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  Contamination-resistant gas sensor elementUSPTO Application #: 20070246360Title: Contamination-resistant gas sensor element Abstract: A contamination-resistant sensor element and methods for making the same are provided. A sensor element may include a contamination-resistant coating on at least a portion thereof. The coating may comprise gamma-delta alumina and lithium oxide and may have a thickness of about 100 to about 600 microns and a porosity of about 20 to about 70 percent. The method may include using gamma-delta alumina and lithium oxide to form a mixture, applying the mixture to at least a portion of a sensor element, and temperature treated the mixture to form a contamination-resistant coating on the surface of the measuring cell. (end of abstract) Agent: Michael Best & Friedrich LLP - Milwaukee, WI, US Inventors: Jens Stefan Schneider, James Richard Waldrop, Velma Viane Massey, Donald Stanley Frost USPTO Applicaton #: 20070246360 - Class: 204429000 (USPTO) Related Patent Categories: Chemistry: Electrical And Wave Energy, Apparatus, Electrolytic, Analysis And Testing, Solid Electrolyte, Gas Sample Sensor, With Gas Reference Material, , The Patent Description & Claims data below is from USPTO Patent Application 20070246360. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a divisional of and claims priority to U.S. patent application Ser. No. 10/361,872, filed on Feb. 10, 2003, the entire content of which is hereby incorporated by reference. BACKGROUND OF THE INVENTION [0002] A wide variety of gas sensors and gas sensor elements are used to measure different gases. More particularly, a sensor element of an exhaust gas sensor may be used in automotive applications to measure different gases (e.g., oxygen) in the exhaust gas. [0003] Over time, however, different components in the exhaust gases tend to contaminate different parts of the gas sensor. More specifically, components such as lead, phosphorus, silicon, manganese, zinc, calcium, phosphates, oil ashes, rusts, metal oxides and other elements in the exhaust gas may tend to contaminate the electrode. More particularly, an outer electrode of the sensing element may be contaminated, and the porosity of the protective layer system may also be clogged, eventually affecting the functioning of the sensor and sometimes rendering the sensor or sensor element inoperable. Acidic exhaust components such as P.sub.xO.sub.y and SO.sub.x, wherein x and y are positive whole numbers, may also contaminate the sensor element, as well as reactive catalyst poisons such as lead, silicon and bismuth compounds. As a result, protective coatings are continually being sought in order to inhibit and/or prevent contamination of sensor elements and gas sensors. SUMMARY OF THE INVENTION [0004] In one aspect, the invention may provide a sensor element comprising a contamination-resistant coating on at least a portion thereof. The coating may comprise gamma-delta alumina and lithium oxide. The coating may or may not further comprise at least one of titanium oxide, lanthanum oxide, boehmite alumina and a combination thereof. [0005] In another aspect, the invention may provide a method of making a contamination-resistant sensor element. The method generally includes using gamma--delta alumina and a lithium compound to form a mixture, applying the mixture to at least a portion of a sensor element, and temperature treating the mixture to form a contamination-resistant coating on the sensor element. The other oxides listed above may or may not be used to form the mixture. BRIEF DESCRIPTION OF THE DRAWINGS [0006] FIG. 1 shows a cross-section through an exhaust-gas-side part of a sensor element. [0007] FIG. 2 shows an enlarged view of a layer system of the sensor element illustrated in FIG. 1. [0008] FIG. 3 shows a cross-section (similar to FIG. 1), in which a contamination-resistant coating is applied using an adhesive. [0009] FIG. 4 shows a cross-section (similar to FIG. 1), in which another contamination-resistant coating is applied using a different adhesive application technique. [0010] FIG. 5 shows a cross-section (similar to FIG. 1), in which another contamination-resistant coating is applied using a different adhesive application technique. [0011] FIG. 6 shows a cross-section (similar to FIG. 1), in which another contamination-resistant coating is applied using a different adhesive application technique. [0012] FIG. 7 shows a cross-section (similar to FIG. 1), in which no protective porous layer is applied to the sensor element, to which the contamination-resistant coating adheres. DETAILED DESCRIPTION OF THE INVENTION [0013] A plate-shaped or planar sensor element 10 of an automotive gas sensor element is illustrated in the figures as described above. The protective coatings described herein may be applied to this specific sensor planar sensor element (described below), as well as to a wide variety of sensor elements as will be understood by those of ordinary skill in the art. In other words, the application of the protective coatings of the present invention as described herein should in no way be limited to the particular sensor element described below. Sensor element 10 is intended to be one illustrative example. [0014] The sensor element 10 of the figures has an electrochemical measuring cell 12 and a heating element 14. Measuring cell 12 has, for example, a first solid electrolyte foil 21 with a top surface 22 on the measured gas side and a large surface 23 on the reference gas side, as well as a second solid electrolyte foil 25 with a reference channel 26 integrated therein. On large surface 22 on the measured gas side there is a measuring electrode 31 with a printed conductor 32 and a first terminal contact 33. On large surface 23 on the reference gas side of first solid electrolyte foil 21, there is a reference electrode 35 with a printed conductor 36. Furthermore, a through-plating 38 is provided in first solid electrolyte foil 21, through which printed conductor 36 of reference electrode 35 is guided to large surface 22 on the measured gas side. In addition, first terminal contact 33, a second terminal contact 39, connected to through-plating 38 and thus forming the contact point for reference electrode 35, is also located on large surface 22. Measuring electrode 31 is covered with a porous protective layer 28. [0015] The porous protective layer 28 may comprise at least one of a zirconium oxide, aluminum oxide, titanium oxide, magnesium oxide, and a combination thereof. The porosity of the coating is generally greater than about 10 percent, and more particularly, greater than about 25 percent. The porosity is usually less than about 75 percent, and more particularly, less than about 55 percent. Generally the protective layer 28 is sintered at a high temperature and is mechanically very robust but its capacity to absorb contaminants is considerably lower than that of protective layer 62. The thickness of the layer 28 may be greater than about 30 microns. Generally, the thickness of the layer 28 is less than about 250 microns. [0016] The heating element 14 has, for example, a support foil 41 with an outer large surface 43 and an inner large surface 43', which, in this embodiment is composed of the material of the two solid electrolyte foils 21, 25. An outer insulation layer 42 may be applied to inner large surface 43' of support foil 41. A resistance heater 44 with a wave-form heating conductor 45 and two terminal conductors 46 is located on outer insulation layer 42. Outer insulation layer 42 and support foil 41 have two heater through-platings 48 each flush to one another, which run from the two terminal conductors 46 to outer large surface 43 of support foil 41. Two heater terminal contacts 49 are arranged on outer large surface 43 of support foil 41, which are connected to heater through-platings 48. [0017] An inner insulation layer 50 is on resistance heater 44. The large surface of inner insulation layer 50 is connected to the large surface of the second solid electrolyte foil 25. Thus heating element 14 is thermally connected to measuring cell 12 via inner insulation layer 50. [0018] The two solid electrolyte foils 21 and 25 and support foil 41 may be composed of ZrO.sub.2, partially stabilized with 5 mol. percent Y.sub.2O.sub.3, for example. Electrodes 31, 35, printed conductors 32, 36, through-platings 38 and terminal contacts 33, 39 are made of platinum cermet, for example. In this embodiment, a platinum cermet is also used as the material for the resistance heater, the ohmic resistance of leads 46 being selected to be less than that of heating conductor 45. [0019] Two of the properties of a contamination protective layer may be the following: a) high mechanical and hydrothermal stability, even when applied as a thick layer; and b) high absorbency for contaminants, i.e., chemical reactivity. However, these two properties may in part, conflict with each other. Generally, the more reactive a material, the less durable and robust it is. The compositions, application methods, and design features described herein may allow for the manufacturing of a protective layer with superior protective power while maintaining sufficient mechanical and hydrothermal robustness for long term use. Continue reading... Full patent description for Contamination-resistant gas sensor element Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Contamination-resistant gas sensor element patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Contamination-resistant gas sensor element or other areas of interest. ### Previous Patent Application: Gas sensing element, gas sensor using the same and related manufacturing method Next Patent Application: Gas sensor with increased sealing performance Industry Class: Chemistry: electrical and wave energy ### FreshPatents.com Support Thank you for viewing the Contamination-resistant gas sensor element patent info. 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