JP3032441B2 - Ozone sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small-sized electric sensor used for controlling ozone concentration in an ozone generator or an ozone utilization device, or detecting leaked ozone.

[0002]

2. Description of the Related Art Since ozone has a strong oxidizing effect, it is used in various fields such as treatment of water supply and sewerage, medical treatment, food industry, and air conditioning for the purpose of deodorization and sterilization. However, while having such useful utility value, even a very small amount of ozone is extremely harmful to the human body, so it is necessary to reliably control the amount of generated ozone and detect leaked ozone. By the way, the measurement of the ozone concentration, which has become more necessary,
Conventionally, redox titration, absorption spectroscopy, ultraviolet absorption spectroscopy, and the like have been generally used for detection.
These methods have the drawback that they require time and labor, and require large and expensive equipment. On the other hand, recently, a simpler method for measuring the ozone concentration has been demanded. As one of the methods, for example, an In ₂ O ₃ metal oxide such as that disclosed in JP-A-63-298148 is used. A simple method using an ozone sensor as an electric element has been proposed.

[0003]

All of the above-mentioned methods of analytical measurement, which have been generally performed in the past, generally require large-scale equipment and complicated operations, and are expensive everywhere. It has the disadvantage that it cannot be used for On the other hand, in the case of an ozone sensor using a metal oxide such as In ₂ O ₃ as a sensitive body, which has been proposed as a simple method for measuring ozone concentration, the sensitivity and response of a thin-film sensor manufactured by printing or the like are particularly high. Although it has excellent properties, it has a problem in terms of stability over time. Accordingly, there has been a strong demand for a small, lightweight, and inexpensive sensor that has a long life, is highly reliable, and is inexpensive. The present invention has been made in view of this problem, and has as its object to improve the temporal stability of an ozone sensor.

[0004]

Means for Solving the Problems] ozone sensor of the present invention of claim 1, an In ₂ O3 containing 2-7% of SnO ₂ by weight
And a pair of electrodes provided at portions of the gas sensitizer that are separated from each other and formed of a coating layer containing bismuth as an additive.

In the ozone sensor according to the second aspect of the present invention, the amount of bismuth added is Bi ₂ O with respect to the total amount of In ₂ O ₃ and SnO _2.
It is characterized by being ₃ to 15 wt% in ₃ conversion.

According to a third aspect of the present invention, in the ozone sensor according to the first aspect, the gas sensitizer has a structure including particles, and bismuth exists in at least a grain boundary layer of the particles. It is characterized by.

According to a fourth aspect of the present invention, in the ozone sensor according to the first aspect, the gas sensitizer has a structure including particles, and the average particle diameter of the particles in the particle group is one.
It is characterized in that it is 0 to 50 nm.

According to a fifth aspect of the present invention, in the ozone sensor according to the first aspect, the gas sensitive body is formed in a film shape.

According to a sixth aspect of the present invention, there is provided a method for manufacturing an ozone sensor, wherein a solution or dispersion containing bismuth as an additive to a compound containing indium and a compound containing tin is wet-coated on a substrate.
Forming a coating layer by drying after coating by a method, and providing a pair of electrodes at mutually separated portions of the coating layer.

[0010] manufacturing process of the ozone sensor of the invention of claim 7, further in the production method of the ozone sensor according to claim 6, by firing the coating layer of the at 700 ° C. to 900 ° C., and In ₂ O ₃ A sensitive body in which bismuth is present in at least a grain boundary layer of a group of particles mixed with SnO ₂ is formed on a substrate.

[0011]

[Action] According to an invention of claim 1 and 6, the sensitive ozone sensor element as the In ₂ O ₃ containing 2-7% of SnO ₂ in a weight ratio main structure and then the coating layer containing as additives bismuth The use of a body improves the stability over time. In particular, the amount of bismuth added is Bi _2.
O ₃ in terms of in In ₂ O ₃ and of the total amount of SnO ₂ 3 to 15%
Within this range, the stability over time is improved. As in the invention of claim 3, when bismuth exists at least in the grain boundary layer of the particle group constituting the sensitive body, the ozone detection sensitivity is improved. Bismuth can be added to the sensitizer in a simple substance, an oxide, a salt or other forms. The existence state of bismuth in the sensitizer is considered to have various forms depending on the manufacturing conditions of the sensor and the like. However, it was confirmed by elemental analysis that the bismuth usually exists as Bi ₂ O ₃ . When the average particle diameter of the particle group is 10 to 50 nm as in the invention of claim 4, the initial characteristics and the aging characteristics show desirable stability. When the sensitive body is in the form of a film as in the invention of claim 5, the performance of the sensitive body can be easily controlled to a desired value, and the productivity and the yield are high. The coating layer is formed at a temperature of 700 ° C.
By constituting at 900 ° C. can effectively to reach the grain boundary layer of particles of bismuth controls the average diameter of the particles of the coating layer to the desired range.

[0012]

【Example】

[Structure and Production] FIG. 1 is a schematic sectional view showing one embodiment of a thin film ozone sensor element 10 according to the present invention. As shown in the figure, 2.5 mm width × 1.5 mm length × 2.5 mm width × 5.0 mm length × 0.5 mm thickness
A sensitive film 2 having a thickness of about 100 nm is provided. Sensitive body membrane 2
Is a compound of In and Sn, preferably, indium 2-ethylhexanoate and tin p-toluate (Sn / (In + Sn) = 5/1 by weight ratio of metal indium and metal tin)
The mixture was prepared by applying a solution prepared by adding bismuth as an additive mainly to the alumina substrate (a mixture having a ratio of 00). In addition to the above, an experiment was conducted on a sample in which the ratio of the amounts of Sn and In was changed, but Sn / (In + S
Those with n) in the range of 3/100 to 10/100 showed high sensitivity (see FIG. 7). A number of samples were prepared with varying amounts of bismuth. The alumina substrate coated with the solution is fired at 800 ° C. to obtain a sensitive body. In addition, as a coating method, an aqueous solution containing each component, a wet film forming method such as a dip method using a dispersion liquid, a spin coating method, a screen printing method, and the like are used for uniformity of film thickness, high productivity, and yield. It is suitable in this respect. The amount of bismuth added is 0 (no addition) in terms of Bi ₂ O ₃ , 1, ₃ , 5, 10, 15, 20, 2,
Eight kinds of 5 wt% were used. Bismuth was added by dispersing a separately prepared ultrafine powder of Bi ₂ O ₃ having an average particle size of 1 nm in the solution. Reference numerals 3, 3 ', 7, and 7' denote gold electrodes for the sensitive body and the heater, respectively, formed on the substrate in advance. 1. On the back surface of the alumina substrate, a known printing method is used.
A RuO ₂ thick film heater having a width of 5 mm × a length of 3 mm × a thickness of 10 μm was formed. The reason why RuO ₂ is used as the heater 4 is that it is hardly affected by ozone. As the heater 4, a thin film such as Pt can be used in addition to RuO ₂ .
When the prepared sensitizer was observed with a transmission electron microscope and subjected to elemental analysis, the additive Bi ₂ O ₃ was found to be In ₂
Mixed particles composed of a solid solution or the like in which ₂ O ₃ and SnO ₂ are mixed and a metal element of both oxides is partially substituted in part (average particle diameter: 1
(0-50 nm) group and on the grain boundary layer. When the amount of added Bi ₂ O ₃ was small, the proportion of Bi ₂ O ₃ present in the grain boundary layer tended to be relatively large. The firing temperature and the average particle size will be described later.

[Measurement of Response Characteristics] Using the sensor element sample 10 thus manufactured, response characteristics to ozone were measured by the method described below. First, the sensor element 10 is set in a measurement box having a capacity of about 1.5 liters filled with clean air, and 6 V is applied to a RuO ₂ thick film heater 4 formed on the back surface of the substrate 1 of the sensor element 10 by a DC power supply (not shown). By applying the voltage, the temperature of the sensor element 10 was maintained at 300 ° C., and the resistance value (R _A ) of the sensor element 10 was measured. The measurement of the resistance value of the sensor element 10 was performed by the circuit shown in FIG. That is, a load resistor 6 having a resistance value of 100 KΩ is connected in series with the sensor element 10, and a voltage of 1 V is applied by the DC power supply 5. Both ends of the load resistor 6 are connected to a voltmeter (not shown) via output terminals 8 and 9. A circuit for actually using the sensor element 10 is substantially the same as the circuit.

Then, ozone is injected into the measuring box and uniformly diffused so as to have a concentration of 0.1 ppm. Wait until the resistance value of the sensor element 10 becomes stable, and then the resistance value of the sensor element 10 at that time ( R _G ) was measured to determine the sensitivity.
The sensitivity was represented by a value (R _G / R _A ) obtained by dividing the resistance value (R _G ) of the sensor element 10 in the ozone mixed air by the resistance value (R _A ) of the sensor element 10 in the air. The measurements for each respective ones of the added amount of the eight kinds of bismuth performed for a sample sensor five increments for each kind, the resistance value of each five element (R _A) and sensitivity (R _G / R _A 4) are shown in FIG. The resistance value of each sample sensor element 10 was 1 when no bismuth was added.
The relative values are shown below. As the amount of added Bi ₂ O ₃ increased, the resistance of the sensor element 10 increased. According to the observation with an electron microscope, it is inferred that the resistance value of the sensor element largely depends on the amount of Bi ₂ O ₃ having high resistance at the grain boundary. On the other hand, the sensitivity was _{3 when} the amount of Bi ₂ O ₃ was 3
Approximately the same was observed in the range of 感 度 15 wt%, but when the amount of Bi ₂ O ₃ exceeded 15 wt%, the sensitivity sharply decreased. From a practical point of view, it is desirable that the resistance value of the device is not extremely large and the sensitivity is high. In that sense, it is considered that the amount of bismuth added is preferably up to 15 wt%.

[Change over time] Next, the change over time in the sensor characteristics was measured. 2 sensor elements
Electric current was continuously supplied in air at 0 ° C. and 60% RH, taken out at predetermined time intervals, and the resistance of the element was measured in a measuring box in the same manner as described above to determine the sensor sensitivity. Energization was performed for a total of 5000 hours. Sensor element resistance value (R
FIG. 5 shows the change over time of the change rate of _A ), and the sensitivity (R _G / R)
FIG. 6 shows the change over time in the rate of change in _A ). The addition amount of Bi ₂ O ₃ aging of the sensor element resistance and sensitivity in the case of the sensor in the range of 3 to 15% is remained small and stable, the sensor size have or smaller amount than that range It was found that the change in sensor element resistance and sensitivity with time was large. In particular, it was found that the tendency was large when Bi ₂ O ₃ was not added and when the added amount was 20 wt% or more. The ozone sensor according to the present invention, which contains Bi ₂ O ₃ in an amount of ₃ to 15 wt%, exhibits excellent characteristics such as little change over time and stable initial characteristics. Also, when a bismuth compound other than Bi ₂ O ₃ was used, good results were obtained when the addition amount was ₃ to 15 wt% in terms of Bi ₂ O ₃ .
In the case of the present invention, the average particle size of the particles constituting the sensitive body is 10
If it is less than nm, the sensitivity is rather large, but the change over time of the sensor characteristics due to the progress of sintering of the particles is not preferable. On the other hand, when the average particle size exceeds 50 nm, the change with time is relatively small, but the sensitivity is low because the specific surface area is small. In the present invention, the average particle size is 10 to 50 nm.
It has been found that in the case of the above, desirable initial properties and aging properties are exhibited.

Although the thin-film sensor element has been described in detail in the description of the above embodiment, the average particle size of powder and bismuth It is desirable that the amount added be in the above range.
Further, if the firing temperature of the sensitive body was in the range of 700 to 900 ° C., substantially the same performance as that of the above-described example could be obtained. According to transmission electron micrographs, when the sintering temperature is lower than 700 ° C., the sintering of the particles of the sensitive body is insufficient, so that bismuth does not sufficiently enter the grain boundary layer, and in this case, the characteristics are stabilized. Did not contribute much. On the other hand, when the firing temperature exceeded 900 ° C., most of the added bismuth was concentrated in the grain boundary layer, and in this case, the resistance was extremely high and the sensitivity was low, which was not practical. As is clear from the detailed description of the above embodiments, the ozone sensor according to the present invention has extremely excellent characteristics. In the above embodiment, the case where the coating method was used in the method of manufacturing the gas sensitive body was described.However, various wet film forming methods such as a printing method and a spin coating method can also be used. A sensor having the same characteristics as in the example was obtained. Further, the starting material is not limited to those shown in the examples, and any material suitable for the production of the present invention, such as indium nitrate or tin oxalate, may be appropriately selected and used as long as it is suitable for the production method of the present invention. it can. The structure and configuration of each part of the sensor element, as well as the substrate material and the electrode material, can be freely designed or used without departing from the gist of the invention.

[0017]

The ozone sensor according to the first aspect of the present invention has excellent stability over time in gas detection sensitivity irrespective of the size and weight of the element due to the addition of bismuth. Suitable for applications such as concentration control and ozone detection. The ozone sensor according to the second aspect of the present invention has high stability over time because the added amount of bismuth is in the range of 3 to 15 wt%. In the ozone sensor according to the third aspect of the present invention, the ozone detection sensitivity is improved by the presence of bismuth in at least the grain boundary layer of the particles constituting the sensitive body. In the ozone sensor according to the fourth aspect of the invention, when the average particle diameter of the particle group is 10 to 50 nm, the initial characteristics and the aging characteristics show desirable stability. In the ozone sensor according to the fifth aspect of the present invention, since the sensitive body is in the form of a film, the performance of the sensitive body can be easily controlled to a desired value, and the productivity and the yield are high. According to the method of manufacturing an ozone sensor according to the sixth aspect of the present invention, an ozone sensor element having a uniform sensitive substance thin film can be efficiently manufactured at a high yield by forming a coating layer by a wet method. According to the method for manufacturing an ozone sensor according to the seventh aspect of the present invention, the ozone sensor has a temperature of
By baking at 00 ° C., bismuth is present at least in the grain boundary layer, whereby a device having high temporal stability can be manufactured.

[Brief description of the drawings]

FIG. 1 is a sectional view of an embodiment of an ozone sensor element according to the present invention.

FIG. 2 is a plan view of the ozone sensor element shown in FIG.

FIG. 3 is a circuit diagram for measuring a resistance change of the ozone sensor element shown in FIGS. 1 and 2;

FIG. 4 is a graph showing changes in resistance and sensitivity with respect to changes in the amount of bismuth added to the ozone sensor shown in FIGS. 1 and 2;

FIG. 5 is a diagram showing a change with time of the element resistance of the ozone sensor element shown in FIGS. 1 and 2;

FIG. 6 is a diagram showing a change over time in the sensitivity of the ozone sensor element shown in FIGS. 1 and 2;

FIG. 7 is a diagram illustrating a weight ratio of a metal component of Sn to In: Sn / (In + S);
n) _A diagram showing the relationship between (wt%) and sensitivity (R _G / R _A ).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Ozone sensitive body 3, 3 ', 7, 7' Electrode 4 Heater 5 DC power supply 6 Load resistance 8, 9 Output terminal 10 Sensor element

──────────────────────────────────────────────────続 き Continuation of front page (72) Nobuyuki Yoshiike, Inventor 1006 Kazuma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References 65892 (JP, A) JP-A-5-157718 (JP, A) JP-A-5-26833 (JP, A) JP-A-60-71942 (JP, A) JP-A-2-126146 (JP, A) JP-A-63-194307 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 27/12 JICST file (JOIS)

Claims (7)

(57) [Claims] 1. In ₂ O containing ₂ to 7% by weight of SnO _2
An ozone sensor including a gas sensitive body comprising a coating layer containing ₃ as a main constituent and containing bismuth as an additive, and a pair of electrodes provided at mutually separated portions of the gas sensitive body. 2. The amount of bismuth added is In ₂ O ₃ and SnO _2.
2. The ozone sensor according to claim 1, wherein the total amount of the ozone sensor is ₃ to 15 wt% in terms of Bi2O3. 3. The ozone sensor according to claim 1, wherein the gas sensitizer has a structure composed of particles, and bismuth exists in at least a grain boundary layer of the particles. 4. The ozone sensor according to claim 1, wherein the gas sensitizer has a structure including particles, and the particles of the particles have an average particle diameter of 10 to 50 nm. 5. The ozone sensor according to claim 1, wherein said gas sensitive body is in the form of a film. 6. A step of applying a solution or a dispersion containing bismuth as an additive to a compound containing indium and a compound containing tin as an additive to a substrate by a wet method , followed by drying to obtain a coating layer. Providing a pair of electrodes at portions of the layer that are spaced apart from each other. 7. A sensitizer in which bismuth is present in at least a grain boundary layer of a mixed particle group of In ₂ O ₃ and SnO ₂ by firing the coating layer at 700 ° C. to 900 ° C. 7. The method for manufacturing an ozone sensor according to claim 6, wherein