US4086101A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Photovoltaic cells
Assignee: TOTAL ENERGIE DEVELOPPEMENT
•
Filing: 1975-11-14
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Granted: 1978-04-25
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Expires: 1995-11-14
Abstract
Abstract A method of making low cost photovoltaic cells on a large scale basis by means of a continuous process of coating sheet glass while the sheet glass moves in and has its under surface immersed in a tank of molten material, comprising forming the film of CdS microcrystals on the glass sheet, which has previously been coated with transparent SnO x to a thickness of about 0.3 to 0.6 microns. A water solution of a cadmium salt, a sulphur compound, and an aluminum containing soluble compound is intermittenty sprayed on said glass while its exposed surface is maintained at a constant temperature in the range 500° F to 1100° F and while irradiating the surface with intense ultraviolet light so as to form a film of CdS microcrystals. This CdS film has Al impregnated within the stratum of the film adjacent to the SnO x , but only optionally has Al impregnated in the stratum of the CdS film adjacent to the exposed surface of the CdS film. After the spray process is completed, the temperature of the sheet of glass is brought to the range 450° C to 550° C, 525° being optium. After heating, the glass is cooled to approximately room temperature and the exposed surface of the CdS is converted to Cu x S, the x of Cu x S being as close to 2 as possible, by dipping the coated glass in a solution comprising: a solvent, which may be water; a weak acid, such as tartaric acid, citric acid, or lactic acid; a copper containing compound; and, optionally, a quantity of H 2 Ce(SO 4 ) 4 and NaCl, or some other chloride; or by electroplating to form a film of Cu x S; or, by a combination of dipping and electroplating. The Cu x S forming process proceeds by ion exchange, i.e., S from CdS combines with Cu to form Cu x S. Cu is then applied over the Cu x S, and the cell is cured at a temperature in the range 400° F to 500° F.
Inventors
- 👤 John Francis Jordan
- 👤 Curtis Magill Lampkin
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 23:27
CPC Classifications
H; H10; H10F; H10F10/00; H10F10/10; H10F10/16; H10F10/169; C; C03; C03C; C03C17/00; C03C17/34; C03C17/3411; C03C17/3429; C03C17/3464; C03C17/347; H10P; H10P95/00; Y; Y02; Y02E; Y02E10/00; Y02E10/50
Claims Analysis
Total Claims: 75
Claim 1
Independent Claim
84 words
A method of making a photovoltaic cell of the type having an insulating substrate, a first conductive layer, a second layer comprised of CdS, and a third layer forming a heterojunction with said second layer, comprising the step of forming at least a portion of said CdS layer with a composition comprising a cadmium salt, a sulphur containing compound, and an aluminum containing compound, the aluminum content of the composition being at least 10 molar percent of the total metal content of the composition.
Claim 2
Independent Claim
84 words
A method of making a photovoltaic cell of the type having an insulating substrate, a first conductive layer, a second layer comprised of CdS, and a third layer forming a heterojunction with said second layer, comprising the step of forming at least a portion of said CdS layer with a composition comprising a cadmium salt, a sulphur containing compound, and an aluminum containing compound, the aluminum content of the composition being at least 10 molar percent of the total metal content of the composition.
Claim 3
Dependent Claim
41 words
The method according to claim 1, further comprising the step of heat treating said CdS layer in an oxygen containing atmosphere at a temperature in the range 450° C to 550° C at some time prior to forming said third layer.
Claim 4
Dependent Claim
15 words
The method according to claim 1, wherein said aluminum containing compound is AlCl 3 .
Claim 5
Dependent Claim
21 words
The method according to claim 1, wherein said second layer is sprayed to a thickness of about 2 to 4 microns.
Claim 6
Dependent Claim
13 words
The method according to claim 1, wherein the composition is a water solution.
Claim 7
Dependent Claim
14 words
The method according to claim 1, wherein the cadmium salt is CdCl 2 .
Claim 8
Dependent Claim
13 words
The method according to claim 1, wherein the sulphur containing compound is thiourea.
Claim 9
Dependent Claim
24 words
The method according to claim 1, wherein the method includes the further step of irradiating said CdS layer with ultraviolet light during its formation.
Claim 10
Independent Claim
59 words
A method of making a photovoltaic cell on an insulating substrate comprising the step of applying a solution comprising a cadmium salt, a sulphur containing compound, an aluminum containing compound, and a solvent, the aluminum content of the solution being at least 10 molar percent of the total metal ion content, to form a film of CdS containing aluminum.
Claim 11
Independent Claim
59 words
A method of making a photovoltaic cell on an insulating substrate comprising the step of applying a solution comprising a cadmium salt, a sulphur containing compound, an aluminum containing compound, and a solvent, the aluminum content of the solution being at least 10 molar percent of the total metal ion content, to form a film of CdS containing aluminum.
Claim 12
Independent Claim
59 words
A method of making a photovoltaic cell comprising the step of applying over an insulating substrate a composition containing a cadmium salt, a sulphur containing compound, and an aluminum containing compound, the aluminum content of the composition being at least 10 molar percent of the total metal content of the composition, to form a film of CdS containing aluminum.
Claim 13
Independent Claim
59 words
A method of making a photovoltaic cell comprising the step of applying over an insulating substrate a composition containing a cadmium salt, a sulphur containing compound, and an aluminum containing compound, the aluminum content of the composition being at least 10 molar percent of the total metal content of the composition, to form a film of CdS containing aluminum.
Claim 14
Dependent Claim
12 words
A photovoltaic cell fabricated in accordance with the method of claim 10.
Claim 15
Independent Claim
153 words
A method of making a photovoltaic cell of the type having an insulating substrate, a first conductive layer, a second layer comprised of one or more stratums of CdS, and a third layer forming a heterojunction with said second layer, comprising the steps of: maintaining the substrate having the first layer thereon at a constant temperature in the range 500° F - 1100° F; spraying onto the first layer a solution comprising a cadmium salt, a sulphur containing compound, an aluminum containing compound, and a solvent, the aluminum content of the solution being at least 10 molar percent of the total metal ion content of the solution, to form a first stratum of the second layer comprised of CdS containing aluminum; and spraying onto the first stratum of the second layer a solution comprising a cadmium salt, a sulphur containing compound, and a solvent, to form a second stratum of the second layer.
Claim 16
Independent Claim
153 words
A method of making a photovoltaic cell of the type having an insulating substrate, a first conductive layer, a second layer comprised of one or more stratums of CdS, and a third layer forming a heterojunction with said second layer, comprising the steps of: maintaining the substrate having the first layer thereon at a constant temperature in the range 500° F - 1100° F; spraying onto the first layer a solution comprising a cadmium salt, a sulphur containing compound, an aluminum containing compound, and a solvent, the aluminum content of the solution being at least 10 molar percent of the total metal ion content of the solution, to form a first stratum of the second layer comprised of CdS containing aluminum; and spraying onto the first stratum of the second layer a solution comprising a cadmium salt, a sulphur containing compound, and a solvent, to form a second stratum of the second layer.
Claim 17
Dependent Claim
29 words
The method according to claim 12, further comprising the step of converting the exposed surface of the second layer to Cu X S by a method including ion exchange.
Claim 18
Dependent Claim
25 words
The method according to claim 12, wherein the method includes the further step of irradiating the second layer with ultraviolet light during the spray process.
Claim 19
Dependent Claim
41 words
The method according to claim 12, further comprising the step of heat treating the cell in an oxygen containing atmosphere at a temperature in the range 450° C to 550° C at some time prior to formation of said third layer.
Claim 20
Dependent Claim
15 words
The method according to claim 15, wherein said aluminum containing compound is AlCl 3 .
Claim 21
Dependent Claim
21 words
The method according to claim 15, wherein said second layer is sprayed to a thickness of about 2 to 4 microns.
Claim 22
Dependent Claim
11 words
The method according to claim 15, wherein the solvent is water.
Claim 23
Dependent Claim
14 words
The method according to claim 15, wherein the cadmium salt is CdCl 2 .
Claim 24
Dependent Claim
13 words
The method according to claim 15, wherein the sulphur containing compound is thiourea.
Claim 25
Independent Claim
97 words
A method of making a photovoltaic cell including forming a film containing CdS and aluminum on a conductive film formed over an insulation substrate comprising maintaining said substrate uniformly at a temperature in the range 500° F-1100° F while spraying CdS forming solutions, in sequence, said solutions including the proportions, first: 2 liters Water 60 cc : 1 Molar CdCl 2 solution 68 cc : 1 Molar thiourea solution 1.95 gm AlCl 3 . 6H 2 O and, second: 5 liters Water 150 cc : 1 Molar CdCl 2 solution 150 cc : 1 Molar thiourea solution.
Claim 26
Independent Claim
97 words
A method of making a photovoltaic cell including forming a film containing CdS and aluminum on a conductive film formed over an insulation substrate comprising maintaining said substrate uniformly at a temperature in the range 500° F-1100° F while spraying CdS forming solutions, in sequence, said solutions including the proportions, first: 2 liters Water 60 cc : 1 Molar CdCl 2 solution 68 cc : 1 Molar thiourea solution 1.95 gm AlCl 3 . 6H 2 O and, second: 5 liters Water 150 cc : 1 Molar CdCl 2 solution 150 cc : 1 Molar thiourea solution.
Claim 27
Independent Claim
78 words
A method of making a photovoltaic cell including forming a film containing CdS and aluminum on a conductive film formed over an insulating substrate, which includes the steps of maintaining said substrate at a constant temperature in the range 500°-1100° F while spraying thereon a water solution of CdCl 2 , thiourea and soluble aluminum containing salt, the aluminum content of said solution being at least 10 molar percent of the total metal ion content of the solution.
Claim 28
Independent Claim
78 words
A method of making a photovoltaic cell including forming a film containing CdS and aluminum on a conductive film formed over an insulating substrate, which includes the steps of maintaining said substrate at a constant temperature in the range 500°-1100° F while spraying thereon a water solution of CdCl 2 , thiourea and soluble aluminum containing salt, the aluminum content of said solution being at least 10 molar percent of the total metal ion content of the solution.
Claim 29
Dependent Claim
15 words
The method according to claim 22, wherein said aluminum containing salt is AlCl 3 .
Claim 30
Dependent Claim
18 words
The method according to claim 22, wherein said film is sprayed to a thickness of about 2-4 microns.
Claim 31
Dependent Claim
28 words
The method according to claim 22, further comprising the step of depositing a further film consisting of essentially only CdS on said film containing cadmium sulfide and aluminum.
Claim 32
Dependent Claim
40 words
The method according to claim 22, wherein the method includes a further step of spraying a solution consisting essentially of cadmium chloride and thiourea on said film containing cadmium sulfide and aluminum to form a further film of cadmium sulfide.
Claim 33
Dependent Claim
36 words
The method according to claim 26, wherein the method includes the further step of heating said substrate after said further cadmium sulfide film is formed to a temperature in the range 450° C to 550° C.
Claim 34
Dependent Claim
31 words
The method according to claim 27, wherein the method includes the further step of coating said further cadmium sulfide film with the CU x S after the heating step is completed.
Claim 35
Dependent Claim
23 words
The method according to claim 27, wherein the method includes the further step of said further cadmium sulfide film a solution including CuCl.
Claim 36
Dependent Claim
58 words
The method according to claim 27, wherein is included the further step of coating said further cadmium sulfide film with a solution essentially in the proportions: 700 cc : Water 1.4 cc : HNO 3 (5-1) 1.5 gm : CuCl 1.5 gm : H 2 Ce(SO 4 ) 4 1.5 gm : NaCl 1.5 gm : (L+)-Tartaric acid
Claim 37
Dependent Claim
20 words
The method according to claim 30, wherein the method includes the further step of applying an electrode to said cell.
Claim 38
Independent Claim
87 words
The method of fabricating a photovoltaic cell on an insulating substrate including forming a film of CdS including at least a stratum containing aluminum, which film is formed by applying over said substrate a composition having an aluminum content of at least 10 molar percent of the total metal content of the composition, forming on said layer containing CdS and aluminum a further film of CdS which is substantially free of said aluminum, and forming over said further film of CdS a layer of Cu x S.
Claim 39
Independent Claim
87 words
The method of fabricating a photovoltaic cell on an insulating substrate including forming a film of CdS including at least a stratum containing aluminum, which film is formed by applying over said substrate a composition having an aluminum content of at least 10 molar percent of the total metal content of the composition, forming on said layer containing CdS and aluminum a further film of CdS which is substantially free of said aluminum, and forming over said further film of CdS a layer of Cu x S.
Claim 40
Dependent Claim
18 words
The method according to claim 32, wherein said layer of Cu x S is stoichiometrically Cu 2 S.
Claim 41
Dependent Claim
21 words
The method according to claim 32, wherein said layer of Cu x S is formed by a method including ion exchange.
Claim 42
Dependent Claim
77 words
The process of fabricating a photovoltaic cell, comprising applying over an insulating substrate a film of CdS containing aluminum in a lower stratum of the cross-section of said film and substantially no aluminum in the remaining cross-section of the film, which is formed by initially using a composition having an aluminum content of at least 10 molar percent of the total metal content of the composition and then using a composition having little or no aluminum content.
Claim 43
Dependent Claim
77 words
The process of fabricating a photovoltaic cell, comprising applying over an insulating substrate a film of CdS containing aluminum in a lower stratum of the cross-section of said film and substantially no aluminum in the remaining cross-section of the film, which is formed by initially using a composition having an aluminum content of at least 10 molar percent of the total metal content of the composition and then using a composition having little or no aluminum content.
Claim 44
Independent Claim
79 words
The method of making a CdS-Cu x S photovoltaic cell which includes forming by ion exchange a layer of Cu x S on a layer of CdS, said layer of CdS being about 2 to 4 microns in thickness and including aluminum, at least through a portion of its thickness, formed by applying over an insulating substrate a composition having an aluminum content of at least 10 molar percent by weight of the total metal content of the composition.
Claim 45
Independent Claim
79 words
The method of making a CdS-Cu x S photovoltaic cell which includes forming by ion exchange a layer of Cu x S on a layer of CdS, said layer of CdS being about 2 to 4 microns in thickness and including aluminum, at least through a portion of its thickness, formed by applying over an insulating substrate a composition having an aluminum content of at least 10 molar percent by weight of the total metal content of the composition.
Claim 46
Independent Claim
48 words
A method of making a photovoltaic cell, comprising the step of forming over an insulating substrate a layer of CdS containing Al in an amount effective to inhibit permeation through said layer of a solution capable of forming Cu x S when applied to said layer of CdS.
Claim 47
Independent Claim
48 words
A method of making a photovoltaic cell, comprising the step of forming over an insulating substrate a layer of CdS containing Al in an amount effective to inhibit permeation through said layer of a solution capable of forming Cu x S when applied to said layer of CdS.
Claim 48
Dependent Claim
12 words
A photovoltaic cell fabricated in accordance with the method of claim 37.
Claim 49
Independent Claim
79 words
The method of making a photovoltaic cell, comprising forming on a conductive film formed over an insulating substrate a layer of CdS containing aluminum in an amount effective to inhibit permeation to said conductive film of a solution capable of forming Cu x S when applied to said layer of CdS and forming a layer of Cu x S over said layer of CdS by applying to said layer of CdS said solution capable of forming Cu x S.
Claim 50
Independent Claim
79 words
The method of making a photovoltaic cell, comprising forming on a conductive film formed over an insulating substrate a layer of CdS containing aluminum in an amount effective to inhibit permeation to said conductive film of a solution capable of forming Cu x S when applied to said layer of CdS and forming a layer of Cu x S over said layer of CdS by applying to said layer of CdS said solution capable of forming Cu x S.
Claim 51
Dependent Claim
42 words
The method according to claim 37, wherein said layer of Cu x S is applied by dipping said substrate in a solution, maintained at a temperature less than 25° C, containing a copper containing compound for ion exchange of Cu for Cd.
Claim 52
Independent Claim
92 words
A method of making a photovoltaic cell including forming a film of CdS microcrystals on a conductive surface of a substrate, comprising maintaining said substrate uniformly at a temperature in the range 500° F-1100° F while spraying thereon CdS forming solutions, in sequence, said solutions including the proportions, first: 8 liters: Water 18.63 gm: CdCl 2 · 21/2 H 2 O 8.77 gm: Thiourea 6.96 gm: AlCl 3 · 6H 2 O 2 cc: Hydrochloric acid and, second: 4 liters: Water 24.70: CdCl 2 · 21/2 H 2 O 10.96 gm: Thiourea
Claim 53
Independent Claim
92 words
A method of making a photovoltaic cell including forming a film of CdS microcrystals on a conductive surface of a substrate, comprising maintaining said substrate uniformly at a temperature in the range 500° F-1100° F while spraying thereon CdS forming solutions, in sequence, said solutions including the proportions, first: 8 liters: Water 18.63 gm: CdCl 2 · 21/2 H 2 O 8.77 gm: Thiourea 6.96 gm: AlCl 3 · 6H 2 O 2 cc: Hydrochloric acid and, second: 4 liters: Water 24.70: CdCl 2 · 21/2 H 2 O 10.96 gm: Thiourea
Claim 54
Independent Claim
78 words
A method of making a photovoltaic cell comprising forming over an insulating substrate a layer of CdS including at least a stratum containing aluminum, which layer is formed by using a composition having an aluminum content of at least 10 molar percent of the total metal content of the composition, and forming a layer of Cu x S over said layer of CdS by electroplating in a copper containing solution to accomplish ion exchange of Cu for Cd.
Claim 55
Independent Claim
78 words
A method of making a photovoltaic cell comprising forming over an insulating substrate a layer of CdS including at least a stratum containing aluminum, which layer is formed by using a composition having an aluminum content of at least 10 molar percent of the total metal content of the composition, and forming a layer of Cu x S over said layer of CdS by electroplating in a copper containing solution to accomplish ion exchange of Cu for Cd.
Claim 56
Dependent Claim
32 words
The process according to claim 42, wherein said step of forming a layer of Cu x S by ion exchange is conducted in an electrolyte containing cupric acetate from a copper anode.
Claim 57
Dependent Claim
28 words
The process according to claim 42, wherein said solution is in the proportions: 700 cc: H 2 O 10 gm: Cupric acetate pentahydrate 15 cc: Acetic acid (20%)
Claim 58
Dependent Claim
33 words
The process according to claim 42, wherein said solution is in the proportions: 700 cc: H 2 O 3.9 gm: Citric acid monohydrate 2.0 gm: NH 4 Cl 7.5 gm: Cupric acetate pentahydrate.
Claim 59
Dependent Claim
28 words
The process according to claim 42, wherein said solution is in the proportions: 700 cc: H 2 O 3.9 gm: Citric acid monohydrate 7.5 gm: Cupric acetate pentahydrate.
Claim 60
Dependent Claim
33 words
The process according to claim 42, wherein said solution is in the proportions: 700 cc: H 2 O 7 gm: Citric acid monohydrate 1.2 gm: NH 4 Cl 5 gm: Cupric acetate pentahydrate.
Claim 61
Dependent Claim
26 words
The process according to claim 42, wherein said ion exchange is accomplished at a current density of about 0.5 ma per cm 2 for 2-5 minutes.
Claim 62
Independent Claim
79 words
A method of making a photovoltaic cell on an insulating substrate of the type having a layer of CdS at least a stratum of which contains aluminum in an amount effective to inhibit penetration by copper containing solutions comprising forming a layer of Cu x S over said layer of CdS by ion exchange of Cu for Cd by a combination of dipping the cell in a first copper containing solution and electroplating in a second copper containing solution.
Claim 63
Independent Claim
79 words
A method of making a photovoltaic cell on an insulating substrate of the type having a layer of CdS at least a stratum of which contains aluminum in an amount effective to inhibit penetration by copper containing solutions comprising forming a layer of Cu x S over said layer of CdS by ion exchange of Cu for Cd by a combination of dipping the cell in a first copper containing solution and electroplating in a second copper containing solution.
Claim 64
Independent Claim
62 words
A method of making a photovoltaic cell, comprising the step of applying over an insulating substrate a solution comprising a cadmium salt, a sulphur containing compound, hydrochloric acid, a solvent, and an aluminum containing compound, the aluminum content of the solution being at least 10 molar percent of the metal content of the solution, to form a film of CdS containing aluminum.
Claim 65
Independent Claim
62 words
A method of making a photovoltaic cell, comprising the step of applying over an insulating substrate a solution comprising a cadmium salt, a sulphur containing compound, hydrochloric acid, a solvent, and an aluminum containing compound, the aluminum content of the solution being at least 10 molar percent of the metal content of the solution, to form a film of CdS containing aluminum.
Claim 66
Independent Claim
60 words
A method of making a photovoltaic cell comprising the step of applying over an insulating substrate a composition comprising a cadmium salt, a sulphur containing compound, hydrochloric acid, and an aluminum containing compound, the aluminum content of the composition being at least 10 molar percent of the metal content of the compositon, to form a film containing CdS and aluminum.
Claim 67
Independent Claim
60 words
A method of making a photovoltaic cell comprising the step of applying over an insulating substrate a composition comprising a cadmium salt, a sulphur containing compound, hydrochloric acid, and an aluminum containing compound, the aluminum content of the composition being at least 10 molar percent of the metal content of the compositon, to form a film containing CdS and aluminum.
Claim 68
Independent Claim
84 words
A method of making a photovoltaic cell of the type having an insulating substrate, first layer of conductive material, a second layer having at least a portion containing aluminum in an amount effective to inhibit penetration of a solution containing a heterojunction-forming material through said second layer to said first layer, a third layer forming said heterojunction with said second layer, wherein at least one of the layers is deposited thereon by a spray process using a spray comprised of essentially uniform droplet sizes.
Claim 69
Independent Claim
84 words
A method of making a photovoltaic cell of the type having an insulating substrate, first layer of conductive material, a second layer having at least a portion containing aluminum in an amount effective to inhibit penetration of a solution containing a heterojunction-forming material through said second layer to said first layer, a third layer forming said heterojunction with said second layer, wherein at least one of the layers is deposited thereon by a spray process using a spray comprised of essentially uniform droplet sizes.
Claim 70
Dependent Claim
24 words
A photovoltaic cell comprising a plurality of films wherein at least one of the films is formed by the method described in claim 52.
Claim 71
Independent Claim
135 words
The method of fabricating a photovoltaic cell comprising the step of forming over an insulating substrate a layer comprised of CdS and containing aluminum in an amount effective to inhibit permeation through said layer of a solution of a material forming a heterojunction with said CdS by a spray process conducted while said substrate is maintained at a constant temperature by contacting a portion of said substrate with a molten material, by said spray process being conducted in repeated intermittent stages, each of said stages spraying only a portion of said surface at any instant of time, and at a sufficiently small rate of spray, so that said molten material is able to supply heat to said substrate at a rate sufficient to maintain the temperature of said substrate essentially constant during the spray process.
Claim 72
Independent Claim
135 words
The method of fabricating a photovoltaic cell comprising the step of forming over an insulating substrate a layer comprised of CdS and containing aluminum in an amount effective to inhibit permeation through said layer of a solution of a material forming a heterojunction with said CdS by a spray process conducted while said substrate is maintained at a constant temperature by contacting a portion of said substrate with a molten material, by said spray process being conducted in repeated intermittent stages, each of said stages spraying only a portion of said surface at any instant of time, and at a sufficiently small rate of spray, so that said molten material is able to supply heat to said substrate at a rate sufficient to maintain the temperature of said substrate essentially constant during the spray process.
Claim 73
Dependent Claim
12 words
A photovoltaic cell fabricated in accordance with the method of claim 54.
Claim 74
Independent Claim
132 words
A method of fabricating a photovoltaic cell on an electrically conductive surface of an insulating substrate comprising: heating said substrate to maintain said substrate at a constant temperature while leaving said electrically conductive surface exposed; spraying onto said electrically conductive surface a solution of plural compounds which interact on said surface to form a layer of CdS at least a portion of which contains aluminum in an amount effective to inhibit permeation through said layer by a solution of material forming a heterojunction with said CdS; said spray process being conducted in repeated, intermittent stages, each of said stages spraying only a portion of said surface at any instant of time and at a sufficiently small rate of spray to maintain the temperature of said surface essentially constant during the spray process.
Claim 75
Independent Claim
132 words
A method of fabricating a photovoltaic cell on an electrically conductive surface of an insulating substrate comprising: heating said substrate to maintain said substrate at a constant temperature while leaving said electrically conductive surface exposed; spraying onto said electrically conductive surface a solution of plural compounds which interact on said surface to form a layer of CdS at least a portion of which contains aluminum in an amount effective to inhibit permeation through said layer by a solution of material forming a heterojunction with said CdS; said spray process being conducted in repeated, intermittent stages, each of said stages spraying only a portion of said surface at any instant of time and at a sufficiently small rate of spray to maintain the temperature of said surface essentially constant during the spray process.
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USPTO Annuity & Maintenance Windows
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| 3.5 Years (Year 4) | 1981-04-24 | 1981-10-24 | 1982-04-25 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1985-04-24 | 1985-10-24 | 1986-04-25 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1989-04-24 | 1989-10-24 | 1990-04-25 | $7700.00 | Window Closed / Lapsed |