Abstract: In a spark plug, a fusion zone where a ground electrode and a noble metal tip are fused together is formed in at least a portion of an interfacial region between the ground electrode and the noble metal tip. When the fusion zone is projected in the axial direction, the projected fusion zone overlaps 70% or more of the area of the noble metal tip. As viewed on a section which passes through the center of gravity of the noble metal tip and is perpendicular to the longitudinal direction of the ground electrode, the relational expression 1.3?B/A is satisfied, where A is the greatest thickness of the fusion zone along the axial direction, and B is the length from a portion having the greatest thickness of the fusion zone to the inner end of the fusion zone.

Abstract: A laser spark plug includes a laser light-producing device and a spark plug housing at the end of which facing the combustion chamber an injection lens for injecting laser light into the combustion chamber of an internal combustion engine is arranged. The spark plug housing includes a fastening zone for fastening the laser spark plug in a cylinder head of the internal combustion engine. A projection on the end of the spark plug housing facing the combustion chamber houses the injection lens. The outer diameter (D1) of the projection is smaller in the area of the injection lens than the outer diameter (D2) of the spark plug housing in the fastening zone.

Abstract: A spark plug for use with internal combustion engines includes a metallic shell housing having a semi-cylindrical shroud partially surrounding the insulator and the center electrode and to which the ground electrode is joined. The semi-cylindrical shroud promotes improved heat dissipation from the ground electrode to the shell housing.

Abstract: A spark plug (20) includes a center electrode (24) and a ground electrode (22). The electrodes (22, 24) include a core (26) formed of a copper (Cu) alloy and a clad (28) formed of a nickel (Ni) alloy enrobing the core (26). The Cu alloy includes Cu in an amount of at least 98.5 weight percent, and at least one of Zr and Cr in an amount of at least 0.05 weight percent. The Cu alloy includes a matrix of the Cu and precipitates of the Zr and Cu dispersed in the Cu matrix. The Ni alloy of the clad (28) includes Ni in an amount of at least 90.0 weight percent. The Ni alloy also includes at least one of a Group 3 element, a Group 4 element, a Group 13 element, chromium (Cr), silicon (Si), and manganese (Mn) in a total amount sufficient to affect the strength of the Ni alloy.

Abstract: A sparkplug including an induction coil and an electrode. The induction coil includes two end portions, the electrode extending in a continuation of one of the two end portions. The induction coil includes a conducting wire wound to form a succession of turns, the one of the two end portions having a terminal turn connected to the electrode. The one of the two end portions includes a plurality of coaxial end turns that extend between the terminal turn and an upstream turn, and the terminal turn has a diameter smaller than the diameter of the upstream turn so to reduce strength of the electric field induced in the one of said two end portions near the terminal turn.

Abstract: A spark plug includes a tubular insulator, a center electrode, a tubular metal shell, a ground electrode, and a pillar body tip. The tubular insulator has an axial hole penetrating in the direction of an axis. The pillar body tip includes one end face that is welded to the ground electrode and another end face that forms a gap with a front end portion of the center electrode. The ground electrode includes a part where the tip is to be welded. The surface forms a clearance with a part including a constituent material of the tip. The ground electrode includes a surface where a plating layer is disposed. The plating layer covers a surface excluding a formation part of the clearance. The clearance has a size A that is equal to or more than 0.01 mm and equal to or less than 0.5 mm.

Abstract: When the first switch is on, the ignition capacitor is charged up to a voltage value whose absolute value is larger than an output voltage value of a DC power source, through resonance caused by a resonance coil and the ignition capacitor; when the second switch is on, the ignition capacitor supplies energy to the ignition coil device, and when the second switch is off, the energy is released and a high voltage is applied across electrodes of an ignition plug.

Abstract: A spark plug includes an insulator having a first end, the insulator having a center axis and a center electrode coupled to the insulator and having a center electrode tip extending beyond the first end of the insulator. The spark plug further includes a ground electrode having an end spaced from an end of the center electrode, the ground electrode having a first portion extending substantially parallel to the center axis and a second portion extending at an angle from the first portion and relative to the center axis. A ground electrode tip is disposed on the second portion of the ground electrode, wherein the ground electrode tip is spaced from the center electrode tip. A ring member is operatively connected to the center electrode proximate the center electrode tip.

Abstract: A task of this invention is to provide a spark plug that is superior in withstand voltage characteristics at high temperatures. A spark plug of this invention is equipped with a center electrode, an insulator, and a metal shell, and is characterized by that the insulator is equipped with an alumina-based sintered body containing silicon component (Si component), magnesium component (Mg component), at least one component of calcium component, strontium component, and barium component, and a rare earth element component (RE component), that a grain boundary phase of the alumina-based sintered body has a hexaaluminate crystal containing the RE component, that, in the alumina-based sintered body, the weight ratio of the RE component to the Mg component is 5.4?RE oxide/MgO?17.5, and that the content of an alkali metal component in terms of oxide in a spot having a diameter of 0.

Abstract: A method for forming a spark plug includes positioning an electrode center wire within an insulator and positioning at least one substance within the insulator and proximate the electrode center wire. The method further includes ultrasonically tamping the at least one substance to the electrode center wire.

Abstract: An adhesion of a nickel plating layer to a metal shell is improved, and an effect of improving a corrosion resistance by providing the nickel plating layer is sufficiently exerted. A spark plug 1 includes a cylindrical metal shell 3 that extends in an axial CL1 direction, and a nickel plating layer 31 that is made of metal containing nickel as a main component and covers an outer surface of the metal shell. In a monochrome image of 256 gradations where black is 0 and white is 255, which is obtained by observing a cross-section perpendicular to an outer surface of the nickel plating layer by a transmission electron microscope with an acceleration voltage of 200 kV, an average value in 256 gradations of the monochrome image is 170 or larger and 230 or smaller.

Abstract: A spark plug is provided having at least one of a center electrode or a ground electrode. The electrode comprises: a core formed of a composite material containing a matrix metal, the matrix metal being copper or a metal containing copper as a main component, and carbon dispersed in the matrix metal in an amount of 10 to 80 vol. %, the carbon having a thermal conductivity higher than that of the matrix metal. The electrode also contains an outer shell which surrounds the core and which is formed of nickel or a metal containing nickel as a main component. The thus-produced electrode exhibits favorable thermal conductivity and good heat dissipation, by virtue of the small difference in thermal expansion coefficient between the core and an outer shell. The spark plug including the above electrode exhibits excellent durability.

Abstract: A spark plug comprises an insulator and a metal shell. The insulator includes a nose length portion at the forward end, and a tapered portion, extending from the rear end of the nose length portion toward the rear end of the insulator, increased in diameter toward the rear end. The metal shell includes a shoulder portion, protruding inward and having a retaining surface by which the tapered portion is retained, and a male thread portion on the outer peripheral side of the shoulder portion, and the thread diameter of the male thread portion is set to M12 or less. When the insulator's cross-sectional area, perpendicular to an axis, passing through the boundary between the nose length section and tapered portion is B (mm2), and the metal shell's cross-sectional area, perpendicular to the axis, passing through the tip of the retaining surface is C (mm2), 2.80?C/B?3.50 is satisfied.

Abstract: A method for producing a spark plug which contains an inner conductor, an insulator surrounding the inner conductor, a spark plug body surrounding the insulator, and two electrodes forming an ignition gap. The first electrode is a center electrode connected to the inner conductor in an electrically conducting manner and the second electrode is a ground electrode connected to the spark plug body in an electrically conducting manner. An iridium component which contains more than 95 percent by weight of iridium is welded onto one of the electrodes. An iridium component that is punched out of an iridium sheet and has a thickness that is less in size than its diameter is also employed.

Abstract: A spark plug and method of construction thereof is provided. The spark plug includes a metal shell having a through cavity, a lower insulator and a plastic upper insulator. The lower insulator is received in the through cavity and has a through passage with a center electrode received therein. A ground electrode is operatively attached to the shell in spaced relation from the ground electrode to provide a spark gap. The plastic upper insulator has a distal end received in the through cavity of the shell and a terminal end extending axially outwardly from the shell. The upper insulator has a through passage extending between the terminal end and the distal end. An elongate conductive member is received in the through passage of the upper insulator and is configured for electrical communication with the center electrode.

Abstract: A spark plug manufacturing method providing a spark plug equipped with an insulator having dielectric strength by means of judging whether or not the insulator has a defect. A defect judgement step judges whether or not the insulator has a defect, by generating an electric potential difference between the center electrode and the metallic shell under conditions such that an assembly of the center electrode, metallic shell, and insulator is disposed within a pressure vessel; a high-pressure atmosphere higher in pressure than the atmospheric pressure is established within the pressure vessel; a space allowing the presence of insulating oil is a space surrounded by the packing, the metallic shell, the insulator, and an imaginary plane containing a forward end surface of the metallic shell; and the insulating oil is present at least in a region of the space where the distance between the ledge and insulator becomes shortest.

Abstract: A spark plug is provided having an insulator with a center axis. A center electrode is coupled to the insulator and has a second end extending from an end of the insulator, the center electrode having a first tip member. A ground electrode is spaced apart from the center electrode, wherein the ground electrode has a first portion extending substantially parallel to the center axis and a second portion extending on an angle from the first portion and relative to the center axis. A second tip member is disposed on the second portion of the ground electrode such that the first tip member and the second tip member cooperate to form a gap.

Abstract: A spark plug is provided with a ground electrode, a noble metal tip made of a Pt alloy, and a relieving layer tip made of a Pt alloy which has a linear expansion coefficient between that of the ground electrode and that of the noble metal tip.

Abstract: A spark plug (20) includes an insulator seat angle (?i) of 35° to 50° and an increased insulator thickness (ti) in selected areas around the insulator seat (28). The insulator seat angle (?i) is greater than or equal to a boundary value provided by the equation: 90°?a cos [1?(R1?R2)÷(R4+R5)], and preferably not greater than 150% of the boundary value. The radii (R1, R2, R3, R4, R5) can be adjusted to maximize R4 while maintaining an acceptable R2. A gasket is compressed between the insulator (22) and shell (58), and the inner gasket thickness (tg2) is greater than or equal to 70% of the outer gasket thickness (tg1).

Abstract: Provided is a technique for limiting the radial displacement between a metal shell and an insulator in a spark plug. At the time of manufacturing a spark plug with a metal shell and an insulator, the metal shell and the insulator are assembled together by, while allowing relative positional displacement between the metal shell and the insulator in an axial direction (O-O), limiting relative positional displacement between the metal shell and the insulator in a radial direction intersecting with the axial direction in such a manner that the amount of deviation between an axis of the metal shell and an axis of the insulator becomes less than or equal to a predetermined level.

Abstract: [Objective] To provide a spark plug which is configured such that an insulation member, from which a center electrode projects, is pressed frontward and held in a metallic shell, and is fixed by means of crimping the rear end of the metallic shell, and which can prevent a drop in gas tightness between the metallic shell and the insulation member due to a difference in thermal expansion therebetween. [Means for Solution] In a spark plug in which a mating shaft portion (10) of an insulation member (1) is loose-fitted into a mating hole portion (30) of a metallic shell (21), a filler (41) for maintaining gas tightness is charged between the outer circumferential surface of the mating shaft portion (10) and the inner circumferential surface of the mating hole portion (30). Despite the thermal expansion difference, the gas tightness is maintained, because the filler (41) for maintaining gas tightness is charged between the inner and outer circumferential surfaces.

Abstract: A spark plug includes a center electrode extending in an axial direction; an insulator formed externally of the outer circumference of the center electrode; a metallic shell formed externally of the outer circumference of the insulator and having a ledge which supports the insulator; and a ground electrode joined to the metallic shell. The insulator has a support portion which faces the ledge. A “frontward direction” is defined as the direction parallel to the axial direction toward a spark portion formed between the center electrode and the ground electrode. The insulator has a diameter reduction portion whose outside diameter reduces along the frontward direction from the support portion, and a diameter increase portion whose outside diameter increases along the frontward direction from the front end of the diameter reduction portion. This restrains the generation of leak current while maintaining heat resistance of the spark plug.

Abstract: A spark plug having a metal shell, the metal shell having a tool engagement portion, a trunk portion and a cylindrical groove disposed between the tool engagement portion and the trunk portion, wherein the following relationship is satisfied: Z1<=Z2, where “Z1” represents a section modulus of a first groove end of the groove, and where “Z2” represents a section modulus of a second groove end of the groove.

Abstract: Disclosed is a spark plug having an insulator with good breakage resistance. A spark plug 1 contains a ceramic insulator 2, a plate packing 22 and a metal shell 3. The ceramic insulator 2 has, on an outer circumferential surface thereof, a step portion 14, a leg portion 13 and a curved surface portion 31 between the step portion 14 and the leg portion 13. The metal shell 3 has, on an inner circumferential surface thereof, a taper portion 21. The ceramic insulator 2 is fixed in the metal shell 3 with the step portion 14 retained on the taper portion 21 via the plate packing 22. Herein, 50% or more of an inner circumferential edge portion IP of the plate packing 22 is in contact with a part of the ceramic insulator 2 located front of a middle region CP of the curved surface portion 31.

Abstract: In some aspects, a spark plug includes a spark gap in an enclosure of the spark plug. The spark plug includes a passage in the interior of the enclosure. During operation of the engine, the passage directs flow through the spark gap, primarily away from a combustion chamber end of the enclosure. The passage can direct flow at a velocity of 5 meters/second or greater.

Abstract: A sparkplug including an induction coil and an electrode. The induction coil includes two end portions, the electrode extending in a continuation of one of the two end portions. The induction coil includes a conducting wire wound to form a succession of turns, the one of the two end portions having a terminal turn connected to the electrode. The one of the two end portions includes a plurality of coaxial end turns that extend between the terminal turn and an upstream turn, and the terminal turn has a diameter smaller than the diameter of the upstream turn so to reduce strength of the electric field induced in the one of said two end portions near the terminal turn.

Abstract: A corner of a distal end of a ground-electrode-side noble metal tip of a spark plug is taken as a first corner; a corner of a leading end of a center-electrode-side noble metal tip is taken as a second corner; a corner formed at a starting point where a diameter of the center electrode is reduced is taken as a third corner; a corner of the ground electrode is taken as a fourth corner; a corner closest to the third corner of the corners on the distal end of the ground-electrode-side noble metal tip is taken as a fifth corner; a length of a virtual flying spark path defined between the first corner and the second corner is taken as L1; a length of a virtual flying spark path defined between the third corner and the fourth corner is taken as L2; a length of a virtual flying spark path defined between the third corner and the fifth corner is taken as L3; and L2 or L3, whichever is shorter, is taken as L4, the spark plug fulfills a relational expression of L4/L1?1.1.

Abstract: A spark plug includes at least one electrode having a sparking end. The sparking end is formed of a high temperature performance alloy including chromium in an amount of 10.0 weight percent to 60.0 weight percent, palladium in an amount of 0.5 weight percent to 10.0 weight percent, and a balance substantially of at least one of molybdenum and tungsten. The sparking end presents a spark contact surface, and at a temperature of at least 500° C., such as during use of the spark plug in an internal combustion engine, a layer of chromium oxide (Cr2O3) forms at said spark contact surface. The layer of Cr2O3 protects the bulk of the sparking end from the extreme conditions of the combustion chamber and prevents erosion, corrosion, and balling.

Abstract: A spark plug having a center electrode, an insulator and a metal shell and satisfying conditions (1) to (5) as defined herein. Also disclosed is a method of manufacturing a spark plug including the step of producing an insulator by preparing a raw material powder in such a manner that the particle size distribution ratio (90% volume diameter/10% volume diameter) between particles of 10% volume diameter and particles of 90% volume diameter in the raw material powder is 3.6 to 5.2, and then, press-forming and sintering the prepared raw material powder.

Abstract: Disclosed herein is a spark plug comprising an insulative sleeve having a central axial bore and an exterior surface and a center electrode extending through the central axial bore of the insulative sleeve. The insulating sleeve is positioned within, and secured to, a metal shell that serves as a mounting platform and interface to an internal combustion engine. The metal sleeve also supports a ground electrode that is positioned in a spaced relationship relative to the center electrode so as to generate a spark gap. The insulating sleeve includes a shaped tip portion that resides in a recessed end portion of the metal shell. A coating is disposed on the exterior surface of the insulative sleeve. The coating comprises a silicone resin, optionally in combination with a filler.

Abstract: A plasma jet ignition plug exhibiting high plasma generation efficiency while restraining occurrence of preignition. P1 represents the position of a rear end of a region of a metallic shell ledge, the region being in contact with an insulator. P2 represents the position of a rear end of a region of the insulator ledge, the region being in contact with the center electrode. Front end surfaces of the metallic shell, the insulator, and center electrode, an imaginary plane S1 which is perpendicular to the axis and contains position P1, and an imaginary plane perpendicular to the axis and contains position P2 are disposed in this order from front side to rear side along the axis. The axial distance A from the front end surface of the insulator to imaginary plane S1 and axial distance B from the imaginary plane S1 to imaginary plane S2 satisfy 0.5×A?B.

Abstract: A plasma jet ignition plug including a wire-wound resistor for restraining the radiation of noise while allowing application of a sufficiently large current for generation of plasma to a spark discharge gap at the time of ignition. The wire-wound resistor having an inductance of 1 ?H to 100 ?H inclusive and a resistance of 1? or less, and is provided on at least one of a center electrode and a ground electrode. The wire-wound resistor restrains current which is generated by the influence of stray capacitance present in the plasma jet ignition plug, thereby reducing noise.

Abstract: A spark plug for an internal combustion engine is provided which is equipped with a tip protrusion disposed on a top of a hollow cylindrical housing of the spark plug. The spark plug also includes a center electrode retained in a porcelain insulator disposed inside the housing and a ground electrode is joined to the housing so as to form a spark gap. The tip protrusion serves to direct a flow of gas to be ignited by a spark produced in the spark gap and is shaped to have a radial width extending in a radial direction of the housing and a circumferential width extending in a circumferential direction of the cylindrical housing. The radial width is greater than the circumferential width. This enhances the efficiency in guiding the flow of gas toward the spark gap.

Abstract: A spark plug manufacturing method provides a reduction in the cost of raw material preparation and the cost of the disposal of unused powder by recycling powder not used in forming a filler layer of another spark plug. The method is used to make a spark plug that includes a metal shell having a through hole, and an insulating body held inside the through hole, and a filler layer containing talc in a space surrounded by an inner peripheral surface of the through hole and an outer peripheral surface of the insulating body. The powder not used in a process of forming a filler layer of another spark plug is recycled for forming the filler layer of the present spark plug, where the forming process is performed after talc and a binder are mixed.

Abstract: A plasma jet spark plug capable of preventing a channeling progress and having excellent heat conduction. The plasma jet spark plug comprised of: a ceramic insulator having a small diameter portion which assumes a linear shape in an axial direction, and a center electrode has an outer diameter increasing in the order of a frontmost portion, a step portion, a front end portion and a body portion.

Abstract: An apparatus and assembly for an igniter is provided. The igniter includes a shell comprising a base, a tip surface, and a sidewall extending therebetween wherein the sidewall surrounds a cavity within the shell. The igniter also includes a shell bore extending from the tip surface to the cavity and a pin embedded into the tip surface extending substantially tangentially with respect to the bore.

Abstract: A spark plug includes an electrode tip assembly located at an axially-facing free end surface of an electrode body. The electrode tip assembly includes an electrode tip body and a firing tip and has a longitudinal axis that is generally perpendicular to a longitudinal axis of the electrode body. The electrode tip body may be a Ni-alloy piece and is attached to the electrode body, and the firing tip may be an Ir-alloy piece with a sparking surface that faces a spark gap. The electrode body may include a groove formed in the axially-facing free end surface that is useful to help position the electrode tip assembly for attachment. The spark gap can be formed between opposing electrode tip assemblies, and the size of the spark gap can be adjusted during assembly without the need for bending the electrode body.

Abstract: A spark plug electrode, which is produced from an electrode material containing nickel as base material, 0.5 to 3 atom % of silicon, and at least 6 atom % of aluminum.

Abstract: Provided is a spark plug which allows a predetermined resistance to be imparted to a resistor with restraint of variation in resistance of the resistor and in turn, enables enhancement of yield. The spark plug includes a ceramic insulator having an axial hole extending in the direction of an axis CL1, a center electrode, and a terminal electrode. A resistor is provided in the axial hole through sintering of a resistor composition which contains a conductive material such as carbon black, glass powder, and ceramic particles other than glass. As viewed on a section of the resistor taken along a direction orthogonal to the axis CL1, 50% or more of sintered glass powder formed through sintering of the glass powder has a circularity of 0.8 or greater.

Abstract: A spark plug having one or more electrodes at least partially fabricated from an aluminum-containing Ni-based alloy. The alloy is a volume-stable alloy that includes a Ni3Al precipitate in a ??-phase distributed in a Ni matrix ?-phase. The precipitate is formed in the alloy prior to the alloy being used to fabricate electrodes and thus prevents additional Ni3Al precipitate from being formed in the alloy once in service in a high-temperature environment. This, in turn, prevents a volume decrease of the alloy that may lead to an increased spark gap and spark plug malfunction. The volume-stable alloy may be made by solution treatment, quenching, and heat aging of a Ni—Cr—Al—Fe alloy.

Abstract: A spark plug (1) including a noble metal tip joined to a ground electrode and forming a spark discharge gap in cooperation with a center electrode. A surface of the noble metal tip which forms the gap has an area of 0.9 mm2 or greater. The noble metal tip (32) is joined to the ground electrode (27) via a fusion zone (35) formed by irradiating at least one surface among a distal end surface and side surfaces of the ground electrode with a laser beam or an electron beam. Further, as viewed on a projection plane orthogonal to a center axis of the noble metal tip and on which the noble metal tip and the fusion zone are projected along the center axis, an overlapping region between the noble metal tip (32) and the fusion zone accounts for 70% or more of a projected region of the noble metal tip.

Abstract: A spark plug which exhibits high dielectric strength at high temperature and which is unlikely to be deteriorated in dielectric strength is provided. The spark plug includes a center electrode, an insulator, and a metallic shell. The insulator includes an alumina-based sintered body which contains a silicon component, a Group II element component, and a rare earth element component. The alumina-based sintered body is composed of a glass phase and an alumina crystal phase as observed through X-ray diffraction analysis. When the grain boundary phase of the alumina-based sintered body is observed under a transmission electron microscope, and the weight ratio between an alkali metal component and the rare earth element component as reduced to oxides thereof [alkali metal/rare earth element] is calculated at 30 circular spots, each having a diameter of 0.3 nm, selected arbitrarily in a field of observation, the average of the weight ratios of the 30 spots falls within a range of 0.01 to 1.0.

Abstract: A spark plug 20 includes a center electrode 22 and a ground electrode 24 providing a spark gap 26 therebetween. At least one of the electrodes 22, 24, but preferably both electrodes 22, 24 include a clad surrounding a core. The clad includes at least one metal, such as nickel, iron, or cobalt. The core includes nanocarbon material embedded in a copper matrix 40 to increase the thermal conductivity and reduce the coefficient of thermal expansion of the core. The nanocarbon material includes a plurality of fibers 42, also referred to as particles, whisks, or tubes, each having a diameter of 1.0 to 150.0 nanometers and a length of 1 ?m to 100 ?m. The core includes the nanocarbon material in an amount of 0.1 to 10.0 wt. %.

Abstract: High-frequency plasma spark plug includes an insulator which has an axial hole extending in the axis direction, a center electrode inserted into a distal end side of the axial hole, a terminal electrode inserted into a rear end side of the axial hole, and being electrically connected to the center electrode, and a cylindrical main fitting mounted on an outer periphery of the insulator. With respect to a coaxial cable, the inner conductor is connected to the terminal electrode and the outer conductor is connected to the main fitting. High frequency power generated by a predetermined high-frequency power source is supplied via the coaxial cable thus generating high frequency plasma. The main fitting includes a large diameter portion which bulges radially outward and a connection portion which is brought into contact with the outer conductor.

Abstract: In joining a composite tip to an electrode, a method is used for properly adjusting the height of radiation of a laser beam to the height of the boundary between two tips used to form the composite tip. Further, a process for joining a first tip and a second tip together by use of a laser beam includes the steps of; (a) disposing the second tip on a support; (b) obtaining, after pressing downward at least the second tip by the use of a pressing jig, a correction value for correcting the height of radiation of a laser beam; (c) correcting the height of radiation of the laser beam on the basis of the correction value; and (d) joining the first and second tips together by use of the laser beam.

Abstract: An alumina sintered body comprises alumina crystals as a main phase and a grain boundary phase made up of crystalline Y2Si2O7 and amorphous SiO2 at grain boundaries of the alumina crystals wherein when the alumina sintered body is taken as 100 wt %, the high melting phase is present in the range of from 0.1 wt % to 15 wt %. There is also provided a method for preparing the alumina sintered body, which method comprising a first mixing step P1 of mixing, at least, a yttria powder having an average particle size of 60 to 100 nm and a silica powder having a given average particle size to provide a mixed slurry and a second mixing step of further mixing an alumina powder having an average particle size of 0.5 to 1.0 ?m in the mixed slurry.

Abstract: Provided is a spark plug that is excellent not only in salt resistance but also in stress corrosion cracking resistance. The spark plug includes a metal shell covered by a composite layer including a nickel plating layer and a chromate layer formed on the nickel plating layer. The chromate layer has a film thickness of 2 to 45 nm and Cr element concentration of not more than 60 at % and contains Ni in addition to Cr.

Abstract: A spark plug 100 has a center electrode tip 90, 95 at an end portion of an electrode. The electrode tip 90, 95 contains Pd as a main component in an amount greater than 40% by weight and contains at least one element of Ir, Ni, Co, and Fe such that Ir, if contained, is contained in an amount of 0.5% by weight to 20% by weight inclusive and at least one element of Ni, Co, and Fe, if contained, is contained in an amount of 0.5% by weight to 40% by weight inclusive on an element basis.

Abstract: A spark plug having a center electrode and a ground electrode including a ground electrode main body part having an end thereof facing the center electrode and a noble metal tip joined to the ground electrode main body part at a position facing a leading end of the center electrode, a spark discharge gap being formed between the leading end of the center electrode and the noble metal tip, wherein at least a portion of the ground electrode main body part, to which the noble metal tip is joined, is made of an Ni alloy containing 12 to 45 mass % of Cr, 7 mass % or less of Fe, 0.5 to 5 mass % of Al, 0.3 to 5 mass % of Si and 50 mass % or more of the balance, and wherein the joined portion and the noble metal tip are joined by laser welding or electron beam welding.

Abstract: A spark plug which provides reliable prevention of adhesion and accumulation of carbon on an insulator, includes a center electrode extending in the direction of an axis CL1, a ceramic insulator having an axial hole which extends in the direction of the axis CL1 and in which the center electrode is provided, a cylindrical metallic shell provided externally of the outer circumference of the insulator and having a support portion formed on the inner circumferential surface thereof, and a ground electrode extending from a front end portion of the metallic shell. The insulator has a stepped portion supported by the support portion of the metallic shell, and a leg portion formed forward of the stepped portion. A space SP formed between the leg portion of the insulator and the inner circumferential surface of the metallic shell has a volume of 100 mm3 to 300 mm3 inclusive.