JP4780628B2 - Insulator for spark plug and manufacturing method thereof - Google Patents
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Description
【０００１】
【産業上の利用分野】
本発明は、高絶縁性及び高耐電圧性を有するアルミナ基焼結体を用いたスパークプラグ用絶縁碍子及びその製造方法に関する。特には、７００℃付近の高温下での耐電圧性を要求されるスパークプラグ用絶縁碍子及びその製造方法として好適なものである。
【０００２】
【従来の技術】
アルミナ基焼結体は、耐電圧性、耐熱性、機械的強度等の各種特性に優れ、しかも安価であるため、スパークプラグ用等の絶縁碍子やＩＣパッケージ等の多層配線基板などの用途に用いられている。特に、スパークプラグ等の絶縁碍子用途においては、室温から７００℃付近の高温の広い温度域にわたって高絶縁性及び高耐電圧性が要求される。
【０００３】
従来より、スパークプラグ等の絶縁碍子用途に用いる材料としては、ＳｉＯ2−ＣａＯ−ＭｇＯからなる三成分系を焼結助剤として用いたアルミナ基焼結体が用いられてきた。しかし、この三成分系焼結助剤が焼成後のアルミナ基焼結体の粒界に低融点ガラスとして存在すると、７００℃付近の高温下で高電圧を印加した際に、低融点ガラスが存在する粒界を通じて絶縁破壊を起こしやすくなる。
【０００４】
そこで、アルミナ基焼結体の粒界のガラス相の耐熱性を向上させて耐電圧性を向上させるために、種々の方法が検討されている。例えば、Ｙ2Ｏ3、Ｌａ2Ｏ３及びＺｒＯ2等を焼結助剤に用いる方法が特公平７−１７４３６号公報に開示されている。また、有機化合物原料を用いて粒界にＹ4Ａｌ2Ｏ9結晶相を生成させる方法が特許第２５６４８４２号公報に開示されている。
【０００５】
【発明が解決しようとする課題】
近年のエンジンの小型化やバルブの大型化に伴い、スパークプラグは小径化され、それに伴い、絶縁碍子の薄肉化を進める必要がある。このため、従来技術を用いたアルミナ基焼結体では、７００℃付近の高温下で使用した場合に十分な耐電圧性が得られない問題がある。本発明は、７００℃付近の高温下で使用した場合でも優れた耐電圧特性を有するアルミナ基焼結体を用いたスパークプラグ用絶縁碍子及びその製造方法を提供することを目的とする。
【０００６】
【課題を解決するための手段】
請求項１の発明は、Ｎａ成分、Ｋ成分、Ｆｅ成分、Ｔｉ成分のうち少なくともいずれか１種を含むアルミナ基焼結体のＮａ成分、Ｋ成分、Ｆｅ成分、Ｔｉ成分の組成比及び組織状態（構成要件（ａ）及び（ｂ））を規定することを要旨とする。以下に、各構成要件について説明する。
【０００７】
（ａ）該アルミナ基焼結体１００重量％に含まれる該Ｎａ成分、該Ｋ成分、該Ｆｅ成分、該Ｔｉ成分の酸化物換算による含有量が０．１２〜０．３重量％、且つ、該Ｎａ成分の酸化物換算による含有量が０．０２〜０．０５重量％であること。
Ｎａ成分、Ｋ成分、Ｆｅ成分、Ｔｉ成分が多く存在すると、イオン伝導性若しくは粒界に局所的な低融点部が存在して耐電圧性を低下させる要因となる。絶縁破壊が発生しやすい箇所を形成するＮａ成分、Ｋ成分、Ｆｅ成分、Ｔｉ成分の含有量を規定することで、アルミナ基焼結体の耐電圧性を低下させる潜在的要素を低減することができる。
【０００８】
これらＮａ成分、Ｋ成分、Ｆｅ成分、Ｔｉ成分はトータルとして０．１２〜０．３重量％であるのみならず、そのうちＮａ成分が０．０５重量％以下であることが重要である。Ｎａ成分は市販のアルミナ原料に比較的多く含まれている（例；０．０４〜０．３１重量％）。Ｎａ成分が多いと、イオン伝導性が発生し、耐電圧性を著しく低下させる。Ｎａ成分がアルミナ基焼結体に０．０５重量％以上含まれると、Ｎａ成分、Ｋ成分、Ｆｅ成分、Ｔｉ成分のトータル量が０．１２〜０．３重量％であっても耐電圧性を向上させることが困難になる。
【０００９】
アルミナ基焼結体の耐電圧性を劣化させる不純物としては、前記のＮａ、Ｋ以外のアルカリ金属（特にはＬｉ）や希土類を除く遷移金属（特にはＶ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ）が挙げられる。したがって、アルミナ基焼結体１００重量％に含まれるこれらの不純物の酸化物換算による含有量も、それぞれ０．１重量％以下であることが好ましい。前記のＮａ成分、Ｋ成分、Ｆｅ成分、Ｔｉ成分と併せてこれらの不純物の含有量をコントロールすることで、７００℃付近の高温下における耐電圧性をより効果的に向上できる。
【００１０】
（ｂ）アルミナ基焼結体の任意の断面に長さ１００μｍの仮想直線を引いた場合において、該仮想直線が横切る粒界及び気孔の合計数が５０個以下であること。
Ｎａ成分、Ｋ成分、Ｆｅ成分、Ｔｉ成分の含有量を規定するだけでは、アルミナ基焼結体の耐電圧性を十分に向上させることは困難である。さらに、特定範囲に存在する粒界の数や気孔の数といった顕在的要素をも規定することが重要である。なぜなら、上記のＮａ成分、Ｋ成分、Ｆｅ成分、Ｔｉ成分はこれら粒界や気孔に偏析して、７００℃付近の高温下でガラス相の耐熱性を低下させ、アルミナ基焼結体の耐電圧性を相乗的に低下させるからである。
【００１１】
ここにいう「長さ１００μｍの仮想直線」は、例えば、アルミナ基焼結体の任意の切断面を鏡面研磨したものを撮影したＳＥＭ写真上に引くことができる。画像解析装置があれば、画面上で仮想直線を引いて自動的に粒界の数や気孔の数を算出することもできる。
【００１２】
仮想直線が横切る粒界及び気孔の合計数が５０個以下であれば、高電圧が印加されても、アルミナ基焼結体に絶縁破壊を生じさせる導電経路が生じにくくなるため、耐電圧性の低下を抑えることができる。粒界及び気孔に不純物が偏析した場合において、絶縁破壊を効果的に回避できる。
【００１３】
すなわち、上記（ａ）及び（ｂ）の構成要素を兼備することで、従来達成が困難であった７００℃付近の高温下における耐電圧性を効果的に向上することができる。
さらに、請求項１の発明は、アルミナ基焼結体１００重量％に希土類元素としてＮｄ、Ｐｒ、Ｄｙ、Ｌａを酸化物換算で１〜４．５重量％含むことを要旨とする。
希土類元素が粒界のガラス相に存在することで、粒界の耐熱性が向上するため、７００℃付近の高温下における耐電圧性を向上することができる。希土類元素としては、Ｎｄ、Ｐｒ、Ｄｙ、Ｌａを用いる。安定した耐電圧性を得るには、Ｎｄを用いるのが特に好ましい。
希土類元素の添加量としては、ＲＥ ２ Ｏ ３ 換算（ＲＥは希土類元素）にてアルミナ基焼結体１００重量％に対して１〜４．５重量％である。かかる範囲であれば、希土類元素添加による製造コストの上昇を抑えつつ、効果的に７００℃付近の高温下における耐電圧性をより効果的に向上できる。特には、希土類元素としてＮｄを添加し、且つ、仮想直線が横切る粒界及び気孔の合計数が２５個以下であることが好ましい。７００℃付近の高温下においても、極めて良好な耐電圧値が得られるからである。
このような高耐電圧性アルミナ基焼結体を用いたスパークプラグ用絶縁碍子は、室温から７００℃付近の高温下での幅広い温度域において優れた耐電圧性を有するスパークプラグを得るのに好適である。特には小径タイプのスパークプラグ用途に好適である。尚、高温下での耐電圧性を要求される箇所にのみ本アルミナ基焼結体を用いたスパークプラグ用絶縁碍子であってもよい。
【００１４】
請求項２の発明は、２０±５℃における熱伝導率が２０Ｗ／ｍ・Ｋ以上であるスパークプラグ用絶縁碍子を要旨とし、請求項１に記載のスパークプラグ用絶縁碍子の好ましい構成を例示したものである。
【００１５】
アルミナ基焼結体には電圧印加によりジュール熱が発生し、局在的な温度上昇によって絶縁破壊が発生する。このとき２０±５℃における熱伝導率が２０Ｗ／ｍ・Ｋ以上であればアルミナ基焼結体の温度上昇速度を低く抑えることができるため、結果として７００℃付近の高温下における耐電圧性を高めることができる。
【００２２】
請求項３の発明は、スパークプラグ用絶縁碍子をその焼成保持温度に対して−１００〜＋１５０℃の温度で熱処理することを要旨とするスパークプラグ用絶縁碍子の製造方法であり、請求項１又は請求項２に記載のスパークプラグ用絶縁碍子の好ましい製造方法を例示したものである。
【００２３】
スパークプラグ用絶縁碍子をその焼成保持温度に対して−１００〜＋１５０℃の温度で熱処理することで、焼結体中の粒界や気孔の大きさを耐電圧性が良好な状態に制御できる。下限値を焼成保持温度に対して−１００℃に限定したのは、これより低い温度では効果が低い若しくは粒界に偏析が発生して耐電圧性が低下するからである。上限値を焼成保持温度に対して＋１５０℃に限定したのは、これより高い温度では組織の異常粒成長による焼結体密度の低下や気孔の増大を招き絶縁性が低下するからである。尚、本発明の熱処理をスパークプラグ用絶縁碍子に用いる場合は、高温下での耐電圧性を要求される箇所にのみ部分的に熱処理するようにしてもよい。
【００２４】
【実施例】
以下に本発明を実施例を用いて説明する。
表２に記載の平均粒径及びＮａ含有量のＡｌ２Ｏ３原料粉末に焼結助剤として平均粒径０.６μｍのＳｉＯ２粉末又は表１に記載の組成の粘土、平均粒径０.８μｍのＣａＣＯ３粉末、平均粒径０.３μｍのＭｇＯ粉末及び平均粒径１〜３μｍのＲＥ2Ｏ3粉末を、表２に示す量比となるように秤量し配合した粉末を製造する。
【００２５】
これらの配合粉末にバインダーを添加し、それぞれボールミルにて、２０ｍｍφのアルミナボールを使用し水中１６時間混合した後、スプレードライにより乾燥、造粒し混合粉末を得る。これらの混合粉末をそれぞれ１５０ＭＰａの静水圧プレスで５０×５０×２０ｍｍの成形体に成形し、次に大気雰囲気下において表２示す焼成温度（１５５０℃から１６７５℃）で２時間保持して焼成する。また、必要に応じて、表２に示す熱処置温度で熱処理を行う。
【００２６】
７００℃における耐電圧値は、焼結体を１５×１５×０.６５ｍｍに加工して、図１に示す装置により測定する。熱伝導率は、φ１０ｍｍ×ｔ２ｍｍの形状に加工した後、ＪＩＳ Ｒ−１６１１に準ずるレーザーフラッシュ法により測定する。Ｎａ成分、Ｋ成分、Ｆｅ成分、Ｔｉ成分の含有量は、焼結体を化学分析してＮａ２Ｏ、Ｋ２Ｏ、Ｆｅ２Ｏ３、ＴｉＯ２換算にて定量する。
【００２７】
仮想直線が横切る粒界及び気孔の合計数は、焼結体の任意の平面を鏡面研磨後、ＳＥＭ観察にて１０００〜２０００倍の倍率で写真を撮り、写真上に数本の直線を引き、直線１００μｍあたりを横切る粒界及び気孔の数を算出する。これらの結果を表３に示す。
【００２８】
【表１】
【表２】
【表３】
表３の結果より、仮想直線が横切る粒界及び気孔の合計数が２５個以下で、且つ、希土類元素としてＮｄを酸化物換算にて４．５重量％添加した実施例である試料番号８では、耐電圧値が７１ｋＶ／ｍｍと、極めて良好な耐電圧値が得られることがわかる。
【００３２】
更に、試料番号１５のように、希土類元素添加系で更に熱処理することで、より効果的に耐電圧値を向上（７５ｋＶ／ｍｍ）することができる。
【００３３】
一方、比較例である試料番号１〜試料番号３では、３３〜４２ｋＶ／ｍｍの低い耐電圧値しか得られないことがわかる。試料番号１では、仮想直線が横切る粒界及び気孔の合計数が５０個を越えるため、耐電圧値が４２ｋＶ／ｍｍと低い。試料番号２では、Ｎａ成分の含有量が０．０６重量％と多いため、耐電圧値が３３ｋＶ／ｍｍとかなり低い。試料番号３では、Ｎａ成分、Ｋ成分、Ｆｅ成分、Ｔｉ成分の総合計量が０．３重量％を越えるため、耐電圧値が４１ｋＶ／ｍｍと低い。
【００３４】
以上の結果より、希土類元素を添加したり、仮想直線が横切る粒界及び気孔の合計数或いはＮａ成分やＮａ成分、Ｋ成分、Ｆｅ成分、Ｔｉ成分の含有量をそれぞれ独立して調整するのみでは、７００℃付近の高温下における耐電圧性を向上できないことがわかる。
【００３５】
【発明の効果】
本発明によれば、７００℃付近の高温下において高絶縁性及び高耐電圧性を有するアルミナ基焼結体及びその製造方法を提供することができる。これらを用いたスパークプラグ用絶縁体及びその製造方法によれば、小径プラグのように肉薄の製品でも優れた絶縁性及び耐電圧性を発揮可能である。
【図面の簡単な説明】
【図１】本発明に使用した耐電圧性の評価方法の模式図である。
【符号の説明】
１ アルミナ基焼結体からなる試験片
２ａ アルミナ製碍筒
２ｂ アルミナ製碍筒
３ 封着ガラス
４ａ 電極
４ｂ 電極
５ 加熱用ヒータ
６ 高電圧発生装置
７ ガラス接合体
８ 加熱用ボックス[0001]
[Industrial application fields]
The present invention relates to an insulator for a spark plug using an alumina-based sintered body having high insulation and high voltage resistance, and a method for manufacturing the same. In particular, it is suitable as an insulator for a spark plug that is required to withstand voltage at a high temperature around 700 ° C. and a method for manufacturing the same .
[0002]
[Prior art]
Alumina-based sintered bodies are excellent in various properties such as voltage resistance, heat resistance, and mechanical strength, and are inexpensive, so they are used for applications such as insulators for spark plugs and multilayer wiring boards for IC packages. It has been. In particular, in an insulator application such as a spark plug, high insulation and high withstand voltage are required over a wide temperature range from room temperature to high temperature around 700 ° C.
[0003]
Conventionally, an alumina-based sintered body using a ternary system composed of SiO 2 —CaO—MgO as a sintering aid has been used as a material used for an insulator such as a spark plug. However, if this ternary sintering aid exists as a low-melting glass at the grain boundary of the alumina-based sintered body after firing, the low-melting glass exists when a high voltage is applied at a high temperature around 700 ° C. It becomes easy to cause dielectric breakdown through the grain boundary.
[0004]
Therefore, various methods have been studied in order to improve the heat resistance of the glass phase at the grain boundary of the alumina-based sintered body and improve the voltage resistance. For example, Japanese Patent Publication No. 7-17436 discloses a method using Y 2 O 3 , La 2 O 3, ZrO 2 or the like as a sintering aid. Further, Japanese Patent No. 2564842 discloses a method for producing a Y 4 Al 2 O 9 crystal phase at a grain boundary using an organic compound raw material.
[0005]
[Problems to be solved by the invention]
With the recent miniaturization of engines and the increase in size of valves, the diameter of spark plugs has been reduced, and accordingly, it is necessary to reduce the thickness of the insulator. For this reason, the alumina-based sintered body using the prior art has a problem that sufficient withstand voltage cannot be obtained when used at a high temperature around 700 ° C. An object of the present invention is to provide an insulator for a spark plug using an alumina-based sintered body having excellent withstand voltage characteristics even when used at a high temperature around 700 ° C., and a method for producing the same.
[0006]
[Means for Solving the Problems]
The invention according to claim 1, Na component, K component, Fe component, Na components including the alumina-based sintered body at least any one of Ti component, K component, Fe component, a Ti component composition ratio and tissue The gist is to define the state (components (a) and (b)). Below, each component requirement is demonstrated.
[0007]
(A) the content of the Na component, the K component, the Fe component, and the Ti component contained in 100% by weight of the alumina-based sintered body in terms of oxides is 0.12 to 0.3% by weight, and The content of the Na component in terms of oxide is 0.02 to 0.05 % by weight .
When there are many Na components, K components, Fe components, and Ti components, a local low melting point portion exists at the ion conductivity or grain boundary, which causes a decrease in voltage resistance. By defining the contents of the Na component, K component, Fe component, and Ti component that form places where dielectric breakdown is likely to occur, potential factors that lower the voltage resistance of the alumina-based sintered body can be reduced. it can.
[0008]
These Na component, K component, Fe component, and Ti component are not only 0.12 to 0.3 wt% in total, but it is important that the Na component is 0.05 wt% or less. A relatively large amount of Na component is contained in a commercially available alumina raw material (for example, 0.04 to 0.31% by weight). When there are many Na components, ion conductivity will generate | occur | produce and a withstand voltage property will fall remarkably. When the Na component is contained in the alumina-based sintered body in an amount of 0.05% by weight or more, even if the total amount of the Na component, the K component, the Fe component, and the Ti component is 0.12 to 0.3% by weight , the voltage resistance It becomes difficult to improve.
[0009]
The non neat that degrade the withstand voltage of the alumina-based sintered body, wherein the Na, alkali metal other than K transition metals (especially where Li) excluding or a rare earth (particularly V, Cr, Mn, Fe, Co, Ni, Cu). Accordingly, the content of an oxide in terms of these non neat contained in the alumina-based sintered body 100 by weight percent, is preferably 0.1 wt% or less, respectively. It said Na component, K component, Fe component, together with the Ti component by controlling the content of these non neat, can be more effectively improved voltage endurance at high temperatures of around 700 ° C..
[0010]
(B) When a virtual straight line having a length of 100 μm is drawn on an arbitrary cross section of the alumina-based sintered body, the total number of grain boundaries and pores crossed by the virtual straight line is 50 or less.
It is difficult to sufficiently improve the voltage resistance of the alumina-based sintered body simply by defining the contents of the Na component, K component, Fe component, and Ti component . Furthermore, it is important to define the obvious factors such as the number of grain boundaries and the number of pores existing in a specific range. This is because the above Na component, K component, Fe component, and Ti component segregate at these grain boundaries and pores, lower the heat resistance of the glass phase at a high temperature around 700 ° C., and the withstand voltage of the alumina-based sintered body. This is because the sex is lowered synergistically.
[0011]
The “virtual straight line having a length of 100 μm” mentioned here can be drawn on an SEM photograph obtained by mirror-polishing an arbitrary cut surface of an alumina-based sintered body, for example. If there is an image analysis device, it is possible to automatically calculate the number of grain boundaries and the number of pores by drawing a virtual straight line on the screen.
[0012]
If the total number of grain boundaries and pores crossed by the imaginary straight line is 50 or less, even if a high voltage is applied, it becomes difficult to generate a conductive path that causes dielectric breakdown in the alumina-based sintered body. The decrease can be suppressed. When impurities are segregated at the grain boundaries and pores, dielectric breakdown can be effectively avoided.
[0013]
That is, by combining the components (a) and (b), it is possible to effectively improve the withstand voltage at a high temperature around 700 ° C., which has been difficult to achieve in the past .
Further, the gist of the invention of claim 1 is that 100% by weight of the alumina-based sintered body contains 1 to 4.5% by weight of Nd, Pr, Dy, and La as rare earth elements in terms of oxides.
Since the rare earth element is present in the glass phase at the grain boundary, the heat resistance at the grain boundary is improved, so that the voltage resistance at a high temperature around 700 ° C. can be improved. Nd, Pr, Dy, and La are used as the rare earth element. In order to obtain stable voltage resistance, it is particularly preferable to use Nd.
The addition amount of the rare earth element is 1 to 4.5 wt% with respect to 100 wt% of the alumina-based sintered body in terms of RE 2 O 3 (RE is a rare earth element). Within such a range, it is possible to effectively improve the withstand voltage at a high temperature around 700 ° C. while suppressing an increase in production cost due to the addition of rare earth elements. In particular, it is preferable that Nd is added as a rare earth element, and the total number of grain boundaries and pores crossed by the virtual straight line is 25 or less. This is because an extremely good withstand voltage value can be obtained even at a high temperature around 700 ° C.
An insulator for a spark plug using such a high voltage endurance alumina-based sintered body is suitable for obtaining a spark plug having excellent voltage endurance in a wide temperature range from room temperature to around 700 ° C. It is. It is particularly suitable for small diameter type spark plug applications. It should be noted that the insulator for a spark plug using the present alumina-based sintered body may be used only in a place where voltage resistance at a high temperature is required.
[0014]
The invention of claim 2 is based on a spark plug insulator having a thermal conductivity of 20 W / m · K or higher at 20 ± 5 ° C., and exemplifies a preferable configuration of the insulator for a spark plug according to claim 1. Is.
[0015]
In the alumina-based sintered body, Joule heat is generated by applying a voltage, and dielectric breakdown is generated by a local temperature rise. At this time, if the thermal conductivity at 20 ± 5 ° C. is 20 W / m · K or more, the temperature rise rate of the alumina-based sintered body can be kept low. As a result, the withstand voltage at a high temperature around 700 ° C. Can be increased.
[0022]
Invention of
[0023]
By heat-treating the insulator for a spark plug at a temperature of −100 to + 150 ° C. with respect to its firing holding temperature, the grain boundaries and pore sizes in the sintered body can be controlled to have a good withstand voltage. The reason why the lower limit value is limited to −100 ° C. with respect to the firing holding temperature is that the effect is low at temperatures lower than this, or segregation occurs at the grain boundaries and the voltage resistance decreases. The reason why the upper limit is limited to + 150 ° C. with respect to the firing holding temperature is that at temperatures higher than this, the sintered body density decreases due to abnormal grain growth in the structure and the pores increase, resulting in a decrease in insulation. In addition, when using the heat treatment of this invention for the insulator for spark plugs, you may make it partially heat-treat only to the location where the withstand voltage property in high temperature is requested | required.
[0024]
【Example】
The present invention will be described below with reference to examples.
Al 2 O 3 raw material powder having an average particle size and Na content shown in Table 2 and an SiO 2 powder having an average particle size of 0.6 μm as a sintering aid or clay having a composition shown in Table 1, an average particle size of 0.5. 8 μm of CaCO 3 powder, MgO powder with an average particle diameter of 0.3 μm, and RE 2 O 3 powder with an average particle diameter of 1 to 3 μm are weighed so as to have the quantitative ratio shown in Table 2 to produce a powder.
[0025]
A binder is added to these blended powders, and each is mixed in water for 16 hours using 20 mmφ alumina balls in a ball mill, and then dried and granulated by spray drying to obtain a mixed powder. Each of these mixed powders is molded into a 50 × 50 × 20 mm compact by a hydrostatic pressure press of 150 MPa, and then calcined by holding at the firing temperature shown in Table 2 (1550 ° C. to 1675 ° C.) for 2 hours in an air atmosphere. . Further, if necessary, heat treatment is performed at the heat treatment temperature shown in Table 2.
[0026]
The withstand voltage value at 700 ° C. is measured with the apparatus shown in FIG. 1 after processing the sintered body to 15 × 15 × 0.65 mm. The thermal conductivity is measured by a laser flash method according to JIS R-1611 after processing into a shape of φ10 mm × t2 mm. The contents of the Na component, K component, Fe component, and Ti component are quantified in terms of Na 2 O, K 2 O, Fe 2 O 3 , and TiO 2 by chemically analyzing the sintered body.
[0027]
The total number of grain boundaries and pores crossed by the virtual straight line is obtained by mirror-polishing an arbitrary plane of the sintered body, taking a photograph at a magnification of 1000 to 2000 times by SEM observation, and drawing several straight lines on the photograph, The number of grain boundaries and pores crossing the straight line per 100 μm is calculated. These results are shown in Table 3.
[0028]
[Table 1]
[Table 2]
[Table 3]
From the results of Table 3, the total number of grain boundaries and pores virtual straight line crosses 25 or less, and Sample No. is an example of adding 4.5 wt% in terms of oxide of Nd as the rare earth element 8 In the withstand voltage value and 7 1 kV / mm, it can be seen that very good withstand voltage value is obtained.
[0032]
Further, the as in sample No. 15, by further heat treatment at the rare-earth-element-doped systems, it is possible to more effectively improve the withstand voltage value (75kV / mm).
[0033]
On the other hand, it can be seen that Sample No. 1 to Sample No. 3, which are comparative examples, can obtain only a low withstand voltage value of 33 to 42 kV / mm. In sample number 1, the total number of grain boundaries and pores crossed by the imaginary straight line exceeds 50, so the withstand voltage value is as low as 42 kV / mm. In sample number 2, since the content of the Na component is as large as 0.06% by weight, the withstand voltage value is as low as 33 kV / mm. In Sample No. 3, since the total measurement of the Na component, K component, Fe component, and Ti component exceeds 0.3% by weight, the withstand voltage value is as low as 41 kV / mm.
[0034]
From the above results, it is not necessary to add rare earth elements or to adjust the total number of grain boundaries and pores crossed by the imaginary straight line or the contents of Na component, Na component, K component, Fe component and Ti component independently. It can be seen that the voltage resistance at high temperatures around 700 ° C. cannot be improved.
[0035]
【The invention's effect】
According to the present invention, it is possible to provide an alumina-based sintered body having a high insulation property and a high withstand voltage at a high temperature around 700 ° C. and a method for producing the same. According to the spark plug insulator and the manufacturing method thereof using these, even a thin product such as a small-diameter plug can exhibit excellent insulation and voltage resistance.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of an evaluation method of withstand voltage used in the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1
Claims (3)
（ａ）該アルミナ基焼結体１００重量％に含まれる該Ｎａ成分、該Ｋ成分、該Ｆｅ成分、該Ｔｉ成分の酸化物換算による含有量が０．１２〜０．３重量％、且つ、該Ｎａ成分の酸化物換算による含有量が０．０２〜０．０５重量％、
（ｂ）該アルミナ基焼結体の任意の断面に長さ１００μｍの仮想直線を引いた場合において、該仮想直線が横切る粒界及び気孔の合計数が５０個以下、
を具備し、
該アルミナ基焼結体１００重量％に希土類元素としてＮｄ、Ｐｒ、Ｄｙ、Ｌａを酸化物換算で１〜４．５重量％含む高耐電圧性アルミナ基焼結体を用いたことを特徴とするスパークプラグ用絶縁碍子。 An alumina-based sintered body containing at least one of a Na component, a K component, a Fe component, and a Ti component, and further comprising the following structural requirements (a) and (b )
(A ) The content of the Na component, the K component, the Fe component, and the Ti component contained in 100% by weight of the alumina-based sintered body in terms of oxides is 0.12 to 0.3% by weight, and Content of the Na component in terms of oxide is 0.02 to 0.05 % by weight,
(B) When a virtual straight line having a length of 100 μm is drawn on an arbitrary cross section of the alumina-based sintered body, the total number of grain boundaries and pores crossed by the virtual straight line is 50 or less ,
Comprising
A high voltage-resistant alumina-based sintered body containing 1 to 4.5% by weight of Nd, Pr, Dy, and La as rare earth elements in 100% by weight of the alumina-based sintered body is used. Insulator for spark plug.
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| JP22079499A JP4780628B2 (en) | 1999-08-04 | 1999-08-04 | Insulator for spark plug and manufacturing method thereof |
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| JP22079499A JP4780628B2 (en) | 1999-08-04 | 1999-08-04 | Insulator for spark plug and manufacturing method thereof |
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| JP4780628B2 true JP4780628B2 (en) | 2011-09-28 |
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| DE10132888A1 (en) * | 2001-07-06 | 2003-01-30 | Bosch Gmbh Robert | Alumina product, especially for use as a spark plug insulator |
| JP4690230B2 (en) * | 2006-03-16 | 2011-06-01 | 日本特殊陶業株式会社 | Spark plug for internal combustion engine and method for manufacturing the same |
| JP5775544B2 (en) * | 2013-05-09 | 2015-09-09 | 日本特殊陶業株式会社 | Spark plug insulator and spark plug |
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| JPS56149319A (en) * | 1980-04-18 | 1981-11-19 | Sumitomo Alum Smelt Co Ltd | Manufacture of low-soda alumina |
| JPS62187156A (en) * | 1986-02-12 | 1987-08-15 | 株式会社デンソー | Manufacture of high insulation high alumina ceramic composition |
| JP3345495B2 (en) * | 1993-12-22 | 2002-11-18 | 太平洋セメント株式会社 | Manufacturing method of high voltage insulator |
| JPH09315849A (en) * | 1996-05-28 | 1997-12-09 | Ngk Spark Plug Co Ltd | Alumina sintered body or insulator for spark plug and method for manufacturing the same |
| JP3872586B2 (en) * | 1997-12-27 | 2007-01-24 | 日本特殊陶業株式会社 | Insulating material for spark plug and spark plug using the same |
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