JP4507148B2 - Heat treatment member made of mullite sintered body - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は耐熱衝撃抵抗性、耐食性および高温下での変形にすぐれたムライト質焼結体からなる熱処理用部材に関する。
【０００２】
【従来技術とその問題点】
熱処理用部材としては耐熱性および耐食性にすぐれていることに加え、被熱処理材料を汚染しない材質であり、かつ被熱処理材料の含有する成分が炉内雰囲気中へ拡散することを防ぎ得ることが要望されている。古くから熱処理用部材としてアルミナ、マグネシア、石英、炭化けい素、ジルコニア等の材質が熱処理用部材として知られている。アルミナ、マグネシア、ジルコニア等の熱処理用部材は耐熱性にすぐれており、１８００℃程度の温度まで使用できる利点はあるが、耐熱衝撃抵抗性に劣り、急速な加熱、冷却ができないという欠点がある。石英は高価であり、加工性が悪く、高温状態において軟化やアルカリ元素の透過などが生じ、さらに失透に伴う劣化や破損が生じやすいという欠点がある。炭化けい素は耐熱衝撃抵抗性にすぐれるものの、酸化雰囲気下や開放雰囲気下では酸化による劣化や表面にガラス相を形成し、被処理材料と反応しやすいという欠点を有している。
【０００３】
一方、前記の欠点を解決する方法として特公平５−７７６２７号公報には緻密なムライト質からなる熱処理用容器が開示されている。しかしながら、この熱処理用容器を用いても、アルミナやマグネシアなどに比べて耐熱衝撃抵抗性の点ではすぐれるものの、まだ十分満足できていないのが現状である。
【０００４】
さらに、最近のリチウム２次電池用正極材料をはじめとする電子材料および蛍光体材料の熱処理においては、蒸発成分を極力少なくして組成の変動を少なくするため、および生産効率を高めるために急速昇温、降温処理がなされている。緻密質の焼結体からなる熱処理用部材は多孔質からなる熱処理用部材に比べて耐食性にはすぐれているものの急速昇温、降温では熱衝撃による割れが発生する危険性を有している。一方、多孔質からなる熱処理用部材は前記のように耐熱衝撃抵抗性では緻密質からなる熱処理用部材に比べてすぐれているものの気密性に劣り、熱処理用部材中の成分が被熱処理材料中に不純物として混入したり、また被熱処理材料と反応したりして被熱処理材料の組成変化が起こったり、また熱処理により被熱処理材料から蒸発する成分の被熱処理材料への吸着や反応がおこり、耐食性の低下、機械的特性の低下などの問題が生じている。
【０００５】
【問題を解決するための手段】
本発明は、前記のような現状を鑑み、鋭意研究を重ねてきた結果、ムライト質焼結体において、ある特定の相対密度を有し、丸みをもった密閉気孔を有し、その密閉気孔径および焼結体の結晶粒径を制御することおよびその密閉気孔径と結晶粒径との比を制御することによりすぐれた耐熱衝撃抵抗性および耐食性を有し、高温での変形が少ないムライト質焼結体からなる熱処理用部材を見出した。なお、本発明では、耐熱衝撃抵抗性は急熱・急冷によるクラックの発生や割れに対する抵抗性だけでなく、加熱・冷却の繰り返しによる耐久性を意味する。
【０００６】
即ち、本発明は、結晶相としてムライト結晶を８０容積％以上含有するムライト質焼結体であって、（ａ）ガラス相が１０容積％以下であり、（ｂ）焼結体に存在する気孔は主として密閉したものであり、（ｃ）その平均密閉気孔径が５〜３０μｍ、（ｄ）焼結体の平均結晶粒径が２〜３０μｍ、（ｅ）焼結体の平均密閉気孔径／平均結晶粒径が０．１〜６、（ｆ）焼結体の相対密度が７０〜９５％であることを特徴とするムライト質焼結体よりなる熱処理用部材に関するものであり、この熱処理用部材は耐熱衝撃抵抗性および耐食性にすぐれ、高温下での変形が少ないという特性を発揮する。
【０００７】
なお、本発明でいう熱処理用部材とは圧電体、誘電体などの電子部品材料、リチウムイオン２次電池正極材料、蛍光体材料およびセラミック材料の熱処理用容器、単結晶育成用ルツボ、金属溶解用ルツボ、各種熱処理用炉芯管、ローラハースキルン用ローラ、サポートチューブ、ラジアントチューブ、ガス吹込管、ガス採取管、測温用熱電対および各種機器用の保護管、サポート用治具材などがある。
【０００８】
以下に本発明の耐熱衝撃抵抗性および耐食性にすぐれ、高温下での変形が少ないムライト質焼結体からなる熱処理用部材が充足すべき各要件について詳細に述べる。
【０００９】
本発明における密閉気孔の形成には、粉砕・分散スラリーに所定の相対密度および気孔径になるように気孔形成剤としてアクリル系樹脂球状粒子や多糖類球状粒子などの有機質球状粒子のような有機質で丸味を帯びた粒子を使用する。この気孔形成剤をセラミック粉体に添加、混合して成形し、これを焼成すると、有機質の気孔形成剤は消失し、跡形としての密閉気孔が残るので、密閉気孔の形状は本質的には気孔形成剤の形状に基因した形状となり、前記請求項１の（ｂ）で規定し、図１（Ａ）、（Ｂ）に示すように気孔は丸味を帯びた密閉したものとなり、また密閉気孔は実質的に独立したものとなる。気孔形状が丸味を帯びていない場合には、焼結体に応力が負荷されると気孔に応力集中がおこりやすくなって、強度や耐熱衝撃抵抗性の低下および高温での変形がおこりやすくなるので好ましくない。なお、本発明でいう密閉気孔とは外部へ通じていない内部気孔のことを指すものである。
【００１０】
（ａ）結晶相としてムライト結晶が８０容積％以上含有するムライト質焼結体である。
本発明においてムライト質焼結体は、結晶相としてムライト結晶が８０容積％以上、より好ましくは９０容積％以上からなることが必要である。ムライト結晶が８０容積％未満の場合は、ムライト結晶以外の結晶がムライト結晶粒界および粒内に存在し、耐熱衝撃抵抗性、耐食性の低下や高温での変形が大きくなるので好ましくない。
【００１１】
また、本発明においてα−Ａｌ２Ｏ３結晶が１０容積％以下まで許容できる。より好ましくは８容積％以下である。α−Ａｌ２Ｏ３結晶が１０容積％を上回る場合は、被熱処理材料や炉壁などの耐火物から高温で揮発するアルカリ成分や熱源の燃料などに含まれているアルカリ成分等がα−Ａｌ２Ｏ３結晶と反応して、焼結体内部にβ−Ａｌ２Ｏ３結晶を形成させ、組織の変質やα−Ａｌ２Ｏ３結晶とムライト結晶との熱膨張の差による歪みが増大や残存膨張の増大等により耐熱衝撃抵抗性が低下するので好ましくない。ここで言うムライト結晶とは化学式３Ａｌ２Ｏ３・２ＳｉＯ２（Ａｌ２Ｏ３ ７１．８重量％、ＳｉＯ２ ２８．２重量％）で表されるムライト結晶だけでなく、ムライト固溶体も含むものとする。
【００１２】
本発明において、α−Ａｌ２Ｏ３結晶相の容積割合は以下の方法により得られる値である。即ち、まず試料の任意の位置から切り出した小片を粉砕し、得られた粉末についてＸ線回折を行う。その結果、得られるムライト結晶の（２１０）面の回折強度〔ＩＭ（２１０）〕およびα−Ａｌ２Ｏ３結晶の（１１３）面の回折強度〔ＩＡ（１１３）〕から次式によりムライト結晶およびα−Ａｌ２Ｏ３結晶の割合を算出する。
【数１】
（ｂ）ガラス相が１０容積％以下である。
本発明ではガラス相が１０容積％以下である。含有しているガラス相が１０容積％を越える場合には、ガラス相と被熱処理材料とが反応して、被熱処理材料を汚染したり、熱処理用部材とひっつきを起こしたりするので好ましくない。また、ムライト結晶とガラス相との熱膨張差によって、高温において気密性、強度の低下や変形が大きくなり、耐久性に劣るので好ましくない。より好ましくは５容積％以下とする。
本発明においてガラス相含有率の測定は以下の方法によって行う。
【００１４】
熱処理用部材の任意の部分から板状試片を切り出し、鏡面仕上げする。鏡面仕上げした試料を０〜５℃の１％ＨＦ水溶液に２４時間浸漬した後、洗浄、乾燥し、ガラス相含有率測定用試料とする。ＨＦ処理前後の試料を走査電子顕微鏡により１０００〜５０００倍で観察する。ＨＦ処理によってガラス相が存在していた跡はくさび状の空隙として観察される。観察した面積をＳ、ＨＦ処理前の試料で観察した試料で気孔および空隙が占める面積をＢＳｐとし、ＨＦ処理後の試料で観察した試料で気孔、空隙およびガラス相の跡が占める面積（ＡＳｐ）からガラス相含有率を下式により求める。
【数２】
ガラス相含有率（％）＝〔（ＡＳｐ−ＢＳｐ）／Ｓ〕×１００
【００１５】
（ｃ）平均密閉気孔径が５〜３０μｍである。
本発明においては平均密閉気孔径が５〜３０μｍ、好ましくは５〜２５μｍであることが必要である。平均密閉気孔径が５μｍ未満の場合は気孔形成による耐熱衝撃抵抗性や変形に対する抵抗性の向上の効果が少なく、３０μｍを越える場合には密閉気孔が連続状態になったり、強度低下をきたすため好ましくない。
【００１６】
平均密閉気孔径は、焼結体を鏡面仕上げし、走査電子顕微鏡にて観察し、１００個の気孔径を測定し、平均値（Ｐ）を求め、これから下記式により平均密閉気孔径を算出する。
【数３】
平均密閉気孔径＝１．５×Ｐ
【００１７】
（ｄ）平均結晶粒径が２〜３０μｍである。
本発明において平均結晶粒径は２〜３０μｍであることが必要であり、好ましくは２〜２０μｍであることが必要である。平均結晶粒径が２μｍ未満の場合は、耐久性および耐食性の低下や変形に対する抵抗性が低下するので好ましくない。一方、３０μｍを越える場合には耐熱衝撃抵抗性が低下するので好ましくない。平均結晶粒径は焼結体を鏡面仕上げし、熱エッチングを施し、走査電子顕微鏡にて観察し、インターセプト法により１０点平均から求める。算出式は下記のとおりである。
【数４】
Ｄ＝１．５×Ｌ／ｎ
Ｄ：平均結晶粒径（μｍ）、Ｌ：測定長さ（μｍ）、ｎ：長さＬ当たりの結晶数を用いる。
【００１８】
なお、本発明において（ｅ）平均密閉気孔径／平均結晶粒径が０．１〜６、好ましくは０．５〜５であることが必要である。平均密閉気孔径／平均結晶粒径が０．１未満の場合には、密閉気孔の存在による耐熱衝撃抵抗性に対する効果が少なくなるので好ましくない。一方、平均密閉気孔径／平均結晶粒径が６を越える場合には、密閉気孔径が結晶粒径に比べて大きくなりすぎて強度低下をきたし、耐熱衝撃抵抗性が低下するだけでなく、被熱処理材料の浸食が大きくなって耐食性の低下をきたすので好ましくない。
【００１９】
（ｆ）相対密度が７０〜９５％である。この相対密度とは式
【数５】
（焼結体かさ密度／理論密度）×１００（％）
で求めたものである。
本発明において相対密度は７０〜９５％であることが必要であり、より好ましくは７５〜９０％であることが必要である。相対密度が７０％未満の場合は気孔量が多くなり、各々の気孔がつながって密閉気孔径が大きくなり、強度低下や耐食性の低下をきたすので好ましくない。また、相対密度が９５％を越える場合には耐熱衝撃抵抗性の低下をきたすので好ましくない。
【００２０】
本発明においては、ジルコニアを５容積％以下含有していることが好ましい。ジルコニアの結晶相は正方晶であることが好ましいが、立方晶および単斜晶のいずれでも良い。ジルコニア原料粉末はジルコニア粉末だけでなく、ジルコニアゾルや焼成によりジルコニアとなるジルコニウム化合物（ジルコンなど）を用いることもできる。また、ジルコニアにイットリアが１〜５モル％含有していることがより好ましい。ジルコニア添加量が５容積％を越える場合は、熱処理用部材の昇温・降温の繰り返しにより、焼結体にマイクロクラックが発生し、耐熱衝撃抵抗性の低下や耐久性に劣るので好ましくない。
【００２１】
本発明のムライト質焼結体からなる熱処理用部材は種々の方法で作製できるが、その一例を以下に示す。
【００２２】
原料粉末はＡｌ２Ｏ３＋ＳｉＯ２の合計量が９９％以上、平均粒子径が２μｍ以下であることが好ましく、より好ましくは１．５μｍ以下である。平均粒子径が２μｍを越える場合には、焼結体内部の欠陥が多く存在するため、耐熱衝撃抵抗性をはじめとする機械的特性の低下をきたすので好ましくない。原料粉末は共沈法、ゾル−ゲル法等の液状原料から作製したムライト原料はもちろんのこと、アルミニウム化合物とシリカ化合物を均一に混合し、仮焼合成した原料粉末などが使用できる。
【００２３】
なお、焼結体に含有するＴｉＯ２、Ｆｅ２Ｏ３、ＣａＯ、Ｎａ２ＯおよびＫ２Ｏの合計含有量は２重量％以下であることが好ましく、より好ましくは１重量％以下である。不純物量が２重量％越えると結晶粒界に第２相およびガラス相を多く形成し、高温特性の低下をきたすので好ましくない。ジルコニアを添加する場合はジルコニア含有量が所定量となるように各原料粉末に配合し、溶媒として水または有機溶媒を用いて、ポットミル、アトリッションミル等の粉砕機により粉砕・分散・混合する。
【００２４】
前記のようにして得られた粉体の平均粒子径は１．５μｍ以下であることが必要で、より好ましくは１．０μｍ以下である。粒度がこれらの範囲外の場合は、成形性が低下し、得られた焼結体に欠陥が多く存在するだけでなく、本発明の微構造を有した焼結体が得られず、耐熱衝撃抵抗性が低下するだけでなく、その他の機械的特性および耐食性も低下するので好ましくない。
【００２５】
成形方法としてはプレス成形、ラバープレス成形等の方法を採用する場合には、粉砕・分散スラリーに必要により公知の成形助剤（例えばワックスエマルジョン、ＰＶＡ、アクリル系樹脂等）を加え、スプレードライヤー等の公知の方法で乾燥させて成形粉体を作製し、これを用いて成形する。また、鋳込成形法を採用する場合には、粉砕・分散スラリーに必要により公知のバインダー（例えばワックスエマルジョン、アクリル系樹脂等）を加え、石膏型あるいは樹脂型を用いて排泥鋳込、充填鋳込、加圧鋳込法により成形する。さらに、押出成形法を採用する場合には、粉砕・分散したスラリーを乾燥させ、整粒し、混合機を用いて水、バインダー（例えばメチルセルロース等）を混合して坏土を作製し、押出成形する。
【００２６】
以上のようにして得た成形体を１５００〜１８００℃、より好ましくは１５５０〜１７５０℃で焼成することによって焼結体を得る。
【００２７】
【実施例】
以下に実施例を示し、本発明を説明するが、本発明はこれにより何ら限定されるものでない。
【００２８】
実施例１
所定のＡｌ２Ｏ３／ＳｉＯ２重量比からなり、平均粒子径１．５μｍからなるムライト原料粉末にジルコニアを添加する場合は、所定量のジルコニア粉末を配合し、ポットミルで溶媒に水あるいはエタノールを用いて粉砕・分散・混合し、スラリーを作製した。気孔形成剤としてはアクリル系樹脂球状粒子または多糖類球状粒子を所定の気孔率および気孔径になるように添加、混合した。
前記ジルコニア粉末はＹ２Ｏ３を０〜５モル％含有しており、比表面積が１５ｍ２／ｇである粉末を用いた。得られたスラリーを石膏型を用いて鋳込成形し、１４５０〜１８００℃で焼成して、一辺が１００ｍｍの正方形で、高さが５０ｍｍの角型熱処理用容器を作製した。得られた熱処理用容器の耐熱衝撃抵抗性を調べるため、得られた熱処理用容器の中に４０メッシュの電融ジルコニア粉末を５００ｇ入れ、フタをして、所定の温度に保持した電気炉に入れ、３０分加熱保持し、炉外へ即座に取り出し、室温下で急冷し、割れの有無により耐熱衝撃抵抗性を評価した。
また、上記と同条件で５８０℃で繰り返しによるクラック発生に有無について評価した。
試料Ｎｏ．１〜８は本発明のムライト質焼結体からなる熱処理用部材であり、試料Ｎｏ．９〜１７は本発明の要件を少なくとも１つ以上満足しない試料である。すなわち、
試料Ｎｏ．９は、ムライト結晶相が７７容量％と少なく、
試料Ｎｏ．１０は、（平均密閉気孔径）／（平均結晶粒径）が高すぎ、
試料Ｎｏ．１１は、相対密度が９７％と高すぎ、
試料Ｎｏ．１２は、相対密度が６７％と低すぎ、
試料Ｎｏ．１３は、平均結晶粒径が１．３μｍと小さすぎ、
試料Ｎｏ．１４は、平均密閉気孔径が６１μｍと大きすぎ、
試料Ｎｏ．１５は、ガラス相含有率が１６容量％と多すぎ、
試料Ｎｏ．１６は、ジルコニア含有量が多すぎ、
試料Ｎｏ．１７は、平均結晶粒径が１．６μｍと小さすぎ、また密閉気孔ではない
点で本発明外のものである。
【００２９】
【表１】
【表２】
【発明の効果】
本発明は耐熱衝撃抵抗性、耐食性および高温下での変形にすぐれるため、熱処理用部材として圧電体、誘電体などの電子部品材料、リチウムイオン２次電池正極材料、蛍光体材料およびセラミック材料の熱処理用容器、単結晶育成用ルツボ、金属溶解用ルツボ、各種熱処理用炉芯管、ローラハースキルン用ローラ、サポートチューブ、ラジアントチューブ、ガス吹込管、ガス採取管、測温用熱電対および各種機器用の保護管、サポート用治具材などに有効である。
【図面の簡単な説明】
【図１】（Ａ）は、本発明のムライト質焼結体の１つのサンプルの微構造写真であり、（Ｂ）は、本発明のムライト質焼結体の１つのサンプルの気孔分布状態を示す。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a heat treatment member comprising a mullite sintered body excellent in thermal shock resistance, corrosion resistance, and deformation at high temperatures.
[0002]
[Prior art and its problems]
In addition to excellent heat resistance and corrosion resistance, the heat treatment member is a material that does not contaminate the material to be heat treated, and is capable of preventing the components contained in the material to be heat treated from diffusing into the furnace atmosphere. Has been. For a long time, materials such as alumina, magnesia, quartz, silicon carbide, and zirconia have been known as heat treatment members. A heat-treating member such as alumina, magnesia, zirconia has excellent heat resistance and has an advantage that it can be used up to a temperature of about 1800 ° C., but has a disadvantage that it is inferior in thermal shock resistance and cannot be rapidly heated and cooled. Quartz is expensive, has poor processability, has a disadvantage that it is softened or permeated with alkali elements at high temperatures, and is susceptible to deterioration and breakage due to devitrification. Although silicon carbide is excellent in thermal shock resistance, it has the disadvantage that it easily deteriorates due to oxidation and forms a glass phase on the surface under an oxidizing atmosphere or an open atmosphere, and easily reacts with the material to be treated.
[0003]
On the other hand, JP-B-5-77627 discloses a heat treatment container having a dense mullite quality as a method for solving the above-mentioned drawbacks. However, even if this heat treatment container is used, although it is superior in terms of thermal shock resistance as compared with alumina, magnesia and the like, it is not fully satisfied yet.
[0004]
Furthermore, in recent heat treatments of electronic materials and phosphor materials, including positive electrode materials for lithium secondary batteries, rapid rises have been made in order to minimize evaporation components and reduce composition fluctuations, and to increase production efficiency. Temperature and temperature reduction treatments have been made. A heat-treating member made of a dense sintered body is superior in corrosion resistance to a porous heat-treating member, but has a risk of cracking due to thermal shock when rapidly raising or lowering temperature. On the other hand, the heat-treating member made of a porous material is superior in heat shock resistance to the heat-treating member made of a dense material as described above, but is inferior in airtightness, and the components in the heat-treating member are contained in the heat-treated material. Mixing as impurities, reacting with the heat-treated material, causing a change in the composition of the heat-treated material, and adsorption or reaction of the components evaporating from the heat-treated material due to the heat treatment to the heat-treated material, resulting in corrosion resistance. There are problems such as degradation and degradation of mechanical properties.
[0005]
[Means for solving problems]
The present invention, as a result of intensive research in view of the current situation as described above, has a specific relative density, rounded closed pores in the mullite sintered body, and the closed pore diameter. In addition, by controlling the crystal grain size of the sintered body and controlling the ratio between the closed pore size and the crystal grain size, it has excellent thermal shock resistance and corrosion resistance, and has little deformation at high temperatures. The member for heat processing consisting of a knot was found. In the present invention, the thermal shock resistance means not only the occurrence of cracks due to rapid heating / cooling and resistance to cracking, but also the durability due to repeated heating / cooling.
[0006]
That is, the present invention is a mullite sintered body containing 80% by volume or more of mullite crystals as a crystal phase, wherein (a) the glass phase is 10% by volume or less, and (b) pores present in the sintered body. Is mainly sealed, (c) the average sealed pore diameter is 5 to 30 μm, (d) the average crystal grain size of the sintered body is 2 to 30 μm, (e) the average sealed pore diameter of the sintered body / The present invention relates to a heat treatment member comprising a mullite-based sintered body, wherein the average crystal grain size is 0.1 to 6 and (f) the relative density of the sintered body is 70 to 95%. The member has excellent thermal shock resistance and corrosion resistance, and exhibits the characteristics that deformation at high temperatures is small.
[0007]
The heat treatment member referred to in the present invention is an electronic component material such as a piezoelectric material or a dielectric material, a lithium ion secondary battery positive electrode material, a phosphor material and a ceramic material heat treatment vessel, a single crystal growth crucible, and a metal melting material. There are crucibles, various heat treatment furnace core tubes, rollers for roller hearth kilns, support tubes, radiant tubes, gas blowing tubes, gas sampling tubes, thermocouples for temperature measurement and protective tubes for various devices, support jig materials, etc. .
[0008]
Hereinafter, each requirement to be satisfied by the heat treatment member made of a mullite sintered body having excellent thermal shock resistance and corrosion resistance according to the present invention and less deformation at high temperature will be described in detail.
[0009]
In the present invention, the closed pores are formed by organic substances such as organic spherical particles such as acrylic resin spherical particles and polysaccharide spherical particles as a pore forming agent so as to have a predetermined relative density and pore diameter in the pulverized / dispersed slurry. Use rounded particles. When this pore-forming agent is added to ceramic powder, mixed and molded, and then fired, the organic pore-forming agent disappears and the closed pores remain as traces, so the shape of the closed pores is essentially a pore. The shape is based on the shape of the forming agent, as defined in (b) of claim 1, and the pores are rounded and sealed as shown in FIGS. 1 (A) and (B). It becomes substantially independent. When the pore shape is not rounded, stress is easily concentrated on the pores when stress is applied to the sintered body, and the strength and thermal shock resistance decrease, and deformation at high temperatures is likely to occur. It is not preferable. In addition, the closed pore as used in the field of this invention refers to the internal pore which is not connected outside.
[0010]
(A) A mullite sintered body containing 80% by volume or more of mullite crystals as a crystal phase.
In the present invention, the mullite sintered body needs to be composed of 80% by volume or more, more preferably 90% by volume or more of mullite crystals as a crystal phase. When the mullite crystal is less than 80% by volume, crystals other than the mullite crystal are present in the mullite crystal grain boundary and in the grain, which is not preferable because the thermal shock resistance and the corrosion resistance are lowered and the deformation at high temperature is increased.
[0011]
Further, in the present invention, α-Al 2 O 3 crystals can be allowed up to 10% by volume or less. More preferably, it is 8 volume% or less. When the α-Al 2 O 3 crystal exceeds 10% by volume, the alkali component volatilized at a high temperature from the refractory material such as the heat-treated material and the furnace wall, the alkali component contained in the fuel of the heat source, etc. is α-Al by reacting with 2 O 3 crystals to form a beta-Al 2 O 3 crystals inside the sintered body, strain Ya increased due to the difference in thermal expansion between the tissue deterioration or alpha-Al 2 O 3 crystals and mullite crystals This is not preferable because the thermal shock resistance decreases due to an increase in residual expansion. The mullite crystal mentioned here includes not only the mullite crystal represented by the chemical formula 3Al 2 O 3 .2SiO 2 (Al 2 O 3 71.8 wt%, SiO 2 28.2 wt%) but also a mullite solid solution.
[0012]
In the present invention, the volume ratio of the α-Al 2 O 3 crystal phase is a value obtained by the following method. That is, first, a small piece cut out from an arbitrary position of a sample is pulverized, and X-ray diffraction is performed on the obtained powder. As a result, from the diffraction intensity [I M (210)] of the (210) plane of the obtained mullite crystal and the diffraction intensity [I A (113) of the (113) plane of α-Al 2 O 3 crystal, The ratio of the crystal and α-Al 2 O 3 crystal is calculated.
[Expression 1]
(B) The glass phase is 10% by volume or less.
In the present invention, the glass phase is 10% by volume or less. When the glass phase contained exceeds 10% by volume, the glass phase and the material to be heat-treated react to contaminate the material to be heat-treated or cause a sticking with the member for heat treatment. Moreover, due to the difference in thermal expansion between the mullite crystal and the glass phase, the airtightness, strength decrease and deformation become large at high temperatures, and the durability is inferior. More preferably, it is 5 volume% or less.
In the present invention, the glass phase content is measured by the following method.
[0014]
A plate-like specimen is cut out from an arbitrary part of the heat treatment member and mirror-finished. The mirror-finished sample is immersed in a 1% HF aqueous solution at 0 to 5 ° C. for 24 hours, then washed and dried to obtain a glass phase content measurement sample. The sample before and after the HF treatment is observed at 1000 to 5000 times with a scanning electron microscope. Traces of the presence of the glass phase by HF treatment are observed as wedge-shaped voids. The observed area is S, the area occupied by pores and voids in the sample observed with the sample before HF treatment is BSp, and the area occupied by pores, voids and glass phase traces in the sample observed with the sample after HF treatment (ASp) The glass phase content is determined from the following formula.
[Expression 2]
Glass phase content (%) = [(ASp−BSp) / S] × 100
[0015]
(C) The average closed pore diameter is 5 to 30 μm.
In the present invention, it is necessary that the average closed pore diameter is 5 to 30 μm, preferably 5 to 25 μm. When the average closed pore diameter is less than 5 μm, the effect of improving the thermal shock resistance and deformation resistance due to pore formation is small, and when it exceeds 30 μm, the closed pores become continuous or the strength decreases. Therefore, it is not preferable.
[0016]
The average closed pore diameter is obtained by mirror-finishing the sintered body, observing with a scanning electron microscope, measuring 100 pore diameters, obtaining an average value (P), and calculating the average closed pore diameter from the following formula. .
[Equation 3]
Average closed pore size = 1.5 x P
[0017]
(D) The average crystal grain size is 2 to 30 μm.
In the present invention, the average crystal grain size needs to be 2 to 30 μm, preferably 2 to 20 μm. An average crystal grain size of less than 2 μm is not preferable because durability and corrosion resistance are lowered and resistance to deformation is lowered. On the other hand, if it exceeds 30 μm, the thermal shock resistance is lowered, which is not preferable. The average crystal grain size is obtained from the average of 10 points by the intercept method after mirror-finishing the sintered body, applying thermal etching, and observing with a scanning electron microscope. The calculation formula is as follows.
[Expression 4]
D = 1.5 × L / n
D: average crystal grain size (μm), L: measurement length (μm), n: number of crystals per length L are used.
[0018]
In the present invention, it is necessary that (e) average closed pore diameter / average crystal grain diameter is 0.1 to 6, preferably 0.5 to 5. When the average closed pore diameter / average crystal grain size is less than 0.1, the effect on the thermal shock resistance due to the presence of the closed pores is not preferable. On the other hand, when the average closed pore diameter / average crystal grain size exceeds 6, the closed pore size becomes too large compared to the crystal grain size, resulting in a decrease in strength and not only a decrease in thermal shock resistance, This is not preferable because the erosion of the heat treatment material is increased and the corrosion resistance is lowered.
[0019]
(F) The relative density is 70 to 95%. This relative density is the formula:
(Sintered body bulk density / theoretical density) x 100 (%)
It is what I asked for.
In the present invention, the relative density needs to be 70 to 95%, more preferably 75 to 90%. When the relative density is less than 70%, the amount of pores is increased, and the pores are connected to increase the diameter of the sealed pores, resulting in a decrease in strength and corrosion resistance. On the other hand, when the relative density exceeds 95%, the thermal shock resistance is lowered, which is not preferable.
[0020]
In this invention, it is preferable to contain 5 volume% or less of zirconia. The crystal phase of zirconia is preferably tetragonal, but may be either cubic or monoclinic. As the zirconia raw material powder, not only zirconia powder, but also a zirconia sol or a zirconium compound (such as zircon) that becomes zirconia by firing can be used. Moreover, it is more preferable that 1-5 mol% of yttria is contained in zirconia. When the added amount of zirconia exceeds 5% by volume, microcracks are generated in the sintered body due to repeated heating and lowering of the heat treatment member, which is not preferable because the thermal shock resistance is deteriorated and the durability is inferior.
[0021]
Although the member for heat processing which consists of a mullite sintered body of this invention can be produced with various methods, the example is shown below.
[0022]
The raw material powder preferably has a total amount of Al 2 O 3 + SiO 2 of 99% or more and an average particle size of 2 μm or less, more preferably 1.5 μm or less. When the average particle diameter exceeds 2 μm, there are many defects inside the sintered body, which is not preferable because mechanical properties such as thermal shock resistance are deteriorated. As the raw material powder, not only a mullite raw material prepared from a liquid raw material such as a coprecipitation method or a sol-gel method, but also a raw material powder obtained by calcining and synthesizing an aluminum compound and a silica compound uniformly can be used.
[0023]
The total content of TiO 2 , Fe 2 O 3 , CaO, Na 2 O and K 2 O contained in the sintered body is preferably 2% by weight or less, more preferably 1% by weight or less. If the amount of impurities exceeds 2% by weight, a large amount of the second phase and glass phase are formed at the grain boundaries and the high temperature characteristics are deteriorated. When adding zirconia, mix with each raw material powder so that the zirconia content becomes a predetermined amount, and use water or an organic solvent as a solvent, and pulverize, disperse, and mix with a pulverizer such as a pot mill or an attrition mill. .
[0024]
The average particle size of the powder obtained as described above is required to be 1.5 μm or less, more preferably 1.0 μm or less. When the particle size is outside these ranges, the moldability is lowered, and not only the obtained sintered body has many defects, but also the sintered body having the microstructure of the present invention cannot be obtained, Not only is the resistance lowered, but other mechanical properties and corrosion resistance are also lowered, which is not preferable.
[0025]
When a method such as press molding or rubber press molding is adopted as a molding method, a known molding aid (for example, wax emulsion, PVA, acrylic resin, etc.) is added to the pulverized / dispersed slurry as necessary, and a spray dryer or the like. The powder is dried by a known method to produce a molded powder, which is then molded. In addition, when adopting the casting method, a known binder (for example, wax emulsion, acrylic resin, etc.) is added to the pulverized / dispersed slurry as required, and the waste mud is cast and filled using a gypsum mold or a resin mold. Molded by casting or pressure casting. Furthermore, when adopting the extrusion molding method, the pulverized / dispersed slurry is dried, sized, and mixed with water and a binder (for example, methylcellulose) using a mixer to produce a clay, and then extrusion molding. To do.
[0026]
The molded body obtained as described above is fired at 1500 to 1800 ° C., more preferably 1550 to 1750 ° C., to obtain a sintered body.
[0027]
【Example】
The present invention will be described below with reference to examples, but the present invention is not limited thereby.
[0028]
Example 1
When zirconia is added to a mullite raw material powder having a predetermined Al 2 O 3 / SiO 2 weight ratio and an average particle diameter of 1.5 μm, a predetermined amount of zirconia powder is blended, and water or ethanol is added to the solvent in a pot mill. The slurry was pulverized, dispersed, and mixed to prepare a slurry. As the pore forming agent, acrylic resin spherical particles or polysaccharide spherical particles were added and mixed so as to have a predetermined porosity and pore diameter.
The zirconia powder contained 0 to 5 mol% of Y 2 O 3 and a specific surface area of 15 m 2 / g. The obtained slurry was cast using a plaster mold and fired at 1450 to 1800 ° C. to produce a square heat treatment container having a square of 100 mm on one side and a height of 50 mm. In order to investigate the thermal shock resistance of the obtained heat treatment container, 500 g of 40-mesh fused zirconia powder was put into the obtained heat treatment container, and a lid was placed in an electric furnace maintained at a predetermined temperature. , Held for 30 minutes, immediately taken out of the furnace, rapidly cooled at room temperature, and evaluated thermal shock resistance by the presence or absence of cracks.
Moreover, the presence or absence of the crack generation by repetition at 580 degreeC on the same conditions as the above was evaluated.
Sample No. 1 to 8 are members for heat treatment made of the mullite sintered body of the present invention. Samples 9 to 17 do not satisfy at least one of the requirements of the present invention. That is,
Sample No. 9 has a low mullite crystal phase of 77% by volume,
Sample No. 10 is (average closed pore diameter) / (average crystal grain size) is too high,
Sample No. 11 has a relative density of 97% too high,
Sample No. 12 , the relative density is too low, 67%,
Sample No. No. 13 , the average crystal grain size is too small as 1.3 μm,
Sample No. No. 14 has an average hermetic pore diameter of 61 μm which is too large,
Sample No. 15 , the glass phase content is too much as 16% by volume,
Sample No. 16 has too much zirconia content,
Sample No. No. 17 is outside the scope of the present invention in that the average crystal grain size is too small at 1.6 μm and it is not a closed pore.
[0029]
[Table 1]
[Table 2]
【The invention's effect】
Since the present invention is excellent in thermal shock resistance, corrosion resistance, and deformation at high temperatures, it can be used as a heat treatment member for electronic parts such as piezoelectrics and dielectrics, lithium ion secondary battery positive electrode materials, phosphor materials and ceramic materials. Heat treatment containers, crucibles for single crystal growth, crucibles for melting metals, furnace tubes for various heat treatments, rollers for roller hearth kilns, support tubes, radiant tubes, gas blowing tubes, gas sampling tubes, thermocouples for temperature measurement, and various devices It is effective for protective pipes and jigs for support.
[Brief description of the drawings]
1A is a microstructure photograph of one sample of the mullite sintered body of the present invention, and FIG. 1B shows the pore distribution state of one sample of the mullite sintered body of the present invention. Show.
Claims (3)
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| JP2000323994A JP4507148B2 (en) | 2000-10-24 | 2000-10-24 | Heat treatment member made of mullite sintered body |
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| JP2000323994A JP4507148B2 (en) | 2000-10-24 | 2000-10-24 | Heat treatment member made of mullite sintered body |
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| FR2859203B1 (en) * | 2003-09-01 | 2006-02-10 | Saint Gobain Ct Recherches | RAW PIECE FOR THE MANUFACTURE OF A FRITTE REFRACTORY PRODUCT WITH IMPROVED BULLAGE BEHAVIOR |
| DE102012004987B4 (en) * | 2012-03-14 | 2014-03-06 | Heraeus Electro-Nite International N.V. | Apparatus for measuring the temperature in molten metals |
| KR20150091072A (en) * | 2012-12-05 | 2015-08-07 | 다우 글로벌 테크놀로지스 엘엘씨 | Porous mullite bodies having improved thermal stability |
| CN104837789B (en) * | 2012-12-05 | 2017-05-24 | 陶氏环球技术有限责任公司 | Porous mullite bodies having improved thermal stablity |
| WO2016104251A1 (en) * | 2014-12-26 | 2016-06-30 | 日本碍子株式会社 | Ceramic base material and method for producing same |
| JP2016150989A (en) * | 2015-02-18 | 2016-08-22 | 日東電工株式会社 | Method for producing phosphor ceramic |
| WO2016148217A1 (en) * | 2015-03-17 | 2016-09-22 | 日本碍子株式会社 | Wiring substrate |
| WO2021132150A1 (en) * | 2019-12-27 | 2021-07-01 | Ａｇｃ株式会社 | Molding device, production facility equipped with said molding device, and method for producing glass plate |
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| JPS623069A (en) * | 1985-06-25 | 1987-01-09 | 株式会社ニッカト− | Heat treating vessel and manufacture |
| JP2549976B2 (en) * | 1993-02-03 | 1996-10-30 | 株式会社ニッカトー | Heat-resistant mullite sintered body |
| JPH06321620A (en) * | 1993-05-14 | 1994-11-22 | Noritake Co Ltd | High toughness ceramic material |
| JPH07291715A (en) * | 1993-10-21 | 1995-11-07 | Harima Ceramic Co Ltd | Spinel refractory brick |
| JPH11130523A (en) * | 1997-10-30 | 1999-05-18 | Toshiyuki Hashida | Calcium silicate complex sintered compact and its production |
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