EP2697405B1 - Spark plug electrode material and spark plug - Google Patents

Description

State of the art

The present invention relates to a spark plug electrode material, and a spark plug including an electrode formed of the spark plug electrode material and a method of manufacturing the spark plug electrode material.

Spark plugs are known in the prior art in various configurations. Spark plugs in spark ignition engines generate sparking between their electrodes to ignite the fuel-air mixture. In this case, the spark plugs have ground electrodes and center electrodes, with spark plug designs having two to five electrodes being known. In this case, the electrodes are introduced either onto the spark plug housing (ground electrode) or as center electrodes in a ceramic insulator. The life of a spark plug is affected by the corrosion and erosion resistance of the electrode material. Conventional electrode materials are based on nickel alloys containing aluminum. However, these have the problem that under operating conditions in the engine compartment, ie at high temperatures and oxidizing atmosphere, a large part of the nickel surface as well as a part of the nickel inside the electrode material oxidized by reactions with the surrounding oxygen. As a result, a nickel oxide layer is formed, which also contains aluminum oxide and has both heat-insulating and electrical conductivity-inhibiting properties. As a result, it tends to corrode or spark erosion after only a short time. As a result, the electrode gap is increased, which ultimately leads to failure of the spark plug. The formation of an oxide layer under normal conditions The use of the spark plug can at best be achieved by using pure noble metal or precious metal based electrode materials, such as platinum or platinum alloys with iridium, which have increased resistance to spark erosion attack. However, such electrode materials, in particular platinum, lead to enormous costs, which are problematic in such mass components as spark plugs.

Spark plug electrodes made of an alloy based on nickel with 1.8-22% silicon and with a fraction of one percent magnesium, copper and manganese, are for example from US 2,955,598 known.

From the FR 858 196 For example, other alloys containing nickel, copper and silicon are known.

Disclosure of the invention

The spark plug electrode material according to the invention with the features of claim 1 has the advantage that it is based on a nickel-based alloy, which keeps the cost of the electrode material and thus that of the spark plug low. Furthermore, this spark plug electrode material consisting of nickel, silicon and copper and optionally yttrium and unavoidable metallic and non-metallic impurities such as iron, chromium, titanium, manganese, sulfur, sulfur compound, carbon, carbon compound and oxygen, has the advantage that under normal conditions Use, so at elevated temperature and presence of oxygen, at least on a portion of its surface within a very short time, usually after a few hours, forms a specifically structured, particularly homogeneous, relatively thin oxide layer of nickel oxide. The structure of the oxide layer is characterized in that between the oxide grain boundaries of the forming nickel oxide layer, a boundary layer - a so-called grain boundary phase - forms, which has an advantageous effect on the spark erosive wear, thus reducing the removal of the electrode material by spark erosion and thus the Service life of the spark plug electrode is increased. Through the targeted addition of silicon to the nickel-based Starting electrode material (nickel-based alloy) includes the grain boundary phase of the nickel oxide grains when the electrode material is used as intended, silicon and / or silicon oxide. Before the intended use of the spark plug electrode material, the content of silicon is 0.7 to 1.3% by weight of the content of copper is 0.5 to 1.0% by weight and the content of nickel is 97.5 to 98.5% by weight % and 0.07 to 0.13 wt .-% yttrium and the proportion of metallic impurities in total less than 0.2 wt .-%, wherein the content of iron and / or chromium and / or titanium is less than 0.05 wt .-%, and the content of sulfur and / or sulfur compounds and / or carbon and / or carbon compounds is less than 0.01 wt .-%, and the content of oxygen is less than 0.003 wt .-% , The grain boundary phase of the nickel oxide grains is preferably formed from silicon and / or silicon oxide when the electrode material is used as intended. As a result of this design of the grain boundary phase, comprising silicon and / or silicon oxide, the thermomechanical, electrical or thermally conductive properties of the oxide layer are advantageously influenced. Furthermore, in addition to the electrical conductivity of the forming oxide layer, and the oxidation resistance of the same, as well as their thermodynamic stability is improved, which in turn the spark erosive
Wear of the electrode material is reduced. Thus, during operation of the spark plug electrode material according to the invention, at least part of the surface of the electrode material is formed with an oxide layer of, in particular, nickel oxide grains having a grain boundary phase which comprises silicon and / or silicon oxide or which consists of silicon and / or silicon oxide. This oxide layer has a high thermal conductivity of preferably 6 W / mK, in particular at least 8 W / mK or even 10 W / mK and more, and has a particularly high electrical conductivity. As a result, the voltage and the applied temperature applied to the electrode material during its intended use can be uniformly distributed evenly over the entire electrode material, thereby limiting localized maximum temperatures and maximum stresses to a small area of the electrode surface, which clearly shows the corrosion and erosion of the electrode material reduced. The invention thus goes a new way, as is optimized by targeted choice of the components of the electrode material, namely nickel, copper and silicon, forming during normal use oxide layer, and not as in the prior art, the emphasis is placed on the highest possible corrosion resistance ,

The dependent claims show preferred developments of the invention.

Quantities of the individual elements and compounds refer in the following, unless otherwise stated, each on the total weight of the spark plug electrode material.
The spark plug electrode material according to the invention is preferably characterized in that the grain boundary phase of the nickel oxide grains also contains copper and / or copper oxide in addition to silicon and / or silicon oxide. However, the majority of copper and / or copper oxide deposits mainly in the nickel oxide grains. By means of a grain boundary phase of the nickel oxide grains, which also comprises or contains copper and / or copper oxide in addition to silicon and / or silicon oxide, the thermomechanical, electrical or heat-conducting properties of the oxide layer are further advantageously influenced.

Preferably, the spark plug electrode material according to the invention is characterized in that the content of silicon and / or silicon oxide in the nickel oxide layer 1 to 5 wt .-%, in particular 2 to 4 wt .-% and in particular 3 wt .-% based on the total weight of the nickel oxide layer. The content of silicon and / or silicon oxide in the nickel oxide layer is understood to mean the proportion of silicon and / or silicon oxide present in the grain boundary phase. This proportion is easily measurable by, for example, energy dispersive X-ray spectroscopy (EDX) on a scanning electron microscope. Already from a small proportion of about 1 wt .-% silicon and / or silicon oxide at the grain boundary phases of the nickel oxide grains, a significant increase in the electrical conductivity of the oxide layer is measurable, up to a content of silicon and / or silicon oxide of about 5 wt. % at the grain boundary phases increases. At even higher proportions, however, an opposite effect occurs. The content of silicon and / or silicon oxide is therefore preferably in a range from 2 to 4% by weight, based on the total weight of the nickel oxide layer.

Further preferably, the spark plug electrode material is characterized in that about 90% of the nickel oxide grains and in particular about 95% of the nickel oxide grains has a particle size of less than 15 microns. The formation of nickel oxide grains with the smallest possible grain size is essential for the formation of a nickel oxide layer of nickel oxide grains, which has a homogeneous distribution of the silicon-containing grain boundary phase. The smaller the grain size of the nickel oxide grains, the more stable is the oxide layer that forms. This is due to the fact that small grains form a denser structure of nickel oxide grains, whereby the formation of larger cavities, and thus of so-called predetermined breaking points, is avoided. A sufficient stability of the electrode material according to the invention comprising a nickel oxide layer of nickel oxide grains with grain boundary phases is achieved if at least 90% and in particular 95% of the nickel oxide grains forming during normal use of the spark plug electrode material have a particle size of less than 15 μm. A grain size of the nickel oxide grains of less than 15 μm can be produced, for example, by the action of a spark plasma on the electrode material according to the invention.

It is particularly preferred if, before the intended use of the spark plug electrode material, the content of silicon 0.9 to 1.1 wt .-%, in particular 1 wt .-% and the content of
Copper 0.60 to 0.85 wt .-%, in particular 0.75 wt .-% based on the total weight of the electrode material is. Even with a small proportion of silicon of 0.7 wt .-%, the oxidation behavior of the electrode material and the electrical resistance of the electrode material forming on the oxide layer is positively influenced by the fact that when the spark plug electrode material is used as intended, a sufficient amount of silicon and / or Silicon oxide of about 1 to 5 wt .-% of the silicon used in the grain boundary phase of the nickel oxide grains is included. However, from a total content of silicon of more than 1.3 wt .-%, an opposite effect occurs. By adding copper in a proportion of 0.5 to 1.0% by weight based on the total weight of the electrode material, the electric resistance of the electrode material is further reduced because the copper ions are mainly intercalated into the nickel oxide grid, whereby the electrical conductivity of the electrode forming oxide layer is increased. This effect can be measured even at a low copper content of 0.5% by weight. The proportion of copper, however, should not exceed 1% by weight, since otherwise adequate mechanical strength of the spark plug electrode material can no longer be sufficiently ensured. The spark plug electrode material therefore particularly preferably has a content of silicon of from 0.9 to 1.1% by weight and in particular of 1% by weight and a content of copper of from 0.6 to 0.85% by weight, in particular of 0.75 wt .-%, on. In these proportions, the attached elements silicon and copper by addition and accumulation of silicon and / or silicon or silicon and / or silicon oxide and copper and / or copper oxide at the grain boundary phases of the nickel oxide grains in the intended use of the spark plug electrode material forming nickel oxide layer to one particularly high electrical conductivity of the oxide layer. The forming oxide layer is also thermodynamically and mechanically sufficiently stable, so that the spark erosive wear and corrosion of the spark plug electrode material according to the invention are effectively reduced.

Further preferably, the spark plug electrode material according to the invention is characterized in that the layer thickness of the grain boundary phase is smaller than 0.3 .mu.m, in particular smaller than 0.2 .mu.m and in particular smaller than 0.1 .mu.m. The thinner the grain boundary phase is formed, the smaller are the Voids between the nickel oxide grains and the more closed and inherently stable is the oxide layer surface, so that it is better protected against spark erosion attacks, since it then, if only a small proportion of predetermined breaking points. However, the layer thickness of the grain boundary phases is preferably at least as great that individual silicon atoms and / or silicon oxide particles can attach to it. In particular, therefore, the layer thickness of the grain boundary phases is greater than 0.1 nm and less than 0.2 microns and in particular less than 0.1 microns.

According to a further preferred embodiment of the invention, the spark plug electrode material according to the invention is characterized in that it contains in addition to nickel, copper and silicon 0.09 to 0.11 wt .-% and in particular 0.10 wt .-% yttrium. Addition of such small amounts of yttrium prevents abnormal grain growth during proper use of a spark plug having the spark plug electrode material of the present invention. The yttrium content can be kept deliberately low, for example, by a low oxygen content of the alloy. From a proportion of yttrium of more than 0.13 wt .-%, the oxidation behavior and thus the electrical resistance of the forming oxide layer is adversely affected because form yttrium-containing precipitates in the electrode material.

According to a further preferred embodiment of the invention, the spark plug electrode material is characterized by a proportion of metallic impurities, which is less than 0.1 wt .-% in total. Metallic impurities include elements and compounds such as iron, titanium, chromium, manganese and the like. Such impurities reduce the effect of increasing the electrical conductivity as achieved by adding silicon and copper in the specified range to the nickel base material. In addition, these impurities reduce the thermal conductivity of the alloy.

It is particularly preferred if the nickel oxide grains do not contain silicon and / or silicon oxide. If silicon or silicon oxide is incorporated in the nickel oxide grains, it competes there with the copper particles (copper ions) or with them Copper oxide, whereby the electrical conductivity of the electrode material according to the invention can not be increased efficiently.

Particularly preferably, the electrode material is substantially free of aluminum and / or aluminum compounds and / or intermetallic phases. Aluminum and its compounds reduce the electrical conductivity of the electrode material and the forming oxide layer and thus promote the spark erosive wear of the electrode material. By dispensing with aluminum, the oxidation behavior and in particular the electrical resistance of the oxide layer forming and thus the erosion behavior of the spark plug electrode material is significantly improved, thus measurably improved. In addition, the formability of the material is significantly improved. A similar effect is also the absence of intermetallic phases, because intermetallic phases exist as precipitates in the nickel matrix and lead to thermomechanical stresses and a reduction of the thermal conductivity, whereby the spark erosive wear and corrosion of the electrode material are increased.

It is particularly preferred if the content of iron and / or chromium and / or titanium is less than 0.01% by weight and / or the content of sulfur and / or sulfur compounds and / or carbon and / or carbon compounds is less than 0.005 Wt .-% and in particular less than 0.001 wt .-% is. Especially the elements iron and / or chromium and / or titanium adversely affect the electrical conductivity of the electrode material. More preferably, the content of sulfur and / or sulfur compounds and / or carbon and / or carbon compounds is less than 0.005 wt .-% and in particular less than 0.001 wt .-%, since these elements and compounds have a negative effect on the oxidation behavior of the alloy In particular, they can lead to increased corrosion of the electrode material.

It is particularly preferred if the content of oxygen in the spark plug electrode material is less than 0.002% by weight, since oxygen is the oxidation of not only the nickel material,
but also promotes any impurities, which in turn contributes to increased wear of the electrode material.

According to a further preferred embodiment of the invention, the spark plug electrode material consists essentially of, therefore, apart from technical, unavoidable impurities, from 1 wt .-% silicon, 0.75 wt .-% copper and 0.1 wt .-% yttrium, said remaining material consists of nickel and makes up about 98.15 wt .-%. When used properly, such an electrode material forms a stable, thin and uniform nickel oxide layer with fine grain boundary phases to which silicon and / or silicon oxide or silicon and / or silicon oxide and copper and / or copper oxide are attached. This electrode material has a high thermal conductivity of more than 10 W / mK and a low electrical resistance, ie a high electrical conductivity. The spark plug electrode material thus has a reduced spark erosive wear and a significantly reduced tendency to corrosion and is thus ideally suited for long-term use at high temperatures.

Further preferably, the spark plug electrode material consists essentially of 0.7 to 1.3 wt .-%, in particular 1 wt .-% silicon, 0.5 to 1.0 wt .-%, apart from technically related, unavoidable impurities, in particular 0.75% by weight of copper, 0.07 to 0.13% by weight, in particular 0.1% by weight of yttrium, and contains less than 0.003% by weight, in particular less than 0.002% by weight, of oxygen , 0.001% by weight of sulfur and 0.003% by weight of carbon, with the remainder being nickel, the total amount of metallic impurities being less than 0.1% by weight. Due to its composition, this electrode material has minimal spark erosive wear and a minimal tendency to corrode.

Furthermore, the present invention relates to a method for producing the spark plug electrode material according to the invention, the method comprising the steps of producing a nickel-based alloy and adding other elements such as silicon, copper and optionally yttrium.

By the intended use of the invention thus prepared Spark plug electrode material is formed on at least a part of the surface of the spark plug electrode material, an oxide layer having an optimized structure. In this context, an optimized structure is understood to mean that the oxide layer is characterized by a uniform and stable composite and, moreover, is relatively thin and even at the surface in comparison to oxide layers which form on conventional electrodes. Furthermore, grain boundary phases containing silicon and / or silicon oxide are formed between the nickel oxide grains. This allows the formation of an electrode material having a low electrical resistance of the oxide layer on the electrode surface, resulting in improved electrical conductivity of this oxide layer. In addition, the thermal conductivity of the electrode material is increased. The inventive method thus provides a spark plug electrode made of cost-effective electrode material, which is characterized by an extremely high temperature resistance and a significantly reduced spark erosive wear and electrode erosion and has excellent resistance to oxidation and corrosion. The spark plug electrode produced according to the invention is therefore stable and resistant to wear even at high temperatures under the extreme conditions prevailing in the combustion chamber of an engine.

Further, the present invention relates to an electrode made of the above-described spark plug electrode material, which electrode can be used, for example, as a center electrode and / or as a ground electrode of a spark plug, and both as a single-material electrode or as a two-electrode electrode with the electrode material of the present invention as a cladding material and a copper core.

Furthermore, the invention relates to the use of nickel, silicon and copper for producing an alloy for a spark plug electrode material, which is characterized by a very good electrical conductivity and high thermal conductivity, and thus by a long service life.

Short description of the drawing

Figur 1

Schematische Schnittansicht des erfindungsgemäßen Zündkerzenelektrodenmaterials,

Figur 2

eine weitere schematische Darstellung eines Ausschnitts der Oxidschicht des erfindungsgemäßen Zündkerzenelektrodenmaterials,

Figur 3

eine Darstellung des umrandeten Abschnitts aus Figur 2 mit vergrößerter Ansicht des Ausschnittes aus der Oxidschicht des erfindungsgemäßen Zündkerzenelektrodenmaterials, und

Figur 4

eine Zündkerze umfassend das erfindungsgemäßen Zündkerzenelektrodenmaterial.

Hereinafter, an embodiment of the invention will be described in detail with reference to the accompanying drawings. In the drawing is:

FIG. 1

Schematic sectional view of the spark plug electrode material according to the invention,

FIG. 2

a further schematic representation of a section of the oxide layer of the spark plug electrode material according to the invention,

FIG. 3

a representation of the outlined section FIG. 2 with enlarged view of the section of the oxide layer of the spark plug electrode material according to the invention, and

FIG. 4

a spark plug comprising the spark plug electrode material according to the invention.

Embodiment of the invention

FIG. 1 shows a schematic sectional view of the spark plug electrode material according to the invention 1. On the surface of the nickel alloy 11 is formed by the intended use of the electrode material 1, a nickel oxide layer 10 comprising nickel oxide grains 2 with grain boundaries 3, wherein between the nickel oxide grains 2 is a grain boundary phase 4, wherein the grain boundary phases are exaggerated in size in this schematic sectional view. The nickel oxide grains 2 contain copper particles (copper ions) 8 and copper oxide particles 9 embedded in the nickel oxide grid (not shown) of the nickel oxide layer 10. The grain boundary phase 4 comprises silicon particles 6 and silicon oxide particles 7. A nickel oxide layer 10 formed in this way is characterized by high thermodynamic stability, high thermal conductivity and excellent electrical conductivity.

FIG. 2 is a schematic representation of a section of the nickel oxide layer 10 of the spark plug electrode material 1 according to the invention, wherein the spark plug electrode material prior to formation of the oxide layer consisting essentially of 1 wt .-% silicon, 0.75 wt .-% copper and 98.25 wt .-% nickel , Between the nickel oxide grains 2 with their grain boundaries 3 are Grain boundary phases 4 formed, the silicon 6 is included. By way of example, two cracks 8 are shown, which can form in the nickel oxide layer 10.

FIG. 3 is an enlarged view of the edged portion of the spark plug electrode material according to the invention FIG. 2 , Here, the silicon 6 or silicon oxide 7 enriched in the grain boundary phases 4 can be seen particularly well.

FIG. 4 shows a spark plug 20 according to the invention, with a center electrode 21 and a ground electrode 22, wherein both the center electrode 21 and the ground electrode 22 is formed from the spark plug electrode material according to the invention and wherein the ground electrode 22 is formed as a single-material electrode and the center electrode 21 as a two-electrode.

Thus, according to the present invention, there is provided a spark plug electrode material for producing a spark plug electrode or a spark plug which is characterized by the formation of an oxide layer particularly under normal use, low spark erosion wear, and excellent corrosion resistance with minimized manufacturing costs and sufficient thermodynamic and mechanical stability.

Claims (16)

1. Spark plug electrode material consisting of nickel, silicon and copper and optionally yttrium and unavoidable metallic and nonmetallic impurities such as iron, chromium, titanium, manganese, sulfur, sulfur compound, carbon, carbon compound and oxygen, characterized in that the electrode material, when used as intended, forms a nickel oxide layer composed of nickel oxide grains in at least part of its surface area, where the grain boundary phase of the nickel oxide grains comprises silicon and/or silicon oxide, where, prior to use of the spark plug electrode material as intended, the silicon content is 0.7% to 1.3% by weight, the copper content is 0.5% to 1.0% by weight and the nickel content is 97.5% to 98.5% by weight, and optionally 0.07% to 0.13% by weight of yttrium, and the proportion of metallic impurities is less than 0.2% by weight in total, where the iron and/or chromium and/or titanium content is less than 0.05% by weight, and the content of sulfur and/or sulfur compounds and/or carbon and/or carbon compounds is less than 0.01% by weight, and the oxygen content is less than 0.003% by weight.
2. Spark plug electrode material according to Claim 1, characterized in that the grain boundary phase of the nickel oxide grains further comprises copper and/or copper oxide.
3. Spark plug electrode material according to Claim 1 or 2, characterized in that the silicon and/or silicon oxide content in the nickel oxide layer is 1% to 5% by weight, especially 2% to 4% by weight and especially 3% by weight, based on the total weight of the oxide layer.
4. Spark plug electrode material according to any of the preceding claims, characterized in that about 90% of the nickel oxide grains and especially about 95% of the nickel oxide grains have a grain size of less than 15 µm.
5. Spark plug electrode material according to any of the preceding claims, characterized in that, prior to the use of the spark plug electrode material as intended, the silicon content is 0.9% to 1.1% by weight, especially 1% by weight, and the copper content is 0.6% to 0.85% by weight, especially 0.75% by weight.
6. Spark plug electrode material according to any of the preceding claims, characterized in that the layer thickness of the grain boundary phases is less than 0.3 µm, especially less than 0.2 µm and especially less than 0.1 µm.
7. Spark plug electrode material according to any of the preceding claims, characterized in that the electrode material further contains 0.09% to 0.11% by weight and especially 0.10% by weight of yttrium.
8. Spark plug electrode material according to any of the preceding claims, characterized in that the proportion of metallic impurities is less than 0.1% by weight in total.
9. Spark plug electrode material according to any of the preceding claims, characterized in that the nickel oxide grains do not contain any silicon and/or silicon oxide.
10. Spark plug electrode material according to any of the preceding claims, characterized in that the electrode material, apart from unavoidable impurities for technical reasons, is free of aluminium and/or aluminium compounds and/or intermetallic phases.
11. Spark plug electrode material according to any of the preceding claims, characterized in that the iron and/or chromium and/or titanium content is less than 0.01% by weight and/or the content of sulfur and/or sulfur compounds and/or carbon and/or carbon compounds is less than 0.005% by weight and especially less than 0.001% by weight.
12. Spark plug electrode material according to any of the preceding claims, characterized in that the oxygen content is less than 0.002% by weight.
13. Spark plug electrode material according to any of the preceding claims, consisting, apart from unavoidable impurities for technical reasons, of:

    a) 98.15% by weight of nickel,

    b) 1% by weight of silicon,

    c) 0.75% by weight of copper and

    d) 0.1% by weight of yttrium.
14. Process for producing a spark plug electrode material according to any of Claims 1 to 13, comprising the steps of:

    - producing a nickel-base alloy

    - adding further elements.
15. Spark plug comprising an electrode made from a spark plug electrode material according to any of Claims 1 to 13.
16. Spark plug according to Claim 15, characterized in that the electrode is a centre electrode and/or an earth electrode, and this can be used either with or without a copper core in the centre electrode and/or earth electrode.

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