CA1221736A - Gas detecting elements and process for producing the same - Google Patents
Gas detecting elements and process for producing the sameInfo
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- CA1221736A CA1221736A CA000490569A CA490569A CA1221736A CA 1221736 A CA1221736 A CA 1221736A CA 000490569 A CA000490569 A CA 000490569A CA 490569 A CA490569 A CA 490569A CA 1221736 A CA1221736 A CA 1221736A
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- thin film
- gas detecting
- organic compound
- detecting element
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
- G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
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- Life Sciences & Earth Sciences (AREA)
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- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
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- Investigating Or Analyzing Materials By The Use Of Fluid Adsorption Or Reactions (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A gas detecting element capable of detecting with high sensitivity and selectivity a reducing gas having a low concentration is obtained by providing a thick catalyst layer having one or more metals of the platinum group, on an In-Sn-O thin film disposed on an insulating substrate.
A gas detecting element capable of detecting with high sensitivity and selectivity a reducing gas having a low concentration is obtained by providing a thick catalyst layer having one or more metals of the platinum group, on an In-Sn-O thin film disposed on an insulating substrate.
Description
~2;~736 GAS DETECTING ELEMENTS AND
PROCESS FOR PRODUCING Lowe SAME
BACKGROUND OF THE INVENTION
This invention relates to cJas detecting elements and to processes for producing the same and more particularly to a gas detecting element capable of detecting a reducing gas in air with high sensitivity and selectivity and a process for producing the same.
Heretofore, known elements for detecting a reduce in gas in air are those gas detecting elements where-in a sistered body of a metal oxide semiconductor exhibiting N-type semiconductor characteristics such as Snow, Zoo, or Foe is used. In such elements, when these metal oxide semiconductors come into con tact with a reducing gas, their electric conductivity is increased. A gas is detected by measuring the change of electric resistance value.
In recent years, compact and multi functional elements have been sought. Studies have been carried out on the use of thin film-type elements in place of the sistered body-type gas detecting elements describe Ed above. Such a thin film-type element has a thin film structure obtained by depositing a metal oxide semiconductor having gas sensitivity as described above by a thin film-forming process such as sputter-in, vapor deposition, or CUD.
'I
I
In both sistered body-type yes detecting elements and thin ~ilm-type gas detecting elements, the use of a metal oxide semiconductor alone generally provides a gas detecting element having low sensitivity and insufficient selectivity. For this reason, ordinarily noble metals such as platinum (Pi) and palladium (Pod) are being used as catalysts with the aim of increasing the sensitivity of the element. That is, Pi or Pod is directly added to the metal oxide semiconductor.
Alternatively, a catalyst layer supporting Pi or Pod is formed on the metal oxide semiconductor.
When such measures are carried out, the sensitivity is improved as compared with that in the case wherein no catalyst is used. However, the gas detecting element still does not exhibit sufficient sensitivity to detect a reducing gas having a low concentration. Further, when various reducing gases are present, highly sense-live and selective detection of a particular reducing gas is extremely difficult because erroneous function-in of the element is induced by the influence of other reducing gases. Particularly in the case of gases which adversely affect a human body even at a low concentra-lion, such as COY it has been extremely difficult to eliminate erroneous functioning due to the other reduce in gases in order to detect them. Furthermore, when the gas detecting element is to be used in a general home, the elimination of erroneous functioning of the gas detecting element due to miscellaneous gases, particularly alcohol vapor is an important problem.
While an element having a stunk oxide thin film (Japanese Patent Laid Open Publn. Noah/
198~) and an element having an indium oxide thin film (Japanese Patent Laid-Open Publn. Noah/
1984) are known as gas detecting elements heretofore proposed, even greater improvement of sensitivity as well as selectivity is desired.
SUMMARY OF THE INVENTION
It is therefore an object of the present invent lion to provide a thin film-type gas detecting element by which a reducing gas having a low concentration can be detected with high sensitivity, particularly a detecting element by which carbon monoxide (CO) can be selectively detected with high sensitivity at a low temperature range (from room temperature to about 120C), and methane (SHEA) and propane (C3H8) can be selectively detected with high sensitivity at a high -0 temperature range (from 350 to 450C).
It is another object of the present invention to provide a process for producing a thin film-type gas detecting element.
According to one aspect of the present invention, there is provided a gas detecting element comprising an insulating substrate provided with a pair of electrodes, an Insane thin film so provided on the surface of said insulating substrate as to cover said electrodes, and a catalyst layer laminated on said thin elm and comprising a carrier and a-t least one of platinum group metals supported on said carrier.
According to another aspect of the present invent lion, there is provided a process for producing gas detecting element which comprises a first step of forming an Insane thin film on the surface of an insulating substrate provided with a pair of electrodes by applying as a coating a thin film-forming starting-material solution obtained by dissolving an organic compound containing In and an organic compound contain-in Sun in a solvent, onto the surface of said insulate in substrate so as to cover said electrodes, drying said applied solution, and thereafter firing resulting structure to pyrolyze said organic compounds; and (2) a second step of laminating a catalyst layer on said thin film by applying onto said thin film a slurry containing a catalyst powder obtained from an aqueous solution containing one or more compounds of platinum group metal wherein a carrier powder is immersed there-in, drying said slurry, and thereafter firing the result-in structure.
BRIEF DESCRIPTION OF THE DRAWINGS
While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the present 12;~ I
invention, it is believed that the invention will be better understood from the following detailed descrip-lion taken in connection with the accompanying drawings, in which:
FIG. 1 is a cross-sectional view of a gas detect-in element according to the present invention;
FIG. 2 is a perspective view of a gas detecting device in which the element shown in FIG. 1 is used;
and I FIG. 3 is a graph indicating the variation of sensitivity with compositional ratio of In and Sun.
DETAILED DESCRIPTION OF THE INVENTION
-FIGS. 1 and 2 illustrate an example of an element according to the present invention. FIG. 1 is a cross-sectional view of a cylindrical element, and FIG. 2 is a perspective view showing one example of the state of use of the element.
Referring to FIG. 1, the outer cylindrical sun-face of a cylindrical substrate 1 made of an insulate in material such as alumina or Malta is provided with a pair of electrodes 2. The substrate 1 and the electrodes 2 are covered with an Insane thin layer 3.
The thin layer 3 is covered with a catalyst layer 4.
Thus an element of the present invention is formed The film thickness of the Insane thin film is preferably in the range of from 1,000 A to 1 micrometer.
If the film thickness is more than 1 micrometer, its ~;~Z~'73~
sensitivity to reducing gases is reduced. If -the film thickness is less than 1,000 A, sufficient sensitivity cannot be obtained. The thickness of the catalyst layer 4 is preferably in the range of from 10 to 50 micrometers. If the thickness of the catalyst layer is outside this range, catalytic effects such as those on sensitivity and selectivity are reduced.
As shown in FIG. 2, the thus constituted clement of the present invention is mounted and retained on pins 6 vertically provided on an insulating plate 5 in such a state that the element does not come into con-tact with other parts. Lead wires 7 are provided for electrodes. A heater 8 is provided centrally through the element in order to adjust the surface temperature (working temperature) of the element.
A process for producing an Insane thin film will be described.
The Insane thin film according to the present invention is formed by pyrolyzing an organic compound containing In and an organic compound containing Sun.
Specific amounts of In-containing organic compounds such as In metal soap (e.g., indium octylate), In-containing resin salts, alkoxides and Run wherein R is an alkyd or aureole group, and specific amounts of Sun-containing compounds such as Sun metal soap (e.g., tinoctylate), Sn~con~aining resin salts, alkoxides and Run wherein R is an alkyd or aureole group art dissolved 9L'~2~'73~
in suitable solvents such as Tulane, Bunsen and n-bottle alcohol -to prepare thin film forming starting-material solutions having desired concentrations.
A solution of this character is then applied to the outer cylindrical surface of the insulatincJ sub-stroke 1 having a pair of electrodes 2. It is allow-Ed to stand for a specific period of time ordinarily from 30 minutes to one hour) in air. Thereafter, the coated substrate is heated to a suitable temperature (ordinarily about 120C) to evaporate the solvent used and then fired for from 30 minutes to one hour in air at a temperature of from 400C to 700C. Thus, the organic compound containing In and the organic come pound containing Sun are pyrolyzed to form an Insane thin film.
The number of repetitions of this application-firing step varies depending upon the concentration of the starting material solution used and thus cannot be generally specified. when the application-firing step (a firs-t step) is repeated from once to four times, a thin film having a specific film thickness is formed.
It is believed that when the content of Sun in the thin film it less than about 10~ of In in atomic ratio percent ((Sn/In)xlOO), Sun acts as an impurity of indium oxide, whereas when the content of Sun is 10% or more, polyp crystals of indium oxide and tin oxide are formed.
In a second step, a catalyst layer 4 is then I
laminated on the thus formed thin film 3 by the follow-in process.
The catalyst layer 4 according to the present invention comprises a catalyst wherein at least one of platinum group metals, e.g. any one of palladium (Pod), platinum (Pi) and rhodium (Rho) or any one of palladium-platinum (Pd-Pt), palladium-rhodium (Pd-Rh) and platinum-rhodium (Try) is supported on a carrier, e.g., aluminum oxide (Allah).
lo This catalyst is prepared as follows:
First, chlorides such as H2PtCl6 OWE, PdC12 and RhCl3 OWE or ammonium salts such as (MH~)2PtCl6, (NH4)2PdC16, and (NH4)3RhC16 are used to prepare an aqueous solution containing Pod, Pi or oh at a specific temperature. When Pod, Pi or Rho alone is supported on Allah, a specified amount of Allah is immersed in the respective solutions. When Pd-Pt, Pd-Rh or Try is supported on AYE, aqueous solutions containing Pod, Pi or Rho are mixed at a specific ratio to prepare a mixture, and a specific amount of OWE is immersed in the mixture.
oh components are thoroughly stirred and mixed.
The mixture is then dried for, for example, l to 2 hours under reduced pressure and heated and dried at a temperature of about 100C. The dried material is ground into a powder, for example, in a mortar. The powder is placed in a quartz crucible and fired at a '73~
temperature of from 400 to 800C. As a result, a catalyst wherein a predetermined amount of Pi, Pi, Rho Pd-Pt, Pd-Rh or Try is supported on OWE is obtain-Ed The amount of Pod, Pi or Rho supported on AYE is as follows: when each component is used, it is prefer-able that Pod, Pi or Rho be in the range of from 0.05%
to 2Ø0% by weight based on the weight of AYE. If the amount is outside this range the amount of Pod, Pi or Rho will not contribute to the improvement of the sensitivity of the element. The amount of Pd-Pt, Pod--Rho or Try supported on OWE is as else in the cases of Pd-Pt and Pd-Rh, it is preferable that Pod be present in an amount of from 0.05% to 20.0% by weight based on the weight of AYE, and Pi or Rho be present in an atomic ratio of Pi or Rho to Pod (Pt/Pd or Rh/Pd) of from 0.05 to 1.0; and in the case of Try, it is preferable that Pi be present in an amount of from 0.05% to 20.0% by weight based on the weight of AYE
and Rho be present in an atomic ratio of Rho to Pi Rapt of from 0.05 to 1Ø
The thus prepared catalyst is then slurries by using, for example, an aqueous solution containing aluminum hydroxychloride or the like as a binder. This slurry is applied onto the thin film and dried to obtain a prescribed thickness. Thereafter, the whole assembly is fired at a temperature of from 300 to 400C to form I
a catalyst layer according to the present invention.
The following non-limiting examples are set forth to more fully illustrate the present invention.
Indium octylate and tin octylate were used as starting materials for an Insane thin film. These materials were so dissolved in Tulane that the con-tent of metal atoms became 50% in atomic ratio percent ((Sn/In)xlO0), whereby a starting-material solution was obtained.
This solution was then applied onto the outer cylindrical surface of a cylinder of an insulating substrate 1 previously provided with a pair of elect-nodes 2 as shown in FIG. 1. The substrate thus coated was allowed to stand for one hour in air and thereafter heated to a temperature of 120C to evaporate off the Tulane.
The resulting structure was then fired for one hour at a temperature of 500C in air. This apply-cation-firing step was repeated three times to form a thin film having a thickness of about 3,000 A.
Thereafter, a catalyst layer was formed on this thin film. First, PdC12 was dissolved in water to form an aqueous solution containing 1.0~ by weight of Pd. AYE fine powder having a surface area of about 100 m go was i~nersed in the aqueous solution, and the mixture was thoroughly stirred. The mixture was dried for 1.5 hours under reduced pressure to remove -10~
~Z~'7~
moisture and then evaporated to dryness. The dried material was then ground in a mortar and -the result-in powder was placed in a quartz crucible and fired at a temperature of 400C.
This catalyst powder was placed in an aluminum hydroxychloride azaleas solution (1% AYE) with water to form a slurry. This slurry was applied onto the Insane thin film and dried. The structure thus obtain-Ed was fired at a temperature of 400C. Thus, a Pod-AYE catalyst layer having a thickness of 20 micro-meters and containing 1.0% by weight of Pod in supported state was formed.
In a similar manner, elements were prepared where-in Tao or Roy catalysts as well as Pd-Pt-AYE, Pd-Rh-A12O3 and Try catalysts were used.
In catalysts wherein any one of Pal, Pi and Rho was supported on AYE, the amount of Pod, Pi or Rho was 1.0%
by weight based on the weight of AYE. In the cases of Pd-Pt and Pd-Rh, the amount of Pod supported was 1.0%
by weight based on the weight of AYE, and the atomic ratio of Pi or Rho to Pod was 0.5. In the case of Try, the amount of Pi was 1.0% by weight based on the weight of AYE, and the atomic ratio of Rho to Pi was 0.5.
A device as shown in FIG. 2 was assembled by using each of thus prepared gas detecting elements wherein the type of each catalyst layer was different. the sensitivity to CO, Ho, SHEA, and C3H8 having concentrations ~22~'~3~
of 200 Pam and KIWI having a concentration of 1,000 Pam was measured as Roarers using each device.
The measurement was carried out at working tempera-lures of 100C and ~00C. As used herein, Roger is the resistance value exhibited by elements in air con-twinning no measuring gas, and Russ is the resistance value exhibited by elements in air containing the above gases having respective concentrations. Accord-tingly the larger the ratio Reargues lo is the sensitivity.
The results obtained are shown in the following Table.
. .
73~
o o o o o o o ___ owe o o o o o o o . . . . . .
mu O O O I , 1 co co owe, . r-i Q o o o o o o o o o o o o Q . . . . . . . . . . . .
Jo Jo Jo or I ED ED
I o __ _ Jo N I 1~1 K I Q o o o o Jo o o o o o o o m Jo Jo Jo 00 ox Jo ___ _ _ __ _ rJ
I: R o ;` In us I o o o o o o Al m O Jo I or En I _ _ __ O O O O O O Us I
ox O O O O O O Jo Jo Jo __ _ __ Jo ox ox ox ox ox ox o I I r-l 1-l o o o o o o ICKY
rl I
O I! I; K lo I K I;
I Al) I I) Ed Ed Ed Ed Jo O I K Jo I 11 Pi Pi K Pi Pi Pi U U
_ __ _ _ _ _ I U
Ed o o o I O o o S l I it!
o a En I I
As can be seen from the Table, in all catalysts, the sensitivity of CO (200 Pam) is higher than that of KIWI (1,000 Pam) at a working temperature of 100 C. It is apparent that the gas detecting elements exhibit extremely high sensitivity to CO gas. On the other hand, it is apparent that the sensitivity of C3H8 and SHEA (200 Pam) is higher than that of KIWI
(1,000 Pam) at a working temperature of 400C.
Elements were produced as in Example 1 except that the contents of In and Sun in the Insane thin film were varied. The sensitivity to the percent content of Sun to In was measured under the same conditions as described in Example 1.
The results obtained by using an element having a Pd-A12O3 catalyst as a catalyst layer to measure -the sensitivity to SHEA (200 Pam) gas at a working tempera-lure of 400C are shown in FIG. 3 as one example. As can be seen from FIG. 3, when tune atomic ratio percent con-tent ((Sn/In)xlO0) is Nero, i.e., the thin film is free of Sun and contains only Inn (In-O system), the sense-tivity is low. The sensitivity is increased as the percent content of Sun is gradually increased. However the sensitivity is gradually decreased from about 50~D
When the percent content is 100r i.e., the thin film is free of In and contains only Snow (Snow system), the sensitivity is approximately the same as that of the 73Ç;
thin film having a percent content of zero.
As can be seen Eros the foregoing, the Insane thin film provides higher sensitivity as compared with the thin film formed from :[n~03 (In-O system) only or Snow (Snow system) only. Particularly, when the atomic ratio percent of Sun to In is about 50%, the gas detecting element exhibits excellent sensitivity.
Such a tendency was similarly observed even when the type of the catalyst layer and gases to be measured were varied.
As can be also seen from the results of Examples set forth above, the gas detecting element of the present invention exhibits high sensitivity to reduce in gases of low concentration and shows excellent sensitivity to CO gas at a Ion temperature range ox from room temperature to about 120C and high sense-tivity to SHEA and C3H8 at a high temperature range of from 350 to 450C. Thus, the gas detecting element of the present invention exhibits excellent silicate-viny. Accordingly, by varying the working tempera-lure, erroneous functioning due to miscellaneous gases such as KIWI can be eliminated to achieve highly sensitive detection of various reducing gases.
PROCESS FOR PRODUCING Lowe SAME
BACKGROUND OF THE INVENTION
This invention relates to cJas detecting elements and to processes for producing the same and more particularly to a gas detecting element capable of detecting a reducing gas in air with high sensitivity and selectivity and a process for producing the same.
Heretofore, known elements for detecting a reduce in gas in air are those gas detecting elements where-in a sistered body of a metal oxide semiconductor exhibiting N-type semiconductor characteristics such as Snow, Zoo, or Foe is used. In such elements, when these metal oxide semiconductors come into con tact with a reducing gas, their electric conductivity is increased. A gas is detected by measuring the change of electric resistance value.
In recent years, compact and multi functional elements have been sought. Studies have been carried out on the use of thin film-type elements in place of the sistered body-type gas detecting elements describe Ed above. Such a thin film-type element has a thin film structure obtained by depositing a metal oxide semiconductor having gas sensitivity as described above by a thin film-forming process such as sputter-in, vapor deposition, or CUD.
'I
I
In both sistered body-type yes detecting elements and thin ~ilm-type gas detecting elements, the use of a metal oxide semiconductor alone generally provides a gas detecting element having low sensitivity and insufficient selectivity. For this reason, ordinarily noble metals such as platinum (Pi) and palladium (Pod) are being used as catalysts with the aim of increasing the sensitivity of the element. That is, Pi or Pod is directly added to the metal oxide semiconductor.
Alternatively, a catalyst layer supporting Pi or Pod is formed on the metal oxide semiconductor.
When such measures are carried out, the sensitivity is improved as compared with that in the case wherein no catalyst is used. However, the gas detecting element still does not exhibit sufficient sensitivity to detect a reducing gas having a low concentration. Further, when various reducing gases are present, highly sense-live and selective detection of a particular reducing gas is extremely difficult because erroneous function-in of the element is induced by the influence of other reducing gases. Particularly in the case of gases which adversely affect a human body even at a low concentra-lion, such as COY it has been extremely difficult to eliminate erroneous functioning due to the other reduce in gases in order to detect them. Furthermore, when the gas detecting element is to be used in a general home, the elimination of erroneous functioning of the gas detecting element due to miscellaneous gases, particularly alcohol vapor is an important problem.
While an element having a stunk oxide thin film (Japanese Patent Laid Open Publn. Noah/
198~) and an element having an indium oxide thin film (Japanese Patent Laid-Open Publn. Noah/
1984) are known as gas detecting elements heretofore proposed, even greater improvement of sensitivity as well as selectivity is desired.
SUMMARY OF THE INVENTION
It is therefore an object of the present invent lion to provide a thin film-type gas detecting element by which a reducing gas having a low concentration can be detected with high sensitivity, particularly a detecting element by which carbon monoxide (CO) can be selectively detected with high sensitivity at a low temperature range (from room temperature to about 120C), and methane (SHEA) and propane (C3H8) can be selectively detected with high sensitivity at a high -0 temperature range (from 350 to 450C).
It is another object of the present invention to provide a process for producing a thin film-type gas detecting element.
According to one aspect of the present invention, there is provided a gas detecting element comprising an insulating substrate provided with a pair of electrodes, an Insane thin film so provided on the surface of said insulating substrate as to cover said electrodes, and a catalyst layer laminated on said thin elm and comprising a carrier and a-t least one of platinum group metals supported on said carrier.
According to another aspect of the present invent lion, there is provided a process for producing gas detecting element which comprises a first step of forming an Insane thin film on the surface of an insulating substrate provided with a pair of electrodes by applying as a coating a thin film-forming starting-material solution obtained by dissolving an organic compound containing In and an organic compound contain-in Sun in a solvent, onto the surface of said insulate in substrate so as to cover said electrodes, drying said applied solution, and thereafter firing resulting structure to pyrolyze said organic compounds; and (2) a second step of laminating a catalyst layer on said thin film by applying onto said thin film a slurry containing a catalyst powder obtained from an aqueous solution containing one or more compounds of platinum group metal wherein a carrier powder is immersed there-in, drying said slurry, and thereafter firing the result-in structure.
BRIEF DESCRIPTION OF THE DRAWINGS
While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the present 12;~ I
invention, it is believed that the invention will be better understood from the following detailed descrip-lion taken in connection with the accompanying drawings, in which:
FIG. 1 is a cross-sectional view of a gas detect-in element according to the present invention;
FIG. 2 is a perspective view of a gas detecting device in which the element shown in FIG. 1 is used;
and I FIG. 3 is a graph indicating the variation of sensitivity with compositional ratio of In and Sun.
DETAILED DESCRIPTION OF THE INVENTION
-FIGS. 1 and 2 illustrate an example of an element according to the present invention. FIG. 1 is a cross-sectional view of a cylindrical element, and FIG. 2 is a perspective view showing one example of the state of use of the element.
Referring to FIG. 1, the outer cylindrical sun-face of a cylindrical substrate 1 made of an insulate in material such as alumina or Malta is provided with a pair of electrodes 2. The substrate 1 and the electrodes 2 are covered with an Insane thin layer 3.
The thin layer 3 is covered with a catalyst layer 4.
Thus an element of the present invention is formed The film thickness of the Insane thin film is preferably in the range of from 1,000 A to 1 micrometer.
If the film thickness is more than 1 micrometer, its ~;~Z~'73~
sensitivity to reducing gases is reduced. If -the film thickness is less than 1,000 A, sufficient sensitivity cannot be obtained. The thickness of the catalyst layer 4 is preferably in the range of from 10 to 50 micrometers. If the thickness of the catalyst layer is outside this range, catalytic effects such as those on sensitivity and selectivity are reduced.
As shown in FIG. 2, the thus constituted clement of the present invention is mounted and retained on pins 6 vertically provided on an insulating plate 5 in such a state that the element does not come into con-tact with other parts. Lead wires 7 are provided for electrodes. A heater 8 is provided centrally through the element in order to adjust the surface temperature (working temperature) of the element.
A process for producing an Insane thin film will be described.
The Insane thin film according to the present invention is formed by pyrolyzing an organic compound containing In and an organic compound containing Sun.
Specific amounts of In-containing organic compounds such as In metal soap (e.g., indium octylate), In-containing resin salts, alkoxides and Run wherein R is an alkyd or aureole group, and specific amounts of Sun-containing compounds such as Sun metal soap (e.g., tinoctylate), Sn~con~aining resin salts, alkoxides and Run wherein R is an alkyd or aureole group art dissolved 9L'~2~'73~
in suitable solvents such as Tulane, Bunsen and n-bottle alcohol -to prepare thin film forming starting-material solutions having desired concentrations.
A solution of this character is then applied to the outer cylindrical surface of the insulatincJ sub-stroke 1 having a pair of electrodes 2. It is allow-Ed to stand for a specific period of time ordinarily from 30 minutes to one hour) in air. Thereafter, the coated substrate is heated to a suitable temperature (ordinarily about 120C) to evaporate the solvent used and then fired for from 30 minutes to one hour in air at a temperature of from 400C to 700C. Thus, the organic compound containing In and the organic come pound containing Sun are pyrolyzed to form an Insane thin film.
The number of repetitions of this application-firing step varies depending upon the concentration of the starting material solution used and thus cannot be generally specified. when the application-firing step (a firs-t step) is repeated from once to four times, a thin film having a specific film thickness is formed.
It is believed that when the content of Sun in the thin film it less than about 10~ of In in atomic ratio percent ((Sn/In)xlOO), Sun acts as an impurity of indium oxide, whereas when the content of Sun is 10% or more, polyp crystals of indium oxide and tin oxide are formed.
In a second step, a catalyst layer 4 is then I
laminated on the thus formed thin film 3 by the follow-in process.
The catalyst layer 4 according to the present invention comprises a catalyst wherein at least one of platinum group metals, e.g. any one of palladium (Pod), platinum (Pi) and rhodium (Rho) or any one of palladium-platinum (Pd-Pt), palladium-rhodium (Pd-Rh) and platinum-rhodium (Try) is supported on a carrier, e.g., aluminum oxide (Allah).
lo This catalyst is prepared as follows:
First, chlorides such as H2PtCl6 OWE, PdC12 and RhCl3 OWE or ammonium salts such as (MH~)2PtCl6, (NH4)2PdC16, and (NH4)3RhC16 are used to prepare an aqueous solution containing Pod, Pi or oh at a specific temperature. When Pod, Pi or Rho alone is supported on Allah, a specified amount of Allah is immersed in the respective solutions. When Pd-Pt, Pd-Rh or Try is supported on AYE, aqueous solutions containing Pod, Pi or Rho are mixed at a specific ratio to prepare a mixture, and a specific amount of OWE is immersed in the mixture.
oh components are thoroughly stirred and mixed.
The mixture is then dried for, for example, l to 2 hours under reduced pressure and heated and dried at a temperature of about 100C. The dried material is ground into a powder, for example, in a mortar. The powder is placed in a quartz crucible and fired at a '73~
temperature of from 400 to 800C. As a result, a catalyst wherein a predetermined amount of Pi, Pi, Rho Pd-Pt, Pd-Rh or Try is supported on OWE is obtain-Ed The amount of Pod, Pi or Rho supported on AYE is as follows: when each component is used, it is prefer-able that Pod, Pi or Rho be in the range of from 0.05%
to 2Ø0% by weight based on the weight of AYE. If the amount is outside this range the amount of Pod, Pi or Rho will not contribute to the improvement of the sensitivity of the element. The amount of Pd-Pt, Pod--Rho or Try supported on OWE is as else in the cases of Pd-Pt and Pd-Rh, it is preferable that Pod be present in an amount of from 0.05% to 20.0% by weight based on the weight of AYE, and Pi or Rho be present in an atomic ratio of Pi or Rho to Pod (Pt/Pd or Rh/Pd) of from 0.05 to 1.0; and in the case of Try, it is preferable that Pi be present in an amount of from 0.05% to 20.0% by weight based on the weight of AYE
and Rho be present in an atomic ratio of Rho to Pi Rapt of from 0.05 to 1Ø
The thus prepared catalyst is then slurries by using, for example, an aqueous solution containing aluminum hydroxychloride or the like as a binder. This slurry is applied onto the thin film and dried to obtain a prescribed thickness. Thereafter, the whole assembly is fired at a temperature of from 300 to 400C to form I
a catalyst layer according to the present invention.
The following non-limiting examples are set forth to more fully illustrate the present invention.
Indium octylate and tin octylate were used as starting materials for an Insane thin film. These materials were so dissolved in Tulane that the con-tent of metal atoms became 50% in atomic ratio percent ((Sn/In)xlO0), whereby a starting-material solution was obtained.
This solution was then applied onto the outer cylindrical surface of a cylinder of an insulating substrate 1 previously provided with a pair of elect-nodes 2 as shown in FIG. 1. The substrate thus coated was allowed to stand for one hour in air and thereafter heated to a temperature of 120C to evaporate off the Tulane.
The resulting structure was then fired for one hour at a temperature of 500C in air. This apply-cation-firing step was repeated three times to form a thin film having a thickness of about 3,000 A.
Thereafter, a catalyst layer was formed on this thin film. First, PdC12 was dissolved in water to form an aqueous solution containing 1.0~ by weight of Pd. AYE fine powder having a surface area of about 100 m go was i~nersed in the aqueous solution, and the mixture was thoroughly stirred. The mixture was dried for 1.5 hours under reduced pressure to remove -10~
~Z~'7~
moisture and then evaporated to dryness. The dried material was then ground in a mortar and -the result-in powder was placed in a quartz crucible and fired at a temperature of 400C.
This catalyst powder was placed in an aluminum hydroxychloride azaleas solution (1% AYE) with water to form a slurry. This slurry was applied onto the Insane thin film and dried. The structure thus obtain-Ed was fired at a temperature of 400C. Thus, a Pod-AYE catalyst layer having a thickness of 20 micro-meters and containing 1.0% by weight of Pod in supported state was formed.
In a similar manner, elements were prepared where-in Tao or Roy catalysts as well as Pd-Pt-AYE, Pd-Rh-A12O3 and Try catalysts were used.
In catalysts wherein any one of Pal, Pi and Rho was supported on AYE, the amount of Pod, Pi or Rho was 1.0%
by weight based on the weight of AYE. In the cases of Pd-Pt and Pd-Rh, the amount of Pod supported was 1.0%
by weight based on the weight of AYE, and the atomic ratio of Pi or Rho to Pod was 0.5. In the case of Try, the amount of Pi was 1.0% by weight based on the weight of AYE, and the atomic ratio of Rho to Pi was 0.5.
A device as shown in FIG. 2 was assembled by using each of thus prepared gas detecting elements wherein the type of each catalyst layer was different. the sensitivity to CO, Ho, SHEA, and C3H8 having concentrations ~22~'~3~
of 200 Pam and KIWI having a concentration of 1,000 Pam was measured as Roarers using each device.
The measurement was carried out at working tempera-lures of 100C and ~00C. As used herein, Roger is the resistance value exhibited by elements in air con-twinning no measuring gas, and Russ is the resistance value exhibited by elements in air containing the above gases having respective concentrations. Accord-tingly the larger the ratio Reargues lo is the sensitivity.
The results obtained are shown in the following Table.
. .
73~
o o o o o o o ___ owe o o o o o o o . . . . . .
mu O O O I , 1 co co owe, . r-i Q o o o o o o o o o o o o Q . . . . . . . . . . . .
Jo Jo Jo or I ED ED
I o __ _ Jo N I 1~1 K I Q o o o o Jo o o o o o o o m Jo Jo Jo 00 ox Jo ___ _ _ __ _ rJ
I: R o ;` In us I o o o o o o Al m O Jo I or En I _ _ __ O O O O O O Us I
ox O O O O O O Jo Jo Jo __ _ __ Jo ox ox ox ox ox ox o I I r-l 1-l o o o o o o ICKY
rl I
O I! I; K lo I K I;
I Al) I I) Ed Ed Ed Ed Jo O I K Jo I 11 Pi Pi K Pi Pi Pi U U
_ __ _ _ _ _ I U
Ed o o o I O o o S l I it!
o a En I I
As can be seen from the Table, in all catalysts, the sensitivity of CO (200 Pam) is higher than that of KIWI (1,000 Pam) at a working temperature of 100 C. It is apparent that the gas detecting elements exhibit extremely high sensitivity to CO gas. On the other hand, it is apparent that the sensitivity of C3H8 and SHEA (200 Pam) is higher than that of KIWI
(1,000 Pam) at a working temperature of 400C.
Elements were produced as in Example 1 except that the contents of In and Sun in the Insane thin film were varied. The sensitivity to the percent content of Sun to In was measured under the same conditions as described in Example 1.
The results obtained by using an element having a Pd-A12O3 catalyst as a catalyst layer to measure -the sensitivity to SHEA (200 Pam) gas at a working tempera-lure of 400C are shown in FIG. 3 as one example. As can be seen from FIG. 3, when tune atomic ratio percent con-tent ((Sn/In)xlO0) is Nero, i.e., the thin film is free of Sun and contains only Inn (In-O system), the sense-tivity is low. The sensitivity is increased as the percent content of Sun is gradually increased. However the sensitivity is gradually decreased from about 50~D
When the percent content is 100r i.e., the thin film is free of In and contains only Snow (Snow system), the sensitivity is approximately the same as that of the 73Ç;
thin film having a percent content of zero.
As can be seen Eros the foregoing, the Insane thin film provides higher sensitivity as compared with the thin film formed from :[n~03 (In-O system) only or Snow (Snow system) only. Particularly, when the atomic ratio percent of Sun to In is about 50%, the gas detecting element exhibits excellent sensitivity.
Such a tendency was similarly observed even when the type of the catalyst layer and gases to be measured were varied.
As can be also seen from the results of Examples set forth above, the gas detecting element of the present invention exhibits high sensitivity to reduce in gases of low concentration and shows excellent sensitivity to CO gas at a Ion temperature range ox from room temperature to about 120C and high sense-tivity to SHEA and C3H8 at a high temperature range of from 350 to 450C. Thus, the gas detecting element of the present invention exhibits excellent silicate-viny. Accordingly, by varying the working tempera-lure, erroneous functioning due to miscellaneous gases such as KIWI can be eliminated to achieve highly sensitive detection of various reducing gases.
Claims (15)
1. A gas detecting element comprising an insu-lating substrate provided with a pair of electrodes, an In-Sn-O thin film so provided on the surface of said insulating substrate as to cover said electrodes, and a catalyst layer laminated on said thin film and comprising a carrier and at least one of platinum group metals supported on said carrier.
2. The gas detecting element according to claim 1 wherein said thin film is prepared by pyrolyzing an organic compound containing In and an organic compound containing Sn.
3. The gas detecting element according to claim 2 wherein said organic compound containing In is an indium metal soap, and said organic compound contain-ing Sn is a tin metal soap.
4. The gas detecting element according to claim 1 wherein said thin film has a film thickness in the range of from 1,000 .ANG. to 1 micrometer.
5. The gas detecting element according to claim 1 wherein said platinum group metal is selected from the group consisting of Pt, Pd, Rh and mixtures there-of.
6. The gas detecting element according to claim 1 wherein said carrier is Al2O3.
7. The gas detecting element according to claim 1 wherein said catalyst layer has a thickness of from 10 to 50 microns.
8. A process for producing a gas detecting element which comprises:
(1) a first step of forming an In-Sn-O thin film on the surface of an insulating substrate provid-ed with a pair of electrodes by applying as a coating a thin film-forming starting-material solution obtained by dissolving an organic compound containing In and an organic compound containing Sn in a solvent, onto the surface of said insulating substrate so as to cover said electrodes, drying said applied solution, and thereafter firing the resulting structure to pyrolyze said organic compounds; and (2) a second step of laminating a catalyst layer on said thin film by applying onto said thin film a slurry containing a catalyst powder obtained from an aqueous solution containing one or more compounds of platinum group metal wherein a carrier powder is immersed therein, drying said slurry, and thereafter firing the resulting structure.
(1) a first step of forming an In-Sn-O thin film on the surface of an insulating substrate provid-ed with a pair of electrodes by applying as a coating a thin film-forming starting-material solution obtained by dissolving an organic compound containing In and an organic compound containing Sn in a solvent, onto the surface of said insulating substrate so as to cover said electrodes, drying said applied solution, and thereafter firing the resulting structure to pyrolyze said organic compounds; and (2) a second step of laminating a catalyst layer on said thin film by applying onto said thin film a slurry containing a catalyst powder obtained from an aqueous solution containing one or more compounds of platinum group metal wherein a carrier powder is immersed therein, drying said slurry, and thereafter firing the resulting structure.
9. The process according to claim 8 wherein said organic compound containing In is an indium metal soap, and said organic compound containing Sn is a tin metal soap.
10. The process according to claim 8 wherein the pyrolysis of said organic compound containing In and said organic compound containing Sn is carried out at a temperature of from 400° to 700°C.
11. The process according to claim 8 wherein said In-Sn-O thin film has a film thickness of from 1,000 .ANG.
to 1 micrometer.
to 1 micrometer.
12. The process according to claim 8 wherein said first step is repeated several times until the thin film having a desired thickness is obtained.
13. The process according to claim 8 wherein said compound of platinum group metal is a chloride or ammonium salt of Pt, Pd or Rh.
14. The process according to claim 8 wherein said carrier powder is Al2O3 powder.
15. The process according to claim 8 wherein said catalyst layer has a thickness of from 10 to 50 microns.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP192339/1984 | 1984-09-13 | ||
| JP59192339A JPS6170449A (en) | 1984-09-13 | 1984-09-13 | Gas detecting element |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1221736A true CA1221736A (en) | 1987-05-12 |
Family
ID=16289632
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000490569A Expired CA1221736A (en) | 1984-09-13 | 1985-09-12 | Gas detecting elements and process for producing the same |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS6170449A (en) |
| KR (1) | KR890000390B1 (en) |
| CA (1) | CA1221736A (en) |
| GB (1) | GB2166549B (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS61197551U (en) * | 1985-05-30 | 1986-12-10 | ||
| JPH0750054B2 (en) * | 1986-09-29 | 1995-05-31 | 株式会社東芝 | Gas sensor manufacturing method |
| JP2588217B2 (en) * | 1987-10-31 | 1997-03-05 | 株式会社東芝 | Gas sensor manufacturing method |
| GB8804717D0 (en) * | 1988-02-29 | 1988-03-30 | Atomic Energy Authority Uk | Gas sensing |
| JP2573323B2 (en) * | 1988-08-18 | 1997-01-22 | 株式会社東芝 | Gas sensor |
| JPH0827248B2 (en) * | 1990-10-16 | 1996-03-21 | 松下電器産業株式会社 | Ozone sensor |
| KR100551225B1 (en) * | 2002-05-10 | 2006-02-09 | 전자부품연구원 | Method for the preparation of catalyst-dopped tin oxide powders for a semiconductor-type gas sensor |
| DE102010027070A1 (en) * | 2010-07-13 | 2012-01-19 | Eberhard-Karls-Universität Tübingen | Gas sensor and method for its production |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| BE788501A (en) * | 1971-09-17 | 1973-01-02 | Libbey Owens Ford Co | PROCESS FOR APPLYING TIN OXIDE COATINGS TO TRANSPARENT SUBSTRATES |
| US4030340A (en) * | 1976-07-22 | 1977-06-21 | General Monitors, Inc. | Hydrogen gas detector |
| JPS5395097A (en) * | 1977-01-31 | 1978-08-19 | Toshiba Corp | Gas-sensitive element |
| JPS5424096A (en) * | 1977-07-26 | 1979-02-23 | Fuji Electric Co Ltd | Carbon monoxide detector |
| US4313338A (en) * | 1978-08-18 | 1982-02-02 | Matsushita Electric Industrial Co., Ltd. | Gas sensing device |
| DE2942516C2 (en) * | 1979-10-20 | 1982-11-11 | Drägerwerk AG, 2400 Lübeck | Gas detection element for the detection of hydrogen sulfide |
| SE8105260L (en) * | 1980-09-13 | 1982-03-14 | Matsushita Electric Works Ltd | Gas Detector |
| AU558390B2 (en) * | 1981-01-14 | 1987-01-29 | Westinghouse Electric Corporation | Thick film sensor for hydrogen and carbon monoxide |
-
1984
- 1984-09-13 JP JP59192339A patent/JPS6170449A/en active Pending
-
1985
- 1985-08-24 KR KR1019850006138A patent/KR890000390B1/en not_active IP Right Cessation
- 1985-09-10 GB GB08522434A patent/GB2166549B/en not_active Expired
- 1985-09-12 CA CA000490569A patent/CA1221736A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| GB2166549A (en) | 1986-05-08 |
| GB8522434D0 (en) | 1985-10-16 |
| GB2166549B (en) | 1988-11-02 |
| JPS6170449A (en) | 1986-04-11 |
| KR890000390B1 (en) | 1989-03-16 |
| KR860002716A (en) | 1986-04-28 |
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