JP3845057B2 - Hydrogen storage alloy and heat treatment method of hydrogen storage alloy - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、水素貯蔵・供給用材料、熱変換用材料、Ｎｉ−水素電池用負極材料、水素精製回収用材料、水素ガスアクチュエータ用水素吸収材料等に用いられる水素吸蔵合金および該水素吸蔵合金の熱処理方法に関するものであり、特に環境温度（２０℃〜８０℃）で優れた特性を有する合金に関するものである。
【０００２】
【従来の技術】
水素吸蔵合金は、水素と可逆的に反応して、反応熱の出入りを伴う水素吸放出特性を有している。この現象を利用して、近年、水素貯蔵用材料やヒートポンプ・冷凍システム用などの熱変換用材料としての実用化が積極的に進められている。代表的な水素吸蔵合金としてはＬａＮｉ５、ＴｉＦｅ、ＴｉＭｎ１．５等がよく知られている。
【０００３】
なお、各種用途の実用化においては、水素貯蔵用材料の特性を一層向上させる必要があり、例えば、水素貯蔵量の増加、原料の低廉化、プラトー特性の改善、耐久性の向上などが大きな課題として挙げられる。中でも、Ｖ、ＴｉＭｎＶ系、ＴｉＣｒＶ系などの体心立方構造（以下ＢＣＣ構造と呼ぶ）の金属は、すでに実用化されている前記の金属間化合物の水素吸蔵合金に比べ大量の水素（４００ｃｃ／ｇ程度）を吸蔵することが古くから知られている。しかし、有効に吸蔵・放出できる水素量は、その半分程度であり、その他は水素と化合した固溶相として残存するため、効率が悪いという欠点がある。また、金属間化合物の水素吸蔵合金と比べ水素の吸放出に要する反応速度が遅く、活性化が困難という問題点も挙げられ実用化には至っていないため、活性化、プラトー特性、耐久性等改善するべき点が多々ある。これらの課題に対しては特許文献１や特許文献２などに改善策が提案されている。
【０００４】
しかし、水素貯蔵用材料に望まれる特性は、適当な温度で容易且つ大量の水素を吸放出することであり、この要望にこたえるためには、水素吸蔵合金の合金特性において、水素吸放出反応の反応速度を加速させ、平衡水素圧力−水素吸収量−等温曲線のプラトー領域の傾斜を減少させ、且つプラトー領域の平衡水素圧力値を、水素吸蔵合金を利用するシステムで許容される圧力範囲に制御し、その圧力範囲内おける有効水素移動量を増大させる必要がある。
このような合金特性の改善には合金の構成成分比の変更や一部他元素置換などの方法の他に、従来より熱処理方法を採用した製造方法の開発（例えば特許文献３）が進められている。この方法では、ＢＣＣ構造単相またはＢＣＣ構造主相を有すると考えられる成分の設計範囲で、熱処理条件を制御して合金の微細組織、特に母相であるＢＣＣ構造の変調構造組織をコントロールし水素吸蔵量及び水素の吸放出速度の改善を試みている。
【０００５】
【特許文献１】
特開平１０−１１０２２５号公報（第２頁）
【特許文献２】
特開平１１−１０６８５９号公報（第２頁）
【特許文献３】
特開平１０−２４５６６３号公報（第２頁）
【０００６】
【発明が解決しようとする課題】
従来の熱処理方法を用いた合金特性改善では、母相であるＢＣＣ構造の変調構造組織をコントロールして水素吸蔵量及び水素の吸放出速度の改善を試みており、各種用途に対する実用性は、発見当初のＢＣＣ構造の水素吸蔵合金と比べ格段に向上している。しかし、これらの従来技術では成分組成と熱処理制御によって、ナノオーダーの微細組織を制御するとしているが、実際の製造プロセスにおいては溶解や熱処理施設の環境問題もあり、ミクロオーダーの微細組織制御を前提としなければならないが、そのような従来技術は開発されていない。
【０００７】
本発明の対象となるＴｉＣｒＶ系合金では、溶解時の微量酸素混入によりＢＣＣ構造とは異なるα−Ｔｉが平衡析出することが知られており、ＴｉＣｒ２の組成に近い成分比を有するＴｉＣｒＶ系合金では１０００℃近傍より低い温度においてＣ１５Ｌａｖｅｓ相の平衡析出が懸念される。これらの異相析出は酸素量や熱処理条件の保持温度、保持時間、冷却速度に大きく依存することを本発明者らは確認し、従来ＢＣＣ構造単相であると考えられてきた成分比のＴｉＣｒＶ系合金において、熱処理条件によっては異相の合金内の体積比は１０体積％程度まで増加することが判明した。
【０００８】
また、熱処理炉内の清浄度によっては、表面酸化の影響で合金の表面近傍に設計組成から逸脱したＢＣＣ構造の領域が幅広く形成され、合金の水素吸蔵特性を悪化させることが判明した。従来技術の製造方法で、これまで指摘した問題を抑制し、ナノオーダーの微細組織制御を行うには、極めて高真空の溶解及び熱処理施設を要し、商業生産の点で現実的ではない。さらに、従来技術では熱処理の冷却過程を水又は油による焼入れ処理等の急冷処理が望ましいとしているが、本発明者らの研究により、ＢＣＣ構造のＴｉＣｒＶ系合金の内部、特に結晶粒内では、急冷処理を施すと針状α−Ｔｉの析出量が２体積％を超えて増加し、多数の核発生を伴うことが判明しており、ＢＣＣ構造と整合な結晶粒内の針状α−Ｔｉの存在は合金の水素吸蔵特性、主に有効水素移動量や水素吸放出の反応速度、耐久性等に悪影響を及ぼすことが考えられる。加えて、Ｃ１５Ｌａｖｅｓ相の過剰析出はＢＣＣ構造を有するＴｉＣｒＶ系合金の水素吸蔵特性の悪化、特に有効水素移動量の減少を招くことが知られているが、本発明者らの研究により、Ｃ１５Ｌａｖｅｓ相がＢＣＣ構造の母相結晶粒の粒界上に薄く存在する場合には、有効水素移動量を減らさず合金の水素吸放出の反応速度が加速することが判明している。しかし、ＢＣＣ構造のＴｉＣｒＶ系合金の従来技術で、そのようなミクロオーダーの組織制御を試みている例は無い。
【０００９】
本発明は、前記のような従来の課題を解決するものであり、不活性ガス気中又は水素ガスなどの還元ガス気中又は真空下で１２００℃〜融点直下の極めて高温の均質化熱処理を行った後、不活性ガス気中又は水素ガスなどの還元ガス気中又は真空下で２００℃／ｈｏｕｒ以下の冷却速度を用いた遅い冷却過程を採用することにより、ＢＣＣ構造の結晶粒内に析出するα−Ｔｉの過剰析出を抑制し、且つ結晶粒内に析出したα−Ｔｉを結晶粒界へ移動・排出させることでＢＣＣ構造の結晶粒の水素吸蔵量を維持又は増加させ、さらに結晶粒界に薄くＣ１５Ｌａｖｅｓ相を析出させることで活性化及び水素吸放出の反応速度を加速させる高容量の水素吸蔵合金の熱処理方法および上記組織形態を有する水素吸蔵合金を提供することを目的とする。
【００１０】
【課題を解決するための手段】
前記の目的を達成させるために、本発明の水素吸蔵合金のうち請求項１記載の発明は、式：ＴｉaＣｒｂＶｃＭｄで表され、低温平衡相としてＣ１５Ｌａｖｅｓ相を含み、主相がＢＣＣ構造からなるとともに、合金結晶粒内の針状α−Ｔｉの析出量が２体積％以下で、析出するＣ１５Ｌａｖｅｓ相のうちの８０体積％以上が結晶粒界上に存在することを特徴とする。
ただし、ａは２０〜４５原子量％、ｂは３０〜７０原子量％、ｃは５〜４５原子量％、ｄは０〜１５原子量％範囲に設定され、ＭはＦｅ、Ａｌ、Ｃｕ、Ｎｉ、Ｍｏの一種又は二種以上である。
【００１１】
請求項２記載の水素吸蔵合金の熱処理方法は、式：ＴｉaＣｒｂＶｃＭｄで表され、低温平衡相としてＣ１５Ｌａｖｅｓ相を含み、主相がＢＣＣ構造からなる水素吸蔵合金の熱処理方法において、合金の溶解・鋳造後、１２００℃〜融点の温度で、不活性ガス気中又は還元ガス気中又は真空下で１〜２４時間の範囲で均質化熱処理し、その後、不活性ガス気中又は還元ガス気中又は真空下で少なくともＢＣＣ構造相とＣ１５Ｌａｖｅｓ相の混相領域となる温度に至るまで１０℃〜２００℃／時間の冷却速度で降温することを特徴とする。
ただし、ａは２０〜４５原子量％、ｂは３０〜７０原子量％、ｃは５〜４５原子量％、ｄは０〜１５原子量％範囲に設定され、ＭはＦｅ、Ａｌ、Ｃｕ、Ｎｉ、Ｍｏの一種又は二種以上である。
【００１２】
請求項３記載の水素吸蔵合金の熱処理方法は、請求項２記載の発明において、合金の原材料にフェロバナジウムを含むことを特徴とする。
【００１３】
請求項４記載の水素吸蔵合金の熱処理方法は、請求項２または請求項３に記載の発明において、合金結晶粒内の針状α−Ｔｉの析出量を２体積％以下に抑制し、析出するＣ１５Ｌａｖｅｓ相の８０体積％以上を結晶粒界上に存在させることを特徴とする。
【００１４】
すなわち、本発明の熱処理方法によれば、均質化熱処理の後に１０〜２００℃／時間の冷却速度でＢＣＣ構造相とＣ１５Ｌａｖｅｓ相の混相領域まで降温されるため、結晶粒内の針状α−Ｔｉの析出が抑制されて、ＢＣＣ構造の結晶完全性が改善して有効水素移動量が増加し、且つ結晶粒界上にＣ１５Ｌａｖｅｓ相が薄く析出することから、初期活性化や水素吸放出の際にＣ１５Ｌａｖｅｓ相がＢＣＣ構造の主相への水素移動の短絡経路として活用され、水素吸放出の反応速度が加速される。その結果、各種用途に利用される際の環境温度（２０℃〜８０℃）で優れた特性を有する高容量の水素吸蔵合金を提供することが出来る。
【００１５】
【発明の実施の形態】
以下に本発明における成分及び熱処理条件の限定理由を含めて詳細に説明する。
本発明は、前記のようにＴｉ、Ｃｒ、Ｖを構成元素とした三元系合金もしくはＴｉ、Ｃｒ、Ｖに添加元素としてＦｅ、Ａｌ、Ｃｕ、Ｎｉ、Ｍｏの一種又は二種以上を添加した多元系合金からなるものであり、結晶構造としてＢＣＣ構造の主相（ＢＣＣ構造相が８０体積％以上、望ましくは９０体積％以上）を有する。結晶構造がこれ以外であると良好な水素吸蔵特性が得られない。
【００１６】
Ｔｉ：２０〜４５原子量％
Ｔｉの組成比を２０原子量％未満にすると、初期活性化が困難になるとともに、水素吸蔵量が低下して実用的でなくなる。一方、Ｔｉの組成比が４５原子量％を越えるとプラトー特性が悪化するため、Ｔｉの組成比を前記範囲内とする。なお、同様の理由で下限を２５原子量％、上限を４０原子量％とするのが望ましい。
【００１７】
Ｃｒ：３０〜７０原子量％
Ｃｒの組成比を３０原子量％未満とすると、プラトー特性が悪化し、７０原子量％を越えると水素吸蔵量及び水素放出量が低下するためＣｒの組成比を前記範囲内とする。なお、同様の理由で下限を４０原子量％、上限を６０原子量％とするのが望ましい。
【００１８】
Ｖ：５〜４５原子量％
Ｖは、ＢＣＣ構造の安定化元素としてＣｒの一部を置換する元素として添加される。Ｖの組成比を５原子量％未満とするとＢＣＣ構造が安定となりうる組成範囲が狭まり、製造過程で合金の主相をＢＣＣ構造に維持することが困難となり、水素吸蔵量が低下する。また、Ｖの組成比が４５原子量％を越えると合金中の水素の安定性が著しく高くなり実用的でないためＶの組成比を前記範囲内とする。
【００１９】
Ｍ群（Ｆｅ、Ａｌ、Ｃｕ、ＮＩ、Ｍｏの一種又は二種以上）：０〜１５原子量％ＢＣＣ構造の主相を有するＴｉＣｒＶ系合金は水素吸蔵時に面心立方構造（ＦＣＣ構造）に可逆的に変態する。Ｆｅ、Ａｌ、Ｃｕ、Ｎｉ、Ｍｏは、ＢＣＣ構造の主相を有するＴｉＣｒＶ系合金のプラトー特性、特に吸放出時の水素平衡圧力調整の目的あるいは水素吸蔵時におけるＦＣＣ構造の積層欠陥エネルギーの増減による耐久性改善の目的で所望により添加する。但し、Ｆｅ、Ａｌ、Ｃｕ、Ｎｉ、Ｍｏの過剰添加は、水素吸蔵量の減少など合金特性に悪影響を及ぼすことからＦｅ、Ａｌ、Ｃｕ、Ｎｉ、Ｍｏの組成比は前記範囲内とする。
【００２０】
均質化熱処理温度（１２００℃〜融点）
一般にＴｉＣｒＶ系合金のＢＣＣ構造は高温平衡相であり、溶解・鋳造時に形成される各成分の凝固偏析、特にＴｉ成分とＶ成分のデンドライト状の凝固偏析を解消して均質化するためには、ＢＣＣ構造相の安定な高温域における均質化熱処理が必要となる。特に、合金全体に構成元素が短時間で移動可能にするためには、合金の成分組成にもよるが少なくとも１２００℃以上で融点以下の高温が必要である。合金の部分的溶融を招かないように上限は融点から２０℃低い温度に設定するのが望ましい。また、熱処理による均質化効果を確実に得るためには、熱処理温度は合金の融点直下（詳しくは合金融点より２０〜１００℃低い温度域）であることが望ましい。
【００２１】
また、発明の熱処理方法では、上記温度に至るまでの昇温過程について特別な制限はないが、熱処理炉の負担を軽減する為に昇温速度は６００℃／時間以下とすることが望ましい。
なお、上記熱処理に用いる加熱炉の構造については、本発明は特に限定するものではなく、既設の加熱炉等を用いることができる。
【００２２】
均質化熱処理時間（１〜２４時間）
均質化効果を十分に得るために１時間以上の保持時間が必要である。一方、２４時間を超えて保持しても効果は飽和するので、１〜２４時間の範囲内で均質化熱処理を行う。
【００２３】
不活性ガス気中又は還元ガス気中又は真空下
本発明における水素吸蔵合金は、原材料に酸素含有量の多いＶが含有されることから合金内酸素含有量が無視できない。また、原材料にフェロバナジウムを使用した場合でも合金内酸素含有量は多くなる。さらに、均質化熱処理に用いる熱処理炉内に酸素が混入していると合金表面近傍にはＴｉ酸化物及びＣｒ酸化物、粗大なα−Ｔｉとともに設計した成分組成から逸脱したＢＣＣ構造の領域が幅広く形成され、最大水素吸蔵量や有効水素移動量が減少し合金特性に悪影響を及ぼすため、合金表面を充分に切削して除去する必要が生じ、作業効率の低下、歩留まりの低下を招く。これに対し、熱処理炉内を不活性ガス雰囲気又は水素などの還元ガス雰囲気又は真空（例えば１×１０−１Ｔｏｒｒ以下、真空下圧力は工業性を考慮して１×１０−６Ｔｏｒｒ以上であってもよい。）に制御して均質化熱処理時およびその後の冷却時に炉内の酸素混入量を抑えることが可能になり、水素吸蔵合金の表面酸化を防止して、上記切削作業を必要とすることなく良好な合金特性を得ることが可能になる。
【００２４】
冷却速度（１０℃〜２００℃／時間）
冷却速度の制御は、ＢＣＣ構造の結晶粒内に析出するα−Ｔｉの析出頻度を制御する上で、極めて重要である。均質化熱処理温度からの水や油による焼入れ処理等の急冷処理では、結晶粒内に針状α−Ｔｉが微細に多数析出する。このようなα−Ｔｉの析出を抑制するためには、降温過程の冷却速度は合金製造の許容範囲内で、極力抑えられなくてはならない。また、ＴｉＣｒＶ系合金の常温〜１１００℃の温度範囲には、Ｃ１５Ｌａｖｅｓ相が低温平衡相として存在するため、ＢＣＣ構造相とＣ１５Ｌａｖｅｓ相の混相領域を構成する。Ｘ線回折法で検出又は同定できないほどの少量のＣ１５Ｌａｖｅｓ相を結晶粒界上に薄く析出させるためには、降温過程の冷却速度を前記範囲内とする必要があり、該冷却速度は、上記混相領域に至るまで上記範囲内に維持する必要がある。混相領域に達した後の降温過程において特別な制限はない。したがってそのまま冷却速度を上記範囲内に維持してもよく、また、以降は該範囲を逸脱する冷却速度で冷却してもよい。
ただし、水素吸蔵特性に悪影響を及ぼすと考えられるα−ＴｉはＢＣＣ構造相とＣ１５Ｌａｖｅｓ相の混相領域の温度範囲でも析出可能な第二相であることから、合金組成によってはα−Ｔｉの析出抑制のために、最適な降温速度で常温まで制御することが望ましい。
【００２５】
なお、上記冷却速度を採用しているので、水や油による焼入れ処理等の急冷処理が不要であり、高温域で合金が大気に接触する機会は無く、合金への余分な酸素の混入が極力抑えられる。さらに急冷処理が不要なことから急冷処理用の設備は必要なく設備投資や合金製造コストが抑えられるため、商業生産の点で有利である。
【００２６】
原材料フェロバナジウム（ＶとＦｅを主成分とする合金）の使用
上記の組成範囲を厳守する形での原材料フェロバナジウム採用の場合、合金製造コストの低減効果が極めて大きい。但し、溶解時の脱酸剤等からによる意図しない不純物元素の微量混入があるため、最大水素吸蔵量の変動等の不都合が発生する。しかし、組成範囲を厳守する形でフェロバナジウムを採用する場合は、最大水素吸蔵量の変動は少なく抑えられ、本発明の熱処理方法の適用によって、同様の合金特性改善が得られる。
【００２７】
本発明において、水素吸蔵合金の溶解法については特別な制限は無く、アーク溶解法、高周波誘導溶解法等、種々の溶解法が適用できるが、本発明の水素吸蔵合金の熱処理方法を採用して確実に合金特性改善の効果を得るには、多量の酸素混入による合金特性の悪化を防ぐ為、溶解は不活性ガス気中又は１×１０−１〜１×１０−６Ｔｏｒｒの真空下で行われることが望ましい。
なお且つ、溶解凝固過程で形成される結晶粒等の合金組織の違いによって凝固偏析の幅や濃度変動値が変化するため、合金重量に対する鋳型との接触面積等、合金に対する充分な凝固面積を確保して、充分な冷却速度を獲得することが望ましい。
【００２８】
【実施例】
以下に、本発明の実施例について図表を交えて説明する。基本となる構成成分比をＴｉ：３０原子量％、Ｃｒ：５０原子量％、Ｖ：２０原子量％として原料を配合し、アルゴン雰囲気中アーク溶解炉で溶解し、表１に示した組成を有する合金５０ｇを作製した。次いで、アルゴン雰囲気熱処理炉を使用して昇温速度５５０℃／時間で昇温し、１４００℃で３時間の均質化熱処理を行い、３０℃／時間の冷却速度で炉内にて常温まで冷却した。得られた水素吸蔵合金を本発明の実施例としての測定試料とした。また、比較の為、同じく基本となる構成成分比をＴｉ：３０原子量％、Ｃｒ：５０原子量％、Ｖ：２０原子量％として原料を配合し、アーク溶製した表１に示すような組成を有する合金５０ｇに、アルゴン雰囲気熱処理炉を使用して昇温速度５５０℃／時間で昇温し、１４００℃で３時間の均質化熱処理を行い水焼入れ処理した。得られた水素吸蔵合金を比較例としての測定試料とした。なお、上記水焼入れ処理時の冷却速度は約３．６×１０５℃／時間である。
【００２９】
【表１】
上記各測定試料の一部は、約２００メッシュ以下に粉砕してＸ線回折法による合金分析に使用し、他の一部は約５０〜２００メッシュの範囲に粉砕して水素ガス雰囲気での水素吸放出量測定（Ｐ（水素圧力）−Ｃ（組成）−Ｔ（温度）測定）に使用した。残りの合金塊は光学顕微鏡観察及び電解放射型走査型電子顕微鏡観察（ＦＥ−ＳＥＭ観察）の観察試料に使用した。
【００３１】
最初に、実施例と比較例の観察試料について、光学顕微鏡観察を実施して結晶粒内の針状α−Ｔｉの析出状況を調べた。図１に実施例の光学顕微鏡写真を、図２に比較例の光学顕微鏡写真を示す。実施例では粗大な針状α−Ｔｉが若干量存在する程度に抑制されていた。一方、比較例では微細な針状α−Ｔｉが多量に析出していた。
【００３２】
また、実施例と比較例で観察された析出物の性状を確認するためにＦＥ−ＳＥＭのエネルギー分散型Ｘ線分光分析（ＥＤＳ分析）による面分析を実施した。図３に実施例で観察された結晶粒界上に存在するＣ１５Ｌａｖｅｓ相のＶ成分の面分析結果を、図４に比較例で観察された結晶粒内に存在する針状α−ＴｉのＴｉ成分の面分析結果を示す。実施例で観察された結晶粒界上のＣ１５Ｌａｖｅｓ相は、析出したＣ１５Ｌａｖｅｓ相の全量のうち９０体積％以上を占めていた。また、結晶粒界上のＣ１５Ｌａｖｅｓ相のＴｉ及びＣｒの成分比は母相のＢＣＣ構造相とほぼ同様であったが、図３に示すようにＶ成分は結晶内部のＢＣＣ構造相よりも欠乏していることが判明した。比較例で観察された結晶粒内の針状α−Ｔｉは、図４に示すようにＢＣＣ構造相よりも極めて高い濃度でＴｉが濃化していることが判明し、約７５〜９５原子量％のＴｉが存在していた。
【００３３】
さらに、実施例と比較例の測定試料を、それぞれＸ線回折法により結晶構造を調べた。このときのＸ線はＣｕＫα線を用いた。図５に実施例と比較例の測定結果を示す。図５で観察された両者のＸ線回折ピークはＢＣＣ構造相のものであり、異相の存在はＸ線回折法では明確ではなかった。実施例では、図５に示すように本発明の熱処理によりＢＣＣ構造相の結晶完全性が改善され、比較例よりもＢＣＣ構造相の回折強度が増加した。なお、実施例と比較例のＢＣＣ構造相の格子定数はほぼ等しい値である。
【００３４】
図６にＸ線回折法で得られたＢＣＣ構造相の（１１０）ピークの回折強度と結晶粒内の針状α−Ｔｉの析出量との相関を示す。図６に示すように、実施例は比較例よりも析出量が減少して回折強度が増加していることから、結晶粒内の針状α−Ｔｉの析出量を抑制することによってＢＣＣ構造相の結晶完全性が改善され得ることが証明された。
【００３５】
次に、実施例及び比較例について、平衡水素圧力−水素吸収量−等温曲線を求めた。図７に実施例と比較例の曲線を示す。実施例では、図７に示すように本発明の熱処理によるＢＣＣ構造の結晶粒内の針状α−Ｔｉ析出抑制により、比較例よりも水素吸蔵量が増加し、プラトー領域が平坦化した。
【００３６】
さらに、実施例及び比較例について、初期活性化の水素吸蔵量−時間曲線を求めた。図８に実施例と比較例の曲線を示す。実施例では、図８に示すようにＣ１５Ｌａｖｅｓ相の微量粒界析出により、初期活性化を実施してまもなく水素吸蔵が開始されて活性化速度も極めて速いが、比較例では水素吸蔵が開始されるのに一定時間を要し、水素吸蔵開始後も活性化速度は実施例よりも遅いことがわかる。
【００３７】
以上実施例で説明したように、ＢＣＣ構造の主相を有し、低温平衡相としてＣ１５Ｌａｖｅｓ相を有するＴｉＣｒＶ系水素吸蔵合金において、本発明の熱処理方法を実施することにより、ＢＣＣ構造の結晶粒内に析出するα−Ｔｉの過剰析出を抑制し、且つ結晶粒内に析出したα−Ｔｉを結晶粒界へ移動・排出させ、さらに結晶粒界に薄くＣ１５Ｌａｖｅｓ相を析出させることにより、水素吸蔵量を維持又は増加させ、活性化及び水素吸放出の反応速度を加速させることができ、実用性に優れた水素吸蔵合金を得ることができる。
【００３８】
次に、表２に本発明の熱処理を施した各種合金と水焼入れ処理を施した各種合金の熱処理冷却条件と有効水素移動量を示す。なお、表２に記載した合金の構成成分比は本発明に記載した組成範囲内であり、全ての合金でＢＣＣ構造が主相となっている。また、全ての合金はアルゴン雰囲気熱処理炉を使用して昇温速度５５０℃／時間で昇温し、１４００℃で３時間の均質化熱処理を行っている。表２に示すように、本発明の熱処理を施した合金は、同一成分比の水焼入れ処理を施した合金よりも有効水素移動量が増加した。
【００３９】
【表２】
【発明の効果】
以上説明したように本発明によれば、従来の方法では達成が困難であったＢＣＣ構造の主相を有するＴｉＣｒＶ系水素吸蔵合金の活性化や水素吸放出の反応速度の増加、水素吸蔵量の増加といった合金特性改善が、急冷処理等の為の設備投資や合金製造コストの増大を伴うことなく達成される。この結果、本発明の水素吸蔵合金は、実用的な特性を有しつつ安価且つ生産量増大を図ることが可能となり、特に可逆的な水素吸放出を利用する水素貯蔵システムへの高性能化・低コスト化への寄与は多分に大きい。
【図面の簡単な説明】
【図１】 本発明の実施例の光学顕微鏡写真を示す図面代用写真である。
【図２】 比較例の光学顕微鏡写真を示す図面代用写真である。
【図３】 本発明の実施例で観察された結晶粒界上のＣ１５Ｌａｖｅｓ相のＦＥ−ＳＥＭ像と同一視野のＶ成分面分析像を示す図面代用写真である。
【図４】 比較例で観察された結晶粒内の針状α−Ｔｉ析出物のＦＥ−ＳＥＭ像と同一視野のＴｉ成分面分析像を示す図面代用写真である。
【図５】 本発明の実施例と比較例のＸ線回折パターンを示す図である。
【図６】 本発明の実施例と比較例の（１１０）面のＸ線回折強度と結晶粒内の針状α−Ｔｉ析出量の相関図である。
【図７】 本発明の実施例と比較例の平衡水素圧力−水素吸収量−等温曲線を示す図である。
【図８】 本発明の実施例と比較例の初期活性化の水素吸蔵量−時間曲線を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hydrogen storage alloy used for a hydrogen storage / supply material, a heat conversion material, a negative electrode material for a Ni-hydrogen battery, a hydrogen purification and recovery material, a hydrogen absorption material for a hydrogen gas actuator, and the like. The present invention relates to a heat treatment method, and particularly relates to an alloy having excellent characteristics at an environmental temperature (20 ° C. to 80 ° C.).
[0002]
[Prior art]
The hydrogen storage alloy reacts reversibly with hydrogen and has a hydrogen absorption / release characteristic that involves the entry and exit of reaction heat. In recent years, utilization of this phenomenon as a material for heat conversion such as a hydrogen storage material or a heat pump / refrigeration system has been actively promoted. As typical hydrogen storage alloys, LaNi 5 , TiFe, TiMn 1.5 and the like are well known.
[0003]
In the practical application of various applications, it is necessary to further improve the characteristics of the hydrogen storage material.For example, increasing the amount of hydrogen storage, lowering the cost of raw materials, improving the plateau characteristics, improving the durability, etc. As mentioned. Among them, metals of body-centered cubic structure (hereinafter referred to as BCC structure) such as V, TiMnV system, TiCrV system, etc. have a large amount of hydrogen (400 cc / g) compared with the hydrogen storage alloys of the intermetallic compounds already in practical use. Has been known for a long time. However, the amount of hydrogen that can be effectively occluded / released is about half that amount, and the remaining amount remains as a solid solution phase combined with hydrogen. Also, compared to hydrogen storage alloys of intermetallic compounds, the reaction rate required to absorb and release hydrogen is slow, and it has been difficult to activate, so it has not been put to practical use, so improvement in activation, plateau characteristics, durability, etc. There are many things to do. For these problems, improvement measures have been proposed in
[0004]
However, the desired property of the hydrogen storage material is that it absorbs and releases a large amount of hydrogen easily at an appropriate temperature. To meet this demand, in the alloy properties of hydrogen storage alloys, hydrogen Accelerates the reaction rate, reduces the slope of the plateau region of the equilibrium hydrogen pressure-hydrogen absorption-isotherm curve, and controls the equilibrium hydrogen pressure value in the plateau region to a pressure range allowed by a system using a hydrogen storage alloy However, it is necessary to increase the amount of effective hydrogen transfer within the pressure range.
In order to improve such alloy characteristics, development of a manufacturing method employing a heat treatment method has been promoted (for example, Patent Document 3) in addition to methods such as changing the constituent component ratio of the alloy or replacing some other elements. Yes. In this method, hydrogen is controlled by controlling the heat treatment conditions to control the microstructure of the alloy, particularly the modulation structure of the BCC structure as the parent phase, within the design range of the components that are considered to have a BCC structure single phase or a BCC structure main phase. We are trying to improve the amount of occlusion and the rate of hydrogen absorption / release.
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-110225 (page 2)
[Patent Document 2]
Japanese Patent Laid-Open No. 11-106859 (page 2)
[Patent Document 3]
Japanese Patent Laid-Open No. 10-245663 (2nd page)
[0006]
[Problems to be solved by the invention]
In the improvement of alloy properties using conventional heat treatment methods, we are trying to improve the hydrogen storage capacity and hydrogen absorption / release rate by controlling the modulation structure of the BCC structure, which is the parent phase. Compared to the original hydrogen storage alloy with BCC structure, it is much improved. However, in these conventional technologies, the nano-order microstructure is controlled by controlling the composition of components and heat treatment. However, in the actual manufacturing process, there are environmental problems in the melting and heat treatment facilities, and therefore micro-order microstructure control is assumed. However, no such prior art has been developed.
[0007]
In the TiCrV-based alloy that is the subject of the present invention, it is known that α-Ti different from the BCC structure precipitates due to the incorporation of a small amount of oxygen during melting, and the TiCrV-based alloy has a component ratio close to the composition of TiCr 2. Then, there is a concern about equilibrium precipitation of the C15 Loves phase at a temperature lower than around 1000 ° C. The present inventors have confirmed that these heterophasic precipitations greatly depend on the amount of oxygen and the holding temperature, holding time, and cooling rate of the heat treatment conditions, and the TiCrV system having a component ratio that has been considered to be a single BCC structure single phase. It has been found that the volume ratio of the alloy in a different phase increases to about 10% by volume depending on the heat treatment conditions.
[0008]
Further, it has been found that depending on the cleanliness in the heat treatment furnace, a region of the BCC structure deviating from the design composition is formed in the vicinity of the surface of the alloy due to the effect of surface oxidation, which deteriorates the hydrogen storage characteristics of the alloy. In order to suppress the problems pointed out so far and to control the microstructure on the nano order with the manufacturing method of the prior art, an extremely high vacuum melting and heat treatment facility is required, which is not practical in terms of commercial production. Furthermore, in the prior art, the cooling process of the heat treatment is preferably a quenching process such as a quenching process with water or oil. However, according to the study by the present inventors, the quenching process is carried out inside the TiCrV alloy having a BCC structure, particularly in the crystal grains. When the treatment is applied, the amount of acicular α-Ti deposited exceeds 2% by volume, and it has been found that many nucleation occurs, and the acicular α-Ti in the crystal grains consistent with the BCC structure is found. Existence may adversely affect the hydrogen storage characteristics of the alloy, mainly the amount of effective hydrogen transfer, the reaction rate of hydrogen absorption / release, and durability. In addition, it is known that excessive precipitation of the C15 Loves phase causes deterioration of the hydrogen storage characteristics of the TiCrV-based alloy having the BCC structure, in particular, a decrease in the effective hydrogen transfer amount. Is thinly present on the grain boundary of the parent phase crystal grains of the BCC structure, it has been found that the reaction rate of hydrogen absorption / release of the alloy is accelerated without reducing the effective hydrogen transfer amount. However, there is no example in which such a micro-order structure control is attempted in the prior art of a TiCrV alloy having a BCC structure.
[0009]
The present invention solves the conventional problems as described above, and performs an extremely high-temperature homogenization heat treatment at 1200 ° C. to just below the melting point in an inert gas atmosphere or a reducing gas atmosphere such as hydrogen gas or under vacuum. After that, by adopting a slow cooling process using a cooling rate of 200 ° C./hour or less in an inert gas atmosphere or a reducing gas atmosphere such as hydrogen gas or under vacuum, the precipitate is precipitated in the crystal grains of the BCC structure. It suppresses excessive precipitation of α-Ti and moves or discharges α-Ti precipitated in the crystal grains to the crystal grain boundary to maintain or increase the hydrogen storage amount of the crystal grains of the BCC structure. An object of the present invention is to provide a high-capacity hydrogen storage alloy heat treatment method that accelerates the reaction rate of activation and hydrogen absorption / release by precipitating a thin C15 Laves phase, and a hydrogen storage alloy having the above-described structure.
[0010]
[Means for Solving the Problems]
To achieve the above object, the invention of
However, a is set to 20-45 atomic weight%, b is set to 30-70 atomic weight%, c is set to 5-45 atomic weight%, d is set to 0-15 atomic weight%, and M is Fe, Al, Cu, Ni, Mo. One type or two or more types.
[0011]
Heat treatment method of the hydrogen storage alloy of
However, a is set to 20-45 atomic weight%, b is set to 30-70 atomic weight%, c is set to 5-45 atomic weight%, d is set to 0-15 atomic weight%, and M is Fe, Al, Cu, Ni, Mo. One type or two or more types.
[0012]
According to a third aspect of the present invention, there is provided a method for heat-treating a hydrogen storage alloy according to the second aspect of the present invention, wherein the raw material of the alloy contains ferrovanadium.
[0013]
The heat treatment method for a hydrogen storage alloy according to claim 4 is the invention according to
[0014]
That is, according to the heat treatment method of the present invention, after the homogenization heat treatment, the temperature is lowered to the mixed phase region of the BCC structure phase and the C15 Loves phase at a cooling rate of 10 to 200 ° C./hour. Precipitation is suppressed, the crystal integrity of the BCC structure is improved, the amount of effective hydrogen transfer is increased, and the C15 Loves phase is thinly deposited on the grain boundaries, so that during initial activation and hydrogen absorption / release The C15 Loves phase is utilized as a short-circuit path for hydrogen transfer to the main phase of the BCC structure, and the reaction rate of hydrogen absorption / release is accelerated. As a result, it is possible to provide a high-capacity hydrogen storage alloy having excellent characteristics at ambient temperatures (20 ° C. to 80 ° C.) when used in various applications.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Below, it explains in detail including the reasons for limiting the components and heat treatment conditions in the present invention.
In the present invention, as described above, one or more of Fe, Al, Cu, Ni, and Mo are added as additive elements to the ternary alloy containing Ti, Cr, and V as constituent elements, or Ti, Cr, and V. It is made of a multi-component alloy and has a BCC structure main phase (the BCC structure phase is 80 volume% or more, preferably 90 volume% or more) as a crystal structure. If the crystal structure is other than this, good hydrogen storage characteristics cannot be obtained.
[0016]
Ti: 20-45 atomic weight%
If the composition ratio of Ti is less than 20 atomic weight%, initial activation becomes difficult, and the hydrogen storage amount decreases, making it impractical. On the other hand, if the Ti composition ratio exceeds 45 atomic weight%, the plateau characteristics deteriorate, so the Ti composition ratio is set within the above range. For the same reason, it is desirable that the lower limit is 25 atomic weight% and the upper limit is 40 atomic weight%.
[0017]
Cr: 30-70 atomic weight%
If the Cr composition ratio is less than 30 atomic weight%, the plateau characteristics deteriorate, and if it exceeds 70 atomic weight%, the hydrogen storage amount and hydrogen release amount decrease, so the Cr composition ratio is within the above range. For the same reason, it is desirable that the lower limit is 40 atomic weight% and the upper limit is 60 atomic weight%.
[0018]
V: 5-45 atomic weight%
V is added as an element that substitutes a part of Cr as a stabilizing element of the BCC structure. When the composition ratio of V is less than 5 atomic%, the composition range in which the BCC structure can be stabilized is narrowed, and it becomes difficult to maintain the main phase of the alloy in the BCC structure during the manufacturing process, and the hydrogen storage amount decreases. On the other hand, if the V composition ratio exceeds 45 atomic weight%, the stability of hydrogen in the alloy is remarkably increased and is not practical, so the V composition ratio is within the above range.
[0019]
M group (one or more of Fe, Al, Cu, NI, and Mo): TiCrV alloy having a main phase of 0 to 15 atomic weight% BCC structure is reversible to a face-centered cubic structure (FCC structure) when storing hydrogen To metamorphosis. Fe, Al, Cu, Ni, and Mo are the plateau characteristics of TiCrV-based alloys having the main phase of the BCC structure, especially the purpose of adjusting the hydrogen equilibrium pressure during absorption and release or the increase or decrease in stacking fault energy of the FCC structure during hydrogen storage It is added as desired for the purpose of improving durability. However, excessive addition of Fe, Al, Cu, Ni, and Mo adversely affects the alloy characteristics such as reduction of the hydrogen storage amount, so the composition ratio of Fe, Al, Cu, Ni, and Mo is within the above range.
[0020]
Homogenization heat treatment temperature (1200 ℃-melting point)
In general, the BCC structure of a TiCrV alloy is a high temperature equilibrium phase, and in order to eliminate and solidify the solidification segregation of each component formed during melting and casting, particularly the dendritic solidification segregation of the Ti component and the V component, Homogenization heat treatment in a stable high temperature region of the BCC structural phase is required. In particular, in order to allow constituent elements to move throughout the alloy in a short time, a high temperature of at least 1200 ° C. and below the melting point is required, depending on the composition of the alloy. The upper limit is desirably set to a
[0021]
In the heat treatment method of the present invention, there is no particular restriction on the temperature raising process up to the above temperature, but the temperature raising rate is preferably 600 ° C./hour or less in order to reduce the burden on the heat treatment furnace.
In addition, about the structure of the heating furnace used for the said heat processing, this invention is not specifically limited, The existing heating furnace etc. can be used.
[0022]
Homogenization heat treatment time (1-24 hours)
In order to obtain a sufficient homogenizing effect, a holding time of 1 hour or more is required. On the other hand, since the effect is saturated even if it is maintained for more than 24 hours, the homogenization heat treatment is performed within the range of 1 to 24 hours.
[0023]
In the inert gas atmosphere or the reducing gas atmosphere or under vacuum, the hydrogen storage alloy in the present invention contains V having a high oxygen content in the raw material, so the oxygen content in the alloy cannot be ignored. Even when ferrovanadium is used as a raw material, the oxygen content in the alloy increases. Furthermore, when oxygen is mixed in the heat treatment furnace used for the homogenization heat treatment, there is a wide range of BCC structures that deviate from the component composition designed together with Ti oxide, Cr oxide and coarse α-Ti near the alloy surface. As a result, the maximum hydrogen occlusion amount and effective hydrogen transfer amount are reduced, which adversely affects the alloy characteristics. Therefore, it is necessary to sufficiently cut and remove the alloy surface, resulting in a decrease in working efficiency and a yield. On the other hand, the inside of the heat treatment furnace is an inert gas atmosphere or a reducing gas atmosphere such as hydrogen or vacuum (for example, 1 × 10 −1 Torr or less, and the pressure under vacuum is 1 × 10 −6 Torr or more in consideration of industrial properties. It is possible to control the amount of oxygen mixed in the furnace during the homogenization heat treatment and the subsequent cooling, preventing the surface oxidation of the hydrogen storage alloy and requiring the above cutting work. It is possible to obtain good alloy characteristics without any problems.
[0024]
Cooling rate (10 ° C to 200 ° C / hour)
Control of the cooling rate is extremely important in controlling the precipitation frequency of α-Ti precipitated in the crystal grains of the BCC structure. In a rapid cooling treatment such as a quenching treatment with water or oil from the homogenization heat treatment temperature, a large number of fine acicular α-Ti precipitates in the crystal grains. In order to suppress such precipitation of α-Ti, the cooling rate in the temperature lowering process must be suppressed as much as possible within the allowable range of alloy production. In addition, since the C15 Loves phase exists as a low temperature equilibrium phase in the temperature range of the TiCrV-based alloy from room temperature to 1100 ° C., it constitutes a mixed phase region of the BCC structural phase and the C15 Loves phase. In order to deposit a small amount of C15 Laves phase that cannot be detected or identified by X-ray diffraction thinly on the grain boundary, it is necessary to set the cooling rate in the temperature-falling process within the above range. It is necessary to maintain within the above range until reaching the area. There is no special restriction in the temperature lowering process after reaching the multiphase region. Accordingly, the cooling rate may be maintained within the above range as it is, and thereafter, cooling may be performed at a cooling rate that deviates from the range.
However, α-Ti, which is considered to have an adverse effect on the hydrogen storage characteristics, is a second phase that can be precipitated even in the temperature range of the mixed phase region of the BCC structural phase and the C15 Loves phase. Therefore, it is desirable to control to room temperature at an optimal temperature drop rate.
[0025]
In addition, since the above cooling rate is adopted, there is no need for quenching such as quenching with water or oil, there is no opportunity for the alloy to come into contact with the atmosphere at high temperatures, and extra oxygen is mixed into the alloy as much as possible. It can be suppressed. Furthermore, since no rapid cooling treatment is required, no equipment for rapid cooling treatment is required, and capital investment and alloy production costs can be reduced, which is advantageous in terms of commercial production.
[0026]
Use of raw material ferrovanadium (alloy containing V and Fe as main components) When adopting raw material ferrovanadium in a form that strictly observes the above composition range, the effect of reducing the alloy manufacturing cost is extremely large. However, since there is a trace amount of unintentional impurity elements due to a deoxidizer or the like at the time of dissolution, inconveniences such as fluctuations in the maximum hydrogen storage amount occur. However, when ferrovanadium is employed in a form that strictly observes the composition range, the fluctuation of the maximum hydrogen storage amount is suppressed to a small extent, and the same improvement in alloy characteristics can be obtained by applying the heat treatment method of the present invention.
[0027]
In the present invention, the melting method of the hydrogen storage alloy is not particularly limited, and various melting methods such as arc melting method and high frequency induction melting method can be applied, but the method of heat treatment of the hydrogen storage alloy of the present invention is adopted. In order to reliably obtain the effect of improving the alloy characteristics, the melting is performed in an inert gas atmosphere or in a vacuum of 1 × 10 −1 to 1 × 10 −6 Torr in order to prevent deterioration of the alloy characteristics due to mixing of a large amount of oxygen. It is desirable that
In addition, since the solidification segregation width and concentration fluctuation value change depending on the alloy structure such as crystal grains formed in the melting and solidification process, sufficient solidification area for the alloy, such as the contact area with the mold against the alloy weight, is secured. Thus, it is desirable to obtain a sufficient cooling rate.
[0028]
【Example】
Examples of the present invention will be described below with reference to the drawings. 50 g of an alloy having the composition shown in Table 1 was prepared by mixing the raw materials with the basic component ratios of Ti: 30 atomic weight%, Cr: 50 atomic weight%, and V: 20 atomic weight% and melting in an arc melting furnace in an argon atmosphere. Was made. Next, using an argon atmosphere heat treatment furnace, the temperature was raised at a temperature rising rate of 550 ° C./hour, subjected to a homogenizing heat treatment at 1400 ° C. for 3 hours, and cooled to room temperature in the furnace at a cooling rate of 30 ° C./hour. . The obtained hydrogen storage alloy was used as a measurement sample as an example of the present invention. In addition, for comparison, the basic constituent ratios are as follows: Ti: 30 atomic weight%, Cr: 50 atomic weight%, and V: 20 atomic weight%. 50 g of the alloy was heated at a rate of temperature increase of 550 ° C./hour using an argon atmosphere heat treatment furnace, and subjected to water quenching treatment by homogenization heat treatment at 1400 ° C. for 3 hours. The obtained hydrogen storage alloy was used as a measurement sample as a comparative example. The cooling rate during the water quenching process is approximately 3.6 × 10 5 ° C./hour.
[0029]
[Table 1]
Part of each of the above measurement samples is pulverized to about 200 mesh or less and used for alloy analysis by X-ray diffractometry, and the other part is pulverized to a range of about 50 to 200 mesh and hydrogen in a hydrogen gas atmosphere. It was used for absorption / release measurement (P (hydrogen pressure) -C (composition) -T (temperature) measurement). The remaining alloy lump was used as an observation sample for optical microscope observation and electrolytic emission scanning electron microscope observation (FE-SEM observation).
[0031]
First, about the observation sample of an Example and a comparative example, the optical microscope observation was implemented and the precipitation condition of acicular (alpha) -Ti in a crystal grain was investigated. FIG. 1 shows an optical micrograph of the example, and FIG. 2 shows an optical micrograph of the comparative example. In the examples, the amount of coarse acicular α-Ti was suppressed to a certain level. On the other hand, in the comparative example, a large amount of fine acicular α-Ti was precipitated.
[0032]
Moreover, in order to confirm the property of the precipitate observed in the Example and the comparative example, the surface analysis by the energy dispersive X-ray spectroscopic analysis (EDS analysis) of FE-SEM was implemented. FIG. 3 shows the surface analysis result of the V component of the C15 Laves phase existing on the grain boundary observed in the example, and FIG. 4 shows the Ti component of acicular α-Ti existing in the crystal grain observed in the comparative example. The surface analysis results are shown. The C15 Loves phase on the grain boundary observed in the Examples accounted for 90% by volume or more of the total amount of the precipitated C15 Loves phase. Further, the component ratio of Ti and Cr in the C15 Laves phase on the crystal grain boundary was almost the same as that of the BCC structure phase of the parent phase, but the V component was deficient in comparison with the BCC structure phase inside the crystal as shown in FIG. Turned out to be. As shown in FIG. 4, the acicular α-Ti in the crystal grains observed in the comparative example was found to be enriched in Ti at an extremely higher concentration than the BCC structure phase, and was about 75 to 95 atomic weight%. Ti was present.
[0033]
Further, the crystal structures of the measurement samples of Examples and Comparative Examples were examined by X-ray diffraction method, respectively. At this time, CuKα rays were used as the X-rays. FIG. 5 shows the measurement results of the example and the comparative example. Both X-ray diffraction peaks observed in FIG. 5 are of the BCC structure phase, and the presence of the heterogeneous phase was not clear by the X-ray diffraction method. In the example, as shown in FIG. 5, the crystal perfection of the BCC structure phase was improved by the heat treatment of the present invention, and the diffraction intensity of the BCC structure phase was increased as compared with the comparative example. In addition, the lattice constant of the BCC structure phase of an Example and a comparative example is a substantially equal value.
[0034]
FIG. 6 shows the correlation between the diffraction intensity of the (110) peak of the BCC structural phase obtained by the X-ray diffraction method and the precipitation amount of acicular α-Ti in the crystal grains. As shown in FIG. 6, in the example, the precipitation amount is decreased and the diffraction intensity is increased as compared with the comparative example, so that the BCC structure phase is suppressed by suppressing the precipitation amount of acicular α-Ti in the crystal grains. It has been demonstrated that the crystal integrity of can be improved.
[0035]
Next, an equilibrium hydrogen pressure-hydrogen absorption amount-isothermal curve was determined for the examples and comparative examples. FIG. 7 shows curves of the example and the comparative example. In the example, as shown in FIG. 7, the hydrogen occlusion amount increased and the plateau region was flattened as compared with the comparative example due to the suppression of acicular α-Ti precipitation in the crystal grains of the BCC structure by the heat treatment of the present invention.
[0036]
Further, for the examples and comparative examples, initial activated hydrogen storage amount-time curves were obtained. FIG. 8 shows curves of the example and the comparative example. In the example, as shown in FIG. 8, the hydrogen storage is started soon after the initial activation is performed due to the minute grain boundary precipitation of the C15 Loves phase, and the activation rate is very fast, but in the comparative example, the hydrogen storage is started. It takes a certain amount of time, and it can be seen that the activation rate is slower than in the examples even after the start of hydrogen storage.
[0037]
As described in the above examples, in the TiCrV-based hydrogen storage alloy having the main phase of the BCC structure and the C15 Loves phase as the low-temperature equilibrium phase, by performing the heat treatment method of the present invention, By suppressing the excessive precipitation of α-Ti that precipitates in the crystal, moving and discharging α-Ti precipitated in the crystal grains to the crystal grain boundary, and further depositing a thin C15 Laves phase in the crystal grain boundary, Can be maintained or increased, the reaction rate of activation and hydrogen absorption / release can be accelerated, and a hydrogen storage alloy having excellent practicality can be obtained.
[0038]
Next, Table 2 shows heat treatment cooling conditions and effective hydrogen transfer amounts of various alloys subjected to the heat treatment of the present invention and various alloys subjected to water quenching. In addition, the component ratio of the alloy described in Table 2 is within the composition range described in the present invention, and the BCC structure is the main phase in all alloys. In addition, all the alloys were heated at a heating rate of 550 ° C./hour using an argon atmosphere heat treatment furnace and subjected to homogenization heat treatment at 1400 ° C. for 3 hours. As shown in Table 2, the amount of effective hydrogen transfer increased in the alloy subjected to the heat treatment of the present invention as compared with the alloy subjected to the water quenching treatment with the same component ratio.
[0039]
[Table 2]
【The invention's effect】
As described above, according to the present invention, activation of the TiCrV-based hydrogen storage alloy having the main phase of the BCC structure, which has been difficult to achieve by the conventional method, an increase in the hydrogen storage / release reaction rate, and the hydrogen storage amount Improvements in alloy properties, such as an increase, can be achieved without capital investment for rapid cooling and the like and an increase in alloy production costs. As a result, the hydrogen storage alloy of the present invention can be inexpensive and increase the production volume while having practical characteristics. In particular, the performance of the hydrogen storage system utilizing reversible hydrogen storage and release can be improved. The contribution to cost reduction is quite large.
[Brief description of the drawings]
FIG. 1 is a drawing-substituting photograph showing an optical micrograph of an example of the present invention.
FIG. 2 is a drawing-substituting photograph showing an optical micrograph of a comparative example.
FIG. 3 is a drawing-substituting photograph showing a V-component plane analysis image having the same field of view as an FE-SEM image of a C15 Laves phase on a grain boundary observed in an example of the present invention.
FIG. 4 is a drawing-substituting photograph showing a Ti component plane analysis image having the same field of view as an FE-SEM image of acicular α-Ti precipitates in crystal grains observed in a comparative example.
FIG. 5 is a diagram showing X-ray diffraction patterns of an example of the present invention and a comparative example.
FIG. 6 is a correlation diagram between the X-ray diffraction intensity of the (110) plane and the amount of acicular α-Ti precipitates in crystal grains in the examples of the present invention and comparative examples.
FIG. 7 is a graph showing an equilibrium hydrogen pressure-hydrogen absorption amount-isothermal curve of an example of the present invention and a comparative example.
FIG. 8 is a diagram showing hydrogen storage amount-time curves of initial activation of an example of the present invention and a comparative example.
Claims (4)
ただし、ａは２０〜４５原子量％、ｂは３０〜７０原子量％、ｃは５〜４５原子量％、ｄは０〜１５原子量％範囲に設定され、ＭはＦｅ、Ａｌ、Ｃｕ、Ｎｉ、Ｍｏの一種又は二種以上である。Formula: Ti a is represented by Cr b V c M d, wherein the C15Laves phase as a low-temperature equilibrium phase, together with the main phase consists BCC structure, the precipitation amount of the acicular alpha-Ti in the alloy grains 2 vol% or less And 80% by volume or more of the C15 Laves phase is present on the grain boundary.
However, a is set to 20-45 atomic weight%, b is set to 30-70 atomic weight%, c is set to 5-45 atomic weight%, d is set to 0-15 atomic weight%, and M is Fe, Al, Cu, Ni, Mo. One type or two or more types.
ただし、ａは２０〜４５原子量％、ｂは３０〜７０原子量％、ｃは５〜４５原子量％、ｄは０〜１５原子量％範囲に設定され、ＭはＦｅ、Ａｌ、Ｃｕ、Ｎｉ、Ｍｏの一種又は二種以上である。Formula: Ti a Cr b V c is represented by M d, wherein the C15Laves phase as a low-temperature equilibrium phase, the main phase in the heat treatment method of the hydrogen storage alloy consisting of BCC structure, after melting and casting of the alloy, of 1200 ° C. ~ mp Homogenization heat treatment in a range of 1 to 24 hours in an inert gas atmosphere or a reducing gas atmosphere or under vacuum at a temperature, and then at least a BCC structural phase in an inert gas atmosphere or a reducing gas atmosphere or under vacuum. A method for heat-treating a hydrogen storage alloy, wherein the temperature is lowered at a cooling rate of 10 ° C. to 200 ° C./hour until the temperature reaches a mixed phase region of a C15 Loves phase .
However, a is set to 20-45 atomic weight%, b is set to 30-70 atomic weight%, c is set to 5-45 atomic weight%, d is set to 0-15 atomic weight%, and M is Fe, Al, Cu, Ni, Mo. One type or two or more types.
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| KR101488195B1 (en) | 2014-04-24 | 2015-01-30 | 한국지질자원연구원 | Method for manufacturing titanium-based alloy using ferro-vanadium and titanium-based alloy manufactured thereof |
| KR20170007284A (en) * | 2014-05-14 | 2017-01-18 | 바스프 코포레이션 | Hydrogen storage multi-phase alloys |
| CN106086491A (en) * | 2016-07-07 | 2016-11-09 | 厦门理工学院 | A kind of Mg-based composite hydrogen storage material and preparation method thereof |
| CN109881075B (en) * | 2019-03-13 | 2020-07-14 | 内蒙古科技大学 | High-hydrogen-release-efficiency multi-phase hydrogen storage alloy and preparation method and application thereof |
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