JP3600658B2 - Ceramic heater and method of manufacturing the same - Google Patents

Description

【００２２】
なお，上記においてＭｏＳｉ ₂ とＳｉＣとの重量比（ＭｏＳｉ ₂ の重量％／ＳｉＣの重量％）は，１〜４０である。この範囲内において上記重量比を増加すると，抵抗変化率は増加し，逆に減少すると抵抗変化率も減少する。そして，重量比が１未満の場合には，導電体セラミック体の抵抗変化率の変動はみられない。逆に，重量比が４０を越える場合には，導電性セラミック体の耐久性が低下するという問題がある。
【００２３】
次に，上記の参考としてのセラミックヒータを製造する方法としては，例えば，外部から供給される電力により発熱可能な導電性セラミック体を有するセラミックヒータの製造方法において，
上記導電性セラミック体は，
Ｓｉ ₃ Ｎ ₄ とＭｏＳｉ ₂ とＳｉＣとよりなる原料粉末に，焼結助材を添加，混合してなる混合粉末を用い，該混合粉末を成形し，加熱焼結したものであり，
Ｓｉ ₃ Ｎ ₄ は，上記原料粉末の総量１００重量％に対して，２０〜８０重量％含有されており，ＭｏＳｉ ₂ とＳｉＣとの重量比（ＭｏＳｉ ₂ の重量％／ＳｉＣの重量％）は１〜４０であることを特徴とするセラミックヒータの製造方法がある。
【００２４】
【作用及び効果】
上記参考としてのセラミックヒータにおいては，焼結時に，一部のＳｉＣはＳｉとＣに分解する。Ｓｉはガス化して飛散する。Ｃは一部のＭｏＳｉ₂と反応してＭｏ5Ｓｉ₃より抵抗変化率が小さいＭｏ_5-XＳｉ₃Ｃ_1-Yとなる。導電パスでは，少なくともＭｏＳｉ₂とＭｏ_5-XＳｉ₃Ｃ_1-Yとの混在組織となる。
【００２５】
また，導電部では，Ｓｉ_３ Ｎ_４ 粒子を包む少なくともＭｏＳｉ_２ とＭｏ_５−Ｘ Ｓｉ_３ Ｃ_１−Ｙ とが互いに連続する組織となる。即ち，Ｍｏ_５−Ｘ Ｓｉ_３ Ｃ_１−Ｙ は，ＭｏＳｉ_２ と共に混在して導電パスを形成する。また，このＭｏＳｉ_２ とＭｏ_５−Ｘ Ｓｉ_３ Ｃ_１−Ｙ との混在組織は，Ｓｉ_３ Ｎ_４ 粒子を包み，連続した組織からなる導電部を構成する。上記のＭｏＳｉ_２ とＭｏ_５−Ｘ Ｓｉ_３ Ｃ_１−Ｙ とは，導電材であり，これらの総量により常温抵抗値が決定される。
【００２６】
そして，ＳｉＣの添加量を増やす場合にはＭｏ_５−Ｘ Ｓｉ_３ Ｃ_１−Ｙ の形成量が増加し，逆にＳｉＣの添加量を減らす場合にはＭｏ_５−Ｘ Ｓｉ_３ Ｃ_１−Ｙ の形成量が減少する。このようにして，ＳｉＣの添加量を増減することにより，ＭｏＳｉ_２ とＭｏ_５−Ｘ Ｓｉ_３ Ｃ_１−Ｙ との生成比率が変化する。ＭｏＳｉ_２ は抵抗変化率が大きく，Ｍｏ_５−Ｘ Ｓｉ_３ Ｃ_１−Ｙ は抵抗変化率が小さい。そのため，導電性セラミック体の抵抗変化率は，ＭｏＳｉ_２ とＭｏ_５−Ｘ Ｓｉ_３ Ｃ_１−Ｙ との生成比率により決定される。
【００２７】
従って，Ｓｉ_３ Ｎ_４ の添加量と，ＭｏＳｉ_２ の添加量と，ＳｉＣの添加量とを変更するのみで，一定のホットプレス条件下において任意の常温抵抗値と任意の抵抗変化率とを，容易に得ることができる。
【００２８】
また，分解しないＳｉＣの大部分は，焼結助材により形成される粒界ガラスの中に取り込まれて，その他の微細なＳｉＣはＳｉ_３ Ｎ_４ の中に取り込まれる。これにより，粒界ガラス内の元素の拡散及び粒界ガラスの分解が抑制され，粒界ガラスの耐久性が向上する。そのため，耐久性の高いセラミックヒータを得ることができる。
【００２９】
また，上記セラミックヒータの製造方法によれば，上記の優れたセラミックヒータを容易に製造することができる。
【００３０】
本願第１発明のセラミックヒータにおいては，焼結時，本発明の導電体セラミック体の組成では，一部のＭｏＳｉ₂と添加材のＭｏと有機物質の分解残留物たる炭素若しくは添加材に含まれる炭素との間に，
３ＭｏＳｉ₂ ＋ （７─２Ｘ）Ｍｏ ＋ （２─２Ｙ）Ｃ →２Ｍｏ_5-XＳｉ₃Ｃ_1-Y
なる反応が起こり，Ｍｏ_5-XＳｉ₃Ｃ_1-Yが生成する。
【００３１】
上記Ｍｏ_５−Ｘ Ｓｉ_３ Ｃ_１−Ｙ の生成量は，添加材の量により決まり，本発明のように適当な添加量にすれば，ＭｏＳｉ_２ とＭｏ_５−Ｘ Ｓｉ_３ Ｃ_１−Ｙ とを混在させることができ，その結果，導電パスは少なくともＭｏＳｉ_２ とＭｏ_５−Ｘ Ｓｉ_３ Ｃ_１−Ｙ との混在組織となり，Ｓｉ_３ Ｎ_４ 粒子を包む少なくともＭｏＳｉ_２ とＭｏ_５−Ｘ Ｓｉ_３ Ｃ_１−Ｙ とが互いに連続する導電部組織となる。
【００３２】
ここに，常温抵抗値は導電材であるＭｏＳｉ_２ とＭｏ_５−Ｘ Ｓｉ_３ Ｃ_１−Ｙ との総量により決まり，抵抗変化率は抵抗変化率の大きいＭｏＳｉ_２ と抵抗変化率の小さいＭｏ_５−Ｘ Ｓｉ_３ Ｃ_１−Ｙ の比で決まる。
【００３３】
従って，Ｓｉ_３ Ｎ_４ の添加量とＭｏＳｉ_２ の添加量と添加材の添加量との重量比を変えれば，一定のホットプレス条件下において，任意の常温抵抗値と任意の抵抗変化率を容易に得ることができる。
また，添加材の余剰炭素又はホウ素の大部分は，焼結助材により形成される粒界ガラス中に取り込まれる。これにより，粒界ガラスの移動及び粒界ガラスの分解が抑制され，粒界ガラスの耐久性が向上する。そのため，セラミックヒータの耐久性が高くなる。
【００３４】
また，上記セラミックヒータの製造方法によれば，上記の優れたセラミックヒータを容易に製造することができる。
【００３５】
以上のごとく，本発明にかかるセラミックヒータによれば，多種多様のヒータ生産において，加熱焼結時に窒素とアルゴンガスの混合比をその都度調整する必要がなく，セラミックヒータの耐久性及び生産性を高くすることができる。
【００３６】
本発明によれば，抵抗変化率を任意にかつ容易に設定でき，耐久性及び生産性に優れた，セラミックヒータ及びその製造方法を提供することができる。
【００３７】
【実施例】
参考例１
参考例にかかるセラミックヒータについて，図１，図２を用いて説明する。本例のセラミックヒータは，ディーゼルエンジン用のグロープラグに用いたものである。
【００３８】
セラミックヒータ１は，図１に示すごとく，電極線４，５により外部から供給される電力によって発熱可能な発熱体２を有している。発熱体２は，導電性セラミック体であって，Ｓｉ_３ Ｎ_４ （平均粒径１０μｍ）とＭｏＳｉ_２ （平均粒径１μｍ）とＳｉＣ（平均粒径０．３μｍ）とよりなる原料粉末に，焼結助材としてのＹ_２ Ｏ_３ を添加，混合し，成形し，加熱焼成したものである。
Ｓｉ_３ Ｎ_４ は，原料粉末の総量１００重量％に対して５０重量％含有されている。ＭｏＳｉ_２ とＳｉＣとの重量比（ＭｏＳｉ_２ の重量％／ＳｉＣの重量％）は１〜３２．３である。
【００３９】
焼結時の反応においては，少なくともＭｏ_５−Ｘ Ｓｉ_３ Ｃ_１−Ｙ （０≦Ｘ≦２，０≦Ｙ≦１）が形成する。焼結後は少なくともＳｉ_３ Ｎ_４ とＭｏＳｉ_２ とＭｏ_５−Ｘ Ｓｉ_３ Ｃ_１−Ｙ とが混在し，Ｓｉ_３ Ｎ_４ 粒子を包む少なくともＭｏＳｉ_２ とＭｏ_５−Ｘ Ｓｉ_３ Ｃ_１−Ｙ 粒子とが互いに連続する組成が得られる。
以下，これらにつき詳細に説明する。
【００４０】
即ち，上記セラミックヒータ１は，図１に示すごとく，円棒状の絶縁性セラミック体よりなる支持体３と，支持体３の先端部に埋設されたＵ字状の上記導電性セラミック体よりなる発熱体２と，支持体３の基端部及び中央部に埋設された断面円形の電極線４，５とからなる。
【００４１】
電極線４，５の基端部は，支持体３の外周に露出してターミナル４３，５３を形成している。電極線４，５の先端部４１，５１は，発熱体２の両端面に接続されている。電極線４，５は通常タングステン，モリブデン等の高融点金属又はその合金からなるが，本例においては断面円形のタングステン線を用いている。ターミナル４３，５３の曲率半径は，支持体３の半径に等しい。
【００４２】
次に，上記セラミックヒータ１の製造方法について説明する。
発熱体２である導電性セラミック体を製造するに当たり，まず，平均粒径１０μｍのＳｉ_３ Ｎ_４ 粉末と，平均粒径１μｍのＭｏＳｉ_２ 粉末と，平均粒径０．３μｍのβ─ＳｉＣ粉末とを原料粉末とする。原料粉末の総量１００重量％に対して，Ｓｉ_３ Ｎ_４ 粉末は５０．０重量％含有されている。ＭｏＳｉ_２ 粉末は２５．０〜４８．５重量％，β─ＳｉＣ粉末は１．５〜２５．０重量％の間で変化させる。ＭｏＳｉ_２ とＳｉＣとの重量比（ＭｏＳｉ_２ の重量％／ＳｉＣの重量％）は１〜３２．３である。
【００４３】
上記原料粉末に，その総量を１００重量部として，焼結助材としてのＹ_２ Ｏ_３ 粉末１０重量部を添加する。これをエタノール等の溶媒にて混合，攪拌し，乾燥後パラフィン，アタックチックポリプロピレン，高密度ポリエチレンよりなるバインダを加え，ニーダにより１８０℃で３時間混練して，導電性セラミック体の混合粉末を得る。
【００４４】
また，支持体３である絶縁性セラミック体を製造するに当たり，まず，平均粒径０．７μｍのＳｉ_３ Ｎ_４ 粉末５０．０重量％と平均粒径１μｍのＭｏＳｉ_２ 粉末５０．０重量％とを混合して原料粉末とする。この原料粉末に，その総量を１００重量部として，焼結助材としてのＹ_２ Ｏ_３ 粉末１０重量部を添加し，上記の導電性セラミック体と同様の方法により，絶縁性セラミック体の混合粉末を得る。
【００４５】
次に，上記の導電性セラミック体用の混合粉末と，絶縁性セラミック体用の混合粉末とを用いて，射出成形法により一体成形体を作製する。このとき，上記電極線４，５は一体的に内蔵させておく。次に，この一体成形体を一旦窒素雰囲気中５００℃まで加熱して，上記バインダを飛散させる。その後，１７５０℃，アルゴン雰囲気において，ホットプレス法により加熱焼結して，導電体セラミック体を得る。
【００４６】
加熱焼結後，外形をφ３．５ｍｍまで削り，図１の形状にする。ここで，導電性セラミック体は半円状断面で，断面積が２ｍｍ^２ ，電極線４，５のプラス側端面から一端面までの導電部長さは１４ｍｍとする。
【００４７】
上記セラミックヒータ１は，図２に示すごとく，ディーゼルエンジン用のグロープラグ１９の先端に取り付けられる。即ち，セラミックヒータは，支持体３の側面に施したニッケルメッキ層を介して金属の中空パイプ６に嵌着，ロウ付けされている。中空パイプ６は，セラミックヒータ１を保持するとともに，電極線５のターミナル５３と電気的に接続されている。中空パイプ６の外周には，両端開口筒状の金属ハウジング１０の先端部が嵌着，ロウ付けされている。金属ハウジング１０は，図示しないエンジンへの取り付けネジ１０１を有している。
【００４８】
電極線４のターミナル４３には，支持体３の基端部を覆うように，金属キャップ７がロウ付けされている。金属キャップ７には，金属線８の一端が溶接されている。金属線８の他端は中軸９の先端に溶接されている。中軸９の基端部に形成された雄ネジ部９１は図示しない電極と接続されている。中軸９は，ハンジング１０内に嵌入されている。
中軸９は，ハウジング１０からガラスシール１１および絶縁ブッシュ１２により電気的に絶縁されている。絶縁ブッシュ１２は，雄ネジ部９１に螺着されたナット１３により固定されている。
【００４９】
上記のグロープラグ１９は，図示しない電源から中軸９，金属線８，金属キャップ７，電極線４，発熱体２，電極線５，中空パイプ６，ハウジング１０を介して，図示しないグロープラグへの通電が可能となっている。
【００５０】
次に，本例のセラミックヒータの諸特性を測定した。その結果，常温抵抗値は０．１６２〜３．０１６Ω，１０００℃での抵抗値は０．６５３〜４．３１３Ωであった。
抵抗変化率（１０００℃の抵抗値／常温の抵抗値）は，１．４３〜４．０３の間で変化した。そして，ＭｏＳｉ_２ 量を増加するに連れて導電体セラミック体の抵抗変化率が増加し，逆にＭｏＳｉ_２ 量を減らす場合には抵抗変化率も減少した。
このことから，本例のセラミックヒータは，ＭｏＳｉ_２ とＳｉＣとの添加量を増減することにより，任意の抵抗変化率を容易に設定することができることがわかる。
【００５１】
次に，セラミックヒータが１２００℃となる電圧にて通電１分と通電停止１分とを繰り返して耐久試験を行ったところ，１９０００〜２５０００サイクル目で，抵抗値が試験前に対して１０％変化した。１００００サイクル以上であれば，実用上問題がないことから，本例のセラミックヒータは，その目標値をはるかに上回っており，優れた耐久性を有しているといえる。
【００５２】
参考例２
本例においては，導電性セラミック体の混合粉末の組成を変えて，セラミックヒータを作製し，その諸特性を測定した。
導電性セラミック体の混合粉末は，表２に示すごとく，Ｓｉ₃Ｎ₄とＭｏＳｉ₂とβ─ＳｉＣとからなる原料粉末，及びＡｌ₂Ｏ₃とＹ₂Ｏ₃とからなる焼結助材の配合割合を変えて調製した。
【００５３】
その他は，参考例１と同様にして，各々のセラミックヒータを製造し，試料ａ〜ｑとした。また，Ｓｉ₃Ｎ₄，ＭｏＳｉ₂，ＳｉＣの配合割合を，図３の三元組成図に示した。なお，図３の三元組成図中に示す点ａ〜ｑは，試料ａ〜ｑに対応している。
各セラミックヒータについて，参考例１と同様の方法により，表２に示す抵抗値，抵抗変化率，及び耐久性を測定した。その結果を表２に示した。
【００５４】
【表２】

【００５５】
次に，測定結果について説明する。
まず，β─ＳｉＣ無添加の，ＭｏＳｉ_２ とＳｉ_３ Ｎ_４ とを原料粉末とした試料ａ，ｈ，ｎについて説明する。ＭｏＳｉ_２ は導電性セラミックであるため，ＭｏＳｉ_２ 添加量が多いａは，低い抵抗値，高い抵抗変化率となった。逆に，その添加量が少ないｎは，抵抗値は高く，抵抗変化率は小さくなった。この結果から，ＭｏＳｉ_２ の添加量を変化させるだけでも抵抗変化率を変え得るが，抵抗値も大きく変化し，一定形状の発熱体で所定の抵抗値と抵抗変化率とを実現することは困難であることがわかる。
【００５６】
上記のように，Ｓｉ_３ Ｎ_４ とＭｏＳｉ_２ との比率を変えるのみで，導電性セラミック体の抵抗値が変化する理由は，導電パスの大きさがＭｏＳｉ_２ の添加量で決定されるためであると考えられる。
【００５７】
また，Ｓｉ_３ Ｎ_４ とＭｏＳｉ_２ との比率を変えるのみで，導電性セラミック体の抵抗変化率が変化する理由は，文献等に示される導電性セラミック体の抵抗変化率が導電部全体が導電体よりなるヒータの値であるのに対し，本例のようにセラミックヒータが導電性セラミック体と絶縁性セラミック体との混合組織の場合は，絶縁性セラミック体の混在による実質導電部の減少，絶縁性セラミック体と導電体セラミック体との線膨張係数の差による各粒子への熱応力により生ずる接触抵抗等が，複雑に影響しているためであると考えられる。
【００５８】
次に，β─ＳｉＣ添加の効果について，Ｓｉ_３ Ｎ_４ 量が５０重量％の試料ｈ，ｉ，ｊ，ｋ，ｌ，ｍにより説明する。β─ＳｉＣ量をｉ，ｊ，ｋ，ｌ，ｍと増してゆくと，抵抗変化率は小さくなる。そして，試料ｌ，ｍの結果より，所定量以上のβ─ＳｉＣを添加しても，もはや抵抗変化率は変わらなくなる。このことは，Ｓｉ_３ Ｎ_４ 量が２０重量％の試料ａ，ｂ，ｃ，ｄ，ｅ，ｆ，ｇ，及びＳｉ_３ Ｎ_４ 量が８０重量％の試料ｎ，ｏ，ｐについてもいえる。
【００５９】
以上の結果をまとめると，β─ＳｉＣ量はＭｏＳｉ₂量の１／４０からＭｏＳｉ₂量と同量までの間，即ちＭｏＳｉ₂量とβ─ＳｉＣ量との重量比（ＭｏＳｉ₂の重量％／β─ＳｉＣの重量％）が１〜４０の間において，ＭｏＳｉ₂量とβ─ＳｉＣ量を適当に設定することにより，導電性セラミック体の寸法を変えることなく一定形状の発熱体で所定の抵抗値と所定の抵抗変化率を有するセラミックヒータを容易に得ることができることがわかる。また，β─ＳｉＣを添加すると耐久性も大幅に向上すること，更に，本例のセラミックヒータの特性は焼結助材の影響を受けないこともわかる。
【００６０】
ここで，Ｓｉ_３ Ｎ_４ は，８０重量％を越えて添加すると，早期に常温抵抗値が変化し，実用化が困難となる。その理由は，絶縁性セラミックであるＳｉ_３ Ｎ_４ の量が多くなりすぎ，導電パスの断面積が小さくなってしまい，通電時のストレスが過大となり，導電部の変質が促進されるものと考えられる。また，２０重量％未満の場合には，高い強度を実現するＳｉ_３ Ｎ_４ が少なくなりすぎ，使用中にクラックが発生するため，この場合にも実用に適さない。
【００６１】
以上のことより，Ｓｉ_３ Ｎ_４ が２０〜８０重量％と，ＭｏＳｉ_２ とβ─ＳｉＣが総量で８０〜２０重量％であり，ＭｏＳｉ_２ 量とβ─ＳｉＣ量の重量比（ＭｏＳｉ_２ の重量％／β─ＳｉＣの重量％）が１〜４０である原料粉末を出発原料とすることが望ましいといえる。即ち，図３の三元組成図において，ｂ，ｆ，ｐ，ｏを直線により結ぶことより囲まれた組成範囲内の適当な組成を選定することが望ましい。
【００６２】
以上はβ─ＳｉＣの添加の例で述べたが，焼結時のＳｉＣの分解により本発明の抵抗値，抵抗変化率，及び耐久性が得られること，並びに焼結時にα─ＳｉＣがβ─ＳｉＣに一部変化することから，α─ＳｉＣでも同様の効果が得られることが言える。
また，原料粉末のＳｉ₃Ｎ₄はα─Ｓｉ₃Ｎ₄粉末，β─Ｓｉ₃Ｎ₄粉末，α─Ｓｉ₃Ｎ₄粉末とβ─Ｓｉ₃Ｎ₄粉末との混合粉末により確認したが，全て，同様の優れた効果が確認された。
【００６３】
また，平均粒径については，１０μｍのＳｉ_３ Ｎ_４ 粉末と，１μｍのＭｏＳｉ_２ 粉末と，０．３μｍのβ─ＳｉＣ粉末の例で述べたが，要は，焼結後にＳｉ_３ Ｎ_４ 粒子を包む少なくともＭｏＳｉ_２ とＭｏ_５−Ｘ Ｓｉ_３ Ｃ_１−Ｙ 粒子が互いに連続した組織となった導電性セラミック体が形成されればよい。
【００６４】
我々の経験からは，Ｓｉ_３ Ｎ_４ の平均粒径は，ＭｏＳｉ_２ 及びＳｉＣの平均粒径の３倍以上であればよい。３倍未満の場合には，ＭｏＳｉ_２ とＭｏ_５−Ｘ Ｓｉ_３ Ｃ_１−Ｙ 粒子が連続した組織を形成しない場合があった。３倍以上としたのは，平均粒径が０．０１〜０．０３μｍと超微粒子のＳｉＣを用いても，同様の結果が得られたため，上限は設定しなかった。
【００６５】
実施例１
本発明の実施例に係るセラミックヒータにおいては，導電体セラミック体が，Ｓｉ₃Ｎ₄とＭｏＳｉ₂とＭｏのホウ化物（添加材）と焼結助材とを用いて製造されたものである。
【００６６】
上記導電体セラミック体の製造方法について説明する。
まず，平均粒径１０μｍのα─Ｓｉ_３ Ｎ_４ 粉末と，平均粒径１μｍのＭｏＳｉ_２ 粉末と，平均粒径１μｍのＭｏＢ粉末とを原料粉末とする。原料粉末の総量１００重量％に対して，α─Ｓｉ_３ Ｎ_４ 粉末は５０．０重量％添加されている。ＭｏＳｉ_２ 粉末は２５．０〜４９．０重量％，ＭｏＢ粉末は２５．０〜１．０重量％の間でそれぞれ変化させる。
【００６７】
上記原料粉末に，その総量を１００重量部として，焼結助材としてのＹ_２ Ｏ_３ 粉末１０重量部添加する。これをエタノール等の溶媒にて混合，攪拌し，乾燥後パラフィン，アタックチックポリプロピレン，高密度ポリエチレンよりなるバインダを加え，ニーダにより１８０℃で３時間混練して，導電性セラミック体の混合粉末を得る。
【００６８】
また，支持体である絶縁性セラミック体は，平均粒径１μｍのα─Ｓｉ₃Ｎ₄粉末５０．０重量％と平均粒径１μｍのＭｏＳｉ₂粉末５０．０重量％とを用いて，上記と同様にして，絶縁性セラミック体の基本原料を得る。
次に，上記の導電性セラミック体の混合粉末と絶縁性セラミック体の混合粉末とを用いて，射出成形法により一体成形体を作製する。一体成形体を一旦窒素雰囲気中５００℃まで加熱して，上記バインダを飛散させる。その後，１７３０℃，アルゴン雰囲気において，ホットプレス法により加熱焼結する。これにより，セラミックヒータを得る。
その他は，参考例１と同様である。
【００６９】
次に，本例のセラミックヒータの諸特性を測定した。その結果，常温抵抗値は０．２５８〜３．３８２，１０００℃での抵抗値は１．０７８〜６．７９８Ωであった。抵抗変化率（１０００℃の抵抗値／常温の抵抗値）は，４．１８〜２．０１と変化した。このことから，本例のセラミックヒータは，ＭｏＳｉ_２ と添加材との添加量を増減することにより，任意の抵抗変化率を容易に設定することができることがわかる。
【００７０】
次に，セラミックヒータの耐久試験を参考例１と同様にして行なったところ，１７０００〜１８０００サイクル目で，抵抗値が試験前に対して，１０％変化した。実用上問題がない１００００サイクルを遙に上回っているので，本例のセラミックヒータは優れた耐久性を有しているといえる。
【００７１】
実施例２
本例においては，導電体セラミック体の混合粉末の組成とセラミックヒータの諸特性との関係を調査した。
まず，Ｓｉ₃Ｎ₄とＭｏＳｉ₂との配合比がセラミックヒータの諸特性に与える影響を調査した。
【００７２】
調査に当たり，まず，表３に示すごとく，添加材を用いることなく，Ｓｉ₃Ｎ₄粉末とＭｏＳｉ₂粉末との配合比を変えて導電性セラミック体の混合粉末を調製し，該混合粉末より各々セラミックヒータを作製して，試料１〜７とした。これらについて，表３に示すの諸特性を，参考例１と同様に測定した。
【００７３】
表３より明らかなように，常温抵抗値は絶縁材であるＳｉ_３ Ｎ_４ 量が少ない試料１が低い。Ｓｉ_３ Ｎ_４ 量を試料２〜７へと多くすると，常温抵抗値は順次高くなる。
また，耐久性については，Ｓｉ_３ Ｎ_４ 量が２０重量％未満の試料１は使用中の繰り返し熱応力により４０００サイクルでクラックが発生し，実用化に適さない。この理由は，Ｓｉ_３ Ｎ_４ は，セラミックヒータの強度向上に寄与するものであり，このＳｉ_３ Ｎ_４ 量が少なく，強度が低下したものと考えられる。
【００７４】
Ｓｉ_３ Ｎ_４ を８０重量％を越えて添加した試料７も，早期に常温抵抗値が変化して，実用化が困難であった。この理由は，絶縁性セラミックであるＳｉ_３ Ｎ_４ の量が多くなりすぎ，導電パスの断面積が小さくなってしまい，通電時のストレスが過大となり導電部の変質が促進されるものと考えられる。表３の結果より，実用化を考えると，導電性の発熱体を形成するためのＳｉ_３ Ｎ_４ 量は，２０〜８０重量％であることが望ましいといえる。
【００７５】
次に，表３の結果を踏まえ，Ｓｉ₃Ｎ₄とＭｏＳｉ₂と添加材としての金属Ｍｏとの配合比がセラミックヒータの諸特性に与える影響を調査した。
即ち，Ｓｉ₃Ｎ₄とＭｏＳｉ₂と金属Ｍｏとよりなる原料粉末を，表４，表５に示す配合割合で調製した。これらを用いて作製したセラミックヒータを，各々試料２，４，６，８〜２１とし，これらの諸特性を参考例１と同様に測定した。その結果を表４，表５に示した。
【００７６】
上記の結果について説明する。
両表の中，Ｂ／Ａは，Ｓｉ_３ Ｎ_４ 量とＭｏＳｉ_２ 量と添加材としてのＭｏ量との総重量１００重量％に対する，ＭｏＳｉ_２ に含まれるＭｏ量をＡ重量％とし，添加材としてのＭｏ量をＢ重量％としたときの重量比（Ｂ／Ａ）である。ＭｏＳｉ_２ に含まれるＭｏの量（Ａ重量％）は，表５の中のＭｏＳｉ_２ の重量％の下の括弧内に記してある。
【００７７】
次に，上記測定結果について，考察する。
まず，添加材としてのＭｏの添加のない，Ｓｉ₃Ｎ₄とＭｏＳｉ₂とを原料粉末とした試料２，４，６，の結果より（表３），Ｓｉ₃Ｎ₄とＭｏＳｉ₂との重量比のみを変えるだけであっても抵抗変化率は変わるが，常温，１０００℃での抵抗値も大きく変化してしまい，一定形状の発熱体で所定の常温抵抗値と抵抗変化率とを得ることは困難であることがわかる。その理由は，参考例２で述べた。
【００７８】
次に，本発明の添加材としての金属Ｍｏの添加の効果を，Ｓｉ_３ Ｎ_４ の添加量が５０重量％である試料４，１３，１４，１５，１６，１７において説明する。Ｍｏを添加しない試料４の抵抗変化率は４．２１である。そして，Ｍｏ量を試料１３〜１７と増してゆくと，抵抗変化率が小さくなる。そして，試料１６，１７の結果より，所定量以上Ｍｏを添加しても，もはや抵抗変化率は変わらなくなる。この結果は，Ｓｉ_３ Ｎ_４ の添加量が８０重量％である試料６，１８，１９，２０，２１についてもいえる。
【００７９】
表４，表５の結果をまとめると，ＭｏＳｉ₂に含まれるＭｏの量（Ａ重量％）と添加材としてのＭｏの量（Ｂ重量％）との比（Ｂ／Ａ）が，０．０２５〜３になるようにＭｏＳｉ₂量とＭｏ量とを設定することにより，必要に応じて若干導電部の寸法を変えるのみで所定の抵抗値及び所定の抵抗変化率を有するセラミックヒータが，容易に得られることがわかる。更に，焼結助材の影響を受けないこともわかる。
【００８０】
【表３】

【００８１】
【表４】

【００８２】
【表５】

【００８３】
実施例５
本例においては，添加材として，表６に示すＭｏの炭化物又はＭｏのホウ化物を添加材として用い，該添加材とＭｏＳｉ_２ との配合比を変えて，セラミックヒータ（試料２２〜３３）を製造した。その他は，実施例４と同様である。これらの試料の諸特性について測定し．表６に示した。
【００８４】
表５に示す結果より，実施例４の表４，表５の結果と同様に，ＭｏＳｉ_２ に含まれるＭｏの量（Ａ重量％）とＭｏの炭化物，Ｍｏのホウ化物からなる添加材に含まれるＭｏの量（Ｂ重量％，表６の括弧内の値）の比（Ｂ／Ａ）が，０．０２５≦Ｂ／Ａ≦３である原料粉末を出発原料にすることが望ましいといえる。
【００８５】
結局，Ｓｉ₃Ｎ₄とＭｏＳｉ₂と添加材とよりなる原料粉末１００重量％に対して，Ｓｉ₃Ｎ₄が２０〜８０重量％であり，ＭｏＳｉ₂に含まれるＭｏの量（Ａ重量％）と，金属Ｍｏ，Ｍｏの炭化物，ホウ化物の１種又は２種以上に含まれるＭｏの量（Ｂ重量％）との比（Ｂ／Ａ）が，０．０２５〜３である組成が望ましい。
【００８６】
また，本例のセラミックヒータにおいても，参考例２と同様に，Ｓｉ₃Ｎ₄の平均粒径は，ＭｏＳｉ₂とＭｏとの平均粒径の３倍以上であることが望ましい。
【００８７】
【表６】

【図面の簡単な説明】
【図１】実施例１のセラミックヒータの断面図。
【図２】実施例１のセラミックヒータを設けたグロープラグの断面図。
【図３】実施例２の導電体セラミック体の三元組成図。
【符号の説明】
１．．．セラミックヒータ，
１９．．．グロープラグ，
２．．．発熱体，
３．．．支持体，
４，５．．．電極線，[0001]
[Industrial applications]
The present invention relates to a ceramic heater used for a ceramic blow plug of a diesel engine and a method for manufacturing the same.
[0002]
[Prior art]
High heat resistant ceramic heaters have been used in various products. For this reason, the requirements for the normal-temperature resistance value and the rate of change in resistance (the ratio of the normal-temperature resistance value to the high-temperature resistance value) of the conductive ceramic body used for the ceramic heater are diversifying. Here, the room temperature resistance can be easily changed by changing the cross-sectional area and length of the conductive part, or the composition of the conductive material. However, the resistance change rate is almost uniquely determined by the conductive material. The conductive material needs to be changed.
[0003]
As a method for obtaining an arbitrary resistance change rate, for example, as disclosed in Japanese Patent Application Laid-Open No. 60-28194, MoSi₂  And Si₃  N₄  And MgAl₂  O₄  Using (sintering aid) as a raw material, the mixing ratio of the nitrogen gas and the argon gas is changed as the atmosphere gas during hot pressing. Thereby, Mo formed after sintering₅  Si₃  And MoSi₂  MoSi with high resistance change rate by changing the ratio of₂  And Mo with small resistance change rate₅  Si₃  An arbitrary rate of change in resistance of the conductive material can be obtained in between.
[0004]
For the conductive material obtained by this method, the inventors conducted a test of the rate of change in resistance. The resistance change rate was determined as a ratio of the resistance value at 1000 ° C. to the normal temperature resistance value. MoSi₂  Has a resistance change rate of 5.0 and Mo₅  Si₃  Has a resistance change rate of 1.4. Then, it was confirmed that by changing the mixture ratio of the two materials, a conductive ceramic body having the resistance change rate described in the above publication can be obtained.
[0005]
[Problem to be solved]
However, if the nitrogen partial pressure of the mixed gas is set to 0.3 atm or more as described in the above-mentioned publication, the resistance value increases after the endurance by the current test, and the durability becomes insufficient. Conversely, when the nitrogen partial pressure of the mixed gas is low, Mo₅  Si₃  Is too small to set an arbitrary resistance change rate. Therefore, MoSi₂  And Mo₅  Si₃  It is difficult to obtain a conductive material having an arbitrary resistance change rate and excellent durability between the above resistance change rates.
[0006]
Therefore, we conducted intensive research on durability. As a result, the resistance value after endurance increases due to the movement of the grain boundary glass formed by the sintering aid consisting of the metal oxide existing on the plus side of the highest temperature part of the heating element and in the center of the support under high temperature. In addition, the grain boundary glass is decomposed and the oxygen atoms therein diffuse to the plus side of the highest temperature part, so that the diffused oxygen becomes MoSi at the plus side of the highest temperature part.₂  Decomposes on the surface and reacts with MoSi₂  It was found that this was because the conductive path was cut off by changing from. That is, the heat resistance of the grain boundary glass was insufficient. However, the effect of nitrogen partial pressure on the movement of grain boundary glass and the decomposition of grain boundary glass was not found.
[0007]
Further, usually, the production equipment of the ceramic heater has a large production capacity and the introduction cost of the equipment is high. Therefore, it is difficult to introduce equipment in accordance with a wide variety of normal temperature resistance values and resistance change rates of conductive materials. Therefore, efficient production with one facility is essential. However, in the production of a wide variety of heaters, it is necessary to adjust the mixture ratio of nitrogen gas and argon gas each time during sintering, which makes it easy to make mistakes in the mixture ratio, complicates management, and reduces productivity. .
[0008]
Various ceramic heaters are also disclosed in JP-A-59-8829, JP-A-62-82685, and JP-A-1-317170, all of which can easily set the resistance change rate. And durability are not satisfied.
[0009]
SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a ceramic heater and a method of manufacturing the same, which are capable of arbitrarily and easily setting a resistance change rate, have excellent durability and productivity.
[0010]
[Means for solving the problem]
The first invention according to the present application is:In a ceramic heater having a conductive ceramic body capable of generating heat by electric power supplied from the outside,
The conductive ceramic body is
Si _Three N _Four And MoSi _Two And a mixed powder obtained by adding and mixing a sintering aid to a raw material powder comprising one or more additives selected from metal Mo, a carbide of Mo or a boride of Mo. The mixed powder is molded and sintered by heating. _Three N _Four Is contained in an amount of 20 to 80% by weight with respect to 100% by weight of the total amount of the raw material powder, and MoSi is contained with respect to 100% by weight of the total amount of the raw material powder. _Two When the weight ratio of Mo included in the additive is A weight% and the weight ratio of Mo included in the additive is B weight%, the relationship of A and B is 0.025 ≦ B / A ≦ 3. Made up,
And at least Mo during sintering _5-X Si _Three C _1-Y (0 ≦ X ≦ 2, 0 ≦ Y <1), and after sintering, at least Si _Three N _Four And MoSi _Two And Mo _5-X Si _Three C _1-Y Is mixed with Si _Three N _Four At least MoSi wrapping particles _Two Particles and Mo _5-X Si _Three C _1-Y A ceramic heater characterized in that the particles and the particles have a continuous structure.
[0011]
The most remarkable point in the present invention is that the raw material of the conductive ceramic body is Si _Three N _Four And MoSi _Two A raw material powder comprising a metal Mo, a carbide of Mo, or an additive selected from one or more selected from borides of Mo; MoSi _Two The ratio (B / A) of the amount of Mo (A wt%) contained in the additive and the amount of Mo (B wt%) contained in the additive material is set to 0.025 to 3.
[0012]
In the presence of Mo, MoSi _Two Reacts with Mo Five Si _Three And Mo in the presence of Mo and carbon _5-X Si _Three C _1-Y (0 ≦ X ≦ 2, 0 ≦ Y <1). Mo _5-X Si _Three C _1-Y Is Mo Five Si _Three Although C is a basic composition, Mo and C easily cause lattice defects as in the first invention. _5-X Si _Three C _1-Y It is expressed as
[0013]
Si_ThreeN_FourContains 20 to 80% by weight in 100% by weight of the raw material powder.Possessioning. When the content is less than 20% by weight, Si for realizing high strength of the conductive ceramic body is used._ThreeN_FourIs too small, cracks may occur during use, and it cannot be put to practical use. On the other hand, if it exceeds 80% by weight, the durability of the conductive ceramic body is insufficient, and it is difficult to put it to practical use. This is because the insulating ceramic Si_ThreeN_FourIt is considered that the amount of the conductive layer becomes too large, the cross-sectional area of the conductive path becomes small, the stress at the time of energization becomes excessive, and the deterioration of the conductive part is promoted.
The conductive path is a path of a continuous conductive ceramic body. The conductive part is Si_ThreeN_FourIt refers to a mixed structure with a continuous conductive ceramic surrounding the particles.
[0014]
A sintering aid is added to and mixed with the raw material powder. As the sintering aid, for example, Al _Two O _Three , SiO _Two , MgAl _Two O _Four , MgO, ZrO _Two , Ta _Two O _Five Metal oxides such as Y _Two O _Three , Nd _Two O _Four , CeO _Two , La _Two O _Three , Yb _Two O _Three One or more selected from the group consisting of a metal oxide containing a rare earth element such as Al, a metal compound such as AlN, and a metal such as Si can be used.
The sintering aid is preferably added and mixed in an amount of 3 to 30 parts by weight based on 100 parts by weight of the raw material powder. If the amount is less than 3 parts by weight, sinterability may deteriorate. On the other hand, when it exceeds 30 parts by weight, the specific resistance may be increased. In addition, heat resistance may be significantly reduced.
[0015]
When the mixed powder comprising the raw material powder and the sintering aid is molded and sintered by heating, Mo _5-X Si _Three C _1-Y (0 ≦ X ≦ 2, 0 ≦ Y <1) are formed. Mo _5-X Si _Three C _1-Y Is Mo _Five Si _Three Although C is a basic composition, two of the five Mo atoms are liable to cause lattice defects, and C is also liable to cause lattice defects. _5-X Si _Three C _1-Y It is expressed as
[0016]
As a method of manufacturing the ceramic heater, for example, in a method of manufacturing a ceramic heater having a conductive ceramic body capable of generating heat by electric power supplied from the outside,
The conductive ceramic body is
Si _Three N _Four And MoSi _Two And a mixed powder obtained by adding and mixing a sintering aid to a raw material powder comprising one or more additives selected from metal Mo, a carbide of Mo or a boride of Mo. The mixed powder is molded and sintered by heating. _Three N _Four Is contained in an amount of 20 to 80% by weight with respect to 100% by weight of the total amount of the raw material powder, and MoSi is contained with respect to 100% by weight of the total amount of the raw material powder. _Two When the weight ratio of Mo included in the additive is A weight% and the weight ratio of Mo included in the additive is B weight%, the relationship of A and B is 0.025 ≦ B / A ≦ 3. There is a method for manufacturing a ceramic heater characterized by being satisfied.
[0017]
The firing atmosphere for heat sintering is preferably a non-oxidizing atmosphere. As a result, deterioration of the conductive ceramic can be reduced. The non-oxidizing atmosphere can be made of, for example, argon gas, but may be any atmosphere as long as the effects of the present invention can be obtained.
[0018]
The firing temperature may be any temperature at which the effects of the present invention can be obtained. The firing method includes, for example, a hot press method, but is not limited thereto, and may be any method that can obtain the effects of the present invention.
The mixed powder is mixed with an organic binder and formed into a desired shape. At this time, a plasticizer can be added and mixed.
[0019]
As a reference, in a ceramic heater having a conductive ceramic body capable of generating heat by electric power supplied from the outside,
The conductive ceramic body is
Si _Three N _Four And MoSi _Two A mixed powder obtained by adding and mixing a sintering aid to a raw material powder composed of SiC and SiC, molding the mixed powder, and sintering the mixture;
Si _Three N _Four Is contained in an amount of 20 to 80% by weight based on the total amount of the raw material powder of 100% by weight. _Two And SiC weight ratio (MoSi _Two Weight% / weight of SiC) is 1 to 40,
In addition, at least the Mo _5-X Si _Three C _1-Y (0 ≦ X ≦ 2, 0 ≦ Y <1), and after sintering, at least Si _Three N _Four And MoSi _Two And Mo _5-X Si _Three C _1-Y Is mixed with Si _Three N _Four At least MoSi wrapping particles _Two And Mo _5-X Si _Three C _1-Y There is a ceramic heater characterized in that particles have a continuous structure with each other.
[0020]
In the above, the conductive ceramic body is made of Si _Three N _Four And MoSi _Two The raw material powders consisting of SiC and SiC are used, and their compounding ratio is determined by the range (b, f, p) surrounded by the quadrilateral connecting the four points b, f, p, and o in the ternary composition diagram shown in FIG. , O). The compositions of b, f, p, and o are the values shown in Table 1 (values with the second decimal place rounded off).
[0021]
[Table 1]

[0022]
In the above, MoSi _Two And SiC weight ratio (MoSi _Two % /% By weight of SiC) is 1 to 40. When the weight ratio is increased within this range, the resistance change rate increases, and conversely, when the weight ratio decreases, the resistance change rate decreases. When the weight ratio is less than 1, no change in the resistance change rate of the conductive ceramic body is observed. Conversely, when the weight ratio exceeds 40, there is a problem that the durability of the conductive ceramic body is reduced.
[0023]
Next, as a method of manufacturing the ceramic heater as the above reference, for example, in a method of manufacturing a ceramic heater having a conductive ceramic body capable of generating heat by electric power supplied from the outside,
The conductive ceramic body is
Si _Three N _Four And MoSi _Two A mixed powder obtained by adding and mixing a sintering aid to a raw material powder composed of SiC and SiC, molding the mixed powder, and sintering the mixture;
Si _Three N _Four Is contained in an amount of 20 to 80% by weight based on the total amount of the raw material powder of 100% by weight. _Two And SiC weight ratio (MoSi _Two (Weight% / weight% of SiC) is 1 to 40.
[0024]
[Action and effect]
the aboveFor referenceIn a ceramic heater, part of SiC is decomposed into Si and C during sintering. Si gasifies and scatters. C is part of MoSi_TwoReacts with Mo5Si_ThreeMo with smaller resistance change rate_5-XSi_ThreeC_1-YIt becomes. In the conductive path, at least MoSi_TwoAnd Mo_5-XSi_ThreeC_1-YAnd a mixed organization.
[0025]
In the conductive part, Si₃  N₄  At least MoSi wrapping particles₂  And Mo_5-XSi₃  C_1-YAre continuous with each other. That is, Mo_5-XSi₃  C_1-YIs MoSi₂  And a conductive path together. In addition, this MoSi₂  And Mo_5-XSi₃  C_1-YIs mixed with Si₃  N₄  It wraps the particles and forms a conductive part consisting of a continuous tissue. MoSi above₂  And Mo_5-XSi₃  C_1-YIs a conductive material, and the normal temperature resistance value is determined by the total amount of these.
[0026]
When increasing the amount of SiC added,_5-XSi₃  C_1-YWhen the amount of SiC increases and the amount of SiC added decreases,_5-XSi₃  C_1-YIs reduced. By increasing or decreasing the amount of SiC added in this manner, MoSi₂  And Mo_5-XSi₃  C_1-YAnd the generation ratio changes. MoSi₂  Has a large rate of change in resistance,_5-XSi₃  C_1-YHas a small resistance change rate. Therefore, the resistance change rate of the conductive ceramic body is MoSi₂  And Mo_5-XSi₃  C_1-YIs determined by the generation ratio.
[0027]
Therefore, Si₃  N₄  And the amount of MoSi₂  By simply changing the amount of SiC added and the amount of SiC added, it is possible to easily obtain an arbitrary room temperature resistance value and an arbitrary resistance change rate under a constant hot pressing condition.
[0028]
Most of the undecomposed SiC is taken into the grain boundary glass formed by the sintering aid, and the other fine SiC is₃  N₄  It is taken in. This suppresses the diffusion of elements in the grain boundary glass and the decomposition of the grain boundary glass, and improves the durability of the grain boundary glass. Therefore, a highly durable ceramic heater can be obtained.
[0029]
Further, according to the method for manufacturing a ceramic heater, the excellent ceramic heater can be easily manufactured.
[0030]
Application No. 1In the ceramic heater of the present invention, at the time of sintering, a part of MoSi_TwoBetween the Mo of the additive and the carbon which is the decomposition residue of the organic substance or the carbon contained in the additive,
3MoSi_Two  + (7─2X) Mo + (2─2Y) C → 2Mo_5-XSi_ThreeC_1-Y
Reaction occurs, Mo_5-XSi_ThreeC_1-YIs generated.
[0031]
Mo above_5-XSi₃  C_1-YIs determined by the amount of the additive, and if the amount is appropriately adjusted as in the present invention, MoSi₂  And Mo_5-XSi₃  C_1-YCan be mixed, so that the conductive path is at least MoSi₂  And Mo_5-XSi₃  C_1-YAnd a mixed structure with Si₃  N₄  At least MoSi wrapping particles₂  And Mo_5-XSi₃  C_1-YForm a continuous conductive structure.
[0032]
Here, the room temperature resistance value is MoSi which is a conductive material.₂  And Mo_5-XSi₃  C_1-YThe resistance change rate is determined by the MoSi having a large resistance change rate.₂  And Mo with small resistance change rate_5-XSi₃  C_1-YIs determined by the ratio of
[0033]
Therefore, Si₃  N₄  Amount of MoSi and MoSi₂  By changing the weight ratio between the amount of the additive and the amount of the additive, it is possible to easily obtain an arbitrary room temperature resistance value and an arbitrary resistance change rate under a constant hot pressing condition.
Most of the surplus carbon or boron in the additive is taken into the grain boundary glass formed by the sintering aid. Thereby, movement of the grain boundary glass and decomposition of the grain boundary glass are suppressed, and the durability of the grain boundary glass is improved. Therefore, the durability of the ceramic heater increases.
[0034]
Further, according to the method for manufacturing a ceramic heater, the excellent ceramic heater can be easily manufactured.
[0035]
As described above, according to the ceramic heater according to the present invention, in the production of various heaters, it is not necessary to adjust the mixing ratio of nitrogen and argon gas each time during heating and sintering, and the durability and productivity of the ceramic heater are reduced. Can be higher.
[0036]
ADVANTAGE OF THE INVENTION According to this invention, the resistance change rate can be set arbitrarily and easily, The ceramic heater excellent in durability and productivity, and its manufacturing method can be provided.
[0037]
【Example】
referenceExample 1
referenceAn example of a ceramic heater will be described with reference to FIGS. The ceramic heater of this example is used for a glow plug for a diesel engine.
[0038]
As shown in FIG. 1, the ceramic heater 1 has a heating element 2 that can generate heat by electric power supplied from the outside through the electrode wires 4 and 5. The heating element 2 is a conductive ceramic body and is made of Si.₃  N₄  (Average particle size 10μm) and MoSi₂  (Average particle size 1 μm) and raw material powder composed of SiC (average particle size 0.3 μm)₂  O₃  Was added, mixed, molded and heated and fired.
Si₃  N₄  Is contained in an amount of 50% by weight based on the total amount of the raw material powders of 100% by weight. MoSi₂  And SiC weight ratio (MoSi₂  % /% By weight of SiC) is 1 to 32.3.
[0039]
In the reaction during sintering, at least Mo_5-XSi₃  C_1-Y(0 ≦ X ≦ 2, 0 ≦ Y ≦ 1). After sintering, at least Si₃  N₄  And MoSi₂  And Mo_5-XSi₃  C_1-YIs mixed with Si₃  N₄  At least MoSi wrapping particles₂  And Mo_5-XSi₃  C_1-YA composition in which the particles and the particles are continuous with each other is obtained.
Hereinafter, these will be described in detail.
[0040]
That is, as shown in FIG. 1, the ceramic heater 1 has a support 3 made of a circular insulating ceramic body and a U-shaped conductive ceramic body embedded at the tip of the support 3. It comprises a body 2 and electrode wires 4 and 5 having a circular cross section buried at the base end and the center of the support 3.
[0041]
The base ends of the electrode wires 4 and 5 are exposed to the outer periphery of the support 3 to form terminals 43 and 53. Tip portions 41 and 51 of the electrode wires 4 and 5 are connected to both end surfaces of the heating element 2. The electrode wires 4 and 5 are usually made of a refractory metal such as tungsten or molybdenum or an alloy thereof, but in this embodiment, a tungsten wire having a circular cross section is used. The radius of curvature of the terminals 43, 53 is equal to the radius of the support 3.
[0042]
Next, a method for manufacturing the ceramic heater 1 will be described.
In manufacturing the conductive ceramic body as the heating element 2, first, an Si having an average particle diameter of 10 μm was used.₃  N₄  Powder and MoSi with average particle size of 1μm₂  Powder and β─SiC powder having an average particle diameter of 0.3 μm are used as raw material powders. For 100% by weight of the total amount of the raw material powder,₃  N₄  The powder contains 50.0% by weight. MoSi₂  The powder varies between 25.0 and 48.5% by weight, and the β @ SiC powder varies between 1.5 and 25.0% by weight. MoSi₂  And SiC weight ratio (MoSi₂  % /% By weight of SiC) is 1 to 32.3.
[0043]
A total amount of 100 parts by weight was added to the above raw material powder, and Y as a sintering aid was used.₂  O₃  10 parts by weight of powder are added. This is mixed and stirred with a solvent such as ethanol, dried, then added with a binder made of paraffin, attack polypropylene and high-density polyethylene, and kneaded with a kneader at 180 ° C. for 3 hours to obtain a mixed powder of a conductive ceramic body. .
[0044]
In manufacturing the insulating ceramic body as the support 3, first, an Si having an average particle size of 0.7 μm was used.₃  N₄  MoSi with powder 50.0% by weight and average particle size 1μm₂  And 50.0% by weight of the powder to obtain a raw material powder. The total amount of this raw material powder was set to 100 parts by weight, and Y as a sintering aid was added.₂  O₃  10 parts by weight of the powder is added, and a mixed powder of an insulating ceramic body is obtained in the same manner as in the above-described conductive ceramic body.
[0045]
Next, using the mixed powder for the conductive ceramic body and the mixed powder for the insulating ceramic body, an integrated molded body is produced by an injection molding method. At this time, the electrode wires 4 and 5 are integrally incorporated. Next, the integrally molded body is once heated to 500 ° C. in a nitrogen atmosphere to scatter the binder. Then, it is heated and sintered by a hot press method at 1750 ° C. in an argon atmosphere to obtain a conductive ceramic body.
[0046]
After heat sintering, the outer shape is cut to φ3.5 mm to obtain the shape shown in FIG. Here, the conductive ceramic body has a semicircular cross section and a cross sectional area of 2 mm.²  The length of the conductive portion from the positive end surface to the one end surface of the electrode wires 4 and 5 is 14 mm.
[0047]
The ceramic heater 1 is attached to the tip of a glow plug 19 for a diesel engine, as shown in FIG. That is, the ceramic heater is fitted and brazed to the metal hollow pipe 6 via a nickel plating layer provided on the side surface of the support 3. The hollow pipe 6 holds the ceramic heater 1 and is electrically connected to the terminal 53 of the electrode wire 5. The distal end of a cylindrical metal housing 10 having both ends open is fitted and brazed to the outer periphery of the hollow pipe 6. The metal housing 10 has a screw 101 for attachment to an engine (not shown).
[0048]
The metal cap 7 is brazed to the terminal 43 of the electrode wire 4 so as to cover the base end of the support 3. One end of a metal wire 8 is welded to the metal cap 7. The other end of the metal wire 8 is welded to the tip of the center shaft 9. A male screw portion 91 formed at the base end of the center shaft 9 is connected to an electrode (not shown). The center shaft 9 is fitted into the housing 10.
The center shaft 9 is electrically insulated from the housing 10 by a glass seal 11 and an insulating bush 12. The insulating bush 12 is fixed by a nut 13 screwed to the male screw portion 91.
[0049]
The glow plug 19 is connected to a glow plug (not shown) from a power source (not shown) via the central shaft 9, metal wire 8, metal cap 7, electrode wire 4, heating element 2, electrode wire 5, hollow pipe 6, and housing 10. Electricity can be supplied.
[0050]
Next, various characteristics of the ceramic heater of this example were measured. As a result, the room temperature resistance was 0.162 to 3.016Ω, and the resistance at 1000 ° C. was 0.653 to 4.313Ω.
The rate of change in resistance (resistance at 1000 ° C./resistance at room temperature) changed between 1.43 and 4.03. And MoSi₂  As the amount increases, the rate of change in resistance of the conductive ceramic body increases.₂  When the amount was reduced, the rate of change in resistance also decreased.
For this reason, the ceramic heater of this example is MoSi₂  It can be seen that an arbitrary resistance change rate can be easily set by increasing or decreasing the amount of addition of Si and SiC.
[0051]
Next, a durability test was performed by repeating the current application for 1 minute and the current application stop for 1 minute at a voltage at which the ceramic heater became 1200 ° C. At 19000-25000 cycles, the resistance value changed by 10% from the value before the test. did. If it is 10,000 cycles or more, there is no practical problem. Therefore, the ceramic heater of the present example far exceeds its target value, and can be said to have excellent durability.
[0052]
referenceExample 2
In this example, a ceramic heater was manufactured by changing the composition of the mixed powder of the conductive ceramic body, and its characteristics were measured.
As shown in Table 2, the mixed powder of the conductive ceramic body was made of Si._ThreeN_FourAnd MoSi_TwoRaw material powder consisting of and β─SiC, and Al_TwoO_ThreeAnd Y_TwoO_ThreeThe sintering aid was prepared by changing the mixing ratio of the sintering aid.
[0053]
OthersreferenceEach of the ceramic heaters was manufactured in the same manner as in Example 1 to obtain samples a to q. In addition, Si_ThreeN_Four, MoSi_Two, SiC are shown in the ternary composition diagram of FIG. Note that points a to q shown in the ternary composition diagram of FIG. 3 correspond to samples a to q.
For each ceramic heater,referenceIn the same manner as in Example 1, the resistance value, the rate of change in resistance, and the durability shown in Table 2 were measured. The results are shown in Table 2.
[0054]
[Table 2]

[0055]
Next, the measurement results will be described.
First, MoSi without β─SiC was added.₂  And Si₃  N₄  Samples a, h, and n using the above as raw material powders will be described. MoSi₂  Is a conductive ceramic, MoSi₂  In the case of a with a large amount of addition, a low resistance value and a high resistance change rate were obtained. Conversely, when n was added in a small amount, the resistance value was high and the rate of change in resistance was small. From this result, MoSi₂  It can be seen that the resistance change rate can be changed only by changing the amount of addition, but the resistance value also changes greatly, and it is difficult to realize a predetermined resistance value and a predetermined resistance change rate with a heating element having a fixed shape.
[0056]
As described above, Si₃  N₄  And MoSi₂  The reason that the resistance of the conductive ceramic body changes only by changing the ratio of₂  It is considered that this is because it is determined by the amount of addition.
[0057]
In addition, Si₃  N₄  And MoSi₂  The reason that the rate of change of resistance of the conductive ceramic body changes only by changing the ratio of the conductive ceramic body is that the resistance change rate of the conductive ceramic body shown in the literature is the value of the heater in which the entire conductive portion is made of a conductive material. On the other hand, when the ceramic heater has a mixed structure of a conductive ceramic body and an insulating ceramic body as in this example, the substantially conductive portion is reduced by the mixture of the insulating ceramic bodies, and the insulating ceramic body and the conductive ceramic body are mixed. This is considered to be because the contact resistance and the like caused by the thermal stress on each particle due to the difference in the coefficient of linear expansion between the particles has a complicated influence.
[0058]
Next, regarding the effect of β─SiC addition,₃  N₄  The explanation will be made by using the samples h, i, j, k, l, and m in an amount of 50% by weight. As the β─SiC amount is increased to i, j, k, l, m, the resistance change rate decreases. According to the results of the samples 1 and m, even if β 所 定 SiC is added in a predetermined amount or more, the resistance change rate no longer changes. This means that Si₃  N₄  Samples a, b, c, d, e, f, g, and Si in an amount of 20% by weight₃  N₄  The same can be said for the samples n, o, and p whose amounts are 80% by weight.
[0059]
Summarizing the above results, the amount of β─SiC is MoSi_Two1/40 to MoSi_TwoUp to the same amount, ie, MoSi_TwoWeight ratio of the amount of β─SiC (MoSi_TwoIs between 1 and 40, the MoSi_TwoBy appropriately setting the amount and the amount of β─SiC, it is possible to easily obtain a ceramic heater having a predetermined resistance value and a predetermined resistance change rate with a heating element of a fixed shape without changing the dimensions of the conductive ceramic body. We can see that we can do it. Also, the addition of βＣSiC greatly improves the durability.An exampleIt can also be seen that the characteristics of the ceramic heater are not affected by the sintering aid.
[0060]
Where Si₃  N₄  When added in excess of 80% by weight, the room temperature resistance value changes early, making practical use difficult. The reason is that the insulating ceramic Si₃  N₄  It is considered that the amount of the metal layer becomes too large, the cross-sectional area of the conductive path becomes small, the stress at the time of energization becomes excessive, and the deterioration of the conductive portion is promoted. If less than 20% by weight, high strength Si₃  N₄  Is too small and cracks occur during use, which is not suitable for practical use in this case as well.
[0061]
From the above, Si₃  N₄  20-80% by weight, MoSi₂  And the total amount of β８０SiC is 80 to 20% by weight.₂  Weight ratio of the amount of β─SiC (MoSi₂  It can be said that it is desirable to use a raw material powder having a ratio of 1% to 40% by weight (% by weight of β─SiC) as a starting material. That is, in the ternary composition diagram of FIG. 3, it is desirable to select an appropriate composition within a composition range surrounded by connecting b, f, p, and o by a straight line.
[0062]
that's allIsAs described in the example of the addition of β─SiC, the resistance, resistance change rate, and durability of the present invention can be obtained by decomposition of SiC during sintering, and α─SiC becomes β─SiC during sintering. Since some changes occur, it can be said that the same effect can be obtained with α─SiC.
The raw material powder Si_ThreeN_FourIs α─Si_ThreeN_FourPowder, β─Si_ThreeN_FourPowder, α─Si_ThreeN_FourPowder and β─Si_ThreeN_FourConfirmed by powder mixed with powder, but all,sameExcellent effect was confirmed.
[0063]
The average particle size was 10 μm.₃  N₄  Powder and 1μm MoSi₂  As described in the examples of the powder and the 0.3 μm β─SiC powder,₃  N₄  At least MoSi wrapping particles₂  And Mo_5-XSi₃  C_1-YWhat is necessary is just to form a conductive ceramic body in which the particles have a continuous structure.
[0064]
From our experience, Si₃  N₄  The average particle size of₂  And at least three times the average particle size of SiC. If less than three times, MoSi₂  And Mo_5-XSi₃  C_1-YIn some cases, the particles did not form a continuous structure. The reason for setting it to be three times or more was that no upper limit was set because similar results were obtained even when using ultrafine SiC particles having an average particle size of 0.01 to 0.03 μm.
[0065]
Example1
In the ceramic heater according to the embodiment of the present invention, the conductive ceramic body is made of Si._ThreeN_FourAnd MoSi_TwoAnd Mo borides (additives) and a sintering aid.
[0066]
A method for manufacturing the conductive ceramic body will be described.
First, α─Si with an average particle size of 10 μm₃  N₄  Powder and MoSi with average particle size of 1μm₂  The powder and the MoB powder having an average particle size of 1 μm are used as raw material powders. Α─Si with respect to 100% by weight of the total amount₃  N₄  The powder is added at 50.0% by weight. MoSi₂  The powder varies between 25.0 and 49.0% by weight, and the MoB powder varies between 25.0 and 1.0% by weight.
[0067]
A total amount of 100 parts by weight was added to the above raw material powder, and Y as a sintering aid was used.₂  O₃  Add 10 parts by weight of powder. This is mixed and stirred with a solvent such as ethanol, dried, then added with a binder made of paraffin, attack polypropylene and high-density polyethylene, and kneaded with a kneader at 180 ° C. for 3 hours to obtain a mixed powder of a conductive ceramic body. .
[0068]
The insulating ceramic body as a support is made of α─Si having an average particle size of 1 μm._ThreeN_FourMoSi with powder 50.0% by weight and average particle size 1μm_TwoA basic raw material for an insulating ceramic body is obtained in the same manner as described above using 50.0% by weight of the powder.
Next, using the above-mentioned mixed powder of the conductive ceramic body and the mixed powder of the insulating ceramic body, an integrally molded body is produced by an injection molding method. The integrally molded body is once heated to 500 ° C. in a nitrogen atmosphere to scatter the binder. Then, it is heated and sintered by hot pressing at 1730 ° C. in an argon atmosphere. Thereby, a ceramic heater is obtained.
OthersreferenceSame as Example 1.
[0069]
Next, various characteristics of the ceramic heater of this example were measured. As a result, the room temperature resistance was 0.258 to 3.382 and the resistance at 1000 ° C. was 1.078 to 6.798Ω. The rate of change in resistance (resistance at 1000 ° C./resistance at room temperature) changed from 4.18 to 2.01. For this reason, the ceramic heater of this example is MoSi₂  It can be seen that an arbitrary resistance change rate can be easily set by increasing or decreasing the amount of addition of the metal and the additive.
[0070]
Next, the durability test of the ceramic heater was performed.referenceWhen the test was performed in the same manner as in Example 1, the resistance value changed by 10% from the value before the test at the 17000 to 18000th cycle. Since the number of cycles exceeds 10,000 which is practically acceptable, it can be said that the ceramic heater of this example has excellent durability.
[0071]
Example2
In this example, the relationship between the composition of the mixed powder of the conductive ceramic body and various characteristics of the ceramic heater was investigated.
First, Si_ThreeN_FourAnd MoSi_TwoThe effect of the compounding ratio on the characteristics of the ceramic heater was investigated.
[0072]
In the investigation, first, as shown in Table 3, without using additives,_ThreeN_FourPowder and MoSi_TwoA mixed powder of a conductive ceramic body was prepared by changing the mixing ratio with the powder, and ceramic heaters were prepared from the mixed powder to obtain samples 1 to 7, respectively. For these, the characteristics shown in Table 3 werereferenceThe measurement was performed in the same manner as in Example 1.
[0073]
As is evident from Table 3, the room temperature resistance is the same as that of the insulating material Si.₃  N₄  Sample 1 with a small amount is low. Si₃  N₄  When the amount is increased to Samples 2 to 7, the room temperature resistance value sequentially increases.
As for durability, Si₃  N₄  Sample 1 having an amount of less than 20% by weight is not suitable for practical use because cracks occur in 4000 cycles due to repeated thermal stress during use. This is because Si₃  N₄  Contributes to the improvement of the strength of the ceramic heater.₃  N₄  It is considered that the amount was small and the strength decreased.
[0074]
Si₃  N₄  The sample 7 containing more than 80% by weight also had a change in the room temperature resistance value at an early stage, and was difficult to put into practical use. This is because the insulating ceramic Si₃  N₄  Is considered to be too large, the cross-sectional area of the conductive path becomes small, the stress at the time of energization becomes excessive, and the deterioration of the conductive part is promoted. From the results in Table 3, considering practical use, Si for forming a conductive heating element was₃  N₄  It can be said that the amount is desirably 20 to 80% by weight.
[0075]
Next, based on the results in Table 3, Si_ThreeN_FourAnd MoSi_TwoThe effect of the compounding ratio of the additive and the metal Mo as an additive on the various characteristics of the ceramic heater was investigated.
That is, Si_ThreeN_FourAnd MoSi_TwoA raw material powder composed of and metal Mo was prepared in the proportions shown in Tables 4 and 5. The ceramic heaters manufactured using these were designated as Samples 2, 4, 6, 8 to 21, respectively, and these characteristics were measured.referenceThe measurement was performed in the same manner as in Example 1. The results are shown in Tables 4 and 5.
[0076]
The above result will be described.
In both tables, B / A is Si₃  N₄  Quantity and MoSi₂  MoSi with respect to a total weight of 100% by weight of the amount of Mo and the amount of Mo as an additive₂  Is the weight ratio (B / A) when the amount of Mo contained in is set to A weight% and the amount of Mo as an additive is set to B weight%. MoSi₂  The amount of Mo (A weight%) contained in₂  In parentheses below the weight percent of
[0077]
Next, the above measurement results will be considered.
First, Si without the addition of Mo as an additive was used._ThreeN_FourAnd MoSi_TwoFrom the results of Samples 2, 4, and 6 using_ThreeN_FourAnd MoSi_TwoEven if only the weight ratio is changed, the resistance change rate changes, but the resistance value at room temperature and 1000 ° C. also greatly changes. Is difficult to obtain. The reason is,referenceAs described in Example 2.
[0078]
Next, the effect of the addition of metal Mo as an additive of the present invention will be described with reference to Si.₃  N₄  Will be described in Samples 4, 13, 14, 15, 16, and 17 in which the addition amount of is 50% by weight. The resistance change rate of Sample 4 to which Mo was not added was 4.21. Then, as the amount of Mo increases with samples 13 to 17, the rate of change in resistance decreases. According to the results of Samples 16 and 17, even if Mo is added in a predetermined amount or more, the resistance change rate no longer changes. This result is₃  N₄  This is also true for Samples 6, 18, 19, 20, and 21 in which the amount of added is 80% by weight.
[0079]
Summarizing the results in Tables 4 and 5, MoSi_TwoMoSi so that the ratio (B / A) of the amount of Mo (A weight%) contained in the steel and the amount of Mo as an additive (B weight%) becomes 0.025-3._TwoIt can be seen that by setting the amount and the Mo amount, a ceramic heater having a predetermined resistance value and a predetermined resistance change rate can be easily obtained only by slightly changing the size of the conductive portion as needed. Further, FiringIt can be seen that it is not affected by the binder.
[0080]
[Table 3]

[0081]
[Table 4]

[0082]
[Table 5]

[0083]
Example 5
In this example, as an additive, a carbide of Mo or a boride of Mo shown in Table 6 was used as an additive, and the additive and MoSi were used.₂  The ceramic heaters (Samples 22 to 33) were manufactured by changing the compounding ratio of these. Others are the same as the fourth embodiment. Various properties of these samples were measured. The results are shown in Table 6.
[0084]
From the results shown in Table 5, MoSi was found to be similar to the results shown in Tables 4 and 5 of Example 4.₂  (B / A) between the amount of Mo (A wt%) contained in the additive and the amount of Mo (B wt%, the value in parentheses in Table 6) contained in the additive consisting of Mo carbide and Mo boride However, it can be said that it is desirable to use a raw material powder satisfying 0.025 ≦ B / A ≦ 3 as a starting material.
[0085]
After all, Si_ThreeN_FourAnd MoSi_Two100% by weight of raw material powder consisting of_ThreeN_FourIs 20 to 80% by weight._TwoThe ratio (B / A) of the amount of Mo (B wt%) contained in one or two or more of the metals Mo, the carbides and borides of Mo, Mo contained in A composition of 0.025 to 3 is desirable.
[0086]
Also, in the ceramic heater of this example,referenceAs in Example 2, Si_ThreeN_FourThe average particle size of_TwoIt is desirable that the average particle diameter of Mo and Mo is three times or more.
[0087]
[Table 6]

[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a ceramic heater according to a first embodiment.
FIG. 2 is a cross-sectional view of a glow plug provided with the ceramic heater of the first embodiment.
FIG. 3 is a ternary composition diagram of a conductive ceramic body of Example 2.
[Explanation of symbols]
1. . . Ceramic heater,
19. . . Glow plug,
2. . . Heating element,
3. . . Support,
4,5. . . Electrode wire,

Claims (2)

In a ceramic heater having a conductive ceramic body capable of generating heat by electric power supplied from the outside,
The conductive ceramic body is
A sintering aid is added to and mixed with a raw material powder composed of Si ₃ N ₄ , MoSi ₂ , metal Mo, a carbide of Mo or one or more additives selected from borides of Mo. Using a mixed powder that is molded and heat-sintered,
Si ₃ N ₄ is contained in an amount of 20 to 80% by weight based on 100% by weight of the total amount of the raw material powder, and the weight ratio of Mo contained in MoSi ₂ to the total amount of 100% by weight of the raw material powder is represented by A weight. %, And when the weight ratio of Mo contained in the additive material is B weight%, the relationship of 0.025 ≦ B / A ≦ 3 holds for A and B,
In addition, at least Mo _5-X Si ₃ C _1-Y (0 ≦ X ≦ 2, 0 ≦ Y <1) is formed during sintering, and at least Si ₃ N ₄ , MoSi ₂ and Mo _5-X after sintering. Si ₃ C _{1 -Y} is mixed, and at least MoSi ₂ particles and Mo ₅ -x Si ₃ C _{1 -Y} particles surrounding Si ₃ N ₄ particles have a continuous structure with each other. Ceramic heater. In a method of manufacturing a ceramic heater having a conductive ceramic body capable of generating heat by electric power supplied from the outside,
The conductive ceramic body is
A sintering aid is added to and mixed with a raw material powder composed of Si ₃ N ₄ , MoSi ₂ , metal Mo, a carbide of Mo or one or more additives selected from borides of Mo. Using a mixed powder that is molded and heat-sintered,
Si ₃ N ₄ is contained in an amount of 20 to 80% by weight based on 100% by weight of the total amount of the raw material powder, and the weight ratio of Mo contained in MoSi ₂ to the total amount of 100% by weight of the raw material powder is represented by A weight. %, And when the weight ratio of Mo contained in the additive is B weight%, the above A and B satisfy the relationship of 0.025 ≦ B / A ≦ 3. Method.

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