CA2344486A1 - Thin film heating element - Google Patents
Thin film heating element Download PDFInfo
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- CA2344486A1 CA2344486A1 CA002344486A CA2344486A CA2344486A1 CA 2344486 A1 CA2344486 A1 CA 2344486A1 CA 002344486 A CA002344486 A CA 002344486A CA 2344486 A CA2344486 A CA 2344486A CA 2344486 A1 CA2344486 A1 CA 2344486A1
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- Prior art keywords
- heating element
- thin film
- rare earth
- solution
- element according
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- 238000010438 heat treatment Methods 0.000 title claims abstract description 40
- 239000010409 thin film Substances 0.000 title claims abstract description 24
- 229910052761 rare earth metal Inorganic materials 0.000 claims abstract description 21
- 239000000758 substrate Substances 0.000 claims abstract description 19
- 229910052684 Cerium Inorganic materials 0.000 claims abstract description 13
- GWXLDORMOJMVQZ-UHFFFAOYSA-N cerium Chemical compound [Ce] GWXLDORMOJMVQZ-UHFFFAOYSA-N 0.000 claims abstract description 13
- 229910052746 lanthanum Inorganic materials 0.000 claims abstract description 13
- FZLIPJUXYLNCLC-UHFFFAOYSA-N lanthanum atom Chemical compound [La] FZLIPJUXYLNCLC-UHFFFAOYSA-N 0.000 claims abstract description 13
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 claims abstract description 7
- 229910052787 antimony Inorganic materials 0.000 claims abstract description 7
- WATWJIUSRGPENY-UHFFFAOYSA-N antimony atom Chemical compound [Sb] WATWJIUSRGPENY-UHFFFAOYSA-N 0.000 claims abstract description 7
- 229910052725 zinc Inorganic materials 0.000 claims abstract description 7
- 239000011701 zinc Substances 0.000 claims abstract description 7
- 238000000197 pyrolysis Methods 0.000 claims abstract description 6
- XOLBLPGZBRYERU-UHFFFAOYSA-N tin dioxide Chemical compound O=[Sn]=O XOLBLPGZBRYERU-UHFFFAOYSA-N 0.000 claims abstract description 5
- 229910001887 tin oxide Inorganic materials 0.000 claims abstract description 5
- YMLFYGFCXGNERH-UHFFFAOYSA-K butyltin trichloride Chemical compound CCCC[Sn](Cl)(Cl)Cl YMLFYGFCXGNERH-UHFFFAOYSA-K 0.000 claims abstract description 4
- 229910044991 metal oxide Inorganic materials 0.000 claims description 19
- 150000004706 metal oxides Chemical class 0.000 claims description 19
- 238000000034 method Methods 0.000 claims description 15
- 229910052731 fluorine Inorganic materials 0.000 claims description 6
- 239000011737 fluorine Substances 0.000 claims description 6
- 125000002524 organometallic group Chemical group 0.000 claims description 6
- 238000000151 deposition Methods 0.000 claims description 5
- 238000005118 spray pyrolysis Methods 0.000 claims description 4
- JIAARYAFYJHUJI-UHFFFAOYSA-L zinc dichloride Chemical group [Cl-].[Cl-].[Zn+2] JIAARYAFYJHUJI-UHFFFAOYSA-L 0.000 claims description 4
- 238000000137 annealing Methods 0.000 claims description 2
- FAPDDOBMIUGHIN-UHFFFAOYSA-K antimony trichloride Chemical group Cl[Sb](Cl)Cl FAPDDOBMIUGHIN-UHFFFAOYSA-K 0.000 claims description 2
- 238000004519 manufacturing process Methods 0.000 claims description 2
- 235000005074 zinc chloride Nutrition 0.000 claims description 2
- 239000011592 zinc chloride Substances 0.000 claims description 2
- 150000001805 chlorine compounds Chemical class 0.000 claims 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 claims 2
- PXGOKWXKJXAPGV-UHFFFAOYSA-N Fluorine Chemical compound FF PXGOKWXKJXAPGV-UHFFFAOYSA-N 0.000 claims 2
- NPAIMXWXWPJRES-UHFFFAOYSA-N butyltin(3+) Chemical compound CCCC[Sn+3] NPAIMXWXWPJRES-UHFFFAOYSA-N 0.000 claims 1
- 239000010408 film Substances 0.000 description 25
- 239000002019 doping agent Substances 0.000 description 8
- 239000002585 base Substances 0.000 description 7
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 description 4
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 4
- 239000002241 glass-ceramic Substances 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 150000002910 rare earth metals Chemical class 0.000 description 3
- 230000008901 benefit Effects 0.000 description 2
- 230000008021 deposition Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 230000001105 regulatory effect Effects 0.000 description 2
- 239000007921 spray Substances 0.000 description 2
- 230000003019 stabilising effect Effects 0.000 description 2
- HPGGPRDJHPYFRM-UHFFFAOYSA-J tin(iv) chloride Chemical compound Cl[Sn](Cl)(Cl)Cl HPGGPRDJHPYFRM-UHFFFAOYSA-J 0.000 description 2
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 1
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 1
- 229910052581 Si3N4 Inorganic materials 0.000 description 1
- 229910021627 Tin(IV) chloride Inorganic materials 0.000 description 1
- 238000004378 air conditioning Methods 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- 239000004411 aluminium Substances 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 229910052796 boron Inorganic materials 0.000 description 1
- 230000001680 brushing effect Effects 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 239000012777 electrically insulating material Substances 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 229910052738 indium Inorganic materials 0.000 description 1
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 description 1
- 239000000976 ink Substances 0.000 description 1
- 229910052744 lithium Inorganic materials 0.000 description 1
- 230000000873 masking effect Effects 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 230000002028 premature Effects 0.000 description 1
- 239000010453 quartz Substances 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 description 1
- -1 silicon nitrides Chemical class 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/10—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor
- H05B3/12—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material
- H05B3/14—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material the material being non-metallic
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/10—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor
- H05B3/12—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material
- H05B3/14—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material the material being non-metallic
- H05B3/141—Conductive ceramics, e.g. metal oxides, metal carbides, barium titanate, ferrites, zirconia, vitrous compounds
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/10—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor
- H05B3/12—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Ceramic Engineering (AREA)
- Resistance Heating (AREA)
- Surface Heating Bodies (AREA)
Abstract
A thin film heating element capable of withstanding power densities of 10-20 watts cm-2 and/or temperatures up to 650~C is disclosed. The preferred form of the heating element includes a layer of tin oxide doped with relatively large quantities of cerium and lanthanum deposited on an insulating substrate by pyrolysis of a solution of monobutyl tin trichloride containing the above rare earth elements. The solution and subsequent oxide layer further include donor and acceptor elements such as antimony and zinc to enhance the conductivity of the heating element.
Description
THIN FILM HEATING ELEMENT
BACKGROUND OF THE INVENTION
Received 4 April 2000 This invention relates to heating elements of the kind including an electrically conductive metal oxide film on an electrically insulating substrate.
Such devices are known, and may for example consist of a thin film of tin oxide deposited on a glass substrate by means of pyrolitic deposition.
If such thin film heating elements are to be used in electrical appliances such as cooktops, it is desirable that they be capable of operating at high temperatures, up to 650°C. In applications such as electric kettles where the heating element is small, the element must be capable of handling high power densities, of the order of 10-Watts cm~'. Prior art devices have not proved satisfactory in these conditions. It has been found by the present applicants that tin oxide layers tend to become unstable with increasing temperature, due to the tendency for the oxide to change state. It has also been found that where fluorine is employed as an electron donor or conductivity carrier the properties of the film change irreversibly with increasing temperature, apparently due to the fluorine tending to leave the film at temperatures above 400°C.
We have also found that the tin chloride solutions used in the prior art, for example in the spray pyrolysis process, are not stable in conditions of high humidity due to their hygroscopic properties, and this can lead to lack of uniformity in the oxide films produced.
US Patent No. 4,889,974 of Auding, et al. describes thin film elements intended for temperatures beyond 600°C, using oxide films doped at high levels with pairs of compensating foreign atoms. The metal oxide films are doped with, maximally, mol % of each of the foreign atoms compensating each other in pairs, the quantity of said acceptor-forming elements and said donor-forming elements differing maximally 4MtNDED SHEET
~EA/AU
BACKGROUND OF THE INVENTION
Received 4 April 2000 This invention relates to heating elements of the kind including an electrically conductive metal oxide film on an electrically insulating substrate.
Such devices are known, and may for example consist of a thin film of tin oxide deposited on a glass substrate by means of pyrolitic deposition.
If such thin film heating elements are to be used in electrical appliances such as cooktops, it is desirable that they be capable of operating at high temperatures, up to 650°C. In applications such as electric kettles where the heating element is small, the element must be capable of handling high power densities, of the order of 10-Watts cm~'. Prior art devices have not proved satisfactory in these conditions. It has been found by the present applicants that tin oxide layers tend to become unstable with increasing temperature, due to the tendency for the oxide to change state. It has also been found that where fluorine is employed as an electron donor or conductivity carrier the properties of the film change irreversibly with increasing temperature, apparently due to the fluorine tending to leave the film at temperatures above 400°C.
We have also found that the tin chloride solutions used in the prior art, for example in the spray pyrolysis process, are not stable in conditions of high humidity due to their hygroscopic properties, and this can lead to lack of uniformity in the oxide films produced.
US Patent No. 4,889,974 of Auding, et al. describes thin film elements intended for temperatures beyond 600°C, using oxide films doped at high levels with pairs of compensating foreign atoms. The metal oxide films are doped with, maximally, mol % of each of the foreign atoms compensating each other in pairs, the quantity of said acceptor-forming elements and said donor-forming elements differing maximally 4MtNDED SHEET
~EA/AU
Received 4 April 2000 by 10%. The Auding patent describes the use of indium, boron, aluminium or zinc as the acceptor-forming dopant, and antimony or fluorine as the donor-forming dopant.
However, these films using stannic chloride have been found to be difficult to deposit in humid atmospheres and have been found to be unstable in the power densities of approximately 20 Watts per cm2 required for rapid rise-time applications.
To the applicants' knowledge the films described in the Auding patent have not seen commercial use and are known only from this document.
SUMMARY OF THE INVENTION
The present applicants have found that a metal oxide layer of satisfactory stability in high power density applications may be obtained by doping with at least one and preferably two rare earth elements and that stability can be further enhanced by depositing the layer from different starting solutions than previously employed. The rare earth dopants are preferably cerium and lanthanum. Preferably these two rare earths are present in substantially equal concentrations. The presence of the rare earth dopants in the thin film layer has been found by the present applicants to have the effect of stabilising the oxidation state of the metal.
We have also found that stability at high temperatures may be obtained by further doping with equal quantities of donor and acceptor elements, and by avoiding the use of fluorine as a dopant. The preferred donor and acceptor elements for this purpose are respectively antimony and zinc.
In one aspect, the invention resides in a thin film electrical heating element including a layer of an electrically conducting metal oxide on an electrically insulating substrate, said metal oxide layer being doped with at least one rare earth element and being deposited on said substrate from an organometallic base solution.
AMENO~ED SHEET
However, these films using stannic chloride have been found to be difficult to deposit in humid atmospheres and have been found to be unstable in the power densities of approximately 20 Watts per cm2 required for rapid rise-time applications.
To the applicants' knowledge the films described in the Auding patent have not seen commercial use and are known only from this document.
SUMMARY OF THE INVENTION
The present applicants have found that a metal oxide layer of satisfactory stability in high power density applications may be obtained by doping with at least one and preferably two rare earth elements and that stability can be further enhanced by depositing the layer from different starting solutions than previously employed. The rare earth dopants are preferably cerium and lanthanum. Preferably these two rare earths are present in substantially equal concentrations. The presence of the rare earth dopants in the thin film layer has been found by the present applicants to have the effect of stabilising the oxidation state of the metal.
We have also found that stability at high temperatures may be obtained by further doping with equal quantities of donor and acceptor elements, and by avoiding the use of fluorine as a dopant. The preferred donor and acceptor elements for this purpose are respectively antimony and zinc.
In one aspect, the invention resides in a thin film electrical heating element including a layer of an electrically conducting metal oxide on an electrically insulating substrate, said metal oxide layer being doped with at least one rare earth element and being deposited on said substrate from an organometallic base solution.
AMENO~ED SHEET
Received 4 April 2000 Preferably the metal oxide is deposited on the substrate by pyrolysis of an organometallic base solution containing the at least one rare earth element.
In a preferred form the metal oxide layer is tin oxide and contains two rare earth elements such as cerium and lanthanum.
This aspect of the invention provides a thin film heating element which is capable of withstanding power densities of up to 10-20 Watts cm~' and/or temperatures in excess of 600°C.
In another aspect, the invention resides in a method for the manufacture of a thin film heating element including the step of depositing a layer of metal oxide onto an electrically insulating substrate by pyrolysis of an organometallic base solution containing at least one rare earth element.
Preferably the base solution contains both cerium and lanthanum in concentrations up to 5 moi %.
We have found that superior results can be obtained if the film is prepared by spray pyrolysis from a solution of monobutyl tin trichloride. The stability of this material in high humidity enables consistent results to be obtained across varying atmospheric conditions, by reducing premature oxidation.
BRIEF DESCRIPTION OF THE DRAWINGS - -Fig. 1 is graph showing the power dissipation versus time relationship for a thin film heating element made according to the invention.
Fig. 2 shows the relationship between temperature and power at steady state for five elements having power ratings between 500 and 1330 watts.
DESCRIPTION OF PREFERRED EMBODIMENTS
AMENDED SHEET
~PEA/AU
In a preferred form the metal oxide layer is tin oxide and contains two rare earth elements such as cerium and lanthanum.
This aspect of the invention provides a thin film heating element which is capable of withstanding power densities of up to 10-20 Watts cm~' and/or temperatures in excess of 600°C.
In another aspect, the invention resides in a method for the manufacture of a thin film heating element including the step of depositing a layer of metal oxide onto an electrically insulating substrate by pyrolysis of an organometallic base solution containing at least one rare earth element.
Preferably the base solution contains both cerium and lanthanum in concentrations up to 5 moi %.
We have found that superior results can be obtained if the film is prepared by spray pyrolysis from a solution of monobutyl tin trichloride. The stability of this material in high humidity enables consistent results to be obtained across varying atmospheric conditions, by reducing premature oxidation.
BRIEF DESCRIPTION OF THE DRAWINGS - -Fig. 1 is graph showing the power dissipation versus time relationship for a thin film heating element made according to the invention.
Fig. 2 shows the relationship between temperature and power at steady state for five elements having power ratings between 500 and 1330 watts.
DESCRIPTION OF PREFERRED EMBODIMENTS
AMENDED SHEET
~PEA/AU
Received 4 April 2000 While some benefit will be obtained from quite low concentrations of the rare earth dopant, minimal effects will be observed with concentrations in the pyrolysis solution of 0.01 mol %, preferred concentrations of each of the cerium and lanthanum are between approximately 1.25 mol % and approximately 3.75 mol %. Preliminary tests have shown that stability of the metal oxide layer is maximised when substantially equal concentrations of two rare earth elements, such as cerium and lanthanum, are used. Generally speaking the concentration of these rare earths will be chosen as that which contributes to film stability at the power densities for which the film is intended. Best results for films intended for operation at 20 Watts cm-' have been obtained using equal concentrations of approximately 2.5 mol %.
The film is preferably doped with substantially equal quantities of donor and acceptor elements, the preferred dopants being antimony and zinc. The concentrations of both antimony and zinc will be influenced by the resistivity which is required. We have found base solution concentrations for these materials in the region of 2.8 mol % to be suitable for heating element applications.
A useful characteristic of such films in their application as heating elements arises from the positive temperature coefficient resistance of the film. This enables elements to be produced which are self regulating, in that they will initially operate at a higher wattage and, with increasing temperature, stabilise at the lower design wattage.
The substrate-material will of course be chosen to suit the application.
Suitable substrates include glass ceramics, silicon nitrides and other ceramic substrates as well as metallic substrates coated with high-temperature stable, electrically-insulating materials.
The preferred substrate temperatures for applying the base solution with dopants range from 500 to 750°C. Preferably, for application at 500°C, post annealing at approximately 600°C for at least one hour is carried out to assist in stabilising the film.
AAAEwuED SHEET
Received 4 April 2000 Films according to this invention were manufactured from a solution using the spray pyrolysis process. For this purpose, monobutyl tin trichloride was used as a base solution, with 2.8 mol % antimony chloride, 2.8 mol % zinc chloride, 2.5 mol 5 cerium and 2.5 mol % lanthanum.
These films were fabricated with effective resistances of 26 ohm, 30 ohm and 45 ohm to enable heaters of 2.2 kW, 1.8 kW and 1.2 kW respectively to be used, powered by a 240V mains supply voltage. The films were selectively deposited using high temperature masking inks which were removed by brushing after deposition of the film. The films deposited had a high degree of transparency. The resistive properties of the heating elements remained unchanged after 3500 cycles (40 minutes on and 20 minutes off) at 650°C.
As indicated above, the positive temperature coefficient of resistance of these elements enables a self regulating characteristic to be obtained, with an initially high power dissipation which may be of advantage in achieving more rapid rise to operating temperature. Fig. 1 shows the typical behaviour of the elements, where power dissipation is plotted against time of operation. As will be observed, the dissipation of the element commences at a high level and decreases as the resistance of the element increases with temperature, until a steady state condition is achieved at the design power consumption. Upon temporary cooling of the element, for example through contact with a cooler body to be heated, power dissipation will temporarily increase, assisting in achieving rapid heating.
Fig. 2 shows the relationship between temperature and power at steady state for five elements having power ratings between 500 and 1330 watts.
Life tests have shown that the films are particularly stable on inert substrates like quartz 96% silica in temperatures up to 650°C with power densities in excess of 15.5W/cm' . The films on lower grades of glass ceramics having alkali impurities such as lithium and sodium were stable to 500°C at extremely high power densities.
AMENDED SHEET
PC'T/AU99/00791 Received 4 April 2000 Sheet resistances varying from around 60 ohms to above 400 ohms have been fabricated by varying the number of spray passes. The thin film thickness could be varied between 2000 Angstrom Units to around 14000 Angstrom Units by varying the number of spray passes. The films were deposited on various substrates including glass ceramics, alumina, silica glass and silicon nitride.
As well as their suitability in high temperature and/or high rise time applications, films made in accordance with the invention may be used in low temperature applications, such as comfort heating, refrigerating defrost, and general heating.
Heating elements of tubular shape manufactured using the above technology can be used in heat exchangers for flow applications, air-conditioning re-heaters, hair dryers, washing and drying appliances, and can also be used as radiating surfaces.
While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
AMENDED SHEET _ ~PEA/AU
The film is preferably doped with substantially equal quantities of donor and acceptor elements, the preferred dopants being antimony and zinc. The concentrations of both antimony and zinc will be influenced by the resistivity which is required. We have found base solution concentrations for these materials in the region of 2.8 mol % to be suitable for heating element applications.
A useful characteristic of such films in their application as heating elements arises from the positive temperature coefficient resistance of the film. This enables elements to be produced which are self regulating, in that they will initially operate at a higher wattage and, with increasing temperature, stabilise at the lower design wattage.
The substrate-material will of course be chosen to suit the application.
Suitable substrates include glass ceramics, silicon nitrides and other ceramic substrates as well as metallic substrates coated with high-temperature stable, electrically-insulating materials.
The preferred substrate temperatures for applying the base solution with dopants range from 500 to 750°C. Preferably, for application at 500°C, post annealing at approximately 600°C for at least one hour is carried out to assist in stabilising the film.
AAAEwuED SHEET
Received 4 April 2000 Films according to this invention were manufactured from a solution using the spray pyrolysis process. For this purpose, monobutyl tin trichloride was used as a base solution, with 2.8 mol % antimony chloride, 2.8 mol % zinc chloride, 2.5 mol 5 cerium and 2.5 mol % lanthanum.
These films were fabricated with effective resistances of 26 ohm, 30 ohm and 45 ohm to enable heaters of 2.2 kW, 1.8 kW and 1.2 kW respectively to be used, powered by a 240V mains supply voltage. The films were selectively deposited using high temperature masking inks which were removed by brushing after deposition of the film. The films deposited had a high degree of transparency. The resistive properties of the heating elements remained unchanged after 3500 cycles (40 minutes on and 20 minutes off) at 650°C.
As indicated above, the positive temperature coefficient of resistance of these elements enables a self regulating characteristic to be obtained, with an initially high power dissipation which may be of advantage in achieving more rapid rise to operating temperature. Fig. 1 shows the typical behaviour of the elements, where power dissipation is plotted against time of operation. As will be observed, the dissipation of the element commences at a high level and decreases as the resistance of the element increases with temperature, until a steady state condition is achieved at the design power consumption. Upon temporary cooling of the element, for example through contact with a cooler body to be heated, power dissipation will temporarily increase, assisting in achieving rapid heating.
Fig. 2 shows the relationship between temperature and power at steady state for five elements having power ratings between 500 and 1330 watts.
Life tests have shown that the films are particularly stable on inert substrates like quartz 96% silica in temperatures up to 650°C with power densities in excess of 15.5W/cm' . The films on lower grades of glass ceramics having alkali impurities such as lithium and sodium were stable to 500°C at extremely high power densities.
AMENDED SHEET
PC'T/AU99/00791 Received 4 April 2000 Sheet resistances varying from around 60 ohms to above 400 ohms have been fabricated by varying the number of spray passes. The thin film thickness could be varied between 2000 Angstrom Units to around 14000 Angstrom Units by varying the number of spray passes. The films were deposited on various substrates including glass ceramics, alumina, silica glass and silicon nitride.
As well as their suitability in high temperature and/or high rise time applications, films made in accordance with the invention may be used in low temperature applications, such as comfort heating, refrigerating defrost, and general heating.
Heating elements of tubular shape manufactured using the above technology can be used in heat exchangers for flow applications, air-conditioning re-heaters, hair dryers, washing and drying appliances, and can also be used as radiating surfaces.
While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
AMENDED SHEET _ ~PEA/AU
Claims (29)
1. A thin film electrical heating element including a layer of an electrically conducting metal oxide on an electrically insulating substrate, said metal oxide layer being doped with at least one rare earth element and being deposited on said substrate from an organometallic base solution.
2. A thin film heating element according to claim 1 wherein said metal oxide layer includes at least two rare earth elements.
3. A thin film heating element according to claim 2 wherein said two rare earth elements are present in said metal oxide layer in substantially equal concentrations.
4. A heating element according to claim 2 or 3 wherein said at least two rare earth elements include both cerium and lanthanum.
5. A heating element according to claim 1 wherein said metal oxide is tin oxide.
6. A heating element according to claim 2 wherein said metal oxide layer further includes substantially equal quantities of donor and acceptor elements.
7. A heating element according to claim 6 wherein said donor and acceptor elements are respectively antimony and zinc.
8. A heating element according to claim 6 wherein said metal oxide layer is substantially free of fluorine.
9. A heating element according to claim 1 wherein said heating element is stable at a power density of 20 watts cm-2.
10. A heating element according to claim 1 wherein said heating element is stable at a temperature of 650°C.
11. A thin film heating element according to claim 1 wherein the or each rare earth element is present in said base solution at a concentration up to 5 mol %.
12. A thin film heating element according to claim 11 wherein said at least one rare earth element includes both cerium and lanthanum.
13. A thin film heating element according to claim 12 wherein cerium and lanthanum are each present in said base solution in the range of approximately 1.25 mol % to approximately 3.75 mol %.
14. A thin film heating element according to claim 13 wherein the concentration of each of cerium and lanthanum in said solution is approximately 2.5 mol %.
15. A thin film heating element according to claim 1 wherein said base solution further includes substantially equal quantities of donor and acceptor elements.
16. A thin film heating element according to claim 15 wherein each of said donor and acceptor elements are respectively antimony and zinc and are each present in said solution at a concentration of approximately 2.8 mol %.
17. A thin film heating element according to claim 1 or 12 wherein said base solution is monobutyl tin trichloride.
18. A thin film heating element according to Claim 1 wherein said metal oxide layer is deposited on said substrate from an organometallic base solution using a spray pyrolysis process.
19. A method for the manufacture of a thin film heating element including the step of depositing a layer of metal oxide onto an electrically insulating substrate by pyrolysis of an organometallic base solution containing at least one rare earth element.
20. A method according to claim 19 wherein said solution contains at least two rare earth elements.
21. A method according to claim 20 wherein said two rare earth elements are present in said solution in substantially equal concentrations.
22. A method according to claim 19 wherein said at least one rare earth element is present in said solution in the range of approximately 1.25 mol % to approximately 3.75 mol %.
23. A method according to claim 20 wherein said at least two rare earth element includes both cerium and lanthanum.
24. A method according to claim 23 wherein said cerium and lanthanum are each present in said solution in substantially equal concentrations.
25. A method according to claim 19 wherein said base solution is monobutyl tin trichlorde.
26. A method according to claim 19 wherein said solution further includes chlorides of at least one donor and at least one acceptor element, said donor chlorides and acceptor chlorides being present in said solution in substantially equal concentrations.
27. A method according to claim 26 wherein said donor chloride is antimony chloride and said acceptor chloride is zinc chloride.
28. A method according to claim 19 wherein said solution is substantially free of fluorine.
29. A method according to claim 19 further including the step of annealing said metal oxide layer on said substrate for at least one hour at a temperature higher than the substrate temperature used during said pyrolysis.
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AUPP5995 | 1998-09-18 | ||
AUPP5995A AUPP599598A0 (en) | 1998-09-18 | 1998-09-18 | Self-regulating nanoscale heating element |
PCT/AU1999/000791 WO2000018189A1 (en) | 1998-09-18 | 1999-09-17 | Thin film heating element |
Publications (1)
Publication Number | Publication Date |
---|---|
CA2344486A1 true CA2344486A1 (en) | 2000-03-30 |
Family
ID=3810212
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
CA002344486A Abandoned CA2344486A1 (en) | 1998-09-18 | 1999-09-17 | Thin film heating element |
Country Status (10)
Country | Link |
---|---|
EP (1) | EP1120014A4 (en) |
JP (1) | JP2002525829A (en) |
KR (1) | KR20010079859A (en) |
CN (1) | CN1146301C (en) |
AU (1) | AUPP599598A0 (en) |
BR (1) | BR9913812A (en) |
CA (1) | CA2344486A1 (en) |
ID (1) | ID29148A (en) |
NZ (1) | NZ510655A (en) |
WO (1) | WO2000018189A1 (en) |
Families Citing this family (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE10110789C1 (en) * | 2001-03-06 | 2002-07-04 | Schott Glas | Electrical cooking appliance with non-planar three-dimensional cooking surface of glass or glass ceramic material directly contacted on its outside by resistance heating device |
DE10110792B4 (en) * | 2001-03-06 | 2004-09-23 | Schott Glas | Ceramic cooking system with glass ceramic plate, insulation layer and heating elements |
WO2005051042A1 (en) | 2003-11-20 | 2005-06-02 | Koninklijke Philips Electronics N.V. | Thin- film heating element |
CN100466865C (en) * | 2005-03-21 | 2009-03-04 | 冷同桂 | Composite metal electrothermic film sol and preparing process thereof |
US7926209B2 (en) | 2007-02-13 | 2011-04-19 | Advanced Materials Enterprises Company Limited | Electric iron |
US8193475B2 (en) * | 2007-02-13 | 2012-06-05 | Advanced Materials Enterprises Company Limited | Heating apparatus and method for making the same |
WO2009105945A1 (en) * | 2008-02-28 | 2009-09-03 | Advanced Materials Enterprises Co., Ltd. | Electric iron |
Family Cites Families (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
SU886328A1 (en) * | 1980-03-28 | 1981-11-30 | Институт Электроники Ан Белсср | Current conducting material for film electric heaters |
DE3324647A1 (en) * | 1983-07-08 | 1985-01-17 | Schott Glaswerke, 6500 Mainz | DIVING METHOD FOR THE PRODUCTION OF TRANSPARENT, ELECTRICALLY CONDUCTIVE, DOPED INDIUMOXIDE LAYERS |
DE3705639A1 (en) * | 1987-02-21 | 1988-09-01 | Philips Patentverwaltung | THICK LAYER HEATING ELEMENT |
JPH07105282B2 (en) * | 1988-05-13 | 1995-11-13 | 富士ゼロックス株式会社 | Resistor and method of manufacturing resistor |
CN1036432C (en) * | 1992-07-09 | 1997-11-12 | 连铁军 | Thermostable transparent electric heating film and its producing method |
US5616266A (en) * | 1994-07-29 | 1997-04-01 | Thermal Dynamics U.S.A. Ltd. Co. | Resistance heating element with large area, thin film and method |
-
1998
- 1998-09-18 AU AUPP5995A patent/AUPP599598A0/en not_active Abandoned
-
1999
- 1999-09-17 KR KR1020017003505A patent/KR20010079859A/en not_active Application Discontinuation
- 1999-09-17 CN CNB998107727A patent/CN1146301C/en not_active Expired - Fee Related
- 1999-09-17 NZ NZ510655A patent/NZ510655A/en unknown
- 1999-09-17 CA CA002344486A patent/CA2344486A1/en not_active Abandoned
- 1999-09-17 EP EP99947118A patent/EP1120014A4/en not_active Withdrawn
- 1999-09-17 BR BR9913812-3A patent/BR9913812A/en not_active IP Right Cessation
- 1999-09-17 ID IDW20010871A patent/ID29148A/en unknown
- 1999-09-17 JP JP2000571716A patent/JP2002525829A/en active Pending
- 1999-09-17 WO PCT/AU1999/000791 patent/WO2000018189A1/en not_active Application Discontinuation
Also Published As
Publication number | Publication date |
---|---|
CN1317223A (en) | 2001-10-10 |
BR9913812A (en) | 2001-08-14 |
AUPP599598A0 (en) | 1998-10-08 |
JP2002525829A (en) | 2002-08-13 |
EP1120014A4 (en) | 2004-06-16 |
WO2000018189A1 (en) | 2000-03-30 |
EP1120014A1 (en) | 2001-08-01 |
KR20010079859A (en) | 2001-08-22 |
NZ510655A (en) | 2003-05-30 |
ID29148A (en) | 2001-08-02 |
CN1146301C (en) | 2004-04-14 |
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