and lc, the entire body was heat-treated at 700°C for 1 hour to form electrodes 2,
Electrodes 3 were each formed to form an oxygen sensor element.

For this type of sensor, the generated electromotive force was measured under the same conditions as in Example 1, and the concentration gradient was determined. The results are shown in Table 3.

Table 3 () shows the ratio (%) to the theoretical concentration gradient.Example 4 Carbon dioxide was measured in the same manner as in Example 1, except that carbon dioxide sensor element B was of the type shown in Figure 4.・Manufactured an oxygen sensor.

The carbon dioxide sensor element shown in FIG. 4 was manufactured as follows.

First, the sintered block of ittria-stabilized zirconia produced in Example 1 was processed using a diamond cutter and a lathe to form a disk 8 with a diameter of 4 mm and a thickness of 0.5+nn+.

Next, this disk was manufactured in Example 1 with a diameter of 20 mm.
, was placed on one end face of a NASIC○N cylinder 4 having a length of 8 cm, and the whole was heated to about 1350° C. on a ceramic heater to fuse the two together. At this time, the end face of the cylinder 4 has a NAS
ICON powder was attached to facilitate fusion.

Next, a reference electrode 5 and a lead wire 5a are attached to the end surface of the disk 8.
, a detection electrode 6 and a lead wire 6a, Na2 on the end face of the cylinder 4.
A COa film 7 was formed in the same manner as in Example 1 to obtain a carbon dioxide sensor element.

For this type of sensor, the generated electromotive force was measured under the same conditions as in Example 1, and the concentration gradient was determined. The results are shown in Table 4.

(Margins below) Table 4: The ratio (%) to the theoretical concentration gradient (effects of the invention) As is clear from the above explanation, the carbon dioxide/oxygen sensor of the present invention can be By doing so, it is possible to make the operating temperatures of the oxygen sensor element and the carbon dioxide sensor element the same and measure the oxygen gas concentration and carbon dioxide gas concentration in the test gas in real time. Moreover, the measured values are highly stable and highly accurate, as is clear from Tables 1 to 4. In addition, the shape can be made smaller,
It is also possible to manufacture it at low cost.

Therefore, this carbon dioxide gas/oxygen sensor, for example,
It can be used as a device for monitoring or controlling a medical treatment atmosphere in a medical field, a device for monitoring or controlling a biotechnology-related experiment atmosphere, a device for preventing oxygen deficiency, and further, an industrial measuring device.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing a sensor according to an embodiment of the present invention and an electromotive force measurement system incorporating the same, Fig. 2 is a front view showing an example of a carbon dioxide sensor element used, and Fig. 3 is a diagram showing another carbon dioxide sensor. FIG. 4 is a front view showing an example of the element, FIG. 4 is a front view showing another example of the carbon dioxide sensor element, FIG. 5 is a sensor configuration diagram showing another embodiment of the present invention, and FIG. 6 is still another embodiment. It is a sensor configuration diagram showing an aspect. 1...0 conductive solid electrolyte, 1a...hollow part, i
b...inner wall surface, lc...outer wall surface, 1d...opening (test gas introduction part), le...opening (test gas outlet part), 2...electrode ( (Detection electrode of oxygen sensor element)
, 2a... Lead wire, 3... Electrode (reference electrode of oxygen sensor element), 3a... Lead wire, 4... Na+ conductive solid electrolyte, 5... Reference electrode of carbon dioxide sensor element, 5a ...Lead wire, 6...Detection electrode of carbon dioxide sensor element, 6a...Lead wire, 7...Na2COa
membrane of, 8...02-disk of conductive solid electrolyte, 9
... Heating element, 9a, 9b... Riet wire for heating element, l
O...sensor cell, 10a...opening (test gas inlet), 10b...opening (test gas outlet),
DESCRIPTION OF SYMBOLS 11... Flowmeter, 12... Pump, 13... Signal processing circuit, 14... Display circuit, 15... Temperature control circuit, 16... Power supply.

Claims (1)

[Claims] An oxygen sensor element comprising a cylindrical oxygen ion conductive solid electrolyte and electrodes formed on an inner wall surface and an outer wall surface of the oxygen ion conductive solid electrolyte; installed inside the oxygen ion conductive solid electrolyte; a sodium ion conductive solid electrolyte, a reference electrode formed at one end of the sodium ion conductive solid electrolyte in contact with the sodium ion conductive solid electrolyte, and the other end of the sodium ion conductive solid electrolyte. a carbon dioxide gas sensor element comprising: a sensing electrode formed in contact with or separated from the sodium ion conductive solid electrolyte; and sodium carbonate bridging between the sodium ion conductive solid electrolyte and the sensing electrode; , a heating element surrounding the oxygen ion conductive solid electrolyte.