Abstract:
Robust ceramic igniters are provided that include an improved sealing system which can significantly enhance operational life of the igniter. Preferred igniters comprise a conductive cold zone and hot zone with higher resisitivity. A hermetic sealant material covers one or more electrical connections on the of each cold zone, thus shielding the electrical connections from environmental exposure, and thereby avoiding igniter failure resulting from electrical shorts and/or undesired oxidation.

Description:
[0001]    The present application claims the benefit of U.S. provisional application No. 60/313,113, filed Aug. 18, 2001, which is incorporated herein by reference in its entirety. 
     
    
     
       1. FIELD OF THE INVENTION  
         [0002]    The invention relates generally to ceramic igniters and, more particularly, to ceramic igniters that contain improved sealing for electrical contact portions of the device.  
         2. BACKGROUND  
         [0003]    Ceramic igniters have found increased use in certain ignition applications such as gas fired furnaces, stoves and clothes dryers. See, generally, U.S. Pat. Nos. 3,875,477, 3,928,910, 3,974,106, 4,260,872, 4,634,837, 4,804,823, 4,912,305, 5,085,237, 5,191,508, 5,233,166, 5,378,956, 5,405,237, 5,543,180, 5,785,911, 5,786,565, 5,801,361, 5,820,789, 5,892,201, 6,028,292, and 6,078,028.  
           [0004]    While ceramic igniter designs and performance have improved, problems still exist that can prevent optimal functioning. One persistant problem is pentration of moisture or other fluids into the igniter electrical lead or contact portion, i.e. where electrical contacts mate with the igniter element, typically via a lead frame.  
           [0005]    Penetrating fluids can originate from a variety of sources, including moisture from the surrounding area and the ambient atmosphere as well as liquid fuels such as kerosone that the ceramic element ignites.  
           [0006]    Cooking evironments are especially problematic. Ceramic igniters used in gas stove settings frequently come into contact with spilled or splashed fluids (e.g. liquids, steam, etc.) emanating from pots or other apparatus on the stove.  
           [0007]    Protective housing elements, particularly used in combination with a potting cement material (often an epoxy-based sealant), have been employed to avoid such fluid penetration, but such housings have not consistently provided satisfactory results. If fluid penetrates the igniter&#39;s protective housing, and contacts the electric leads therewithin, the igniter can short circuit and fail. Fluid penetration also can accelerate oxidation of the protected lead portion, which can result in premature igniter failure.  
           [0008]    It thus would be desirable to have new ceramic igniters that could provide enhanced performance properties. It would be particularly desirable to have new ceramic igniters that have enhanced resistance to undesired fluid penetration and/or oxidation of the igniter&#39;s electrical contact portion.  
         SUMMARY OF THE INVENTION  
         [0009]    We now provide new ceramic igniters that can exhibit significantly enhanced resistance to undesired moisture and/or oxygen penetration.  
           [0010]    Preferred igniters of the invention are coated with or otherwise comprise at least in part a material that effectively inhibits entry of moisture and/or oxygen to an igniter&#39;s electrical contact portion. These coating compositions are generally referred to herein as a hermetic sealant material or composition. The hermetic sealant material suitably surrounds the electrical lead contact portion (typically distal to the igniter&#39;s hot zone region) to thereby insulate the electrical contact portion from undesired fluid/environmental contact.  
           [0011]    A preferred hermetic sealant composition is a ceramoplastic material, e.g. a glass/mica material. We have found that ceramoplastic materials can surprisingly provide significantly enhanced resistance to moisture penetration relative to other materials, such as prior potting compositions. See, for instance, the comparative results set forth in Example 2, which follows.  
           [0012]    We also have found that use of a hermetic sealant material in accordance with the invention can enable manufacture of an igniter element with reduced cross-sectional profile. Igniters of such reduced dimensions can be useful in a variety of applications, including to retrofit gas burning apparatus designed for spark ignition.  
           [0013]    Methods are also provided for manufacture of igniters of the invention, which include coating, particularly encapsulating, the electrical contact portion of an igniter with a sealant material in accordance with the invention. Suitably, the sealant material is applied to the igniter in an insert molding-type or batch-type process, i.e. where at least one igniter element, preferably a plurality of igniter elements, reside within a mold and a sealant composition is applied to the igniter electrical contact portion areas. An injection molding process also is preferred and can enable reduced manufacturing costs and times. Other approaches also are suitable, including transfer molding and compression molding.  
           [0014]    In a preferred aspect, ceramic igniters of the invention may be produced as a unitary or integral structure with other devices. For instance, an igniter element may be formed in an integral structure with a sensing element (e.g. a gas flame sensor) where those elements (igniter and sensor) are molded as a single integral structure through use of a hermetic sealant composition alone or together with other molding material. Use of a hermetic sealant composition as the predominant molding composition is preferred because of the thermal stability of such material. Reference that the hermetic sealant composition is the predoiminat material used as the molding material means that the hermetic sealant composition is present in an amount of greater than about 50, 60, 70, 80 or 90 weight percent based on total weight of the molding composition employed.  
           [0015]    In another preferred system, a ceramic igniter element is produced with a hermetic sealant composition as disclosed above. The formed element is adapted to mate with a sizing element, which element can provide a desired shape and size to the formed igniter element. By this approach, a single igniter element can be utilized in a variety of distinct applications and environments.  
           [0016]    More particularly, an igniter element can be formed with the exposed surface of the hermetic sealant composition preferably comprising threads, keyway, or other engagement surfaces that can reliably nest or otherwise fit with or within larger structures (e.g. rounded or edged blocks) that provide desired external dimensions. That larger structure then can be mounted in a particular environment, such as a gas cooking or heating unit.  
           [0017]    The invention also provides igniter elements that are adapted to receive electrical connections, particularly where an electrical connection can be releasably engaged with the igniter element. Such a “plug-in” configuration can enable a single igniter to be used with multiple, distinct electrical connection or leads. Suitably, a housing element that surrounds at least a bottom portion of an igniter element is adapted to receive an electrical connection, e.g. by a snap-fit or other releasable engagement of an electrical lead. That housing can be formed in whole or part with a hermetic sealant material, preferably with the hermetic sealant composition encasing at least the electrical contact portions of the igniter.  
           [0018]    As mentioned above, prior igniter elements often have included a sealant housing (e.g. a ceramic block) that surrounds the igniter electrical contact portions. A potting cement, typically an epoxy material, has been applied to fill the housing and thereby encase the igniter electrical contact areas. The epoxy or other sealant is generally manually applied which can result in undesired voids that can facilitate fluid penetration into the device as well as compromise the device&#39;s aesthetic appearance.  
           [0019]    In contrast, igniters of the invention do not require any such ceramic block, or other separate housing. Rather, the sealant composition itself can form an integral sealing member on the igniter, obviating the need for a separate housing unit. The absence of a separate housing unit also can provide an igniter system of smaller cross-sectional size and lower manufacturing cost.  
           [0020]    Igniters of the invention will have significant utility in a large number of applications. In particular, igniters of the invention will be especially useful in in environments where fluid is frequently present, e.g. cooking environments such as to ignite a cooktop gas burner where regular exposure to fluids can occur.  
           [0021]    Other aspects of the invention are disclosed infra. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    [0022]FIG. 1 depicts a hairpin-type ceramic igniter of the invention;  
         [0023]    [0023]FIG. 2 depicts the igniter of FIG. 1 with its wire leads are covered with a sealant composition in accordance with the invention;  
         [0024]    [0024]FIG. 3 shows a particular igniter design of the invention that includes a plurality of distinct sealant compositions;  
         [0025]    [0025]FIG. 4 shows a preferred integral structure that comprises both igniter and sensor elements;  
         [0026]    [0026]FIG. 5 shows a preferred igniter system of the invention; and  
         [0027]    [0027]FIG. 6 shows a further preferred igniter system of the invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]    As discussed above, we now provide ceramic igniters that can exhibit significantly enhanced resistance to undesired moisture or other environemental infiltration. Electrical contact portions of of an igniter element are preferably coated at least in part with or otherwise comprise a hermetic sealant material, such as a ceramoplastic material.  
         [0029]    We have found that incorporation of a hermetic sealant material in accordance with the invention not only renders the igniter moisture resistant/impervious, but also allows for a reduction in the overall dimensions of the igniter. This, in turn, enables the igniter to be more easily used in conjunction with, and/or retrofitted into, certain usage environments that previously may have been unavailable to ceramic igniters.  
         [0030]    Preferred hermetic sealant materials for use in accordance with the invention exhibit extremely low moisture and/or oxygen penetration, e.g. exhibiting a porosity of approximately zero. A sealant material is considered herein to have a porosity of approximately zero of the sealant material shows (naked eye examination) minimal or essentially no pentration of a dye compound relative to prior potting compositions as determined by the procotol of Example 2 which follows. Such low porosity materials are generally referred to and designated to mean herein a “hermetic sealant material” or other similar term.  
         [0031]    Preferred hermetic sealant materials are substantially inorganic compostions, i.e. the materials have minimal carbon content (e.g. less than 5, 10, 20 or 30 mole percent carbon) and preferably the composition is essentially or completely carbon-free (zero or less than one mole percent carbon). Preferred hermetic sealant compositions will exhibit thermal properties superior to most organic plastics, and have a wide temperature operation range, e.g. from about −400° F. to about 1400° F. Preferred hermetic sealant materials will have a high resistance to thermal degradation or deformation, e.g. the formed hermetic sealant material coating on an igniter element will not deform upon extended exposure (e.g. at least 0.5, 1, 2, 3 or 4 minutes, or at least 5, 6, 7, 8, 10, 12, 15, 20, 30 minutes) to temperatures such as at least about 350° C., more typically at least about 400° C. or 500° C., or even 550° C., 600° C., 650° C., 700° C., 750° C. or 800° C., as may result from the ignited gas or other fuel source. However, as discussed in detail below, hermetic sealant materials also can be employed that have lower thermal stabilities.  
         [0032]    Igniters of the invention contain both hot and cold zone portions. The hot zone(s) are comprised of a sintered composition containing both a conductive material and an insulating material, as well as, optionally but typically, a semiconductor material. Conductive or cold zone portions of ceramic igniters of the present invention will contain a sintered composition of similar components as the hot zone(s) of the igniter, but with comparably higher concentrations of the conductive material.  
         [0033]    Referring now in detail to the drawings, FIGS. 1 and 2 depict an exemplary igniter  10  of the present invention that includes a hot zone portion  12  in contact with, and disposed between, cold zones  14   a  and  14   b.  Heat sink  16  is interposed between the cold zones  14   a  and  14   b  and is in contact with hot zone  12 . Cold zone ends  14   a ′ and  14   b ′ are located distal from hot zone  12 , and are in electrical connection to a power source (not shown) through leads  50   a,    50   b  as is generally known in the art, typically through use of some type of lead frame mounting.  
         [0034]    [0034]FIG. 2 depicts the igniter of FIG. 1 with protective hermetic sealant material barrier  100  surrounding the leads  50   a,    50   b  located at the ends  14   a ′,  14   b ′ of the cold zones  14   a,    14   b.  This barrier  100  should be made of a material that effectively prevents or significantly deters fluid from contacting leads  50   a,    50   b,  but which does not adversely affect the connection between the leads  50   a,    50   b  and a power source (not shown) to which the leads are electrically connected.  
         [0035]    As discussed above, preferred heremetic sealant materials for use in accordance with the invention are inorganic materials that are not only excellent thermal and electrical insulators, but that also are impervious to moisture and/or oxygen (i.e., have a porosity of about zero) and that do not burn, outgas or carbonize.  
         [0036]    As discussed above, a preferred hermetic barrier sealant material is a ceramoplastic composition, such as a glass bonded mica. A particularly preferred cermoplastic sealant material is a glass bonded mica material available from the Saint-Gobain Company and has high thermal stability as discussed above. A further preferred ceramoplastic composition is commercially available from Mykroy/Mycalex Ceramics of Clifton, N.J., USA in sheet, rod, and custom fabricated/molded configurations of various grades. A specifically preferred material is Mykroy/Mycalex Grade 561-V (cermoplastic materiual that is a moldable glass bonded to synthetic mica) available from Mykroy/Mycalex Ceramics of Clifton, N.J.. That Mykroy/Mycalex Grade 561-V materials has a specific gravity of 3.2; nil moisture absorption; dielectric strength of 350 V/mil; tensil strength of 7500 psi; and Rockwell H hardness of 93.  
         [0037]    Because of these materials properties, formation of the hermetic barrier  100  requires only a small amount of material in order to effectively protect the leads  50   a,    50   b  from contacting any moisture. This, in turn, allows for a reduction in the overall dimensions of the igniter, thus enabling the igniter to be more easily used in conjunction with, and/or retrofitted into, certain usage environments that previously may have been unavailable to ceramic igniters.  
         [0038]    More particularly, a relatively thin coating of a cermoplastic material can be applied to an igniter element to provide effective sealing of the igniter electrical contacts. For instance, thickness x (i.e. distance from igniter outer surface to barrier layer  100  outer surface) as shown in FIG. 2 suitably can be less than about 3 mm, more preferably less than 2 mm, 1 mm, 0.5 mm, 0.3 mm, or even 0.2 mm, or 0.1 mm.  
         [0039]    In this regard, preferred hermetic sealant materials will exhibit significantly greater dielectric strength (v/ml) than potting cement used in prior systems, which can facilitate use of thin coating layers. More particularly, preferred cermoplastic materials can exhibit a dielectric strength (v/ml) at least about two times, more preferred at least about three times greater than prior potting cements.  
         [0040]    The hermetic barrier coating also does not need to extend extensively along the length of the igniter element beyond the electrical contacts. For instance, distance y (i.e. distance from igniter bottom surface surface  14   a ′ and  14   b ′ to the top surface  100 ′ of barrier  100 ) as shown in FIG. 2 suitably can be less than about 4 mm, more preferably less than about 3.5 mm, 3.0 mm, 2.5 mm or 2.0 mm, or even 1.0 mm.  
         [0041]    A hermetic sealant composition also may be used in combination with other materials, including prior potting cements. For instance, a thin layer of a hermetic sealant material may be applied to encapsulate the electrical lead portions of an igniter element. That thin layer then may be coated with a distinct material that is preferably stable to high temperatures, but need not exhibit low levels of moisture and/or oxygen porosity. For instance, the hermetic sealant composition may be overcoated with a potting cement, such as an epoxy-based material, as has been employed in prior systems as the sole sealant.  
         [0042]    Alternatively, a layer of a potting cement may be initially applied to the igniter electrical contact portions, which is then encapsulated or otherwise capped with a hermetic sealant material of the invention.  
         [0043]    Such combined sealant composition systems can facilitate use of a hermetic sealant composition that has a lower thermal stability. That is, by use of an additional, distinct sealant that may not have extremely low porosity, but does have high thermal stability, hermetic sealant materials with a range of thermal stabilities may be effectively employed. By that design, the additional material (i.e. other than the hermetic sealant) satisfies the thermal stability requirements of the sealant unit.  
         [0044]    Thus, hermetic sealant materials may be employed with relatively lower heat stabilities such as e.g. stability at about 300° C., 400° C., 500° C. or 600° C. before visibile (naked eye) degradation occurs upon one minute exposure to such temperature. A glass or glass/mica composite may be a suitable hermetic sealant material with such lower temperature stability. The additional, non-hermetic material should have a high thermal stability, such the ability to withstand prolonged (0.5 to 5 minutes) exposure to at least about 400° C., 500° C., 600° C., 700° C. or 800° C. without visible (naked eye) degradation.  
         [0045]    In a preferred aspect of the invention, the exterior of the sealant unit (which may be the integral hermetic sealant composition) may be configured as desired. For instance, the exterior surface may be desagianed to facilitate attachment of the igniter element within a larger system such as a cookstove or the like, e.g. the exterior surface may be threaded or grooved to facilitate releaseably attachment of the formed igniter element. Such configured exterior surface can be readily provided through the molding manufacturing process as discussed above.  
         [0046]    [0046]FIG. 3 depicts such a system having a plurality of sealant compositions. Igniter  60  includes hot zone  62 , cold zones  64  and leads  66   a  and  66   b  encased within an epoxy-based potting composition  68  which in turn is housed within rigid sealant housing  70 . Hermetic sealant material  72  forms a type of seal or plug of the system, preventing moisture or other fluid to contact leads  66   a  and  66   b.    
         [0047]    As shown in FIG. 1, hot zone  12  may have a non-linear, substantially U-shaped electrical path length “e” (shown with dotted line to emphasize minimum path) that extends down the length of each side of the igniter. Such non-linear hot zone geometries are believed to more effectively diffuse power density throughout the hot zone region, and to enhance operational life of the igniter, and thus are generally preferred.  
         [0048]    The dimensions of the hot zone region may suitably vary provided that the overall hot zone electrical path length is within the predetermined ranges disclosed herein. In the generally rectangular igniter design depicted in FIG. 1, the hot zone width between the cold zones (depicted as distance “a” in FIG. 1) should be sufficient to avoid electrical shorts or other defects. In one preferred system, that distance “a” is 0.5 cm.  
         [0049]    The hot zone bridge height (depicted as distance “b” in FIG. 1) also should be of sufficient size to avoid igniter defects, including excessive localized heating, which can result in igniter degradation and failure as discussed above. For example, for the design depicted in FIG. 1, preferred hot zone bridge heights will be in the range of about 0.03 cm to about 0.5 cm. The term “hot zone bridge height” as used herein is understood to mean the dimension of a hot zone that extends parallel to the length or long dimension of a generally rectangular ceramic igniter, as exemplified by dimension “b” depicted in FIG. 1.  
         [0050]    The hot zone “legs” that extend down the length of the igniter will be limited to a size sufficient to maintain the overall hot zone electrical path length to within about 2 cm.  
         [0051]    The composition of the hot zone  12 , cold zones  14   a,    14   b  and heat sink  16  of a ceramic igniter of the present invention may suitably vary; however, suitable compositions for those regions are disclosed in U.S. Pat. No. 5,786,565 to Willkens et al. as well as in U.S. Pat. No. 5,191,508 to Axelson et al.  
         [0052]    More particularly, the composition of the hot zone  12  should be such that the hot zone exhibits a high temperature (i.e. 1350° C.) resistivity of between about 0.01 ohm-cm and about 3.0 ohm-cm, and a room temperature resistivity of between about 0.01 ohm-cm and about 3 ohm-cm.  
         [0053]    A preferred hot zone  12  contains a sintered composition of an electrically insulating material, a metallic conductor, and, in an optional yet preferred embodiment, a semiconductor material as well. As used herein, the term “electrically insulating material” or variations thereof refer to a material having a room temperature resistivity of at least about 10 10  ohm-cm, while the terms “metallic conductor,” “conductive material” and variations thereof signify a material that has a room temperature resistivity of less than about 10 −2  ohm-cm, and the terms “semiconductive ceramic,” “semiconductor material” or variations thereof denote a material having a room temperature resistivity of between about 10 and 10 8  ohm-cm.  
         [0054]    In general, an exemplary composition for a hot zone  12  of the ceramic igniter  10  includes (a) between about 50 and about 80 volume percent (vol % or v/o) of an electrically insulating material having a resistivity of at least about 10 10  ohm-cm; (b) between about 5 and about 45 v/o of a semiconductive material having a resistivity of between about 10 and about 10 8  ohm-cm; and (c) between about 5 and about 25 v/o of a metallic conductor having a resistivity of less than about 10 −2  ohm-cm.  
         [0055]    Preferably, the hot zone  12  comprises 50-70 v/o of the electrically insulating material, 10-45 v/o of the semiconductive ceramic, and 6-16 v/o of the conductive material.  
         [0056]    Typically, the metallic conductor is selected from the group consisting of molybdenum disilicide, tungsten disilicide, and nitrides such as titanium nitride, and carbides such as titanium carbide, with molybdenum disilicide being a generally preferred metallic conductor. In certain preferred embodiments, the conductive material is MoSi 2 , which is present in an amount of from about 9 to 15 vol % of the overall composition of the hot zone, more preferably from about 9 to 13 vol % of the overall composition of the hot zone.  
         [0057]    Generally preferred semiconductor materials, when included as part of the overall composition of the hot  12  and cold zones  14   a,    14   b  of the igniter  10 , include, but are not limited to, carbides, particularly silicon carbide (doped and undoped), and boron carbide. Silicon carbide is a generally preferred semiconductor material for use in the ceramic igniter  10 .  
         [0058]    Suitable electrically insulating material components of hot zone compositions include, but are not limited to, one or more metal oxides such as aluminum oxide, a nitride such as a aluminum nitride, silicon nitride or boron nitride; a rare earth oxide (e.g., yttria); or a rare earth oxynitride. Aluminum nitride (AlN) and aluminum oxide (Al 2 O 3 ) are generally preferred.  
         [0059]    Particularly preferred hot zone compositions of the invention contain aluminum oxide and/or aluminum nitride, molybdenum disilicide, and silicon carbide. In at least certain embodiments, the molybdenum disilicide is preferably present in an amount of from 9 to 12 vol %.  
         [0060]    As discussed above, igniters  10  of the invention typically also contain at least one or more low resistivity cold zone region  14   a,    14   b  in electrical connection with the hot zone  12  to allow for attachment of wire leads  50   a,    50   b  to the igniter. Typically, a hot zone  12  is disposed between two cold zones  14   a,    14   b,  which are generally comprised of, e.g., AlN and/or Al 2 O 3  or other insulating material; SiC or other semiconductor material; and MoSi 2  or other conductive material.  
         [0061]    Preferably, cold zone regions  14   a,    14   b  will have a significantly higher percentage of the conductive and/or semiconductive materials (e.g., SiC and MoSi 2 ) than are present the hot zone. Accordingly, cold zone regions  14   a,    14   b  typically have only about ⅕ to {fraction (1/1000)} of the resistivity of the hot-zone region  12 , and do not rise in temperature to the levels of the hot zone. More preferred is where the cold zone(s)  14   a,    14   b  room temperature resistivity is from 5 to 20 percent of the room temperature resistivity of the hot zone  12 .  
         [0062]    A preferred cold zone composition for use in igniter of the invention comprises about 15 to 65 v/o of aluminum oxide, aluminum nitride or other insulator material, and about 20 to 70 v/o MoSi 2  and SiC or other conductive and semiconductive material in a volume ratio of from about 1:1 to about 1:3. More preferably, the cold zones  14   a,    14   b  comprise about 15 to 50 v/o of aluminum oxide and/or aluminum nitride, about 15 to 30 v/o SiC, and about 30 to 70 v/o MoSi 2 . For ease of manufacture, the cold zone composition is preferably formed of the same materials as the hot zone composition, but with the relative amounts of semiconductive and conductive materials being greater in the cold zone(s)  14   a,    14   b  than the hot zone(s)  12 .  
         [0063]    The electrically insulating heat sink  16  should be comprised of a composition that provides sufficient thermal mass to mitigate convective cooling of the hot zone  12 . Additionally, when disposed as an insert between two conductive legs as exemplified by the system shown in FIG. 1, the heat sink  16  must provide mechanical support for the extended cold zone portions  14   a  and  14   b,  and must serve to make the igniter  10  more rugged.  
         [0064]    In some embodiments, insert  16  may be provided with a slot (not shown) to reduce the mass of the system. Preferably, the electrically insulating heat sink  16  has a room temperature resistivity of at least about 10 4  ohm-cm and a strength of at least about 150 MPa. More preferably, the heat sink material has a thermal conductivity that is not so high as to heat the entire heat sink  16  and transfer heat to the leads, and not so low as to negate its beneficial heat sink function.  
         [0065]    Suitable ceramic compositions for the heat sink  16  include compositions comprising at least about 90 vol % of at least one of aluminum nitride, boron nitride, silicon nitride, alumina and mixtures thereof. Where a hot zone composition of AlN—MoSi 2 —SiC is employed, a heat sink material comprising at least 90 vol % aluminum nitride and up to 10 vol % alumina can be preferred for compatible thermal expansion and densification characteristics. A preferred heat sink composition is disclosed in co-pending U.S. patent application Ser. No. 09/217,793, the entire disclosure of which is incorporated herein by reference.  
         [0066]    Ceramic igniters  10  of the invention can be employed with a variety of voltages, including, but not limited to, nominal voltages of 6, 8, 12, 24, 120, 220, 230 or 240 volts. Preferred igniters of the invention can heat rapidly from room temperature to operational temperatures, e.g. to about 1350° C. in about 4 seconds or less, even 3 seconds or less, or even 2.75 or 2.5 second or less.  
         [0067]    Preferred igniters  10  of the invention also can provide a stable ignition temperature with a hot zone power density (surface loading) of from 60 to 200 watts per cm 2  of the hot zone region.  
         [0068]    [0068]FIG. 4 exemplifies a preferred system of the invention where an igniter element is formed in an integral structure (i.e. single molded, bonded or otherwise joined structure) with one or more other functioning or operational devices such as a sensor element. References herein to “an operational element” or other similar term indicates that the element can react to the environment or other input (e.g. electrical or thermal input) in some manner, typically by providing an output such as resistive heating, an electrical signal or the like. More specifically, as shown in FIG. 4, an integral structure  80  may contain igniter element  10  (shown as a slotted element) and an operational element of a sensor element  82  that can detect flame, heat or the like. Integral structure  80  can be a variety of configurations and is suitably adapted to fit within an intended usage environment. FIG. 4 shows a preferred configuration, where structure  80  includes planar surface  84  into which igniter  10  and sensor  82  are mounted through blocks  86  and  88  respectively. Structure  80  may be formed entirely or predominately from a hermetic sealant composition. Alternatively, structure  80  suitably may be formed with distinct materials, with the hermetic sealant composition being employed at least to encapsulant igniter end portions where contact is made with electrical leads. Materials other than a hermetic sealant composition suitable for forming structure  80  include e.g. an epoxy material.  
         [0069]    [0069]FIG. 5 shows a preferred system of the invention where igniter  10  is mated with sizing element  90 , which is depicted as a preferred oval-shaped element, although other configurations also will be suitable such as a squared block and the like. References herein to a “sizing element” or other similar term indicate that the element provides increased dimensions to an igniter element when mated (in physical contact) with the igniter element, e.g. increasing the width of the igniter element by about 10, 20, 30, 40, 50, 60, 70, 80 or 100 percent or more. In FIG. 5, the depicted element  90  includes a mating groove for securing the element within the usage environment. Igniter  10  suitably is press fit engaged within the sizing element, or otherwise secured therein, e.g. with an adhesive, threaded engagement and the like.  
         [0070]    [0070]FIG. 6 shows a further preferred system of the invention where igniter element  10  is adapted to releasably receive eletrical connection elements  100  and  102 . Suitable electrical connections include electrical lead lines that provide electrical power to the igniter element during use thereof.  
         [0071]    In the preferred system depicted in FIG. 6, connection elements  100  and  102  releasably secure to igniter housing portion  104  that includes electrical receiving portions  106  and  108 . Those portions  106  and  108  receive connection elements  100  and  102  respectively and releasably retain them. The system depicted in FIG. 6 depicts a preferred groove (on connection elements  106  and  108 ) and flange (within housing  104 , not shown in FIG. 6) securing system. Other engagement systems also will be suitable such as a threaded engagement. The connection elements can be removed and replaced with other connection elements (electrical leads) as desired.  
         [0072]    The processing of the ceramic component (i.e., green body processing and sintering conditions) and the preparation of the igniter  10  from the densified ceramic can be done by conventional methods. Typically, such methods are carried out in substantial accordance with U.S. Pat. No. 5,786,565 to Willkens et al. and U.S. Pat. No. 5,191,508 to Axelson et al., the disclosures of which are explicitly incorporated by reference herein.  
         [0073]    Igniters can be produced in accordance with generally known procedures, such as disclosed in U.S. Pat. No. 5,405,237 to Washburn. See also Example 1 which follows, for illustrative conditions.  
         [0074]    For example, a formed billet of green body igniters can be subjected to a first warm press (e.g. less than 1500° C. such as 1300° C.), followed by a second high temperature sintering (e.g. 1800° C. or 1850° C.). The first warm sintering provides a densification of about 65 or 70% relative to theoretical density, and the second higher temperature sintering provides a final densification of greater than 99% realtive to theoretical density.  
         [0075]    In preferred igniter production methods a billet sheet is provided that comprises a plurality of affixed or physically attached “latent” igniter elements. The billet sheet has hot and cold zone compositions that are in a green state (not densified to greater than about 96% or 98% theoretical density), but preferably have been sintered to greater than about 40% or 50% theoretical density and suitably up to 90 ort 95% theoretical density, more preferably up to about 60 to 70% theoretical density. Such a partial densification is suitably achieved by a warm press treatment, e.g. less than 1500° C. such as 1300° C., for about 1 hour under pressure such as 3000 psi and under argon atmosphere.  
         [0076]    It has been found that if the hot and cold zones compositions are densified at greater than 75 or 80 percent of theoretical density, the billet will be difficult to cut in subsequent processing steps. Additionally, if the hot and cold zones compositions are densified at less than about 50 percent, the compositions often degrade during subsequent processing. The hot zone portion extends across a portion of the thickness of the billet, with the balance being the cold zone.  
         [0077]    The billet may be of a relatively wide variety of shapes and dimensions. Preferably, the billet is suitably substantially square, e.g. a 9 inch by 9 inch square, or other suitable dimensions or shapes such as rectangular, etc. The billet is then preferably cut into portions such as with a diamond cutting tool. Preferably those portions have substantially equal dimensions. For instance, with a 9 inch by 9 inch billet, preferably the billet is cut into thirds, where each of the resulting sections is 9 inches by 3 inches.  
         [0078]    The billet is then further cut (suitably with a diamond cutting tool) to provide individual igniters. A first cut will be through the billet, to provide physical separation of one igniter element from an adjacent element. Alternating cuts will not be through the length of the billet material, to enable insertion of the insulating zone (heat sink) into each igniter. Each of the cuts (both through cuts and non-through cuts) may be spaced e.g. by about 0.2 inches.  
         [0079]    After insertion of the heat sink zone, the igniters then can be further densified, preferably to greater than 99% of theoretical density. Such further sintering is preferably conducted at high temperatures, e.g. at or slightly above 1800° C., under a hot isostatic press.  
         [0080]    The several cuts made into the billet can be suitably accomplished in an automated process, where the billet is positioned and cut by a cutting tool by an automated system, e.g. under computer control.  
         [0081]    Once densified, electrical contacts are suitably applied to the cold region end of the igniter element, distal to hot zone regions, as generally depicted in FIGS. 1 and 2 above. The electrical contacts may be affixed to the igniter element by e.g. an adhesive. A lead frame is generally attached to each contact to enable communication with a power source.  
         [0082]    Thereafter, the electrical contacts are coated, covered or encased with a sealant compositions as disclosed herein. Preferably, the sealant is applied to the igniter element by an insert molding process, where the igniter with the one or more electrical contacts thereon are positioned within a mold adapted to provide the encapsulating sealant portion. Sealant composition then may be added to the mold and cured to provide a seal or cap coating encasing the contacts.  
         [0083]    As indicated above, igniters of the invention may be used in many applications, including gas phase fuel ignition applications such as furnaces and cooking appliances, baseboard heaters, boilers, and stove tops.  
         [0084]    Igniters of the invention also may be employed in other applications, including for use as a heating element in a variety of systems. More particularly, an igniter of the invention can be utilized as an infrared radiation soruce (i.e. the hot zone provides an infrared output) e.g. as a heating element such as in a furnace or as a glow plug, in a monitoring or detection device including spectrometer devices, and the like.  
         [0085]    The following non-limiting examples are illustrative of the invention. All documents mentioned herein are incorporated herein by reference in their entirety.  
       EXAMPLE 1  
       [0086]    An igniter of the invention is suitably prepared as follows.  
         [0087]    Hot zone and cold zone compositions were prepared for a first igniter. The hot zone composition comprised 70.8 volume % (based on total hot zone composition) AlN, 20 volume % (based on total hot zone composition) SiC, and 9.2 volume % (based on total hot zone composition) MoSi 2 . The cold zone composition comprised 20 volume % (based on total cold zone composition) AlN, 20 volume % (based on total cold zone composition) SiC, and 60 volume % (based on total cold zone composition) MoSi 2 . The cold zone composition was loaded into a hot die press die and the hot zone composition loaded on top of the cold zone composition in the same die. The combination of compositions was densified together under heat and pressure to provide the igniter.  
       EXAMPLE 2  
       [0088]    Electrical contacts were applied with a braze joint to two essentially identical igniters produced as described above in Example 1. Those two igniters are referred to as Igniter A and Igniter B below.  
         [0089]    Igniter A was further processed in accordance with the invention. Specifically, Igniter A with electrical contacts thereon was placed in a mold and a ceramoplastic material available from Mykroy/Mycalex Ceramics added to the mold to encapsulate the contacts to provide an element of the design generally represented in FIG. 2.  
         [0090]    For Igniter B, a cylindrical ceramic housing element was placed around the electrical contacts. An epoxy sealant was added to fill the housing element and encapsulate the contacts. The epoxy sealant was allowed to dry to cure.  
         [0091]    The encapsulated electrical contact ends of each of Igniters A and B were placed in colored penetrating dye for about ten minutes. Upon cross-section analysis by visual (naked eye) inspection, no fluid was absorbed into the ceramoplastic cap of Igniter A, while the fluid was extensively absorbed into the epoxy/ceramic-housing element of Igniter B.  
         [0092]    The invention has been described in detail with reference to particular embodiments thereof. However, it will be appreciated that those skilled in the art, upon consideration of this disclosure, may make modifications and improvements within the spirit and scope of the invention.