CN1134190A - Tin oxide based gas sensors and method for their manufacture - Google Patents
Tin oxide based gas sensors and method for their manufacture Download PDFInfo
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- CN1134190A CN1134190A CN 94194024 CN94194024A CN1134190A CN 1134190 A CN1134190 A CN 1134190A CN 94194024 CN94194024 CN 94194024 CN 94194024 A CN94194024 A CN 94194024A CN 1134190 A CN1134190 A CN 1134190A
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- 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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Abstract
A method for fabricating gas sensors having reproducible gas sensitivity characteristics and the gas sensors so produced. The method comprises the steps: a) hydrolysis of sterically hindered tin(IV) alkoxide dissolved in a polar organic solvent in the presence of a polymer of relatively low molecular weight having a functional group capable of coordinating to tin; b) treatment of the resulting solution with a strong mineral acid to remove the polymer; c) isolation of the solid suspension; d) deposition and subsequent heat treatment at temperatures below 500 DEG C of an amount of the solid on a suitable substrate to produce a gas sensor head and e) sensitization of the gas sensor head.
Description
The present invention relates to the improvement of tin oxide, especially relate to the improvement of this sensitive element manufacture method for the gas detecting element of base.
Unless otherwise indicated, " tin oxide " used herein all refers to tin oxide (IV), i.e. SnO
2
As everyone knows, tin oxide can be used for the manufacturing of gas detecting element.For example, at BrP U.K.1,282,993 and U.K.1,288,809 and people such as N.Butta at " Sensors and Actuators " B, the typical method for making of sensitive element has all been described in the paper of 2 (1990) p151-161, these methods comprise: at the stannic oxide powder of 500-1000 sintering temperature chemical doping, to obtain the porous pill.Produce the intrinsic worn-out sick structure and the form that can not control them exactly of high temperature that this pill adopts, this causes can not reproducing behavior between the sensitive element.In addition, the insufficient sensitivity of the commercially available sensitive element that obtains in this way can not detect the inflammable gas in the ppm level concentration.
The objective of the invention is by use a kind of temperature be lower than 500 ℃ down the manufacture methods of operation the gas detecting element of a kind of tin oxide as base is provided, it can detect in the Asia-inflammable gas of ppm level.
Tin oxide is a kind of ion-type solid, the small nonstoichiometry that causes owing to the variable oxidation state of tin, this ion-type solid generally shows as the behavior of n-N-type semiconductor N, it is generally acknowledged tin oxide as a kind of function of gas detecting element be depend on this sensitive element by oxygen in the absorption on tin oxide surface and sensitization, thereby the oxygen of absorption removes out the electronics of conductive shield and reduces its conductor from n-section bar material.When inflammable gas arrives the tin oxide surface of handling through oxygen, remove the oxide material on surface by chemical oxidation reaction, make product gas with surface desorption, thereby electronics return conductive strips again.This just causes the increase of fin oxide condutire rate (conductivity) in the gas detecting element of making, and voltage that the increase of this conductance can be by tin oxide or electric current change and detected.
From as can be known above-mentioned, for make tin oxide be the sensitivity of sensitive element of base for the highest, wish that the tin oxide that obtains has high surface area (so that surface reaction can be controlled any basic process) and low initial conductivity (make be minimum for the number that obtains the required charge carrier of detectable variation).The high temperature that uses in routine fashion is easy to reduce the surface area of tin oxide, also can cause the increase of n-type conductance owing to non-stoichiometric increase.In addition, (usually have) uncontrollable variation generation in the general defect chemistry that uses high like this temperature may cause tin oxide in the material that uses in the presence of impurity in making tin oxide, this also harms the manufacturing of the sensitive element with the behavior of can reproducing.
Have now found that, use sol-gel process to produce tin oxide, the stoichiometric substantially material that can fully be condensed, it can be formed directly in the gas sensitization head, and need not to rely on the too high temperature of use.Therefore the tin oxide of making like this can keep high surface area, also has low initial conductivity and therefore is suitable for making very much high-sensitive inflammable gas sensitive element.
According to a first aspect of the present invention, a kind of manufacture method of tin oxide gas sensitization head is provided, the method comprises:
A) sterically hindered tin (IV) alkoxide that is dissolved in a polar organic solvent in the presence of a polymkeric substance is hydrolyzed, the molecular weight of this polymkeric substance quite low and have can with the functional group of tin coordination;
B) with a kind of strong acid treatment gained solution to remove this polymkeric substance;
C) separate this solid suspension;
D) a certain amount of solid of deposition and then heat-treating to obtain the gas sensitization head being lower than 500 ℃ on a suitable matrix; With
E) sensitization of this gas sensitization head.
If the alkoxide hydrolysis of tin is too fast, will make to connect the network variation.Because the speed of hydrolysis is the degree of polarization that depends on the alkoxide of tin, alkoxide faster that hydrolysis takes place of more polarizing, therefore wish to use the alkoxide of the tin with strong covalency, tin-tert-butyl group oxide or tin-isopropyl oxide for example is to reduce hydrolysis rate.
Because of polymkeric substance exists the advantage of carrying out this hydrolysis down to be because this tin oxide of coordination effect nucleation around polymer chain.Continue remove " hollow " shell that then stays tin oxide behind this polymkeric substance, this also just guarantees from surface area and poriness.
Ground more commonly used, the speed that solid condenses during hydrolysis can also be subjected to hydrolysis to leave the control of carrying out at a kind of sequestrant.This sequestrant (for example diacetone) has ligand, can hinder the formation of oxide structure after hydrolysis with the tin coordination, thereby increases the control to condensing.
For the structure that helps controlling solid and form and thereby the behavior of control sensitive element, being lower than about 500 ℃ in temperature, to heat-treat be necessary.The temperature of using should be from the reality of the physical property of control solid and low as far as possible, but want enough high with enough unlikely again sintering that causes particle of bonding between the assurance solids simultaneously.Therefore, the temperature of thermal treatment use is advantageously basically in the 400-500 scope.
According to a second aspect of the present invention, provide the tin oxide of making as stated above to be basic gas sensitization head.
To describe in detail below and use the inventive method to make the example of tin oxide as the gas detecting element of base.
High-purity (common 99.99% purity) tin-tert-butyl group oxide (0.375g) by Britain Inorgtech Specialist Chemicals of Mildenhall supply is dissolved in the interior tetrahydrofuran (10.6 milliliters) of a Schlenk flask.Add molecular weight then and be about 2000 polyacrylic acid (0.066g), gained solution stirred 18 hours under the nitrogen atmosphere.Add entry (1 milliliter, about 10 molar equivalents of each remaining alkoxide ligand) and make gained solution generation hydrolysis, this solution stirred 3 hours again.
Add red fuming nitric acid (RFNA) (0.5 milliliter) then, to remove this polymkeric substance and to filter this last solution, water and washing with acetone are to remove the nitrate that nitric acid and this acid form.The solid of telling in 118 ℃ of baking ovens dry 30 hours then.
The solid of a certain amount of drying mixes mutually with a kind of ratio of solvent such as THF, forms slurries.These slurries are deposited on interdigitated electrodes that gold is housed and on the standard Rosemount alumina substrate of the platinum well heater in front, to form the gas sensitization head.Because pass through the variation of the electric current of platinum well heater, this sensing head can use under the different operating temperature, this provides the chance of chemo-selective perception.This selectivity is because this fact: different energy of activation is arranged in the reaction of different inflammable gases on the sensitive element surface and therefore their reaction rate also can be by to the variation of sensitive element heat supply and controlled.
After the slurry dried, sensing head in a dry air, heat 400 ℃ 48 hours.This bonding that will be created in minimum between solids is and unlikely because sintering reduces the surface area of tin oxide, and this also makes device obtain sensitization.
The tin oxide of this gas sensitization head and then carry out further sensitization with following method, promptly alternately each 2 minutes 200 ℃ of heating at least 10 times in 1% methyl alcohol/air and pure air.
Comprise the tin oxide made by this routine described method exemplary functions, below will be only be example and discussed with reference to accompanying drawing with predicting of toluene for the gas detecting element of the gas sensitization head of base.
Fig. 1 is the comparison diagram of sensitive element function of the present invention and the commercially available sensitive element that gets.
Fig. 2 shows the response of sensitive element of the present invention to straight 100ppb toluene concentration in the air.
Fig. 3 is with respect to toluene concentration, the calibration curve of sensitive element output.
Fig. 4 show two sensitive elements to the sensitivity of acetone with variation of temperature (sensitivity definition is:
Fig. 5 shows that sensitive element of the present invention is to the response of concentration until the dimethylbenzene of about 36ppm.
Because of more commercially available getting in the detection that contains 15.6ppm toluene in the air The gas detecting element of metal oxide and the merit of sensing element of the present invention Energy. Commercially available sensing element is from Britain Ayleburron Gloucester Envin Scientific Instruments supplies with (the lower responsive unit of TGS that is called Part), and sensing element of the present invention hereinafter referred to as the SGS sensing element. These are two years old Individual sensing element periodically is exposed to and contains in the toluene air then pure air In and their output signal as the function of time and monitored.
From top discussion as can be known, sensing element is exposed to the air of toluene vapor In, can expect that semi-conductive conductance increases, thereby this sensing element output electricity Stream increases. Otherwise, when sensing element is exposed in the pure air again, then partly lead The conductance of body should reduce, thereby correspondingly the sensing element output current also subtracts Little.
With reference now to Fig. 1,, stitching A representative in top operates under optimum condition The output signal with microampere (μ A) expression that the TGS sensing element provides, And the responsive unit of the SGS that stitching B representative in bottom operates under optimum condition again The output signal that part provides.
Bottom stitching B shows, when the SGS sensing element is exposed to toluene vapor Conductance at tin oxide has the increase that clearly can predict (from output signal Obvious increase find out), when to be exposed to pure air then opposite. Can see Going out this behavior is reproducible for 5 cycle index.
On the contrary, top stitching A shows that then the TGS sensing element follows 5 times The output signal of ring does not almost have anything to change, thereby can not be used for credibly the place In the detection of hanging down so dense toluene vapor.
Fig. 2 illustrate this SGS sensing element in the air until 100ppb The time response of the pulse of toluene vapor, wherein pulse A is corresponding to exposing to the open air The 60ppb toluene vapor, the corresponding 70ppb of pulse B, the corresponding 80ppb of pulse C, The corresponding 90ppb of pulsed D and pulse E are corresponding to 100ppb. As seen with millimicro The size of the output signal that peace (nA) is measured is to depend on dense that toluene exists Degree and signal noise ratio show that the so low output current of 0.1nA also is to examine Survey.
The output signal that Fig. 3 illustrates the SGS sensing element to toluene concentration (very In the wide concentration range) relation curve. The extrapolation line shows for sensing element Electric current is 0.1nA (log value for-1) to the detectable limit of toluene is 1ppb Magnitude.
Fig. 4 respectively with symbol ■ and ● the dependence of the sensitivity of two different SGS sensitive elements to temperature is shown.Just as can be seen, obtain essentially identical temperature dependence for two sensitive elements of the air that contains 16.4ppm acetone, this can illustrate that the function of these different detecting devices is basic identical and has given prominence to the advantage of using manufacture method of the present invention.The narrow degree of this temperature distribution history also provides a proof, promptly by the chemical homogeneity on the sensitive element surface of the inventive method preparation, though also show the limited range of the catalytic site that gas can react and thereby show energy of activation and the limited range of the useful heat energy that interrelates.
Sensitive element by manufacturing of the present invention also can be used for detecting other gas, and SGS sensitive element for example shown in Figure 5 responded the burst length of xylene steam in the air up to about 36ppm.Wherein, pulse A is corresponding to the xylene steam that is exposed to 9.1ppm, and pulse B is equivalent to 11.2ppm, and pulse C is 14.5ppm, and pulsed D is that 20.5ppm and pulse E are 35.2ppm.As seen, the output signal of measuring from microampere (μ A) is to depend on the concentration that dimethylbenzene exists.
Claims (11)
1. the manufacture method of tin oxide gas sensitization head, the method comprises:
A) polymkeric substance exists sterically hindered tin (IV) alkoxide that is dissolved in a polar organic solvent down to be hydrolyzed, the molecular weight of this polymkeric substance quite low and have can with the functional group of tin coordination;
B) with a kind of strong acid treatment gained solution to remove this polymkeric substance;
C) separate this solid suspension;
D) a certain amount of solid of deposition and then heat-treating to obtain the gas sensitization head being lower than 500 ℃ on a suitable matrix; With
E) sensitization of this gas sensitization head.
2. the method for claim 1 is characterized in that this sterically hindered stannane oxide has strong covalant character.
3. the method for claim 2 is characterized in that this sterically hindered stannane oxide is a tin tert-butyl group oxide.
4. the method for claim 2 is characterized in that this sterically hindered stannane oxide is the different base oxide of tin.
5. arbitrary method in the aforementioned claim, the polymkeric substance that exists when it is characterized in that being hydrolyzed is a polyacrylic acid.
6. arbitrary method in the aforementioned claim is characterized in that strong inorganic acid is a nitric acid.
7. the arbitrary method in the aforementioned claim is characterized in that thermal treatment is to carry out basically in 400-500 ℃ temperature range.
8. the method for claim 7 is characterized in that thermal treatment is to carry out 400 ℃ temperature basically.
9. the arbitrary method in the aforementioned claim is characterized in that the sensitization of gas sensitization head comprises: alternately the neutralization of the air of 1% methyl alcohol then in peace and quiet air this sensing head to 260 of heating ℃ at least ten times each two minutes.
10. the arbitrary method in the aforementioned claim is characterized in that hydrolysis is to carry out having in the presence of the reagent of ligand, this ligand after hydrolysis can with the tin coordination, thereby prevent the formation of oxide structure.
11. the gas detecting element that comprises tin-oxide gas sensitization head according to aforementioned claim 4 either party manufactured.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9319456.1 | 1993-09-23 | ||
| GB939319456A GB9319456D0 (en) | 1993-09-23 | 1993-09-23 | Improvements in tin oxide based gas sensors |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN1134190A true CN1134190A (en) | 1996-10-23 |
Family
ID=10742281
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN 94194024 Pending CN1134190A (en) | 1993-09-23 | 1994-08-22 | Tin oxide based gas sensors and method for their manufacture |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0720738A1 (en) |
| JP (1) | JPH09503860A (en) |
| CN (1) | CN1134190A (en) |
| CA (1) | CA2172515A1 (en) |
| GB (2) | GB9319456D0 (en) |
| WO (1) | WO1995008764A1 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2010032343A (en) * | 2008-07-29 | 2010-02-12 | Figaro Eng Inc | MANUFACTURING METHOD OF SnO2 GAS SENSOR, AND MANUFACTURING METHOD OF SnO2 CARRYING HAVING NOBLE METAL NANOPARTICLES |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1282993A (en) * | 1970-05-22 | 1972-07-26 | Naoyoshi Taguchi | Gas detecting devices |
| JPS58180936A (en) * | 1982-04-17 | 1983-10-22 | Fuigaro Giken Kk | Element for detecting combustion state and preparation thereof |
-
1993
- 1993-09-23 GB GB939319456A patent/GB9319456D0/en active Pending
-
1994
- 1994-08-22 JP JP7509619A patent/JPH09503860A/en active Pending
- 1994-08-22 GB GB9605970A patent/GB2296978B/en not_active Expired - Fee Related
- 1994-08-22 WO PCT/GB1994/001832 patent/WO1995008764A1/en not_active Application Discontinuation
- 1994-08-22 CN CN 94194024 patent/CN1134190A/en active Pending
- 1994-08-22 EP EP94924914A patent/EP0720738A1/en not_active Withdrawn
- 1994-08-22 CA CA 2172515 patent/CA2172515A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| WO1995008764A1 (en) | 1995-03-30 |
| EP0720738A1 (en) | 1996-07-10 |
| GB2296978B (en) | 1997-12-24 |
| GB9605970D0 (en) | 1996-05-22 |
| JPH09503860A (en) | 1997-04-15 |
| GB2296978A (en) | 1996-07-17 |
| GB9319456D0 (en) | 1993-11-03 |
| CA2172515A1 (en) | 1995-03-30 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| C06 | Publication | ||
| PB01 | Publication | ||
| AD01 | Patent right deemed abandoned | ||
| C20 | Patent right or utility model deemed to be abandoned or is abandoned |