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Ammonia sensor element, heater, and method for making the sameRelated Patent Categories: Metal Working, Method Of Mechanical Manufacture, Electrical Device MakingAmmonia sensor element, heater, and method for making the same description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060200969, Ammonia sensor element, heater, and method for making the same. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND [0001] Exhaust gas generated by combustion of fossil fuels in furnaces, ovens, and engines, for example, contains nitrogen oxides (NOx), unburned hydrocarbons (HC), and carbon monoxide (CO). Vehicles, e.g., diesel vehicles, utilize various pollution-control after treatment devices such as, for example, a NOx absorber or Selective Catalytic Converter (SCR), to reduce NOx. For diesel vehicles using SCR, the NOx reduction can be accomplished by using ammonia gas (NH.sub.3). In order for SCR catalyst to work efficiently, and to avoid pollution breakthrough, an effective feedback control loop is needed. To develop such control technology, there is an ongoing need for an economically-produced and reliable commercial ammonia sensors. SUMMARY [0002] Disclosed herein are ammonia sensors, heaters, and methods for making the same. In one embodiment, the sensor element can comprise a co-fired heater section, a sensing section, and a third insulating layer disposed between the electrode portion and the temperature sensor. The heater section can comprise a heater, a shield, and a temperature sensor, with a first insulating layer disposed between the heater and the shield, and a second insulating layer disposed between the shield and the temperature sensor. The sensing section can comprise an electrode portion and a sensing portion, wherein the sensing portion is disposed on a side of the electrode portion opposite the heater section. [0003] In another embodiment, the sensor element can comprise: a heater section, a sensing section, and a third insulating layer disposed between the heater section and the sensing section. The heater section can comprise a heater, a shield, and a temperature sensor, with a first insulating layer disposed between the heater and the shield, and a second insulating layer disposed between the shield and the temperature sensor. The heater can comprise a serpentine and leads in electrical communication with the serpentine, wherein the serpentine comprises center inner legs, second inner legs, and outer legs, and wherein the second inner leg has a varying second width. The sensing section can comprise an electrode portion and a sensing portion, wherein the sensing portion is disposed on a side of the electrode portion opposite the heater section. [0004] In one embodiment, the heater can comprise a serpentine and leads. The serpentine can comprise center inner legs, second inner legs, and outer legs, wherein the outer legs are in electrical communication with the leads. The center inner legs, second inner legs, and/or the outer legs can have a convexo-convex geometry. [0005] In one embodiment, the method for making a sensor element can comprise disposing a shield between a heater and a temperature sensor to form a green laminate with a first insulating layer disposed between the heater and the shield, and a second insulating layer disposed between the shield and the temperature sensor. The laminate can be co-fired to form a co-fired substrate. A capacitor precursor can be printed on the temperature sensor side of the substrate. The capacitor can be patterned and a sensor portion can be disposed on a side of the capacitor opposite the substrate. [0006] The above-described and other features will be appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims. BRIEF DESCRIPTION OF THE DRAWINGS [0007] Refer now to the figures, which are meant to be exemplary, not limiting, and wherein the like elements are numbered alike. [0008] FIG. 1 is an exploded, isometric view of an exemplary ammonia sensor element. [0009] FIG. 2 is a partial, planar view of an exemplary heater. [0010] FIG. 3 is a graphical representation of an ammonia sensing model and impedance sweep for the ammonia sensor element of FIG. 1. DETAILED DESCRIPTION [0011] It should be noted that the terms "first," "second," and the like herein do not denote any order or importance, but rather are used to distinguish one element from another, and the terms "a" and "an" herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. Furthermore, all ranges disclosed herein are inclusive and combinable (e.g., ranges of "up to about 25 weight percent (wt. %), with about 5 wt. % to about 20 wt. % desired, and about 10 wt. % to about 15 wt. % more desired," are inclusive of the endpoints and all intermediate values of the ranges, e.g., "about 5 wt. % to about 25 wt. %, about 5 wt. % to about 15 wt. %", etc.). [0012] The ammonia sensor element comprises a sensing section and a co-fired heater section. The co-fired heater section comprises a heater (e.g., a ceramic heater), a shield, and a temperature sensor, while the sensing section comprises an ammonia sensing material. FIG. 1 illustrates an exemplary ammonia sensor element. The heater section comprises heater 1 (comprising a heater serpentine 15 and heater leads 23), insulating layers (e.g., alumina layers L1-L8), shield 3, and temperature sensor 5 (comprising a temperature element and temperature leads). The sensor section can comprise a capacitor 7 (comprising a capacitor element and capacitor leads), a protective divider 9, a sensing portion 11 at a sensor end of the ammonia sensor element, and a covering 13, with a insulating layer L8 disposed between the temperature sensor 5 and the capacitor 7. [0013] The heater 1 can be any heater capable of maintaining the sensor end of the ammonia sensor element at a sufficient temperature to enable the sensing of ammonia. The heater 1 can comprise be platinum, palladium, tungsten, molybdenum, and the like, or alloys or combinations comprising at least one of the foregoing, or any other heater compatible with the environment. The heater 1 can be printed (e.g., thick film printed) onto an alumina layer (e.g., L1 and/or L2) to a sufficient thickness to attain the desired resistance and heating capability. The heater thickness can be, for example, about 10 micrometers to about 50 micrometers, or so. [0014] Optionally, the heater 1 can be designed to attain a substantially uniform temperature (e.g., a temperature gradient across the sensing portion 11 of less than or equal to about 5.degree. C.). The heater 1 can have a serpentine 15 with variable width serpentine legs (outer legs 17, second inner legs 19, and center inner legs 21) and with leg separation distances between the centerlines of the legs "A", "B", "C". For example, the separation "C", between the outer legs 17, can be about 4.5 mm to about 5.5 mm; the separation "B", between the second inner legs 19, can be about 3.0 mm to about 4.0 mm; and the separation "A", between the center inner legs 21, can be about 1.5 mm to about 2.0 mm. These separation distances provide a variable spacing between different legs. Namely, the spacing between the centerlines of the two inner legs "A" can be about 1.5 mm to about 2.0 mm. The spacing between the centerlines of the center inner leg to second inner leg can be about 0.75 mm to about 1.25 mm. The spacing between the centerline of the second inner leg to the centerline of the outer leg can be about 0.65 mm to about 1.0 mm. [0015] One or more of the serpentine legs 17, 19, 21 can vary in width. Optionally, one or more of these legs can have a convexo-convex geometry (i.e., broader in the center than at the ends). For example the center inner legs 21 can have a center width that varies from about 0.20 mm to about 0.30 mm, or, more specifically, from about 0.27 mm to about 0.34 mm. The second inner legs 19 can have a width that varies from about 0.30 mm to about 0.50 mm, or, more specifically, from about 0.35 mm to about 0.45 mm. The outer legs 17 can have an width varies from about 0.20 mm to about 0.35 mm, or, more specifically, by about 0.25 mm to about 0.32 mm. It is noted that, unless specified otherwise, all widths disclosed herein are prior to firing (i.e., in the green state). [0016] Due to the design of the heater, namely the varying width of one or more of the legs, the heater attains a more uniform temperature distribution during operation. For example, during operation, the heater can have a longitudinal temperature gradient (i.e., a gradient measured perpendicular to the leg separation widths "A", "B", "C") of less than or equal to about 5.degree. C., or, more specifically, less than or equal to about 3.degree. C. The heater may also have, during operation, a latitudinal temperature gradient (i.e., a gradient measured parallel to the leg separation widths "A", "B", "C") of less than or equal to about 5.degree. C., or, more specifically, less than or equal to about 3.degree. C., and, even more specifically, less than or equal to about 1.degree. C. [0017] The shield 3 is disposed between the heater 1 and the temperature sensor 5. The shield 3 can comprise, for example, a closed layer, a line pattern (connected parallel lines, serpentine, and/or the like), and/or the like. The shield 3 can comprise any material capable of enhancing the electrical isolation of the heater from the temperature sensor. Possible shield materials include precious metal (such as platinum (Pt), palladium (Pd), gold (Au), and the like), and the like, as well as alloys and combinations comprising at least one of the foregoing materials. [0018] The temperature sensor 5 can be any temperature sensor capable of monitoring the temperature of the sensing end of the ammonia sensor element, such as a resistance temperature detector (RTD). Potential materials for the temperature sensor 5 can be any material having a sufficient temperature coefficient of resistance to enable temperature determinations, and have a sufficient melting point to withstand the co-firing temperature (e.g., of about 1,400.degree. C. or so). Some possible materials include those employed for the heater 1. The temperature sensor can comprise a serpentine portion with a line width of less than or equal to about 0.15 mm. [0019] The sensing section is disposed on a side of the temperature sensor 5, opposite the heater 1. For example, the sensing section can comprise the sensing portion 11, and an electrode portion 7, and optionally the protective divider 9. The sensing portion 11 comprises zeolite. The sensor can be designed such that the impedance (e.g., complex impedance) of the sensor portion, or the derived variables, serve as the measured variable. Possible zeolites that can be used in the sensor portion include, for example, alumino-silicates of the pentasil and/or beta crystal structure, in the hydrogen form. The ratio of silica to alumina (often called the modulus of the zeolite) can vary be about 25 to about 400. One possible zeolite is an alumino-silicate pentasil with a modulus of about 80 to about 90. Additionally, the ammonia form of the alumino-silicate pentasil and/or beta crystal structure having a modulus of about 25 to about 400 can also be used. This form is converted to the hydrogen form by a heat treatment (e.g., heated to about 600.degree. C. for a short period of time). [0020] The electrode portion 7 can comprise various designs capable of sensing ammonia, such as an interdigitated structure, a two electrode arrangement, a four conductor arrangement, and the like. When a capacitor is employed, for example, it can resemble inter-digitating fingers (such a structure is referred to also as an interdigited capacitor (IDC)). This capacitor can comprise various materials, including gold (Au), and alloys and combinations comprising gold, such as gold-platinum alloys and gold-palladium alloys. Continue reading about Ammonia sensor element, heater, and method for making the same... Full patent description for Ammonia sensor element, heater, and method for making the same Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Ammonia sensor element, heater, and method for making the same 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 Ammonia sensor element, heater, and method for making the same or other areas of interest. ### Previous Patent Application: Process and apparatus for producing a vial in a sterile environment Next Patent Application: Transcutaneous analyte sensor Industry Class: Metal working ### FreshPatents.com Support Thank you for viewing the Ammonia sensor element, heater, and method for making the same patent info. 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