GB2202948A - Metal oxide gas sensors - Google Patents
Metal oxide gas sensors Download PDFInfo
- Publication number
- GB2202948A GB2202948A GB08804887A GB8804887A GB2202948A GB 2202948 A GB2202948 A GB 2202948A GB 08804887 A GB08804887 A GB 08804887A GB 8804887 A GB8804887 A GB 8804887A GB 2202948 A GB2202948 A GB 2202948A
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- United Kingdom
- Prior art keywords
- sensor
- sensitive material
- ammonia
- ammonia sensitive
- electrodes
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 229910044991 metal oxide Inorganic materials 0.000 title 1
- 150000004706 metal oxides Chemical class 0.000 title 1
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims abstract description 194
- 229910021529 ammonia Inorganic materials 0.000 claims abstract description 97
- 239000000463 material Substances 0.000 claims abstract description 84
- 239000008246 gaseous mixture Substances 0.000 claims abstract description 24
- IOOQQSNBRQKBBI-UHFFFAOYSA-N [Ti+4].[O-2].[Cr+3] Chemical compound [Ti+4].[O-2].[Cr+3] IOOQQSNBRQKBBI-UHFFFAOYSA-N 0.000 claims abstract description 8
- 238000000034 method Methods 0.000 claims description 28
- 239000000843 powder Substances 0.000 claims description 16
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 claims description 15
- 239000010931 gold Substances 0.000 claims description 15
- 229910052737 gold Inorganic materials 0.000 claims description 15
- 239000000203 mixture Substances 0.000 claims description 13
- 239000007858 starting material Substances 0.000 claims description 13
- 238000007650 screen-printing Methods 0.000 claims description 12
- 239000000758 substrate Substances 0.000 claims description 11
- 238000010304 firing Methods 0.000 claims description 9
- 238000004544 sputter deposition Methods 0.000 claims description 9
- 238000001354 calcination Methods 0.000 claims description 8
- 239000000725 suspension Substances 0.000 claims description 8
- 238000002156 mixing Methods 0.000 claims description 6
- 239000002243 precursor Substances 0.000 claims description 6
- 238000000151 deposition Methods 0.000 claims description 5
- 238000003825 pressing Methods 0.000 claims description 5
- 238000001246 colloidal dispersion Methods 0.000 claims description 4
- 238000004891 communication Methods 0.000 claims description 4
- 230000008021 deposition Effects 0.000 claims description 4
- 238000001035 drying Methods 0.000 claims description 4
- 238000000227 grinding Methods 0.000 claims description 4
- 150000001242 acetic acid derivatives Chemical class 0.000 claims description 3
- 239000011230 binding agent Substances 0.000 claims description 3
- 150000003891 oxalate salts Chemical class 0.000 claims description 3
- 150000004649 carbonic acid derivatives Chemical class 0.000 claims description 2
- 239000000356 contaminant Substances 0.000 claims description 2
- 238000010438 heat treatment Methods 0.000 claims description 2
- 238000002844 melting Methods 0.000 claims description 2
- 230000008018 melting Effects 0.000 claims description 2
- 150000002823 nitrates Chemical class 0.000 claims description 2
- 238000001556 precipitation Methods 0.000 claims description 2
- 238000003980 solgel method Methods 0.000 claims description 2
- 238000001694 spray drying Methods 0.000 claims description 2
- 238000004519 manufacturing process Methods 0.000 claims 4
- 239000007789 gas Substances 0.000 abstract description 25
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 6
- 239000008188 pellet Substances 0.000 description 6
- PNEYBMLMFCGWSK-UHFFFAOYSA-N Alumina Chemical compound [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 4
- 238000005259 measurement Methods 0.000 description 3
- 238000010345 tape casting Methods 0.000 description 3
- 229910000831 Steel Inorganic materials 0.000 description 2
- 238000005530 etching Methods 0.000 description 2
- 239000011888 foil Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 239000012071 phase Substances 0.000 description 2
- 238000000206 photolithography Methods 0.000 description 2
- 230000001737 promoting effect Effects 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 239000010959 steel Substances 0.000 description 2
- 229920002472 Starch Polymers 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 239000003990 capacitor Substances 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 239000004020 conductor Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 239000003989 dielectric material Substances 0.000 description 1
- 230000005669 field effect Effects 0.000 description 1
- 239000007792 gaseous phase Substances 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 229910001960 metal nitrate Inorganic materials 0.000 description 1
- 239000013307 optical fiber Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 235000019698 starch Nutrition 0.000 description 1
- 239000008107 starch Substances 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/0004—Gaseous mixtures, e.g. polluted air
- G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
- G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
- G01N33/0036—General constructional details of gas analysers, e.g. portable test equipment concerning the detector specially adapted to detect a particular component
- G01N33/0054—Ammonia
-
- 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
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
- Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
Landscapes
- Chemical & Material Sciences (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Health & Medical Sciences (AREA)
- Immunology (AREA)
- Engineering & Computer Science (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- Pathology (AREA)
- General Physics & Mathematics (AREA)
- Physics & Mathematics (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Combustion & Propulsion (AREA)
- Food Science & Technology (AREA)
- Medicinal Chemistry (AREA)
- Investigating Or Analyzing Materials By The Use Of Fluid Adsorption Or Reactions (AREA)
Abstract
A sensor for sensing ammonia in gases and gaseous mixtures includes an ammonia sensitive material containing or comprising a non-stoichiometric chromium-titanium oxide of the general formula Cr2Ti2-x07-2x where 2>x>0. The resistance, capacitance or impedance of the oxide is monitored by means of a pair of electrodes bridged thereby.
Description
Sensors
The present invention relates to sensors and more particularly to sensors suitable for use in sensing ammonia in gases and gaseous mixtures.
According to one aspect of the present invention there is provided a sensor suitable for use in sensing ammonia in a gas or gaseous mixture which sensor includes an ammonia sensitive material (as hereinafter defined) containing or comprising a non-stoichiometric chromium-titanium oxide of the general formula Cr2Ti2-x 7-2x where 2 x 0.
In one preferred embodiment of the present invention x is 1.8.
In one embodiment of the present invention a sensor comprises an ammonia sensitive material (as hereinafter defined) containing or comprising a non-stoichiometric chromium-titanium oxide of the general formula Cr2Ti2-x07-2x where 2 > x 0, O, and two or more electrodes in communication with the said ammonia sensitive material and said ammonia sensitive material is arranged so as to be capable of being contacted with a gas or a gaseous mixture.
A sensor in accordance with the present invention may be used as an ammonia sensor in quantitative and/or qualitative determinations of ammonia in gases and gaseous mixtures.
The electrodes may be in direct communication with the ammonia sensitive material by being in contact.therewith.
In this Specification the term "gas" embraces a gas as such and any material which may be present in a gaseous phase, one example of which is a vapour.
Also, in this Specification the term "ammonia sensitive material" means a material which is sensitive to ammonia in respect of an electrical property of the material.
It will be appreciated that the resistance and/or capacitance and/or impedance of the ammonia sensitive material depends upon the amount of ammonia in the gas or gaseous mixture contacting the gas sensitive material.
Thus, by measuring the resistance and/or capacitance and/or impedance of the ammonia sensitive material ammonia in a gas or gaseous mixture can be sensed.
Since the resistance and/or capacitance and/or impedance of the ammonia sensitive material tends also to be temperature dependant, the sensor also preferably includes a temperature sensing means.
The sensor may also, optionally, include a heating means to enable operating temperature to be adjusted and/or contaminants to be burnt off if required.
It is to be understood that the sensitivity of an ammonia sensitive material within the general formula hereinbefore given to ammonia in a particular gas or gaseous mixture may depend upon the composition of the ammonia sensitive material. Thus, by selection of the composition of the ammonia sensitive material its response may be chosen.
The resistance and/or conductance and/or impedance may be measured directly. Alternatively, the measurement may be carried out indirectly by incorporating the ammonia sensitive material in a feedback circuit of an oscillator such that the oscillator frequency varies with ammonia concentration in a gas or gaseous mixture to which the sensor is exposed. Ammonia concentration may then be determined using an electronic counter. The signal thus produced may be used to modulate a radio signal and thereby be transmitted over a distance (e.g. by telemetry or as a pulse train along an optical fibre).
It has been found that a sensor for ammonia in accordance with the present invention may be such that it does not suffer significant interference from other reducing gases commonly encountered (e.g. H2, CO, CH4 and C2H4).
Ammonia has been sensed with a sensor in accordance with the present invention in air.
According to another aspect of the present invention there is provided a method for effecting determinations of ammonia in a gas or gaseous mixture which comprises contacting a sensor with the gas or gaseous mixture and measuring the electrical response of the sensor, said sensor including an ammonia sensitive material containing or comprising a non-stoichiometric chromium-titanium oxide of the general formula Cr2Ti2-Xo7-2x where 2 x 0.
In one embodiment of the immediately preceding aspect of the present invention the sensor comprises an ammonia sensitive material containing or comprising a non-stoichiometric chromium-titanium oxide of the general formula Cr2Ti2xO72x where 2 > x > 0 and two or more electrodes in communication with the said ammonia sensitive material, said ammonia sensitive material and said electrodes being in contact with the same gas or gaseous mixture.
It is preferred that the ammonia sensitive material has porosity to give a satisfactory surface area for contact with a gas or gaseous mixture when in use.
The ammonia sensitive material may, for example, be prepared from a mixture of powders of appropriate starting materials.
It will be understood that "appropriate starting materials" in this Specification means materials which can be processed to give the required ammonia sensitive material. Oxides and oxide precursors are examples of materials from which the ammonia sensitive material may be prepared. The oxides or oxide precursors may be, for example, of laboratory reagent grade. Examples of oxide precursors are carbonates, nitrates, oxalates and acetates that may be converted to the corresponding oxide.
Oxides and oxide precursors may optionally be prepared by a gel process such as a sol-gel process or a gel precipitation process.
In preparing the ammonia sensitive material, by way of example, finely ground powders of the appropriate starting materials in appropriate proportions (i.e. in proportions appropriate to the desired composition of the desired ammonia sensitive material) may be thoroughly mixed in suspension (e.g. in acetone) by using a mill apparatus in which materials are ground, mixed and dispensed (e.g. by use of small alumina ceramic balls agitated in a steel pot by a steel blade).
Mixing time and speed may be minimised to avoid unnecessary contamination of the starting materials.
After mixing the resulting powder mixture may be dried and calcined (e.g. for about 16 hours) at a temperature in the range 700 - 13000 (conveniently about 800"C or about 12000C) depending upon the melting temperature of the starting materials or the particular composition of ammonia sensitive material being prepared.
The product resulting from calcination, which may be in the form of a cake,. may be ground as required to give a fine powder. (If required, grinding and calcination may be repeated several times in order to obtain a more fully reacted product powder).
Subsequently the fine powder may be pressed (e.g. with the optional addition of a binder, such as a solution of starch or PVA) into any suitable shape (e.g. a pellet).
The pressing may be followed by firing (e.g. at the same temperature as the calcination step(s) described above, or at a somewhat higher temperature, for about 16 hours).
In addition to assisting binding the powder into the desired shape the binder also burns out during the firing stage and may give rise to porosity.
As an alternative to mixing powders in suspension a powder mixture for subsequent calcination may be prepared, for example, by spray drying a solution (e.g. an aqueous solution) of appropriate starting materials (e.g. metal oxalates, metal acetates or metal nitrates) in appropriate proportions.
Electrodes may be applied to the ammonia sensitive material once prepared in any suitable manner. For example, electrodes (e.g. gold electrodes) may be applied by means of screen printing or sputtering.
Alternatively to preparing a sensor by forming a pellet and applying electrodes as disclosed above, a sensor in accordance with the present invention may be formed in any suitable manner. Thus, for example, a parallel plate configuration may be fabricated by applying a first electrode (e.g. of gold) to an insulating substrate (e.g.
by screen printing or sputtering), forming an ammonia sensitive material layer covering at least a portion of the first electrode (e.g. by deposition, for example by screen printing or doctor-blading, from a suspension or a colloidal dispersion and firing at a temperature in the range 450 - 9500C to promote adhesion and mechanical integrity) and forming a second electrode (e.g. of gold) on the ammonia sensitive material layer (e.g. by screen printing or sputtering).
The second electrode is preferably permeable to facilitate access of gas or gaseous mixture in which the sensor is to be used to the gas sensitive material layer.
By way of further example, a coplanar configuration can be used in the preparation of a sensor in accordance with the present invention.
In such a coplanar configuration interdigitated electrodes (e.g. of gold) may be formed on an insulating substrate (e.g. by screen printing, or by sputtering, or by photolithography and etching). The interdigitated electrodes are subsequently covered with an ammonia sensitive material layer (e.g. by means of deposition, for example by screen printing or doctor-blading, from a suspension or a colloidal dispersion) and firing at a temperature in the range of 450 - 9500C to promote adhesion and mechanical integrity.
Sensors in accordance with the present invention fabricated in a coplanar configuration may include another layer or layers interposed between the ammonia sensitive material layer and the electrodes. By way of example, an interposed layer may be a layer of a dielectric material, or a layer for promoting adhesion of the ammonia sensitive material (e.g. a layer of glass material or a layer fabricated from a powder prepared from a gel). By way of further example, a layer for promoting adhesion may be interposed between a dielectric layer and the ammonia sensitive material layer.
By way of further example, sensors in accordance with the present invention may be fabricated by depositing an ammonia sensitive material layer on electrodes of any suitable configuration for example those fabricated in the form of "wander tracks". By way of yet further example, an ammonia sensitive material layer may be deposited onto a semi-conductor device such as a field effect transistor,
MOS capacitor or gate-controlled diode.
It is to be understood that ammonia sensitive materials in accordance with the present invention may fall within the so-called "E - phase" of the Ti02-Cr203 phase field (J. Sol. St. Chem.25, 273-284 (1978)).
The present invention will now be further described, by way of example only, with reference to Examples 1 and 2 and with reference to Figures 1 to 6 of the accompanying drawings.
Example 1
An ammonia sensitive material comprising Ti02 48.7 mole % Cr203 was prepared by mixing appropriate finely ground starting materials (oxides) in suspension in acetone in a mill, drying, calcining (at a temperature in the range 700 - 13000C for about 16 hours, grinding to a fine powder and pressing and firing for about 16 hours (at a temperature in the range 8()00C to 10000C) to give a pellet (approximately 2mm thick and lcm in diameter).
Sputtered gold electrodes were applied to opposing faces of the pellet and the sensor constituted thereby was mounted between gold foils in a furnace tube in a flowing gas stream (of chosen composition) and electrical measurements were made.
Example 2
An ammonia sensitive material comprising
Ti02 - 90 mole % Cr203 was prepared by mixing appropriate finely ground starting materials (oxides) in suspension in acetone in a mill, drying, calcining (at a temperature in the range 700 - 13000C for about 16 hours, grinding to a fine powder and pressing and firing for about 16 hours (at a preferred temperature in the range 8000C to 10000C) to give a pellet (approximately 2mm thick and lcm in diameter).
Sputtered gold electrodes were applied to opposing faces of the pellet and the sensor constituted thereby was mounted between gold foils in a furnace tube in a flowing gas stream (of chosen composition) and electrical measurements were made.
The present invention will now be further described, by way of example only, with reference to the accompanying drawings in which:
Figure 1 is a diagrammatic representation of one form
of sensor in accordance with the present
invention;
Figure 2 and Figure 2a represent diagrammatically a parallel plate sensor in accordance with the present invention and a partially completed parallel plate sensor respectively;
Figure 3 is a diagrammatic representation of a coplanar sensor in accordance with the present invention;
Figure 4 is a diagrammatic representation of a further form of sensor in accordance with the present invention;;
Figure 5 is the response to 1% ammonia in air at 5250C, in terms of resistance at 10KHz, of a sensor in accordance with the present invention having an ammonia sensitive material comprising Ti02 - 48.7 mole % Cr203.
Figure 6 is the response to 1% ammonia in air at approximately 490"C in terms of resistance at 10KHZ, of a sensor in accordance with the present invention having an ammonia sensitive material comprising Ti02 - 90 mole % Cr203.
Referring now to Figure 1 of the drawings there is shown a sensor comprising an ammonia sensitive material 1 and, in contact with the ammonia sensitive material 1 gold electrodes 2 and 3. (The ammonia sensitive material may be carried by a substrate (e.g. of alumina) (not shown)).
Conductors 4 and 5 are provided to connect the electrodes 2 and 3 respectively to electrical measuring means 6 for measuring the resistance and/or capacitance and/or impedance of the ammonia sensitive material 1.
In operation a gas or gaseous mixture is contacted with the ammonia sensitive material 1.
The resistance and/or capacitance and or impedance is measured by the electrical measuring means 6. Changes in concentration of ammonia in the gas or gaseous mixture which result in a change of resistance and/or capacitance and/or impedance are observed as changes in the resistance and/or capacitance and/or impedance recorded by the measuring means 6.
Referring now to Figure 2 of the drawings there is shown (in plan view) an insulating substrate 1 (e.g. an alumina ceramic tile) upon which is formed a first electrode 2 (e.g. of gold), an ammonia sensitive material layer 3 comprising an ammonia sensitive material in accordance with the present invention and a second electrode 4 (e.g. of gold).
A parallel plate sensor as shown in Figure 2 may be fabricated by applying the first electrode 2 (e.g. of gold) to the insulating substrate 1 (e.g. by screen printing or sputtering), forming an ammonia sensitive material layer 3 covering at least a portion of the first electrode 2 (e.g.
by deposition, for example by screen printing or doctorblading, from a suspension or a colloidal dispersion and firing at a temperature in the range 450 - 9500C to promote adhesion and mechanical integrity) and forming a second electrode 4 (e.g. of gold) on the ammonia sensitive material layer 3 (e.g. by screen printing or sputtering).
To facilitate understanding of the construction of the sensor of Figure 2 reference may be made to Figure 2a which shows a parallel plate sensor of the type shown in the
Figure 2 partially completed inasmuch as the second electrode 4 has not been formed. Figure 2a thus shows the isulaing substrate 1, the first electrode 2 and the ammonia sensitive material layer 3 and it can be seen that the portion of the first electrode 2 covered by the ammonia sensitive material layer 3 may extend in area to substantially the same extent as the second electrode 4.
In operation the first electrode 2 and second electrode 4 are connected to an electrical measuring means
(not shown) for measuring the resistance and/or capacitance and/or impedance of the ammonia sensitive material layer 3 and the sensor is contacted with a gas or gaseous mixture.
The resistance and/or capacitance and/or impedance is measured by the electrical measuring means and changes in the ammonia concentration in the gas or gaseous mixture which result in changes of resistance and/or capacitance and/or impedance are observed as changes in the resistance and/or capacitance and/or impedance recorded by the measuring means.
Referring now to Figure 3 there is shown (plan view) an insulating substrate 1 (e.g. an alumina ceramic tile) upon which are formed electrodes 2 and 3 (e.g. both of gold), and an ammonia sensitive material layer 4 (comprising an ammonia sensitive material in accordance with the present invention) covering at least a portion of both electrodes 2 and 3. It will be seen from the lines shown in dotted form in Figure 3 the portions of the first electrode 2 and second electrode 3 covered by the ammonia sensitive material layer 4 are interdigitated.
The first electrode 2 and the second electrode 3 may be provided on the insulating substrate 1 by any suitable method. For example th-e methods disclosed for providing electrodes 2 and 4 in the parallel plate sensor described hereinbefore with reference to Figure 2 and Figure 2a may be used.
The ammonia sensitive material layer 4 shown in Figure 3 may be prepared by any suitable method. For example the methods disclosed for preparing an ammonia sensitive material layer 2 in Figure 2 and Figure 2a may he used.
Referring now to Figure 4 of the drawings there is shown a diagrammatic representation in cross-section of a sensor having an insulating substrate 1, electrodes represented as 2, a dielectric layer 3 and an ammonia sensitive material layer 4.
The electrodes 2 and the layers 3 and 4 may be prepared by any suitable method. Thus, for example, screen printing or sputtering or photolithography and etching may be used as is appropriate.
Referring now to Figures 5 and 6 of the drawings there are shown the responses of two ammonia sensitive materials in accordance with the present invention. The peak in
Figure 5 corresponds with exposure, in a flowing air stream, to the passage, for a brief period, of air containing 1% ammonia, the temperature being 525 C. Figure 6 shows the response, at approximately 4900C of a sensor having a different composition of ammonia sensitive material
Claims (29)
- Claims: 1. A sensor suitable for use in sensing ammonia in a gas or gaseous mixture which sensor includes an ammonia sensitive material (as herein defined) containing or comprising a non-stoichiometric chromium-titanium oxide of the general formula Cr2Ti2-x07-2x where 2 x0.
- 2. A sensor as claimed in claim 1, wherein x is 1.8.
- 3. A sensor comprising an ammonia sensitive material (as herein defined) containing or comprising a non-stoichiometric chromium-titanium oxide of the general formula Cr2Ti2-x07-2x where 2 > x > 0, and two or more electrodes in communication with the said ammonia sensitive material and said ammonia sensitive material is arranged so as to be capable of being contacted with a gas or gaseous mixture.
- 4. A sensor as claimed in claim 3, wherein the electrodes are in contact with the ammonia sensitive material.
- 5. A sensor as claimed in claim 3 or claim 4, wherein means are provided for measuring resistance and/or capacitance and/or impedance of the ammonia sensitive material.
- 6. A sensor as claimed in claim 5, wherein the ammonia sensitive material is incorporated in a feedback circuit of an oscillator such that the oscillator frequency varies with ammonia concentration in a gas or a gaseous mixture to which the sensor is exposed.
- 7. A sensor as claimed in claim 6, wherein the said frequency is measured using an electronic counter.
- 8. A sensor as claimed in any of the preceding claims, wherein heating means are provided for controlling the operating temperature of the sensor and/or for burning off contaminants.
- 9. A sensor as claimed in any of the preceding claims, wherein the ammonia sensitive material has porosity to give a satisfactory surface area for contact with a gas or gaseous mixture when in use.
- 10. A method for effecting determinations of ammonia in a gas or gaseous mixture which comprises contacting a sensor with the gas or gaseous mixture and measuring the electrical response of the sensor, said sensor including an ammonia sensitive material containing or comprising a non-stoichiometric chromium-titanium oxide of the general formula Cr2Ti2-,07-2, where 2 > x 5 0.
- 11. A method of manufacturing a sensor, wherein ammonia sensitive material is prepared from a mixture of powders of appropriate starting materials.
- 12. A method as claimed in claim 11, wherein the starting materials comprise oxides or oxide precursors such as carbonates, nitrates, oxalates and acetates.
- 13. A method as claimed in claim 11 or claim 12, wherein the mixture of powders is prepared by spray drying a solution of appropriate starting materials in appropriate proportions.
- 14. A method as claimed in claim 12, wherein the oxide or oxide precursor is prepared by a gel process such as a sol-gel process or a gel precipitation process.
- 15. A method as claimed in any of claims 11 to 14, wherein the finely divided starting materials are subjected if necessary to mixing and drying, and are then calcined at a temperature in the range of 700"C to 13000C for a period of about 16 hours, the temperature being chosen in dependence upon the melting temperature of the starting materials and the particular composition desired for the ammonia sensitive material.
- 16. A method as claimed in claim 15, wherein the calcination product is ground to produce a fine powder, the steps of calcination and grinding being repeated if necessary and if it is desired to obtain a more fully reacted product.
- 17. A method as claimed in claim 16, wherein the fine powder is pressed into a predetermined shape.
- 18. A method as claimed in claim 17, wherein binder is incorporated prior to pressing.
- 19. A method as claimed in claim 17 or claim 18, wherein the pressing is followed by firing.
- 20. A method as claimed in any of claims 17 to 19, wherein electrodes are applied to the ammonia sensitive material.
- 21. A method as claimed in claim 20, wherein the electrodes are applied by screen printing or sputtering.
- 22. A method of manufacturing a sensor having a parallel plate configuration, which method comprises applying a first electrode to an insulating substrate, forming an ammonia sensitive material layer covering at least a portion of the first electrode, and forming a second electrode on the ammonia sensitive material layer.
- 23. A method of manufacturing a sensor having a coplanar configuration, which method comprises applying to an insulating substrate first and second electrodes spaced apart from one another, and forming a layer of ammonia sensitive material which is in contact with both electrodes and extends across the space therebetween.
- 24. A method as claimed in claim 23, wherein the electrodes are interdigitated.
- 25. A method as claimed in any of claims 22 to 24, wherein the first and second electrodes are of gold.
- 26. A method as claimed in any of claims 22 to 25, wherein the electrodes are formed by a screen printing or sputtering process.
- 27. A method as claimed in any of claims 22 to 26, wherein the ammonia sensitive material layer is formed by deposition from a suspension or a colloidal dispersion followed by drying and firing at a temperature in the range 4500C to 9500C.
- 28. A sensor substantially as herein described in any of the Examples.
- 29. A method of manufacturing a sensor substantially as herein described in any of the Examples.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB878704873A GB8704873D0 (en) | 1987-03-02 | 1987-03-02 | Sensors |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8804887D0 GB8804887D0 (en) | 1988-03-30 |
| GB2202948A true GB2202948A (en) | 1988-10-05 |
| GB2202948B GB2202948B (en) | 1991-10-16 |
Family
ID=10613197
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB878704873A Pending GB8704873D0 (en) | 1987-03-02 | 1987-03-02 | Sensors |
| GB8804887A Expired - Lifetime GB2202948B (en) | 1987-03-02 | 1988-03-01 | Ammonia sensors |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB878704873A Pending GB8704873D0 (en) | 1987-03-02 | 1987-03-02 | Sensors |
Country Status (1)
| Country | Link |
|---|---|
| GB (2) | GB8704873D0 (en) |
Cited By (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0701123A1 (en) | 1994-09-10 | 1996-03-13 | United Kingdom Atomic Energy Authority | Formaldehyde vapour detector |
| US6046054A (en) * | 1994-02-19 | 2000-04-04 | Capteur Sensors & Analysers, Ltd. | Semiconducting oxide gas sensors |
| EP1059528A2 (en) | 1999-06-11 | 2000-12-13 | Siemens Aktiengesellschaft | Gassensor using the principle of workfunction |
| EP0942281A3 (en) * | 1998-03-13 | 2002-03-20 | Epcos Ag | Measuring circuit for determining the concentration of one or more gases in a gaseous mixture |
| WO2001088517A3 (en) * | 2000-05-15 | 2002-04-11 | Capteur Sensors And Analysers | Gas sensors with improved resistance to humidity interference |
| WO2003023387A1 (en) * | 2001-09-12 | 2003-03-20 | Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. | Chromium/titanium oxide semiconductor gas sensor and method for production thereof |
| US8133598B2 (en) * | 2008-04-03 | 2012-03-13 | Kobe Steel, Ltd. | Hard coating film, method of formation thereof, and material coated with hard coating film |
| WO2022058413A1 (en) * | 2020-09-16 | 2022-03-24 | Gueder Firat | Gas sensor with first and second electrodes and a reagent for binding the target gas |
| US11513091B2 (en) * | 2016-05-27 | 2022-11-29 | Carrier Corporation | Gas detection device and method of manufacturing the same |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1498384A (en) * | 1975-02-03 | 1978-01-18 | Matsushita Electric Industrial Co Ltd | Sensors |
| EP0045950A2 (en) * | 1980-08-08 | 1982-02-17 | Kabushiki Kaisha Toshiba | Moisture sensitive element |
| GB2149120A (en) * | 1983-10-31 | 1985-06-05 | Atomic Energy Authority Uk | Improvements in or relating to sensors |
-
1987
- 1987-03-02 GB GB878704873A patent/GB8704873D0/en active Pending
-
1988
- 1988-03-01 GB GB8804887A patent/GB2202948B/en not_active Expired - Lifetime
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1498384A (en) * | 1975-02-03 | 1978-01-18 | Matsushita Electric Industrial Co Ltd | Sensors |
| EP0045950A2 (en) * | 1980-08-08 | 1982-02-17 | Kabushiki Kaisha Toshiba | Moisture sensitive element |
| GB2149120A (en) * | 1983-10-31 | 1985-06-05 | Atomic Energy Authority Uk | Improvements in or relating to sensors |
Cited By (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6046054A (en) * | 1994-02-19 | 2000-04-04 | Capteur Sensors & Analysers, Ltd. | Semiconducting oxide gas sensors |
| EP0701123A1 (en) | 1994-09-10 | 1996-03-13 | United Kingdom Atomic Energy Authority | Formaldehyde vapour detector |
| EP0942281A3 (en) * | 1998-03-13 | 2002-03-20 | Epcos Ag | Measuring circuit for determining the concentration of one or more gases in a gaseous mixture |
| EP1059528A2 (en) | 1999-06-11 | 2000-12-13 | Siemens Aktiengesellschaft | Gassensor using the principle of workfunction |
| EP1059528A3 (en) * | 1999-06-11 | 2003-01-02 | Siemens Aktiengesellschaft | Gassensor using the principle of workfunction |
| WO2001088517A3 (en) * | 2000-05-15 | 2002-04-11 | Capteur Sensors And Analysers | Gas sensors with improved resistance to humidity interference |
| US7010957B2 (en) | 2000-05-15 | 2006-03-14 | City Technology Limited | Gas sensors with improved resistance to humidity interference |
| WO2003023387A1 (en) * | 2001-09-12 | 2003-03-20 | Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. | Chromium/titanium oxide semiconductor gas sensor and method for production thereof |
| US7406856B2 (en) | 2001-09-12 | 2008-08-05 | Fraunhofer-Gesellschaft Zur Forderung Der Angewandten Forschung E.V. | Chromium/titanium oxide semiconductor gas sensor and method for production thereof |
| US8133598B2 (en) * | 2008-04-03 | 2012-03-13 | Kobe Steel, Ltd. | Hard coating film, method of formation thereof, and material coated with hard coating film |
| US11513091B2 (en) * | 2016-05-27 | 2022-11-29 | Carrier Corporation | Gas detection device and method of manufacturing the same |
| WO2022058413A1 (en) * | 2020-09-16 | 2022-03-24 | Gueder Firat | Gas sensor with first and second electrodes and a reagent for binding the target gas |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8704873D0 (en) | 1987-04-08 |
| GB8804887D0 (en) | 1988-03-30 |
| GB2202948B (en) | 1991-10-16 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| 732E | Amendments to the register in respect of changes of name or changes affecting rights (sect. 32/1977) | ||
| 732E | Amendments to the register in respect of changes of name or changes affecting rights (sect. 32/1977) | ||
| PE20 | Patent expired after termination of 20 years |
Effective date: 20080229 |