JP3701046B2

JP3701046B2 - Manufacturing method of ceramic heater

Info

Publication number: JP3701046B2
Application number: JP12667495A
Authority: JP
Inventors: 保幸佐藤; 敦倉野; 郁也安藤; 勝則山田; 信雄神谷
Original assignee: Denso Corp; Toyota Central R&D Labs Inc
Current assignee: Denso Corp; Toyota Central R&D Labs Inc
Priority date: 1995-05-25
Filing date: 1995-05-25
Publication date: 2005-09-28
Anticipated expiration: 2020-09-28
Also published as: JPH08321376A

Description

【０００１】
【産業上の利用分野】
本発明はセラミックヒータの製造方法に関し、例えば、ディーゼルエンジンのセラミックグロープラグ等に用いられるセラミックヒータの製造方法に適用されるものである。
【０００２】
【従来の技術】
導電性セラミック部材又は高融点金属部材を含む電気抵抗体からなる発熱体を窒化珪素質電気絶縁性セラミック部材からなる棒状の基体内に埋設又は基体表面に配置し、発熱体の両端にその先端が個別に接続される一対の高融点金属部材からなる電極線を基体に埋設したセラミックヒータは、焼成時に電極線とセラミックの境界部で反応が進み、焼成後に基体と電極線に比べて熱膨張係数が大きく、厚い反応生成物層が形成される。そして、使用時の高温環境及び冷熱繰り返しを受けることにより、この反応生成物層にはその熱膨張係数差によりクラックが発生し、そのクラックがセラミックヒータの表面まで進展し、クラックを通して酸素が供給され断線等の不具合に至ることが知られている。その解決のため特開平１−１５７０８４号公報には抵抗線の表面に、抵抗線の構成金属元素と同一金属元素の金属粉末またはその窒化物、炭化物、珪化物、珪化炭化物などの非酸化物セラミック粉末をペースト状にして被着し、窒化珪素質粉末の成形体中に埋設してホットプレス焼成することにより、反応生成物層の形成を抑制する方法が提案されている。
【０００３】
上記方法においては、高融点金属線の表面にペーストを均一にかつ全面に塗布することは難しく、さらに、成形体中に埋設するための電極線の搬送時および成形時の圧力等により塗布層が剥離を起こす場合がある。その結果焼成時に塗布層の剥離部分で反応生成物層が形成され、信頼性が劣るものがある。また、剥離の発生を防ぐため、製造にあたって細心の注意が必要とされ、生産性が悪くなるという問題点がある。
【０００４】
【発明が解決しようとする課題】
本発明は、上記問題点を鑑みてなされたものであり、窒化珪素質等の電気絶縁性セラミック部材に埋設された電極線とセラミックの焼成時の反応を容易に抑制できる構成とし、信頼性が高く、かつ、生産性の良いセラミックヒータの製造方法を提供するものである。
【０００５】
【課題を解決するための手段】
そこで、請求項１は、電気絶縁性セラミック部材（代表的には窒化珪素質電気絶縁性セラミック部材）からなる基体と、基体内に埋設又は基体表面に配置される発熱体と、一対の電極線とを備え、両電極線は発熱体に個別に接続されるセラミックヒータの製造方法において、電極線の周囲面に浸炭処理による浸炭層を形成した後、電極線をセラミックヒータの成形体中に埋設し、焼成する製造方法を採用するものである。
【０００６】
また請求項２は、電極線の引き抜き細径化加工を行う時に少なくともカーボンを含有する潤滑剤を用いて電極線の周囲面に潤滑剤よりなる層を形成し、該電極線をセラミックヒータの成形体中に埋設し、焼成する製造方法を採用するものである。
また請求項３は、電極線の周囲面にＲｈ，Ｒｕ，Ｉｒから選ばれる１種以上の高融点貴金属の層を形成し、該電極線をセラミックヒータの成形体中に埋設し、焼成する製造方法を採用するものである。
【０００７】
【作用および効果】
第１の発明の浸炭処理による浸炭層は電極線と強固な一体構造となっており、電極線をセラミックヒータの成形体中に埋設する時にも剥離等の配慮が不要になり生産性が非常に良くなる。さらに、浸炭層では浸炭処理時および焼成時にタングステンなどの電極材料とカーボンの化合物が形成され、焼成時の雰囲気下において、電極線とセラミックの反応に対する保護層の役割を確実に果たす。その結果、焼成時に電極線とセラミックの境界部での反応生成物の形成が大幅に抑制され、電極線の周囲面における反応生成物の形成量は極めて僅かになり、高い信頼性が得られる。
【０００８】
第２の発明の潤滑剤よりなる層は電極線に固着しており、電極線をセラミックヒータの成形体中に埋設する時にも剥離等は起こらず生産性が非常に良くなる。さらに、焼成時の昇温過程で、潤滑剤は炭化し、生成したカーボンはタングステンなどの電極材料と化合物を形成し、焼成時の雰囲気下において、電極線とセラミックの反応に対する保護層の役割を確実に果たす。その結果、焼成時に電極線とセラミックの境界部での反応生成物の形成が大幅に抑制され、電極線の周囲面における反応生成物の形成量は極めて僅かになり、高い信頼性が得られる。
【０００９】
第３の発明のごとく、Ｒｈ，Ｒｕ，Ｉｒから選ばれる１種以上の高融点貴金属の層は電極線に固着しており、電極線をセラミックヒータの成形体中に埋設する時にも剥離等は起こらず生産性が非常に良くなる。さらに、上記層は焼成時の雰囲気下において、電極線とセラミックの反応に対する保護層の役割を確実に果たす。その結果、焼成時に電極線とセラミックの境界部での反応生成物の形成が大幅に抑制され、電極線の周囲面における反応生成物の形成量は極めて僅かになり、高い信頼性が得られる。
【００１０】
以上、第１の発明または第２の発明または第３の発明を採用することにより、生産性が良く、信頼性の高いセラミックヒータを提供することができる。
【００１１】
【実施例】
以下、本発明を具体的実施例により説明する。
（実施例１）
図１は第１の発明のセラミックヒータ１の実施例を示した断面図である。
このセラミックヒータ１は、丸棒状の基体３と、基体３の先端部に埋設されるＵ字状の発熱体２と、基体３の基端部及び中央部に埋設される電極線４，５とからなる。
【００１２】
基体３は、Ｓｉ₃Ｎ₄からなる絶縁性セラミック粉末に、ＭｏＳｉ₂からなる導電性セラミック粉末を少量分散させた断面円形の絶縁性セラミック焼結体からなる。
発熱体２は、ＭｏＳｉ₂からなる導電性セラミック粉末と、Ｓｉ₃Ｎ₄からなる絶縁性セラミック粉末とを含む断面略半円形の導電性セラミック焼結体である。
【００１３】
電極線４，５の基端部は基体３の外周に露出して部分円筒面４ｂ，５ｂとなっており、それらの先端部は発熱体２に接続され、電気的に導通されている。電極線４，５は、高融点金属であるタングステン、モリブデンまたはその合金からなるが、ここでは断面円形のタングステン線とされている。部分円筒面４ｂ，５ｂの曲率半径は基体３の半径に等しくされている。
【００１４】
本実施例において重要な点は、電極線４，５の表面に浸炭処理による浸炭層４ａ，５ａが形成されている点にある。
以下、本発明の作用効果を表わす試験結果を説明する。ただし、発熱体２は小粒径の二珪化モリブデン（ＭｏＳｉ₂）３０重量％と大粒径の窒化珪素（Ｓｉ₃Ｎ₄）７０重量％の合計１００重量％に対して焼結助剤としてＹ₂Ｏ₃１０重量％とし、基体３は小粒径の二珪化モリブデン（ＭｏＳｉ₂）３０重量％と小粒径の窒化珪素（Ｓｉ₃Ｎ₄）７０重量％の合計１００重量％に対して焼結助剤としてＹ₂Ｏ₃１０重量％とし、基体３の直径は３．５mm、長さは４５mmとされ、発熱体２は半径が１．２mmの半円形とされ、電極線４，５の直径は０．４mmとされている。電極線４，５は、電極線をカーボン粉末に埋設し、非酸化雰囲気で９００℃に放置して浸炭処理を行い、浸炭厚さは高温での放置時間の長さにより調整した。
【００１５】
前記発熱体材料、支持体材料は、各々、エタノールを溶剤としてボールミルにて２４時間混合したのち、可塑剤、結合剤を添加し、更に混練を行った後、一対のタングステン線をセットした型内にＵ字状に発熱体を射出成型し、その後、タングステン線と発熱体が一体となったものの全周部に支持体を射出成型することによりセラミックヒータの成型体を作る。焼成は、アルゴン雰囲気１気圧で、加圧力は５００kgf ／cm²とし、焼成温度は１７００℃で実施した。
【００１６】
そして、このセラミックヒータに図示しない電力供給用のリード線を部分円筒面４ｂ，５ｂにロウ付けで接合し、通電発熱できるようにした。
試験は、電極線４，５に大きな熱応力が発生しやすいよう冷熱試験を行った。条件は、高温条件として、前記セラミックヒータの通電がＯＮ（ヒータの最高温度は１３００℃）の状態で１分、低温条件として、前記セラミックヒータの通電がＯＦＦでファンによる強制冷却（ヒータ温度は５０℃以下まで冷却）の状態で１分実施するサイクルを、２００００サイクル実施した。
【００１７】
この後、基体３表面のクラックの有無を調査した。その結果を表１に示す。さらに、表１には各試験品の反応生成層（分析によるとタングステン内にＳｉの侵入が認められる）の厚さも記してある。
浸炭処理を施さないものは、反応生成層厚さが５０ミクロンあり、４本中３本にクラックが発生し、浸炭層厚さ１ミクロンのものは、反応生成層厚さが３０ミクロンあり、４本中１本にクラックが発生した。しかし、浸炭層厚さ２ミクロン以上のものは、反応生成層厚さも最大２０ミクロンと小さく、クラックの発生もない。従って、表１の結果より浸炭層厚さを２ミクロン以上とすることにより、信頼性が大幅に向上することが分かる。なお、浸炭層厚さは、タングステン内に珪素（Ｓｉ）の侵入している部分の厚さを表わし、９０°間隔で４ヶ所の厚さを測定し、その平均値をもって浸炭層厚さとした。
【００１８】

（実施例２）
第２の発明は電極線にカーボンを含有する潤滑剤の表面層を形成したものであり、その他の部分の構成は第１の発明と同じである。潤滑剤の表面層の形成方法を以下に記す。タングステンの電極線は焼結等によりインゴットがつくられ、鍛造によりφ２０〜３０mmの丸棒が作られ、その後、引抜き細径化加工を繰り返すことによりφ０．４mmの電極線が作られる。そして、表面層を形成するため、細径化加工毎にカーボンの微粉を潤滑剤として用いる。その結果、カーボンの微粉がタングステン線の表面に強固に固着した表面層となる。
【００１９】
第２の発明品についても第１の発明品と同じ試験を行った。その結果を表２に示す。
表２より、第２の発明品は反応生成層の厚さが１５ミクロンと小さく、クラックの発生も無く、信頼性が大幅に向上することが分かる。

（実施例３）
第３の発明は電極線に高融点貴金属であるＲｈ，Ｒｕ，Ｉｒのメッキ層を形成したものであり、その他の部分の構成は第１の発明と同じである。
【００２０】
第３の発明品についても第１の発明品と同じ試験を行った。その結果を表３に示す。
メッキ無品は、反応生成層の厚さが５０ミクロンあり、４本中３本にクラックが発生し、Ｒｕメッキを施したものはクラックの発生がなく、メッキ厚さを厚くするほど反応生成層厚さも小さくなる。又、Ｒｈメッキ、Ｉｒメッキについても試験したが同様な効果が得られた。以上、表２の結果より高融点貴金属のメッキを施すことにより、信頼性が大幅に向上することが分かる。
【００２１】
第３の発明については高融点貴金属の表面層をスパッタリングで形成したものでも評価したが良好な結果となった。従って、タングステンに高融点貴金属の表面層が形成されていれば、反応生成層の形成が抑制され、信頼性の高いものになることが分かる。

以上、第１の発明、第２の発明、第３の発明について述べたが、次に、本発明品が、非酸化物セラミック粉末をペースト状にして電極線に被着した従来技術品に比べて優れている試験結果について説明する。本発明品として、浸炭層厚さ５ミクロン品を、従来技術品として、ＷＣ粉末をペースト状にして電極線に被着したものでヒータを製造し、前述の評価を実施した。その結果を表４に示す。
【００２２】
本発明品は、反応生成層厚さは最大１５ミクロンであり、１００本中クラック発生が認められなかったのに対して、従来技術品は、反応生成層厚さが本発明品と同じ１５ミクロンであるが、１００本中５本にクラックが発生した。そこで、クラックの発生した試料を分解調査した結果、クラックの発生した内部の電極線からはＷＣが検出されない部分があり、かつ、その部分には５０ミクロン近い反応生成層が形成されていた。従って、本発明の方法によれば、信頼性と生産性が大幅に向上することが分かる。
【００２３】

本発明のように信頼性と生産性に優れるセラミックヒータは、グロープラグの発熱部、酸素センサのヒータ等高耐熱性が要求される部分への適用が特に有効である。また、第１の発明、第２の発明、第３の発明の表面層はタングステン線の全面に形成してもよく、高温になる部分のみに形成してもよい。また、電気絶縁性セラミック部材からなる基体の形状は、棒状であっても、それ以外の形状であってもよい。
【図面の簡単な説明】
【図１】本発明の実施例であるセラミックヒータの断面図である。
【符号の説明】
１…セラミックヒータ
２…発熱体
３…基体
４…電極線
５…電極線[0001]
[Industrial application fields]
The present invention relates to a method for manufacturing a ceramic heater, and is applied to a method for manufacturing a ceramic heater used for, for example, a ceramic glow plug of a diesel engine.
[0002]
[Prior art]
A heating element made of an electric resistor including a conductive ceramic member or a refractory metal member is embedded in a rod-shaped base made of a silicon nitride-based electrically insulating ceramic member or arranged on the surface of the base, and the tips of both ends of the heating element are A ceramic heater in which an electrode wire made of a pair of refractory metal members that are individually connected is embedded in the substrate, the reaction proceeds at the boundary between the electrode wire and the ceramic during firing, and the coefficient of thermal expansion compared to the substrate and electrode wire after firing. And a thick reaction product layer is formed. Then, by receiving high temperature environment and repeated cooling at the time of use, cracks are generated in the reaction product layer due to the difference in thermal expansion coefficient, the cracks propagate to the surface of the ceramic heater, and oxygen is supplied through the cracks. It is known to lead to problems such as disconnection. In order to solve this problem, Japanese Patent Application Laid-Open No. 1-157084 discloses a non-oxide ceramic such as a metal powder of the same metal element as the constituent metal element of the resistance wire or a nitride, carbide, silicide, silicide carbide, etc. A method has been proposed in which the powder is deposited in a paste form, embedded in a molded body of silicon nitride powder, and subjected to hot press firing to suppress the formation of a reaction product layer.
[0003]
In the above method, it is difficult to apply the paste uniformly and entirely on the surface of the refractory metal wire, and further, the coating layer is formed by the pressure at the time of transporting and forming the electrode wire for embedding in the molded body. May cause peeling. As a result, a reaction product layer is formed at the peeled portion of the coating layer during firing, and the reliability is inferior. In addition, in order to prevent the occurrence of peeling, careful attention is required in production, and there is a problem that productivity is deteriorated.
[0004]
[Problems to be solved by the invention]
The present invention has been made in view of the above problems, and has a configuration that can easily suppress a reaction during firing of an electrode wire embedded in an electrically insulating ceramic member such as silicon nitride and ceramic and has high reliability. The present invention provides a method for producing a ceramic heater that is high and has high productivity.
[0005]
[Means for Solving the Problems]
Accordingly, the first aspect of the present invention provides a base made of an electrically insulating ceramic member (typically a silicon nitride-based electrically insulating ceramic member), a heating element embedded in the base or disposed on the surface of the base, and a pair of electrode wires. In a method of manufacturing a ceramic heater in which both electrode wires are individually connected to a heating element, after forming a carburized layer by carburizing treatment on the peripheral surface of the electrode wires, the electrode wires are embedded in a ceramic heater molded body Then, the manufacturing method for firing is adopted.
[0006]
According to a second aspect of the present invention, a layer made of a lubricant is formed on the peripheral surface of the electrode wire by using a lubricant containing at least carbon when the electrode wire is drawn and thinned, and the electrode wire is formed into a ceramic heater. A manufacturing method of embedding and firing in the body is adopted.
According to a third aspect of the present invention, at least one refractory metal layer selected from Rh, Ru and Ir is formed on the peripheral surface of the electrode wire, and the electrode wire is embedded in a ceramic heater molded body and fired. The method is adopted.
[0007]
[Action and effect]
The carburized layer formed by the carburizing process of the first invention has a strong integrated structure with the electrode wire, and even when the electrode wire is embedded in the molded body of the ceramic heater, consideration such as peeling is not required and productivity is very high. Get better. Further, in the carburized layer, an electrode material such as tungsten and a carbon compound are formed at the time of carburizing treatment and firing, and the role of a protective layer against the reaction between the electrode wire and the ceramic is surely performed in the atmosphere during firing. As a result, formation of the reaction product at the boundary between the electrode wire and the ceramic during firing is significantly suppressed, and the amount of reaction product formed on the peripheral surface of the electrode wire is extremely small, thereby obtaining high reliability.
[0008]
The layer made of the lubricant of the second invention is fixed to the electrode wire, and even when the electrode wire is embedded in the molded body of the ceramic heater, peeling does not occur and the productivity becomes very good. Furthermore, the lubricant is carbonized during the heating process during firing, and the generated carbon forms a compound with an electrode material such as tungsten, and serves as a protective layer against the reaction between the electrode wire and the ceramic in the firing atmosphere. Surely fulfill. As a result, formation of the reaction product at the boundary between the electrode wire and the ceramic during firing is significantly suppressed, and the amount of reaction product formed on the peripheral surface of the electrode wire is extremely small, thereby obtaining high reliability.
[0009]
As in the third aspect of the invention, one or more refractory noble metal layers selected from Rh, Ru, and Ir are fixed to the electrode wire, and even when the electrode wire is embedded in a ceramic heater molded article, peeling or the like is not caused. Productivity is greatly improved without happening. Furthermore, the above layer reliably plays the role of a protective layer against the reaction between the electrode wire and the ceramic in the atmosphere during firing. As a result, formation of the reaction product at the boundary between the electrode wire and the ceramic during firing is significantly suppressed, and the amount of reaction product formed on the peripheral surface of the electrode wire is extremely small, thereby obtaining high reliability.
[0010]
As described above, by adopting the first invention, the second invention, or the third invention, it is possible to provide a ceramic heater with high productivity and high reliability.
[0011]
【Example】
Hereinafter, the present invention will be described with reference to specific examples.
(Example 1)
FIG. 1 is a sectional view showing an embodiment of a ceramic heater 1 of the first invention.
The ceramic heater 1 includes a round bar-shaped base body 3, a U-shaped heating element 2 embedded in a distal end portion of the base body 3, and electrode wires 4 and 5 embedded in a base end portion and a central portion of the base body 3. Consists of.
[0012]
The substrate 3 is made of an insulating ceramic sintered body having a circular cross section in which a small amount of conductive ceramic powder made of MoSi ₂ is dispersed in insulating ceramic powder made of Si ₃ N ₄ .
The heating element 2 is a conductive ceramic sintered body having a substantially semicircular cross section including a conductive ceramic powder made of MoSi ₂ and an insulating ceramic powder made of Si ₃ N ₄ .
[0013]
The base end portions of the electrode wires 4 and 5 are exposed to the outer periphery of the base 3 to form partial

cylindrical surfaces

4b and 5b, and the tip ends thereof are connected to the heating element 2 and are electrically connected. The electrode wires 4 and 5 are made of tungsten, molybdenum, or an alloy thereof, which is a refractory metal, but here are tungsten wires having a circular cross section. The curvature radii of the partial

cylindrical surfaces

4 b and 5 b are set equal to the radius of the base 3.
[0014]
The important point in the present embodiment is that carburized layers 4a and 5a are formed on the surfaces of the electrode wires 4 and 5 by carburizing treatment.
Hereinafter, test results representing the effects of the present invention will be described. However, the heating element 2 is Y as a sintering aid for a total of 100% by weight of 30% by weight of molybdenum disilicide (MoSi ₂ ) having a small particle size and 70% by weight of silicon nitride (Si ₃ N ₄ ) having a large particle size. ₂ O _{3 is} 10% by weight, and the substrate 3 is fired for a total of 100% by weight of 30% by weight of small particle size molybdenum disilicide (MoSi ₂ ) and 70% by weight of small particle size silicon nitride (Si ₃ N ₄ ). The binder is 10% by weight of Y ₂ O ₃ , the substrate 3 has a diameter of 3.5 mm and a length of 45 mm, the heating element 2 has a semicircular shape with a radius of 1.2 mm, and the electrode wires 4 and 5 The diameter is 0.4 mm. For the electrode wires 4 and 5, the electrode wires were embedded in carbon powder and left at 900 ° C. in a non-oxidizing atmosphere to perform carburizing treatment, and the carburized thickness was adjusted according to the length of the standing time at high temperature.
[0015]
Each of the heating element material and the support material was mixed in a ball mill using ethanol as a solvent for 24 hours, added with a plasticizer and a binder, kneaded, and then set in a mold in which a pair of tungsten wires were set. Then, a heating element is injection-molded into a U-shape, and then a support body is injection-molded on the entire periphery of the tungsten wire and the heating element integrated together to form a ceramic heater molded body. Firing was performed at 1 atm in an argon atmosphere, a pressing force of 500 kgf / cm ² , and a firing temperature of 1700 ° C.
[0016]
Then, a power supply lead wire (not shown) is joined to the partial

cylindrical surfaces

4b and 5b by brazing the ceramic heater so that energization heat can be generated.
In the test, a cold heat test was performed so that a large thermal stress was easily generated on the electrode wires 4 and 5. The high temperature condition is 1 minute when the ceramic heater is energized (maximum heater temperature is 1300 ° C.), and the low temperature condition is that the ceramic heater is off and forced cooling by the fan (heater temperature is 50 A cycle that was carried out for 1 minute in a state of (cooled to below ℃) was carried out 20000 cycles.
[0017]
Thereafter, the presence or absence of cracks on the surface of the substrate 3 was investigated. The results are shown in Table 1. Further, Table 1 also shows the thickness of the reaction product layer of each test product (according to analysis, Si intrusion is recognized in tungsten).
Those not subjected to carburizing treatment had a reaction product layer thickness of 50 microns, cracks occurred in three of the four, and those having a carburization layer thickness of 1 micron had a reaction product layer thickness of 30 microns. Cracks occurred in one of the books. However, when the thickness of the carburized layer is 2 microns or more, the reaction product layer thickness is as small as 20 microns at the maximum, and no cracks are generated. Therefore, it can be seen from the results of Table 1 that the reliability is greatly improved by setting the thickness of the carburized layer to 2 microns or more. The thickness of the carburized layer represents the thickness of the portion where silicon (Si) penetrates into tungsten. The thickness of four places was measured at 90 ° intervals, and the average value was taken as the carburized layer thickness.
[0018]

(Example 2)
In the second invention, a surface layer of a lubricant containing carbon is formed on the electrode wire, and the configuration of the other parts is the same as that of the first invention. A method for forming the surface layer of the lubricant will be described below. The tungsten electrode wire is made into an ingot by sintering or the like, a round bar having a diameter of 20 to 30 mm is made by forging, and then a diameter of φ0.4 mm is made by repeating the drawing and thinning process. And in order to form a surface layer, the fine powder of carbon is used as a lubrication agent for every diameter reduction process. As a result, a surface layer in which fine carbon powder is firmly fixed to the surface of the tungsten wire is obtained.
[0019]
The same test as the first invention product was performed for the second invention product. The results are shown in Table 2.
From Table 2, it can be seen that in the second invention product, the thickness of the reaction product layer is as small as 15 microns, there is no occurrence of cracks, and the reliability is greatly improved.

(Example 3)
In the third invention, a plating layer of Rh, Ru, Ir, which is a high melting point noble metal, is formed on the electrode wire, and the configuration of the other parts is the same as that of the first invention.
[0020]
The same test as that of the first invention product was performed for the third invention product. The results are shown in Table 3.
For the unplated product, the reaction product layer has a thickness of 50 microns, 3 out of 4 cracks occur, and in the case of Ru plating, there is no crack, and the reaction product layer increases as the plating thickness increases. The thickness is also reduced. Further, Rh plating and Ir plating were also tested, and similar effects were obtained. As described above, it can be seen from the results shown in Table 2 that the reliability is greatly improved by plating the high melting point noble metal.
[0021]
The third invention was evaluated even with a surface layer of a refractory noble metal formed by sputtering, but a good result was obtained. Therefore, it can be seen that if a surface layer of a refractory noble metal is formed on tungsten, the formation of the reaction product layer is suppressed and the reliability is high.

The first invention, the second invention, and the third invention have been described above. Next, the product of the present invention is compared with the prior art product in which the non-oxide ceramic powder is pasted to the electrode wire. Explain the test results that are excellent. A heater was manufactured as a product of the present invention by using a carburized layer thickness of 5 microns as a prior art product and applying WC powder as a paste to the electrode wire as a conventional product, and performing the above-described evaluation. The results are shown in Table 4.
[0022]
The product of the present invention has a maximum reaction product layer thickness of 15 microns, and no cracks were observed in 100, whereas the product of the prior art had a reaction product layer thickness of 15 microns, the same as the product of the present invention. However, 5 out of 100 cracks occurred. As a result of disassembling and investigating the cracked sample, there was a portion where WC was not detected from the inner electrode wire where the crack occurred, and a reaction product layer of nearly 50 microns was formed in that portion. Therefore, according to the method of the present invention, it can be seen that reliability and productivity are greatly improved.
[0023]

The ceramic heater excellent in reliability and productivity as in the present invention is particularly effective when applied to a portion requiring high heat resistance such as a heat generating portion of a glow plug and a heater of an oxygen sensor. In addition, the surface layer of the first invention, the second invention, and the third invention may be formed on the entire surface of the tungsten wire, or may be formed only on a portion where the temperature is high. Further, the shape of the base made of the electrically insulating ceramic member may be a rod shape or other shapes.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a ceramic heater according to an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Ceramic heater 2 ... Heat generating body 3 ... Base | substrate 4 ... Electrode wire 5 ... Electrode wire

Claims

A ceramic heater comprising a base made of an electrically insulating ceramic member, a heating element embedded in the base or disposed on the surface of the base, and a pair of electrode wires, both of which are individually connected to the heating element. In the manufacturing method,
A method for manufacturing a ceramic heater, wherein a carburized layer formed by carburizing treatment is formed on a peripheral surface of the electrode wire, the electrode wire is embedded in a ceramic heater molded body, and fired.

A ceramic heater comprising a base made of an electrically insulating ceramic member, a heating element embedded in the base or disposed on the surface of the base, and a pair of electrode wires, both of which are individually connected to the heating element. In the manufacturing method,
The electrode wire is drawn and thinned using a lubricant containing at least carbon, and the electrode wire is embedded in a ceramic heater molded body and fired. Production method.

A ceramic heater comprising a base made of an electrically insulating ceramic member, a heating element embedded in the base or disposed on the surface of the base, and a pair of electrode wires, both of which are individually connected to the heating element. In the manufacturing method, one or more refractory noble metal layers selected from Rh, Ru, and Ir are formed on the surface of the connection portion of the electrode wire to the heating element that becomes high temperature . A method for producing a ceramic heater, wherein the ceramic heater is embedded in a molded body and fired.