JP2015159002A - Electrode material for spark plug - Google Patents

Abstract

An object of the present invention is to provide a spark plug electrode material capable of further improving oxidation wear resistance and spark wear resistance. A spark plug electrode material used for noble metal tips (31, 32) of a spark plug (1) comprises a first phase made of an alloy containing Ir and an oxide of at least one of SrZrO3, SrHfO3, BaZrO3 and BaHfO3. a second phase, the balance being made of unavoidable impurities, the first phase alloy containing 1.0 to 35.0% by mass of Rh, 1.0 to 35.0% by mass of Rh, A second alloy containing 5.0 to 20.0 mass % of Ru, a third alloy containing 1.0 to 35.0 mass % of Rh, and a third alloy containing 0.4 to 3.0 mass % of Ni, and a Rh of 1.0 to 35.0 mass %. 0% by mass, 5.0 to 20.0% by mass of Ru, and 0.4 to 3.0% by mass of Ni. % or more and 13.0 volume % or less. [Selection drawing] Fig. 2

Description

  The present invention relates generally to an electrode material for a spark plug, and more particularly to an electrode material for a spark plug used for ignition of an internal combustion engine such as an automobile engine.

  In a spark plug used for ignition of an internal combustion engine such as an automobile engine, the temperature in the fuel chamber tends to increase for the purpose of increasing the output of the engine and improving the fuel consumption. In addition, in order to improve the ignitability of the spark plug, there is a tendency to increase the type of engine in which the discharge portion corresponding to the spark discharge gap of the spark plug protrudes into the fuel chamber, and the electrode portion is exposed to a higher temperature. It is in an environment where spark consumption and oxidation consumption are promoted.

In order to suppress spark consumption against such a technical background, for example, Japanese Patent Laid-Open No. 7-37677 (hereinafter referred to as Patent Document 1) discloses a rare earth oxide such as yttria (Y ₂ O ₃ ). It is disclosed that the discharge voltage is lowered and the spark wear resistance is improved by adding an appropriate amount of.

  In order to suppress oxidative exhaustion, for example, in International Publication No. WO 2004/107517 (hereinafter referred to as Patent Document 2), the electrode is mainly composed of iridium (Ir) having a high melting point and a high melting point of Ir ( In order to prevent oxidation and volatilization at about 900 ° C. or higher), it is disclosed that the resistance to oxidation and consumption can be greatly improved by adding rhodium (Rh), ruthenium (Ru), and nickel (Ni). .

JP 7-37677 A International Publication No. WO 2004/107517

  By the way, in recent years, the development of automobiles equipped with higher performance and lower fuel consumption engines has become mainstream. With this technological development, the load on the spark plug has become higher. For this reason, there is a demand for an electrode material for a spark plug that can improve oxidation consumption resistance equal to or higher than that of a conventional level and can suppress spark consumption more than ever.

  However, it is difficult for the conventional electrode material for spark plugs to satisfy required oxidation resistance and spark resistance.

  Therefore, an object of the present invention is to provide an electrode material for a spark plug that can further improve the resistance to oxidation and resistance to sparks.

The electrode material for a spark plug according to the present invention includes a first phase made of an alloy containing iridium, and at least one oxide selected from the group consisting of SrZrO ₃ , SrHfO ₃ , BaZrO ₃ , and BaHfO _3. An alloy containing iridium in the first phase, the balance being 1.0% by mass or more and 35.0% by mass or less of rhodium. 2 mass% or more and 35.0 mass% or less, 2nd alloy containing 5.0 mass% or more and 20.0 mass% or less of ruthenium, 1.0 mass% or more and 35.0 mass% or less of rhodium, and 0.4 mass of nickel 3 to 3.0% by mass, rhodium 1.0% to 35.0% by mass, ruthenium 5.0% to 20.0% by mass, nickel 0.4% mass% Any one alloy selected from the group consisting of a fourth alloy containing 3.0% by mass or less and containing 1.0% by volume or more and 13.0% by volume or less of the oxide of the second phase.

  In the electrode material for a spark plug of the present invention, the occupation area ratio of the oxide observed in the cross section of the electrode material for the spark plug is preferably 1.0% or more and 13.0% or less.

  In the spark plug electrode material of the present invention, the average grain size of the alloy grains containing iridium constituting the first phase is preferably 3 μm or more and 150 μm or less.

  In the spark plug electrode material of the present invention, the average major axis of the oxide particles constituting the second phase is preferably 0.05 μm or more and 30 μm or less.

  Furthermore, in the spark plug electrode material of the present invention, the average grain size of the alloy particles containing iridium constituting the first phase is 10 μm or more and 70 μm or less, and the average major axis of the oxide particles constituting the second phase Is preferably 0.1 μm or more and 3.0 μm or less.

  In the spark plug electrode material of the present invention, the relative density is preferably 95.0% or more, and more preferably 98.0% or more.

  According to the present invention, it is possible to further improve oxidation wear resistance and spark wear resistance.

BRIEF DESCRIPTION OF THE DRAWINGS It is the front view which showed the structure of the spark plug as one Embodiment with which the electrode material for spark plugs of this invention is applied, and a part fractured | ruptured. It is a partial expanded sectional view of the spark plug shown by FIG.

  First, the structure of the spark plug as one embodiment to which the electrode material for a spark plug of the present invention is applied will be described.

  As shown in FIG. 1, the spark plug 1 includes an insulator 10 as a long insulator and a cylindrical metal shell 20 that holds the insulator 10.

  A shaft hole 11 is formed through the insulator 10 along the axis C. A center electrode 30 is inserted and fixed on the tip end side (lower side in FIG. 1) of the shaft hole 11. A terminal electrode 40 is inserted and fixed on the rear end side (upper side in FIG. 1) of the shaft hole 11. A resistor 50 is disposed between the center electrode 30 and the terminal electrode 40 in the shaft hole 11. Both ends of the resistor 50 are electrically connected to the center electrode 30 and the terminal electrode 40 through conductive glass seal layers 60 and 70, respectively.

  The center electrode 30 is fixed in a state of protruding from the tip of the insulator 10. The terminal electrode 40 is fixed in a state of protruding from the rear end of the insulator 10. A noble metal tip 31 made of the spark plug electrode material of the present invention is joined to the tip of the center electrode 30 by welding.

  The insulator 10 is formed of a fired body such as alumina, and includes a flange-shaped large-diameter portion 12 formed so as to protrude radially outward at a substantially central portion in the axis C direction, and a large-diameter portion 12. Are formed so as to have an outer diameter thinner than that of the large-diameter portion 12 on the distal end side, and to have an outer diameter thinner than that of the middle barrel portion 13 on the distal end side of the intermediate trunk portion 13. And a leg portion 14 exposed to the combustion chamber of the internal combustion engine (engine). Of the insulator 10, the distal end side including the large-diameter portion 12, the middle body portion 13, and the leg long portion 14 is accommodated in a metal shell 20 formed in a cylindrical shape. A stepped portion 15 is formed at the connecting portion between the long leg portion 14 and the middle trunk portion 13. At the step portion 15, the insulator 10 is locked to the metal shell 20.

  The metal shell 20 is formed in a cylindrical shape with a metal such as low carbon steel. A threaded portion (male threaded portion) 21 for attaching the spark plug 1 to the engine head is formed on the outer peripheral surface of the metal shell 20. A seat portion 22 is formed on the outer peripheral surface on the rear end side of the screw portion 21. A ring-shaped gasket 24 is fitted into the screw neck 23 located at the rear end of the screw portion 21. A tool engagement portion 25 having a hexagonal cross section is provided on the rear end side of the metal shell 20 in order to engage a tool such as a wrench when the metal shell 20 is attached to the engine head. A caulking portion 27 for holding the insulator 10 is provided at the rear end portion of the tool engaging portion 25.

  A step portion 26 for locking the insulator 10 is provided on the inner peripheral surface of the metal shell 20. The insulator 10 is inserted from the rear end side to the front end side of the metal shell 20, and the stepped portion 15 of the insulator 10 is locked to the step portion 26 of the metal shell 20. The opening is fixed by caulking inward in the radial direction, that is, by forming the caulking portion 27. An annular plate packing 28 is interposed between the step portion 15 of the insulator 10 and the step portion 26 of the metal shell 20. Thereby, the airtightness in the combustion chamber is maintained, and the fuel air entering the gap between the leg long portion 14 of the insulator 10 exposed to the combustion chamber and the inner peripheral surface of the metal shell 20 is prevented from leaking to the outside.

  Furthermore, in order to make the sealing by caulking more complete, on the rear end side of the metal shell 20, annular ring members 29a and 29b are interposed between the metal shell 20 and the insulator 10, and the ring members 29a, 29b, Between 29b, talc (talc) 29c powder is filled. That is, the metal shell 20 holds the insulator 10 via the plate packing 28, the ring members 29a and 29b, and the talc 29c.

  A ground electrode 80 having a substantially L shape is joined to the front end surface 201 of the metal shell 20. That is, the proximal end portion of the ground electrode 80 is welded to the distal end surface 201 of the metal shell 20, the distal end side of the ground electrode 80 is bent back, and the inner side surface of the ground electrode 80 is the distal end portion (noble metal tip) of the center electrode 30. 31). The ground electrode 80 is provided with a noble metal tip 32 made of the spark plug electrode material of the present invention so as to face the noble metal tip 31. An interval between these noble metal tips 31 and 32 forms a spark discharge interval 33.

  As shown in FIG. 2, the center electrode 30 includes an inner layer 301 made of copper or a copper alloy and an outer layer 302 made of a nickel (Ni) alloy. The ground electrode 80 is made of a Ni alloy or the like.

  The center electrode 30 has a reduced diameter on the tip side, a rod shape (cylindrical shape) as a whole, and a tip surface formed flat. A cylindrical noble metal tip 31 is superposed on the front end surface of the center electrode 30 and welded by laser welding, electron beam welding, resistance welding, or the like along the outer edge portion of the joint surface. The center electrode 30 is melted and a melted portion 91 is formed. That is, the noble metal tip 31 is bonded to the tip of the center electrode 30 by being fixed by the melting portion 91. Further, the noble metal tip 31 has an exposed portion 93 that is not covered with the melted portion 91 on the tip surface and the side surface on the tip side. On the other hand, the noble metal tip 32 opposite to the noble metal tip 31 is aligned with a predetermined position of the ground electrode 80 and welded along the outer edge portion of the joining surface to be joined by forming a melting portion 92. Yes. Similar to the noble metal tip 31, the noble metal tip 32 has an exposed portion 94 that is not covered with the melted portion 92 on the tip surface and the side surface on the tip side. One of the noble metal tip 31 and the noble metal tip 32 may be omitted. In this case, a spark discharge interval 33 is formed between the noble metal tip 31 and the main body portion of the ground electrode 80 or between the main body portion of the center electrode 30 and the noble metal tip 32.

  In the above embodiment, both the noble metal tips 31 and 32 are formed of the spark plug electrode material of the present invention. However, at least one of the noble metal tips 31 and 32 is formed of the spark plug electrode material of the present invention. It only has to be formed.

The electrode material for a spark plug of the present invention includes a first phase made of an alloy containing iridium (Ir), and at least one oxide selected from the group consisting of SrZrO ₃ , SrHfO ₃ , BaZrO ₃ , and BaHfO ₃ . And the remainder consists of inevitable impurities. The alloy containing iridium of the first phase is a first alloy containing rhodium (Rh) in an amount of 1.0% by mass to 35.0% by mass, rhodium in an amount of 1.0% by mass to 35.0% by mass, ruthenium (Ru). ) From 5.0 mass% to 20.0 mass%, rhodium from 1.0 mass% to 35.0 mass%, nickel (Ni) from 0.4 mass% to 3.0 mass% A third alloy containing: rhodium 1.0 mass% to 35.0 mass%, ruthenium 5.0 mass% to 20.0 mass%, nickel 0.4 mass% to 3.0 mass% %, Any one kind of alloy selected from the group consisting of a fourth alloy containing no more than%. The electrode material for a spark plug of the present invention contains 1.0% by volume or more and 13.0% by volume or less of the second phase oxide.

As described above, in the electrode material for a spark plug of the present invention, at least one oxide of SrZrO ₃ , SrHfO ₃ , BaZrO ₃ , and BaHfO ₃ is added to the first phase made of an alloy containing iridium having a predetermined composition. Is dispersed in a predetermined volume as the second phase, so that the resistance to oxidation and the resistance to sparks can be improved as compared with the prior art.

  If the content of the second phase is less than 3.0% by volume, the effect of suppressing spark consumption cannot be sufficiently obtained. When the content of the second phase exceeds 13.0% by volume, a low-density sintered body is obtained, so that not only spark consumption is likely to occur, but also there is a risk of causing cracks during spark discharge. As a method for producing an electrode for a spark plug, a sintered body may be plastically processed. However, if the content of the second phase exceeds 13.0% by volume, a sintered body having a low density that cannot be plastically processed is obtained. can get.

Note that the oxide constituting the second phase is expressed by a chemical formula ABO _{3. In} the oxide constituting the second phase, the element A is Sr, Ba, the element B is Zr, and Hf. In addition to Sr and Br, Mg, Ca, and element B other than Zr and Hf, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Y, Nb, Mo, Ru, Ta Even if the second phase is composed of oxides using W, P, Pb, and Bi, the effect of suppressing the above spark consumption can be obtained.

  In the electrode material for a spark plug of the present invention, the occupation area ratio of the oxide observed in the cross section of the electrode material for the spark plug is preferably 1.0% or more and 13.0% or less. The occupation area ratio of the oxide is measured and calculated by the method described below.

  First, the cross section of the spark plug electrode material of the present invention is polished using SiC polishing paper or diamond abrasive grains. Further, the polished cross section is precisely polished by CP (Cross-section Polishing) or ion milling. The cross-sectional area of the oxide observed in the obtained cross-section is measured, and the occupation area ratio of the oxide is calculated by the following formula from the total cross-sectional area of the electrode material for the spark plug and the total cross-sectional area of the oxide.

  Occupied area ratio of oxide (%) = (total cross-sectional area of oxide / total cross-sectional area of electrode material) × 100

  The total cross sectional area of the oxide is calculated as follows.

  For example, an enlarged photograph of the cross section of the electrode material for a spark plug of the present invention is taken using a field emission scanning electron microscope (FE-SEM). In principle, the oxide particles existing in a rectangular visual field having a size of 50 μm × 50 μm are observed to measure the total cross-sectional area of the oxide. However, the magnification is arbitrarily changed in accordance with the observed particle size of the oxide particles, and is set to a visual field range in which at least 50 oxide particles can be observed. The enlarged photograph taken is binarized using image analysis software (for example, Image Pro Plus, Media Cybernetics, Inc.), and then the total cross-sectional area of the oxide is counted.

  In the case of the spark plug electrode material of the present invention, the oxide area ratio calculated as described above is in the range of 1.0% to 13.0%.

In general, when an oxide represented by the chemical formula ABO ₃ is quantified, a method of quantifying a solution obtained by chemically dissolving the oxide by high frequency inductively coupled plasma (ICP) emission spectroscopic analysis or the like can be considered. However, in a material containing a large amount of rhodium or ruthenium, such as the electrode material for a spark plug of the present invention, the oxide in the material is difficult to be chemically dissolved, so the reliability of the quantitative value may be lowered. In such a case, whether the occupation area ratio of the oxide calculated as described above is within the range of the present invention, that is, the oxide constituting the second phase in the spark plug electrode material of the present invention. This is an effective value for determining whether the content volume ratio is 1.0% by volume or more and 13.0% by volume or less.

  In an alloy containing iridium of the first phase, if the rhodium content is less than 1.0% by mass, the effect of sufficiently suppressing oxidation consumption cannot be obtained. When the rhodium content exceeds 35.0% by mass, the melting point of the matrix of the alloy containing iridium is low and the sintered density is low, so that spark consumption tends to occur.

  The spark plug electrode material becomes a material superior in oxidation resistance and spark wear resistance by further adding ruthenium in addition to rhodium. Ruthenium has a higher melting point than rhodium, so it is effective in improving the resistance to spark discharge during spark discharge, and it is less likely to cause oxidative consumption at higher temperatures than iridium, so it contributes to the improvement in resistance to oxidation. . In the alloy containing iridium of the first phase, if the ruthenium content is less than 5.0% by mass, the effect of sufficiently suppressing the spark consumption and the oxidation consumption cannot be obtained. When the content of ruthenium exceeds 20.0 mass%, the melting point of the matrix of the alloy containing iridium is lowered, and spark consumption is likely to occur.

  In the spark plug electrode material, since nickel acts as a sintering aid, the addition of a suitable amount can increase the density of the sintered body and also has the effect of suppressing spark consumption. In the alloy containing iridium of the first phase, when the nickel content is less than 0.4 mass%, the alloy does not sufficiently function as a sintering aid. When the nickel content exceeds 3.0% by mass, spark consumption tends to occur.

  In addition, the composition of the alloy containing the first phase iridium that is the matrix of the electrode material for the spark plug of the present invention, that is, the content% by mass of each element in the alloy is a value determined by ICP emission spectroscopic analysis, or a cross section of the material Any of the values (quantity of analysis values) corrected and quantified by the ZAF method using an electron beam microanalyzer (EPMA) for 10 points arbitrarily selected from the above may be used.

  In the spark plug electrode material of the present invention, the average grain size of the alloy grains containing iridium constituting the first phase is preferably 3 μm or more and 150 μm or less.

  If the average grain size of the iridium-containing alloy grain is less than 3 μm, the proportion of the number of individuals in the grain boundary of the alloy grain containing the iridium oxide particles constituting the second phase increases. As a result, the effect of suppressing spark consumption cannot be obtained by causing crystal grains to fall off during spark discharge. If the average grain size of the alloy grain containing iridium exceeds 150 μm, the internal oxidation distance through the grain boundary becomes longer in the oxidation reaction that occurs at the time of spark discharge, which may cause dropout of the grain. In addition, when the average grain size of the alloy grain containing iridium in the electrode material exceeds 150 μm, it is considered that impurities segregate at a part of the grain boundary. In this case, in the reaction such as melting or oxidation that occurs during the spark discharge of impurities, the strength of the crystal grain boundaries is lowered, and the crystal grains are likely to fall off due to a spark impact.

  In order to prevent cracking, chipping, etc. of the electrode material that occurs during the production of the spark plug, the average grain size of the crystal grains of the alloy containing iridium constituting the first phase is more preferably 10 μm or more and 70 μm or less. preferable.

  The crystal grain size of the alloy containing iridium is measured by the line intercept method described below. Specifically, first, a cross section as a measurement location is polished using, for example, SiC polishing paper or diamond abrasive grains, and then precisely polished by CP (Cross-section Polishing) so that a crystal grain boundary can be confirmed. An enlarged photograph is taken using an emission scanning electron microscope (FE-SEM) or the like. On this photograph, a straight line is arbitrarily drawn, and the grain size of each crystal grain that is the target of crossing the straight line is measured to calculate the total grain size. Next, the average crystal grain size is calculated from the sum of the grain sizes and the number of particles to be measured. It should be noted that the magnification is arbitrarily changed according to the size of the crystal grains to be observed, and is set to a visual field range in which at least 50 crystal grains can be observed.

  In the spark plug electrode material of the present invention, the average major axis of the oxide particles constituting the second phase is preferably 0.05 μm or more and 30 μm or less.

  If the average major axis of the oxide particles is less than 0.05 μm, the oxide particles easily fall off during spark discharge, and the effect of suppressing spark consumption cannot be obtained. When the average major axis of the oxide particles exceeds 30 μm, heat sinking is worse during spark discharge, and spark consumption tends to occur. When the average major axis of the oxide particles is less than 0.1 μm, aggregated powder is likely to be generated as the raw material powder added at the time of manufacturing the electrode material. Therefore, it is preferable to use oxide particles having an average major axis of 0.1 μm or more. .

  The average major axis of the oxide particles is measured by the method described below. Specifically, first, a cross section as a measurement location is polished using, for example, SiC polishing paper or diamond abrasive grains, and then precisely polished by CP (Cross-section Polishing) or ion milling, for example, field emission scanning electron The magnification is arbitrarily changed so that the shape of the oxide particles can be confirmed using a microscope (FE-SEM), and an enlarged photograph is set to a field of view in which at least 50 oxide particles can be observed. Take a picture. In the enlarged photograph taken, the major axis of the oxide particles is measured using image analysis software (for example, Image Pro Plus, Media Cybernetics, Inc.), and the average value of the obtained measured values is defined as the average major axis.

  Furthermore, in the spark plug electrode material of the present invention, the average grain size of the alloy particles containing iridium constituting the first phase is 10 μm or more and 70 μm or less, and the average major axis of the oxide particles constituting the second phase Is more preferably 0.1 μm or more and 3.0 μm or less.

  In the spark plug electrode material of the present invention, the relative density is preferably 95.0% or more. If the relative density is less than 95%, the effect of suppressing oxidation consumption and spark consumption cannot be obtained. In order to obtain an electrode material for a spark plug having further excellent oxidation consumption resistance and spark consumption resistance, the relative density is more preferably 98.0% or more.

  Hereinafter, the manufacturing method of the electrode material for spark plugs of this invention is demonstrated.

  (1) Raw material preparation process

An iridium-containing powder, a rhodium-containing powder, a ruthenium-containing powder, a nickel-containing powder, and an oxide powder of any one of SrZrO ₃ , SrHfO ₃ , BaZrO ₃ , and BaHfO ₃ are prepared. Rhodium is contained in an amount of 1.0 to 35.0 mass%, ruthenium is contained in an amount of 5.0 to 20.0 mass%, nickel is contained in an amount of 0.4 to 3.0 mass%, and the balance is The raw materials are blended and prepared so as to be composed of iridium, the above oxide and inevitable impurities.

As long as rhodium, ruthenium and nickel are included within the above range, the starting material powder is not limited to pure metal powder (pure iridium powder, pure rhodium powder, pure ruthenium powder, pure nickel powder), and is a solid solution. alloy powder (Ir-Rh solid solution alloy powder, etc.), it may be prepared by combining powder such as chloride powder (RhCl _3, etc.). As long as a sintered body having a relative density of 95% or more can be obtained so as to exhibit sufficient spark wear resistance and oxidation wear resistance, the powder properties such as particle size and bulk density are not limited. The particle sizes of the iridium-containing powder, rhodium-containing powder, ruthenium-containing powder, and nickel-containing powder constituting the alloy containing iridium in the phase are preferably 50 μm or less, and more preferably 20 μm or less.

  (2) Mixing process

Mixing the iridium-containing powder prepared above, rhodium-containing powder, ruthenium-containing powder, nickel-containing powder, and oxide powder of any of SrZrO ₃ , SrHfO ₃ , BaZrO ₃ , BaHfO ₃ to obtain a mixture . Mixing can be performed using a known mixing device such as a ball mill, a shaker mixer, a rocking mixer, or the like. The mixing apparatus is not limited as long as a uniform mixed powder can be obtained. The mixed form may be dry or wet. Furthermore, in order to improve the press formability in the next step, a suitable amount of a binder such as paraffin or polyvinyl alcohol (PVA) may be added.

  (3) Molding process

  Pressure is applied to the mixture obtained above to form a molded body. Pressure is applied to the mixture using a known pressing device such as a single-screw press or a cold isostatic press (CIP). As long as a sintered body having a relative density of 95% or more can be obtained so as to exhibit sufficient spark wear resistance and oxidation wear resistance, the pressing device, the press pressure, and the density of the formed body are not limited.

  (4) Sintering process

  The molded body obtained above is sintered to obtain a sintered body. When a binder is added, it is sintered after a degreasing process. As an atmosphere for sintering the molded body, hydrogen gas, vacuum, or an inert gas atmosphere (for example, argon gas) can be used. The sintering temperature is preferably 1500 ° C. or higher and 1800 ° C. or lower. When sintering a molded body in a gas atmosphere, if a sintered body with a relative density of 95% or more can be obtained so as to exhibit sufficient spark consumption and oxidation consumption resistance, sintering time, sintering The pressure in the furnace is not limited.

  (5) Plastic working process

  The electrode for a spark plug of the present invention may be manufactured by using the above-mentioned sintering process as a final process, but a sintered body having a relative density of 95% or more so as to exhibit sufficient spark wear resistance and oxidation wear resistance. May not be obtained by the above-described sintering step, the density may be increased by applying plastic working such as rolling, forging, extrusion, swaging, hot compression (hot pressing), sizing, etc. to the sintered body. . A wire drawing material may be created by performing a net shape forging process on the sintered body, and may be cut in an arbitrary size.

  In addition, even if the relative density of the sintered body is 95.0% or more, by performing plastic working to obtain a higher density and higher hardness, oxidation resistance and spark resistance can be further improved. Can do.

  Hereinafter, Examples 1 to 4 in which an electrode material for a spark plug was produced in order to confirm the effects of the above-described embodiment will be described below.

  (Example 1)

  In this example, the electrode material for spark plugs within the range of the composition of the present invention (example of the present invention: sample numbers 1 to 84) and the electrode material for spark plugs outside the range of the composition of the present invention (comparative example: sample number 85). To 159). That is, the electrode material for spark plugs was produced by performing the above steps (1) to (4). Sample numbers 156 and 157 correspond to the spark plug electrode material having the composition described in Patent Document 1, and sample numbers 158 and 159 correspond to the spark plug electrode material having the composition described in Patent Document 2.

First, pure iridium powder having an average particle size of 6.2 μm, pure rhodium powder having an average particle size of 5.4 μm, pure ruthenium powder having an average particle size of 5.0 μm, and average particles, measured by the Fisher sub-sieving method Pure nickel powder having a diameter of 3.1 μm and various oxide powders (SrZrO ₃ , SrHfO ₃ , BaZrO ₃ , BaHfO ₃ , Y ₂ O ₃ ) having an average major axis of 0.06 to 28 μm are shown in Table 1 below. It prepared so that it might contain with the mixture ratio of the mass% shown in Table 2 ((1) raw material preparation process). In addition, the oxide addition amount [volume%] shown in Table 1 and Table 2 was calculated | required by converting the mass% of various oxide powder as follows.

  First, since the alloy containing iridium constituting the first phase is a solid solution, the density and mass% (Tables 1 to 4) of iridium (Ir), rhodium (Rh), ruthenium (Ru), and nickel (Ni) are calculated. The density of the first phase is calculated using the following formula.

  Density of first phase = 100 / {(Ir mass% / Ir density) + (Rh mass% / Rh density) + (Ru mass% / Ru density) + (Ni mass% / Ni density)}

  Next, the calculated density and mass% of the first phase (= 100% -mass% of various oxides (Table 1 to Table 4)) and the density and mass% of various oxides (Table 1 to Table 4). Is used to calculate the volume% of various oxides (second phase) by the following formula.

  Volume% of various oxides (second phase) = (100 × mass% of various oxides / density of various oxides) / {(mass% of first phase / density of first phase) + (of various oxides) Mass% / density of various oxides)}

  Next, the pure iridium powder, the pure rhodium powder, the pure ruthenium powder, the pure nickel powder, and various oxide powders prepared above are mixed for 20 hours in an argon gas atmosphere using a dry ball mill to obtain a mixture. ((2) mixing step).

Then, 2% by mass of paraffin as an organic binder is added to the mixture obtained above, and a pressure of 3 ton / cm ² (about 294 MPa) is applied using a cold isostatic press (CIP). Thus, a molded body was obtained ((3) molding step).

  Further, the molded body obtained above was degreased at a temperature of 500 ° C. and then sintered in a hydrogen gas atmosphere furnace at a temperature of 1600 ° C. for 3 hours to obtain a sintered body as an electrode material ( (4) Sintering step).

When the cross section of the obtained sintered body of each sample was observed with an optical microscope (magnification: 250 times) and measured in the range of the visual field (area: 0.09 mm ² ), the first phase was measured. The average grain size of the crystal grains of the alloy containing iridium constituting was in the range of 8 to 140 μm, and the average major axis of the various oxide particles constituting the second phase was in the range of 0.07 to 29 μm.

  In addition, the relative density of the sintered compact of each obtained sample was computed with the following formula | equation. The values are shown in Tables 1 to 4.

  Relative density of sintered body = density of sintered body / theoretical density of sintered body

  Theoretical density of the sintered body = 100 / {(mass% of Ir / density of Ir) + (mass% of Rh / density of Rh) + (mass% of Ru / density of Ru) + (mass% of Ni / Ni Density) + (mass% of various oxides / density of various oxides)

  Using the sintered body obtained as described above, an oxidation consumption test and a spark consumption test were performed.

  <Oxidation consumption test>

  From the obtained sintered body of each sample, an electrode material of each sample having a cylindrical shape having a diameter of 0.6 mm and a length of 0.8 mm was cut out. An oxidation consumption test was performed by holding the electrode material of each sample at a temperature of 1200 ° C. for 100 hours in the air.

  The decrease in the mass of each sample after the test relative to the mass of each sample before the test was measured. The electrode material after the test has a mass of 98% or more with respect to the mass of the electrode material before the test, the best “◎”, the one in the range of 97.9 to 95% is good “O”, 95% Those with less than were evaluated as bad “x”. The evaluation results are shown in Tables 3 and 4.

  <Spark consumption test>

  Each sample of a cylindrical electrode material having a diameter of 0.6 mm and a length of 0.8 mm was produced from the obtained sintered body of each sample. The electrode material of each sample was used as the noble metal tip 31 of the center electrode 30 in the spark plug 1 shown in FIGS. 1 and 2, and was welded to the tip surface of the center electrode 30 made of INCONEL600 (registered trademark; trade name) by laser welding. . The ground electrode 80 made of INCONEL 600 (registered trademark; trade name) has a base metal chip 32 made of cylindrical platinum (Pt) -20 mass% nickel (Ni) having a diameter of 0.9 mm and a length of 0.6 mm. Were welded by laser welding.

  Each sample of the spark plug 1 configured as described above is prepared, and a spark consumption test is performed by performing an ignition test at a frequency of 60 times per second in a nitrogen gas atmosphere with an atmospheric pressure of 0.6 MPa for 500 hours. Went. However, no fuel was injected and the initial spark discharge interval was 1.1 mm. In this test, since the consumption of the noble metal tip 32 on the ground electrode 80 side is considered to be approximately the same, it can be said that the increase in the spark discharge interval is determined by the degree of consumption of the center electrode 30. In each sample of the spark plug 1, the spark discharge interval increase is less than 0.1 mm, the best is “◎”, and the one in the range of 0.11-0.3 mm is “good”, 0.3 mm The above was evaluated as bad “x”. The evaluation results are shown in Tables 3 and 4.

  From Table 1 to Table 8, in Sample Nos. 1 to 84 within the composition range of the present invention, the evaluation results of the oxidation consumption test and the spark consumption test are both good and good, and the overall evaluation is good and good. It can be seen that it is excellent in chemical consumption and spark consumption. In sample numbers 85 to 159 outside the range of the composition of the present invention, it can be seen that the evaluation result of at least one of the oxidation consumption test and the spark consumption test is poor and the overall evaluation is poor.

  (Example 2)

  For sample No. 71 having excellent oxidation resistance and spark resistance in Example 1 above, the sintering temperature was in the range of 1500 to 1800 ° C. without changing the average major axis of the oxide particles used as the raw material powder. Thus, a sintered body was produced in which the average particle diameter of the crystal grains of the alloy containing iridium constituting the first phase was changed in the range of 2 to 160 μm. Using the obtained sintered body, an oxidation consumption test and a spark consumption test were performed in the same manner as in Example 1. The evaluation results are shown in Table 9.

  From Table 9, if the average grain size of the alloy grain containing iridium constituting the first phase is within the range of 3 to 150 μm, the evaluation results of the oxidation consumption test and the spark consumption test are the best, and the overall evaluation Since it is the best, it turns out that it is especially excellent in oxidation consumption resistance and spark consumption resistance.

  (Example 3)

  For sample No. 71 having excellent oxidation resistance and spark consumption in Example 1 above, the average grain size of the alloy grains containing iridium constituting the first phase is maintained in the range of 20 to 60 μm. And the sintered compact which changed the average major axis of the oxide particle used as raw material powder in the range of 0.04-32 micrometers was produced. Using the obtained sintered body, an oxidation consumption test and a spark consumption test were performed in the same manner as in Example 1. The evaluation results are shown in Table 6.

  From Table 10, if the average major axis of the oxide particles constituting the second phase is in the range of 0.05 to 30 μm, the evaluation results of the oxidation consumption test and the spark consumption test are both the best, and the overall evaluation is the best. Therefore, it can be seen that the oxidation resistance and the spark consumption are particularly excellent.

  (Example 4)

  About the sample number 78 of said Example 1, the sintered compact which changed the relative density in the range of 94.9 to 98.0% was produced by changing sintering temperature variously. Further, the sintered body obtained in Sample No. 78 of Example 1 was subjected to plastic working by sizing, so that a plastic working material having a higher density and a relative density of 99.5% was produced. Using the obtained sintered body and plastic processed material, an oxidation consumption test and a spark consumption test were performed in the same manner as in Example 1. The evaluation results are shown in Table 7.

  From Table 11, when the relative density is 95.0% or more, the evaluation result of the oxidation consumption test is the best, and when the relative density is less than 95.0%, the evaluation result of the oxidation consumption test is satisfactorily lowered. I understand. From the evaluation results shown in Table 11, it can be seen that when the pair density exceeds 98.0%, the evaluation results of the oxidation consumption test and the spark consumption test are both the best.

  It should be considered that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is shown not by the above embodiments and examples but by the scope of claims, and is intended to include all modifications and variations within the meaning and scope equivalent to the scope of claims. .

  The electrode material for a spark plug of the present invention is used as an electrode material for a spark plug used for ignition of an internal combustion engine such as an automobile engine.

  1: Spark plug, 31, 32: Precious metal tip.

Claims (7)

A first phase made of an alloy containing iridium;
_{SrZrO 3, SrHfO 3, BaZrO 3} , and, and at least one second phase consisting of oxides of selected from the group consisting of BaHfO _3, the balance being unavoidable impurities,
An alloy containing iridium of the first phase is
A first alloy containing rhodium in an amount of 1.0% by mass to 35.0% by mass;
A second alloy containing rhodium in an amount of 1.0% by mass to 35.0% by mass and ruthenium in an amount of 5.0% by mass to 20.0% by mass;
A third alloy containing rhodium in an amount of 1.0 mass% to 35.0 mass%, nickel in an amount of 0.4 mass% to 3.0 mass%, and
It is composed of a fourth alloy containing rhodium in an amount of 1.0 mass% to 35.0 mass%, ruthenium in an amount of 5.0 mass% to 20.0 mass%, and nickel in an amount of 0.4 mass% to 3.0 mass%. Any one kind of alloy selected from the group,
An electrode material for a spark plug, comprising 1.0% by volume or more and 13.0% by volume or less of the second phase oxide.   2. The electrode material for a spark plug according to claim 1, wherein an oxide area ratio observed in a cross section of the electrode material for a spark plug is 1.0% or more and 13.0% or less.   3. The spark plug electrode material according to claim 1, wherein an average grain size of the crystal grains of the alloy containing iridium constituting the first phase is 3 μm or more and 150 μm or less. 4.   4. The spark plug electrode material according to claim 1, wherein an average major axis of the oxide particles constituting the second phase is 0.05 μm or more and 30 μm or less. 5. The average grain size of the alloy grains containing iridium constituting the first phase is 10 μm or more and 70 μm or less,
The electrode material for a spark plug according to any one of claims 1 to 4, wherein an average major axis of oxide particles constituting the second phase is 0.1 µm or more and 3.0 µm or less.   The electrode material for a spark plug according to any one of claims 1 to 5, wherein the relative density is 95.0% or more.   The electrode material for a spark plug according to any one of claims 1 to 5, wherein the relative density is 98.0% or more.

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