WO2010109792A1 - スパークプラグ - Google Patents
スパークプラグ Download PDFInfo
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- WO2010109792A1 WO2010109792A1 PCT/JP2010/001655 JP2010001655W WO2010109792A1 WO 2010109792 A1 WO2010109792 A1 WO 2010109792A1 JP 2010001655 W JP2010001655 W JP 2010001655W WO 2010109792 A1 WO2010109792 A1 WO 2010109792A1
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- alumina
- spark plug
- sintered body
- based sintered
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
- H01T13/00—Sparking plugs
- H01T13/20—Sparking plugs characterised by features of the electrodes or insulation
- H01T13/38—Selection of materials for insulation
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- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
- C04B35/10—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on aluminium oxide
- C04B35/111—Fine ceramics
- C04B35/113—Fine ceramics based on beta-aluminium oxide
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Definitions
- the present invention relates to a spark plug, and more particularly to a spark plug including an insulator that exhibits sufficient withstand voltage characteristics and mechanical strength even in a high temperature environment exceeding 700 ° C., for example.
- An alumina-based sintered body containing alumina as a main component is excellent in withstand voltage characteristics, heat resistance, mechanical strength, and the like, and is inexpensive. Therefore, ceramic products, for example, insulators for spark plugs (also referred to as insulators in the present invention). .), And used as a multilayer wiring board of an IC package.
- Such an alumina-based sintered body has been formed by sintering a mixed powder containing a sintering aid such as a ternary sintering aid composed of SiO 2 —CaO—MgO.
- the sintering aid (mainly Si component) is alumina after sintering. It exists as a low melting point glass phase at the grain boundary of crystal grains, and the low melting point glass phase is softened under the environment where the spark plug is used, for example, at a high temperature of about 700 ° C., and the withstand voltage characteristics of the insulator are lowered. .
- the amount of the sintering aid added can be reduced to reduce the low melting point glass phase in the alumina-based sintered body, but in this case, the insulator is not densified, or at first glance densified. However, a large number of pores remain in the grain boundary constituted by the alumina crystal particles, and the withstand voltage characteristic of the insulator is deteriorated.
- the conventional alumina-based sintered body has a low-melting glass phase or pores (residual pores) at the grain boundary, when a spark plug insulator is formed with the conventional alumina-based sintered body, 700
- a high voltage for generating spark discharge is applied to the spark plug in a high-temperature environment of about °C
- the low melting glass phase softens, or the electric field concentrates on the residual pores and the insulator breaks down (spark May be penetrated).
- Patent Document 1 discloses that “alumina-based sintered body containing at least a rare earth element (hereinafter referred to as RE) component, wherein the theoretical density ratio of the alumina-based sintered body is 95% or more. The high withstand voltage characteristic alumina-based sintered body is described.
- RE rare earth element
- Patent Document 2 states that “the total component content is 100% by mass, the Al component oxide content is 95 to 99.8% by mass, and the rare earth element and the Si component are oxidized of the rare earth element. a thing in terms of proportion (R RE), the ratio of the oxide equivalent content of the Si component (R Si) (R RE / R Si) is contained such that 0.1-1.0, further cleavage There is described “insulator for spark plugs” characterized in that the maximum length existing per 1 mm 2 of the surface is 10 ⁇ m or more and the number of alumina particles having an aspect ratio of 3 or more is less than 10.
- alumina-based porcelain composition containing alumina as a main component comprising alumina as the main component and a composition of at least one element selected from Al, Si, Mg, and rare earth elements. It is composed of a composite sintered body, and the composition of at least one element selected from Al, Si, Mg and rare earth elements is 5 parts by weight or less when the main component alumina is 100 parts by weight.
- alumina Porcelain Composition is described. *
- the thinned insulator has a high withstand voltage characteristic and mechanical strength under a higher temperature environment in addition to a withstand voltage characteristic and mechanical strength under a high temperature environment of about 700 ° C. It is becoming important.
- the spark plug insulators and materials thereof described in Patent Documents 1 to 3 have not been examined at all in terms of withstand voltage characteristics and mechanical strength under such a high temperature environment.
- An object of the present invention is to provide a spark plug including an insulator that exhibits sufficient withstand voltage characteristics and mechanical strength even in a high temperature environment exceeding 700 ° C., for example.
- Means for solving the problems are as follows: (1) A center electrode, a substantially cylindrical insulator provided on the outer periphery of the center electrode, and one end of the center electrode facing the center electrode via a spark discharge gap.
- a spark plug including a ground electrode disposed, wherein the insulator includes a Si component and a Group 2 element component of a periodic table based on an IUPAC 1990 recommendation (hereinafter sometimes referred to as a 2A component).
- a rare earth element component hereinafter sometimes referred to as an RE component.
- the alumina-based sintered body includes RE- ⁇ -alumina containing at least the RE component.
- a crystal phase wherein the average crystal grain size D A (RE) of the RE- ⁇ -alumina crystal phase and the average crystal grain size D A (Al) of alumina satisfy the following condition (1): To spark It is a lag. Condition (1): 0.2 ⁇ D A (RE) / D A (Al) ⁇ 3.0
- the crystal grain size D E (RE) of the RE- ⁇ -alumina crystal phase and the average crystal grain size D A of alumina (Al) is a spark plug having three or less RE- ⁇ -alumina crystal phases satisfying the following condition (2).
- the RE- ⁇ -alumina crystal phase is The alkali metal component in the spot where the presence of the RE- ⁇ -alumina crystal phase was confirmed among the circular spots having a diameter of 0.3 nm when observed with a transmission electron microscope was 0.01 to (5)
- the alumina-based sintered body includes an alumina raw material, the Si component, and the spark plug.
- An auxiliary raw material comprising the Mg component, the Group 2 element component, and the RE component is mixed and granulated in a slurry, and then molded and fired.
- the average particle size of the alumina raw material in the slurry and the A spark plug satisfying a particle size ratio (D alumina raw material / D auxiliary raw material ) of 1.3 ⁇ D alumina raw material / D auxiliary raw material ⁇ 4 with respect to the average particle size of the auxiliary raw material , (6) (1) to ( Any of 5)
- the 2A component contains Mg and Ba as essential elements of Group 2 elements of the periodic table based on the IUPAC 1990 recommendation and contains at least one element other than Mg and Ba.
- the RE component is a spark plug that is at least one component selected from the group consisting of a La component, a Pr component, and an Nd component. (7) Any one of (1) to (6) The spark plug according to the item, wherein the insulator is held by a metal shell, and a nominal diameter of a screw portion formed on the outer peripheral surface of the metal shell is 10 mm or less.
- the spark plug insulator according to the present invention is composed of the alumina-based sintered body containing the Si component, the 2A component, and the RE component, and the alumina-based sintered body is made of the RE component.
- the average crystal grain size D A (RE) of the RE- ⁇ -alumina crystal phase and the average crystal grain size D A (Al) of alumina are the above-mentioned conditions (1 ) Is satisfied.
- the alumina-based sintered body having such a configuration can exhibit sufficient withstand voltage characteristics and mechanical strength even in a high temperature environment exceeding 700 ° C., for example, when used as a spark plug insulator. Therefore, according to the present invention, it is possible to provide a spark plug including an insulator that exhibits sufficient withstand voltage characteristics and mechanical strength even in a high temperature environment exceeding 700 ° C., for example.
- FIG. 1 is an explanatory view for explaining a spark plug which is an embodiment of a spark plug according to the present invention
- FIG. 1A is a partial cross-section of the spark plug which is an embodiment of the spark plug according to the present invention
- FIG. 1B is an overall explanatory view
- FIG. 1B is a cross-sectional explanatory view showing a main part of a spark plug as an embodiment of the spark plug according to the present invention.
- FIG. 2 is a schematic cross-sectional view showing an outline of a withstand voltage measuring device.
- FIG. 3 is an X-ray diffraction chart of an alumina-based sintered body (Example 1) having a La- ⁇ -alumina structure (LaAl 11 O 18 ) crystal.
- a spark plug according to the present invention comprises a center electrode, a substantially cylindrical insulator provided on the outer periphery of the center electrode, and a ground electrode disposed so that one end thereof faces the center electrode via a spark discharge gap. I have.
- the spark plug according to the present invention is not particularly limited as long as it is a spark plug having such a configuration, and various configurations can be adopted. *
- FIG. 1 shows a spark plug as an embodiment of the spark plug according to the present invention.
- the lower side of the paper is the front end direction of the axis AX
- the upper side of the paper is the rear end direction of the axis AX
- the upper side of the paper is the front side of the axis AX
- the lower side of the paper is the rear side of the axis AX. This will be described as the end direction.
- the spark plug 1 includes a substantially rod-shaped center electrode 2 and a substantially cylindrical insulator 3 provided on the outer periphery of the center electrode 2.
- a cylindrical metal shell 4 that holds the body 3 and a ground that is arranged so that one end faces the tip surface of the center electrode 2 via the spark discharge gap G and the other end is joined to the end surface of the metal shell 4.
- the metallic shell 4 has a cylindrical shape and is formed so as to hold the insulator 3 by incorporating the insulator 3 therein.
- a threaded portion 9 is formed on the outer peripheral surface in the front end direction of the metal shell 4, and the spark plug 1 is attached to a cylinder head of an internal combustion engine (not shown) using the threaded portion 9.
- the nominal diameter of the screw portion 9 is adjusted to, for example, 10 mm or less.
- the metal shell 4 can be formed of a conductive steel material, for example, low carbon steel. *
- the center electrode 2 is formed by an outer member 7 and an inner member 8 formed so as to be concentrically embedded in an axial center portion inside the outer member 7.
- the center electrode 2 is fixed to the shaft hole of the insulator 3 with its tip portion protruding from the tip surface of the insulator 3, and is insulated and held with respect to the metal shell 4.
- the outer material 7 of the center electrode 2 is formed of a Ni-based alloy having excellent heat resistance and corrosion resistance
- the inner material 8 of the center electrode 2 is formed of a metal material having excellent thermal conductivity such as copper (Cu) or nickel (Ni). Can be done. *
- the ground electrode 6 is formed in, for example, a prismatic body, one end is joined to the end surface of the metal shell 4, and is bent into a substantially L shape in the middle, and the tip is positioned in the axis AX direction of the center electrode 2. As such, its shape and structure are designed. By designing the ground electrode 6 in this way, one end of the ground electrode 6 is disposed so as to face the center electrode 2 with the spark discharge gap G interposed therebetween.
- the spark discharge gap G is a gap between the front end surface of the center electrode 2 and the surface of the ground electrode 6, and this spark discharge gap G is normally set to 0.3 to 1.5 mm. Since the ground electrode 6 is exposed to a higher temperature than the center electrode 2, the ground electrode 6 is preferably formed of a Ni-base alloy or the like that is more excellent in heat resistance and corrosion resistance than the Ni-base alloy that forms the center electrode 2.
- the insulator 3 is held on the inner periphery of the metal shell 4 via a talc (also referred to as talc) and / or packing (not shown), and in the direction of the axis AX of the insulator 3.
- a shaft hole for holding the center electrode 2 is provided along the axis.
- the insulator 3 is fixed to the metal shell 4 with the end of the insulator 3 in the tip direction protruding from the tip surface of the metal shell 4.
- the insulator 3 on the front end surface of the metal shell 4 is set to a thin thickness of 0.7 to 1.0 mm, for example. *
- the insulator 3 is formed of an alumina-based sintered body containing a Si component, a 2A component, and an RE component.
- This alumina-based sintered body contains alumina (Al 2 O 3 ) (hereinafter sometimes referred to as an Al component) as a main component.
- Al component alumina
- the “main component” means a component having the highest content rate.
- the sintered body is excellent in withstand voltage characteristics, heat resistance, mechanical characteristics, and the like.
- the content of the Al component in the alumina-based sintered body is preferably 92% by mass or more and 97% by mass or less, and 93% by mass or more and 96.% by mass, when the total mass of the alumina-based sintered body is 100% by mass. It is particularly preferably 5% by mass or less. If the content of the Al component is within the above range, the content of the sintering aid in the raw powder before sintering to form the alumina-based sintered body is an appropriate ratio. The alumina-based sintered body obtained by sintering the raw material powder becomes dense.
- the content of the Al component is defined as mass% in terms of oxide when converted to “alumina (Al 2 O 3 )” which is an oxide of the Al component.
- the alumina crystal particles present as the Al component have an average crystal grain size D A (Al) of, for example, 0.6 to 3.6 ⁇ m.
- the alumina crystal particles in the alumina-based sintered body are represented as “dark color regions” in the image analysis photograph as described later.
- the average crystal grain size D A (Al) of the crystal particles in the alumina-based sintered body was measured with a scanning electron microscope (SEM) in the same manner as the crystal grain size D E (RE) of the RE- ⁇ -alumina crystal phase described later. Can be obtained by observation. Specifically, it is calculated as follows.
- the surface or arbitrary cross section of the alumina-based sintered body is mirror-polished, and the polished surface is scanned for 10 minutes at a temperature lower by 100 ° C. than the firing temperature of the alumina-based sintered body. Observed with a scanning electron microscope (SEM), the particle diameter of a “dark color region” represented by “binarization” as described later is measured by the intercept method, and these can be obtained by arithmetic averaging. it can.
- SEM scanning electron microscope
- the alumina-based sintered body contains a Si component.
- This Si component is a component derived from a sintering aid and is present in the alumina-based sintered body as an oxide, an ion, or the like.
- the Si component normally melts during sintering to form a liquid phase and functions as a sintering aid that promotes densification of the sintered body.
- a low-melting glass phase or the like is added to the grain boundaries of the alumina crystal particles.
- the Si component preferentially forms a high melting point glass phase or the like together with other components than the low melting point glass phase. As a result, the alumina-based sintered body exhibits high withstand voltage characteristics and mechanical strength.
- the Si component is contained in the alumina-based sintered body at such a content rate that does not substantially form the low-melting glass phase and forms a high-melting glass phase or the like with other components.
- the content of the Si component in the alumina-based sintered body is preferably 1% by mass or more and 5% by mass or less, for example, when the total mass of the alumina-based sintered body is 100% by mass, and 2% by mass or more. It is particularly preferably 5% by mass or less.
- the content of the Si component is defined as mass% in terms of oxide when converted to “SiO 2 ” which is an oxide of the Si component.
- the alumina-based sintered body contains a 2A component.
- Mg, Ca, Sr and Ba are preferably mentioned from the viewpoint of low toxicity and the like.
- the 2A component preferably contains at least two of these 2A components, and the alumina-based sintered body has a withstand voltage characteristic even under a high temperature environment exceeding 700 ° C., for example.
- the 2A component is a component containing Mg and Ba as essential elements of the Group 2 elements of the periodic table and containing at least one other element excluding Mg and Ba, in terms of sufficiently exhibiting mechanical strength. That is, a component of at least one element selected from the group consisting of the Ca component and the Sr component is even more preferable.
- an even more preferable 2A component contains an Mg component, a Ba component and a Ca component, an Mg component, a Ba component and an Sr component, or an Mg component, a Ba component, a Ca component and an Sr. Containing ingredients.
- 2A component containing Mg component, Ba component, and Ca component is particularly preferable.
- the Mg component is a component derived from a sintering aid, is present in the alumina-based sintered body as an oxide, an ion, and the like, and functions as a sintering aid in the same manner as the Si component before sintering.
- the Ba component, the Ca component, and the Sr component are components derived from a sintering aid, and are present in the alumina-based sintered body as oxides, ions, and the like, and are fired in the same manner as the Mg component before sintering. It functions as a binder and has a function of improving the mechanical strength of the obtained alumina-based sintered body.
- a 2A component having a component containing at least two kinds of Group 2 elements functioning in this way, in particular, a component of at least one other element excluding the Mg component, the Ba component, the Mg component, and the Ba component.
- the alumina-based sintered body containing the 2A component exhibits high withstand voltage characteristics and mechanical strength when the insulator 3 is formed, and lowers the sintering temperature during firing and suppresses migration at high temperatures. Can also be achieved.
- the Mg component contributes to a decrease in the sintering temperature during firing, and the Ba component contributes to the suppression of migration at high temperatures.
- the total content of the 2A component in the alumina-based sintered body is preferably 0.1% by mass or more and 2.5% by mass or less when the total mass of the alumina-based sintered body is 100% by mass. It is particularly preferably 8% by mass or more and 2.2% by mass or less.
- each component in the 2A component is adjusted as appropriate within a range not exceeding the total content of the 2A components, and the content ratio of each component is not particularly limited.
- the content of each component is within the range of 0% by mass to 2% by mass, and the content of at least two components is simultaneously It is preferably selected so that it does not become 0% by mass.
- the content of the Mg component is selected from the range of 0.01% by mass or more and 0.4% by mass or less so that the content of the at least two components does not become 0% by mass at the same time
- the content of the Ca component is selected from a range of not less than 0.9% and not more than 0.9% by mass
- the content of the Sr component is selected from the range of not less than 0.2% by mass and not more than 0.9% by mass
- the content of the Ba component is selected from the range of 1.6% by mass or less.
- the alumina-based sintered body does not contain a Mg component, a Ca component, a Sr component or a Ba component, the content is naturally 0% by mass.
- each content rate of the group 2 element containing component which forms 2A component shall be the oxide conversion mass% when converted into the oxide "(2A) O", Specifically, Mg
- the content M of the component is the mass% in terms of oxide when converted to “MgO” which is the oxide of the Mg component
- the content B of the Ba component is when converted to “BaO” which is the oxide of the Ba component.
- the oxide conversion mass%, the Ca component content C is the oxide conversion mass% when converted to the Ca component oxide “CaO”
- the Sr component content Sr is the Sr component oxide. Oxide equivalent mass% when converted to “SrO”.
- the content of the 2A component is the total content of each content of the 2A component. Specifically, the content M of the Mg component, the content B of the Ba component, the content C of the Ca component, and the Sr component The total content of Sr, etc. *
- the alumina-based sintered body contains an RE component derived from a sintering aid.
- This RE component is a component containing Sc, Y and a lanthanoid element. Specifically, the Sc component, Y component, La component, Ce component, Pr component, Nd component, Pm component, Sm component, Eu component, Gd component, Tb component, Dy component, Ho component, Er component, Tm component, Yb component and Lu component.
- the RE component is present in the alumina-based sintered body as an oxide, ion, or the like.
- the RE component is contained at the time of sintering, so that alumina grain growth at the time of sintering is prevented from excessively occurring, and RE-Si glass (rare earth glass) together with the Si component is used as a grain boundary. It can be formed to increase the melting point of the grain boundary glass phase, thereby improving the withstand voltage characteristics of the insulator 3 and also improving the mechanical strength.
- the RE component may be any of the components described above, but is preferably at least one component selected from the group consisting of a La component, a Pr component, and an Nd component.
- the La component, the Pr component, and the Nd component have large ionic radii of the elements La, Pr, and Nd contained therein, and form a high melting point crystal phase together with the Si component.
- a crystal phase of RE- ⁇ -alumina structure having a very high melting point of about 2000 ° C. in combination with 2A component hereinafter sometimes simply referred to as “RE- ⁇ -alumina crystal phase” is easily formed. I think that.
- the alumina-based sintered body contains at least one component selected from the group consisting of La component, Pr component and Nd component as the RE component, an optimal RE- ⁇ -alumina crystal phase is effectively formed.
- the RE component contains at least one component selected from the group consisting of La component, Pr component and Nd component as RE component.
- the RE- ⁇ -alumina crystal phase has a composition represented by this composition formula, the withstand voltage characteristics and mechanical strength of the insulator 3 can be further improved.
- X, y and z in the composition formula are preferably selected from the range of 0 to 1.5, y of 11 to 14, and z of 18 to 24. Examples of the composition formula indicating the composition of the RE- ⁇ -alumina crystal phase include RE (2A) Al 13 O 19 , REAl 11 O 18, and the like.
- Whether or not the RE- ⁇ -alumina crystal phase has a composition satisfying the composition formula is determined based on whether the RE- ⁇ -alumina crystal phase present in the alumina-based sintered body is, for example, a transmission electron microscope (TEM) (Hitachi, “HD-2000”) Attached energy dispersive X-ray analyzer (EDX) (EDAX, EDX: “Genesis4000”, detector: SUT This can be confirmed by performing elemental analysis under the following measurement conditions using W3.3RTEM).
- TEM transmission electron microscope
- EDX Attached energy dispersive X-ray analyzer
- the RE- ⁇ -alumina crystal phase may be present in the alumina-based sintered body, and the location of the RE- ⁇ -alumina crystal phase is not particularly limited, and is preferably present even inside the alumina-based sintered body. It is particularly preferred that it exists at the two-grain grain boundary and / or triple point. *
- the presence of the RE- ⁇ -alumina crystal phase can be identified by X-ray diffraction using, for example, a JCPDS card.
- a JCPDS card For Pr and Nd, since there is no JCPDS card of RE- ⁇ -alumina, identification by X-ray diffraction is not possible directly. However, since the ionic radii of Pr 3+ and Nd 3+ are almost the same as the ionic radius of La 3+ , an X-ray diffraction spectrum similar to the JCPDS card of La- ⁇ -alumina (No. 33-699) is shown. In contrast to the La- ⁇ -alumina JCPDS card, the presence of Pr- ⁇ -alumina and Nd- ⁇ -alumina can be confirmed.
- the RE- ⁇ -alumina crystal phase is mechanical if the RE- ⁇ -alumina crystal phase present in the alumina-based sintered body is considered to be a particle-like crystal grain and the particle size is too large. Since the strength may be lowered, it is important in the present invention to appropriately adjust the particle diameter of the RE- ⁇ -alumina crystal phase in order to exhibit high mechanical strength when the insulator 3 is used. is there. *
- the average crystal grain size D A (RE) of the RE- ⁇ -alumina crystal phase and the average crystal grain size D A (Al) of alumina satisfy the following condition (1).
- the following condition (1) is preferably satisfied when the RE component is at least one component selected from the group consisting of a La component, a Pr component and an Nd component.
- D A (RE) / D A (Al) is more preferably 0.2 to 2, and particularly preferably 0.2 to 1.5.
- the crystal grain size D E (RE) and the average crystal grain size D A (Al) of alumina are The number of RE- ⁇ -alumina crystal phases satisfying the following condition (2) is preferably 3 or less, and in particular, the RE component is at least one component selected from the group consisting of La component, Pr component and Nd component. In this case, the number of RE- ⁇ -alumina crystal phases satisfying the following condition (2) is preferably 3 or less.
- the alumina-based sintering does not deteriorate the withstand voltage characteristics, for example, even in a high temperature environment exceeding 700 ° C. High mechanical strength can be exhibited.
- the RE- ⁇ -alumina crystal phase satisfying the following condition (2) is more preferably 2 or less, and particularly preferably 1 or less. Condition (2): D E (RE) / D A (Al) ⁇ 2
- the crystal grain size D E (RE) and the average crystal grain size D A (RE) can be obtained as follows.
- the surface of the alumina-based sintered body or an arbitrary cross section is mirror-polished, and this polished surface is subjected to thermal etching treatment at a temperature 100 ° C. lower than the firing temperature of the alumina-based sintered body for 10 minutes.
- This treated surface is observed with a scanning electron microscope (SEM), and the observation area is photographed at a magnification of 2000 times.
- SEM scanning electron microscope
- the obtained image is “binarization processing (also referred to as binarization processing)” using the following “binarization processing method and condition” using, for example, image analysis software “WinROOF” (manufactured by Mitani Corporation).
- the RE- ⁇ -alumina crystal phase is represented as “light color region”, and alumina is represented as “dark region”.
- D E (RE) of the RE- ⁇ -alumina crystal phase it was assumed that the “light color region” extracted by the binarization process was a crystal particle of one RE- ⁇ -alumina crystal phase. In this case, the surface area of each “light color region” is calculated, and the circle equivalent diameter of each “light color region” is calculated from this surface area.
- the average crystal grain size D A (RE) of the RE- ⁇ -alumina crystal phase is the arithmetic average value of the crystal grain size D E (RE) thus calculated.
- a secondary electron image and a reflected electron image are confirmed in an image (horizontal 1280 pixels ⁇ vertical 1024 pixels) obtained by photographing the processing surface, and a reflected electron image is obtained.
- a “light color collection region” in which two or more “light color regions” are aggregated or adjacent to each other, a line is formed at the boundary (corresponding to the grain boundary of each crystal) in each “light color region”. To clarify the boundary of each “light color area”.
- the image of the reflected electron image is smoothed while maintaining the edge of the “light color region”.
- a “threshold value” is set in the binarization process for extracting only the “light color region” from the reflected electron image. More specifically, a graph is created from the backscattered electron image with brightness on the horizontal axis and frequency on the vertical axis. Since the obtained graph is a double mountain graph, the midpoint of the two peaks is set as the “threshold value”.
- the “light color region” is extracted by selecting an arbitrary region (width 40 ⁇ m ⁇ length 30 ⁇ m) from the reflected electron image and extracting the “light color region” existing in the image of this region. Do it.
- the average grain size D A (RE) of the RE- ⁇ -alumina crystal phase satisfies the condition (1), or 3 or less RE- ⁇ -alumina crystal phases satisfy the condition (2).
- the range is not particularly limited, but is preferably 0.5 to 5.0 ⁇ m, particularly preferably 0.5 to 3.0 ⁇ m.
- the RE- ⁇ -alumina crystal phase has an average crystal grain size D A (RE) in the above range, when the insulator 3 is used, both withstand voltage characteristics and mechanical strength can be achieved at a high level. it can.
- RE- ⁇ -alumina itself can be used as a raw material powder, but since the anisotropic growth of RE- ⁇ -alumina grains during firing is remarkable, the density of the alumina-based sintered body is high. May be hindered. Therefore, the RE- ⁇ -alumina crystal phase is preferably formed by precipitation during the firing process.
- the RE- ⁇ -alumina crystal phase can be precipitated by sintering raw material powder containing the Si component and the 2A component at the content rates in the presence of the RE component.
- the RE component In order to precipitate the RE- ⁇ -alumina crystal phase satisfying the condition (1) and / or three or less RE- ⁇ -alumina crystal phases satisfying the condition (2), for example, the RE component
- the method of adjusting the content rate more specifically, when the content rate of the RE component is reduced, “D A (RE) / D A (Al)” in the condition (1) and “D A in the condition (2)”
- Both “number of RE- ⁇ -alumina crystal phases satisfying E (RE) / D ( A Al) ⁇ 2” are small or small.
- the content of the RE component in the alumina-based sintered body is not particularly limited.
- the content is such that a RE- ⁇ -alumina crystal phase can be formed. I just need it.
- the content of the RE component is a La component, a Pr component or an Nd component, for example, when the total mass of the alumina-based sintered body is 100% by mass, it exceeds 0% by mass and is 4% by mass. % Or less is preferable.
- the content rate of the RE component in the alumina-based sintered body is defined as mass% in terms of oxide when converted to the oxide of each component.
- the Ce component is the oxide equivalent mass% when converted to the Ce component “CeO 2 ”
- the Pr component is the oxide equivalent mass% when converted to “Pr 6 O 11 ”
- the Ce component and The RE component other than the Pr component is assumed to be an oxide equivalent mass% when converted to “RE 2 O 3 ”.
- the content is the total content of each component.
- the Si component, the 2A component, and the RE component are each preferably contained in the above-described content ratios, and the total of the Si component content ratio, the 2A component content ratio, and the RE component content ratio.
- the content is preferably 3% by mass or more and 8% by mass or less when the total mass of the alumina-based sintered body is 100% by mass, and is 3.5% by mass or more and 7% by mass or less. Particularly preferred.
- the resulting alumina-based sintered body becomes dense, and the insulator 3 formed from this alumina-based sintered body exhibits high withstand voltage characteristics.
- the alumina-based sintered body includes an Al component, a Si component, a 2A component, and an RE component, and substantially includes the Al component, the Si component, the 2A component, and the RE component.
- substantially means that components other than the above components are not actively contained by addition or the like.
- a small amount of inevitable various impurities may be contained in each component of the alumina-based sintered body. Although it is preferable to remove these impurities as much as possible, in reality, they cannot be completely removed. Therefore, the alumina-based sintered body may contain inevitable impurities in addition to the above-described components within a range not impairing the object of the present invention.
- Examples of inevitable impurities that may be contained in such an alumina-based sintered body include alkali metals such as Na, S and N, and the like.
- the content of these inevitable impurities is preferably small.
- the content is preferably 1 part by mass or less.
- the alumina-based sintered body is substantially composed of the above components, but in addition to the inevitable impurities, in addition to the Al component, Si component, 2A component, and RE component, other components such as B A small amount of components, Ti components, Mn components, Ni components and the like may be contained.
- the RE- ⁇ -alumina crystal phase As a preferred embodiment of the RE- ⁇ -alumina crystal phase, an embodiment in which the RE- ⁇ -alumina crystal phase contains 0.01 to 8% by weight of an unavoidable impurity, in particular, an alkali metal such as Na, in terms of oxides. be able to.
- the alkali metal content was confirmed by the presence of the RE- ⁇ -alumina crystal phase in a 0.3 nm diameter circular spot when the RE- ⁇ -alumina crystal phase was observed with a transmission electron microscope. It is the amount when converted to oxide in a spot.
- the RE- ⁇ -alumina crystal phase was observed with a transmission electron microscope, among the circular spots having a diameter of 0.3 nm, the presence of the RE- ⁇ -alumina crystal phase was confirmed.
- it is contained in an amount of 0.01 to 8% by mass in terms of oxide it is difficult to reduce the withstand voltage characteristics and the high temperature strength at high temperatures, and it is possible to prevent a decrease in temperature at which the grain boundary phase softens
- the alumina-based sintered body Since the alumina-based sintered body has an RE- ⁇ -alumina crystal phase that includes at least the RE component and satisfies the condition (1), it is composed of particles having a narrow particle size distribution and becomes extremely dense. I guess that.
- the RE- ⁇ -alumina crystal phase which is a high melting point crystal phase, exists in the grain boundary phase, the alumina-based sintered body can effectively suppress softening of the grain boundary phase at high temperatures. it can. As a result, the alumina-based sintered body has very few pores that can serve as a starting point of fracture, and the grain boundary phase is difficult to soften.
- the insulator 3 even in a high-temperature environment exceeding 700 ° C., for example. A sufficient withstand voltage characteristic and mechanical strength can be exhibited.
- the alumina-based sintered body containing the Si component, the 2A component, and the RE component and having the RE- ⁇ -alumina crystal phase satisfying the condition (1) is an insulator used for a spark plug. 3 and is particularly preferably used as a material for the insulator 3 used for a downsized spark plug and a high-output spark plug for an internal combustion engine.
- the spark plug provided with the insulator 3 formed of the alumina-based sintered body can exhibit sufficient withstand voltage characteristics and mechanical strength even in a high temperature environment exceeding 700 ° C., for example. Therefore, according to the present invention, it is possible to achieve the object of providing a spark plug that exhibits sufficient withstand voltage characteristics and mechanical strength even in a high temperature environment exceeding 700 ° C., for example.
- This alumina-based sintered body is formed by sintering raw material powder satisfying the above composition.
- the alumina-based sintered body includes an Al compound powder, usually an alumina powder, a rare earth element (RE) compound powder, and at least two Group 2 element (2A) compound powders, in particular an Mg compound powder and a Ba compound.
- an Al compound powder usually an alumina (Al 2 O 3 ) powder, a rare earth element (RE) compound powder, an Si compound powder, and a Group 2 element (2A) compound
- the powder is preferably specified to have almost the same content (the total mass of the raw material powder is 100% by mass) as the content of each component converted from the compound powder in the obtained alumina-based sintered body.
- a hydrophilic binder and a solvent are added and mixed to prepare a slurry.
- each powder of the same material as the Al component, the same material as the Si component, the same material as the Mg component, the same material as the Group 2 element component, and the same material as the RE component (these materials)
- the powder can also be referred to as a raw material powder.)
- a slurry prepared by mixing the powder can also be used.
- the raw material powder preferably has a particle size satisfying a certain numerical range. More specifically, the alumina-based sintered body is granulated by mixing an alumina raw material and an auxiliary raw material comprising the Si component, the Mg component, the Group 2 element component, and the RE component in a slurry. After forming and firing, the particle size ratio (D alumina raw material / D auxiliary raw material ) of the average particle diameter of the alumina raw material and the auxiliary raw material in the slurry is 1.3 ⁇ D alumina raw material / It is preferable that the D auxiliary material ⁇ 4.
- the particle size ratio of the raw material powder is 1.3 ⁇ D alumina raw material / D auxiliary raw material ⁇ 4, more preferably 1.6 ⁇ D alumina raw material / D auxiliary raw material ⁇ 3.6, coarse RE- ⁇ -alumina The generation of the crystal phase can be suppressed, the RE- ⁇ -alumina crystal phase can be efficiently generated, and good sinterability can be ensured.
- the Al compound powder is not particularly limited as long as it is an aluminum oxide powder that is an Al component or a compound that is converted to an Al component by firing, and alumina (Al 2 O 3 ) powder is usually used. Since the Al compound powder may actually contain unavoidable impurities such as Na, it is preferable to use a high-purity one. For example, the purity of the Al compound powder is 99.5% or more. Is preferred. As the Al compound powder, in order to obtain a dense alumina-based sintered body, it is usually preferable to use a powder having an average particle size of 0.1 ⁇ m or more and 5.0 ⁇ m or less. Here, the average particle diameter is a value measured by a laser diffraction method (manufactured by HORIBA, “LA-750”).
- the Si compound powder is not particularly limited as long as it is a silicon oxide powder that is a Si component, or a compound that is converted to a Si component by firing, and includes, for example, Si oxides (including complex oxides), hydroxides, Examples thereof include various inorganic powders such as carbonates, chlorides, sulfates, nitrates, and phosphates. Specific examples include SiO 2 powder.
- Si oxides including complex oxides
- hydroxides examples thereof include various inorganic powders such as carbonates, chlorides, sulfates, nitrates, and phosphates. Specific examples include SiO 2 powder.
- the usage-amount is grasped
- the purity and average particle size of the Si compound powder are basically the same as those of the Al compound powder.
- the Group 2 element (2A) compound powder is not particularly limited as long as it is an oxide powder of Group 2 element as the 2A component or a compound that is converted to the 2A component by firing.
- Examples of the Group 2 element (2A) compound powder include various inorganic powders such as hydroxides, carbonates, chlorides, sulfates, nitrates, and phosphates of the Group 2 element (2A). .
- MgO powder, MgCO 3 powder as Mg compound powder, BaO powder, BaCO 3 powder as Ba compound powder, CaO powder, CaCO 3 powder as Ca compound powder, SrO powder, SrCO 3 powder as Sr compound powder, etc. Can be mentioned.
- the usage-amount is grasped
- the purity and average particle size of the Group 2 element (2A) compound powder are basically the same as those of the Al compound powder.
- the Group 2 element (2A) compound powder is preferably at least two Group 2 element (2A) compound powders, more preferably Mg compound powder and Ba compound powder are essential, and Mg compound powder and At least one compound powder selected from the group consisting of Ca compound powder and Sr compound powder, that is, at least one elemental compound powder excluding Ba compound powder. More preferably, the Group 2 element (2A) compound powder is specifically a compound powder of at least one element selected from the group consisting of Mg compound powder, Ba compound powder, Ca compound powder and Sr compound powder. Particularly preferred Group 2 element (2A) compound powders are Mg compound powder, Ba compound powder and Ca compound powder. *
- the rare earth element (RE) compound powder is not particularly limited as long as it is an RE oxide powder that is an RE component, or a compound that is converted into an RE component by firing.
- rare earth element (RE) oxide and composites thereof examples thereof include powders such as oxides.
- the usage-amount is grasped
- the purity and average particle diameter of the rare earth element (RE) compound powder are basically the same as those of the Al compound powder. *
- These raw material powders are usually preferably mixed for 8 hours or more.
- the mixing time of the raw material powder is less than 8 hours, the mixed state of the raw material powder is not highly uniform, and the resulting sintered body may not be highly densified.
- hydrophilic binder examples include polyvinyl alcohol, water-soluble acrylic resin, gum arabic, and dextrin.
- solvent examples include water and alcohol. These hydrophilic binders and solvents can be used alone or in combination of two or more.
- the use ratio of the hydrophilic binder and the solvent can be 0.1 to 5 parts by mass (preferably 0.5 to 3 parts by mass) of the hydrophilic binder when the raw material powder is 100 parts by mass. If water is used as the solvent, the amount can be 40 to 120 parts by mass (preferably 50 to 100 parts by mass). *
- the slurry thus obtained can be prepared, for example, with an average particle size of 1.4 ⁇ m or more and 5.0 ⁇ m or less.
- the slurry thus obtained is spray-dried by a spray drying method or the like, and granulated to an average particle size of 50 ⁇ m to 200 ⁇ m (preferably 70 ⁇ m to 150 ⁇ m).
- the average particle diameter is a value measured by a laser diffraction method (manufactured by HORIBA, “LA-750”). *
- the granulated product is molded to obtain a molded body.
- the obtained molded body is processed into a desired shape by cutting, polishing or the like, if necessary, and then 1450 to 1650 ° C. (more preferably 1500 to 1600 ° C.) in an air atmosphere for 1 to 10 hours (more preferably 2 ⁇ 8 hours) to obtain an alumina-based sintered body.
- the firing temperature is less than 1450 ° C., or if the firing time is less than 1 hour, the resulting alumina-based sintered body cannot be sufficiently densified, while if the firing temperature exceeds 1650 ° C.
- the firing time exceeds 10 hours, the alumina particles grow abnormally during firing, and both the withstand voltage characteristics and mechanical strength of the resulting alumina-based sintered body tend to be reduced.
- the alumina-based sintered body in this manner, for example, if each condition is adjusted based on the above-described method, the condition (1) is satisfied, and the RE- An extremely dense alumina-based sintered body having a ⁇ -alumina crystal phase can be obtained.
- the alumina-based sintered body can exhibit sufficient withstand voltage characteristics and mechanical strength even in a high temperature environment exceeding 700 ° C., for example.
- the RE- ⁇ -alumina crystal phase has a composition represented by the above composition formula, or the 2A component contains Mg and Ba as an essential component and contains at least one other element excluding Mg and Ba.
- this alumina-based sintered body is particularly used as a material for the spark plug including the small and thin insulator 3 and the insulator 3 used in the spark plug for the internal combustion engine with high output. Is preferred.
- This alumina-based sintered body may be shaped again if desired. In this manner, the alumina-based sintered body and the insulator 3 for the spark plug 1 made of the alumina-based sintered body can be produced.
- the spark plug 1 is manufactured, for example, as follows. That is, the center electrode 2 and / or the ground electrode 6 are produced by processing an electrode material such as a Ni-based alloy into a predetermined shape.
- the electrode material can be adjusted and processed continuously. For example, using a vacuum melting furnace, a molten metal such as a Ni-based alloy having a desired composition is prepared, and after the ingot is prepared from each molten metal by vacuum casting, the ingot is subjected to hot working, wire drawing, etc. Then, the center electrode 2 and / or the ground electrode 6 can be manufactured by appropriately adjusting to a predetermined shape and a predetermined dimension. It is also possible to insert the inner member 8 into the outer member 7 formed in a cup shape and form the center electrode 2 by plastic working such as extrusion. *
- one end of the ground electrode 6 is joined to the end face of the metal shell 4 formed into a predetermined shape by plastic working or the like by electric resistance welding or the like, and is washed with about 10% hydrochloric acid and water as required.
- the insulator 3 having a predetermined shape and size is made of the alumina-based sintered body, the center electrode 2 is assembled to the insulator 3 by a known technique, and the insulating metal 3 is joined to the metal shell 4 to which the ground electrode 6 is joined. Assemble the body 3.
- the spark plug 1 is manufactured such that the tip of the ground electrode 6 is bent toward the center electrode 2 so that one end of the ground electrode 6 faces the tip of the center electrode 2.
- a spark plug according to the present invention is used as an ignition plug for an internal combustion engine for automobiles, for example, a gasoline engine, and the screw portion is formed in a screw hole provided in a head (not shown) that defines a combustion chamber of the internal combustion engine. 9 is screwed and fixed at a predetermined position.
- the spark plug according to the present invention can be used in any internal combustion engine, but the alumina-based sintered body forming the insulator 3 has a sufficient withstand voltage characteristic and machine even in a high temperature environment exceeding 700 ° C., for example. Therefore, the spark plug 1 according to the present invention has a high output, for example, a spark plug having a thinned insulator whose nominal diameter of the screw portion 9 is adjusted to 10 mm or less is required. It can be suitably used for an internal combustion engine or the like.
- the spark plug 1 is arranged such that the tip surface of the center electrode 2 and the surface of one end of the ground electrode 6 are opposed to each other via the spark discharge gap G in the axis AX direction of the center electrode.
- the side surface of the center electrode and the tip surface of one end of the ground electrode may be arranged so as to face each other via the spark discharge gap in the radial direction of the center electrode.
- a single ground electrode or a plurality of ground electrodes facing the side surface of the center electrode may be provided.
- the spark plug 1 includes the center electrode 2 and the ground electrode 6.
- a noble metal tip may be provided on the tip of the center electrode and / or the surface of the ground electrode.
- the noble metal tip formed on the tip of the center electrode and the surface of the ground electrode usually has a cylindrical shape, is adjusted to an appropriate size, and the tip of the center electrode is applied by an appropriate welding technique such as laser welding or electric resistance welding. And fused to the surface of the ground electrode.
- the spark discharge gap is formed by the surface of the noble metal tip formed on the tip of the center electrode and the surface of the noble metal tip formed on the surface of the ground electrode. Examples of the material forming the noble metal tip include noble metals such as Pt, Pt alloy, Ir, and Ir alloy.
- Alumina powder having an average particle size of 2.2 ⁇ m and a purity of 99.5% or more (containing a trace amount of Na which is one of alkali metals as an inevitable impurity), and SiO 2 having an average particle size of 2.8 ⁇ m and a purity of 99.5% or more
- MgCO 3 powder having an average particle diameter of 6.0 ⁇ m and a purity of 99.5% or more CaCO 3 powder having an average particle diameter of 2.0 ⁇ m and a purity of 99.5% or more, an average particle diameter of 5.0 ⁇ m, and a purity of 99 and .5% or more BaCO 3 powder, an average particle diameter of 2.0 .mu.m, a SrCO 3 powder than 99.5% purity, an average particle diameter of 9.0 .mu.m, La 2 O 3 powder of more than 99.5% purity, CeO 2 powder having an average particle size of 6.0 ⁇ m and a purity of 99.5% or more, Nd 2 O 3 powder having an average particle size of 4.0 ⁇ m and a purity
- Each raw material powder was put into a resin pot (volume: 2.4 L), mixed and pulverized using alumina cobblestone having a diameter of 10 mm, and then a hydrophilic binder (2 mass per 100 parts by mass of the mixed and pulverized raw material powder). Part) was added and mixed to form a slurry.
- Table 1 shows the results obtained by measuring the average particle size of each slurry by a laser diffraction method (manufactured by HORIBA, “LA-750”). This slurry was spray-dried by a spray drying method and granulated into a powder having an average particle size of about 100 ⁇ m by a laser diffraction method.
- the granulated powder was formed into a compact having a diameter of 23 mm by a hydrostatic pressure press of 100 MPa, and then fired at a predetermined firing temperature for a predetermined firing time in an air atmosphere to produce an alumina-based sintered body.
- the mixing ratio (raw material powder composition) in the raw material powder almost coincided with the content of each component (mass% in terms of oxide) calculated by fluorescent X-ray analysis or chemical analysis of the alumina-based sintered body. . *
- each alumina-based sintered body thus obtained was subjected to X-ray diffraction, and La- ⁇ -alumina JCPDS card No.
- the presence or absence of a crystal phase having a La- ⁇ -alumina structure is determined depending on whether or not a spectrum corresponding to 33-699 exists, and in contrast to this JCPDS card, Pr- ⁇ -alumina, Ce- ⁇ -
- Pr- ⁇ -alumina, Ce- ⁇ - Pr- ⁇ -alumina, Ce- ⁇ -
- the presence or absence of each crystal phase of alumina and Nd- ⁇ -alumina was determined, and the results are shown in Table 1.
- FIG. 3 shows an X-ray diffraction chart of an alumina-based sintered body (Example 1) having a La- ⁇ -alumina structure (LaAl 11 O 18 ) crystal.
- each alumina-based sintered body was mirror-polished, and the polished surface was subjected to thermal etching treatment at a temperature 100 ° C. lower than the firing temperature for 10 minutes.
- the surface subjected to this treatment was observed with a scanning electron microscope (SEM), and the average crystal grain size D A (Al) of the alumina crystal was measured by the intercept method as described above.
- SEM scanning electron microscope
- the surface of each alumina-based sintered body is observed with a scanning electron microscope (SEM), and the equivalent circle diameter of the extracted “light-colored region” is calculated as described above to calculate the RE- ⁇ -alumina crystal phase.
- the crystal grain size D E (RE) was determined, and the arithmetic average value of the crystal grain size D E (RE) was defined as the average crystal grain size D A (RE) of the RE- ⁇ -alumina crystal phase. From the average crystal grain size D A (Al) of the alumina crystal thus calculated, the crystal grain size D E (RE) of the RE- ⁇ -alumina crystal phase, and the average crystal grain size D A (RE), D A (RE) / D A (Al) was determined, and the number of RE- ⁇ -alumina crystal phases satisfying D E (RE) / D A (Al) ⁇ 2 was counted. These results are shown in Table 1. In Table 1, the symbol “-” in Comparative Examples 2 and 3 indicates that the calculation cannot be performed because there is no RE- ⁇ -alumina crystal phase.
- the RE- ⁇ -alumina crystal phase present in each alumina-based sintered body of Examples 1 to 7 and Comparative Example 1 was analyzed using an energy dispersive X-ray analyzer (EDX) attached to a transmission electron microscope (TEM). Elemental analysis was performed under the measurement conditions to determine x, y, and z in the composition formula, and the composition of the RE- ⁇ -alumina crystal phase was confirmed. The results are shown in Table 1. *
- the disk-shaped test piece 21 is sandwiched in the axial direction by alumina rods 24a and 24b so as to surround the electrode 23a and the electrode 23b from the axial direction of the disk-shaped test piece 21. Further, the contact portions between the front and back surfaces of the disk-shaped test piece 21 and the alumina steel cylinders 24a and 24b are fixed by the SiO 2 sealing glass 25 over the entire circumference of the steel cylinders 24a and 24b.
- the tip part in contact with the disk-shaped test piece 21 has a tapered shape whose diameter gradually decreases toward the tip part, and the contact area with the disk-shaped test piece 21 was about 0.75 mm 2 .
- a high voltage of about several tens of kV can be applied to the disk-shaped test piece 21 in the heating box 22 adjusted to 700 ° C. or 800 ° C. by the electric heater 26.
- a high voltage generator 27 applies a constant high voltage to the disk-shaped test piece 21, and the voltage value when dielectric breakdown occurs in the disk-shaped test piece 21 is determined as “withstand voltage” of the disk-shaped test piece 21. Value ". The ratio of the “withstand voltage value” at 800 ° C. to the “withstand voltage value” at 700 ° C. from the “withstand voltage value” at 700 ° C. and 800 ° C. Calculated). Table 2 shows “withstand voltage value” and “decrease rate of withstand voltage value” at 700 ° C. and 800 ° C.
- the disk-shaped test pieces were produced in the same manner as in the production of the alumina-based sintered body in Comparative Example 1, and the withstand voltage value at 700 ° C. was measured.
- the measured value of Comparative Example 1 was 57 kV / mm. *
- test pieces were prepared in the same manner as in the production of the alumina-based sintered body in Comparative Example 1, and the three-point bending strength at room temperature was measured.
- the measured value of Comparative Example 1 was 360 MPa.
- an alumina-based sintered body containing a Si component, a 2A component, and an RE component and having a RE- ⁇ -alumina crystal phase satisfying the condition (1) has a high withstand voltage value at 700 ° C. of 57 kV / mm or more.
- Examples 1 to 7 also have a withstand voltage value at 800 ° C. that is practically sufficient.
- the high-temperature strength at °C was also sufficient for practical use.
- the RE- ⁇ -alumina crystal phase satisfying the condition (2) has a composition satisfying the composition formula, and the 2A component is essentially composed of Mg and Ba.
- the 2A component is a component containing at least one element other than Mg and Ba, and since the RE component is a La component, a Pr component or an Nd component, a higher withstand voltage value at 800 ° C. and a high temperature at 950 ° C. Demonstrated strength.
- Comparative Example 1 which has a RE- ⁇ -alumina crystal phase but does not satisfy both of the above conditions (1) and (2) has a weak strength at room temperature of 360 MPa, and alumina
- alumina The presence of a RE- ⁇ -alumina crystal phase having a larger average crystal grain size D A (RE) or crystal grain size D E (RE) than the average crystal grain size D A (Al) of It is easily estimated that the withstand voltage value at 800 ° C. and the high-temperature strength at 950 ° C. are both insufficient for practical use.
- Comparative Example 2 contains an RE component but does not have an RE- ⁇ -alumina crystal phase
- Comparative Example 3 does not contain an RE component in the first place, it naturally satisfies the above conditions (1) and (2).
- Tables 1 and 2 in Comparative Examples 2 and 3 neither the withstand voltage value at 800 ° C. nor the high-temperature strength at 950 ° C. was practically insufficient. It was.
- the particle size ratio (D alumina raw material / D auxiliary raw material ) between the average particle size of the alumina raw material and the average particle size of the auxiliary raw material in the slurry is 1.
- Examples 1 to 7 that satisfy this numerical range have RE- ⁇ that satisfies the above conditions (1) and (2). -The alumina crystal phase could be generated efficiently.
- a wire rod having a cross-sectional dimension of 1.6 mm ⁇ 2.7 mm was prepared as the ground electrode 6 according to a conventional method using a Ni-based alloy.
- a cylindrical inner member 8 made of copper and an outer member 7 formed in a cup shape from the Ni-based alloy were prepared.
- the produced inner member 8 was inserted into the outer member 7, and the center electrode 2 having a diameter of 4 mm made of the inner member 8 and the outer member 7 was produced by plastic working such as extrusion.
- one end of the ground electrode 6 was joined by electric resistance welding to the end face of the metal shell 4 formed by plastic working and rolling into a predetermined shape and dimensions (especially the nominal diameter of the screw portion was 10 mm).
- an insulator 3 made of an alumina-based sintered body was produced in the same manner as in Examples 1-7.
- the insulator 3 is fired through a grinding shaping process in which the raw material powder is granulated, the granulated powder is molded into a molded body by an isostatic press, and then ground before grinding to adjust its shape.
- the center electrode 2 was assembled to the insulator 3, and this insulator 3 was assembled to the metal shell 4 to which the ground electrode 6 was joined.
- the spark plug 1 was manufactured such that the tip of the ground electrode 6 was bent toward the center electrode 2 so that one end of the ground electrode 6 was opposed to the tip of the center electrode 2.
- the spark plug 1 manufactured in this way had the same results as those in Tables 1 and 2.
- the alumina-based sintered body is an insulator used for a spark plug having a small and thin insulator 3 and an insulation used for a spark plug for an internal combustion engine with high output. It is particularly suitable as a body.
- the spark plug including the insulator 3 formed of the alumina-based sintered body has a thickness of the insulator or is used for an internal combustion engine with high output, for example 700 Sufficient withstand voltage characteristics and mechanical strength were exhibited at high temperatures exceeding °C.
- each spark plug provided with the insulator 3 produced in the same manner as in Examples 1 to 7 exhibited higher withstand voltage values and mechanical strength in addition to the above characteristics.
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Abstract
Description
れることによって、接地電極6の一端が中心電極2と火花放電間隙Gを介して対向するように配置されている。火花放電間隙Gは、中心電極2の先端面と接地電極6の表面との間の間隙であり、この火花放電間隙Gは、通常、0.3~1.5mmに設定される。接地電極6は中心電極2よりも高温に曝されるため、中心電極2を形成するNi基合金よりも耐熱性及び耐食性等により一層優れたNi基合金等で形成されるのがよい。
W3.3RTEM)を用いて下記測定条件等で元素分析を行うことによって、確認することができる。<測定条件等>(1)加速電圧:200kV(2)照射モード:HR(スポットサイズ:約0.3nm)(3)エネルギー分散型X線分析装置(EDX)の測定結果は酸化物換算質量%で算出する。なお、2A成分、RE成分及びAl成分以外の酸化物で、酸化物換算質量%が1質量%以下のものは不純物とする。そして、RE成分のモル数を1としたときの、2A成分の合計モル数をx、Al成分のモル数をy、酸素欠陥がない場合の理論的な酸素成分のモル数をzとする。
記アルミナ基焼結体は、粒界相に高融点結晶相である前記RE-β-アルミナ結晶相が存在しているから、高温時における粒界相の軟化を効果的に抑えることができる。その結果、前記アルミナ基焼結体は、破壊起点となりうる気孔の存在が極めて少なく、また、粒界相が軟化しにくく、絶縁体3としたときに、例えば700℃を超える高温環境下においても十分な耐電圧特性及び機械的強度を発揮できる。
なる内燃機関にも使用することができるが、絶縁体3を形成するアルミナ基焼結体は、例えば700℃を超える高温環境下においても十分な耐電圧特性及び機械的強度を発揮できるから、この発明に係るスパークプラグ1は、例えばネジ部9の呼び径が10mm以下に調整される薄肉化された絶縁体を備えたスパークプラグが求められる、高出力化された内燃機関等に好適に使用されることができる。
の製造> まず、Ni基合金を用いて定法に従い、接地電極6として断面寸法1.6mm×2.7mmの線材を作製した。銅からなる円柱状の内材8と、前記Ni基合金でカップ状に形成した外材7とをそれぞれ作製した。そして、作製した内材8を外材7に挿入し、押し出し加工等の塑性加工にて、内材8と外材7とからなる直径4mmの中心電極2を作製した。次いで、所定の形状及び寸法(特にネジ部の呼び径は10mm)に塑性加工及び転造加工によって形成した主体金具4の端面に、接地電極6の一端部を電機抵抗溶接で接合した。次いで、実施例1~7と同様にしてアルミナ基焼結体で構成された絶縁体3を作製した。なお、絶縁体3は、原料粉末を造粒し、その造粒した粉末を静水圧プレスにて成形体に成形後、焼成前に研削されて自身の形状が整えられる研削整形工程を経て焼成されて作製される。次いで、中心電極2を絶縁体3に組み付け、さらに、接地電極6が接合された主体金具4にこの絶縁体3を組み付けた。次いで、接地電極6の先端部を中心電極2側に折り曲げて、接地電極6の一端が中心電極2の先端部と対向するようにして、スパークプラグ1を製造した。このようにして製造したスパークプラグ1は、第1表及び第2表と同様の結果が得られた。このように、前記アルミナ基焼結体は、小型で薄肉化された絶縁体3を備えたスパークプラグに用いられる絶縁体、及び、高出力化された内燃機関用のスパークプラグ等に用いられる絶縁体として特に好適である。そして、このアルミナ基焼結体で形成した絶縁体3を備えたスパークプラグは、絶縁体の厚さが薄くされていても、また、高出力化された内燃機関に用いられても、例えば700℃を超える高温下において十分な耐電圧特性及び機械的強度を発揮した。特に、実施例1~7と同様にして作製した絶縁体3を備えた各スパークプラグは、前記特性に加えてさらに高い耐電圧値及び機械的強度を発揮した。
Claims (7)
- 中心電極と、前記中心電極の外周に設けられた略円筒状の絶縁体と、一端が前記中心電極と火花放電間隙を介して対向するように配置された接地電極とを備えたスパークプラグであって、 前記絶縁体は、Si成分と、IUPAC1990年勧告に基づく周期表の第2族元素成分(以下、2A成分と称する。)と、希土類元素成分(以下、RE成分と称する。)とを含有するアルミナ基焼結体で構成され、 前記アルミナ基焼結体は、前記RE成分を少なくとも含むRE-β-アルミナ結晶相を有し、このRE-β-アルミナ結晶相の平均結晶粒径DA(RE)とアルミナの平均結晶粒径DA(Al)とが下記条件(1)を満足することを特徴とするスパークプラグ。条件(1):0.2≦DA(RE)/DA(Al)≦3.0
- 前記RE-β-アルミナ結晶相のうち、その結晶粒径DE(RE)とアルミナの前記平均結晶粒径DA(Al)とが下記条件(2)を満足するRE-β-アルミナ結晶相が3個以下であることを特徴とする請求項1に記載のスパークプラグ。条件(2):DE(RE)/DA(Al)≧2
- 前記RE-β-アルミナ結晶相は、組成式:RE(2A)x(Al)yOz(前記x、y及びzはそれぞれ、x=0~2.5、y=11~16及びz=18~28である。)で示される組成を有していることを特徴とする請求項1又は2に記載のスパークプラグ。
- 前記RE-β-アルミナ結晶相は、透過型電子顕微鏡で観察したときに、直径0.3nmの円形のスポットのうち、前記RE-β-アルミナ結晶相の存在が確認されたスポットにおいて、アルカリ金属成分を酸化物換算で0.01~8質量%含有することを特徴とする請求項1~3のいずれか1項に記載のスパークプラグ。
- 前記アルミナ基焼結体は、アルミナ原料と、前記Si成分、前記Mg成分及び前記第2族元素成分、並びに前記RE成分から成る副原料とをスラリー中で混合して造粒した後に成形及び焼成して成り、前記スラリー中の前記アルミナ原料の平均粒径と前記副原料の平均粒径との粒径比(Dアルミナ原料/D副原料)が1.3≦Dアルミナ原料/D副原料≦4を満たすことを特徴とする請求項1~4のいずれか1項に記載のスパークプラグ。
- 前記2A成分は、IUPAC1990年勧告に基づく周期表の第2族元素のうちMg及びBaを必須とするとともにMg及びBaを除く少なくとも他の一元素を含有する成分であり、 前記RE成分は、La成分、Pr成分及びNd成分からなる群より選択される少なくとも一種の成分であることを特徴とする請求項1~5のいずれか1項に記載のスパークプラグ。
- 前記絶縁体は主体金具に保持されてなり、当該主体金具の外周面に形成されたネジ部の呼び径が10mm以下であることを特徴とする請求項1~6のいずれか1項に記載のスパークプラグ。
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US8564183B2 (en) | 2009-09-25 | 2013-10-22 | Ngk Spark Plug Co., Ltd. | Spark plug and method for manufacturing spark plug |
JP5211251B1 (ja) * | 2012-02-27 | 2013-06-12 | 日本特殊陶業株式会社 | スパークプラグ |
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JP6052249B2 (ja) | 2014-07-24 | 2016-12-27 | 株式会社デンソー | アルミナ質焼結体、及びスパークプラグ |
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US11209488B2 (en) | 2017-12-22 | 2021-12-28 | Litech Laboratories, Inc. | Energy delivery system |
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Also Published As
Publication number | Publication date |
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CN102365798A (zh) | 2012-02-29 |
CN102365798B (zh) | 2014-01-29 |
EP2413441A1 (en) | 2012-02-01 |
US8278809B2 (en) | 2012-10-02 |
KR101293884B1 (ko) | 2013-08-06 |
KR20120022738A (ko) | 2012-03-12 |
JP2010251281A (ja) | 2010-11-04 |
EP2413441A4 (en) | 2013-05-22 |
EP2413441B1 (en) | 2018-09-26 |
JP4613242B2 (ja) | 2011-01-12 |
US20120007489A1 (en) | 2012-01-12 |
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