JP4216037B2

JP4216037B2 - Electromagnetic wave heating device, heating sheath used in electromagnetic wave heating device, and method for producing ceramics using them

Info

Publication number: JP4216037B2
Application number: JP2002303771A
Authority: JP
Inventors: 茂半澤; 次朗前田
Original assignee: NGK Insulators Ltd
Current assignee: NGK Insulators Ltd
Priority date: 2002-10-18
Filing date: 2002-10-18
Publication date: 2009-01-28
Anticipated expiration: 2022-10-18
Also published as: JP2004138327A

Description

【０００１】
【発明の属する技術分野】
本発明は、セラミックス成形体あるいはセラミックス仮焼体を電磁波により加熱するための電磁波加熱装置、電磁波加熱装置に用いる加熱用サヤ及びそれらを用いたセラミックスの製造方法に係るものである。
【０００２】
【従来の技術】
各種セラミックスの加熱装置としては、ガス炉、電気炉等が用いられており、これらの加熱装置はバーナーやヒーター等により被処理体の外部から加熱が行われる方式である。そのため、被処理体の表面が先に加熱される事となり、被処理体の内部と表面に温度差が生じ、その内外温度差に起因する熱応力によって被処理体に割れやクラック等の不具合をもたらしている。
【０００３】
これらの不具合を防止するために、緩やかな昇温速度で長時間加熱することで、内外温度差を小さくする方法が採られている。しかしながら、加熱処理工程の長時間化は使用電力量及びガス量が増加することとなり、結果としてコストの増大、環境悪化等の問題をもたらしている。
【０００４】
また電磁波により、被処理体に自己発熱させる加熱法が提案されている。(特許文献１参照)。この加熱法では、外部加熱方式のような被処理体の内外温度差が生じない。従って、急速加熱を行っても被処理体に割れやクラック等が発生しないため短時間処理が期待されている。
【０００５】
しかし現実には、単純に被処理体を電磁波加熱した場合（電子レンジで食品を温めるような場合）、被処理体は加熱されるものの加熱炉の炉壁は低温のままで維持される。従って、被処理体の表面では、大気との熱伝達、炉壁との接触部からの熱伝導等に起因する放熱により温度が低下するので、結局は被処理体に内外温度差が生じることになる。この温度差はガス炉、電気炉による外部加熱時の温度差とは逆の傾向ではあるが、やはり被処理体に割れやクラック等の不具合をもたらしている。
【０００６】
これを防ぐために電磁波吸収率の良い材料、即ちＳｉＣ等の誘電損失の高い材料で炉内壁を構成し、内壁が電磁波により加熱されることで、被処理体の放熱を抑えながら焼結する方法が提案されている。(特許文献２参照)。しかし、一般にＳｉＣ材料を電磁波加熱装置の炉内壁として用いた場合、被処理体が最高焼結温度に到達するまでの時間、即ち昇温速度が処理を行う毎に安定せず工程管理への影響、被処理体の各種特性への影響が懸念される。
【０００７】
【特許文献１】
特開平６−２７９１２７号公報
【特許文献２】
特開昭５９−１３７７８５号公報
【０００８】
【発明が解決しようとする課題】
本発明は、上記の問題を解決するためになされたものであり、被処理体の内外温度差を小さくでき、且つ安定した短時間処理が可能となる電磁波加熱装置を提供する。
【０００９】
【課題を解決するための手段】
第１の発明は、金属製容器の内側に断熱材を配してなる加熱炉と、該加熱炉の内部に配置した被処理体に電磁波を照射する電磁波発生手段とを備えた電磁波加熱装置において、前記断熱材に耐酸化性が高く且つ誘電損失の高い材料が含有されていることを特徴とする。
【０００１０】
また第２の発明は、金属製容器の内側に断熱材を配してなる加熱炉と、該加熱炉の内部に配置した被処理体に電磁波を照射する電磁波発生手段とを備えた電磁波加熱装置において、前記断熱材の炉内部側表面に耐酸化性が高く且つ誘電損失の高い材料が含有されている層が付設されていることを特徴とする。
【００１１】
また第３の発明は、金属製容器の内側に断熱材を配してなる加熱炉と、該加熱炉の内部に配置した被処理体に電磁波を照射する電磁波発生手段とを備えた電磁波加熱装置において、前記断熱材と被処理体との間に耐酸化性が高く且つ誘電損失の高い材料が含有されているセラミックス焼結体を配置したことを特徴とする。
【００１２】
また第４の発明は、前記装置を用いてセラミックス成形体あるいはセラミックス仮焼体を加熱・焼結することを特徴とする、セラミックスの製造方法に係わるものである。
【００１３】
また第５の発明は、セラミックス成形体あるいはセラミックス仮焼体を、前記電磁波加熱装置で加熱・焼結する際にセラミックス成形体あるいは該セラミックス仮焼体を収める加熱用サヤであって、該加熱用サヤ材中に耐酸化性が高く且つ誘電損失の高い材料を含有させたことを特徴とする。
【００１４】
また第６の発明は、前記サヤを用いてセラミックス成形体あるいはセラミックス仮焼体を加熱・焼結することを特徴とする、セラミックスの製造方法に係わるものである。
【００１５】
また第１、第２、第３および第５の発明において、耐酸化性が高く且つ誘電損失の高い材料が平均粒径５００μｍ以上のα-ＳｉＣであることが好ましい。また、耐酸化性が高く且つ誘電損失の高い材料がＳｉ−ＳｉＣであることが好ましい。更に、耐酸化性が高く且つ誘電損失の高い材料がＫ、Ｃａ、Ｓｃ、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ、Ｚｎ、Ｇａ、Ｇｅ、Ａｓ、Ｓｅの少なくとも一種を含む化合物であって、且つ有元素量が合計で０．１ｗｔ％以上であることが好ましい。
【００１６】
ここで本発明を完成するに至った経緯を説明する。本発明者は、ＳｉＣ等の誘電損失の高い材料で炉内壁を構成し被処理体の放熱を抑えながら焼結する方法（特開昭５９−１３７７８５号公報）において、被処理体を所定温度まで昇温する時間、即ち昇温速度が毎回変動する要因について各種の検討・実験を行った。その結果、耐酸化性が高くしかも安定して誘電損失が高い材料を見出し、それを被処理体のまわりに配置することによって被処理体の昇温速度が安定し、且つ被処理体の内外温度差が小さくできる事を見出し、本発明を完成するに至った。
【００１７】
炉内壁の材料として、まずＳｉＣについて検討した。ＳｉＣ粒にはα型とβ型が存在し、α型はβ型に比べて耐酸化性、誘電損失が高いことが一般的に知られている。しかし各種実験の中でα−ＳｉＣを含む焼結体を内壁とした電磁波加熱装置においても、加熱を行う毎に被処理体が最高温度に到達するまでの時間、すなわち昇温速度が変動することが分かった。更なる実験を重ね昇温速度が変動する原因が、実験に用いたα−ＳｉＣの粒径に関係するのではと考えられるデータが得られた。このα−ＳｉＣの粒径と昇温速度の変動要因との関係が、ＳｉＣの酸化の進行によるものではないかと推定した。
【００１８】
そこで、α−ＳｉＣの平均粒径サイズと耐酸化性の関係を確認してみた。評価試料は、アルミナ粉末とα−ＳｉＣ粉末をそれぞれ５０ｗｔ％づつ配合したものに、所定量のバインダー、有機溶媒を加えて混錬し、１００×１００×１０ｍｍのサイズで成形・焼結したものであり、α−ＳｉＣ原料の平均粒径を変更して、それぞれ製作した。評価方法は、実際の加熱処理を模擬して１４００℃、１００時間の条件で大気中にて熱処理し、その後、耐酸化性の指標となるＳｉＣ結晶残存率を測定した。
【００１９】
図１にＳｉＣ原料の平均粒径と熱処理後のＳｉＣ結晶残存率との関係を評価した結果を示す。ＳｉＣ結晶残存率は、Ｘ線回折装置によりＳｉＣとＳｉＯ₂の比率を測定することで算出した。この実験結果から、ＳｉＣ粒径が小さいものではＳｉＣ結晶残存率が低く、平均粒径５００μｍ以上でＳｉＣ結晶残存率が８０％以上と高い値を示すことがわかる。なお、図1は、ＳｉＣ原料の平均粒径とＳｉＣ結晶残存率との関係を示すデータではあるが、焼結後のＳｉＣ粒を観察してみても、部分的に互いに結合してはいるものの、粒径自体の成長は無く、この評価結果は焼結後のＳｉＣ平均粒径とＳｉＣ結晶残存率の関係を示すデータとして置き換えることができる。
【００２０】
このように、β−ＳｉＣに比べ耐酸化性及び誘電損失が高いと言われているα−ＳｉＣであっても、粒径が小さいとＳｉＣ結晶残存率が著しく低下してしまう結果となった。このことは、ＳｉＣの酸化が進み酸化層が形成されいることを意味するものであり、またＳｉＣ結晶残存率が低下すれば必然的に誘電損失が低下することは言うまでもない。従って、α−ＳｉＣの場合は、その平均粒径が５００μｍ以上である事が好ましいことがわかる。
【００２１】
次にＳｉＣがＳｉ−ＳｉＣ化している場合について検討した。Ｓｉ−ＳｉＣを検討した理由は、Ｓｉ−ＳｉＣが誘電損失の高い材料であること及びＳｉＣ内の気孔中にＳｉを含浸させているため気孔率が極めて小さくなることから、耐酸化性も高くなると推定されるからである。
【００２２】
そこで、α−ＳｉＣの評価と同様に平均粒径サイズと耐酸化性の関係を確認してみた。評価試料は、α−ＳｉＣ粉末に所定量のカーボン粉末、バインダー、有機溶媒を加えて混錬し、１００×１００×１０ｍｍのサイズで成形し、その後Ｓｉを含浸させて焼結体としたものであり、α−ＳｉＣ原料の平均粒径を変更して、それぞれ製作した。図２に結果を示す通り、Ｓｉ−ＳｉＣについては、ＳｉＣの平均粒径によらずＳｉＣ結晶残存率が高いことがわかる。
【００２３】
このように、ＳｉＣをＳｉ−ＳｉＣ化した場合、もともと誘電損失が高い材料であるうえに気孔率が極めて小さいため、平均粒径が小さくてもＳｉＣ結晶残存率の低下はほとんどみられず、耐酸化性にも優れた材料であることがわかる。またＳｉ−ＳｉＣ焼結体は強度が高く、種々の化学物質・薬品等に対する耐蝕性も良好であり、破損したり劣化・変質することが極めて少ない材料であることから、電磁波加熱装置の炉壁材として好ましいものと言える。
【００２４】
上記の実験結果を基に、実際の電磁波加熱装置においてその効果を確認するため、更に次の実験を重ねた。アルミナ粉末と平均粒径５００μｍのα−ＳｉＣ粉末をそれぞれ５０％づつ配合したものに、所定量のバインダー、有機溶媒を加えて混錬し、成形・焼結してセラミックスサヤを作成した。このセラミックスサヤを断熱材と被処理体との間に配置し、２．４５ＧＨｚ帯での電磁波加熱を出力一定で加熱したときの、セラミックスサヤ内表面の昇温カーブを調べた。図３に結果を示す通り、３回の加熱例において、いずれも１６００℃までの昇温時間は1時間と安定している事がわかる。
【００２５】
次に、平均粒径が５０μｍのα−ＳｉＣ粉末を５０％含有するセラミックスサヤを、断熱材と被処理体との間に配置した時の昇温カーブを同様に調べた。図４に結果を示す通り、３回の加熱例において１６００℃までの昇温時間が、１〜３回目の順で順次遅くなっており、昇温速度が不安定である事が分かる。
【００２６】
以上の結果から、平均粒径が５００μｍ以上のα−ＳｉＣ原料を５０％含む焼結体であれば昇温速度が安定し、電磁波加熱装置の炉壁として有効であることがわかった。またα−ＳｉＣに比べ耐酸化性の高いＳｉ−ＳｉＣであれば、α−ＳｉＣ原料の平均粒径を５００μｍ以上にしなくても昇温速度が安定することは先の評価から容易に推定される。
【００２７】
続いて、電磁波加熱装置の炉内壁としてアルミナ純度の高いセラミックスが採用できないものかどうかを考えてみた。アルミナ原料を用いた耐火物は、ＳｉＣ原料を含む耐火物と比較して安価で耐酸化性も高いため、電磁波加熱装置の炉内壁に用いることが期待されるが、誘電損失が低く電磁波加熱され難いという問題がある。しかし特定の元素の化合物を、一定量以上含有させることにより誘電損失を高くすれば、急速昇温が可能になるのではないかと考えた。
【００２８】
含有させる元素としては、Ｋ、Ｃａ、Ｓｃ、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ、Ｚｎ、Ｇａ、Ｇｅ、Ａｓ、Ｓｅを選定し評価を行った。これらの元素を含む化合物を、高純度アルミナ耐火物原料に含有させ、成形、焼結を行い焼結体とし、電磁波による加熱具合を調査した。添加した化合物の種類は、それぞれＫＯＨ、ＣａＯ、Ｓｃ₂Ｏ₃、ＴｉＯ₂、Ｖ₂Ｏ₅、ＣｒＯ₃、ＭｎＯ₂、Ｆｅ₃Ｏ₄、Ｃｏ₂Ｏ３、ＮｉＯ、ＣｕＯ、ＺｎＯ、Ｇａ₂Ｏ₃、ＧｅＯ₂、Ａｓ₂Ｏ₃、ＳｅＯ₂であり、添加後の焼結体中の各元素の重量比率が表１に示す値となるように添加量を決定した。これらの焼結体を市販の１ｋＷ電子レンジ（シャープ社製、ＲＥ−ＶＣ１）にて電磁波加熱し、１００℃までの到達時間を計測した。その結果を図５に示す。
【００２９】
図５の結果からＫ、Ｃａ、Ｓｃ、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ、Ｚｎ、Ｇａ、Ｇｅ、Ａｓ、Ｓｅ元素を、一種以上、０．１ｗｔ％以上を含有した、試料Ｎｏ．１〜７の材料が５分以内に１００℃に達しており、アルミナ耐火物の電磁波吸収率が向上していることがわかる。すなわち、アルミナ耐火物の誘電損失が高くなったことが分る。また高純度アルミナ耐火物原料には０．０５ｗｔ％程度前記化合物が、微量不純物として含まれることがあるが、試料Ｎｏ．８の結果より、微量不純物程度では電磁波吸収率が向上しないことが分る。
【００３０】
この結果から、耐酸化性は高いが誘電損失が低く電磁波加熱装置の炉内壁にふさわしくないと考えられているアルミナ材料であっても、誘電損失が高い耐酸化性材料を添加する事で、誘電損失を高くすることが出来、急速昇温が可能になることがわかった。
【００３１】
【表１】

試料Ｎｏ．１，２，３，４，５，６，７：本願発明による実施例
試料Ｎｏ．８，９：比較例
【００３２】
以上の検討及び実験に示す通り、耐酸化性が高くしかも誘電損失が高い材料を、被処理体のまわりに配置することによって、従来技術（特開昭５９−１３７７８５号公報）による電磁波加熱法の欠点が解消されることを見出した。これにより、被処理体の内外温度差を小さくでき、安定した昇温時間が得られるため、被処理体の割れやクラックを防止し短時間処理も可能となる。
【００３３】
【発明の実施の形態】
本発明の実施の形態を説明するに当たり、まず従来の電磁波加熱装置の構成を図６に基づき説明する。図６に示す従来の加熱炉７は、金属製容器４の内側に誘電損失の低い通常の断熱材５を配置しただけの構造である。金属製容器４は、内面が電磁波の反射が可能な材料で形成されており、例えば、ステンレス鋼が挙げられる。金属製容器４の内側に配置される断熱材５は、全温度域において誘電損失ｔａｎδが０．０１以下の低損失のものが好ましく、内側に配置される被処理体６の温度が、金属製容器４に影響を与えない断熱性能が必要であり、例えばニチアス社製１７００ＭＤ等のアルミナファイバーボード、イソライト工業社製ＬＢＫ−３０００等のアルミナ耐火物レンガなどが用いられる。
【００３４】
続いて本発明の電磁波加熱装置を、図７〜１１に基づき説明する。まず断熱材の内部に誘電損失の高い耐酸化性材料を含有させた三つの例を、第１〜第３の実施形態として示す。
【００３５】
図７は第１の実施形態を示すもので、金属製容器４の内側に、従来の電磁波加熱装置である図６とは異なり内部に誘電損失の高い耐酸化性材料を分散して含有させた断熱材９を配置している。
【００３６】
前記第１の実施形態のように、誘電損失の高い耐酸化性材料を分散して含有させた断熱材９を用いた場合は、断熱材自身の発熱が金属製容器へ影響することも考えられる。このため第２の実施形態である図８においては、これを防止するために、金属製容器４の内側に誘電損失の低い通常の断熱材５を配し、更にその内側に、内部に誘電損失の高い耐酸化性材料を分散して含有させた断熱材９を配した二重構造となっている。
【００３７】
上記第1及び第２の実施形態における誘電損失の高い耐酸化性材料を分散して含有させた断熱材９は次の通り製造する。例えばアルミナファイバーボードとする場合は、解繊したセラミックスファイバーをアルミナゾル等の無機結合剤と共に水に分散させ、有機凝集剤などを添加し凝集させる際に、耐酸化性が高く且つ誘電損失の高い材料を添加し凝集させて成形し、その後焼結すれば良い。また、アルミナ耐火物レンガとする場合は、所定量のアルミナ粉末、バインダー、水又は有機溶媒に耐酸化性が高く且つ誘電損失の高い材料を添加したものを混錬し、所望形状に成形し、この成形体を脱脂、焼結する方法が挙げられる。
【００３８】
第1及び第２の実施形態において、断熱材に含有させる耐酸化性が高く且つ誘電損失の高い材料としては次の５種類が考えられる。まず、第1の材料はα−ＳｉＣ原料である。含有させるα−ＳｉＣ原料は市販のα−ＳｉＣ粒で良く平均粒径は５００μｍ以上、２ｍｍ以下とするのが好ましい。また、断熱材中への含有量は断熱効果を確保するために１〜５０ｗｔ％が好ましい。
【００３９】
また第２の材料はα−ＳｉＣの焼結体の粉砕物である。粉砕物の原料となるα−ＳｉＣ焼結体を次の通り製造する。所定量のカーボン粉末、ＳｉＣ粉末、バインダー、水又は有機溶媒を混錬したものを成形し、次いで、この成形体を減圧の不活性ガス又は真空中に配置し焼結することで得られる。このとき焼結体内のα−ＳｉＣ平均粒径が５００μｍ以上にする必要があり、使用するＳｉＣ粉末も平均粒径が５００μｍ以上のものを使用する必要がある。このようにして得られた焼結体を平均粒径５００μｍ以上２ｍｍ以下に粉砕する。断熱材中の粉砕物の含有量は断熱効果を確保するために１〜５０ｗｔ％が好ましい。
【００４０】
第３の材料はＳｉ−ＳｉＣ焼結体の粉砕物である。まず、粉砕物の原料となるＳｉ−ＳｉＣ焼結体を次の通り製造する。所定量のカーボン粉末、ＳｉＣ粉末、バインダー、水又は有機溶媒を混錬し、成形して所望形状の成形体を得る。この場合のＳｉＣ粉末の平均粒径は、前記の通り５００μｍ以下でもかまわない。この成形体と金属Ｓｉを減圧の不活性ガス又は真空中に配置し、成形体中に金属Ｓｉを含浸させ焼結体とする方法を挙げる事が出来る。Ｓｉ含浸量は全体の５〜３０ｗｔ％が好ましい。
【００４１】
このようにして得られたＳｉ−ＳｉＣ焼結体を粉砕して、その粉砕物の平均粒径を５００μｍ以上、２ｍｍ以下にする。粉砕物の添加量は、断熱効果を確保するためにも１〜５０ｗｔ％が好ましい。
【００４２】
第４の材料は、Ｋ、Ｃａ、Ｓｃ、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ、Ｚｎ、Ｇａ、Ｇｅ、Ａｓ、Ｓｅを含む化合物である。添加する化合物種としては、ＫＯＨ、ＣａＯ、Ｓｃ₂Ｏ₃、ＴｉＯ₂、Ｖ₂Ｏ₅、ＣｒＯ₃、ＭｎＯ₂、Ｆｅ₃Ｏ₄、Ｃｏ₂Ｏ₃、ＮｉＯ、ＣｕＯ、ＺｎＯ、Ｇａ₂Ｏ₃、ＧｅＯ₂、Ａｓ₂Ｏ₃、ＳｅＯ₂がある。断熱材中には、上記元素の少なくとも一種を含んいる必要があり、上記元素の合計含有量は微量で良いものの、高純度アルミナ耐火物原料に微量不純物として含まれている０．０５ｗｔ％程度では効果がなく、０．１ｗｔ％以上を含有させるのが好ましい。なお、元素の含有量を変更する事で誘電損失を調整することが可能である。
【００４３】
第５の材料は、Ｋ、Ｃａ、Ｓｃ、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ、Ｚｎ、Ｇａ、Ｇｅ、Ａｓ、Ｓｅを含む化合物を含有させた焼結体の粉砕物である。焼結体の粉砕物を断熱材中に含有させる場合においても、上記元素の少なくとも一種を含んでいる必要があり、元素の合計含有量は０．１ｗｔ％以上とするのが好ましい。
【００４４】
次に、断熱材の内部に誘電損失の高い耐酸化性材料を含有させた別の例を第３の実施形態として図９に示す。この実施形態においては、断熱材としては誘電損失の低い通常の耐火物レンガ１０を用いている。このレンガを、誘電損失の高い耐酸化性材料を含有する接着剤１１を用いて接着した例である。接着剤に含有させる場合においても、前記第１〜第５の材料を使用することが可能であり、材料の粒径及び含有量は第1及び第２の実施態様の場合と同じで良い。
【００４５】
以上、３つの実施の形態は、断熱材中に誘電損失の高い耐酸化性材料を含有させた例を示すものであるが、続いて第４の実施形態として通常の断熱材の内表面に誘電損失の高い耐酸化性材料を付設した例を図１０に示す。図１０は、通常の断熱材５の内表面に、誘電損失の高い耐酸化性材料を含有するペースト状のものを塗布し、塗膜として誘電損失の高い耐酸化性材料を含有する層を付設した構成である。付設方法としては、水ガラス、アルミナ等を有機バインダーとともにペースト状にしたものに、誘電損失の高い耐酸化性材料の粉末、または焼結体の粉砕物を混合し、断熱材内表面に塗布、その後断熱材と共に乾燥、仮焼結を実施する。
【００４６】
第４の実施形態に用いられる耐酸化性が高く且つ誘電損失の高い材料に関しては、基本的には前記第１から第３の実施形態の場合と同様であるが、異なる点としては、断熱性が確保された通常の断熱材に塗布して用いられることから、断熱性に配慮する必要が無く、含有量を多くできる点である。従って、前記第１の材料(α−ＳｉＣ原料)、第２の材料(α−ＳｉＣの焼結体の粉砕物)及び第３の材料(Ｓｉ−ＳｉＣ焼結体の粉砕物)の含有量は、混合物がペースト状になり、断熱材の内表面に塗布することが出来る程度の量迄は許容され、１〜８０ｗｔ％とすることができる。前記第4の材料(Ｋ、Ｃａ等を含む化合物)及び第５の材料(Ｋ、Ｃａ等の元素を含有した耐酸化性焼結体の粉砕物)の含有量は、少なくとも０．１ｗｔ％以上が必要で、通常は数ｗｔ％添加するのが好ましい。塗膜１２の厚さは、いずれの材料を用いる場合においても、被処理体にも電磁波を低出力で照射させたいため、薄いものが好ましく０．１〜５ｍｍ程度が良い。
【００４７】
最後に、誘電損失の高い耐酸化性材料を含有するセラミックス焼結体を加熱用サヤとして配置した例を、第５の実施形態として図１１に示す。図１１は、通常の断熱材５の内側に、誘電損失の高い耐酸化性材料を含有する加熱用サヤ１３を配置した構成となっている。耐酸化性が高く且つ誘電損失の高い材料を含有した加熱用サヤの製造方法は次の通りである。所定量のアルミナ粉末、バインダー、水又は有機溶媒に耐酸化性が高く且つ誘電損失の高い材料を添加したものを混錬し、成形して所望形状の成形体を得る。次いで、この成形体を脱脂、焼結する方法が挙げられる。耐酸化性が高く且つ誘電損失の高い材料の含有量については、断熱性が確保された通常の断熱材が用いられたうえで更にサヤを追加配置していることから、第４の実施形態と同様、含有量を多くすることができる。
【００４８】
前記第１の材料(α−ＳｉＣ原料)を用いる場合、最小は１ｗｔ％以上含有させれば効果があるものの、断熱性が確保された通常の断熱材が用いられたうえで更にサヤを追加配置していることと、更にα−ＳｉＣ原料の成形性が良いこともあって、アルミナ等を主成分とした耐火物材料を用いず、α−ＳｉＣ１００ｗｔ％のサヤにすることもできる。
【００４９】
前記第２の材料(α−ＳｉＣの焼結体の粉砕物)を用いる場合の含有量も、最小は１ｗｔ％以上で効果があることにかわりないが、α−ＳｉＣ原料に比べ成形性が悪いことから、アルミナ等を主成分とした耐火物材料も必要になるため、最大含有量は８０ｗｔ％に留めるのが好ましい。
【００５０】
また前記第３の材料(Ｓｉ−ＳｉＣ焼結体の粉砕物)を用いる場合の含有量も、成形性の観点から１〜８０ｗｔ％が好ましい。なお、この加熱用サヤを用いる第５の実施形態においては、サヤをＳｉ−ＳｉＣ焼結体にすることも可能である。
【００５１】
前記第4の材料(Ｋ、Ｃａ等を含む化合物)及び第５材料(Ｋ、Ｃａ等の元素を含有した耐酸化性焼結体の粉砕物)の含有量は、少なくとも０．１ｗｔ％以上が必要で、通常は数ｗｔ％添加するのが好ましい。また第１〜第５いずれの材料を用いた場合においても、サヤ厚さは被処理体に低出力で電磁波を照射させるために、出来るだけ薄くすることが好ましく、０．１〜１０ｍｍ程度が良い。但し、強度を維持する必要もあるので２〜１０ｍｍ程度が更に好ましい。
【００５２】
【実施例】
(実施例１)
本発明の第1の実施例を図８を参照して説明する。図８において、金属製容器４と断熱材５と誘電損失の高い耐酸化性材料を含有した断熱材９とから構成される加熱炉７に、マイクロ波発振器１が４台設置され、マイクロ波発振器１から、それぞれ導波管２を通して金属製容器４内に電磁波が入射される。炉内８からの反射波がマイクロ波発振器１に戻らないように、導波管２にはアイソレーター３が取りつけてある。本実施例では周波数２．４５ＧＨｚ、発振器出力１．５ｋＷ／１台の電磁波発振装置１を４台設置して、合計６ｋＷの出力とした。
【００５３】
加熱炉７を構成する金属製容器４は、ステンレス製で幅１．５ｍ、奥行１．０ｍ、高さ１．０ｍとなっており、被処理体を設置するための扉が設けてある。
【００５４】
金属製容器の内側に配置された断熱材５は、アルミナファイバーボード（ニチアス社製１７００ＭＤ）で厚みは１００ｍｍ、断熱材５の内側寸法は幅３００ｍｍ、奥行３００ｍｍ、高さ３００ｍｍとした。断熱材５の内側に配置した誘電損失の高い耐酸化性材料を含有した断熱材９としては、粒径５００μｍのα−ＳｉＣ原料を含んだアルミナファイバーボードを用いた。
【００５５】
α−ＳｉＣ原料を含んだアルミナファイバーボード製の断熱材の製作は、解繊したセラミックスファイバーをアルミナゾルと共に水に分散させ、有機凝集剤と粒径５００μｍのα−ＳｉＣ原料を添加し凝集させ成形した。その後１１００℃の焼結を行い、焼結体とした。
【００５６】
焼結後の断熱材内のα−ＳｉＣ粒は、部分的に互いに結合してはいるものの、粒径自体の成長は無く粒径は原料粒径と変わらず５００μｍであった。含有量は２０ｗｔ％で焼結後のアルミナファイバーボードの厚みは５０ｍｍ、内側寸法は幅２５０ｍｍ、奥行２５０ｍｍ、高さ２５０ｍｍとした。
【００５７】
被処理体６としては、９８％純度のアルミナ粉を造粒した原料を、加圧力５００ｋｇ／ｃｍ２で金型成形したアルミナ成形体を用いた。サンプル寸法は幅６０ｍｍ、奥行６０ｍｍ、高さ３０ｍｍとした。
【００５８】
この被処理体６を、上記の電磁波加熱装置を用いて発信器出力６ｋＷのフルパワーで加熱・焼結を行い、被処理体６の表面温度と加熱時間の関係を測定した。温度の測定は、金属容器４、断熱材５、誘電損失の高い耐酸化性材料を含有する断熱材９に測温用穴（Φ１５ｍｍ）を設け、サンプル表面の温度を放射温度計で測定した。結果は図１１に示す通り1時間で１４００℃まで昇温できた。
【００５９】
また、断熱材５の内側に設けた誘電損失の高い耐酸化性材料を含有する断熱材９の内側表面温度も同時に測定した。結果は図１２に示す通りで、図１１のアルミナ成形体の昇温速度とほとんど差が無い事がわかる。
【００６０】
また、比較例として、前記と同じアルミナ成形体からなる被処理体６を、誘電損失の高い耐酸化性材料を含んだ断熱材９で囲まない構成で、同一パワーで加熱・焼結した。結果は図１３に示す通り、１４００℃まで昇温するのに約５時間かかった。
【００６１】
この結果から、誘電損失の高い耐酸化性材料を含有する断熱材９を用いた本発明は、低温域（室温〜１１００℃）での昇温速度が著しく速くなることがわかる。また、焼結後の被処理体や誘電損失の高い耐酸化性材料を含んだ断熱材９には割れやクラックの発生は認められなかった。
【００６２】
(実施例２)
次に、本発明の第２の実施例を、図１０を参照して説明する。図１０において、基本構成は先に記述した実施例１と同じであるが、誘電損失の高い耐酸化性材料を含有する断熱材９の替わりに、誘電損失の高い耐酸化性材料を含有する層１２を塗布している。
【００６３】
誘電損失の高い耐酸化性材料を含有する層１２は、水ガラス、アルミナ粉末原料、有機バインダーであるＰＶＡ、誘電損失の高いＦｅ３Ｏ４を混合し、断熱材内表面に塗布、その後乾燥、１５００℃の仮焼結を実施した。焼結後の塗布層の厚みは２ｍｍ、Ｆｅ元素の含有量は０．２ｗｔ％であった。
【００６４】
被処理体および処理条件を実施例１と同じ条件で評価した結果、１４００℃までの到達時間は約1時間であり、また、焼結後の被処理体や断熱材内側の塗布層には割れやクラックの発生は認められなかった。
【００６５】
(実施例３)
本発明の第３の実施例を図１１を参照して説明する。図１１において、基本構成は先に記述した実施例１と同じであるが、誘電損失の高い耐酸化性材料を含有する断熱材９の替わりに、誘電損失の高い耐酸化性材料を含有する加熱用サヤ１３を配してある。
【００６６】
断熱材５の内側に配置する誘電損失の高い耐酸化性材料を含有する加熱用サヤ１３としては、Ｓｉ−ＳｉＣ焼結体サヤを用いた。Ｓｉ−ＳｉＣサヤの製造は、まず、カーボン粉末５％、ＳｉＣ粉末８５％、バインダーとしてＰＶＡ２％を水で混錬し、その後板状に成形して成形体を得る。次いで、この板状成形体を箱状に組み、１６００℃の真空中で金属Ｓｉと接触させるように配置し、耐酸化性材料としてのＳｉ−ＳｉＣサヤを焼結した。この箱状焼結体の厚みは５ｍｍ、内壁の外寸法は幅２５０ｍｍ、奥行２５０ｍｍ、高さ２５０ｍｍとし、Ｓｉ含浸量は２０ｗｔ％とした。
【００６７】
被処理体および処理条件を実施例１及び２と同じ条件で評価した結果、１４００℃までの到達時間は約1時間であり、また、焼結後の被処理体や断熱材内側の塗布層には割れやクラックの発生は認められなかった。
【００６８】
【発明の効果】
以上述べたように、本願発明の電磁波加熱装置は、耐酸化性が高く、且つ誘電損失が高い材料を被処理体のまわりに配置することによって、被処理体の内外温度差を小さくでき、且つ被処理体の昇温速度を安定させることが可能となる。この結果、被処理体の割れやクラックを防止し、短時間処理も可能となる。また、繰り返し加熱による炉内壁の劣化もなく、安定した加熱が可能となる。
【図面の簡単な説明】
【図１】ＳｉＣを含む焼結体におけるＳｉＣ原料平均粒径と熱処理後のＳｉＣ結晶残存率の関係図。
【図２】Ｓｉ−ＳｉＣ焼結体におけるＳｉＣ原料平均粒径と熱処理後のＳｉＣ結晶残存率の関係図。
【図３】平均粒径５００μｍのＳｉＣ原料を含む耐火物をサヤとした場合の繰り返し加熱時の昇温カーブ推移。
【図４】平均粒径５０μｍのＳｉＣ原料を含む耐火物をサヤとした場合の繰り返し加熱時の昇温カーブ推移。
【図５】特定の元素を含むアルミナ耐火物の電子レンジ加熱実験結果。１００℃までの到達時間。
【図６】従来電磁波加熱装置を示す概略平断面図。
【図７】誘電損失の高い耐酸化性材料を含有する断熱材を使用した場合の概略平断面図１。
【図８】通常の断熱材の内側に誘電損失の高い耐酸化性材料を含有する断熱材を配置した場合の概略平断面図２。
【図９】誘電損失の高い耐酸化性材料を含有する接着剤で耐火物レンガを積み上げ断熱材とした場合の断熱材部分拡大図。
【図１０】断熱材の内表面に誘電損失の高い耐酸化性材料を含有する層を付設した場合の概略平断面図。
【図１１】断熱材の内側に誘電損失の高い耐酸化性材料を含有する加熱用サヤを配置した場合の概略平断面図。
【図１２】α−ＳｉＣを含んだ断熱材を用いて電磁波加熱を行なった時の被処理体表面温度昇温カーブ。
【図１３】α−ＳｉＣを含んだ断熱材を用いて電磁波加熱を行なった時の断熱材内壁表面温度昇温カーブ。
【図１４】α−ＳｉＣを含んだ断熱材を用いず、電磁波加熱を行なった時の被処理体表面温度昇温カーブ結果。
【符号の説明】
１…マイクロ波発振器、２…導波管、３…アイソレーター、４…金属製容器、５…断熱材、６…被処理体、７…加熱炉、８…炉内、９…誘電損失の高い耐酸化性材料を含有する断熱材、１０…耐火物レンガ、１１…誘電損失の高い耐酸化性材料を含有する接着剤、１２…誘電損失の高い耐酸化性材料を含有する層、１３…誘電損失の高い耐酸化性材料を含有する加熱用サヤ。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electromagnetic wave heating apparatus for heating a ceramic molded body or a ceramic calcined body by electromagnetic waves, a heating sheath used in the electromagnetic wave heating apparatus, and a method for producing ceramics using them.
[0002]
[Prior art]
As a heating device for various ceramics, a gas furnace, an electric furnace, or the like is used. These heating devices are systems in which heating is performed from the outside of an object to be processed by a burner, a heater, or the like. For this reason, the surface of the object to be processed is heated first, and a temperature difference is generated between the inside and the surface of the object to be processed. Has brought.
[0003]
In order to prevent these problems, a method of reducing the internal / external temperature difference by heating for a long time at a moderate temperature increase rate is employed. However, the prolonged heat treatment step increases the amount of power used and the amount of gas, resulting in problems such as increased costs and environmental degradation.
[0004]
In addition, a heating method for causing the object to be self-heated by electromagnetic waves has been proposed. (See Patent Document 1). In this heating method, the temperature difference between the inside and outside of the object to be processed does not occur as in the external heating method. Therefore, even if rapid heating is performed, cracks and cracks do not occur in the object to be processed, so that short time processing is expected.
[0005]
However, in reality, when the object to be treated is simply heated by electromagnetic waves (when food is heated in a microwave oven), the object to be treated is heated, but the furnace wall of the heating furnace is maintained at a low temperature. Therefore, on the surface of the object to be processed, the temperature decreases due to heat dissipation due to heat transfer to the atmosphere, heat conduction from the contact part with the furnace wall, etc. Become. Although this temperature difference tends to be opposite to the temperature difference during external heating by a gas furnace or an electric furnace, it also causes defects such as cracks and cracks in the workpiece.
[0006]
In order to prevent this, there is a method in which the furnace inner wall is composed of a material having a high electromagnetic wave absorption rate, that is, a material having a high dielectric loss such as SiC, and the inner wall is heated by electromagnetic waves, thereby sintering while suppressing heat dissipation of the object to be processed. Proposed. (See Patent Document 2). However, in general, when SiC material is used as the furnace inner wall of the electromagnetic wave heating device, the time until the workpiece reaches the maximum sintering temperature, that is, the rate of temperature rise is not stable every time the treatment is performed, and the influence on the process control. There is a concern about the influence on various properties of the object to be processed.
[0007]
[Patent Document 1]
JP-A-6-279127
[Patent Document 2]
JP 59-137785 A
[0008]
[Problems to be solved by the invention]
The present invention has been made to solve the above problems, and provides an electromagnetic wave heating device that can reduce the temperature difference between the inside and outside of the object to be processed and can perform stable short-time processing.
[0009]
[Means for Solving the Problems]
1st invention is an electromagnetic wave heating apparatus provided with the heating furnace which has arrange | positioned the heat insulating material inside the metal container, and the electromagnetic wave generation means to irradiate the to-be-processed object arrange | positioned inside this heating furnace with electromagnetic waves The heat insulating material contains a material having high oxidation resistance and high dielectric loss.
[00010]
According to a second aspect of the present invention, there is provided an electromagnetic wave heating apparatus comprising: a heating furnace in which a heat insulating material is disposed inside a metal container; and an electromagnetic wave generating means for irradiating an object to be processed disposed inside the heating furnace with an electromagnetic wave. In the above, a layer containing a material having high oxidation resistance and high dielectric loss is attached to the surface inside the furnace of the heat insulating material.
[0011]
A third invention is an electromagnetic wave heating apparatus comprising a heating furnace in which a heat insulating material is arranged inside a metal container, and an electromagnetic wave generating means for irradiating an electromagnetic wave to a target object disposed inside the heating furnace. The ceramic sintered body containing a material having high oxidation resistance and high dielectric loss is disposed between the heat insulating material and the object to be processed.
[0012]
According to a fourth aspect of the present invention, there is provided a method for producing a ceramic, characterized in that a ceramic molded body or a ceramic calcined body is heated and sintered using the apparatus.
[0013]
According to a fifth aspect of the present invention, there is provided a heating sheath for accommodating a ceramic molded body or the ceramic calcined body when the ceramic molded body or the ceramic calcined body is heated and sintered by the electromagnetic wave heating device. It is characterized in that the sheath material contains a material having high oxidation resistance and high dielectric loss.
[0014]
According to a sixth aspect of the present invention, there is provided a method for producing a ceramic, comprising heating and sintering a ceramic molded body or a ceramic calcined body using the sheath.
[0015]
In the first, second, third and fifth inventions, it is preferable that the material having high oxidation resistance and high dielectric loss is α-SiC having an average particle size of 500 μm or more. Further, it is preferable that the material having high oxidation resistance and high dielectric loss is Si—SiC. Further, the material having high oxidation resistance and high dielectric loss includes at least one of K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, and Se. It is preferable that the total amount of elements is 0.1 wt% or more.
[0016]
Here, the background to the completion of the present invention will be described. The present inventor uses a material having a high dielectric loss such as SiC to form a furnace inner wall and sinter while suppressing heat dissipation of the object to be processed (Japanese Patent Laid-Open No. 59-137785). Various examinations and experiments were conducted on the factors that cause the temperature rising time, that is, the temperature rising speed to change every time. As a result, a material having high oxidation resistance and stable and high dielectric loss is found, and by placing it around the object to be processed, the temperature increase rate of the object to be processed is stabilized, and the inside / outside temperature of the object to be processed The present inventors have found that the difference can be reduced and have completed the present invention.
[0017]
First, SiC was examined as a material for the furnace inner wall. It is generally known that SiC grains have α-type and β-type, and α-type has higher oxidation resistance and dielectric loss than β-type. However, even in an electromagnetic wave heating apparatus using a sintered body containing α-SiC as an inner wall in various experiments, the time until the workpiece reaches the maximum temperature, that is, the rate of temperature rise fluctuates every time heating is performed. I understood. Further experiments were conducted, and data that the reason why the temperature rising rate fluctuated was related to the particle diameter of α-SiC used in the experiment was obtained. It was estimated that the relationship between the α-SiC particle size and the heating rate fluctuation factor was due to the progress of oxidation of SiC.
[0018]
Therefore, the relationship between the average particle size of α-SiC and the oxidation resistance was examined. The evaluation sample is a mixture of alumina powder and α-SiC powder blended by 50 wt%, kneaded with a predetermined amount of binder and organic solvent, and molded and sintered to a size of 100 × 100 × 10 mm. Yes, the average particle diameter of the α-SiC raw material was changed, and each was produced. In the evaluation method, an actual heat treatment was simulated, heat treatment was performed in the atmosphere at 1400 ° C. for 100 hours, and then the SiC crystal residual ratio serving as an index of oxidation resistance was measured.
[0019]
FIG. 1 shows the result of evaluating the relationship between the average grain size of the SiC raw material and the SiC crystal remaining rate after the heat treatment. The SiC crystal residual rate is determined by using an X-ray diffractometer with SiC and SiO. ₂ It was calculated by measuring the ratio. From this experimental result, it can be seen that the SiC crystal remaining rate is low when the SiC particle size is small, and the SiC crystal remaining rate is as high as 80% or more when the average particle size is 500 μm or more. FIG. 1 is data showing the relationship between the average grain size of the SiC raw material and the SiC crystal residual ratio, but even though the SiC grains after sintering are observed, they are partially bonded to each other. There is no growth of the grain size itself, and this evaluation result can be replaced with data indicating the relationship between the SiC average grain size after sintering and the SiC crystal residual rate.
[0020]
Thus, even with α-SiC, which is said to have higher oxidation resistance and dielectric loss than β-SiC, the result is that the SiC crystal residual rate is significantly lowered when the particle size is small. This means that the oxidation of SiC proceeds and an oxide layer is formed, and it goes without saying that the dielectric loss inevitably decreases as the SiC crystal residual rate decreases. Therefore, in the case of α-SiC, it is understood that the average particle size is preferably 500 μm or more.
[0021]
Next, the case where SiC was converted to Si-SiC was examined. The reason for considering Si-SiC is that Si-SiC is a material with a high dielectric loss, and since the porosity in SiC is impregnated with Si, the porosity is extremely small, so that the oxidation resistance is also high. This is because it is estimated.
[0022]
Therefore, the relationship between the average particle size and the oxidation resistance was confirmed in the same manner as in the evaluation of α-SiC. The evaluation sample is a α-SiC powder which is kneaded by adding a predetermined amount of carbon powder, a binder and an organic solvent, molded to a size of 100 × 100 × 10 mm, and then impregnated with Si to form a sintered body. Yes, the average particle diameter of the α-SiC raw material was changed, and each was produced. As shown in FIG. 2, it can be seen that Si-SiC has a high SiC crystal residual rate regardless of the average grain size of SiC.
[0023]
Thus, when SiC is changed to Si-SiC, since it is a material with a high dielectric loss and the porosity is extremely small, even if the average particle size is small, there is almost no decrease in the residual rate of SiC crystals, and there is no acid resistance. It can be seen that the material has excellent chemical properties. In addition, the Si-SiC sintered body has high strength, good corrosion resistance against various chemical substances and chemicals, and is a material that is extremely unlikely to be damaged, deteriorated or deteriorated. It can be said that it is preferable as a material.
[0024]
Based on the above experimental results, the following experiment was repeated in order to confirm the effect in an actual electromagnetic wave heating apparatus. A ceramic sheath was prepared by blending 50% each of alumina powder and α-SiC powder having an average particle size of 500 μm, adding a predetermined amount of binder and organic solvent, kneading, molding and sintering. The ceramic sheath was placed between the heat insulating material and the object to be processed, and the temperature rise curve on the inner surface of the ceramic sheath when the electromagnetic wave heating in the 2.45 GHz band was heated at a constant output was examined. As can be seen from FIG. 3, in all three heating examples, the heating time up to 1600 ° C. is stable at 1 hour.
[0025]
Next, the temperature rise curve when a ceramic sheath containing 50% α-SiC powder having an average particle size of 50 μm was placed between the heat insulating material and the object to be processed was similarly examined. As shown in FIG. 4, in the three heating examples, the temperature rising time up to 1600 ° C. is sequentially delayed in the order of the first to third times, and it can be seen that the temperature rising rate is unstable.
[0026]
From the above results, it was found that if the sintered body contains 50% of an α-SiC raw material having an average particle size of 500 μm or more, the heating rate is stabilized and it is effective as a furnace wall of an electromagnetic wave heating device. In addition, if Si-SiC has higher oxidation resistance than α-SiC, it is easily estimated from the previous evaluation that the rate of temperature rise is stable even if the average particle size of the α-SiC raw material is not 500 μm or more. .
[0027]
Next, we considered whether ceramics with high alumina purity could not be used as the furnace inner wall of the electromagnetic wave heating device. Refractories using alumina raw materials are cheaper and have higher oxidation resistance than refractories containing SiC raw materials, so they are expected to be used for the inner wall of the furnace of electromagnetic wave heating devices. There is a problem that it is difficult. However, it was thought that rapid increase in temperature would be possible if the dielectric loss was increased by adding a certain amount of a compound of a specific element.
[0028]
As elements to be contained, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, and Se were selected and evaluated. A compound containing these elements was contained in a high-purity alumina refractory raw material, molded and sintered to obtain a sintered body, and the heating condition by electromagnetic waves was investigated. The types of added compounds are KOH, CaO, and Sc, respectively. ₂ O _Three TiO ₂ , V ₂ O _Five , CrO _Three , MnO ₂ , Fe _Three O _Four , Co ₂ O3, NiO, CuO, ZnO, Ga ₂ O _Three , GeO ₂ , As ₂ O _Three , SeO ₂ The addition amount was determined so that the weight ratio of each element in the sintered body after the addition was the value shown in Table 1. These sintered bodies were heated with an electromagnetic wave in a commercially available 1 kW microwave oven (manufactured by Sharp Corporation, RE-VC1), and the arrival time up to 100 ° C. was measured. The result is shown in FIG.
[0029]
From the results of FIG. 5, one or more elements such as K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, and Se were contained in an amount of 0.1 wt% or more. Sample No. It can be seen that the materials 1 to 7 reach 100 ° C. within 5 minutes, and the electromagnetic wave absorption rate of the alumina refractory is improved. That is, it can be seen that the dielectric loss of the alumina refractory is increased. Further, the high purity alumina refractory raw material may contain about 0.05 wt% of the compound as a trace impurity. From the result of 8, it can be seen that the electromagnetic wave absorptivity is not improved with a small amount of impurities.
[0030]
From this result, even if it is an alumina material that has high oxidation resistance but low dielectric loss and is not considered suitable for the inner wall of the furnace of the electromagnetic wave heating device, by adding an oxidation resistant material with high dielectric loss, It was found that loss can be increased and rapid temperature rise is possible.
[0031]
[Table 1]

Sample No. 1, 2, 3, 4, 5, 6, 7: Examples according to the present invention
Sample No. 8, 9: Comparative example
[0032]
As shown in the above examination and experiment, an electromagnetic heating method according to the prior art (Japanese Patent Laid-Open No. 59-137785) is arranged by arranging a material having high oxidation resistance and high dielectric loss around a workpiece. It was found that the drawbacks were eliminated. As a result, the temperature difference between the inside and outside of the object to be processed can be reduced, and a stable temperature raising time can be obtained.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
In describing the embodiment of the present invention, the configuration of a conventional electromagnetic wave heating apparatus will be described with reference to FIG. The conventional heating furnace 7 shown in FIG. 6 has a structure in which a normal heat insulating material 5 having a low dielectric loss is disposed inside the metal container 4. The metal container 4 has an inner surface formed of a material capable of reflecting electromagnetic waves, and examples thereof include stainless steel. The heat insulating material 5 disposed inside the metal container 4 is preferably a low-loss material having a dielectric loss tan δ of 0.01 or less over the entire temperature range, and the temperature of the object 6 disposed inside is made of metal. Heat insulation performance that does not affect the container 4 is necessary, and for example, alumina fiber board such as 1700MD manufactured by NICHIAS Corporation, alumina refractory brick such as LBK-3000 manufactured by Isolite Industrial Co., etc. are used.
[0034]
Then, the electromagnetic wave heating apparatus of this invention is demonstrated based on FIGS. First, three examples in which an oxidation-resistant material having a high dielectric loss is contained in the heat insulating material will be described as first to third embodiments.
[0035]
FIG. 7 shows the first embodiment. Unlike FIG. 6, which is a conventional electromagnetic wave heating device, an oxidation-resistant material having a high dielectric loss is dispersed and contained inside the metal container 4. A heat insulating material 9 is arranged.
[0036]
As in the first embodiment, when the heat insulating material 9 in which an oxidation resistant material having a high dielectric loss is dispersed is used, the heat generated by the heat insulating material itself may affect the metal container. . For this reason, in FIG. 8 which is the second embodiment, in order to prevent this, a normal heat insulating material 5 having a low dielectric loss is arranged inside the metal container 4, and further inside, a dielectric loss inside. It has a double structure in which a heat insulating material 9 in which a high oxidation resistant material is dispersed and contained.
[0037]
The heat insulating material 9 in which the oxidation-resistant material having a high dielectric loss in the first and second embodiments is dispersed and manufactured is manufactured as follows. For example, when alumina fiber board is used, a material with high oxidation resistance and high dielectric loss when disaggregated ceramic fibers are dispersed in water together with an inorganic binder such as alumina sol, and an organic flocculant is added to agglomerate. May be added, agglomerated and molded, and then sintered. In addition, when making an alumina refractory brick, kneading a predetermined amount of alumina powder, a binder, water or an organic solvent with a material having high oxidation resistance and high dielectric loss, and molding it into a desired shape, The method of degreasing and sintering this molded body is mentioned.
[0038]
In the first and second embodiments, the following five types of materials having high oxidation resistance and high dielectric loss may be included in the heat insulating material. First, the first material is an α-SiC raw material. The α-SiC raw material to be contained may be commercially available α-SiC particles, and the average particle size is preferably 500 μm or more and 2 mm or less. Further, the content in the heat insulating material is preferably 1 to 50 wt% in order to ensure the heat insulating effect.
[0039]
The second material is a pulverized product of an α-SiC sintered body. An α-SiC sintered body that is a raw material of the pulverized product is manufactured as follows. A mixture obtained by kneading a predetermined amount of carbon powder, SiC powder, binder, water or an organic solvent is molded, and then the molded body is placed in a vacuum inert gas or vacuum and sintered. At this time, the α-SiC average particle size in the sintered body needs to be 500 μm or more, and the SiC powder to be used needs to have an average particle size of 500 μm or more. The sintered body thus obtained is pulverized to an average particle size of 500 μm to 2 mm. The content of the pulverized material in the heat insulating material is preferably 1 to 50 wt% in order to ensure the heat insulating effect.
[0040]
The third material is a pulverized product of a Si—SiC sintered body. First, a Si—SiC sintered body that is a raw material of the pulverized product is manufactured as follows. A predetermined amount of carbon powder, SiC powder, binder, water or organic solvent is kneaded and molded to obtain a molded body having a desired shape. In this case, the average particle diameter of the SiC powder may be 500 μm or less as described above. An example is a method in which the compact and metal Si are placed in an inert gas or vacuum under reduced pressure, and the compact is impregnated with metal Si to form a sintered body. The Si impregnation amount is preferably 5 to 30 wt% of the whole.
[0041]
The Si—SiC sintered body thus obtained is pulverized so that the average particle size of the pulverized product is 500 μm or more and 2 mm or less. The added amount of the pulverized product is preferably 1 to 50 wt% in order to ensure the heat insulation effect.
[0042]
The fourth material is a compound containing K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, and Se. Compound types to be added include KOH, CaO, and Sc. ₂ O _Three TiO ₂ , V ₂ O _Five , CrO _Three , MnO ₂ , Fe _Three O _Four , Co ₂ O _Three , NiO, CuO, ZnO, Ga ₂ O _Three , GeO ₂ , As ₂ O _Three , SeO ₂ There is. In the heat insulating material, it is necessary to contain at least one of the above elements, and although the total content of the above elements may be a very small amount, in the case of about 0.05 wt% contained as a trace impurity in the high-purity alumina refractory raw material There is no effect and it is preferable to contain 0.1 wt% or more. Note that the dielectric loss can be adjusted by changing the element content.
[0043]
The fifth material is a pulverized product of a sintered body containing a compound containing K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, and Se. It is. Even when the pulverized product of the sintered body is contained in the heat insulating material, it is necessary to contain at least one of the above elements, and the total content of the elements is preferably 0.1 wt% or more.
[0044]
Next, another example in which an oxidation-resistant material having a high dielectric loss is included in the heat insulating material is shown as a third embodiment in FIG. In this embodiment, a normal refractory brick 10 having a low dielectric loss is used as the heat insulating material. This is an example in which this brick is bonded using an adhesive 11 containing an oxidation-resistant material having a high dielectric loss. Even when it is contained in the adhesive, the first to fifth materials can be used, and the particle size and content of the material may be the same as those in the first and second embodiments.
[0045]
As described above, the three embodiments show examples in which an oxidation-resistant material having a high dielectric loss is included in a heat insulating material. Subsequently, as a fourth embodiment, a dielectric is formed on the inner surface of a normal heat insulating material. An example in which an oxidation-resistant material with high loss is attached is shown in FIG. In FIG. 10, a paste-like material containing an oxidation-resistant material having a high dielectric loss is applied to the inner surface of a normal heat insulating material 5, and a layer containing an oxidation-resistant material having a high dielectric loss is provided as a coating film. This is the configuration. As an attachment method, water glass, alumina or the like made into a paste with an organic binder are mixed with a powder of an oxidation-resistant material having a high dielectric loss or a pulverized sintered body, and applied to the inner surface of the heat insulating material. Thereafter, drying and pre-sintering are performed together with the heat insulating material.
[0046]
The material having high oxidation resistance and high dielectric loss used in the fourth embodiment is basically the same as that in the first to third embodiments, except that the heat insulating property is different. Since it is used by applying to a normal heat insulating material in which is secured, there is no need to consider heat insulation, and the content can be increased. Accordingly, the contents of the first material (α-SiC raw material), the second material (crushed product of α-SiC sintered body) and the third material (crushed product of Si-SiC sintered body) are: The mixture becomes a paste and is allowed up to an amount that can be applied to the inner surface of the heat insulating material, and can be 1 to 80 wt%. The content of the fourth material (compound containing K, Ca, etc.) and the fifth material (pulverized product of oxidation-resistant sintered body containing elements such as K, Ca) is at least 0.1 wt% or more Usually, it is preferable to add several wt%. The thickness of the coating film 12 is preferably about 0.1 to 5 mm in order to irradiate the object to be processed with a low output power, regardless of which material is used.
[0047]
Finally, an example in which a ceramic sintered body containing an oxidation-resistant material having a high dielectric loss is arranged as a heating sheath is shown in FIG. 11 as a fifth embodiment. FIG. 11 shows a configuration in which a heating sheath 13 containing an oxidation-resistant material having a high dielectric loss is arranged inside a normal heat insulating material 5. A method of manufacturing a heating sheath containing a material having high oxidation resistance and high dielectric loss is as follows. A predetermined amount of alumina powder, binder, water or organic solvent to which a material having high oxidation resistance and high dielectric loss is added is kneaded and molded to obtain a molded body having a desired shape. Then, the method of degreasing and sintering this molded object is mentioned. With respect to the content of the material having high oxidation resistance and high dielectric loss, since a normal heat insulating material having heat insulating properties is used and further a sheath is additionally arranged, the fourth embodiment and Similarly, the content can be increased.
[0048]
When the first material (α-SiC raw material) is used, it is effective if the minimum content is 1 wt% or more. However, a normal heat insulating material that ensures heat insulation is used, and additional sheath is additionally disposed. In addition, since the moldability of the α-SiC raw material is good, a refractory material mainly composed of alumina or the like is not used, and a α-SiC 100 wt% sheath can be obtained.
[0049]
The content in the case of using the second material (a pulverized product of α-SiC sintered body) is not limited to 1 wt% or more at the minimum, but the moldability is worse than that of the α-SiC raw material. Therefore, since a refractory material mainly composed of alumina or the like is required, the maximum content is preferably limited to 80 wt%.
[0050]
Further, the content in the case of using the third material (crushed product of Si—SiC sintered body) is preferably 1 to 80 wt% from the viewpoint of moldability. In the fifth embodiment using the heating sheath, the sheath can be a Si—SiC sintered body.
[0051]
The content of the fourth material (compound containing K, Ca, etc.) and the fifth material (pulverized product of oxidation-resistant sintered body containing elements such as K, Ca) is at least 0.1 wt% or more. Usually, it is preferable to add several wt%. Even when any of the first to fifth materials is used, the thickness of the sheath is preferably as thin as possible in order to irradiate the object to be processed with an electromagnetic wave with low output, and is preferably about 0.1 to 10 mm. . However, since it is necessary to maintain the strength, about 2 to 10 mm is more preferable.
[0052]
【Example】
(Example 1)
A first embodiment of the present invention will be described with reference to FIG. In FIG. 8, four microwave oscillators 1 are installed in a heating furnace 7 composed of a metal container 4, a heat insulating material 5, and a heat insulating material 9 containing an oxidation-resistant material having a high dielectric loss. 1, electromagnetic waves are incident on the metal container 4 through the waveguide 2. An isolator 3 is attached to the waveguide 2 so that the reflected wave from the furnace 8 does not return to the microwave oscillator 1. In this example, four electromagnetic wave oscillation devices 1 having a frequency of 2.45 GHz and an oscillator output of 1.5 kW / 1 were installed to obtain a total output of 6 kW.
[0053]
The metal container 4 constituting the heating furnace 7 is made of stainless steel, has a width of 1.5 m, a depth of 1.0 m, and a height of 1.0 m, and is provided with a door for installing an object to be processed.
[0054]
The heat insulating material 5 arranged inside the metal container was an alumina fiber board (1700MD manufactured by Nichias), the thickness was 100 mm, and the inner dimensions of the heat insulating material 5 were a width of 300 mm, a depth of 300 mm, and a height of 300 mm. As the heat insulating material 9 containing an oxidation-resistant material having a high dielectric loss disposed inside the heat insulating material 5, an alumina fiber board containing an α-SiC raw material having a particle diameter of 500 μm was used.
[0055]
The production of the heat insulating material made of alumina fiber board containing the α-SiC raw material was performed by dispersing the defibrated ceramic fiber together with alumina sol in water, adding an organic flocculant and an α-SiC raw material having a particle size of 500 μm, and aggregating and molding . Thereafter, sintering was performed at 1100 ° C. to obtain a sintered body.
[0056]
Although the α-SiC grains in the heat insulating material after sintering were partially bonded to each other, there was no growth of the particle size itself, and the particle size was 500 μm unchanged from the raw material particle size. The content was 20 wt%, the thickness of the sintered alumina fiber board was 50 mm, the inner dimensions were width 250 mm, depth 250 mm, and height 250 mm.
[0057]
As the object 6 to be processed, an alumina molded body obtained by die-molding a raw material obtained by granulating 98% purity alumina powder at a pressure of 500 kg / cm 2 was used. The sample dimensions were 60 mm width, 60 mm depth, and 30 mm height.
[0058]
This object 6 was heated and sintered using the electromagnetic wave heating device described above with full power of a transmitter output of 6 kW, and the relationship between the surface temperature of the object 6 and the heating time was measured. The temperature was measured by providing a temperature measuring hole (Φ15 mm) in the metal container 4, the heat insulating material 5, and the heat insulating material 9 containing an oxidation-resistant material having a high dielectric loss, and the temperature of the sample surface was measured with a radiation thermometer. As a result, the temperature could be raised to 1400 ° C. in 1 hour as shown in FIG.
[0059]
Moreover, the inner surface temperature of the heat insulating material 9 containing the oxidation-resistant material with high dielectric loss provided inside the heat insulating material 5 was also measured. The result is as shown in FIG. 12, and it can be seen that there is almost no difference from the temperature rising rate of the alumina molded body of FIG.
[0060]
Further, as a comparative example, the object 6 made of the same alumina molded body as described above was heated and sintered with the same power in a configuration not surrounded by a heat insulating material 9 containing an oxidation-resistant material having a high dielectric loss. As a result, as shown in FIG. 13, it took about 5 hours to raise the temperature to 1400 ° C.
[0061]
From this result, it can be seen that the heating rate in the low temperature range (room temperature to 1100 ° C.) of the present invention using the heat insulating material 9 containing the oxidation resistant material having a high dielectric loss is remarkably increased. In addition, no cracks or cracks were observed in the heat-treated material 9 including the processed object after sintering and the oxidation-resistant material having a high dielectric loss.
[0062]
(Example 2)
Next, a second embodiment of the present invention will be described with reference to FIG. In FIG. 10, the basic configuration is the same as that of the first embodiment described above, but a layer containing an oxidation-resistant material having a high dielectric loss instead of the heat insulating material 9 containing an oxidation-resistant material having a high dielectric loss. 12 is applied.
[0063]
The layer 12 containing an oxidation-resistant material having a high dielectric loss is prepared by mixing water glass, alumina powder raw material, PVA as an organic binder, and Fe3O4 having a high dielectric loss, and coating the inner surface of the heat insulating material, followed by drying at 1500 ° C. Pre-sintering was performed. The thickness of the coating layer after sintering was 2 mm, and the content of Fe element was 0.2 wt%.
[0064]
As a result of evaluating the object to be processed and the processing conditions under the same conditions as in Example 1, the arrival time up to 1400 ° C. was about 1 hour, and the processed object after sintering and the coating layer inside the heat insulating material were cracked. No cracks were observed.
[0065]
Example 3
A third embodiment of the present invention will be described with reference to FIG. In FIG. 11, the basic configuration is the same as that of the first embodiment described above, but instead of the heat insulating material 9 containing an oxidation-resistant material having a high dielectric loss, heating containing an oxidation-resistant material having a high dielectric loss. Saya 13 is provided.
[0066]
A Si—SiC sintered body sheath was used as the heating sheath 13 containing an oxidation resistant material having a high dielectric loss disposed inside the heat insulating material 5. In the production of the Si-SiC sheath, first, 5% carbon powder, 85% SiC powder, and 2% PVA as a binder are kneaded with water, and then molded into a plate shape to obtain a molded body. Next, this plate-like molded body was assembled in a box shape and placed so as to contact with metal Si in a vacuum at 1600 ° C., and a Si—SiC sheath as an oxidation resistant material was sintered. The thickness of this box-shaped sintered body was 5 mm, the outer dimensions of the inner wall were 250 mm wide, 250 mm deep, 250 mm high, and the Si impregnation amount was 20 wt%.
[0067]
As a result of evaluating the object to be processed and the processing conditions under the same conditions as in Examples 1 and 2, the arrival time up to 1400 ° C. is about 1 hour, and the processed object after sintering and the coating layer inside the heat insulating material No cracks or cracks were observed.
[0068]
【The invention's effect】
As described above, the electromagnetic wave heating device of the present invention can reduce the temperature difference between the inside and outside of the object to be processed by disposing a material having high oxidation resistance and high dielectric loss around the object to be processed, and It becomes possible to stabilize the temperature increase rate of the workpiece. As a result, it is possible to prevent the object to be processed from cracking and cracking and to perform processing for a short time. In addition, stable heating is possible without deterioration of the furnace inner wall due to repeated heating.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the SiC raw material average grain size and the SiC crystal remaining rate after heat treatment in a sintered body containing SiC.
FIG. 2 is a graph showing the relationship between the SiC raw material average grain size and the SiC crystal remaining rate after heat treatment in a Si—SiC sintered body.
FIG. 3 shows a temperature rise curve transition during repeated heating when a refractory containing an SiC raw material having an average particle diameter of 500 μm is used as a sheath.
FIG. 4 shows a temperature rise curve transition during repeated heating when a refractory containing an SiC raw material having an average particle size of 50 μm is used as a sheath.
FIG. 5 is a result of a microwave heating experiment of an alumina refractory containing a specific element. Time to reach 100 ° C.
FIG. 6 is a schematic plan sectional view showing a conventional electromagnetic wave heating device.
FIG. 7 is a schematic plan sectional view 1 in the case of using a heat insulating material containing an oxidation resistant material having a high dielectric loss.
FIG. 8 is a schematic plan sectional view 2 in the case where a heat insulating material containing an oxidation resistant material having a high dielectric loss is arranged inside a normal heat insulating material.
FIG. 9 is a partial enlarged view of a heat insulating material when refractory bricks are stacked and used as an insulating material with an adhesive containing an oxidation resistant material having a high dielectric loss.
FIG. 10 is a schematic cross-sectional view in the case where a layer containing an oxidation-resistant material having a high dielectric loss is attached to the inner surface of the heat insulating material.
FIG. 11 is a schematic plan sectional view when a heating sheath containing an oxidation-resistant material having a high dielectric loss is arranged inside the heat insulating material.
FIG. 12 is a temperature rise curve of the surface temperature of an object to be treated when electromagnetic heating is performed using a heat insulating material containing α-SiC.
FIG. 13 is a temperature rise curve of an inner wall surface temperature of an insulating material when electromagnetic wave heating is performed using an insulating material containing α-SiC.
FIG. 14 is a graph showing a temperature rise curve of a surface of an object to be treated when electromagnetic heating is performed without using a heat insulating material containing α-SiC.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Microwave oscillator, 2 ... Waveguide, 3 ... Isolator, 4 ... Metal container, 5 ... Heat insulating material, 6 ... To-be-processed object, 7 ... Heating furnace, 8 ... In-furnace, 9 ... Acid resistance with high dielectric loss Thermal insulation material containing oxidizable material, 10 ... refractory brick, 11 ... Adhesive containing oxidation-resistant material with high dielectric loss, 12 ... Layer containing oxidation-resistant material with high dielectric loss, 13 ... Dielectric loss Saya for heating containing high oxidation resistance material.

Claims

An electromagnetic wave heating apparatus comprising: a heating furnace in which a heat insulating material is disposed inside a metal container; and an electromagnetic wave generating means for irradiating an electromagnetic wave to an object to be processed disposed inside the heating furnace. An electromagnetic wave heating device comprising an α-SiC material having an average particle size of 500 μm or more, having high chemical properties and high dielectric loss.

An electromagnetic wave heating apparatus comprising: a heating furnace in which a heat insulating material is disposed inside a metal container; and an electromagnetic wave generating means for irradiating an electromagnetic wave to an object to be processed disposed inside the heating furnace. An electromagnetic wave heating device, wherein a layer containing an α-SiC material having an average particle size of 500 μm or more and having high oxidation resistance and high dielectric loss is attached to the inner surface.

An electromagnetic wave heating apparatus comprising: a heating furnace in which a heat insulating material is disposed inside a metal container; and an electromagnetic wave generating means for irradiating an electromagnetic wave to an object to be processed disposed inside the heating furnace. An electromagnetic wave heating apparatus comprising: a ceramic sintered body containing an α-SiC material having an average particle size of 500 μm or more and having a high oxidation resistance and a high dielectric loss between the processing body.

A method for producing ceramics, comprising heating and sintering a ceramic formed body or a ceramic calcined body using the electromagnetic wave heating device according to any one of claims 1 to 3.

A heating sheath for storing the ceramic molded body or the ceramic calcined body when the ceramic molded body or the ceramic calcined body is heated and sintered by the electromagnetic wave heating device, and the heating sheath has high oxidation resistance. A heating sheath for use in an electromagnetic wave heating device comprising an α-SiC material having a high dielectric loss and an average particle size of 500 μm or more.

A method for producing ceramics comprising heating and sintering a ceramic molded body or calcined body using the heating sheath used in the electromagnetic wave heating device according to claim 5.