JP3861144B2

JP3861144B2 - Method for producing easily sinterable nanospherical ceria compound powder

Info

Publication number: JP3861144B2
Application number: JP2002275987A
Authority: JP
Inventors: 利之森; ＷａｎｇＹａｒｏｎｇ; ＬｉＪｉ−Ｇｕａｎｇ; 隆康池上; 睦西村
Original assignee: National Institute for Materials Science
Current assignee: National Institute for Materials Science
Priority date: 2002-09-20
Filing date: 2002-09-20
Publication date: 2006-12-20
Anticipated expiration: 2022-09-20
Also published as: JP2004107186A

Description

【０００１】
【発明の属する技術分野】
本発明は、炭酸ガスセンサ、燃料電池用固体電解質、などに利用される原料粉末である易焼結性ナノ球状セリア系化合物粉末の製造方法に関するものである。
【０００２】
【従来の技術と問題点】
セリア系化合物粉末の合成法として、セリウム塩と金属塩の混合溶液に、シュウ酸を加えて沈殿を得る方法、アンモニアや炭酸アンモニウムを沈殿剤として加える方法や金属アルコキシドを用いる方法などが用いられてきた。
シュウ酸塩を沈殿剤として用いる場合には、生成する粉末は、大きな凝集体の固まりとなり、その結晶化温度は最低でも７００℃以上となる。そして、結晶化したセリア系化合物粉末の粒径は、サブミクロン以上と大きいため、センサ、燃料電池用固体電解質などに利用する場合、焼結温度が１５００℃以上の高温においても、空孔を完全に取り除くことができず、特性の向上につながらないという欠点があった。
【０００３】
また、アンモニアや炭酸アンモニウムを沈殿剤に用いる場合には、沈殿剤に含まれるアンモニア成分が、沈殿物質の中に残存し、沈殿物質を乾燥し、仮焼する際、粒子の形状が柱状になりやすく、そのため粉末の比表面積を低下させ、焼結性を低下させることから、ち密化のための温度が１６００℃以上になるという欠点を有していた。
【０００４】
アルコキシドを出発原料に用いる場合には、単分散粉末を作製することが可能であるが、アルコキシド原料が高価であることから、実用化に際しては、薄膜への応用に限定され、技術の利用分野がきわめて限られることから、実用化の妨げとなっていた。
【０００５】
【課題を解決するための手段】
本発明者らは、上記従来技術の問題点に鑑み、鋭意検討を続けた結果、柱状になりやすい粒子の形状を制御し、凝集の少ない、球状粒子を作製するために必要な沈殿物質に求められる組成、仮焼条件などを検討することで、ナノサイズの粒径を有する易焼結性球状セリア系化合物粉末の製造条件を見出し、本発明を完成するに至った。
【０００６】
すなわち、本発明の要旨とするところは、その第１は、（１）２価または３価の金属（Ｍ）硝酸塩とセリウムの硝酸塩をＭ_xＣｅ_1-xＯ₂ _―δ（ただし、０．０５≦ ｘ ≦０．３、δはカチオンとアニオンの電荷のバランスから決定される酸素欠陥量を表す）となるように混合し、この混合溶液と沈殿剤として炭酸水素アンモニウムを、〔２価または３価の金属（Ｍ）硝酸塩とセリウムの硝酸塩水溶液濃度〕／（炭酸アンモニウム水溶液濃度）のモル比が２．５から１５になるように混合して、Ｃｅ_1-xＭ_x（ＯＨ）_y（ＣＯ₃）_z・Ｈ₂Ｏ（ただし、０．０５≦ ｘ ≦０．３、０．０５≦ ｙ ≦ 1、０．０５≦ ｚ ≦２）で表されるセリウムカーボネートを沈殿させた後に、熟成を５０℃以上、７０℃以下の温度範囲で行い、洗浄後、４００℃以上、７５０℃以下の温度で仮焼することで、平均粒径５０ナノメーター以下の球状粒子となし、１０００℃以下の温度で焼結することで、相対密度の９８％以上にまで、ち密にすることを特徴とする、易焼結性ナノ球状セリア系化合物粉末の製造方法である。
【０００７】
また、その第２は、（２）２価（Ｍ²⁺）と３価（Ｍ³⁺）の金属元素を含む硝酸塩とセリウムの硝酸塩を（Ｍ²⁺ _aＭ³⁺ _1-a）_xＣｅ_1-xＯ₂ _―δ（ただし、０．０１≦ a ≦０．５、０．０５≦ ｘ ≦０．３、δはカチオンとアニオンの電荷のバランスから決定される酸素欠陥量を表す）となるように混合し、この混合溶液と沈殿剤として炭酸水素アンモニウムを、〔２価（Ｍ²⁺）と３価（Ｍ³⁺）の金属元素を含む硝酸塩水溶液濃度〕／（炭酸アンモニウム水溶液濃度）のモル比が３から７になるように混合して、Ｃｅ_1-x（Ｍ²⁺ _aＭ³⁺ _1-a）_x（ＯＨ）_y（ＣＯ₃）_z・Ｈ₂Ｏ（ただし、０．０１≦ a ≦０．５、０．０５≦ ｘ ≦０．３、０．０５≦ｙ ≦ 1、０．０５≦ ｚ ≦２）で表されるセリウムカーボネートを沈殿させた後に、熟成を５５℃以上６５℃以下の温度で行い、洗浄後、４００℃以上７５０℃以下の温度で仮焼することで、平均粒径５０ナノメーター以下の球状粒子となし、１０００℃以下の温度で焼結することで、相対密度の９８％以上にまで、ち密にすることを特徴とする、易焼結性ナノ球状セリア系化合物粉末の製造方法である。
【０００８】
本発明における、ナノ球状粉末作製に必要不可欠なセリウムカーボネートの化学組成はＣｅ_1-xＭ_x（ＯＨ）_y（ＣＯ₃）_z・Ｈ₂Ｏ（ただし、０．０５≦ ｘ ≦０．３、０．０５≦ ｙ ≦ 1、０．０５≦ ｚ ≦ ２、Ｍは３価の金属元素を表す）またはＣｅ_1-x（Ｍ²⁺ _aＭ³⁺ _1-a）_x（ＯＨ）_y（ＣＯ₃）_z・Ｈ₂Ｏ（ただし、０．０１≦ a ≦０．５、０．０５≦ ｘ ≦０．３、０．０５≦ ｙ ≦ 1、０．０５≦ ｚ ≦２、Ｍ²⁺及びＭ³⁺はそれぞれ、２価または３価金属元素を表す）でなければならない。沈殿物質にアンモニア成分が含まれると、沈殿が柱状に成長しやくなり、焼結性が低下するので好ましくない。
【０００９】
aの範囲は、０．０１以上０．５以下が好ましく、この範囲を下回ると２価と３価の元素を共存させる効果が十分に発揮されず、上述のセンサ、燃料電池用固体電解質などへ利用した際、特性向上につながらないことから好ましくない。また、この範囲を上回ると２価と３価金属元素が偏析をおこし、かえって、センサ、燃料電池用固体電解質などの特性を低下させることがあるので好ましくない。ｘの範囲は０．０５以上０．３以下でなければならず、この範囲を下回る場合は、上述のセンサ、燃料電池用固体電解質などへの応用に際して、仮焼粉末中に導入される酸素欠陥量が不足し、十分な特性が発揮されないので好ましくない。
【００１０】
また、この範囲を上回ると、過剰な酸素欠陥が仮焼粉末中に導入され、かえってセンサ、燃料電池用固体電解質特性を低下させるので好ましくない。
ｙの範囲は、０．０５以上、1以下とすることが好ましい。ｙの値は、反応溶液と沈殿剤のモル比やｐＨにより制御されるものであり、ｙの値がこの範囲を下回ると十分に沈殿が生成せず、ろ液中に多量のセリウムなどの金属元素が残り、収率が低下するうえ、柱状粒子と球状粒子が混在した凝集体ができてしまい、焼結性を著しく低下させるので好ましくない。また、この範囲を上回ると粒子間の凝集が強くなり、サブミクロンの凝集体となり、焼結性が低下するので好ましくない。
【００１１】
ｚの範囲は、０．０５以上、２以下とすることが好ましい。このｚの値は、沈殿剤の濃度により制御可能であるが、この値が０．０５を下回ると十分に沈殿が生成せず、ろ液中に多量のセリウムなどの金属元素が残り、収率が低下するうえ、柱状粒子と球状粒子が混在した凝集体ができてしまい、焼結性を著しく低下させるので好ましくない。また、この範囲を上回ると粒子間の凝集が強くなり、サブミクロンの凝集体となり、焼結性が低下するので好ましくない。
【００１２】
また、２価または３価の金属（Ｍ）硝酸塩とセリウムの硝酸塩をＭ_xＣｅ_1-xＯ₂―δ（ただし、０．０５≦ ｘ ≦０．３、δはカチオンとアニオンの電荷のバランスから決定される酸素欠陥量を表す）となるように混合する場合、〔２価または３価の金属（Ｍ）硝酸塩水溶液濃度〕／（炭酸アンモニウム水溶液濃度）のモル比は、２．５以上、１５以下とすべきが相当である。この範囲を下回っても、上回っても、上記の好ましい組成の沈殿が作製できないので、この範囲でなければならない。この範囲を下回るかまたは上回る場合、柱状の粒子が沈殿中に残存し、仮焼粉末の焼結性を低下させるので好ましくない。
【００１３】
さらに、２価（Ｍ²⁺）と３価（Ｍ³⁺）の金属元素を含む硝酸塩とセリウムの硝酸塩を（Ｍ²⁺ _aＭ³⁺ _1-a）_xＣｅ_1-xＯ₂ _―δ（ただし、０．０１≦ a ≦０．５、０．０５≦ ｘ ≦０．３、δはカチオンとアニオンの電荷のバランスから決定される酸素欠陥量を表す）となるように混合する場合、〔２価（Ｍ²⁺）と３価（Ｍ³⁺）の金属元素を含む硝酸塩水溶液濃度〕／（炭酸アンモニウム水溶液濃度）のモル比は、３以上、７以下でなければならず、この範囲を下回っても、上回っても、上記の好ましい組成の沈殿が作製できないので、この範囲でなければならない。
この範囲を下回るかまたは上回る場合、柱状の粒子が沈殿中に残存し、仮焼粉末の焼結性を低下させるので好ましくない。
【００１４】
２価または３価の金属硝酸塩、セリウムの硝酸塩と炭酸水素アンモニウムを用いて沈殿を作製した場合は、５０℃以上、７０℃以下の温度で熟成を行なわなければならない。熟成温度がこの範囲を下回ると、沈殿中に柱状の粒子が共存してしまい、仮焼後にも、この柱状粒子が残存し、焼結性を低下させるので好ましくない。また、この温度範囲を超えるとせっかく生成した球状の粒子が凝集し、仮焼後もこの凝集がのこり、焼結性を著しく低下させるので好ましくない。
【００１５】
また、２価（Ｍ²⁺）と３価（Ｍ³⁺）の金属元素を含む硝酸塩、セリウムの硝酸塩と炭酸水素アンモニウムを用いて沈殿を作製した場合は、５５℃以上、６５℃以下の温度で熟成する必要がある。熟成温度がこの範囲を下回ると、沈殿中に柱状の粒子が共存してしまい、仮焼後にもこの柱状粒子が残存し、焼結性を低下させるので好ましくない。この温度範囲を超えるとせっかく生成した球状の粒子が凝集し、仮焼後もこの凝集が残り、焼結性を著しく低下させるので好ましくない。熟成温度については特に制限はないが、あまり長時間の熟成をおこなってもそれなりの効果しかないので、１時間から２時間程度の熟成時間で十分である。
【００１６】
本発明に得られた沈殿物質は、沈殿生成後に水洗しなければならず、水洗を行わないと沈殿物質中にアンモニアが残存し、仮焼粉末中に柱状の粒子が混在するために好ましくない。水洗の回数については特に制限はないが、３回以上の水洗を行うことで、ほぼ完全にアンモニアを除去できるので、３回程度の水洗を行うことが好ましい。
水洗後、粉末は乾燥ガスなどを用いて乾燥を行い、空気中または酸素中で仮焼することで、結晶化させ、ほたる石型の結晶構造単一相にする必要があるが、その仮焼温度は４００℃以上７５０℃以下でなければならない。この温度範囲を下回ると、十分に結晶化が進まず、残存する非晶質が、焼結中に不均一な粒成長を引き起こし、緻密化を妨げることから好ましくない。またこの温度範囲を上回ると、サブミクロン以上の粒径になって、焼結に１５００℃以上の高温を必要とし、空孔が焼結体中に残りやすく、結果としてセンサや燃料電池用固体電解質の特性を低下させるので好ましくない。
【００１７】
仮焼の際の雰囲気は、空気中でも、酸素気流中でも同様な効果を得られるが、なるべく酸素分圧の高い雰囲気で仮焼することが、沈殿物質中に含まれる不純物を完全に燃焼させるうえで好ましい。また、仮焼時間にも特に制限はないが、低い温度で仮焼するほど、粉末中に炭酸ガスや水分が残りやすいので、４００℃または５００℃で仮焼する場合は、１０時間以上仮焼する必要があるが、それ以上の温度で仮焼する場合は、あまり長くしてもさほどの効果は期待できず、１時間から４時間程度仮焼すれば十分である。
得られたナノ球状粉末を焼結するには、特に制限はないが、大気中、９００℃以上で焼結することにより、相対密度９８％以上の高密度焼結体を作製することができる。
【００１８】
次に、本発明の具体的態様とその意義について、以下に記載する実施例と比較例により、開示、説明するが、これらの例は、あくまでも本発明を容易に理解し得るようにする一助としてであって、これによって本発明を限定する趣旨ではない。すなわち、本発明の内容は、これらの実施例及び比較例によって制限されるものではない。
【００１９】
【実施例】
実施例１；
配合がＧｄ_0.2Ｃｅ_0.8Ｏ_1.9になるように、出発原料として、０．２０モル／リットルの硝酸セリウム（純度９９．９９％）及び０．０５モル／リットルの硝酸ガドリウム（純度９９．９％）を用いて、硝酸ガドリウム水溶液と炭酸水素アンモニウム水溶液のモル比が１０となるように炭酸水素アンモニウム水溶液を調製し、出発原料混合水溶液中に炭酸水素アンモニウム水溶液を毎分１ミリリットルの速度で滴下して沈殿を作製した。炭酸水素アンモニウム滴下終了後、６０℃の温度で、１時間熟成を行った。こうして得られた沈殿は水洗処理とろ過を３回繰り返したのち、乾燥窒素ガス中において乾燥し、前駆体粉末を作製した。得られた前駆体粉末の化学分析結果から、その組成は、Ｃｅ_0.8Ｇｄ_0.2（ＯＨ）_0.2（ＣＯ₃）_1.4・Ｈ₂Ｏであった。前駆体粉末は引き続き、空気中７００℃の温度で１時間仮焼してセリア系化合物粉末を作成し、ホタル石単一の結晶相からなることをＸ線回折試験により確認した。図１には、Ｘ線回折試験による結晶相の同定結果を示す。
得られた仮焼粉末の走査型電子顕微鏡観察像（ＳＥＭ像）を図２に示す。得られた粉末は、平均粒子径が３０ナノメーターの球状粒子であった。
この粉末を金型成形した後、２ｔ／ｃｍ²の静水圧成形を行った後、１０００℃、４時間、空気中において焼結を行った。得られた焼結体は、理論密度の９９％にまで高密度化しており、焼結体表面には大きな空孔は認められず、ち密化が進んでいることが分かった。また、焼結体表面のＳＥＭ像を図３に示すとともに、上記の結果を表１にまとめて示した。
【００２０】
実施例２；
配合がＧｄ_0.1Ｃｅ_0.9Ｏ_1.95になるように、出発原料として、０．４５モル／リットルの硝酸セリウム（純度９９．９９％）及び０．０５モル／リットルの硝酸ガドリウム（純度９９．９％）を用いて、硝酸ガドリウム水溶液と炭酸水素アンモニウムの水溶液のモル比が、８となるように炭酸水素アンモニウム水溶液を調製し、出発原料混合水溶液中に炭酸水素アンモニウム水溶液を毎分１ミリリットルの速度で滴下して沈殿を作製した。炭酸水素アンモニウム滴下終了後、６０℃の温度で、１時間熟成を行った。こうして得られた沈殿は水洗処理とろ過を３回繰り返したのち、乾燥窒素ガス中において乾燥し、前駆体粉末を作製した。
得られた前駆体粉末の化学分析結果から、その組成は、Ｃｅ_0.9Ｇｄ_0.1（ＯＨ）_0.2（ＣＯ₃）_1.4・Ｈ₂Ｏであった。前駆体粉末は引き続き、空気中７００℃の温度で１時間仮焼してセリア系化合物粉末を作製した。また、仮焼粉末は実施例１の図１同様、ホタル石単一の結晶相からなっており、実施例１の図２同様に、平均粒子径が３０ナノメーターの球状粒子であった。
この粉末を金型成形した後、２ｔ／ｃｍ²の静水圧成形を行った後、１０００℃、４時間、空気中において焼結を行った。得られた焼結体は、実施例１同様、理論密度の９９％にまで高密度化しており、焼結体表面には大きな空孔は認められず、ち密化が進んでいることが分かった。本実施例においても実施例１同様、上記の結果を表１にまとめて示した。
【００２１】
実施例３；
配合がＹ_0.2Ｃｅ_0.8Ｏ_1.9になるように、出発原料として、０．２０モル／リットルの硝酸セリウム（純度９９．９９％）及び０．０５モル／リットルの硝酸イットリウム（純度９９．９％）を用いて、硝酸イットリウム水溶液と炭酸水素アンモニウム水溶液のモル比が３になるように炭酸水素アンモニウム水溶液を調製し、出発原料混合水溶液中に炭酸水素アンモニウム水溶液を毎分１ミリリットルの速度で滴下して沈殿を作製した。炭酸水素アンモニウム滴下終了後、６５℃の温度で、１時間熟成処理を行った。こうして得られた沈殿は水洗処理とろ過を３回繰り返したのち、乾燥窒素ガス中において乾燥し、前駆体粉末を作製した。得られた前駆体粉末の化学分析結果から、その組成は、Ｃｅ_0.8Ｙ_0.2（ＯＨ）_0.2（ＣＯ₃）_1.4・Ｈ₂Ｏであった。前駆体粉末は引き続き、空気中７００℃の温度で１時間仮焼してセリア系化合物粉末を得た。仮焼粉末は実施例１同様、ホタル石単一の結晶相からなることをＸ線回折試験により確認した。得られた仮焼粉末の平均粒子径は、３５ナノメーターであり、実施例１同様の球状粒子であった。この粉末を金型成形した後、２ｔ／ｃｍ²の静水圧成形を行った後、１０００℃、４時間、空気中において焼結を行った。こうして得られた焼結体は、実施例１同様、理論密度の９９％にまで高密度化しており、焼結体表面には大きな空孔は認められず、ち密化が進んでいることが分かった。
本実施例においても、他の実施例同様に得られた結果を表１にまとめて示した。
【００２２】
実施例４；
配合がＳｍ_0.2Ｃｅ_0.8Ｏ_1.9になるように、出発原料として、０．２０モル／リットルの硝酸セリウム（純度９９．９９％）及び０．０５モル／リットルの硝酸サマリウム（純度９９．９％）を用いて、硝酸サマリウム水溶液と炭酸水素アンモニウム水溶液のモル比が、３になるように炭酸水素アンモニウム水溶液を調製し、出発原料混合水溶液中に炭酸水素アンモニウム水溶液を毎分１ミリリットルの速度で滴下して沈殿を作製した。炭酸水素アンモニウム滴下終了後、５５℃の温度で、１時間熟成処理を行った。こうして得られた沈殿は水洗処理とろ過を３回繰り返したのち、乾燥窒素ガス中において乾燥し、前駆体粉末を作製した。得られた前駆体粉末の化学分析結果から、その組成は、Ｃｅ_0.8Ｓｍ_0.2（ＯＨ）_0.2（ＣＯ₃）_1.4・Ｈ₂Ｏであった。前駆体粉末は引き続き、空気中４５０℃の温度で１２時間仮焼してセリア系化合物粉末を得た。仮焼粉末は実施例１同様、ホタル石単一の結晶相からなることをＸ線回折試験により確認した。得られた仮焼粉末の平均粒子径は２５ナノメーターであり、実施例１同様の球状粒子であった。この粉末を金型成形した後、２ｔ／ｃｍ²の静水圧成形を行った後、９００℃、４時間、空気中において焼結を行った。こうして得られた焼結体は、実施例１同様、理論密度の９９％にまで高密度化しており、焼結体表面には大きな空孔は認められず、ち密化が進んでいることが分かった。
本実施例においても、他の実施例同様、得られた結果を表１にまとめて示した。
【００２３】
実施例５；
配合が（Ｓｍ_0.9Ｓｒ_0.1）_0.175Ｃｅ_0.825Ｏ_1.9になるように、出発原料として、０．２６モル／ｌの硝酸セリウム（純度９９．９９％）、０．０５モル／ｌの硝酸サマリウム（純度９９．９％）及び０．００５５モル／ｌの硝酸ストロンチウムを用いて、硝酸サマリウム水溶液と炭酸水素アンモニウム水溶液のモル比が、５になるように炭酸水素アンモニウム水溶液を調製し、出発原料混合水溶液中に炭酸水素アンモニウム水溶液を毎分１ミリリットルの速度で滴下して沈殿を作製した。炭酸水素アンモニウム滴下終了後、６２℃の温度で、１時間熟成処理を行った。こうして得られた沈殿は水洗処理とろ過を３回繰り返したのち、乾燥窒素ガス中において乾燥し、前駆体粉末を作製した。得られた前駆体粉末の化学分析結果から、その組成は、Ｃｅ_0.825（Ｓｍ_0.9Ｓｒ_0.1）_0.175（ＯＨ）_0.2（ＣＯ₃）_1.4・Ｈ₂Ｏであった。前駆体粉末は引き続き、空気中７００℃の温度で１時間仮焼してセリア系化合物粉末を得た。仮焼粉末は実施例１同様、ホタル石単一の結晶相からなることをＸ線回折試験により確認した。また、仮焼粉末の平均粒子径は４０ナノメーターであり、実施例１同様の球状粒子であった。この粉末を金型成形した後、２ｔ／ｃｍ²の静水圧成形を行った後、１０００℃、４時間、空気中において焼結を行った。こうして得られた焼結体は、実施例１同様、理論密度の９８％にまで高密度化しており、焼結体表面には大きな空孔は認められず、ち密化が進んでいることが分かった。
また本実施例においても上記の結果を表１にまとめて示した。
【００２４】
実施例６；
配合が（Ｇｄ_0.9Ｓｒ_0.1）_0.175Ｃｅ_0.825Ｏ_1.9になるように、出発原料として、０．２６モル／lの硝酸セリウム（純度９９．９９％）、０．０５モル／lの硝酸ガドリウム（純度９９．９％）及び０．００５５モル／lの硝酸ストロンチウムを用いて、硝酸ガドリウム水溶液と炭酸水素アンモニウム水溶液のモル比が、６になるように炭酸水素アンモニウム水溶液を調製し、出発原料混合水溶液中に炭酸水素アンモニウム水溶液を毎分１ミリリットルの速度で滴下して沈殿を作製した。炭酸水素アンモニウム滴下終了後、６０℃の温度で、１時間熟成処理を行った。こうして得られた沈殿は水洗処理とろ過を３回繰り返したのち、乾燥窒素ガス中において乾燥し、前駆体粉末を作製した。得られた前駆体粉末の化学分析結果から、その組成は、Ｃｅ_0.825（Gd_0.9Sr_0.1）_0.175（ＯＨ）_0.2（ＣＯ₃）_1.4・Ｈ₂Ｏであった。
前駆体粉末は引き続き、空気中７００℃の温度で１時間仮焼してセリア系化合物粉末を得た。仮焼粉末は実施例１同様、ホタル石単一の結晶相からなることをＸ線回折試験により確認した。また仮焼粉末の平均粒子径は３５ナノメーターであり、実施例１同様の球状粒子であった。この粉末を金型成形した後、２ｔ／ｃｍ²の静水圧成形を行った後、１０００℃、４時間、空気中において焼結を行ったところ、得られた焼結体は、実施例１同様、理論密度の９９％にまで高密度化しており、焼結体表面には大きな空孔は認められず、ち密化が進んでいることが分かった。
また本実施例においても上記の結果を表１にまとめて示した。
【００２５】
実施例７；
配合が（Y_0.9Ba_0.1）_0.175Ｃｅ_0.825Ｏ_1.9になるように、出発原料として、０．２６モル／ｌの硝酸セリウム（純度９９．９９％）、０．０５モル／ｌの硝酸イットリウム（純度９９．９％）及び０．００５５モル／リットルの硝酸バリウムを用いて、硝酸イットリウム水溶液と炭酸水素アンモニウム水溶液のモル比が、４になるように炭酸水素アンモニウム水溶液を調製し、出発原料混合水溶液中に炭酸水素アンモニウム水溶液を毎分１ミリリットルの速度で滴下して沈殿を作製した。炭酸水素アンモニウム滴下終了後、５７℃の温度で、１時間熟成処理を行った。こうして得られた沈殿は水洗処理とろ過を３回繰り返したのち、乾燥窒素ガス中において乾燥し、前駆体粉末を作製した。得られた前駆体粉末の化学分析結果から、その組成は、Ｃｅ_0.825（Ｙ_0.9Ｂａ_0.1）_0.175（ＯＨ）_0.2（ＣＯ₃）_1.4・Ｈ₂Ｏであった。前駆体粉末は引き続き、空気中４５０℃の温度で１２時間仮焼してセリア系化合物粉末を得た。仮焼粉末は実施例１同様、ホタル石単一の結晶相からなることをＸ線回折試験により確認した。また、仮焼粉末の平均粒子径は３０ナノメーターであり、実施例１同様の球状粒子であった。この粉末を金型成形した後、２ｔ／ｃｍ²の静水圧成形を行った後、９００℃、４時間、空気中において焼結を行ったところ、得られた焼結体は、実施例１同様、理論密度の９９％にまで高密度化しており、焼結体表面には大きな空孔は認められず、ち密化が進んでいることが分かった。
また本実施例においても上記の結果を表１にまとめて示した。
【００２６】
【表１】

【００２７】
比較例１；
配合がＧｄ_0.2Ｃｅ_0.8Ｏ_1.9になるように、出発原料として、０．２０モル／リットルの硝酸セリウム（純度９９．９９％）及び０．０５モル／リットルの硝酸ガドリウム（純度９９．９％）を用いて、硝酸ガドリウムの混合水溶液と炭酸水素アンモニウム水溶液のモル比が、２５となるように炭酸水素アンモニウム水溶液を調製し、出発原料混合水溶液中に炭酸水素アンモニウム水溶液を毎分１ミリリットルの速度で滴下して沈殿を作製した。炭酸水素アンモニウム滴下終了後、６０℃の温度で、１時間熟成を行った。こうして得られた沈殿は水洗処理とろ過を３回繰り返したのち、乾燥窒素ガス中において乾燥し、前駆体粉末を作製した。得られた前駆体粉末の化学分析結果から、その組成は、（ＮＨ₄）_0.15Ｃｅ_0.8Ｇｄ_0.2（ＯＨ）_0.35（ＣＯ₃）_1.4・Ｈ₂Ｏであった。前駆体粉末は引き続き、空気中７００℃の温度で１時間仮焼してセリア系化合物粉末を得た。仮焼粉末は実施例１同様に、ホタル石単一の結晶相からなることをＸ線回折試験により確認した。しかし、仮焼粉末は、主として柱状粒子からなり、その平均粒子径は１００ナノメーターであった。
この粉末を金型成形した後、２ｔ／ｃｍ²の静水圧成形を行った後、１０００℃、４時間、空気中において焼結を行ったところ、得られた焼結体の密度は、理論密度の７９％でしかなかった。焼結体表面には多くの大きな空孔が認められ、緻密化が十分に進んでいないことが分かった。
本比較例の結果を表２にまとめて示した。
【００２８】
比較例２；
配合がＧｄ_0.1Ｃｅ_0.9Ｏ_1.95になるように、出発原料として、０．４５モル／リットルの硝酸セリウム（純度９９．９９％）及び０．０５モル／リットルの硝酸ガドリウム（純度９９．９％）を用いて、硝酸ガドリウム水溶液と炭酸水素アンモニウム水溶液のモル比が、１となるように炭酸水素アンモニウム水溶液を調製し、出発原料混合水溶液中に炭酸水素アンモニウム水溶液を毎分１ミリリットルの速度で滴下して沈殿を作製した。炭酸水素アンモニウム滴下終了後、６０℃の温度で、１時間熟成を行った。こうして得られた沈殿は水洗処理とろ過を３回繰り返したのち、乾燥窒素ガス中において乾燥し、前駆体粉末を作製した。得られた前駆体粉末の化学分析結果から、その組成は、（ＮＨ₄）_0.09Ｃｅ_0.9Ｇｄ_0.1（ＯＨ）_0.02（ＣＯ₃）_0.4・Ｈ₂Ｏであった。前駆体粉末は引き続き、空気中７００℃の温度で１時間仮焼してセリア系化合物粉末を得た。仮焼粉末は実施例１同様に、ホタル石単一の結晶相からなることをＸ線回折試験により確認したが、得られた仮焼粉末は、主として柱状粒子からなり、その平均粒子径は１１０ナノメーターであった。
この粉末を金型成形した後、２ｔ／ｃｍ²の静水圧成形を行った後、１０００℃、４時間、空気中において焼結を行った。得られた焼結体の密度は、理論密度の７５％でしかなく、焼結体表面には多くの大きな空孔が認められ、緻密化が十分に進んでいないことが分かった。
本比較例の結果も比較例１同様、表２にまとめて示した。
【００２９】
比較例３；
配合がＹ_0.2Ｃｅ_0.8Ｏ_1.9になるように、出発原料として、０．２０モル／リットルの硝酸セリウム（純度９９．９９％）及び０．０５モル／リットルの硝酸イットリウム（純度９９．９％）を用いて、硝酸イットリウム水溶液と炭酸水素アンモニウム水溶液のモル比が、１０になるように炭酸水素アンモニウム水溶液を調製し、出発原料混合水溶液中に炭酸水素アンモニウム水溶液を毎分１ミリリットルの速度で滴下して沈殿を作製した。炭酸水素アンモニウム滴下終了後、６５℃の温度で、１時間熟成処理を行った。こうして得られた沈殿は水洗処理とろ過を３回繰り返したのち、乾燥窒素ガス中において乾燥し、前駆体粉末を作製した。得られた前駆体粉末の化学分析結果から、その組成は、Ｃｅ_0.8Ｙ_0.2（ＯＨ）_0.2（ＣＯ₃）_1.4・Ｈ₂Ｏであった。前駆体粉末は引き続き、空気中３００℃の温度で１時間仮焼してセリア系化合物粉末を得た。仮焼粉末は非晶質からなり、結晶相はＸ線回折試験では確認できなかった。得られた仮焼粉末の平均粒子径が１０ナノメーターであり、粒子の形態は球状であったが、この粉末を金型成形した後、２ｔ／ｃｍ²の静水圧成形を行った後、１０００℃、４時間、空気中において焼結を行ったところ、その焼結体の密度は、理論密度の７０％でしかなく、焼結体表面には多くの大きな空孔が認められ、ち密化が十分に進んでいないことが分かった。
本比較例の結果も他の比較例同様、表２にまとめて示した。
【００３０】
比較例４
配合がＳｍ_0.2Ｃｅ_0.8Ｏ_1.9になるように、出発原料として、０．２０モル／リットルの硝酸セリウム（純度９９．９９％）及び０．０５モル／リットルの硝酸サマリウム（純度９９．９％）を用いて、硝酸サマリウム水溶液と炭酸水素アンモニウム水溶液のモル比が、１０になるように炭酸水素アンモニウム水溶液を調製し、出発原料混合水溶液中に炭酸水素アンモニウム水溶液を毎分１ミリリットルの速度で滴下して沈殿を作製した。炭酸水素アンモニウム滴下終了後、５５℃の温度で、１時間熟成処理を行った。こうして得られた沈殿は水洗処理とろ過を３回繰り返したのち、乾燥窒素ガス中において乾燥し、前駆体粉末を作製した。得られた前駆体粉末の化学分析結果から、その組成は、Ｃｅ_0.8Ｓｍ_0.2（ＯＨ）_0.2（ＣＯ₃）_1.4・Ｈ₂Ｏであった。前駆体粉末は引き続き、空気中１０００℃の温度で１時間仮焼してセリア系化合物粉末を作製し、実施例１同様、ホタル石単一の結晶相からなることをＸ線回折試験により確認したが、得られた仮焼粉末の平均粒子径が３５０ナノメーターであり、１次粒子が強く凝集した会合粒子となっていた。この粉末を金型成形した後、２ｔ／ｃｍ²の静水圧成形を行った後、１１００℃、４時間、空気中において焼結を行ったところ、焼結体の密度は、理論密度の７２％であった。焼結体表面には多くの大きな空孔が認められ、ち密化が十分に進んでいないことが分かった。
また、本比較例の結果も他の比較例同様、表２にまとめて示した。
【００３１】
比較例５；
配合が（Ｓｍ_0.9Ｓｒ_0.1）_0.175Ｃｅ_0.825Ｏ_1.9になるように、出発原料として、０．２６モル／ｌの硝酸セリウム（純度９９．９９％）、０．０５モル／ｌの硝酸サマリウム（純度９９．９％）及び０．００５５モル／ｌの硝酸ストロンチウムを用いて、硝酸サマリウム水溶液と炭酸水素アンモニウム水溶液のモル比が、５になるように炭酸水素アンモニウム水溶液を調製し、出発原料混合水溶液中に炭酸水素アンモニウム水溶液を毎分１ミリリットルの速度で滴下して沈殿を作製した。炭酸水素アンモニウム滴下終了後、８０℃の温度で、１時間熟成処理を行った。こうして得られた沈殿は水洗処理とろ過を３回繰り返したのち、乾燥窒素ガス中において乾燥し、前駆体粉末を作製した。得られた前駆体粉末の化学分析結果から、その組成は、Ｃｅ_0.825（Ｓｍ_0.9Ｓｒ_0.1）_0.175（ＯＨ）_0.2（ＣＯ₃）_1.4・Ｈ₂Ｏであった。前駆体粉末は引き続き、空気中７００℃の温度で１時間仮焼してセリア系化合物粉末を作成し、実施例１同様、ホタル石単一の結晶相からなることをＸ線回折試験により確認したが、仮焼粉末の平均粒子径は９０ナノメーターであり、１次粒子が凝集した会合粒子となっていた。この粉末を金型成形した後、２ｔ／ｃｍ²の静水圧成形を行った後、１０００℃、４時間、空気中において焼結を行ったところ、焼結体の密度は、理論密度の７９％であり、焼結体表面には多くの大きな空孔が認められ、ち密化が十分に進んでいないことが分かった。
本比較例の結果も他の比較例同様、表２にまとめて示した。
【００３２】
比較例６；
配合が（Ｓｍ_0.9Ｓｒ_0.1）_0.175Ｃｅ_0.825Ｏ_1.9になるように、出発原料として、０．２６モル／ｌの硝酸セリウム（純度９９．９９％）、０．０５モル／ｌの硝酸サマリウム（純度９９．９％）及び０．００５５モル／ｌの硝酸ストロンチウムを用いて、硝酸サマリウム水溶液と炭酸水素アンモニウム水溶液のモル比が、５になるように炭酸水素アンモニウム水溶液を調製し、出発原料混合水溶液中に炭酸水素アンモニウム水溶液を毎分１ミリリットルの速度で滴下して沈殿を作製した。炭酸水素アンモニウム滴下終了後、４０℃の温度で、１時間熟成処理を行った。こうして得られた沈殿は水洗処理とろ過を３回繰り返したのち、乾燥窒素ガス中において乾燥し、前駆体粉末を作製した。得られた前駆体粉末の化学分析結果から、その組成は、Ｃｅ_0.825（Ｓｍ_0.9Ｓｒ_0.1）_0.175（ＯＨ）_0.2（ＣＯ₃）_1.4・Ｈ₂Ｏであった。前駆体粉末は引き続き、空気中７００℃の温度で１時間仮焼してセリア系化合物粉末を作成し、実施例１同様、ホタル石単一の結晶相からなることをＸ線回折試験により確認したが、仮焼粉末の平均粒子径は１００ナノメーターであり、柱状粒子と球状粒子が共存し、凝集した会合粒子となっていた。この粉末を金型成形した後、２ｔ／ｃｍ²の静水圧成形を行った後、１０００℃、４時間、空気中において焼結を行ったところ、焼結体の密度は、理論密度の７４％であった。焼結体表面には多くの大きな空孔が認められ、緻密化が十分に進んでいないことが分かった。
本比較例の結果も他の比較例同様、表２にまとめて示した。
【００３３】
比較例７；
配合が（Ｇｄ_0.9Ｓｒ_0.1）_0.175Ｃｅ_0.825Ｏ_1.9になるように、出発原料として、０．２６モル／ｌの硝酸セリウム（純度９９．９９％）、０．０５モル／リットルの硝酸ガドリウム（純度９９．９％）及び０．００５５モル／ｌの硝酸ストロンチウムを用いて、硝酸ガドリウム水溶液と炭酸水素アンモニウム水溶液のモル比が、１０になるように炭酸水素アンモニウム水溶液を調製し、出発原料混合水溶液中に炭酸水素アンモニウム水溶液を毎分１ミリリットルの速度で滴下して沈殿を作製した。炭酸水素アンモニウム滴下終了後、６０℃の温度で、１時間熟成処理を行った。こうして得られた沈殿は水洗処理とろ過を３回繰り返したのち、乾燥窒素ガス中において乾燥し、前駆体粉末を作製した。前駆体粉末の化学分析結果から、その組成は、（ＮＨ₄）_0.15Ｃｅ_0.825（Gd_0.9Sr_0.1）_0.175（ＯＨ）_0.35（ＣＯ₃）_1.4・Ｈ₂Ｏであった。前駆体粉末は引き続き、空気中７００℃の温度で１時間仮焼してセリア系化合物粉末を作成し、実施例１同様、ホタル石単一の結晶相からなることをＸ線回折試験により確認したが、その平均粒子径は１１０ナノメーターであり、粉末の形態は、主として柱状粒子からものであった。この粉末を金型成形した後、２ｔ／ｃｍ²の静水圧成形を行った後、１０００℃、４時間、空気中において焼結を行ったところ、焼結体は、理論密度の７２％の密度でしかなかった。焼結体表面には多くの大きな空孔が認められ、ち密化が十分に進んでいないことが分かった。
本比較例の結果も他の比較例同様、表２にまとめて示した。
【００３４】
比較例８；
配合が（Y_0.9Ba_0.1）_0.175Ｃｅ_0.825Ｏ_1.9になるように、出発原料として、０．２６モル／ｌの硝酸セリウム（純度９９．９９％）、０．０５モル／lの硝酸イットリウム（純度９９．９％）及び０．００５５モル／lの硝酸バリウムを用いて、硝酸イットリウムの混合水溶液と炭酸水素アンモニウム水溶液のモル比が、１になるように炭酸水素アンモニウム水溶液を調製し、出発原料混合水溶液中に炭酸水素アンモニウム水溶液を毎分１ミリリットルの速度で滴下して沈殿を作製した。炭酸水素アンモニウム滴下終了後、６０℃の温度で、１時間熟成処理を行った。こうして得られた沈殿は、水洗処理とろ過を３回繰り返したのち、乾燥窒素ガス中において乾燥し、前駆体粉末を作製した。前駆体粉末の化学分析結果から、その組成は、Ｃｅ_0.825（Ｙ_0.9Ｂａ_0.1）_0.175（ＯＨ）_0.02（ＣＯ₃）_0.03・Ｈ₂Ｏであった。前駆体粉末は引き続き、空気中４５０℃の温度で１２時間仮焼してセリア系化合物粉末を作成し、ホタル石単一の結晶相からなることをＸ線回折試験により確認したが、仮焼粉末の平均粒子径は６８ナノメーターであり、柱状粒子と球状粒子が混在した粉末であった。この粉末を金型成形した後、２ｔ／ｃｍ²の静水圧成形を行った後、１０００℃、４時間、空気中において焼結を行った。得られた焼結体は、理論密度の７９％の密度であり、焼結体表面には多くの大きな空孔が認められ、ち密化が十分に進んでいないことが分かった。
本比較例の結果も他の比較例同様、表２にまとめて示した。
【００３５】
【表２】

【００３６】
以上に示す実施例、比較例、そして、これら実施例、比較例をそれぞれ各まとめた表１、表２から明らかなように、反応溶液として調整した硝酸塩溶液とこれに沈殿剤として添加する炭酸水素アンモニウムとの混合モル比、すなわち、（硝酸塩溶液濃度）／（炭酸アンモニウム濃度）のモル比を、２．５から１５、好ましくは、３から７の範囲に入るように調整することを要件事項とした、本件各発明の規定範囲を満たして成るものは、何れも仮焼した段階で単一結晶相の、５０ナノメーター以下の単分散性に富んだ粉末粒子が得られ、１０００℃以下の温度で焼結した段階で理論密度の９８％以上にまで達する緻密化した焼結体が得られたのに対し、上記規定範囲外の比較例によるものは、非晶質を含む生成物が生じることもあり、必ずしも単一結晶相が生成するものではなく、仮焼粒子した段階の粉末粒子も、５０ナノメーターを大幅に超えるものから、極めて微細な粒子までの不揃いな粉末であり、焼結段階でも密度は極めて低いものであった。
【００３７】
【発明の効果】
本発明は、極めて入手容易な硝酸塩から出発し、しかもその主たる要件事項とする操作が、モル比の調整という、操作要領としては極めて平易な操作により、凝集性の少ない、単分散性に富んだナノサイズ球状セリア粒子であって、容易に相対密度が９８％以上にまで緻密にすることが出来る、セリア粉末粒子を得ることに成功したものである。近年、セラミックスの技術分野においても、ますますその材料設計に際しては高精度設計が求められてきている現状にあり、かかる要求は、各種センサ、燃料電池用固体電解質、などに極めて良く利用され、供される原料粉末であるセリア系粉末粒子においてもその例外ではない。本発明は、かかる要求に応えられるセリア粉末を提供するものであり、しかも、前示したように容易に得られる材料から出発し、通常の操作、配慮によって極めて困難な課題を達成することが出来た点は、高く評価することが出来るもので、実用性に富み、その意義は大きい。今後、セリア粉末を利用する技術分野において、その発展に寄与するところ極めて大であると期待される。
【図面の簡単な説明】
【図１】本発明の製造方法による仮焼セリア粉末（実施例１）のＸ線回折図。
【図２】本発明の製造方法による仮焼セリア粉末（実施例１）のＳＥＭ像を示す図。
【図３】本発明の製造方法によるセリア焼結体表面（実施例１）のＳＥＭ像を示す図。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a readily sinterable nanospherical ceria compound powder that is a raw material powder used for a carbon dioxide sensor, a solid electrolyte for a fuel cell, and the like.
[0002]
[Conventional technology and problems]
As a method for synthesizing ceria compound powders, a method of adding oxalic acid to a mixed solution of a cerium salt and a metal salt to obtain a precipitate, a method of adding ammonia or ammonium carbonate as a precipitating agent, a method of using a metal alkoxide, and the like have been used. It was.
When oxalate is used as a precipitating agent, the resulting powder becomes a large aggregate mass, and its crystallization temperature is at least 700 ° C. or higher. And since the particle size of the crystallized ceria compound powder is as large as sub-micron or more, when it is used for sensors, solid electrolytes for fuel cells, etc., even when the sintering temperature is 1500 ° C or higher, the pores are completely removed. Therefore, there is a drawback that it cannot be removed and the characteristics are not improved.
[0003]
In addition, when ammonia or ammonium carbonate is used as a precipitant, the ammonia component contained in the precipitant remains in the precipitate, and when the precipitate is dried and calcined, the particle shape becomes columnar. Therefore, since the specific surface area of the powder is lowered and the sinterability is lowered, the temperature for densification is 1600 ° C. or higher.
[0004]
When an alkoxide is used as a starting material, it is possible to produce a monodispersed powder. However, since the alkoxide raw material is expensive, the practical application is limited to thin film applications. Since it was extremely limited, it was an impediment to practical application.
[0005]
[Means for Solving the Problems]
As a result of intensive investigations in view of the above-mentioned problems of the prior art, the present inventors have sought a precipitated substance necessary for producing spherical particles that control the shape of particles that tend to be columnar and have little aggregation. By studying the composition, calcining conditions, and the like, the inventors have found the production conditions for a readily sinterable spherical ceria compound powder having a nano-size particle size, and have completed the present invention.
[0006]
That is, the gist of the present invention is that, first, (1) a divalent or trivalent metal (M) nitrate and a cerium nitrate are mixed with M._xCe_1-xO₂ _―Δ(However, 0.05 ≦ x ≦ 0.3, where δ represents the amount of oxygen defects determined from the balance of the charge of the cation and anion) and mixed with this mixed solution and ammonium bicarbonate as a precipitant. , [Divalent or trivalent metal (M) nitrate and cerium nitrate aqueous solution concentration] / (ammonium carbonate aqueous solution concentration) in a molar ratio of 2.5 to 15,_1-xM_x(OH)_y(CO_Three)_z・ H₂After precipitating the cerium carbonate represented by O (where 0.05 ≦ x ≦ 0.3, 0.05 ≦ y ≦ 1, 0.05 ≦ z ≦ 2), aging is performed at 50 ° C. or more and 70 ° C. By carrying out in the following temperature range, and calcining at a temperature of 400 ° C. or higher and 750 ° C. or lower after cleaning, spherical particles having an average particle size of 50 nanometers or less are formed and sintered at a temperature of 1000 ° C. or lower. This is a method for producing a readily sinterable nanospherical ceria compound powder characterized in that it is compacted to 98% or more of the relative density.
[0007]
The second is (2) divalent (M²⁺) And trivalent (M³⁺) Nitrate containing metal elements and cerium nitrate (M²⁺ _aM³⁺ _1-a)_xCe_1-xO₂ _―Δ(However, 0.01 ≦ a ≦ 0.5, 0.05 ≦ x ≦ 0.3, where δ represents the amount of oxygen defects determined from the balance of charges of the cation and anion) Ammonium hydrogen carbonate as a mixed solution and a precipitating agent [divalent (M²⁺) And trivalent (M³⁺)) (Nitrate aqueous solution containing metal element)] / (ammonium carbonate aqueous solution concentration)_1-x(M²⁺ _aM³⁺ _1-a)_x(OH)_y(CO_Three)_z・ H₂Cerium carbonate represented by O (0.01 ≦ a ≦ 0.5, 0.05 ≦ x ≦ 0.3, 0.05 ≦ y ≦ 1, 0.05 ≦ z ≦ 2) was precipitated. Later, aging is performed at a temperature of 55 ° C. or more and 65 ° C. or less, and after washing, calcining is performed at a temperature of 400 ° C. or more and 750 ° C. or less, thereby forming spherical particles having an average particle size of 50 nanometers or less, and 1000 ° C. or less. It is a method for producing a readily sinterable nanospherical ceria compound powder characterized in that it is compacted to 98% or more of the relative density by sintering at a temperature.
[0008]
In the present invention, the chemical composition of cerium carbonate, which is indispensable for producing nanospherical powder, is Ce._1-xM_x(OH)_y(CO_Three)_z・ H₂O (however, 0.05 ≦ x ≦ 0.3, 0.05 ≦ y ≦ 1, 0.05 ≦ z ≦ 2, M represents a trivalent metal element) or Ce_1-x(M²⁺ _aM³⁺ _1-a)_x(OH)_y(CO_Three)_z・ H₂O (provided that 0.01 ≦ a ≦ 0.5, 0.05 ≦ x ≦ 0.3, 0.05 ≦ y ≦ 1, 0.05 ≦ z ≦ 2, M²⁺And M³⁺Each represents a divalent or trivalent metal element). If the precipitation substance contains an ammonia component, the precipitate tends to grow in a columnar shape and the sinterability decreases, which is not preferable.
[0009]
The range of a is preferably 0.01 or more and 0.5 or less, and if the range is less than this range, the effect of coexisting divalent and trivalent elements is not sufficiently exhibited, and the above-described sensor, solid electrolyte for fuel cell, etc. When used, it is not preferable because it does not lead to improvement in characteristics. On the other hand, if it exceeds this range, the divalent and trivalent metal elements are segregated, and the characteristics of the sensor, the solid electrolyte for fuel cells and the like may be deteriorated, which is not preferable. The range of x must be not less than 0.05 and not more than 0.3. If the range is less than this range, oxygen defects introduced into the calcined powder when applied to the above-described sensor, solid electrolyte for fuel cell, etc. This is not preferable because the amount is insufficient and sufficient characteristics are not exhibited.
[0010]
On the other hand, exceeding this range is not preferable because excessive oxygen defects are introduced into the calcined powder, which deteriorates the characteristics of the solid electrolyte for the sensor and fuel cell.
The range of y is preferably 0.05 or more and 1 or less. The value of y is controlled by the molar ratio and pH of the reaction solution and the precipitating agent. If the value of y falls below this range, precipitation does not occur sufficiently, and a large amount of metal such as cerium is present in the filtrate. This is not preferable because the element remains, the yield is reduced, and an aggregate in which columnar particles and spherical particles are mixed is formed, and the sinterability is significantly reduced. On the other hand, if it exceeds this range, the aggregation between the particles becomes strong, resulting in a submicron aggregate and the sinterability is lowered, which is not preferable.
[0011]
The range of z is preferably 0.05 or more and 2 or less. The value of z can be controlled by the concentration of the precipitant, but when this value is less than 0.05, precipitation does not occur sufficiently, and a large amount of metal element such as cerium remains in the filtrate, yield. In addition, an aggregate in which columnar particles and spherical particles are mixed is formed, and the sinterability is significantly reduced. On the other hand, if it exceeds this range, the aggregation between the particles becomes strong, resulting in a submicron aggregate and the sinterability is lowered, which is not preferable.
[0012]
Also, divalent or trivalent metal (M) nitrate and cerium nitrate_xCe_1-xO₂In the case of mixing so as to be −δ (where 0.05 ≦ x ≦ 0.3, δ represents the amount of oxygen defects determined from the charge balance between the cation and the anion), the divalent or trivalent metal The molar ratio of (M) nitrate aqueous solution concentration] / (ammonium carbonate aqueous solution concentration) should be 2.5 or more and 15 or less. If it falls below this range or exceeds this range, a precipitate having the above-mentioned preferred composition cannot be produced, so it must be within this range. When it is below or above this range, the columnar particles remain in the precipitation, which is not preferable because the sinterability of the calcined powder is lowered.
[0013]
Furthermore, bivalent (M²⁺) And trivalent (M³⁺) Nitrate containing metal elements and cerium nitrate (M²⁺ _aM³⁺ _1-a)_xCe_1-xO₂ _―Δ(However, 0.01 ≦ a ≦ 0.5, 0.05 ≦ x ≦ 0.3, where δ represents the amount of oxygen defects determined from the balance of the charges of the cation and anion) [Divalent (M²⁺) And trivalent (M³⁺) Nitrate aqueous solution containing metal element concentration] / (ammonium carbonate aqueous solution concentration) molar ratio must be 3 or more and 7 or less. Precipitation of the preferred composition above or below this range Must be within this range.
When it is below or above this range, the columnar particles remain in the precipitation, which is not preferable because the sinterability of the calcined powder is lowered.
[0014]
When a precipitate is formed using divalent or trivalent metal nitrate, cerium nitrate and ammonium hydrogen carbonate, aging must be performed at a temperature of 50 ° C. or higher and 70 ° C. or lower. If the aging temperature is lower than this range, the columnar particles coexist in the precipitation, and the columnar particles remain after calcination, which is not preferable. Further, if the temperature range is exceeded, the spherical particles generated with agglomeration are agglomerated, and this agglomeration remains after calcination, which is not preferable because the sinterability is significantly reduced.
[0015]
Bivalent (M²⁺) And trivalent (M³⁺In the case where a precipitate is prepared using a nitrate containing a metal element), a cerium nitrate and ammonium hydrogen carbonate, it is necessary to age at a temperature of 55 ° C. or more and 65 ° C. or less. If the aging temperature is lower than this range, the columnar particles coexist in the precipitation, and the columnar particles remain even after calcination, which lowers the sinterability. Exceeding this temperature range is not preferable because the spherical particles generated with agglomeration are aggregated and remain after the calcination, and the sinterability is significantly reduced. The aging temperature is not particularly limited, but an aging time of about 1 to 2 hours is sufficient because aging for a very long time has a certain effect.
[0016]
The precipitated substance obtained in the present invention must be washed with water after the precipitation is formed. If the water is not washed, ammonia remains in the precipitated substance and columnar particles are mixed in the calcined powder, which is not preferable. Although there is no restriction | limiting in particular about the frequency | count of water washing, Since ammonia can be removed almost completely by performing water washing 3 times or more, it is preferable to perform water washing about 3 times.
After washing with water, the powder must be dried using a dry gas, etc., and calcined in air or oxygen to crystallize it into a fluorite-type crystal structure single phase. The temperature must be between 400 ° C and 750 ° C. Below this temperature range, crystallization does not proceed sufficiently, and the remaining amorphous material causes non-uniform grain growth during sintering and prevents densification, which is not preferable. If the temperature range is exceeded, the particle size becomes sub-micron or larger, a high temperature of 1500 ° C. or higher is required for sintering, and voids tend to remain in the sintered body, resulting in solid electrolytes for sensors and fuel cells. This is not preferable because the above characteristics are deteriorated.
[0017]
The atmosphere during calcination can achieve the same effect in air or in an oxygen stream, but calcination in an atmosphere with as high an oxygen partial pressure as possible is necessary to completely burn impurities contained in the precipitated substance. preferable. The calcining time is not particularly limited, but carbon dioxide gas and moisture tend to remain in the powder as the calcining is performed at a lower temperature. Therefore, when calcining at 400 ° C. or 500 ° C., the calcining is performed for 10 hours or more. However, in the case of calcining at a temperature higher than that, even if it is made too long, a significant effect cannot be expected, and it is sufficient to calcine for about 1 to 4 hours.
Although there is no restriction | limiting in particular in sintering the obtained nano spherical powder, A high density sintered compact with a relative density of 98% or more can be produced by sintering at 900 degreeC or more in air | atmosphere.
[0018]
Next, specific embodiments of the present invention and the significance thereof will be disclosed and explained by the following examples and comparative examples. However, these examples are only for the purpose of facilitating the understanding of the present invention. However, this is not intended to limit the present invention. That is, the contents of the present invention are not limited by these examples and comparative examples.
[0019]
【Example】
Example 1;
Formulation is Gd_0.2Ce_0.8O_1.9As a starting material, 0.20 mol / liter cerium nitrate (purity 99.99%) and 0.05 mol / liter gadolinium nitrate (purity 99.9%) were used. An aqueous ammonium hydrogen carbonate solution was prepared so that the molar ratio of the aqueous ammonium hydrogen carbonate solution was 10, and the aqueous ammonium hydrogen carbonate solution was dropped into the starting raw material mixed aqueous solution at a rate of 1 ml / min to produce a precipitate. After completion of the dropwise addition of ammonium hydrogen carbonate, aging was performed at a temperature of 60 ° C. for 1 hour. The precipitate thus obtained was repeatedly washed with water and filtered three times, and then dried in dry nitrogen gas to prepare a precursor powder. From the result of chemical analysis of the obtained precursor powder, its composition is Ce_0.8Gd_0.2(OH)_0.2(CO_Three)_1.4・ H₂O. The precursor powder was subsequently calcined in air at a temperature of 700 ° C. for 1 hour to prepare a ceria compound powder, and it was confirmed by an X-ray diffraction test that it consisted of a single crystal phase of fluorite. In FIG. 1, the identification result of the crystal phase by an X-ray diffraction test is shown.
A scanning electron microscope observation image (SEM image) of the obtained calcined powder is shown in FIG. The obtained powder was spherical particles having an average particle size of 30 nanometers.
After molding this powder, 2t / cm²After performing the hydrostatic pressing, sintering was performed in air at 1000 ° C. for 4 hours. The obtained sintered body was densified to 99% of the theoretical density, and no large voids were observed on the surface of the sintered body, indicating that the densification was progressing. Moreover, while showing the SEM image of the surface of a sintered compact in FIG. 3, said result was put together in Table 1 and shown.
[0020]
Example 2;
Formulation is Gd_0.1Ce_0.9O_1.95As a starting material, 0.45 mol / liter cerium nitrate (purity 99.99%) and 0.05 mol / liter gadolinium nitrate (purity 99.9%) were used. An aqueous ammonium hydrogen carbonate solution was prepared so that the molar ratio of the aqueous ammonium hydrogen carbonate solution was 8, and the aqueous ammonium hydrogen carbonate solution was dropped into the starting raw material mixed aqueous solution at a rate of 1 ml / min to produce a precipitate. After completion of the dropwise addition of ammonium hydrogen carbonate, aging was performed at a temperature of 60 ° C. for 1 hour. The precipitate thus obtained was repeatedly washed with water and filtered three times, and then dried in dry nitrogen gas to prepare a precursor powder.
From the result of chemical analysis of the obtained precursor powder, its composition is Ce_0.9Gd_0.1(OH)_0.2(CO_Three)_1.4・ H₂O. The precursor powder was subsequently calcined at 700 ° C. in air for 1 hour to produce a ceria compound powder. The calcined powder was composed of a single crystal phase of fluorite as in FIG. 1 of Example 1, and was spherical particles having an average particle diameter of 30 nanometers as in FIG. 2 of Example 1.
After molding this powder, 2t / cm²After performing the hydrostatic pressing, sintering was performed in air at 1000 ° C. for 4 hours. The obtained sintered body was densified to 99% of the theoretical density as in Example 1, and it was found that no large pores were observed on the surface of the sintered body, and the densification was progressing. . Also in this example, the results are summarized in Table 1 as in Example 1.
[0021]
Example 3;
Formula is Y_0.2Ce_0.8O_1.9As a starting material, 0.20 mol / liter cerium nitrate (purity 99.99%) and 0.05 mol / liter yttrium nitrate (purity 99.9%) were used. An aqueous ammonium hydrogen carbonate solution was prepared so that the molar ratio of the aqueous ammonium hydrogen carbonate solution was 3, and the aqueous ammonium hydrogen carbonate solution was dropped into the starting raw material mixed aqueous solution at a rate of 1 ml / min to produce a precipitate. After completion of the dropwise addition of ammonium hydrogen carbonate, an aging treatment was performed at a temperature of 65 ° C. for 1 hour. The precipitate thus obtained was repeatedly washed with water and filtered three times, and then dried in dry nitrogen gas to prepare a precursor powder. From the result of chemical analysis of the obtained precursor powder, its composition is Ce_0.8Y_0.2(OH)_0.2(CO_Three)_1.4・ H₂O. The precursor powder was subsequently calcined at 700 ° C. in air for 1 hour to obtain a ceria compound powder. As in Example 1, the calcined powder was confirmed to be composed of a single crystal phase of fluorite by an X-ray diffraction test. The average particle size of the obtained calcined powder was 35 nanometers, and the same spherical particles as in Example 1. After molding this powder, 2t / cm²After performing the hydrostatic pressing, sintering was performed in air at 1000 ° C. for 4 hours. The sintered body thus obtained was densified to 99% of the theoretical density as in Example 1, and it was found that no large voids were observed on the surface of the sintered body and the densification was progressing. It was.
Also in this example, the results obtained in the same manner as in the other examples are summarized in Table 1.
[0022]
Example 4;
Formula is Sm_0.2Ce_0.8O_1.9As a starting material, 0.20 mol / liter cerium nitrate (purity 99.99%) and 0.05 mol / liter samarium nitrate (purity 99.9%) were used. An aqueous ammonium hydrogen carbonate solution was prepared so that the molar ratio of the aqueous ammonium hydrogen carbonate solution was 3, and the aqueous ammonium hydrogen carbonate solution was dropped into the starting raw material mixed aqueous solution at a rate of 1 ml / min to produce a precipitate. After completion of the dropwise addition of ammonium hydrogen carbonate, an aging treatment was performed at a temperature of 55 ° C. for 1 hour. The precipitate thus obtained was repeatedly washed with water and filtered three times, and then dried in dry nitrogen gas to prepare a precursor powder. From the result of chemical analysis of the obtained precursor powder, its composition is Ce_0.8Sm_0.2(OH)_0.2(CO_Three)_1.4・ H₂O. The precursor powder was subsequently calcined in air at a temperature of 450 ° C. for 12 hours to obtain a ceria compound powder. As in Example 1, the calcined powder was confirmed to be composed of a single crystal phase of fluorite by an X-ray diffraction test. The average particle size of the obtained calcined powder was 25 nanometers, and the same spherical particles as in Example 1. After molding this powder, 2t / cm²After performing the isostatic pressing, sintering was performed in air at 900 ° C. for 4 hours. The sintered body thus obtained was densified to 99% of the theoretical density as in Example 1, and no large pores were observed on the surface of the sintered body, indicating that the densification was progressing. It was.
Also in this example, the obtained results are summarized in Table 1 like the other examples.
[0023]
Example 5;
Formula (Sm_0.9Sr_0.1)_0.175Ce_0.825O_1.9As starting materials, 0.26 mol / l cerium nitrate (purity 99.99%), 0.05 mol / l samarium nitrate (purity 99.9%) and 0.0055 mol / l Using strontium nitrate, prepare an ammonium hydrogen carbonate aqueous solution so that the molar ratio of the samarium nitrate aqueous solution and the ammonium hydrogen carbonate aqueous solution is 5. A precipitate was prepared by dropping. After completion of the dropwise addition of ammonium hydrogen carbonate, an aging treatment was performed at a temperature of 62 ° C. for 1 hour. The precipitate thus obtained was repeatedly washed with water and filtered three times, and then dried in dry nitrogen gas to prepare a precursor powder. From the result of chemical analysis of the obtained precursor powder, its composition is Ce_0.825(Sm_0.9Sr_0.1)_0.175(OH)_0.2(CO_Three)_1.4・ H₂O. The precursor powder was subsequently calcined at 700 ° C. in air for 1 hour to obtain a ceria compound powder. As in Example 1, the calcined powder was confirmed to be composed of a single crystal phase of fluorite by an X-ray diffraction test. Moreover, the average particle diameter of the calcined powder was 40 nanometers, and the same spherical particles as in Example 1. After molding this powder, 2t / cm²After performing the hydrostatic pressing, sintering was performed in air at 1000 ° C. for 4 hours. The sintered body thus obtained was densified to 98% of the theoretical density as in Example 1, and no large pores were observed on the surface of the sintered body, indicating that the densification was progressing. It was.
Also in this example, the above results are summarized in Table 1.
[0024]
Example 6;
The formulation is (Gd_0.9Sr_0.1)_0.175Ce_0.825O_1.9As starting materials, 0.26 mol / l cerium nitrate (purity 99.99%), 0.05 mol / l gadolinium nitrate (purity 99.9%) and 0.0055 mol / l Using strontium nitrate, prepare an aqueous ammonium hydrogen carbonate solution so that the molar ratio of the aqueous gadolinium nitrate solution and the aqueous ammonium hydrogen carbonate solution is 6. A precipitate was prepared by dropping. After completion of the dropwise addition of ammonium hydrogen carbonate, an aging treatment was performed at a temperature of 60 ° C. for 1 hour. The precipitate thus obtained was repeatedly washed with water and filtered three times, and then dried in dry nitrogen gas to prepare a precursor powder. From the result of chemical analysis of the obtained precursor powder, its composition is Ce_0.825(Gd_0.9Sr_0.1)_0.175(OH)_0.2(CO_Three)_1.4・ H₂O.
The precursor powder was subsequently calcined at 700 ° C. in air for 1 hour to obtain a ceria compound powder. As in Example 1, the calcined powder was confirmed to be composed of a single crystal phase of fluorite by an X-ray diffraction test. Further, the average particle size of the calcined powder was 35 nanometers, and the same spherical particles as in Example 1. After molding this powder, 2t / cm²After performing hydrostatic pressure molding of 1000 ° C. for 4 hours and sintering in the air, the obtained sintered body was densified to 99% of the theoretical density as in Example 1. It was found that no large pores were observed on the surface of the sintered body and the densification was progressing.
Also in this example, the above results are summarized in Table 1.
[0025]
Example 7;
Formula is (Y_0.9Ba_0.1)_0.175Ce_0.825O_1.9As starting materials, 0.26 mol / l cerium nitrate (purity 99.99%), 0.05 mol / l yttrium nitrate (purity 99.9%) and 0.0055 mol / l Using barium nitrate, prepare an aqueous ammonium hydrogen carbonate solution so that the molar ratio of the aqueous yttrium nitrate solution to the aqueous ammonium hydrogen carbonate solution is 4. A precipitate was prepared by dropping. After completion of the dropwise addition of ammonium hydrogen carbonate, an aging treatment was performed at a temperature of 57 ° C. for 1 hour. The precipitate thus obtained was repeatedly washed with water and filtered three times, and then dried in dry nitrogen gas to prepare a precursor powder. From the result of chemical analysis of the obtained precursor powder, its composition is Ce_0.825(Y_0.9Ba_0.1)_0.175(OH)_0.2(CO_Three)_1.4・ H₂O. The precursor powder was subsequently calcined in air at a temperature of 450 ° C. for 12 hours to obtain a ceria compound powder. As in Example 1, the calcined powder was confirmed to be composed of a single crystal phase of fluorite by an X-ray diffraction test. Moreover, the average particle diameter of the calcined powder was 30 nanometers, and the same spherical particles as in Example 1. After molding this powder, 2t / cm²After performing hydrostatic pressure molding of 900 ° C. for 4 hours and sintering in air, the obtained sintered body was densified to 99% of the theoretical density as in Example 1. It was found that no large pores were observed on the surface of the sintered body and the densification was progressing.
Also in this example, the above results are summarized in Table 1.
[0026]
[Table 1]

[0027]
Comparative Example 1;
Formulation is Gd_0.2Ce_0.8O_1.9As a starting material, 0.20 mol / liter cerium nitrate (purity 99.99%) and 0.05 mol / liter gadolinium nitrate (purity 99.9%) were mixed with gadolinium nitrate. An aqueous ammonium hydrogen carbonate solution was prepared so that the molar ratio of the aqueous solution to the aqueous ammonium hydrogen carbonate solution was 25, and an aqueous ammonium hydrogen carbonate solution was dropped into the starting raw material mixed aqueous solution at a rate of 1 ml / min to produce a precipitate. After completion of the dropwise addition of ammonium hydrogen carbonate, aging was performed at a temperature of 60 ° C. for 1 hour. The precipitate thus obtained was repeatedly washed with water and filtered three times, and then dried in dry nitrogen gas to prepare a precursor powder. From the chemical analysis result of the obtained precursor powder, its composition is (NH_Four)_0.15Ce_0.8Gd_0.2(OH)_0.35(CO_Three)_1.4・ H₂O. The precursor powder was subsequently calcined at 700 ° C. in air for 1 hour to obtain a ceria compound powder. It was confirmed by an X-ray diffraction test that the calcined powder was composed of a single crystal phase of fluorite as in Example 1. However, the calcined powder was mainly composed of columnar particles, and the average particle size was 100 nanometers.
After molding this powder, 2t / cm²After performing the hydrostatic pressing, sintering was performed in air at 1000 ° C. for 4 hours. As a result, the density of the obtained sintered body was only 79% of the theoretical density. Many large pores were observed on the surface of the sintered body, and it was found that densification was not sufficiently advanced.
The results of this comparative example are summarized in Table 2.
[0028]
Comparative Example 2;
Formulation is Gd_0.1Ce_0.9O_1.95As a starting material, 0.45 mol / liter cerium nitrate (purity 99.99%) and 0.05 mol / liter gadolinium nitrate (purity 99.9%) were used. An aqueous ammonium hydrogen carbonate solution was prepared so that the molar ratio of the aqueous ammonium hydrogen carbonate solution was 1, and the aqueous ammonium hydrogen carbonate solution was dropped into the starting raw material mixed aqueous solution at a rate of 1 ml / min to produce a precipitate. After completion of the dropwise addition of ammonium hydrogen carbonate, aging was performed at a temperature of 60 ° C. for 1 hour. The precipitate thus obtained was repeatedly washed with water and filtered three times, and then dried in dry nitrogen gas to prepare a precursor powder. From the chemical analysis result of the obtained precursor powder, its composition is (NH_Four)_0.09Ce_0.9Gd_0.1(OH)_0.02(CO_Three)_0.4・ H₂O. The precursor powder was subsequently calcined at 700 ° C. in air for 1 hour to obtain a ceria compound powder. As in Example 1, the calcined powder was confirmed to be composed of a single crystal phase of fluorite by an X-ray diffraction test. The obtained calcined powder was mainly composed of columnar particles, and the average particle size was 110. It was nanometer.
After molding this powder, 2t / cm²After performing the hydrostatic pressing, sintering was performed in air at 1000 ° C. for 4 hours. The density of the obtained sintered body was only 75% of the theoretical density, and many large pores were observed on the surface of the sintered body, indicating that the densification was not sufficiently advanced.
The results of this Comparative Example are also shown in Table 2 together with Comparative Example 1.
[0029]
Comparative Example 3;
Formula is Y_0.2Ce_0.8O_1.9As a starting material, 0.20 mol / liter cerium nitrate (purity 99.99%) and 0.05 mol / liter yttrium nitrate (purity 99.9%) were used. An aqueous ammonium hydrogen carbonate solution was prepared so that the molar ratio of the aqueous ammonium hydrogen carbonate solution was 10, and the aqueous ammonium hydrogen carbonate solution was dropped into the starting raw material mixed aqueous solution at a rate of 1 ml / min to produce a precipitate. After completion of the dropwise addition of ammonium hydrogen carbonate, an aging treatment was performed at a temperature of 65 ° C. for 1 hour. The precipitate thus obtained was repeatedly washed with water and filtered three times, and then dried in dry nitrogen gas to prepare a precursor powder. From the result of chemical analysis of the obtained precursor powder, its composition is Ce_0.8Y_0.2(OH)_0.2(CO_Three)_1.4・ H₂O. The precursor powder was subsequently calcined in air at a temperature of 300 ° C. for 1 hour to obtain a ceria compound powder. The calcined powder was amorphous, and the crystal phase could not be confirmed by the X-ray diffraction test. The obtained calcined powder had an average particle size of 10 nanometers and the shape of the particles was spherical, but after this powder was molded, 2 t / cm²After the hydrostatic pressure forming, the sintered body was sintered in the air at 1000 ° C. for 4 hours, and the density of the sintered body was only 70% of the theoretical density, and there were many on the sintered body surface. Large vacancies were observed, indicating that the densification was not sufficiently advanced.
The results of this comparative example are also shown in Table 2 together with the other comparative examples.
[0030]
Comparative Example 4
Formula is Sm_0.2Ce_0.8O_1.9As a starting material, 0.20 mol / liter cerium nitrate (purity 99.99%) and 0.05 mol / liter samarium nitrate (purity 99.9%) were used. An aqueous ammonium hydrogen carbonate solution was prepared so that the molar ratio of the aqueous ammonium hydrogen carbonate solution was 10, and the aqueous ammonium hydrogen carbonate solution was dropped into the starting raw material mixed aqueous solution at a rate of 1 ml / min to produce a precipitate. After completion of the dropwise addition of ammonium hydrogen carbonate, an aging treatment was performed at a temperature of 55 ° C. for 1 hour. The precipitate thus obtained was repeatedly washed with water and filtered three times, and then dried in dry nitrogen gas to prepare a precursor powder. From the result of chemical analysis of the obtained precursor powder, its composition is Ce_0.8Sm_0.2(OH)_0.2(CO_Three)_1.4・ H₂O. The precursor powder was subsequently calcined in air at a temperature of 1000 ° C. for 1 hour to prepare a ceria-based compound powder, and as in Example 1, it was confirmed by an X-ray diffraction test that it consisted of a single crystal phase of fluorite. However, the average particle diameter of the obtained calcined powder was 350 nanometers, and the primary particles were aggregated particles that were strongly aggregated. After molding this powder, 2t / cm²After performing the hydrostatic pressing, sintering was performed in air at 1100 ° C. for 4 hours. The density of the sintered body was 72% of the theoretical density. Many large pores were observed on the surface of the sintered body, indicating that the densification was not sufficiently advanced.
The results of this comparative example are also shown in Table 2 together with the other comparative examples.
[0031]
Comparative Example 5;
Formula (Sm_0.9Sr_0.1)_0.175Ce_0.825O_1.9As starting materials, 0.26 mol / l cerium nitrate (purity 99.99%), 0.05 mol / l samarium nitrate (purity 99.9%) and 0.0055 mol / l Using strontium nitrate, prepare an ammonium hydrogen carbonate aqueous solution so that the molar ratio of the samarium nitrate aqueous solution and the ammonium hydrogen carbonate aqueous solution is 5. A precipitate was prepared by dropping. After completion of the dropwise addition of ammonium hydrogen carbonate, an aging treatment was performed at a temperature of 80 ° C. for 1 hour. The precipitate thus obtained was repeatedly washed with water and filtered three times, and then dried in dry nitrogen gas to prepare a precursor powder. From the result of chemical analysis of the obtained precursor powder, its composition is Ce_0.825(Sm_0.9Sr_0.1)_0.175(OH)_0.2(CO_Three)_1.4・ H₂O. The precursor powder was subsequently calcined in air at a temperature of 700 ° C. for 1 hour to prepare a ceria compound powder, and it was confirmed by an X-ray diffraction test that it consisted of a single crystal phase of fluorite as in Example 1. However, the average particle diameter of the calcined powder was 90 nanometers, and the aggregated particles were aggregated primary particles. After molding this powder, 2t / cm²After the hydrostatic pressure forming, the sintered body was sintered in the air at 1000 ° C. for 4 hours. The density of the sintered body was 79% of the theoretical density. It was found that pores were observed and densification was not sufficiently advanced.
The results of this comparative example are also shown in Table 2 together with the other comparative examples.
[0032]
Comparative Example 6;
Formula (Sm_0.9Sr_0.1)_0.175Ce_0.825O_1.9As starting materials, 0.26 mol / l cerium nitrate (purity 99.99%), 0.05 mol / l samarium nitrate (purity 99.9%) and 0.0055 mol / l Using strontium nitrate, prepare an ammonium hydrogen carbonate aqueous solution so that the molar ratio of the samarium nitrate aqueous solution and the ammonium hydrogen carbonate aqueous solution is 5. A precipitate was prepared by dropping. After completion of the dropwise addition of ammonium hydrogen carbonate, an aging treatment was performed at a temperature of 40 ° C. for 1 hour. The precipitate thus obtained was repeatedly washed with water and filtered three times, and then dried in dry nitrogen gas to prepare a precursor powder. From the result of chemical analysis of the obtained precursor powder, its composition is Ce_0.825(Sm_0.9Sr_0.1)_0.175(OH)_0.2(CO_Three)_1.4・ H₂O. The precursor powder was subsequently calcined in air at a temperature of 700 ° C. for 1 hour to prepare a ceria compound powder, and it was confirmed by an X-ray diffraction test that it consisted of a single crystal phase of fluorite as in Example 1. However, the average particle size of the calcined powder was 100 nanometers, and columnar particles and spherical particles coexisted to form aggregated associated particles. After molding this powder, 2t / cm²After performing the hydrostatic pressing, sintering was performed in air at 1000 ° C. for 4 hours. As a result, the density of the sintered body was 74% of the theoretical density. Many large pores were observed on the surface of the sintered body, and it was found that densification was not sufficiently advanced.
The results of this comparative example are also shown in Table 2 together with the other comparative examples.
[0033]
Comparative Example 7;
The formulation is (Gd_0.9Sr_0.1)_0.175Ce_0.825O_1.9As starting materials, 0.26 mol / l cerium nitrate (purity 99.99%), 0.05 mol / l gadolinium nitrate (purity 99.9%) and 0.0055 mol / l Using strontium nitrate, prepare an aqueous ammonium hydrogen carbonate solution so that the molar ratio of the aqueous gadolinium nitrate solution to the aqueous ammonium hydrogen carbonate solution is 10. The aqueous ammonium hydrogen carbonate solution is added to the starting raw material aqueous solution at a rate of 1 milliliter per minute. A precipitate was prepared by dropwise addition. After completion of the dropwise addition of ammonium hydrogen carbonate, an aging treatment was performed at a temperature of 60 ° C. for 1 hour. The precipitate thus obtained was repeatedly washed with water and filtered three times, and then dried in dry nitrogen gas to prepare a precursor powder. From the chemical analysis results of the precursor powder, its composition is (NH_Four)_0.15Ce_0.825(Gd_0.9Sr_0.1)_0.175(OH)_0.35(CO_Three)_1.4・ H₂O. The precursor powder was subsequently calcined in air at a temperature of 700 ° C. for 1 hour to prepare a ceria compound powder, and it was confirmed by an X-ray diffraction test that it consisted of a single crystal phase of fluorite as in Example 1. However, the average particle diameter was 110 nanometers, and the powder form was mainly from columnar particles. After molding this powder, 2t / cm²After performing the hydrostatic pressing, sintering was performed in air at 1000 ° C. for 4 hours. As a result, the sintered body had a density of only 72% of the theoretical density. Many large pores were observed on the surface of the sintered body, indicating that the densification was not sufficiently advanced.
The results of this comparative example are also shown in Table 2 together with the other comparative examples.
[0034]
Comparative Example 8;
Formula is (Y_0.9Ba_0.1)_0.175Ce_0.825O_1.9As starting materials, 0.26 mol / l cerium nitrate (purity 99.99%), 0.05 mol / l yttrium nitrate (purity 99.9%) and 0.0055 mol / l Using barium nitrate, an aqueous ammonium hydrogen carbonate solution was prepared so that the molar ratio of the mixed aqueous solution of yttrium nitrate and the aqueous ammonium hydrogen carbonate solution was 1, and the aqueous ammonium hydrogen carbonate solution was added to the starting raw material mixed aqueous solution at 1 ml / min. A precipitate was made by dropping at a rate. After completion of the dropwise addition of ammonium hydrogen carbonate, an aging treatment was performed at a temperature of 60 ° C. for 1 hour. The precipitate thus obtained was repeatedly washed with water and filtered three times, and then dried in dry nitrogen gas to prepare a precursor powder. From the chemical analysis results of the precursor powder, its composition is Ce_0.825(Y_0.9Ba_0.1)_0.175(OH)_0.02(CO_Three)_0.03・ H₂O. The precursor powder was subsequently calcined in air at a temperature of 450 ° C. for 12 hours to prepare a ceria compound powder, and it was confirmed by an X-ray diffraction test that the precursor powder consisted of a single crystal phase of fluorite. The average particle diameter was 68 nanometers, and was a powder in which columnar particles and spherical particles were mixed. After molding this powder, 2t / cm²After performing the hydrostatic pressing, sintering was performed in air at 1000 ° C. for 4 hours. The obtained sintered body had a density of 79% of the theoretical density, and many large pores were observed on the surface of the sintered body, indicating that the densification was not sufficiently advanced.
The results of this comparative example are also shown in Table 2 together with the other comparative examples.
[0035]
[Table 2]

[0036]
As is clear from the examples and comparative examples shown above, and Table 1 and Table 2 that summarize these examples and comparative examples, respectively, a nitrate solution prepared as a reaction solution and a hydrogen carbonate added as a precipitant to the solution. It is a requirement to adjust the mixing molar ratio with ammonium, that is, the molar ratio of (nitrate solution concentration) / (ammonium carbonate concentration) to be in the range of 2.5 to 15, preferably 3 to 7. In the case of satisfying the specified range of each invention of the present invention, powder particles having a single crystal phase and rich in monodispersity of 50 nanometers or less are obtained at the stage of calcining, and the temperature is 1000 ° C. or less. While a sintered body having a density of 98% or more of the theoretical density was obtained at the stage of sintering with, a comparative example outside the above specified range produced a product containing amorphous. There is always A single crystal phase is not formed, and the powder particles at the stage of calcined particles are also irregular powders ranging from greatly exceeding 50 nanometers to extremely fine particles, and the density is extremely high even at the sintering stage. It was low.
[0037]
【The invention's effect】
The present invention starts from nitrates that are very readily available, and the operation that is the main requirement is adjustment of the molar ratio. The present invention has succeeded in obtaining ceria powder particles that are nano-sized spherical ceria particles that can be easily densified to a relative density of 98% or more. In recent years, in the technical field of ceramics, more and more high-precision design has been demanded in the material design, and such a request is very often used for various sensors and solid electrolytes for fuel cells. The ceria-based powder particles that are raw material powders are no exception. The present invention provides a ceria powder that can meet such demands. Moreover, as described above, starting from a material that can be easily obtained, it is possible to achieve extremely difficult problems through ordinary operations and considerations. These points can be highly evaluated, are highly practical, and have great significance. In the future, it is expected to contribute greatly to the development in the technical field using ceria powder.
[Brief description of the drawings]
FIG. 1 is an X-ray diffraction pattern of calcined ceria powder (Example 1) produced by the production method of the present invention.
FIG. 2 is a view showing an SEM image of calcined ceria powder (Example 1) by the production method of the present invention.
FIG. 3 is a view showing an SEM image of the surface of the ceria sintered body (Example 1) according to the manufacturing method of the present invention.

Claims

Divalent or trivalent metal (M) nitrate and cerium nitrate are expressed as M _x Ce _1-x O ₂ _-δ (where 0.05 ≤ x ≤ 0.3, where δ is determined from the charge balance of the cation and anion) The mixed solution and ammonium bicarbonate as a precipitating agent, and the molar ratio of (divalent or trivalent metal nitrate aqueous solution concentration) / (ammonium carbonate aqueous solution concentration) is Mixing so as to be 2.5 to 15, Ce _1-x M _x (OH) _y (CO ₃ ) _z · H ₂ O (however, 0.05 ≦ x ≦ 0.3, 0.05 ≦ y ≦ 1, 0.05 ≦ z ≦ 2), after cerium carbonate is precipitated, aging is performed at a temperature of 50 ° C. or higher and 70 ° C. or lower, and after washing, calcined at a temperature of 400 ° C. or higher and 750 ° C. or lower. By doing so, spherical particles having an average particle diameter of 50 nanometers or less are obtained. 00 ° C. By sintering at temperatures below, characterized by densified to 98% or more of the theoretical density, the production method of the sinterability nano spherical ceria compound powder.

Nitrate containing divalent (M ²⁺ ) and trivalent (M ³⁺ ) metal elements and cerium nitrate (M ²⁺ _a M ³⁺ _1-a ) _x Ce _1-x O ₂ _-δ (where 0.01 ≦ a ≦ 0.5, 0.05 ≦ x ≦ 0.3, and δ represents the amount of oxygen defects determined from the balance of charges between the cation and anion) Ammonium bicarbonate as a precipitating agent, so that the molar ratio of (concentration of aqueous solution of nitrate containing bivalent (M ²⁺ ) and trivalent (M ³⁺ ) metal elements) / (concentration of aqueous ammonium carbonate) is 3 to 7. And mixed with Ce _{1 -x} (M 2 ⁺ _a M ^{3 +} _{1 -a} ) _x (OH) _y (CO ₃ ) _z · H ₂ O (where 0.05 ≦ x ≦ 0.3, 0. After cerium carbonate represented by 05 ≦ y ≦ 1, 0.05 ≦ z ≦ 2) is precipitated, aging is performed at a temperature of 55 ° C. to 65 ° C., and after washing, 400 ° C. By calcining at a temperature of 750 ° C. or less, spherical particles having an average particle diameter of 50 nanometers or less are formed, and by sintering at a temperature of 1000 ° C. or less, the density is increased to 98% or more of the theoretical density. A process for producing a readily sinterable nanospherical ceria compound powder.