JP3786457B2 - Method for producing porous lithium aluminate - Google Patents
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- JP3786457B2 JP3786457B2 JP29606395A JP29606395A JP3786457B2 JP 3786457 B2 JP3786457 B2 JP 3786457B2 JP 29606395 A JP29606395 A JP 29606395A JP 29606395 A JP29606395 A JP 29606395A JP 3786457 B2 JP3786457 B2 JP 3786457B2
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- H—ELECTRICITY
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Description
【０００１】
【発明が属する技術分野】
本発明は、特に溶融炭酸塩型電池（ＭＣＦＣ）の電解質保持板用として有用な微細で多孔質組織を備える多孔質アルミン酸リチウム粉末とその工業的な製造方法に関する。
【０００２】
【従来の技術】
ＭＣＦＣの電解質保持板は、６５０℃付近の高温域においてＬｉ2 ＣＯ3 およびＫ3 ＣＯ3 などの混合溶融炭酸塩からなる電解質を保持する目的で使用されるため、溶融炭酸塩に対する高い保持性や、耐アルカリ性、耐熱性などの特性が要求される。このような要求特性を満たす材料として、現在、電解質保持板の構成材料にはアルミン酸リチウムが用いられており、とくに電解質保持力の優れる比較的比表面積の大きい微細なγ型アルミン酸リチウムが有用されている。
【０００３】
このような高比表面積を備えるアルミン酸リチウムの製造技術としては、特開昭６０−６５７１９号公報、特開昭６０−１５１９７５号公報、特開昭６１−２９５２２７号公報、特開昭６１−２９５２２８号公報、特開昭６３−２７０３１１号公報、特開平１−２５２５２２号公報、特開平２−８０３１９号公報などに記載の方法が提案されている。これら公知の製造技術は、アルミナと水酸化リチウムまたは炭酸リチウムの混合物を６００〜１０００℃の温度範囲で焼成して組織の緻密化を抑制したり、二次的な多孔質化や水和処理などによって比表面積を高める点に製造の要点がある。
【０００４】
また、特公平６−３７２９２号公報には多孔質リチウムアルミネート粗粒子の製造方法が開示されているが、これはシリカ粒子とアルミナ粒子とを結合して粗粒子を調製し、次にリチウムイオンを含む炭酸塩中で５００〜１０００℃に昇温し、粗粒子中のシリカ粒子を炭酸塩中に溶出させて空孔を形成させ、空孔形成されたアルミナをリチウム化してリチウムアルミネートを形成させるものである。
【０００５】
【発明が解決しようとする課題】
しかしながら、上記の従来技術で製造されるアルミン酸リチウムは溶融状態にある電解質中で長時間に亘り高温下に曝されると、γ型構造が一部α型に変態したり、粒子が成長して比表面積が小さくなる等の現象が生じる。したがって、ＭＣＦＣの電解質保持板として形成した場合、使用中に電解質の保持能力が急激に低下して電池寿命を悪化させる欠点がある。
【０００６】
上述した特公平６−３７２９２号公報による多孔質リチウムアミネートの製造方法は、この欠点を改良する技術として提案されたものであるが、シリカアルミナの粗粒子を経た後にリチウムのイオン交換を行う特殊なプロセスを必要とする関係で、工程が長く煩雑であるうえ、イオン交換を完全に進めることに困難性を伴う等の問題がある。
【０００７】
このようなことから、従来技術によるγ型多孔質アルミン酸リチウムの製造方法では、今後、ＭＣＦＣの長寿命化を向上させる目的で益々要求が厳しくなる溶融炭酸塩に対する高度の保持性、耐アルカリ性、耐熱性の付与に十分に対応することができず、また工業的な生産手段としても改善すべき課題が残されている。
【０００８】
本発明者らは、上記の問題点の解消を図るために鋭意研究を重ねた結果、アルミン酸リチウムを製造する際に、アルミナ源として予め水酸化アルミニウムなどを高温焼成して粒子構造を安定化した多孔質アルミナ粒子を用いると、得られるγ型多孔質アルミン酸リチウムは固体電解質中で長時間高温に曝されても粒子構造に変化が生じず、とくに特定のＢＥＴ比表面積ならびに比表面積変化率の範囲にある場合にＭＣＦＣの電解質保持板として優れた性能を発揮することを見出した。
【０００９】
本発明は前記の知見に基づいて完成されたもので、その目的とするところは、とくにＭＣＦＣの電解質保持板用に適用して固体電解質中における優れた熱安定性ならびに化学的安定性が保証されるγ型多孔質アルミン酸リチウムおよびその工業的な製造方法を提供することにある。
【００１０】
【課題を解決するための手段】
上記の目的を達成するための本発明に係る多孔質アルミン酸リチウムの製造方法は、水酸化アルミニウムを１２００℃で焼成して得られる多孔質α−アルミナ粒子と、リチウム化合物を、化学量論比近傍の量比で乾式混合し、該混合物を８００℃以上で焼成処理することを構成上の特徴とする。
【００１２】
【発明の実施の形態】
本発明の多孔質アルミン酸リチウムは、組織中に微細な空隙が均質に分散する多孔質構造を有し、ＢＥＴ比表面積が１〜１５m2/gの範囲にあることが基本的要件となる。ＢＥＴ比表面積が１m2/g未満であると、溶融炭酸塩中の保持能力が不十分となって電解質保持板とした際の機能が発揮されず、他方、１５m2/gを越えると電解質中での変質が大きくなって耐久性（安定性）を損ねる傾向を与える。
【００１３】
上記の基本特性に加え、多孔質アルミン酸リチウム試料を成分組成比がＬｉ2 ＣＯ3 ：Ｋ2 ＣＯ3 ＝６２：３８ mol％の電解質と１：３の重量比で混合したのち、空気／ＣＯ2 が７０／３０の雰囲気に保持された電気炉中で７００℃の温度に２００時間加熱する条件で処理した際に、加熱前のＢＥＴ比表面積（Ｓ1)に対する加熱前後のＢＥＴ比表面積の差（Ｓ2 −Ｓ1)の比率として算定されるＢＥＴ比表面積の変化率（Ｒ）が２５％以下であることが本発明の重要な要件となる。このＢＥＴ比表面積変化率（Ｒ）が２５％を越えると、アルミン酸リチウムの粒子成長が進み、電解質保持板として使用した場合に経時変化が起こって電解液が粒子間から流失する現象が生じ、電池性能を著しく損ねる結果を招く。
【００１４】
上記の本発明に係るアルミン酸リチウムは、結晶構造が概ねγ型であるが、若干のα型結晶が混在しても特に電解質中で安定性能に影響を受けないので、１０重量％以下のα型結晶を含むγ型主体の結晶系も許容される。これらの物性は、ＢＥＴ比表面積(N2SA)測定法およびＸ線回折分析法により容易に確認することができる。
【００１５】
上記の粒子性状を備える多孔質アルミン酸リチウムは、多孔質α−アルミナ粒子とリチウム化合物を化学量論比近傍の量比で乾式混合し、該混合物を焼成処理する方法により工業的に製造することができる。
【００１６】
原料成分となる多孔質α−アルミナ粒子は、工業的に入手できるものを使用することができるが、水酸化アルミニウムを１２００℃付近の温度で焼成処理することによりα−アルミナとしたものが特に好ましく用いられる。このようにして調製されるα−アルミナ粒子は、焼成過程の脱水化作用で粒子組織に微細かつ均質な細孔が形成され、表面が蜂の巣状を呈する特有の多孔質構造を有し、かつ粒子間の凝集が少ない比較的均一に分散した粒子となる。そのうえ、１２００℃付近の高温下でα化することにより極めて安定した構造となる。
【００１７】
一方、リチウム源となるリチウム化合物としては、例えば炭酸リチウム、水酸化リチウム、硝酸リチウムなどが挙げられるが、本発明の目的には炭酸リチウムの使用が最も効果的である。
【００１８】
製造される多孔質アルミン酸リチウムの粒子特性は、原料として用いるアルミナの粒子特性に大きく依存する。このため、多孔質α−アルミナ粒子としてはＢＥＴ比表面積が１〜２０m2/gの範囲にあるものが好ましく選択され、この粒子特性が得られる多孔質アルミン酸リチウムのＢＥＴ比表面積を１〜１５m2/gの範囲に制御する前提条件となる。一方、リチウム化合物は平均粒子径が１０μm 以下、好ましくは５μm 以下の粒度の微粉を使用することが好適であるが、アルミナ原料のように比表面積の範囲として限定されることはない。
【００１９】
多孔質α−アルミナ粒子とリチウム化合物粉末は、アルミン酸リチウムを得るための化学量論比に近い当量比で配合し、乾式条件下で混合する。この混合工程において、粉末間の相互分散が不十分であると反応生成したアルミン酸リチウム粒子が部分的に凝集し、粗粒化するため均質な多孔質組織として得ることが困難となる。このため、原料の均一な混合分散状態を得るためには、例えばヘンシルミキサーのような高速分散混合機、もしくはジェットミル、アトマイザーまたはバンダムミルのような衝撃型粉砕機から選ばれた１種または２種以上の混合装置を用いて処理することが好ましい。従来技術で用いられたボールミルなど磨砕タイプの粉砕混合機は、アルミナの粒子構造を破壊する傾向をもたらすため、本発明の目的には適合しない。
【００２０】
原料混合物は、ついで焼成処理される。焼成処理は、８００℃以上の温度域で０．５〜１６時間、好ましくは９００℃以上の高温下に１〜５時間の条件で行われ、多孔質α−アルミナ粒子とリチウム化合物を反応させて多孔質アルミン酸リチウムに転化させる。得られた生成物がγ型結晶を主体としたアルミン酸リチウムであることの確認は、Ｘ線回折により行うことができる。
【００２１】
本発明に係るγ型を主体とした多孔質アルミン酸リチウム粒子は、ＢＥＴ比表面積が１〜１５m2/gの範囲にあり、粒子の表面が蜂の巣状を呈した特有の多孔質組織を有しており、加熱前後におけるＢＥＴ比表面積の変化率が小さく、化学的安定性に優れた物性を備えている。かかる粒子物性は、原料となるα−アルミナの粒子特性に依存し、該粒子の多孔質なスケルトン構造を反映して形成されるものと推測される。また、本発明の多孔質アルミン酸リチウムは高温下の溶融炭酸塩中における熱安定性、化学的安定性等にも極めて優れているため、前記した特有の多孔質粒子物性と併せ、特にＭＣＦＣの電解質保持板用として好適である。
【００２２】
このような高品質の多孔質アルミン酸リチウム粒子は、特定されたＢＥＴ比表面積範囲の微細な多孔質アルミナとリチウム化合物を乾式混合手段により均一に分散混合させ、その混合物を８００℃以上の高温下で焼成反応させる本発明の製造方法により工業的に生産性よく得ることが可能となる。
【００２３】
【実施例】
以下に、本発明の実施例を比較例と対比して具体的に説明する。しかし、本発明の範囲はこれら実施例に限定されるものではない。
【００２４】
実施例１〜３
(1) γ型多孔質アルミン酸リチウムの製造；
表１に示すような見掛けの平均粒子径が８〜２５μm 、ＢＥＴ比表面積が１〜２m2/gの範囲にある市販の水酸化アルミニウム３種類を１２００℃で４時間焼成し、ＢＥＴ比表面積７．９〜１０．２m2/gのアルミナ粉末を得た。このアルミナ粉末は、ＳＥＭ写真およびＸ線回折により多孔質のα−アルミナ粉末であることが確認された。ついで、得られた各多孔質α−アルミナ粒子と平均粒子径３．２μm の炭酸リチウム粉末をＡｌとＬｉの原子量比が化学量論的に当量になるように配合し、乾式ヘンシルミキサーで十分均一に混合処理し、この混合粉末を９２０℃で２時間焼成した。焼成後、反応生成した粉末を冷却し、Ｘ線回折およびＳＥＭ写真により評価した結果、γ型の多孔質アルミン酸リチウムであることが確認された。得られたγ型多孔質アルミン酸リチウム粒子のＢＥＴ比表面積は、表１に示したとおり５．５〜６．２m2/gの範囲にあった。
【００２５】
【表１】
(2) 溶融炭酸塩下の安定化試験；
実施例１〜３で得られたγ型多孔質アルミン酸リチウム粒子と電解質（成分組成 Li2CO3：K2CO3=62:38mol%)とを１：３の重量比で混合したのち、空気／／ＣＯ2 ＝７０／３０の雰囲気に保持された電気炉に入れ、７００℃の温度で２００時間の条件で加熱試験を行った。加熱処理した粉末の加熱前後のＢＥＴ比表面積を測定し、下記 (1)式（Ｓ1 は加熱前のＢＥＴ比表面積、Ｓ2 は加熱後のＢＥＴ比表面積を示す）によりγ型アルミン酸リチウムの比表面積変化率（Ｒ）を算出して表２に示した。
【００２７】
なお、図１（拡大倍率：5,000 倍）は溶融加熱試験前における多孔質アルミン酸リチウムの粒子構造を示したＳＥＭ写真であり、図２（拡大倍率：5,000 倍）は溶融加熱試験後における多孔質アルミン酸リチウムの粒子構造を示したＳＥＭ写真である。これらＳＥＭ写真を対比すると粒子性状に殆ど変化がないことが認められる。
【００２９】
実施例４
見掛けの平均粒子径が２５μm 、ＢＥＴ比表面積が２m2/gの市販の水酸化アルミニウムを１２００℃で４時間焼成し、ＢＥＴ比表面積７．９m2/gのアルミナ粉末を得た。このアルミナ粉末は、ＳＥＭ写真およびＸ線回折により多孔質のα−アルミナ粉末であることが確認された。ついで、この多孔質α−アルミナ粉末と平均粒子径３．２μm の炭酸リチウム粉末をＡｌとＬｉの原子量比が化学量論的に当量になるように配合し、ヘンシルミキサーで十分均一に乾式混合し、混合粉末を１１００℃の温度で２時間焼成した。焼成後、反応生成した粉末を冷却し、Ｘ線回折およびＳＥＭ写真により評価した結果、γ型の多孔質アルミン酸リチウムであることが確認された。得られたγ型多孔質アルミン酸リチウム粒子のＢＥＴ比表面積は３．１m2/gであった。該γ型多孔質アルミン酸リチウム粒子につき、実施例１と同様に溶融炭酸塩下の安定化試験を行い、結果を表２に併載した。
【００３０】
比較例１
見掛けの平均粒子径が２５μm 、ＢＥＴ比表面積が２m2/gの市販の水酸化アルミニウム粒子と平均粒子径３．２μm の炭酸リチウム粉末をＡｌとＬｉの原子量比が化学量論的に当量となるように配合し、ボールミルを用いて乾式混合した。ついで、均一に混合された粉末を１１００℃で２時間焼成した。焼成後、生成粉末を冷却し、Ｘ線回折およびＳＥＭ写真により物性を確認したところ、γ型構造であったが非多孔質のアルミン酸リチウムであり、そのＢＥＴ比表面積は２．９m2/gであった。該多孔質アルミン酸リチウム粒子につき、実施例１と同様に溶融炭酸塩下の安定化試験を行い、結果を表２に併載した。
【００３１】
また、図３（拡大倍率：5,000 倍）に溶融加熱試験前における非多孔質アルミン酸リチウムの粒子構造のＳＥＭ写真を、また図３（拡大倍率：5,000 倍）に溶融加熱試験後における非多孔質アルミン酸リチウムの粒子構造のＳＥＭ写真を示した。図３と図４のＳＥＭ写真を対比して明らかなように粒子性状に顕著な変化が認められる。
【００３２】
【表２】
【発明の効果】
以上のとおり、本発明によれば比表面積が１〜１５m2/gの範囲にある多孔質組織を有し、溶融炭酸塩中で優れた熱安定性ならびに化学的安定性を備えるγ型を主体とした多孔質アルミン酸リチウム粒子を提供することができる。また、本発明の製造方法に従えば従来の製造技術に比べて簡易な工程により前記した高品位の粒子物性を備える多孔質状アルミン酸リチウムを工業的に有利に製造することが可能となる。したがって、特にＭＣＦＣの電解質保持板用に好適な多孔質状アルミン酸リチウムならびにその製造技術として極めて有用である。
【図面の簡単な説明】
【図１】実施例１の溶融加熱試験前におけるγ型多孔質アルミン酸リチウムの粒子構造を示したＳＥＭ写真（倍率：5,000 倍）である。
【図２】実施例１の溶融加熱試験後におけるγ型多孔質アルミン酸リチウムの粒子構造を示したＳＥＭ写真（倍率：5,000 倍）である。
【図３】比較例１の溶融加熱試験前におけるγ型非多孔質アルミン酸リチウムの粒子構造を示したＳＥＭ写真（倍率：5,000 倍）である。
【図４】比較例１の溶融加熱試験後におけるγ型非多孔質アルミン酸リチウムの粒子構造を示したＳＥＭ写真（倍率：5,000 倍）である。[0001]
[Technical field to which the invention belongs]
The present invention relates to a porous lithium aluminate powder having a fine and porous structure particularly useful for an electrolyte holding plate of a molten carbonate battery (MCFC) and an industrial production method thereof.
[0002]
[Prior art]
The MCFC electrolyte holding plate is used for the purpose of holding an electrolyte composed of a mixed molten carbonate such as Li 2 CO 3 and K 3 CO 3 in a high temperature region around 650 ° C. Properties such as alkali resistance and heat resistance are required. Lithium aluminate is currently used as the material for the electrolyte holding plate as a material that satisfies these required characteristics. In particular, a fine γ-type lithium aluminate with excellent electrolyte retention and a relatively large specific surface area is useful. Has been.
[0003]
As a technique for producing lithium aluminate having such a high specific surface area, JP-A-60-65719, JP-A-60-151975, JP-A-61-295227, JP-A-61-295228 are disclosed. Japanese Patent Laid-Open No. 63-70331, Japanese Patent Laid-Open No. 1-252522, Japanese Patent Laid-Open No. 2-80319, and the like have been proposed. These known manufacturing techniques include firing a mixture of alumina and lithium hydroxide or lithium carbonate in a temperature range of 600 to 1000 ° C. to suppress densification of the structure, secondary pore formation, hydration treatment, etc. Therefore, there is a manufacturing point in that the specific surface area is increased.
[0004]
Japanese Patent Publication No. 6-37292 discloses a method for producing porous lithium aluminate coarse particles, in which coarse particles are prepared by combining silica particles and alumina particles, and then lithium ions. The temperature is raised to 500 to 1000 ° C. in carbonate containing carbon, and the silica particles in the coarse particles are eluted into the carbonate to form vacancies, and the alumina formed into vacancies is lithiated to form lithium aluminate. It is something to be made.
[0005]
[Problems to be solved by the invention]
However, when lithium aluminate produced by the above-mentioned conventional technology is exposed to a high temperature for a long time in an electrolyte in a molten state, the γ-type structure is partially transformed into α-type or particles grow. As a result, the specific surface area becomes small. Therefore, when it is formed as an MCFC electrolyte holding plate, there is a drawback in that the electrolyte holding capacity rapidly decreases during use and the battery life is deteriorated.
[0006]
The method for producing porous lithium aminate according to the above-mentioned Japanese Patent Publication No. 6-37292 is proposed as a technique for improving this drawback, but it is a special technique for performing ion exchange of lithium after passing through coarse particles of silica alumina. In view of the need for a complicated process, there are problems such as a long and complicated process and difficulty in completely carrying out ion exchange.
[0007]
For this reason, in the conventional method for producing γ-type porous lithium aluminate, a high degree of retention for molten carbonate, alkali resistance, which will become increasingly demanding for the purpose of improving the life of MCFC in the future, It is not possible to sufficiently respond to the provision of heat resistance, and there remains a problem to be improved as an industrial production means.
[0008]
As a result of intensive studies to solve the above problems, the present inventors have stabilized the particle structure by pre-baking aluminum hydroxide or the like at a high temperature as an alumina source when producing lithium aluminate. When the porous alumina particles obtained are used, the resulting γ-type porous lithium aluminate does not change in the particle structure even when exposed to a high temperature in a solid electrolyte for a long time. In particular, the specific BET specific surface area and the specific surface area change rate It has been found that when it is within the range, it exhibits excellent performance as an electrolyte holding plate for MCFC.
[0009]
The present invention has been completed on the basis of the above-mentioned findings, and the object of the present invention is to ensure excellent thermal stability and chemical stability in a solid electrolyte, particularly when applied to an MCFC electrolyte holding plate. Γ-type porous lithium aluminate and an industrial production method thereof.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a porous lithium aluminate production method according to the present invention comprises a porous α-alumina particle obtained by firing aluminum hydroxide at 1200 ° C. and a lithium compound in a stoichiometric ratio. A structural feature is that dry mixing is performed at a quantity ratio in the vicinity, and the mixture is fired at 800 ° C. or higher.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The porous lithium aluminate of the present invention basically has a porous structure in which fine voids are uniformly dispersed in the structure and a BET specific surface area in the range of 1 to 15 m 2 / g. If the BET specific surface area is less than 1 m 2 / g, the holding ability in the molten carbonate will be insufficient and the function of the electrolyte holding plate will not be exerted. On the other hand, if the BET specific surface area exceeds 15 m 2 / g, The change in quality increases and the durability (stability) tends to be impaired.
[0013]
In addition to the above basic characteristics, a porous lithium aluminate sample was mixed with an electrolyte having a component composition ratio of Li 2 CO 3 : K 2 CO 3 = 62: 38 mol% in a weight ratio of 1: 3, and then air / CO when 2 was treated under the conditions of heating for 200 hours to a temperature of 700 ° C. in an electric furnace held at an atmosphere of 70/30, the difference between the BET specific surface area before and after heating of the BET specific surface area before the heating (S 1) It is an important requirement of the present invention that the change rate (R) of the BET specific surface area calculated as the ratio of (S 2 -S 1 ) is 25% or less. When this BET specific surface area change rate (R) exceeds 25%, lithium aluminate particle growth proceeds, and when used as an electrolyte holding plate, a change occurs with time, causing a phenomenon in which the electrolyte flows away between the particles, This results in a significant loss of battery performance.
[0014]
The lithium aluminate according to the present invention has a γ-type crystal structure. However, even if some α-type crystals are mixed, the stability performance in the electrolyte is not particularly affected. Γ-type crystal systems including type crystals are also acceptable. These physical properties can be easily confirmed by a BET specific surface area (N 2 SA) measurement method and an X-ray diffraction analysis method.
[0015]
Porous lithium aluminate having the above particle properties is produced industrially by a method in which porous α-alumina particles and a lithium compound are dry-mixed at a quantitative ratio in the vicinity of the stoichiometric ratio, and the mixture is fired. Can do.
[0016]
As the porous α-alumina particles used as the raw material component, industrially available particles can be used, but those obtained by baking aluminum hydroxide at a temperature of around 1200 ° C. to make α-alumina are particularly preferable. Used. The α-alumina particles thus prepared have a unique porous structure in which fine and uniform pores are formed in the particle structure due to the dehydrating action in the firing process, and the surface has a honeycomb shape, and the particles The particles are relatively uniformly dispersed with little aggregation between them. In addition, it becomes a very stable structure by being α-ized at a high temperature around 1200 ° C.
[0017]
On the other hand, examples of the lithium compound serving as the lithium source include lithium carbonate, lithium hydroxide, and lithium nitrate. For the purposes of the present invention, the use of lithium carbonate is most effective.
[0018]
The particle characteristics of the porous lithium aluminate to be produced largely depend on the particle characteristics of alumina used as a raw material. For this reason, as the porous α-alumina particles, those having a BET specific surface area in the range of 1 to 20 m 2 / g are preferably selected, and the BET specific surface area of porous lithium aluminate capable of obtaining this particle characteristic is set to 1 to 15 m. It is a precondition to control in the range of 2 / g. On the other hand, the lithium compound preferably uses fine powder having an average particle size of 10 μm or less, preferably 5 μm or less, but is not limited to a specific surface area range as in the case of an alumina raw material.
[0019]
The porous α-alumina particles and the lithium compound powder are mixed at an equivalent ratio close to the stoichiometric ratio for obtaining lithium aluminate and mixed under dry conditions. In this mixing step, if the interdispersion between the powders is insufficient, the reaction-generated lithium aluminate particles are partially agglomerated and coarsened, making it difficult to obtain a homogeneous porous structure. For this reason, in order to obtain a uniform mixed and dispersed state of the raw material, one or two selected from a high-speed dispersion mixer such as a Hensyl mixer, or an impact type pulverizer such as a jet mill, an atomizer, or a bandham mill. It is preferable to process using the mixing apparatus of a seed | species or more. Grinding type milling mixers such as ball mills used in the prior art are not suitable for the purposes of the present invention because they tend to destroy the particle structure of alumina.
[0020]
The raw material mixture is then fired. The baking treatment is performed at a temperature range of 800 ° C. or higher for 0.5 to 16 hours, preferably at a high temperature of 900 ° C. or higher for 1 to 5 hours, and the porous α-alumina particles and the lithium compound are reacted. Convert to porous lithium aluminate. Confirmation that the obtained product is lithium aluminate mainly composed of γ-type crystals can be performed by X-ray diffraction.
[0021]
The porous lithium aluminate particles mainly composed of γ-type according to the present invention have a BET specific surface area in the range of 1 to 15 m 2 / g, and have a unique porous structure in which the particle surface has a honeycomb shape. The change rate of the BET specific surface area before and after heating is small, and it has physical properties excellent in chemical stability. Such particle physical properties depend on the particle characteristics of α-alumina as a raw material, and are assumed to be formed reflecting the porous skeleton structure of the particles. In addition, the porous lithium aluminate of the present invention is extremely excellent in thermal stability, chemical stability, etc. in molten carbonate at high temperature. It is suitable for an electrolyte holding plate.
[0022]
Such high-quality porous lithium aluminate particles are obtained by uniformly dispersing and mixing fine porous alumina having a specified BET specific surface area range and a lithium compound by a dry mixing means, and subjecting the mixture to a high temperature of 800 ° C. or higher. It is possible to obtain industrially good productivity by the production method of the present invention in which the baking reaction is performed.
[0023]
【Example】
Examples of the present invention will be specifically described below in comparison with comparative examples. However, the scope of the present invention is not limited to these examples.
[0024]
Examples 1-3
(1) Production of γ-type porous lithium aluminate;
As shown in Table 1, three types of commercially available aluminum hydroxide having an apparent average particle diameter of 8 to 25 μm and a BET specific surface area of 1 to 2 m 2 / g were calcined at 1200 ° C. for 4 hours to obtain a BET specific surface area of 7 .9 to 10.2 m 2 / g of alumina powder was obtained. This alumina powder was confirmed to be porous α-alumina powder by SEM photograph and X-ray diffraction. Next, each porous α-alumina particle obtained and lithium carbonate powder having an average particle diameter of 3.2 μm were blended so that the atomic weight ratio of Al and Li was stoichiometrically equivalent, and the dry-type Hensyl mixer was sufficient. The mixed powder was uniformly mixed, and the mixed powder was fired at 920 ° C. for 2 hours. After firing, the reaction-generated powder was cooled and evaluated by X-ray diffraction and SEM photographs. As a result, it was confirmed to be γ-type porous lithium aluminate. As shown in Table 1, the BET specific surface area of the obtained γ-type porous lithium aluminate particles was in the range of 5.5 to 6.2 m 2 / g.
[0025]
[Table 1]
(2) Stabilization test under molten carbonate;
After the γ-type porous lithium aluminate particles obtained in Examples 1 to 3 and the electrolyte (component composition Li 2 CO 3 : K 2 CO 3 = 62: 38 mol%) were mixed at a weight ratio of 1: 3, air // CO 2 = 70/30 atmosphere placed in an electric furnace kept at a heat treatment was performed at test under the conditions of 200 hours at a temperature of 700 ° C.. The BET specific surface area before and after heating of the heat-treated powder was measured, and the following formula (1) (S 1 represents the BET specific surface area before heating, S 2 represents the BET specific surface area after heating) of the γ-type lithium aluminate The specific surface area change rate (R) was calculated and shown in Table 2.
[0027]
1 (magnification: 5,000 times) is an SEM photograph showing the particle structure of porous lithium aluminate before the melt heating test, and FIG. 2 (magnification: 5,000 times) is the porous after the melt heating test. It is the SEM photograph which showed the particle structure of lithium aluminate. When these SEM photographs are compared, it is recognized that there is almost no change in the particle properties.
[0029]
Example 4
Commercially available aluminum hydroxide having an apparent average particle diameter of 25 μm and a BET specific surface area of 2 m 2 / g was calcined at 1200 ° C. for 4 hours to obtain an alumina powder having a BET specific surface area of 7.9 m 2 / g. This alumina powder was confirmed to be porous α-alumina powder by SEM photograph and X-ray diffraction. Next, this porous α-alumina powder and lithium carbonate powder having an average particle diameter of 3.2 μm are blended so that the atomic weight ratio of Al and Li is stoichiometrically equivalent, and then dry-mixed sufficiently uniformly with a Hensyl mixer. The mixed powder was fired at a temperature of 1100 ° C. for 2 hours. After firing, the reaction-generated powder was cooled and evaluated by X-ray diffraction and SEM photographs. As a result, it was confirmed to be γ-type porous lithium aluminate. The obtained γ-type porous lithium aluminate particles had a BET specific surface area of 3.1 m 2 / g. The γ-type porous lithium aluminate particles were subjected to a stabilization test under molten carbonate in the same manner as in Example 1, and the results are also shown in Table 2.
[0030]
Comparative Example 1
Commercially available aluminum hydroxide particles having an apparent average particle diameter of 25 μm and a BET specific surface area of 2 m 2 / g and lithium carbonate powder having an average particle diameter of 3.2 μm, the atomic weight ratio of Al and Li is stoichiometrically equivalent. Were mixed and dry mixed using a ball mill. Next, the uniformly mixed powder was fired at 1100 ° C. for 2 hours. After firing, the resulting powder was cooled and the physical properties were confirmed by X-ray diffraction and SEM photograph. As a result, it was a γ-type structure but nonporous lithium aluminate, and its BET specific surface area was 2.9 m 2 / g. Met. The porous lithium aluminate particles were subjected to a stabilization test under molten carbonate in the same manner as in Example 1, and the results are also shown in Table 2.
[0031]
Fig. 3 (magnification: 5,000 times) shows a SEM photograph of the particle structure of nonporous lithium aluminate before the melt heating test, and Fig. 3 (magnification: 5,000 times) shows the nonporous material after the melt heating test. The SEM photograph of the particle structure of lithium aluminate is shown. As is clear from the comparison of the SEM photographs of FIGS. 3 and 4, a remarkable change is observed in the particle properties.
[0032]
[Table 2]
【The invention's effect】
As described above, according to the present invention, the gamma type mainly has a porous structure having a specific surface area in the range of 1 to 15 m 2 / g and has excellent thermal stability and chemical stability in molten carbonate. Thus, porous lithium aluminate particles can be provided. Further, according to the production method of the present invention, porous lithium aluminate having the above-described high-grade particle physical properties can be produced industrially advantageously by a simple process compared with the conventional production technique. Therefore, it is extremely useful as a porous lithium aluminate suitable for an MCFC electrolyte holding plate and a production technique thereof.
[Brief description of the drawings]
1 is an SEM photograph (magnification: 5,000 times) showing a particle structure of γ-type porous lithium aluminate before a melt heating test in Example 1. FIG.
2 is an SEM photograph (magnification: 5,000 times) showing the particle structure of γ-type porous lithium aluminate after the melt heating test of Example 1. FIG.
3 is an SEM photograph (magnification: 5,000 times) showing the particle structure of γ-type non-porous lithium aluminate before the melt heating test of Comparative Example 1. FIG.
4 is an SEM photograph (magnification: 5,000 times) showing the particle structure of γ-type non-porous lithium aluminate after the melt heating test of Comparative Example 1. FIG.
Claims (2)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP29606395A JP3786457B2 (en) | 1995-10-19 | 1995-10-19 | Method for producing porous lithium aluminate |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP29606395A JP3786457B2 (en) | 1995-10-19 | 1995-10-19 | Method for producing porous lithium aluminate |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH09110422A JPH09110422A (en) | 1997-04-28 |
| JP3786457B2 true JP3786457B2 (en) | 2006-06-14 |
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| JP29606395A Expired - Lifetime JP3786457B2 (en) | 1995-10-19 | 1995-10-19 | Method for producing porous lithium aluminate |
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| JP5873117B2 (en) * | 2013-02-07 | 2016-03-01 | 日本化学工業株式会社 | Method for producing α-lithium aluminate |
| JP6254913B2 (en) | 2014-07-25 | 2017-12-27 | 日本化学工業株式会社 | Method for producing α-lithium aluminate |
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