JP3963412B2

JP3963412B2 - Heating resistor for ceramic heater, ceramic heater, and method for manufacturing ceramic heater

Info

Publication number: JP3963412B2
Application number: JP32731798A
Authority: JP
Inventors: 一穂立松; 進道渡邉
Original assignee: NGK Spark Plug Co Ltd
Current assignee: NGK Spark Plug Co Ltd
Priority date: 1998-11-17
Filing date: 1998-11-17
Publication date: 2007-08-22
Anticipated expiration: 2018-11-17
Also published as: JP2000156275A

Description

【０００１】
【発明の属する技術分野】
本発明は、セラミックヒータ用発熱抵抗体及びセラミックヒータ並びにセラミックヒータの製造方法に関する。更に詳しく言えば、本発明はディーゼルエンジンのグロープラグ又はその他の加熱に用いられるセラミックヒータ用発熱抵抗体、及びそれを用いたセラミックヒータ、並びにそのセラミックヒータの製造方法に関する。
【０００２】
【従来の技術】
従来はグロープラグ等の１０００℃以上の高温で用いられるセラミックヒータにおいて、Ｗ、Ｍｏ、Ｔｉ、Ｚｒ並びにＨｆの金属、又はこれらの炭化物、窒化物、珪化物等が含有されて、種々の昇温特性（抵抗温度係数等）を持たせたセラミックヒータ用発熱抵抗体を用いたものが知られている。
【０００３】
【発明が解決しようとする課題】
しかし、近年は用途に応じて急速昇温特性や定温発熱特性等を求めることが多くなり、上記昇温特性に適合しないことが多くなってきている。また、上記昇温特性は発熱抵抗体によってほぼ決定されるため、これらの昇温特性とは異なった任意の昇温特性を持つセラミックヒータの作製は難しいことが多かった。更に、これらの抵抗体材料は焼成時に焼結が不十分となったり、過大粒成長が起きやすく、これらによる強度低下を起こしやすかった。
本発明は、このような問題点を解決するものであり、発熱抵抗体の抵抗温度係数を任意に調節することができ、抗折強度及び通電耐久性能に優れるセラミックヒータ用発熱抵抗体及びこれを用いたセラミックヒータ、並びにこのセラミックヒータの製造方法を提供することを目的とする。
【０００４】
【課題を解決するための手段】
本第１発明のセラミックヒータ用発熱抵抗体は、焼結体からなり、ＷＣからなる導電成分と、Ｖの炭化物、Ｖの酸化物、Ｖの窒化物、Ｃｒの炭化物、Ｃｒの酸化物、Ｃｒの窒化物、Ｎｂの酸化物、及びＮｂの窒化物の中から選ばれる１種以上の調整成分用原料から生成する、抵抗温度係数を変化させるための調整成分と、を含有し、上記導電成分及び上記調整成分の合計を１００ｗｔ％とした場合、上記調整成分は０．１〜５．０ｗｔ％であり、上記発熱抵抗体を構成する上記導電成分の結晶粒子の平均粒径は１１μｍ以下であることを特徴とする。
本第３発明のセラミックヒータは、セラミック製基体と、この基体中に埋設され、且つ上記第１発明に示される上記セラミックヒータ用発熱抵抗体とを備えることを特徴とする。
【０００５】
上記「導電成分」は、ＷＣからなる。導電成分は、膨張率が、この発熱抵抗体に含有される他のセラミックス成分（窒化珪素質等）又はセラミック製基材に近ければ近いほど好ましい。また、本セラミックセンサは高温で焼成して形成されるので、融点が高いものほど好ましい。
【０００６】
焼結体中における上記導電成分の結晶粒子の平均粒径は、１１μｍ以下（特に好ましくは１０μｍ以下、更に好ましくは９．５μｍ）である。これが１１μｍを越えると、十分な抗折強度を得ることが難しくなり、且つ通電耐久性能が悪くなるからである。また、この粒径を変化させることによっても、抵抗温度係数を適宜変えることができる。
【０００７】
上記「調整成分」は、Ｖの炭化物、Ｖの酸化物、Ｖの窒化物、Ｃｒの炭化物、Ｃｒの酸化物、Ｃｒの窒化物、Ｎｂの酸化物、及びＮｂの窒化物の中から選ばれる１種以上の調整成分用原料から生成し、抵抗温度係数を変化させる成分である。この調整成分としては、第２又は第３発明に示すように、Ｃｒ_２Ｏ_３、ＶＣ及びＮｂ_２Ｏ_５のうちの少なくとも１種の調整成分用原料から生成するものが好ましい。
【０００８】
また、上記導電成分及び上記調整成分の合計を１００ｗｔ％とした場合の上記調整成分の含有割合は０．１〜５．０ｗｔ％（この場合、単に「％」という。、好ましくは、０．２〜５％、より好ましくは０．２〜４．５％）である。この調整成分の含有割合が、０．１％未満では、焼成での抵抗体材料の焼結性のバラツキが激しく、焼結不十分あるいは逆に過大粒成長を起こしやすく、強度・通電耐久性等の性能が低下するし、５．０％を越えると、発熱抵抗体の耐熱性低下や熱膨張の増加を引き起こし、通電耐久性が低下するため、好ましくないからである。
【０００９】
上記「発熱低抗体」に含有されるセラミック成分又は上記「基体」を構成するセラミック成分としては、目的により種々選択でき、例えば、窒化珪素質、アルミナ、窒化アルミニウム等とすることができる。これらのうち、窒化珪素質が好ましい。この「窒化珪素質」には、窒化珪素を主成分とするものが広く含まれ、窒化珪素のみならず、サイアロン等をも含まれる。更に、通常、焼結助剤（Ｙ、Ｙｂ、Ｅｒ等の各酸化物等）が数ｗｔ％（２〜１０ｗｔ％程度）配合されて焼成されるので、この発熱抵抗体中には、この助剤から由来された成分（化合物等）が含有される。
【００１０】
上記導電成分の上記平均粒径を１１μｍ以下とする場合、抗折強度が１２５０ＭＰａ以上（好ましくは１３００ＭＰａ以上）、及び／又は、１４００℃で一分毎に給電して断線しないサイクル数（以下、「耐久性能」という。）が１０，０００サイクル以上とすることができる。
また、導電成分がＷＣで、調整成分の含有割合が０．１〜５％まで変化させ、且つ上記平均粒径を１１μｍ以下とする場合、発熱抵抗体の抵抗温度係数を２．８〜３．９まで変化させることができる。この場合、あわせて、発熱抵抗体の抗折強度が１２５０ＭＰａ以上、上記耐久性能が１００００サイクル以上とすることができる。
【００１１】
本第４発明のセラミックヒータの製造方法は、導電成分用原料と、焼成後に抵抗温度係数を変化させる調整成分となる調整成分用原料とを含む混合粉末を調製し、該混合粉末を用いて発熱抵抗体形状の成形体を得、その後、該成形体をセラミック粉末からなる基体用原料中に埋入させ、一体に成形してセラミック成形体とし、次いで、焼成するセラミックヒータの製造方法であって、
上記導電成分用原料は、ＷＣからなり、上記調整成分用原料は、Ｖの炭化物、Ｖの酸化物、Ｖの窒化物、Ｃｒの炭化物、Ｃｒの酸化物、Ｃｒの窒化物、Ｎｂの酸化物、及びＮｂの窒化物の中から選ばれる１種以上からなり、上記導電成分用原料及び上記調整成分原料の合計を１００ｗｔ％とした場合、上記調整成分原料は０．１〜５．０ｗｔ％であり、上記成形体が焼成されて得られる発熱抵抗体を構成する導電成分の結晶粒子の平均粒径が１１μｍ以下であることを特徴とする。
【００１２】
上記「導電成分用原料」は、上記に示すように、ＷＣからなる。また、前記の「導電成分」の説明おいて示すと同様に、この膨張率が他のセラミックス成分（窒化珪素質等）又はセラミック製基材に近いものが好ましく、また、融点が高いものほど好ましい。
更に、この導電成分用原料の粉末粒子径は、焼成後の焼結体中の導電成分の結晶粒子径が１１μｍ以下となるようなものであれば良く、例えば、この粉末粒子径を１．８μｍ以下（特に０．５μｍ以上）、好ましくは０．５〜１．５μｍ、より好ましくは０．５〜１．２μｍとすることができる。特に、この粉末粒子径を１．８μｍ以下（特に０．５μｍ以上）とすることにより、導電成分の結晶粒子径を１１μｍ以下とすることができ、この粉末粒子径を１．５μｍ以下（特に０．５μｍ以上）とすることによりこの結晶粒子径を１０μｍ以下（特に０．５μｍ以上）、粉末粒子径を１．２μｍ以下（特に０．５μｍ以上）とすることにより結晶粒子径を５μｍ以下（特に４μｍ以下）とすることができる。
【００１３】
また、上記「調整成分用原料」は、焼結後のセラミック用発熱抵抗体にて抵抗温度係数を調整することとなるものであり、配合量が０．５％以上の配合により強度及び耐久性能を大きく低下させるようなものでないものであればよい。この具体例としては、（１）ＶＣ、Ｖ₂Ｏ₅、ＶＮ、（２）Ｃｒ₃Ｃ₂、Ｃｒ₂Ｏ₃ _、ＣｒＮ_、（３）ＮｂＮ等を挙げることができる。
【００１４】
また、上記調整成分原料の配合量は、前記の調整成分の説明において示すと同様に、０．１〜５．０％（好ましくは０．２〜５．０％、より好ましくは０．２〜４．５％）である。これが０．１％未満では、焼成での抵抗体材料の焼結性のバラツキが激しく、焼結不十分あるいは逆に過大粒成長を起こしやすく、強度・通電耐久性等の性能が低下するし、５．０％を越えると、発熱抵抗体の耐熱性低下や熱膨張の増加を引き起こし、通電耐久性が低下するため、好ましくないからである。
【００１５】
また、所定の成形体を埋設する上記「セラミック粉末材料」又は上記「基体用原料」の種類としては、目的により種々選択できるが、前記に示すように、通常、窒化珪素質のセラミック粉末材料が用いられる。この「窒化珪素質」の意味は前記に示す通りであり、また焼結助剤が前記に示すように適宜用いられる。
更に、上記の各原料粉末の形態は特に限定されず、単なる粉末品でも、造粒品でも、破砕品等であってもよいし、その粒径も特に限定されない。
【００１６】
【作用】
セラミックヒータ用発熱抵抗体において、上記調整成分の一部又は全部が上記導電成分の結晶粒子内に固溶される。そして、調整成分用原料の配合量を多くして焼成させれば、このセラミックヒータ内に含有される調整成分の量、ひいては、この調整成分が固溶される量が多くなり、それに従って、抵抗温度係数が小さくなる（表１参照）。従って、上記調整成分を上記導電成分に任意の割合で含有させることで、本発熱抵抗体の抵抗温度係数を任意に設定することができる。
尚、この調整成分は、上記導電成分の結晶粒子内に固溶されるのみならず、その一部は、粒界相に種々の化合物となって偏析する。この粒界に偏析する上記調整成分においても本発熱抵抗体の抵抗温度特性の変化に影響を与えると思われるが、固溶したとき程の大きな影響は生じないと考えられる。
【００１７】
また、焼結体である発熱低抗体を構成する導電成分の平均粒子径を所定大きさ以下にすることにより、抗折強度及び耐久性能に優れたものとすることができるし、更に、抵抗温度係数をも調整できる。
また、上記調整成分は少量の添加で大きな効果が得られるため、上記調整成分の添加が本発熱抵抗体の抵抗温度係数以外の諸特性（例えば、強度、耐熱性、耐熱衝撃性及び密着性等）に悪影響を与えることは少ない。
【００１８】
【発明の実施の形態】
以下、本発明のセラミックヒータ及びセラミックヒータの製造方法を実施例によって詳細に説明する。
（１）セラミックヒータの作製
導電成分用原料としてのＷＣ粉末、所定量の調整用成分用原料（ＶＣ粉末、Ｃｒ₃Ｏ₂粉末、Ｎｂ₂Ｏ₅粉末、表１及び表２参照）と、絶縁用セラミック粉末（Ｓｉ₃Ｎ₄粉末）３４ｗｔ％（以下、単に「％」という。）と、焼結助剤（Ｙｂ₂Ｏ₃又はＥｒ₂Ｏ₃）６％を配合する。この場合、ＷＣ粉末と所定量の調整用成分用原料の合計量を６０％とする。これらを７２時間湿式で混合した。その後、乾燥させて混合粉末を得、この混合粉末とバインダーとを混練機に投入し、４時間混練した。次いで、この混練物を裁断してペレット状とし、これを射出成型機に投入して、タングステン製のリード線が両端に嵌合されたＵ字状の未焼結ヒータ本体を得た。
【００１９】
【表１】

【００２０】
【表２】

【００２１】
一方、Ｓｉ₃Ｎ₄粉末に焼結助剤粉末（約６％）を配合し、４０時間湿式混合したものをスプレードライヤー法によって造粒し、この造粒物中に上記未焼結ヒータ本体を埋入した後、これらを一体にプレスを行い未焼結セラミックヒータを得た。次いで、この未焼結セラミックヒータを６００℃、約２時間で仮焼してバインダーを除去し、仮焼体を得た。その後、この仮焼体をホットプレス用カーボン型にセットし、窒素雰囲気下、表１及び表２に示す焼成温度及び焼成時間でホットプレス焼成し、セラミックヒータを作製した。尚、導電成分の粒径は、導電成分用原料（本実施例ではＷＣ粉末）の粒径を変えることで調節した。表１及び表２において、使用した各ＷＣ粉末の平均粒径は、（１）Ｎｏ．１〜８、１７、１９〜２０（表１参照）、Ｎｏ．１（表２参照）の場合０．６μｍ、（２）Ｎｏ．９〜１６、１８、２１〜２２（表１参照）、Ｎｏ．２（表２参照）の場合１．０μｍ、（３）Ｎｏ．３〜４（表２参照）の場合１．５μｍ、（４）Ｎｏ．５〜６（表２参照）の場合２．０μｍである。
【００２２】
（２）セラミックヒータの構成
上記製造方法で作製したセラミックヒータ２を図２に示す。また、本セラミックヒータ２を用いたグロープラグ１を図１に示す。
このグロープラグ１は、発熱する部位となる先端側にセラミックヒータ２を備える。また、このセラミックヒータ２は、基体２１と、発熱抵抗体２２と、給電部２３ａ、２３ｂとを備える。
【００２３】
基体２１はＳｉ₃Ｎ₄を主としたセラミックスであり、埋設される発熱抵抗体２２、及び給電部２３ａ、２３ｂを保護する。また、発熱抵抗体２２はＵ字形の棒状体であり、基体２１内に埋設される形で配設されている。更に、この発熱抵抗体２２は、導電成分、抵抗温度係数を調節するための調整成分、及び絶縁成分であるセラミック成分を含有している。
また、給電部２３ａ、２３ｂは図２に示すように、セラミックヒータ２外から供給される電力を基体２１内の発熱抵抗体２２へ給電できるように、各一端は基体２１の表面に配設され、各他端は発熱抵抗体２２の各端部に接続されている。
【００２４】
（３）セラミックヒータの評価
上記により作製された各セラミックヒータにおいて、その発熱抵抗体（発熱部）の抗折強度及び抵抗温度係数と、通電耐久試験とを行い、その結果を表１及び表２に示した。
上記抗折強度は、３点曲げ強さ試験（スパン；２０ｍｍ、クロスヘッドスピード；０．５ｍｍ／秒）によって求めた。上記抵抗温度係数は、１０００℃と２５℃での各発熱抵抗体の抵抗値の比である。上記通電耐久試験は、通電によって最高となる温度部位の飽和温度（２０秒程度で飽和する）が１４００℃となる電圧を印加した後、印加を止めて一分間放置することを１サイクルとし、断線するまでのサイクル数を測定した。上記導電成分の結晶粒子径は、電子顕微鏡写真によって求めた。
【００２５】
表１の結果によれば、調整成分を含有しない比較例の場合（Ｎｏ．１７、１８）は、強度が各々１１８０ＭＰａ、１１７０ＭＰａと小さく、また、耐久性能も、各々１５００サイクル、１２００サイクルで断線した。また、この調整成分の含有量が６．２〜８．０％と多い場合（Ｎｏ．１９〜２２）は、抗折強度は優れるものの、耐久性能が１０００〜２２００サイクルで断線した。
一方、調整成分の粒子径が１．４〜３．８μｍであって、調整成分の含有量が０．２〜４．３％である実施例の場合（Ｎｏ．１〜１６）は、抗折強度が１２９０〜１３４０ＭＰａと大きく、しかも耐久性能はいずれも１００００サイクルでも断線せず、極めて優れた耐久性能を示した。更に、導電成分をＷＣとした場合の抵抗温度係数を、その調整成分の含有量（０．２〜４．３％）に従って、３．７〜２．９の範囲で適宜調整できた。
【００２６】
調整成分の結晶粒子径の大きさの効果を検討した表２によれば、この平均粒径が各々１２．５μｍ、１５．４μｍの比較例の場合（Ｎｏ．５、６）は、抗折強度が各々１２１０ＭＰａ、１０８０ＭＰａと小さく、また、耐久性能は、各々１２００サイクル、８００サイクルで断線し、著しく悪かった。
一方、調整成分の粒子径が１．５〜９．４μｍの実施例の場合（Ｎｏ．１〜４）は、その順に従って抗折強度が僅かに低下するものの、１３００〜１３４０ＭＰａと大きく、しかも耐久性能はいずれも１００００サイクルでも断線せず、優れた耐久性能を示した。尚、これら場合（Ｎｏ．１〜５）は調整成分の含有量（０．８％又は０．９％）はほとんど変わらないので、抵抗温度係数はほとんど同じであった。
【００２７】
尚、本発明においては、上記実施例に限らず、目的、用途に応じて本発明の範囲内で種々変更した実施例とすることができる。即ち、発熱抵抗体の成形方法は、上記射出成形に限らず、厚膜印刷等の任意の方法とすることができる。
【００２８】
更に、図３に示すような、発熱抵抗体２２を発熱部２２１と制御抵抗部２２２とに分けた二材式セラミックヒータ２Ａの場合は、発熱部２２１の抵抗温度特性を大きくし、制御抵抗部２２２を低抵抗とすることによって、発熱の必要が無い周辺部の発熱が少なくし、発熱が必要な先端側で集中的に発熱させることができる消費電力の少ないセラミックヒータを作製することができる。また、発熱部２２１と制御抵抗部２２２を互いに入れ換え、発熱範囲（発熱ボリューム）が大きいセラミックヒータを作製することができる。
【００２９】
このような二材式セラミックヒータ２Ａにおいて本発熱抵抗体を用いることで、導電成分を共通とし、導電成分の結晶粒子径及び／又は調整成分の含有比率を変化させることで発熱部２２１と制御抵抗部２２２で異なった抵抗温度係数とすることができるとともに、優れた抗折強度及び通電耐久性能を備えた物とすることもできる。
また、発熱部２２１と制御抵抗部２２２とで導電成分を共通とし、調整成分の含有比率のみを変更することにより、同時に焼成できるので、それぞれの焼成条件のずれを少なくすることができる。また、同種の導電成分用原料及び調整成分用原料を用い且つ一体成形ができるので、密着性を高め、境界で破断することを防ぐことができる。
【００３０】
【発明の効果】
本各発明のセラミックヒータ用発熱抵抗体又はセラミックヒータによれば、優れた抗折強度及び通電耐久性能を維持しつつ、抵抗温度係数を変化させて、所望の発熱特性の発熱抵抗体又はセラミックヒータを得ることができる。また、焼結体である発熱低抗体を構成する導電成分の平均粒子径を所定の大きさ以下にすることにより、抗折強度及び耐久性能に極めて優れたものとすることができる。
本発明のセラミックヒータの製造方法によれば、上記有用なセラミックヒータを容易に且つ確実に製造できる。
【図面の簡単な説明】
【図１】本セラミックヒータを用いたグロープラグを説明するための断面図である。
【図２】本セラミックヒータを説明するための断面図である。
【図３】二材式のセラミックヒータを説明するための断面図である。
【符号の説明】
１；グロープラグ、２；セラミックヒータ、２Ａ；二材式セラミックヒータ、２１；基体、２２；発熱抵抗体、２２１；発熱部、２２２；制御抵抗部、２３ａ、２３ｂ；給電部。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a heating resistor for a ceramic heater, a ceramic heater, and a method for manufacturing the ceramic heater. More particularly, the present invention relates to a heating resistor for a ceramic heater used for heating a diesel engine glow plug or other, a ceramic heater using the same, and a method for manufacturing the ceramic heater.
[0002]
[Prior art]
Conventionally, ceramic heaters used at high temperatures of 1000 ° C or higher such as glow plugs contain metals such as W, Mo, Ti, Zr and Hf, or their carbides, nitrides, silicides, etc. One using a heating resistor for a ceramic heater having characteristics (resistance temperature coefficient, etc.) is known.
[0003]
[Problems to be solved by the invention]
However, in recent years, rapid temperature rise characteristics, constant temperature exothermic characteristics, and the like are often obtained depending on the application, and the temperature rise characteristics are often not met. Further, since the temperature rise characteristic is almost determined by the heating resistor, it is often difficult to manufacture a ceramic heater having an arbitrary temperature rise characteristic different from these temperature rise characteristics. Furthermore, these resistor materials were not sufficiently sintered during firing, or overgrowth was liable to occur, and the strength was liable to decrease.
The present invention solves such a problem, and the resistance temperature coefficient of the heating resistor can be arbitrarily adjusted, and the heating resistor for a ceramic heater excellent in bending strength and energization durability performance, and It is an object of the present invention to provide a ceramic heater used and a method for manufacturing the ceramic heater.
[0004]
[Means for Solving the Problems]
The heating resistor for a ceramic heater according to the first aspect of the present invention is made of a sintered body, and includes a conductive component made of WC , V carbide, V oxide, V nitride, Cr carbide, Cr oxide, Cr nitrides, oxides of Nb, and generates the one or more adjusting components for raw material selected from the nitrides of Nb, contains an adjustment component for changing the temperature coefficient of resistance, the conductive components of When the total of the adjusting components is 100 wt%, the adjusting component is 0.1 to 5.0 wt%, and the average particle size of the crystal grains of the conductive component constituting the heating resistor is 11 μm or less. It is characterized by that.
A ceramic heater according to a third aspect of the present invention includes a ceramic base and the heating resistor for a ceramic heater embedded in the base and shown in the first aspect of the present invention.
[0005]
The “conductive component” is made of WC. The conductive component is preferably as close as possible to the other ceramic component (such as silicon nitride) or the ceramic substrate contained in the heating resistor . Further, since the present ceramic sensor is formed by firing at a high temperature, the one having a higher melting point is preferable.
[0006]
The average particle diameter of the crystal grains of the conductive component in the sintered body is 11 μm or less (particularly preferably 10 μm or less, more preferably 9.5 μm). This is because if it exceeds 11 μm, it will be difficult to obtain a sufficient bending strength, and the current-carrying durability will deteriorate. Also, the temperature coefficient of resistance can be appropriately changed by changing the particle diameter.
[0007]
The “adjusting component” is selected from V carbide, V oxide, V nitride, Cr carbide, Cr oxide, Cr nitride, Nb oxide, and Nb nitride. generated from one or more of the adjustment components for the raw material, it is a component to vary the temperature coefficient of resistance. As this adjustment component, as shown in the second or third invention, a component produced from at least one adjustment component raw material of Cr ₂ O ₃ , VC and Nb ₂ O ₅ is preferable.
[0008]
The content of the adjustment component is 0.1 to 5.0 wt% (in this case, simply referred to as “%”, preferably 0.2%) when the total of the conductive component and the adjustment component is 100 wt%. -5%, more preferably 0.2-4.5%). If the content of the adjusting component is less than 0.1%, the sinterability of the resistor material during firing is severe and insufficient sintering or conversely overgrowth is likely to occur. This is because it is not preferable to reduce the heat resistance of the heating resistor and increase the thermal expansion, and decrease the durability of energization.
[0009]
The ceramic component contained in the “exothermic low antibody” or the ceramic component constituting the “substrate” can be variously selected depending on the purpose, and can be, for example, silicon nitride, alumina, aluminum nitride or the like. Of these, silicon nitride is preferable. The “silicon nitride” includes a wide variety of silicon nitride as a main component, and includes not only silicon nitride but also sialon and the like. Furthermore, since a sintering aid (such as each oxide of Y, Yb, Er, etc.) is usually blended and fired by several wt% (about 2 to 10 wt%), this heating resistor contains this auxiliary. Contains components (compounds, etc.) derived from the agent.
[0010]
When the average particle diameter of the conductive component is 11 μm or less, the bending strength is 1250 MPa or more (preferably 1300 MPa or more) and / or the number of cycles in which power is not supplied and disconnected at 1400 ° C. every minute (hereinafter, “ Durability performance ") can be 10,000 cycles or more.
Further, when the conductive component is WC, the content ratio of the adjustment component is changed to 0.1 to 5%, and the average particle size is 11 μm or less, the resistance temperature coefficient of the heating resistor is 2.8 to 3. It can be changed up to 9. In this case, in addition, the bending resistance of the heating resistor can be 1250 MPa or more, and the durability can be 10,000 cycles or more.
[0011]
The method for manufacturing a ceramic heater according to the fourth aspect of the present invention prepares a mixed powder containing a conductive component raw material and an adjustment component raw material to be an adjustment component that changes the resistance temperature coefficient after firing, and generates heat using the mixed powder. A method of manufacturing a ceramic heater in which a resistor-shaped molded body is obtained, and then the molded body is embedded in a raw material for a substrate made of ceramic powder, integrally molded into a ceramic molded body, and then fired. ,
The conductive component raw material is made of WC, and the adjustment component raw material is V carbide, V oxide, V nitride, Cr carbide, Cr oxide, Cr nitride, Nb oxide. , and consists of one or more selected from among nitrides of Nb, the sum of the conductive components for raw material and the adjusting ingredient material when a 100 wt%, the adjusting component ingredients with 0.1 to 5.0% In addition, the average particle size of the conductive component crystal particles constituting the heating resistor obtained by firing the molded body is 11 μm or less.
[0012]
As described above, the “conductive component raw material” is made of WC. In addition, as shown in the description of the above “conductive component”, it is preferable that this expansion coefficient is close to other ceramic components (such as silicon nitride) or a ceramic substrate, and the higher the melting point, the more preferable. .
Furthermore, the powder particle diameter of the conductive component raw material may be any material as long as the crystal particle diameter of the conductive component in the sintered body after firing is 11 μm or less. For example, the powder particle diameter is 1.8 μm. Below (especially 0.5 μm or more), preferably 0.5 to 1.5 μm, more preferably 0.5 to 1.2 μm. In particular, by setting the powder particle diameter to 1.8 μm or less (particularly 0.5 μm or more), the crystal particle diameter of the conductive component can be made to 11 μm or less, and the powder particle diameter is 1.5 μm or less (particularly 0 μm). The crystal particle diameter is 10 μm or less (especially 0.5 μm or more), and the powder particle diameter is 1.2 μm or less (particularly 0.5 μm or more). 4 μm or less).
[0013]
In addition, the above-mentioned “raw material for adjusting component” is to adjust the resistance temperature coefficient with the ceramic heating resistor after sintering, and the strength and durability performance by the blending amount of 0.5% or more. As long as it is not something that significantly lowers. Specific examples thereof include (1) VC, V ₂ O ₅ , VN, (2) Cr ₃ C ₂ , Cr ₂ O ₃ _, CrN _{, and} (3) NbN.
[0014]
Moreover, the compounding quantity of the said adjustment component raw material is 0.1-5.0% (preferably 0.2-5.0%, More preferably, 0.2-5.0 similarly to showing in description of the said adjustment component. 4.5%). If this is less than 0.1%, the sinterability of the resistor material during firing is severe, insufficient sintering or conversely overgrowth is likely to occur, and performance such as strength and durability against electric power decreases. This is because if it exceeds 5.0%, the heat resistance of the heat generating resistor is reduced and the thermal expansion is increased, and the current-carrying durability is lowered.
[0015]
Further, the type of the “ceramic powder material” or the “base material” for embedding a predetermined molded body can be variously selected depending on the purpose, but as shown above, usually a silicon nitride ceramic powder material is used. Used. The meaning of “silicon nitride” is as described above, and a sintering aid is appropriately used as described above.
Furthermore, the form of each raw material powder is not particularly limited, and may be a simple powder product, a granulated product, a crushed product, or the like, and the particle size is not particularly limited.
[0016]
[Action]
In the heating resistor for a ceramic heater, a part or all of the adjustment component is dissolved in the crystal grains of the conductive component. If the blending amount of the raw material for the adjustment component is increased and fired, the amount of the adjustment component contained in the ceramic heater, and thus the amount of the adjustment component dissolved, increases, and the resistance is accordingly increased. The temperature coefficient becomes smaller (see Table 1). Therefore, the resistance temperature coefficient of the heating resistor can be arbitrarily set by adding the adjustment component to the conductive component in an arbitrary ratio.
The adjusting component is not only solid-solved in the crystal grains of the conductive component, but a part thereof segregates as various compounds in the grain boundary phase. The adjustment component that segregates at the grain boundaries also seems to affect the change in resistance temperature characteristics of the heating resistor, but it is considered that the effect is not as great as when it is dissolved.
[0017]
In addition, by making the average particle diameter of the conductive component constituting the exothermic low antibody that is a sintered body not more than a predetermined size, it can be excellent in bending strength and durability performance, and further, resistance temperature The coefficient can also be adjusted.
In addition, since the adjustment component has a large effect when added in a small amount, the addition of the adjustment component has characteristics other than the resistance temperature coefficient of the heating resistor (for example, strength, heat resistance, thermal shock resistance, adhesion, etc.) ) Is not adversely affected.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the ceramic heater of the present invention and the method for manufacturing the ceramic heater will be described in detail with reference to examples.
(1) Production of ceramic heater WC powder as a conductive component raw material, a predetermined amount of raw material for adjustment component (VC powder, Cr ₃ O ₂ powder, Nb ₂ O ₅ powder, see Table 1 and Table 2) and insulation Ceramic powder (Si ₃ N ₄ powder) 34 wt% (hereinafter simply referred to as “%”) and a sintering aid (Yb ₂ O ₃ or Er ₂ O ₃ ) 6% are blended. In this case, the total amount of the WC powder and the predetermined amount of raw material for adjustment component is 60%. These were wet mixed for 72 hours. Then, it was made to dry and the mixed powder was obtained, this mixed powder and the binder were thrown into the kneading machine, and knead | mixed for 4 hours. Next, the kneaded product was cut into pellets, which were put into an injection molding machine to obtain a U-shaped unsintered heater body in which tungsten lead wires were fitted at both ends.
[0019]
[Table 1]

[0020]
[Table 2]

[0021]
On the other hand, a sintering aid powder (about 6%) is blended into Si ₃ N ₄ powder and wet mixed for 40 hours and granulated by a spray dryer method, and the unsintered heater body is placed in the granulated product. After embedding, these were pressed together to obtain an unsintered ceramic heater. Next, this unsintered ceramic heater was calcined at 600 ° C. for about 2 hours to remove the binder, and a calcined body was obtained. Thereafter, the calcined body was set in a carbon mold for hot pressing, and was subjected to hot press firing at a firing temperature and firing time shown in Tables 1 and 2 in a nitrogen atmosphere to produce a ceramic heater. The particle size of the conductive component was adjusted by changing the particle size of the conductive component raw material (WC powder in this example). In Tables 1 and 2, the average particle size of each WC powder used was (1) No. 1-8, 17, 19-20 (see Table 1), No. 1 1 (see Table 2) 0.6 μm, (2) No. 1 9-16, 18, 21-22 (see Table 1), No. 2 (see Table 2), 1.0 μm, (3) No. 3 to 4 (see Table 2), 1.5 μm, (4) No. In the case of 5-6 (refer Table 2), it is 2.0 micrometers.
[0022]
(2) Configuration of Ceramic Heater A ceramic heater 2 manufactured by the above manufacturing method is shown in FIG. A glow plug 1 using the ceramic heater 2 is shown in FIG.
The glow plug 1 is provided with a ceramic heater 2 on the tip side that is a part that generates heat. The ceramic heater 2 includes a base body 21, a heating resistor 22, and power feeding units 23a and 23b.
[0023]
The base 21 is a ceramic mainly composed of Si ₃ N ₄ , and protects the embedded heating resistor 22 and the power feeding portions 23a and 23b. The heating resistor 22 is a U-shaped rod-like body, and is disposed in a form embedded in the base 21. Furthermore, the heating resistor 22 contains a conductive component, an adjustment component for adjusting the temperature coefficient of resistance, and a ceramic component which is an insulating component.
Further, as shown in FIG. 2, each of the power feeding portions 23 a and 23 b is arranged on the surface of the base 21 so that power supplied from outside the ceramic heater 2 can be fed to the heating resistor 22 in the base 21. Each other end is connected to each end of the heating resistor 22.
[0024]
(3) Evaluation of ceramic heater In each ceramic heater manufactured as described above, the bending strength and resistance temperature coefficient of the heat generating resistor (heat generating portion), and the energization durability test were performed, and the results are shown in Table 1 and Table 2. It was shown to.
The bending strength was determined by a three-point bending strength test (span: 20 mm, crosshead speed: 0.5 mm / second). The temperature coefficient of resistance is a ratio of resistance values of the heating resistors at 1000 ° C. and 25 ° C. In the energization durability test, after applying a voltage at which the saturation temperature (saturated in about 20 seconds) of the highest temperature portion is 1400 ° C after energization, the application is stopped and left for one minute as one cycle. The number of cycles until it was measured. The crystal particle diameter of the conductive component was determined from an electron micrograph.
[0025]
According to the result of Table 1, in the case of the comparative example which does not contain an adjustment component (No. 17, 18), the strength is as small as 1180 MPa and 1170 MPa, respectively, and the durability is also broken at 1500 cycles and 1200 cycles, respectively. . Moreover, when content of this adjustment component is as many as 6.2 to 8.0% (No. 19-22), although the bending strength was excellent, durability performance was disconnected in 1000-2200 cycles.
On the other hand, in the case of Examples (No. 1 to 16) in which the particle diameter of the adjustment component is 1.4 to 3.8 μm and the content of the adjustment component is 0.2 to 4.3%, The strength was as large as 1290 to 1340 MPa, and the durability was not broken even at 10,000 cycles, and extremely excellent durability was exhibited. Furthermore, the resistance temperature coefficient when the conductive component was WC could be appropriately adjusted in the range of 3.7 to 2.9 according to the content (0.2 to 4.3%) of the adjustment component.
[0026]
According to Table 2 in which the effect of the crystal grain size of the adjusting component was examined, in the case of comparative examples (Nos. 5 and 6) having average particle sizes of 12.5 μm and 15.4 μm, respectively, the bending strength Were as small as 1210 MPa and 1080 MPa, respectively, and the durability performance was remarkably bad with breakage at 1200 cycles and 800 cycles, respectively.
On the other hand, in the case of Examples (Nos. 1 to 4) in which the particle diameter of the adjusting component is 1.5 to 9.4 μm, the bending strength is slightly decreased according to the order, but it is as large as 1300 to 1340 MPa and durable. All of the performances were not broken even at 10,000 cycles and showed excellent durability performance. In these cases (Nos. 1 to 5), the content of the adjustment component (0.8% or 0.9%) was almost the same, so the resistance temperature coefficient was almost the same.
[0027]
In addition, in this invention, it can be set as the Example variously changed within the range of this invention not only according to the said Example but according to the objective and the use. That is, the method for forming the heating resistor is not limited to the above-described injection molding, and may be any method such as thick film printing.
[0028]
Further, in the case of a two-material ceramic heater 2A in which the heating resistor 22 is divided into a heating part 221 and a control resistance part 222 as shown in FIG. 3, the resistance temperature characteristic of the heating part 221 is increased, and the control resistance part By making 222 low resistance, it is possible to manufacture a ceramic heater with low power consumption that can reduce heat generation in the peripheral portion that does not require heat generation and can intensively generate heat at the tip side that requires heat generation. Further, the heat generating part 221 and the control resistance part 222 can be interchanged to produce a ceramic heater having a large heat generating range (heat generating volume).
[0029]
By using this heat generating resistor in such a two-material ceramic heater 2A, the heat generating part 221 and the control resistor can be controlled by changing the crystal particle diameter of the conductive component and / or the content ratio of the adjusting component by making the conductive component common. While the temperature coefficient of resistance can be different in the portion 222, it is also possible to provide a material having excellent bending strength and energization durability performance.
In addition, since the heat generating part 221 and the control resistance part 222 share the same conductive component and change only the content ratio of the adjustment component, firing can be performed at the same time, so that deviations in the respective firing conditions can be reduced. Moreover, since the same kind of raw material for conductive component and raw material for adjustment component can be used and can be integrally formed, it is possible to improve adhesion and prevent breakage at the boundary.
[0030]
【The invention's effect】
According to the heating resistor or ceramic heater for ceramic heaters of the present inventions, a heating resistor or ceramic heater having desired heat generation characteristics can be obtained by changing the resistance temperature coefficient while maintaining excellent bending strength and durability for energization. Can be obtained. Further, by making the average particle diameter of the conductive component constituting the exothermic low antibody that is a sintered body equal to or less than a predetermined size, it is possible to obtain extremely excellent bending strength and durability performance.
According to the method for producing a ceramic heater of the present invention, the useful ceramic heater can be produced easily and reliably.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view for explaining a glow plug using the ceramic heater.
FIG. 2 is a cross-sectional view for explaining the present ceramic heater.
FIG. 3 is a cross-sectional view for explaining a two-material type ceramic heater.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1; Glow plug, 2; Ceramic heater, 2A; Two material type ceramic heater, 21; Base | substrate, 22; Heat generating resistor, 221; Heat generating part, 222; Control resistance part, 23a, 23b;

Claims

In the heating resistor for ceramic heaters, which is used for ceramic heaters and consists of a sintered body,
Conductive component composed of WC and selected from V carbide, V oxide, V nitride, Cr carbide, Cr oxide, Cr nitride, Nb oxide, and Nb nitride An adjustment component for changing a resistance temperature coefficient, which is generated from one or more kinds of adjustment component raw materials, and the total of the conductive component and the adjustment component is 100 wt%, the adjustment component is 0. 1 to 5.0 wt%,
The heating resistor for a ceramic heater, wherein an average particle diameter of crystal grains of the conductive component constituting the heating resistor is 11 μm or less.

The heating resistor for a ceramic heater according to claim 1, wherein the raw material for adjusting component is at least one of Cr ₂ O ₃ , VC and Nb ₂ O ₅ .

A ceramic heater comprising a ceramic substrate and the heating resistor for a ceramic heater according to claim 1 or 2 embedded in the substrate.

A mixed powder containing a conductive component raw material and an adjustment component raw material to be an adjustment component that changes the resistance temperature coefficient after firing is prepared, and a heating resistor-shaped molded body is obtained using the mixed powder. A method for producing a ceramic heater in which a molded body is embedded in a raw material for a substrate made of a ceramic powder, integrally molded into a ceramic molded body, and then fired.
The conductive component raw material is made of WC, and the adjustment component raw material is V carbide, V oxide, V nitride, Cr carbide, Cr oxide, Cr nitride, Nb oxide. , and consists of one or more selected from among nitrides of Nb, the sum of the conductive components for raw material and the adjusting ingredient material when a 100 wt%, the adjusting component ingredients with 0.1 to 5.0% A method for producing a ceramic heater, characterized in that the average particle size of crystal grains of the conductive component constituting the heating resistor obtained by firing the molded body is 11 μm or less.

The method for manufacturing a ceramic heater according to claim 4, wherein the raw material for adjusting component is at least one of Cr ₂ O ₃ , VC, and Nb ₂ O ₅ .