JP7359381B2 - Hydrogen separation alloy - Google Patents
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- 239000001257 hydrogen Substances 0.000 title claims description 148
- 229910052739 hydrogen Inorganic materials 0.000 title claims description 148
- 229910045601 alloy Inorganic materials 0.000 title claims description 51
- 239000000956 alloy Substances 0.000 title claims description 51
- 238000000926 separation method Methods 0.000 title claims description 32
- 125000004435 hydrogen atom Chemical class [H]* 0.000 title 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 114
- 150000002431 hydrogen Chemical class 0.000 claims description 34
- 229910052742 iron Inorganic materials 0.000 claims description 11
- 239000012535 impurity Substances 0.000 claims description 6
- 239000000203 mixture Substances 0.000 claims description 4
- 239000006104 solid solution Substances 0.000 description 18
- 230000035699 permeability Effects 0.000 description 13
- 238000010438 heat treatment Methods 0.000 description 12
- 125000004429 atom Chemical group 0.000 description 9
- 238000000034 method Methods 0.000 description 9
- 230000007423 decrease Effects 0.000 description 8
- 229910052759 nickel Inorganic materials 0.000 description 8
- 238000005096 rolling process Methods 0.000 description 8
- 230000008018 melting Effects 0.000 description 7
- 238000002844 melting Methods 0.000 description 7
- 229910052751 metal Inorganic materials 0.000 description 7
- 239000002184 metal Substances 0.000 description 7
- 239000000446 fuel Substances 0.000 description 6
- 239000012528 membrane Substances 0.000 description 6
- 229910000765 intermetallic Inorganic materials 0.000 description 4
- 230000008569 process Effects 0.000 description 4
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 230000008094 contradictory effect Effects 0.000 description 3
- 238000005259 measurement Methods 0.000 description 3
- 229910001000 nickel titanium Inorganic materials 0.000 description 3
- 239000001301 oxygen Substances 0.000 description 3
- 229910052760 oxygen Inorganic materials 0.000 description 3
- 229910052719 titanium Inorganic materials 0.000 description 3
- 230000008901 benefit Effects 0.000 description 2
- 229910002091 carbon monoxide Inorganic materials 0.000 description 2
- 238000005266 casting Methods 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 239000011261 inert gas Substances 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 229910052758 niobium Inorganic materials 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 238000002407 reforming Methods 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 229910001316 Ag alloy Inorganic materials 0.000 description 1
- 229910000881 Cu alloy Inorganic materials 0.000 description 1
- 229910001257 Nb alloy Inorganic materials 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 230000002301 combined effect Effects 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005868 electrolysis reaction Methods 0.000 description 1
- 238000000921 elemental analysis Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 229910052735 hafnium Inorganic materials 0.000 description 1
- 238000005098 hot rolling Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000009776 industrial production Methods 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 239000002574 poison Substances 0.000 description 1
- 231100000614 poison Toxicity 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000001953 recrystallisation Methods 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 238000007711 solidification Methods 0.000 description 1
- 230000008023 solidification Effects 0.000 description 1
- 238000004544 sputter deposition Methods 0.000 description 1
- 238000005482 strain hardening Methods 0.000 description 1
- 229910052715 tantalum Inorganic materials 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 229910052726 zirconium Inorganic materials 0.000 description 1
Classifications
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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
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
Description
本発明は、高純度水素を得るために用いられる水素分離合金に関するものである。 The present invention relates to a hydrogen separation alloy used to obtain high purity hydrogen.
最近、クリーンエネルギーとして燃料電池が注目されている。燃料電池の燃料である水素ガスは自然界に多量に存在しないため人工的に作り出さなければならない。その方法の一つとして水の電気分解によって水素を得る方法があるが、現在の技術レベルではコストがかかりすぎるため、現在は化石資源の改質によって水素が製造されている。
しかし、この方法では水素と同時にＣＯ、ＣＯ２、Ｈ２Ｏ等の不純物ガスが発生する。特にＣＯは燃料電池の電極を被毒するため、化石資源の改質によって得られた水素を燃料電池で使用するためには、水素をこれらの不純物ガスから分離・精製して、高純度化しなければならない。
Recently, fuel cells have been attracting attention as a clean energy source. Hydrogen gas, the fuel for fuel cells, does not exist in large quantities in nature, so it must be produced artificially. One method is to obtain hydrogen by electrolysis of water, but it is too costly with the current level of technology, so hydrogen is currently produced by reforming fossil resources.
However, in this method, impurity gases such as CO, CO 2 and H 2 O are generated simultaneously with hydrogen. In particular, CO poisons fuel cell electrodes, so in order to use hydrogen obtained by reforming fossil resources in fuel cells, hydrogen must be separated and purified from these impurity gases to achieve high purity. Must be.
水素の精製方法としては金属膜を用いた膜分離法が簡便で且つ高純度な水素を得る方法として知られている。ここで用いられる水素分離膜には水素透過性能と耐水素脆性という相反する性質が求められている。この両者を満足し、現在実用化されている水素分離金属膜はＰｄ－Ａｇ合金膜、Ｐｄ－Ｃｕ合金膜等のＰｄ基合金である。しかし将来、燃料電池が広く使用されるようになれば、高価で希少なＰｄが制約となり、需要に対応することができないと予測される。したがってＰｄ基合金に替わる新たな金属膜材料の開発が必要とされている。 As a method for purifying hydrogen, a membrane separation method using a metal membrane is known as a simple method for obtaining highly pure hydrogen. The hydrogen separation membrane used here is required to have contradictory properties: hydrogen permeability and hydrogen embrittlement resistance. Hydrogen separation metal membranes that satisfy both of these requirements and are currently in practical use are Pd-based alloys such as Pd--Ag alloy membranes and Pd--Cu alloy membranes. However, if fuel cells become widely used in the future, it is predicted that the expensive and rare Pd will become a constraint and it will not be possible to meet the demand. Therefore, there is a need to develop new metal film materials to replace Pd-based alloys.
中でもＶ、Ｎｂ、Ｔａが単体で高い水素透過性能を有することに着目し、これらと他の金属、例えばＴｉ、Ｚｒ、Ｈｆ、Ｎｉ、Ｃｏ等とを複相合金化することで高い水素透過性能と耐水素脆性とを併せ持つ水素分離合金の開発が盛んに行われている。例えば、特開２００６－２７４２９７号公報（特許文献１）や特開２００５－２３２４９１号公報（特許文献２）で提案した水素透過性を担う相と耐水素脆化性を担う相との複合相からなるＮｉ－Ｔｉ－Ｎｂ系複相合金は注目を集めている。
また、特開２０１２－２５０２３４号公報（特許文献３）や特開２０１４－０７４２１１号公報（特許文献４）ではＮｂの高い水素透過能を活用する目的でＷを微量添加することで水素分離合金を提供しようという試みも広く知られている。
Among them, we focused on the fact that V, Nb, and Ta alone have high hydrogen permeability, and by forming a multi-phase alloy with these and other metals such as Ti, Zr, Hf, Ni, Co, etc., we have achieved high hydrogen permeability. Hydrogen separation alloys that have both hydrogen embrittlement resistance and hydrogen embrittlement resistance are being actively developed. For example, from the composite phase of a phase responsible for hydrogen permeability and a phase responsible for hydrogen embrittlement resistance proposed in JP2006-274297A (Patent Document 1) and JP2005-232491A (Patent Document 2), The Ni-Ti-Nb multi-phase alloy is attracting attention.
Furthermore, in JP-A No. 2012-250234 (Patent Document 3) and JP-A No. 2014-074211 (Patent Document 4), a hydrogen separation alloy is created by adding a small amount of W to take advantage of the high hydrogen permeability of Nb. Attempts to provide such services are also widely known.
上述した特許文献１及び２に開示される合金は、水素透過性能と耐水素脆性のバランスに優れるものの、実用化に当たっては更なる耐水素脆性の向上が求められていた。特許文献３に開示される合金は、水素透過性能に優れるＮｂを多量に含むため極めて高い水素透過性能を有するが、一方で耐水素脆性が極めて低く実用に耐えないという課題があった。特許文献４に開示される合金は、上記特許文献１～３の複合効果を狙った合金であるが、合金の熱間加工性に関してのみ開示されており、その水素透過性能と耐水素脆性に関しては全く不明であった。
本発明の目的は、水素分離合金において耐水素脆性が高く耐久性に優れる水素分離合金を提供することである。
Although the alloys disclosed in Patent Documents 1 and 2 described above have an excellent balance between hydrogen permeability and hydrogen embrittlement resistance, further improvement in hydrogen embrittlement resistance has been required for practical use. The alloy disclosed in Patent Document 3 has extremely high hydrogen permeation performance because it contains a large amount of Nb, which has excellent hydrogen permeation performance, but on the other hand, there was a problem in that it had extremely low hydrogen embrittlement resistance and was not suitable for practical use. The alloy disclosed in Patent Document 4 is an alloy aiming at the combined effects of Patent Documents 1 to 3 above, but it is only disclosed regarding the hot workability of the alloy, and the hydrogen permeation performance and hydrogen embrittlement resistance are disclosed. It was completely unclear.
An object of the present invention is to provide a hydrogen separation alloy that has high hydrogen embrittlement resistance and excellent durability.
本願発明者は、既存のＮｂ合金の水素脆化の原因を詳細に調査し、その水素固溶量が極めて大きいために水素脆化しやすくなっていることを見出した。さらに一般に相反するとされる水素透過性能を低下させることなく、合金の水素固溶量を低減し耐水素脆性を改善する添加元素について鋭意検討を行い、本発明に到達した。
すなわち本発明は、原子比における組成式：Ｎｂ１００－（α＋β＋γ＋δ）ＴｉαＮｉβＷγＦｅδ（１０≦α≦６０、１０≦β≦５０、０．５≦γ≦１０、０．５≦δ≦１０、α＋β＋δ≦９０、不純物を含む）で表される水素分離合金において、該水素分離合金は、Ｎｂ－Ｔｉ－Ｗ相でなる水素透過相と（Ｎｉ，Ｆｅ）－Ｔｉ相でなる耐水素脆性相との二相でなる水素分離合金である。
好ましくは、前記組成式において３≦γ≦７である。
The inventors of the present application investigated in detail the cause of hydrogen embrittlement in existing Nb alloys, and found that hydrogen embrittlement easily occurs because the amount of hydrogen in solid solution is extremely large. Furthermore, we have conducted intensive studies on additive elements that reduce the amount of hydrogen solid solution in the alloy and improve hydrogen embrittlement resistance without reducing the hydrogen permeation performance, which is generally considered to be contradictory, and have arrived at the present invention.
That is, the present invention has a composition formula in atomic ratio: Nb 100-(α+β+γ+δ) Ti α Ni β W γ Fe δ (10≦α≦60, 10≦β≦50, 0.5≦γ≦10, 0.5≦ δ≦10, α+β+δ≦90 (including impurities), the hydrogen separation alloy has a hydrogen-permeable phase consisting of a Nb-Ti-W phase and a (Ni,Fe)-Ti phase. It is a hydrogen separation alloy consisting of two phases, a hydrogen brittle phase and a hydrogen brittle phase.
Preferably, in the compositional formula, 3≦γ≦7.
本発明の水素分離合金は水素固溶量が少なく耐水素脆性に優れているため、耐久性に優れる水素分離合金を提供することができる。また本発明は耐水素脆性と相反する性質である水素透過性能についても公知の水素分離合金と同等以上の特性を有しており、優れた水素分離合金として利用ができる。 Since the hydrogen separation alloy of the present invention has a small amount of hydrogen in solid solution and is excellent in hydrogen embrittlement resistance, it is possible to provide a hydrogen separation alloy with excellent durability. Furthermore, the present invention has properties equivalent to or better than known hydrogen separation alloys in terms of hydrogen permeability, which is a property contradictory to hydrogen embrittlement resistance, and can be used as an excellent hydrogen separation alloy.
上述したように、本発明の重要な特徴は水素固溶量を低下させて耐水素脆性を向上させながら、水素透過性能を従来材同等以上となるような合金成分を見出したことにある。すなわち本発明の水素分離合金は、原子比における組成式が「Ｎｂ１００－（α＋β＋γ＋δ）ＴｉαＮｉβＷγＦｅδ（１０≦α≦６０、１０≦β≦５０、０．５≦γ≦１０、０．５≦δ≦１０、α＋β＋δ≦９０、不純物を含む）」で表される合金組成を有する。
本発明の水素分離合金において、上記の範囲で各化学組成を規定した理由は以下の通りである。なお、特に記載のない限り原子％として記す。
As mentioned above, an important feature of the present invention is the discovery of an alloy component that lowers the amount of hydrogen solid solution and improves hydrogen embrittlement resistance while providing hydrogen permeation performance equal to or higher than that of conventional materials. That is, the hydrogen separation alloy of the present invention has a compositional formula in atomic ratio of "Nb 100-(α+β+γ+δ) Ti α Ni β W γ Fe δ (10≦α≦60, 10≦β≦50, 0.5≦γ≦10 , 0.5≦δ≦10, α+β+δ≦90, including impurities).
In the hydrogen separation alloy of the present invention, the reason why each chemical composition is defined within the above range is as follows. In addition, it is expressed as atomic % unless otherwise specified.
Ｎｂは本発明合金においてＮｂ－Ｔｉ－Ｗ相を形成し、水素透過性能を担う元素である。特に高い水素透過能を得るためのＮｂの含有量としては、１００－（α＋β＋γ＋δ）として１０原子％以上となることが好ましい。本発明の水素分離合金はＮｂ－Ｔｉ－Ｗ相と（Ｎｉ，Ｆｅ）Ｔｉ相の二相でなる合金であり、ＷはＮｂとともにＮｂ－Ｔｉ－Ｗ相を形成するため、実質的には（Ｎｉ，Ｆｅ）Ｔｉ相を形成するα＋β＋δの総和が重要である。十分な（Ｎｉ，Ｆｅ）Ｔｉ相を形成するに必要なα＋β＋δの総和の上限は９０原子％以下であることが好ましく、８５原子％以下であることがより好ましく、８０原子％以下であることがさらに好ましい。特に、好ましいα＋β＋δの総和は５０～７０％の範囲である。Ｎｂを過度に含む場合、水素透過性能は向上するものの、耐水素脆性が著しく低下するだけでなく、合金の融点が大きく上昇するため工業的な生産が極めて困難になることから、上述の範囲とした。 Nb is an element that forms a Nb-Ti-W phase in the alloy of the present invention and is responsible for hydrogen permeation performance. In order to obtain particularly high hydrogen permeability, the Nb content is preferably 10 atomic % or more as 100-(α+β+γ+δ). The hydrogen separation alloy of the present invention is an alloy consisting of two phases, the Nb-Ti-W phase and the (Ni,Fe)Ti phase, and since W forms the Nb-Ti-W phase together with Nb, substantially ( The sum of α+β+δ forming the Ni, Fe)Ti phase is important. The upper limit of the sum of α + β + δ necessary to form a sufficient (Ni, Fe) Ti phase is preferably 90 atomic % or less, more preferably 85 atomic % or less, and preferably 80 atomic % or less. More preferred. In particular, the preferred sum of α+β+δ is in the range of 50 to 70%. If too much Nb is contained, hydrogen permeation performance will improve, but not only will the hydrogen embrittlement resistance be significantly reduced, but the melting point of the alloy will also greatly increase, making industrial production extremely difficult. did.
Ｔｉは主にＮｉ、Ｆｅとともに（Ｎｉ，Ｆｅ）Ｔｉ相を形成し、本合金の耐水素脆性を担う働きを有する。このため、Ｔｉ量はＮｉ量とのバランスで決定されるものであり、その上限は、上述したとおりα＋β＋δで９０原子％以下である。またＴｉについてはＮｂ－Ｔｉ－Ｗ相にも少量含まれる元素であることから、α≧βとなることが好ましい。Ｔｉを過度に含む場合、ＮｉＴｉ２に代表される金属間化合物を形成しやすくなり、耐水素脆性が低下する。またＴｉが少なくなるにつれて（Ｎｉ，Ｆｅ）Ｔｉ相の量が低下し、耐水素脆性が低下するだけでなく、特にＴｉ量がＮｉ量よりも少なくなる場合、後述するようにＮｉを主体とした金属間化合物を形成し、耐水素脆性が大きく低下する要因となるため、Ｔｉの含有量は１０原子％以上６０原子％以下とした。 Ti mainly forms a (Ni, Fe)Ti phase together with Ni and Fe, and has the function of contributing to the hydrogen embrittlement resistance of this alloy. Therefore, the amount of Ti is determined by the balance with the amount of Ni, and its upper limit is 90 atomic % or less for α+β+δ as described above. Further, since Ti is an element that is also contained in a small amount in the Nb-Ti-W phase, it is preferable that α≧β. When Ti is contained excessively, intermetallic compounds such as NiTi 2 are likely to be formed, resulting in a decrease in hydrogen embrittlement resistance. Furthermore, as the amount of Ti decreases, the amount of the (Ni, Fe)Ti phase decreases, and not only does the hydrogen embrittlement resistance decrease, but especially when the amount of Ti is less than the amount of Ni, as will be described later, Since Ti forms an intermetallic compound and becomes a factor that significantly reduces hydrogen embrittlement resistance, the content of Ti is set to 10 atomic % or more and 60 atomic % or less.
Ｎｉは上述したようにＴｉ、Ｆｅとともに（Ｎｉ，Ｆｅ）Ｔｉ相を形成して本合金の耐水素脆性を担う働きを有する。このためＮｉ量はＴｉ量とのバランスで決定する。Ｎｉ量が過度に多くなるとＮｉ量を主体とする金属間化合物が形成し、耐水素脆性を低下させる。また一方、Ｎｉ量が少なくなるとＮｉＴｉ２に代表される金属間化合物を形成するだけでなく、塑性加工プロセス（例：圧延）において、加工性を低下させ、工業生産性が低下する。このためＮｉの含有量は１０原子％以上５０原子％以下とする。 As mentioned above, Ni forms a (Ni, Fe)Ti phase together with Ti and Fe, and has the function of contributing to the hydrogen embrittlement resistance of the present alloy. Therefore, the amount of Ni is determined in balance with the amount of Ti. When the amount of Ni increases excessively, an intermetallic compound mainly composed of the amount of Ni is formed, reducing the hydrogen embrittlement resistance. On the other hand, when the amount of Ni decreases, it not only forms intermetallic compounds such as NiTi 2 but also reduces workability in plastic working processes (eg, rolling) and reduces industrial productivity. For this reason, the Ni content is set to 10 atomic % or more and 50 atomic % or less.
Ｗは本発明においてＮｂ－Ｔｉ－Ｗ相を形成する元素である。本発明の水素分離合金において、水素は主にＮｂ－Ｔｉ－Ｗ相に固溶し、拡散していくことで水素分離現象が達成される。この時、ＷはＮｂ－Ｔｉ－Ｗ相の水素固溶量を低下させる働きを有している。一般に水素脆化は合金中に固溶した拡散性水素によって引き起こされる現象であり、水素固溶量が低下すれば耐水素脆性が向上することは言うまでもない。水素固溶量低減の効果を得るためには０．５原子％以上のＷを含むことが必要であり、より好ましくは１原子％以上含むことが良い。さらに好ましくは３原子％以上であり、特に好ましくは５原子％以上である。一方、Ｗは水素固溶を阻害する元素でもあり、過度に含む場合には水素透過性能が減少する可能性がある。またＷは極めて高融点の金属であることから、過剰な添加はＷの溶け残りを生じさせ、合金の均一性に悪影響を与える虞がある。このため、Ｗの上限は１０原子％とする。好ましい上限は７原子％である。 W is an element that forms a Nb-Ti-W phase in the present invention. In the hydrogen separation alloy of the present invention, hydrogen mainly forms a solid solution in the Nb-Ti-W phase and diffuses to achieve the hydrogen separation phenomenon. At this time, W has the function of reducing the amount of hydrogen solid solution in the Nb-Ti-W phase. Generally, hydrogen embrittlement is a phenomenon caused by diffusible hydrogen dissolved in solid solution in an alloy, and it goes without saying that the hydrogen embrittlement resistance improves as the amount of hydrogen in solid solution decreases. In order to obtain the effect of reducing the amount of hydrogen in solid solution, it is necessary to contain W in an amount of 0.5 atomic % or more, more preferably 1 atomic % or more. More preferably, it is 3 atom % or more, particularly preferably 5 atom % or more. On the other hand, W is also an element that inhibits hydrogen solid solution, and when it is included in an excessive amount, hydrogen permeation performance may be reduced. Furthermore, since W is a metal with an extremely high melting point, excessive addition may result in undissolved W, which may adversely affect the uniformity of the alloy. Therefore, the upper limit of W is set to 10 atomic %. A preferable upper limit is 7 at.%.
Ｆｅは本発明において重要なＷを溶解するために必要な元素である。Ｗ単独の融点は約３０００℃と高融点であり、完全に溶融させることは難しいが、ＦｅＷを原料として使用することで、融点が約１５００℃まで下がり、Ｗを安定して溶融させることが可能である。添加されたＦｅは本発明の主要な構成相であるＮｉＴｉ相に多く分配されて（Ｎｉ，Ｆｅ）Ｔｉ相を形成するが、水素透過性能などの諸特性に影響を及ぼさずに上述した溶融性向上の利点を得ることが可能である。Ｆｅの添加量はＷ添加量に応じて調整することもでき、０．５原子％以上とする。より好ましくは１原子％以上であり、さらに好ましくは３原子％以上であり、特に好ましくは５原子％以上である。Ｆｅ添加量の上限は１０原子％とし、好ましくは７原子％である。 Fe is an element necessary to dissolve W, which is important in the present invention. W alone has a high melting point of approximately 3000°C, and it is difficult to melt it completely, but by using FeW as a raw material, the melting point drops to approximately 1500°C, making it possible to stably melt W. It is. The added Fe is largely distributed in the NiTi phase, which is the main constituent phase of the present invention, to form a (Ni,Fe)Ti phase, but it maintains the above-mentioned meltability without affecting various properties such as hydrogen permeability. It is possible to obtain improved benefits. The amount of Fe added can also be adjusted depending on the amount of W added, and is set to 0.5 atomic % or more. The content is more preferably 1 atom % or more, further preferably 3 atom % or more, particularly preferably 5 atom % or more. The upper limit of the amount of Fe added is 10 atomic %, preferably 7 atomic %.
また本願発明において他の元素は不可避不純物として含まれることに差し支えないが、特に酸素の含有量を０．１質量％以下とすることが好ましい。酸素が０．１質量％を越えて含まれる場合、塑性加工プロセスにおいて加工硬化を誘起しやすくなり、工業生産性が著しく低下するためである。 Further, in the present invention, other elements may be included as unavoidable impurities, but it is particularly preferable that the content of oxygen is 0.1% by mass or less. This is because when oxygen is contained in an amount exceeding 0.1% by mass, work hardening is likely to be induced in the plastic working process, and industrial productivity is significantly reduced.
次に好ましい合金組織に関する規定について説明する。
＜水素透過層の平均厚さが５μｍ以下＞
水素分離合金の水素透過量は一般にその板厚に反比例することが知られている。このため水素分離合金の板厚は薄いほど好ましいが、本願発明においては、例えば圧延工程を経ることで、水素透過相と耐水素脆化相が伸展した組織とすることができる。また水素分離合金の伸展方向断面を電子顕微鏡により観察したとき、各水素透過層の平均厚さが５μｍ以下であることが好ましい。
本願発明の合金は鋳造時点において大きくは球状の水素透過相とそれを取り囲む耐水素脆化相を有しており、その結晶粒径は不均一である。水素固溶は水素透過層で優先的に発生するため、結晶粒径が不均一な状態では局所的な水素固溶とそれに続く水素脆化が発生しやすくなる。このため、合金組織の微細均一化を図るため、また同時に板厚を減ずるために合金を伸展させることが非常に有効である。例えば圧延により一方向に組織を伸展させることができる。十分な組織の微細均一化を図る上で、総圧下率は９０％以上となることが好ましい。特に、熱間圧延などの熱間加工工程を経て総圧下率を９５％以上とすることがより好ましい。
一方、圧延工程等を経ることで水素透過相と耐水素脆化相が伸展した組織となり、層状の水素透過相と耐水素脆化相とが互いに積層したような合金組織となる。この時、固溶した水素は水素透過相を主な経路として拡散していくため、水素透過相と水素透過相の間に耐水素脆化相が挟まれている場合、水素拡散が阻害され、結果として水素透過性能が低下することになる。このため、水素透過相と水素透過相とは十分に近接した位置にあり、かつ適度に密接していることが好ましい。この条件を満足するため、水素分離合金の伸展方向断面を電子顕微鏡により観察したとき、水素透過層の平均厚さは５μｍ以下となることが好ましい。水素透過層の平均厚さについて下限は特に規定しないが、固溶した水素は圧延工程によって生じた歪みに留まりやすく、水素透過を阻害する要因となるため、適切な熱処理によって再結晶化させることが必要であり、これによって水素透過層の平均厚さは一般的に０．５μｍ以上となる。この時の熱処理は十分な再結晶化、並びに上述した酸素の増加を抑制するため、真空または不活性ガス中で９００～１１００℃、５分～１７０時間程度行うのが良い。なお水素透過相の平均厚さを測定するに当たっては、下記の方法で計測すれば経験上十分である。すなわち、まず電子顕微鏡で１００００倍の倍率で３視野程度を観察し、各視野任意５カ所を縦断する直線をひく。続いて、直線が通過した水素透過相の厚さをそれぞれ計測し（視野端部に存在する水素透過相は除く）、その平均を算出する。
Next, regulations regarding preferred alloy structures will be explained.
<Average thickness of hydrogen permeable layer is 5 μm or less>
It is known that the amount of hydrogen permeation through a hydrogen separation alloy is generally inversely proportional to its plate thickness. For this reason, the thinner the plate thickness of the hydrogen separation alloy is, the more preferable it is, but in the present invention, by passing through a rolling process, for example, it is possible to form a structure in which the hydrogen permeable phase and the hydrogen embrittlement resistant phase are extended. Further, when a cross section of the hydrogen separation alloy in the stretching direction is observed using an electron microscope, it is preferable that the average thickness of each hydrogen permeable layer is 5 μm or less.
At the time of casting, the alloy of the present invention has a largely spherical hydrogen permeable phase and a hydrogen embrittlement resistant phase surrounding it, and the crystal grain size thereof is non-uniform. Since hydrogen solid solution occurs preferentially in the hydrogen permeable layer, local hydrogen solid solution and subsequent hydrogen embrittlement are likely to occur when the crystal grain size is non-uniform. For this reason, it is very effective to stretch the alloy in order to make the alloy microstructure fine and uniform, and at the same time to reduce the plate thickness. For example, the tissue can be stretched in one direction by rolling. In order to achieve sufficient fineness and uniformity of the structure, the total rolling reduction ratio is preferably 90% or more. In particular, it is more preferable to carry out a hot working process such as hot rolling so that the total rolling reduction is 95% or more.
On the other hand, through a rolling process or the like, a structure in which the hydrogen permeable phase and the hydrogen embrittlement resistant phase are extended is formed, resulting in an alloy structure in which the layered hydrogen permeable phase and the hydrogen embrittlement resistant phase are stacked on top of each other. At this time, the dissolved hydrogen mainly diffuses through the hydrogen-permeable phase, so if a hydrogen embrittlement-resistant phase is sandwiched between the hydrogen-permeable phases, hydrogen diffusion is inhibited. As a result, hydrogen permeation performance will be reduced. For this reason, it is preferable that the hydrogen-permeable phase and the hydrogen-permeable phase are located sufficiently close to each other and are in moderately close contact with each other. In order to satisfy this condition, the average thickness of the hydrogen permeable layer is preferably 5 μm or less when a cross section of the hydrogen separation alloy in the stretching direction is observed using an electron microscope. There is no particular lower limit for the average thickness of the hydrogen permeable layer, but dissolved hydrogen tends to remain in the distortion caused by the rolling process and becomes a factor that inhibits hydrogen permeation, so it is necessary to recrystallize it by appropriate heat treatment. This generally results in an average thickness of the hydrogen permeable layer of 0.5 μm or more. The heat treatment at this time is preferably carried out at 900 to 1100° C. for about 5 minutes to 170 hours in vacuum or inert gas in order to achieve sufficient recrystallization and to suppress the above-mentioned increase in oxygen. In addition, in measuring the average thickness of the hydrogen permeable phase, it is sufficient from experience to measure it by the following method. That is, first, approximately three fields of view are observed with an electron microscope at a magnification of 10,000 times, and a straight line is drawn longitudinally through five arbitrary points in each field of view. Subsequently, the thickness of each hydrogen permeable phase through which the straight line passes is measured (excluding the hydrogen permeable phase present at the edge of the field of view), and the average thereof is calculated.
＜水素透過相内のＷの最大濃度差が２０原子％以下＞
本発明の水素分離合金において、Ｗは鋳造時点で水素透過相の中心部分に強く偏析する傾向がある。上述した通りＷは高融点金属であることから、溶湯からの凝固過程においてまずＷが核を形成し、次いでＮｂとＴｉが凝固することで、Ｎｂ－Ｔｉ－Ｗ水素透過相が形成されるためであると考えられる。しかしＷは水素固溶量を抑制する元素であることから、Ｗの偏析によって水素透過相内で不均一な水素固溶が発生することになり、耐水素脆性を低下させる要因となる。また水素透過を担う相の一部が局所的に水素を固溶しにくくなることは、水素透過性能の低下を招くことにつながる。従い、水素透過相内にＷが実質的に均一に分布していることが好ましく、水素透過相内のＷの最大濃度差が２０原子％以下とする。
ここで、水素透過相内にＷが実質的に均一に分布しているとは、電子顕微鏡を用いて水素透過相内の少なくとも中心付近と端付近を含む任意５点について元素分析を行い、Ｗ濃度の最大値と最小値の差（最大濃度差）が２０原子％以下であることをいう。好ましくは１５原子％以下であり、より好ましくは１０原子％以下であり、さらに好ましくは５原子％以下であり、特に好ましくは３原子％以下である。Ｗの均一化を図る方法としては、Ｗが水素透過相内で十分に拡散できる熱処理を行うのが良いが、Ｗは高融点であることから熱処理の長時間化を招きやすい。しかし圧延を施し、合金組織を微細化した水素分離合金においてはＷの拡散距離を短くすることが可能であるため、熱処理条件の簡略化を行うことができる。このため、本願発明の水素分離合金においては真空または不活性ガス中で９００～１１００℃、５分～１７０時間程度の熱処理を行えば十分である。
<The maximum concentration difference of W in the hydrogen permeable phase is 20 atomic % or less>
In the hydrogen separation alloy of the present invention, W tends to be strongly segregated in the center of the hydrogen permeable phase at the time of casting. As mentioned above, since W is a high melting point metal, during the solidification process from molten metal, W first forms a nucleus, and then Nb and Ti solidify, forming a Nb-Ti-W hydrogen permeable phase. It is thought that. However, since W is an element that suppresses the amount of hydrogen in solid solution, the segregation of W causes non-uniform hydrogen solid solution in the hydrogen-permeable phase, which becomes a factor that reduces hydrogen embrittlement resistance. Furthermore, part of the phase responsible for hydrogen permeation becomes difficult to dissolve hydrogen locally, leading to a decrease in hydrogen permeation performance. Therefore, it is preferable that W is distributed substantially uniformly in the hydrogen permeable phase, and the maximum concentration difference of W in the hydrogen permeable phase is 20 at % or less.
Here, the fact that W is substantially uniformly distributed within the hydrogen-permeable phase means that elemental analysis is performed at five arbitrary points in the hydrogen-permeable phase, including at least the vicinity of the center and the vicinity of the edges, using an electron microscope. It means that the difference between the maximum concentration value and the minimum concentration value (maximum concentration difference) is 20 atomic % or less. Preferably it is 15 atom % or less, more preferably 10 atom % or less, still more preferably 5 atom % or less, particularly preferably 3 atom % or less. A good way to make W uniform is to perform a heat treatment that allows W to sufficiently diffuse within the hydrogen-permeable phase, but since W has a high melting point, the heat treatment tends to take a long time. However, in a hydrogen separation alloy whose alloy structure is refined by rolling, it is possible to shorten the diffusion distance of W, so that the heat treatment conditions can be simplified. For this reason, it is sufficient for the hydrogen separation alloy of the present invention to be heat treated at 900 to 1100° C. for about 5 minutes to 170 hours in vacuum or inert gas.
以下の実施例で本発明を更に詳しく説明する。
真空中のボタンアーク溶解で３０ｇの水素分離合金を作製した。化学組成を表１に示す。
The invention will be explained in more detail in the following examples.
30 g of hydrogen separation alloy was produced by button arc melting in vacuum. The chemical composition is shown in Table 1.
表１で示す４つの合金の３００℃で測定したＰＣＴ（Ｐｒｅｓｓｕｒｅ－Ｃｏｍｐｏｓｉｔｉｏｎ－Ｔｅｍｐｅｒａｔｕｒｅ）曲線を図１に示す。図１より、ＦｅＷが添加されている試料Ｎｏ．１～３は、ＦｅＷが添加されていない試料Ｎｏ．４と比較して水素固溶量が低下しており、耐水素脆性の向上に寄与していることが確認できる。水素固溶量はＷの添加量が増加するにつれて少なくなっており、本発明例の中で最もＷ添加量が多い試料Ｎｏ．３が、水素固溶量が最も低下しており、耐水素脆性が本発明例の中で最も優れている傾向にあることも確認できた。このように本発明は耐水素脆性に優れているため、高純度水素を安価に製造する水素分離装置に適用できる。 FIG. 1 shows PCT (Pressure-Composition-Temperature) curves measured at 300° C. for the four alloys shown in Table 1. From FIG. 1, sample No. to which FeW is added. 1 to 3 are sample No. 1 to which FeW is not added. It can be confirmed that the amount of hydrogen solid solution is lower than in Sample No. 4, which contributes to improving the hydrogen embrittlement resistance. The amount of solid solution hydrogen decreases as the amount of W added increases, and among the examples of the present invention, sample No. 1 has the highest amount of W added. It was also confirmed that Sample No. 3 had the lowest hydrogen solid solution amount and tended to have the best hydrogen embrittlement resistance among the invention examples. As described above, since the present invention has excellent resistance to hydrogen embrittlement, it can be applied to a hydrogen separation device that produces high-purity hydrogen at low cost.
続いて、前記のＮｏ．１～Ｎｏ．４の合金について水素透過測定を行った。試料は（１）鋳造まま（熱処理前）、（２）１１００℃×１６８ｈの熱処理を施した試料を準備した。ワイヤーカットにて板厚を０．５ｍｍにスライスした後、表面を研磨紙、アルミナ粉末を用いた研磨剤にて鏡面研磨した。最後に表面にＰｄをスパッタにて約２００ｎｍ成膜し水素透過測定用試料を作製した。測定の結果得られた熱処理前の水素透過係数を図２に、熱処理後の水素透過係数を図３に示す。図２、図３よりＮｏ．１～Ｎｏ．３は、Ｎｏ．４と比較して、熱処理前と熱処理後の両方においてもほぼ同等の水素透過係数を示していうることが確認された。これにより本発明例は、図１で示すように水素固溶量が低下して耐水素脆性が向上しているとともに、公知の水素分離合金と同等の水素透過性能も有していることが確認できた。
Subsequently, the above-mentioned No. 1~No. Hydrogen permeation measurements were conducted on alloy No. 4. Samples were prepared: (1) as-cast (before heat treatment) and (2) heat treatment at 1100° C. for 168 hours. After slicing the plate to a thickness of 0.5 mm by wire cutting, the surface was mirror-polished with an abrasive using abrasive paper and alumina powder. Finally, a Pd film of about 200 nm was formed on the surface by sputtering to prepare a sample for hydrogen permeation measurement. The hydrogen permeability coefficient before heat treatment obtained as a result of measurement is shown in FIG. 2, and the hydrogen permeation coefficient after heat treatment is shown in FIG. From FIGS. 2 and 3, No. 1~No. 3 is No. 4, it was confirmed that the hydrogen permeability coefficients were almost the same both before and after heat treatment. As a result, it was confirmed that the present invention example has a lower hydrogen solid solution amount and improved hydrogen embrittlement resistance as shown in Figure 1, and also has hydrogen permeation performance equivalent to known hydrogen separation alloys. did it.
Claims (2)
The hydrogen separation alloy according to claim 1, wherein in the compositional formula, 3≦γ≦7.
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