JP3604210B2 - Method for producing NiO / YSZ composite powder - Google Patents
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Description
【０００１】
【産業上の利用分野】
本発明は、固体電解質型燃料電池（以下ＳＯＦＣとも言う）の燃料電極材料等に用いられるＮｉＯ／ＹＳＺ複合粉末の製造方法に関する。特には、ＳＯＦＣの発電特性及び耐久性の向上に寄与し得る、粉体の組成と組織の均一性の向上したＮｉＯ／ＹＳＺ複合粉末の製造方法に関する。
【０００２】
【従来の技術】
ＳＯＦＣの燃料電極用材料を例にとって従来技術を説明する。ＳＯＦＣの燃料電極用材料としては、ＮｉＯとＹ２Ｏ３安定化ＺｒＯ２（ＹＳＺ ）とを混合複合化した複合粉末の焼結膜が主に用いられている（特開昭６１−１５３２８０ 、特開昭６１−１９８５７０ 等）。なお、焼結膜中のＮｉＯは、ＳＯＦＣの運転中に還元されてＮｉとなる。
【０００３】
このようなＮｉ／ＹＳＺ複合焼結膜用のＮｉＯ／ＹＳＺ複合粉末の製造方法は、一般的に、ＮｉＯ粉とＹＳＺ粉を両者とも固体の状態で混合し、その後昇温して若干焼結することにより複合化する方法が採られている。混合方法としては、ボールミルを用いるものや、メカノケミカル的機械混合によるものが知られている。Ｎｉ／ＹＳＺ複合焼結膜は、各成分（ＮｉとＹＳＺの）が交錯した微構造を有するが、Ｎｉが網目のようにつながっているものは導電性が良く、ＹＳＺ粒の凝集が生じてＮｉの網目が切断されているものは導電性が悪い。ＳＯＦＣの燃料電極の導電性が悪いとＳＯＦＣの発電効率は低下する。したがって、塗膜の焼成後において、ＹＳＺの凝集がなく、Ｎｉの網目構造がしっかりと形成されうるようなＮｉＯ／ＹＳＺ複合粉末が求められる。
【０００４】
【発明が解決しようとする課題】
上述の従来の製造方法にあっては、次のような問題があった。
▲１▼ ボールミル混合法：
混合粉のうち、比重の大きな成分（ＮｉＯ）や粒径の大きな成分が沈降して、粉末の組成むらが起こりやすい。特に、液体を媒体として湿式混合を行う場合、混合処理後の乾燥工程で、このような沈降現象が起こりやすい。
【０００５】
▲２▼ メカノケミカル的機械混合：
この方法は、一例を挙げれば、容器中に回転刃が設置され、容器または回転刃自体の回転による遠心力、攪拌によって粉末混合を促進するものである。このとき自然発生する熱により自然に温度が上がった状態、または強制的に温度を上げた状態で粉末同士の混合を行う。つまり熱によって粉末間の結合を促進させることがメカノケミカル手法の大きな特徴である。そして、この手法は、主には粗粉体と微粉体との混合において、粗粉体表面上に微粉体を吸着させて、殻と核から構成される複合粉末を作成する表面改質手法として今日広く用いられるようになってきている。
【０００６】
しかし、このメカノケミカル表面改質手法は、粗粒子表面に微粒子を固着させるといった粒径差を利用する場合が多く、そのために使用原料に制限が加えられ、微粒子間の混合といった目的に対しては効果は発揮され難い。
【０００７】
本発明は、ＳＯＦＣの発電特性及び耐久性の向上に寄与し得る、粉体の組成と組織の均一性の向上したＮｉＯ／ＹＳＺ複合粉末の製造方法を提供することを目的とする。
【０００８】
【課題を解決するための手段及び作用】
上記課題を解決するため、本発明のＮｉＯ／ＹＳＺ複合粉末の製造方法は、Ｎｉイオン、Ｚｒイオン、Ｙイオンを所望割合で含む原料溶液を調整する溶液調整工程と、上記各金属の１種以上及び酸素を含む固体物質を上記原料溶液から共沈させる共沈溶液を上記原料溶液に混合し、該固体物質（共沈物質）を共沈させる共沈工程と、該共沈物質を分解して上記各金属の酸化物を含む粉粒体（ＮｉＯ／ＹＳＺ複合粉末）を得る分解工程と、を含むことを特徴とする。
【０００９】
本発明の１態様のＮｉＯ／ＹＳＺ複合粉末の製造方法においては、原料溶液として硝酸水溶液をベースとする溶液を用い、共沈溶液として蓚酸水溶液を用いる。この場合、以下のような共沈反応が生じる。
Ｎｉ２＋＋（ＣＯＯＨ）２ →Ｎｉ（ＣＯＯ）２ ↓＋２Ｈ＋
Ｚｒ４＋＋２（ＣＯＯＨ）２ →Ｚｒ（ＣＯＯ）４ ↓＋４Ｈ＋
２Ｙ３＋＋３（ＣＯＯＨ）２ →Ｙ２ （ＣＯＯ）６ ↓＋６Ｈ＋
【００１０】
上記態様のＮｉＯ／ＹＳＺ複合粉末の製造方法においては、原料溶液及び共沈溶液をあらかじめ６０℃〜沸点に昇温させてから混合することが好ましい。
上記反応のうち蓚酸Ｎｉの沈降反応は、一般的には、常温においては生じにくい。そのため、均一な組成の共沈物質を得にくい。それに対して、上記温度域においては、上述の３反応がほぼ均等に起こるため、均一な組成の共沈物質を能率よく得ることができる。
【００１１】
本発明のＮｉＯ／ＹＳＺ複合粉末をＳＯＦＣの燃料電極材として用いる場合には、ＮｉＯ／ＹＳＺ複合粉末中におけるＮｉＯとＹＳＺとの重量比が３０：７０〜７０：３０であることが好ましい。ＹＳＺの比が７０を越えると粉末の焼成膜の導電率が低くなるので好ましくない。このような観点からは、上記混合物中における酸化ニッケル重量（換算値）と、ＹＳＺ重量（換算値）との比が、５０：５０〜７０：３０であることがより好ましい。しかし、固体電解質膜と燃料極との間の傾斜層用としては、低Ｎｉのものが、膜そのものの導電率は小さいが、高Ｎｉ含有層と電解質との間の熱膨張差に起因する応力を緩和できるので好ましい。
【００１２】
本発明のＮｉＯ／ＹＳＺ複合粉末をＳＯＦＣの燃料電極材として用いる場合には、複合粉末の仮焼後の粒径を０．１〜１０μｍとすることが好ましい。ガス透過性と導電率とのバランスが良好だからである。この際、燃料電極の上層を比較的粗い粒を用い、下層を比較的細かい粒を用いて形成することもできる。
【００１３】
【実施例】
以下、本発明の実施例を説明する。
図１は、本発明の標準的な実施例に係るＮｉＯ／ＹＳＺ複合粉末の製造方法の工程を示すフローチャートである。このフローチャートを参照しつつ説明する。
【００１４】
（１） 原料溶液調整：
ＹＳＺ原料としての硝酸ジルコニウム・イットリウム水溶液（８ｍｏｌ％Ｙ２ Ｏ３ 含有、酸化物換算含有量２３．４ｗｔ％）、ＮｉＯ原料としての硝酸ニッケル６水和物結晶、共沈物質濃度を調整するための純水を表１の組成で混合し、よく攪拌する。
【００１５】
【表１】
（２） 共沈溶液調整：
本実施例においては、共沈溶液として蓚酸水溶液を用いた。容器に純水を取り、約８０℃程度に加熱する。この温水を攪拌しながら蓚酸２水和物結晶を徐々に添加して溶解し、８０℃〜９０℃に保持した。蓚酸水溶液の量については、共沈工程において金属イオンが完全に沈殿するように、蓚酸量を化学量論比よりもわずかに過剰となるようすることが好ましい。今回の過剰量は約５ｍｏｌ％とし、その量は表１中に示した。
【００１７】
（３） 溶液混合→共沈：
硝酸ニッケルと蓚酸水溶液を室温で反応させても蓚酸ニッケル結晶は生成しにくい。したがって、蓚酸ニッケルは硝酸塩などのニッケル含有水溶液を加熱した状態で硝酸を加えることで生成速度が速くなる。
原料溶液（ＮｉＯ／ＹＳＺ複合粉末水溶液）を８０℃〜９０℃に加熱し、これを８０℃〜９０℃に加熱保持した硝酸水溶液中に、よく攪拌しながら徐々に添加していくことで、蓚酸共沈法による沈殿生成を行った。反応により、粉体が生成するので、溶液の攪拌にはトルクのある攪拌機を使用することが好ましい。この共沈反応により溶液は発熱反応を起こすので、反応後は溶液温度が初期状態よりも１０〜２０℃程度上昇することが普通である。全溶液を混合し終えた後、室温まで攪拌を継続しながら自然冷却した。
【００１８】
（４） 乾燥：
乾燥機内に反応物を静置し、１２０℃の熱風を送り沈殿物の水分を蒸発させた。
（５） 熱分解：
乾燥後の試料は５００℃、５時間の熱処理により、硝酸成分と残留蓚酸を除去した。その際の反応は以下と推定される。
Ｎｉ（ＣＯＯ）２ →ＮｉＯ＋ＣＯ＋ＣＯ２
Ｚｒ（ＣＯＯ）４ →ＺｒＯ２ ＋２ＣＯ＋２ＣＯ２
Ｙ２ （ＣＯＯ）６ →Ｙ２ Ｏ３ ＋３ＣＯ＋３ＣＯ２
【００１９】
（６） ボールミル粉砕：
２φと３φのＰＳＺボールを用いた湿式粉砕処理を行った。これは、二次粒子の紛砕と均一化を目的とする。ただし、本共沈法による粉末は、湿式レーザー回折粒度分布測定によれば、１μｍ以下の粒子が全体の約８０％を占め、二次粒子の大きなものでさえその粒径は１０〜２０μｍにあることから、このボールミル粉砕処理を省略することも可能である。
【００２０】
（７） 粗粉砕：
ボールミル処理後のスラリーを乾燥させて得られる塊状試料を解砕処理した。この粉末は湿式レーザー回折粒度分布測定によれば、二次粒子でさえ最大径は１０μｍであった。
【００２１】
（８） 仮焼：
得られた粉末を、仮焼条件の粉体特性への影響を調べる目的で、９００℃×１０ｈｒ、１０００℃×３ｈｒ，１１００℃×２ｈｒ、１１００℃×１０ｈｒ、１１５０℃×５ｈｒ，１２００℃×５ｈｒ、１２５０℃×５ｈｒの各条件で仮焼（熱処理）を行った。なお、仮焼の目的は、成膜後の本焼成時における粉末の燒結性を適当な範囲に調節して、焼成膜の特性（導電性、通気性、耐久性等）を最適化することにある。仮焼時には、主にＮｉＯの微粉が燒結現象により他のＮｉＯ粉に合体する。また、Ｙ２ Ｏ３ がＺｒＯ ２に徐々に固溶して結晶化する。
【００２２】
（９） 焼結体作製：
上記工程で得られた粉末に対して、１０ｗｔ％ＰＶＡ（ポリビニルアルコール）水溶液をバインダーとして添加した。この粉末をプレス成形した後、１４００℃で２時間焼成した。次いで、この焼結体を、３％水素含有窒素雰囲気下で１０００℃、４０時間の還元処理を行い、Ｎｉ／ＹＳＺ複合焼結体を得た。
【００２３】
この焼結体の気孔率をアルキメデス法により、導電率を四端子法により評価した。比較のために、本実施例の共沈法に使用したＮｉＯ／ＹＳＺ複合粉末水溶液から蒸発乾固法により粉体を合成し、その特性も調べた。その結果、比較例の焼結体の気孔率が約３０％以上であったのに対して、実施例の焼結体の気孔率は９００〜１０００℃の場合は、２２〜２４％であった。したがって緻密な焼結体または焼成膜を得ることもできる。なお、仮焼温度１１００℃以上では気孔率は２７〜３４％となる。
また、蒸発乾固法を原料にするものの導電率が１７００Ｓ／ｃｍ近辺であったのに対して、共沈法粉末を原料とするものの導電率は２５００〜３０００Ｓ／ｃｍときわめて高いことが確認された。
【００２４】
仮焼温度を高くすると、粒子が大きく成長することと、仮焼による粉体の表面活性の低下によって、焼結が進行しにくくなり、気孔率が大きくなる傾向がある（データ例、仮焼温度９００℃：２１．９％、１０００℃：２２．５％、１１００℃：２３．９％）。また、気孔率が大きくなると、導電率も低下する傾向が見られる（データ例、仮焼温度９００℃：２９７５Ｓ／ｃｍ，１０００℃：２９７２Ｓ／ｃｍ、１１００℃：２６６０Ｓ／ｃｍ）。しかしながら、これらの値は、従来法による試料よりも大きな導電率を示している。
【００２５】
また、焼結体の破面のＳＥＭによる観察では、図２に示されているように、従来品ではＮｉとＹＳＺの粒子の凝集が見られたことに比べて、本体発明品では、粒径の揃った均一な組織となっていることが確認された。また、これらの試料のＮ２ ；８５、Ｈ２ ；１５％雰囲気、１０５０℃で１００時間の長時間還元処理後は、Ｎｉの還元の進行によって導電率は更に大きくなり、微構造においても変化は認められなかった。従って、本実験で作製した粉末により、より高性能で耐久性のある燃料極が作製されうる。
【００２６】
本実験で得られた粉末は熱分解後の一時粒子径がすべてサブミクロン領域の微粉であることが走査型電子顕微鏡（ＳＥＭ）により確認された。但し、レーザー回折粒度分布測定法では、二次粒子を計測しているために、１μｍ以上の粒径も測定される。
【００２７】
９００℃で１０時間仮焼処理した粉末を使用して、以下のようにスラリー・成膜し、発電試験セルを作製して評価した。すなわち、紛体をアルコールを主成分とした有機系溶媒に混ぜてスラリーとした。これを空気極と電解質からなる基体管に塗膜、乾燥、１４００℃で焼成して、３％Ｈ２ 雰囲気で還元処理した。燃料；１１％Ｈ２ Ｏ，８９％Ｈ２ 、酸化剤；空気４倍等量、燃料利用率４０％、温度１０００℃の運転条件で発電評価した結果、最大出力０．４８Ｗ／ｃｍ２ の高出力を示し、従来の粉末混合による粉末を用いて作製したセルの最大出力（約０．４２Ｗ／ｃｍ２ ）より高いことが確認された。
【００２８】
【発明の効果】
以上の説明から明らかなように、本発明のＮｉＯ／ＹＳＺ複合粉末の製造方法は以下の効果を発揮する。
▲１▼ ＳＯＦＣ燃料電極の導電率を向上させることができ、それによって、ＳＯＦＣの発電性能を向上することができる。
▲２▼ 同じ組成の従来粉体よりも導電率が大きいので、ＳＯＦＣ燃料電極を薄膜化することができ、それによって、ＳＯＦＣの発電性能を向上することができる。
▲３▼ 焼結体及び焼成膜の組織の分散性に優れているため、高温環境下においてもＹＳＺの凝集が生じないため、導電特性の経時劣化を防止し信頼性を向上することができる。
▲４▼製造部留まりが良く、また反応装置が簡便のため量産性に優れた粉体製造方法を提供できる。
【図面の簡単な説明】
【図１】本発明の一実施例にかかるＮｉＯ／ＹＳＺ複合粉末の製造工程の一例を示す図である。
【図２】本発明の実施例と比較例にかかわる粉末を原料とするＮｉ／ＹＳＺ焼結体の破面のＳＥＭ写真である。[0001]
[Industrial applications]
The present invention relates to a method for producing a NiO / YSZ composite powder used for a fuel electrode material of a solid oxide fuel cell (hereinafter also referred to as SOFC). In particular, the present invention relates to a method for producing a NiO / YSZ composite powder that can contribute to improvement in power generation characteristics and durability of an SOFC and has improved powder composition and texture uniformity.
[0002]
[Prior art]
The prior art will be described using a fuel electrode material of an SOFC as an example. The fuel electrode material of SOFC, NiO and Y 2 O 3 stabilized ZrO 2 (YSZ) and the sintered membrane of the mixed composite composite powder is mainly used (JP 61-153280, JP 1986-198570). Note that NiO in the sintered film is reduced to Ni during operation of the SOFC.
[0003]
The method for producing the NiO / YSZ composite powder for the Ni / YSZ composite sintered film generally involves mixing the NiO powder and the YSZ powder in a solid state, and then raising the temperature and slightly sintering. A method of compounding is adopted. As a mixing method, a method using a ball mill and a method using mechanochemical mechanical mixing are known. The Ni / YSZ composite sintered film has a microstructure in which each component (Ni and YSZ) is intersected. However, those in which Ni is connected like a network have good conductivity, and YSZ particles are aggregated to form Ni. Those with a cut mesh have poor conductivity. If the conductivity of the fuel electrode of the SOFC is poor, the power generation efficiency of the SOFC decreases. Therefore, there is a need for a NiO / YSZ composite powder that does not agglomerate YSZ after the baking of the coating film and can form a network structure of Ni firmly.
[0004]
[Problems to be solved by the invention]
The conventional manufacturing method described above has the following problems.
(1) Ball mill mixing method:
Of the mixed powder, a component having a large specific gravity (NiO) and a component having a large particle diameter are settled, and the composition of the powder tends to be uneven. In particular, when wet mixing is performed using a liquid as a medium, such a sedimentation phenomenon is likely to occur in a drying step after the mixing treatment.
[0005]
(2) Mechanochemical mechanical mixing:
In this method, for example, a rotary blade is provided in a container, and powder mixing is promoted by centrifugal force and stirring by rotation of the container or the rotary blade itself. At this time, the powders are mixed with each other in a state where the temperature is naturally increased by heat generated naturally or in a state where the temperature is forcibly increased. In other words, a major feature of the mechanochemical method is that the bonding between powders is promoted by heat. This method is mainly used as a surface modification method in which a fine powder is adsorbed on the surface of a coarse powder in the mixing of a coarse powder and a fine powder to create a composite powder composed of a shell and a core. It is becoming widely used today.
[0006]
However, this mechanochemical surface modification technique often utilizes the difference in particle size such as fixing fine particles to the surface of coarse particles, which limits the raw materials used, and for purposes such as mixing between fine particles. The effect is hard to be exhibited.
[0007]
An object of the present invention is to provide a method for producing a NiO / YSZ composite powder having improved powder composition and texture uniformity, which can contribute to improvement in power generation characteristics and durability of an SOFC.
[0008]
Means and Action for Solving the Problems
In order to solve the above-mentioned problems, a method for producing a NiO / YSZ composite powder of the present invention includes a solution adjusting step of adjusting a raw material solution containing Ni ions, Zr ions, and Y ions at a desired ratio, and at least one of the above metals. A coprecipitation solution for coprecipitating a solid material containing oxygen and oxygen from the raw material solution, mixing the raw material solution, coprecipitating the solid material (coprecipitated material), and decomposing the coprecipitated material. And a decomposition step of obtaining a powder (NiO / YSZ composite powder) containing an oxide of each of the above metals.
[0009]
In the method for producing a NiO / YSZ composite powder according to one embodiment of the present invention, a solution based on a nitric acid aqueous solution is used as a raw material solution, and an oxalic acid aqueous solution is used as a coprecipitation solution. In this case, the following coprecipitation reaction occurs.
Ni 2+ + (COOH) 2 → Ni (COO) 2 ↓ + 2H +
Zr 4+ +2 (COOH) 2 → Zr (COO) 4 ↓ + 4H +
2Y 3+ +3 (COOH) 2 → Y 2 (COO) 6 ↓ + 6H +
[0010]
In the method for producing a NiO / YSZ composite powder of the above embodiment, it is preferable that the raw material solution and the coprecipitated solution are heated to 60 ° C. to the boiling point in advance and then mixed.
In general, the precipitation reaction of Ni oxalate hardly occurs at room temperature. Therefore, it is difficult to obtain a coprecipitated substance having a uniform composition. On the other hand, in the above-mentioned temperature range, the above-mentioned three reactions occur almost uniformly, so that a coprecipitated substance having a uniform composition can be obtained efficiently.
[0011]
When the NiO / YSZ composite powder of the present invention is used as a fuel electrode material for an SOFC, the weight ratio of NiO to YSZ in the NiO / YSZ composite powder is preferably 30:70 to 70:30. If the YSZ ratio exceeds 70, the conductivity of the fired film of the powder decreases, which is not preferable. From such a viewpoint, it is more preferable that the ratio between the weight (converted value) of nickel oxide and the weight (converted value) of YSZ in the mixture is 50:50 to 70:30. However, for the graded layer between the solid electrolyte membrane and the fuel electrode, the one with low Ni has low conductivity of the membrane itself, but the stress caused by the difference in thermal expansion between the high Ni-containing layer and the electrolyte. Is preferable because it can alleviate the problem.
[0012]
When the NiO / YSZ composite powder of the present invention is used as a fuel electrode material for an SOFC, the particle size of the composite powder after calcination is preferably 0.1 to 10 μm. This is because the balance between gas permeability and conductivity is good. In this case, the upper layer of the fuel electrode may be formed using relatively coarse particles, and the lower layer may be formed using relatively fine particles.
[0013]
【Example】
Hereinafter, examples of the present invention will be described.
FIG. 1 is a flowchart showing steps of a method for producing a NiO / YSZ composite powder according to a standard embodiment of the present invention. Description will be made with reference to this flowchart.
[0014]
(1) Raw material solution adjustment:
Zirconium nitrate / yttrium aqueous solution (containing 8 mol% Y 2 O 3 , oxide equivalent content 23.4 wt%) as YSZ raw material, nickel nitrate hexahydrate crystal as NiO raw material, co-precipitated substance concentration Mix pure water with the composition shown in Table 1 and stir well.
[0015]
[Table 1]
(2) Preparation of coprecipitation solution:
In this example, an oxalic acid aqueous solution was used as the coprecipitation solution. Take pure water in a container and heat to about 80 ° C. Oxalic acid dihydrate crystals were gradually added and dissolved while stirring the warm water, and the temperature was maintained at 80 ° C to 90 ° C. Regarding the amount of the aqueous oxalic acid solution, it is preferable that the amount of the oxalic acid be slightly larger than the stoichiometric ratio so that the metal ions are completely precipitated in the coprecipitation step. The excess amount at this time was about 5 mol%, and the amount is shown in Table 1.
[0017]
(3) Solution mixing → coprecipitation:
Even if nickel nitrate and oxalic acid aqueous solution are reacted at room temperature, nickel oxalate crystals are hardly generated. Therefore, the production rate of nickel oxalate is increased by adding nitric acid while heating an aqueous solution containing nickel such as nitrate.
The raw material solution (NiO / YSZ composite powder aqueous solution) is heated to 80 ° C. to 90 ° C., and gradually added to a nitric acid aqueous solution heated and maintained at 80 ° C. to 90 ° C. with good stirring to obtain oxalic acid. Precipitation was produced by the coprecipitation method. Since powder is produced by the reaction, it is preferable to use a stirrer with a torque for stirring the solution. Since the solution causes an exothermic reaction due to the coprecipitation reaction, the temperature of the solution usually rises by about 10 to 20 ° C. from the initial state after the reaction. After all the solutions were mixed, the mixture was naturally cooled while continuing stirring to room temperature.
[0018]
(4) Drying:
The reaction product was allowed to stand in the dryer, and hot air at 120 ° C. was sent to evaporate the water content of the precipitate.
(5) Pyrolysis:
The dried sample was subjected to a heat treatment at 500 ° C. for 5 hours to remove a nitric acid component and residual oxalic acid. The reaction at that time is estimated as follows.
Ni (COO) 2 → NiO + CO + CO 2
Zr (COO) 4 → ZrO 2 + 2CO + 2CO 2
Y 2 (COO) 6 → Y 2 O 3 + 3CO + 3CO 2
[0019]
(6) Ball mill grinding:
Wet pulverization using 2φ and 3φ PSZ balls was performed. This aims at crushing and homogenizing the secondary particles. However, in the powder obtained by the present coprecipitation method, particles having a particle size of 1 μm or less occupy about 80% of the whole according to the wet laser diffraction particle size distribution measurement, and even the large secondary particles have a particle size of 10 to 20 μm. Therefore, it is possible to omit the ball mill pulverizing process.
[0020]
(7) Coarse crushing:
A lump sample obtained by drying the slurry after the ball mill treatment was crushed. According to wet laser diffraction particle size distribution measurement, this powder had a maximum diameter of 10 μm even for secondary particles.
[0021]
(8) Calcination:
The obtained powder was subjected to 900 ° C. × 10 hr, 1000 ° C. × 3 hr, 1100 ° C. × 2 hr, 1100 ° C. × 10 hr, 1150 ° C. × 5 hr, 1200 ° C. × 5 hr for the purpose of examining the influence of the calcining conditions on the powder properties. Calcination (heat treatment) was performed at each condition of 1250 ° C. × 5 hours. The purpose of calcination is to adjust the sinterability of the powder during the main firing after forming the film to an appropriate range to optimize the characteristics (such as conductivity, air permeability, and durability) of the fired film. is there. At the time of calcination, mainly NiO fine powder is combined with other NiO powder by a sintering phenomenon. Further, Y 2 O 3 gradually dissolves in ZrO 2 and crystallizes.
[0022]
(9) Sintered body production:
An aqueous solution of 10 wt% PVA (polyvinyl alcohol) was added as a binder to the powder obtained in the above step. After press-molding this powder, it was baked at 1400 ° C. for 2 hours. Next, this sintered body was subjected to a reduction treatment at 1000 ° C. for 40 hours in a nitrogen atmosphere containing 3% hydrogen to obtain a Ni / YSZ composite sintered body.
[0023]
The porosity of this sintered body was evaluated by the Archimedes method, and the conductivity was evaluated by the four-terminal method. For comparison, a powder was synthesized from the aqueous solution of the NiO / YSZ composite powder used in the coprecipitation method of this example by the evaporation to dryness method, and the characteristics were also examined. As a result, the porosity of the sintered body of the comparative example was about 30% or more, whereas the porosity of the sintered body of the example was 22 to 24% when the porosity was 900 to 1000 ° C. . Therefore, a dense sintered body or fired film can be obtained. At a calcination temperature of 1100 ° C. or higher, the porosity is 27 to 34%.
Further, it was confirmed that the conductivity obtained by using the evaporative drying method as a raw material was around 1700 S / cm, whereas the conductivity obtained by using a coprecipitated powder as a raw material was as high as 2500 to 3000 S / cm. Was.
[0024]
When the calcination temperature is increased, the particles grow larger and the surface activity of the powder decreases by calcination, so that sintering becomes difficult to progress and the porosity tends to increase (data example, calcination temperature 900 ° C: 21.9%, 1000 ° C: 22.5%, 1100 ° C: 23.9%). When the porosity increases, the conductivity tends to decrease (data example: calcination temperature: 900 ° C .: 2975 S / cm, 1000 ° C .: 2972 S / cm, 1100 ° C .: 2660 S / cm). However, these values show a higher conductivity than the conventional sample.
[0025]
In addition, in SEM observation of the fracture surface of the sintered body, as shown in FIG. 2, the aggregation of Ni and YSZ particles was observed in the conventional product, whereas the particle size was smaller in the product of the present invention. It was confirmed that the structure was uniform. Further, after a long-time reduction treatment of these samples in an atmosphere of N 2 ; 85, H 2 ; 15% at 1050 ° C. for 100 hours, the conductivity further increases due to the progress of the reduction of Ni, and the change in the microstructure does not change. I was not able to admit. Therefore, a fuel electrode having higher performance and durability can be produced by the powder produced in this experiment.
[0026]
It was confirmed by a scanning electron microscope (SEM) that the powders obtained in this experiment were all fine powders having a temporary particle diameter in the submicron region after thermal decomposition. However, in the laser diffraction particle size distribution measuring method, since the secondary particles are measured, a particle size of 1 μm or more is also measured.
[0027]
Using the powder calcined at 900 ° C. for 10 hours, a slurry and a film were formed as follows, and a power generation test cell was prepared and evaluated. That is, the powder was mixed with an organic solvent mainly containing alcohol to form a slurry. This was coated on a base tube composed of an air electrode and an electrolyte, dried, fired at 1400 ° C., and reduced in a 3% H 2 atmosphere. Fuel: 11% H 2 O, 89% H 2 , oxidizing agent: 4 times equivalent of air, fuel utilization 40%, power generation evaluation under operating conditions of temperature 1000 ° C. As a result, the maximum output was 0.48 W / cm 2 . It was confirmed that the output was higher than the maximum output (approximately 0.42 W / cm 2 ) of the cell manufactured using the powder obtained by the conventional powder mixing.
[0028]
【The invention's effect】
As is clear from the above description, the method for producing a NiO / YSZ composite powder of the present invention exhibits the following effects.
{Circle around (1)} The electric conductivity of the SOFC fuel electrode can be improved, whereby the power generation performance of the SOFC can be improved.
(2) Since the conductivity is higher than that of the conventional powder having the same composition, the thickness of the SOFC fuel electrode can be reduced, thereby improving the power generation performance of the SOFC.
{Circle around (3)} Since the dispersibility of the structures of the sintered body and the fired film is excellent, YSZ does not agglomerate even in a high-temperature environment, so that it is possible to prevent deterioration of the conductive properties over time and improve reliability.
(4) It is possible to provide a powder production method which is excellent in mass production because the production unit is well retained and the reaction apparatus is simple.
[Brief description of the drawings]
FIG. 1 is a view showing an example of a manufacturing process of a NiO / YSZ composite powder according to one embodiment of the present invention.
FIG. 2 is an SEM photograph of a fracture surface of a Ni / YSZ sintered body using powders according to examples of the present invention and comparative examples as raw materials.
Claims (5)
上記各金属の１種以上及び酸素を含む固体物質を上記原料溶液から共沈させる共沈溶液を上記原料溶液に混合し、該固体物質（共沈物質）を共沈させる共沈工程と、
該共沈物質を分解して上記各金属の酸化物を含む粉粒体（ＮｉＯ／ＹＳＺ複合粉末）を得る分解工程と、
を含むことを特徴とするＮｉＯ／ＹＳＺ複合粉末の製造方法。A solution adjusting step of adjusting a raw material solution containing Ni ions, Zr ions, and Y ions at a desired ratio;
A coprecipitation step of mixing a coprecipitation solution for coprecipitating a solid substance containing at least one of the metals and oxygen from the raw material solution with the raw material solution, and coprecipitating the solid substance (coprecipitated substance);
A decomposition step of decomposing the coprecipitated substance to obtain a powder (NiO / YSZ composite powder) containing the oxide of each of the above metals;
A method for producing a NiO / YSZ composite powder, comprising:
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP26463995A JP3604210B2 (en) | 1995-09-20 | 1995-09-20 | Method for producing NiO / YSZ composite powder |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP26463995A JP3604210B2 (en) | 1995-09-20 | 1995-09-20 | Method for producing NiO / YSZ composite powder |
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| JPH0986934A JPH0986934A (en) | 1997-03-31 |
| JP3604210B2 true JP3604210B2 (en) | 2004-12-22 |
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| KR100622711B1 (en) * | 2004-07-13 | 2006-09-14 | 현대자동차주식회사 | The anode of solid oxide fuel cell with networking structure and the preparing method of it |
| JP5191166B2 (en) * | 2007-05-25 | 2013-04-24 | 株式会社田中化学研究所 | Material for anode of solid oxide fuel cell |
| JP5175154B2 (en) * | 2008-09-29 | 2013-04-03 | 株式会社田中化学研究所 | Production method of nickel composite oxide, nickel composite oxide obtained by the method, nickel oxide-stabilized zirconia composite oxide using the nickel composite oxide, and nickel oxide-stabilized zirconia composite oxide Fuel electrode for solid oxide fuel cell |
| JP2011190148A (en) * | 2010-03-15 | 2011-09-29 | Sumitomo Osaka Cement Co Ltd | Composite ceramic powder and method for producing the same, and solid oxide fuel cell |
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