JP2005272970A - Alloy particle and production method therefor - Google Patents
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本発明は、２種以上の金属が原子レベルで均一に混合した合金粒子の製造方法に関し、この製造方法の適用により得ることが可能となった新たな合金粒子に関する。 The present invention relates to a method for producing alloy particles in which two or more kinds of metals are uniformly mixed at an atomic level, and relates to new alloy particles that can be obtained by application of this production method.
合金粒子は、触媒、導電性ペーストの原料等として広く用いられており、水素吸蔵体としての使用も提案されている。合金粒子の製造方法は種々知られており、合金粒子は、目標とする形状、粒径、特性等に応じて適宜選択された方法により、所望の成分比となるように製造される。 Alloy particles are widely used as raw materials for catalysts, conductive pastes, and the like, and their use as hydrogen storage materials has also been proposed. Various methods for producing alloy particles are known, and alloy particles are produced so as to have a desired component ratio by a method appropriately selected according to a target shape, particle size, characteristics, and the like.
例えば、合金粒子は、原料を溶融、凝固させて得た合金を粉砕することにより得ることができる。しかし、この方法は、高温への加熱を要し、特に微細に粉砕するべき場合において均一な粒径を得ることが容易ではない。また、パラジウムと白金の組み合わせのように、溶融により混合しても相分離する合金の場合は、均一な組成の合金粒子を得ることができない。 For example, alloy particles can be obtained by pulverizing an alloy obtained by melting and solidifying raw materials. However, this method requires heating to a high temperature, and it is not easy to obtain a uniform particle size particularly when finely pulverizing. In addition, in the case of an alloy that undergoes phase separation even when mixed by melting, such as a combination of palladium and platinum, alloy particles having a uniform composition cannot be obtained.
触媒の分野では、金属微粒子触媒が注目されており、多くの二元系金属微粒子が提案されている。触媒としての活性は、添加成分および微粒子化の影響を大きく受けるからである。例えば特許文献１には、水素化触媒として有用であるニッケル／貴金属二元金属クラスターが開示されている。この金属クラスターは、有機高分子（ポリ−（Ｎ−ビニル−２−ピロリドン；以下「ＰＶＰ」という）の存在下、アルコール中でニッケル塩と貴金属（例えばパラジウム）の金属塩を還元する、いわゆるアルコール還元法により得ることができる。 In the field of catalysts, metal fine particle catalysts have attracted attention, and many binary metal fine particles have been proposed. This is because the activity as a catalyst is greatly affected by additive components and micronization. For example, Patent Document 1 discloses a nickel / noble metal bimetallic cluster that is useful as a hydrogenation catalyst. This metal cluster is a so-called alcohol that reduces a metal salt of a nickel salt and a noble metal (for example, palladium) in an alcohol in the presence of an organic polymer (poly- (N-vinyl-2-pyrrolidone; hereinafter referred to as “PVP”)). It can be obtained by a reduction method.
特許文献１の「従来の技術」の欄に記載されているとおり、金／白金系、白金／パラジウム系等の二元金属クラスターも、上記と同様、アルコール還元法により作製できる。この二元金属クラスターは、有機高分子と金属との相互作用が同一ではないことに起因し、コア・シェル型構造を有する。例えば、ＰＶＰを用いたアルコール還元法により金／白金系二元金属クラスターを作製すると、ＰＶＰが金よりも白金と強い相互作用を有するために、まず金イオンが還元されてコアが形成され、その表面に白金からなるシェルが被着する。 As described in Patent Document 1, “Prior Art”, binary metal clusters such as gold / platinum and platinum / palladium can be produced by the alcohol reduction method as described above. This binary metal cluster has a core-shell structure due to the fact that the interaction between the organic polymer and the metal is not the same. For example, when a gold / platinum binary metal cluster is produced by an alcohol reduction method using PVP, since PVP has a stronger interaction with platinum than gold, first, gold ions are reduced to form a core. A platinum shell is deposited on the surface.
アルコール還元法は、２種以上の金属を含む金属微粒子を製造する方法としては有用である。しかし、この方法により得られる微粒子は、上記のとおり、コア・シェル型構造を有し、完全に均一な合金から構成されているわけではない。 The alcohol reduction method is useful as a method for producing fine metal particles containing two or more metals. However, the fine particles obtained by this method have a core-shell type structure as described above, and are not composed of a completely uniform alloy.
２種以上の金属が原子レベルで均一に混じり合った合金粒子は、特性の発現が粒子における原子レベルの微細構造と関連している用途、例えば触媒、水素吸蔵体としての用途、において、従来の方法による金属粒子とは異なる特性やより優れた特性を発現する可能性がある。 Alloy particles in which two or more metals are uniformly mixed at the atomic level are used in conventional applications where the development of properties is related to the atomic microstructure in the particles, such as applications as catalysts and hydrogen storage materials. There is a possibility that a characteristic different from the metal particles by the method or a superior characteristic may be exhibited.
そこで、本発明は、２種以上の金属が原子レベルで均一に固溶した合金粒子の製造方法を確立することを目的とする。本発明の別の目的は、この製造方法により得ることが可能となった新たな合金粒子を提供することにある。 Accordingly, an object of the present invention is to establish a method for producing alloy particles in which two or more kinds of metals are uniformly dissolved at the atomic level. Another object of the present invention is to provide new alloy particles that can be obtained by this production method.
本発明の合金粒子の製造方法は、２種以上の金属原子を含み、２種以上の結晶格子が内在する金属粒子に対し、水素を吸収させ、この水素の少なくとも一部を放出させる水素吸収／放出サイクルを所定回数適用することにより、上記２種以上の金属原子を含み、単一種の結晶格子が内在する合金粒子を得ることを特徴とする。 In the method for producing alloy particles of the present invention, hydrogen absorption / absorption in which hydrogen is absorbed into metal particles containing two or more kinds of metal atoms and two or more kinds of crystal lattices are contained, and at least a part of the hydrogen is released. By applying the release cycle a predetermined number of times, alloy particles containing two or more kinds of metal atoms and having a single kind of crystal lattice are obtained.
本発明は、その別の側面から、従来の方法では得られなかった新たな合金粒子、例えば、パラジウム原子および白金原子を含み、パラジウム原子と白金原子とが単一種の結晶格子を形成するように固溶した合金粒子、を提供する。 Another aspect of the present invention is a new alloy particle that has not been obtained by a conventional method, for example, including palladium atoms and platinum atoms, so that palladium atoms and platinum atoms form a single kind of crystal lattice. Solid solution alloy particles are provided.
本発明の製造方法では、必要回数だけ水素吸収／放出サイクルを適用すればよく、金属が溶融する程度の高温が必要とされない。このため、バルクよりも雰囲気の影響を受けやすい合金粒子、特に粒径が小さい合金微粒子、の製造に適している。 In the production method of the present invention, the hydrogen absorption / release cycle may be applied as many times as necessary, and a high temperature sufficient to melt the metal is not required. For this reason, it is suitable for the production of alloy particles that are more susceptible to the atmosphere than the bulk, particularly alloy fine particles having a small particle size.
本発明の製造方法は、アルコール還元法等の既知の液相析出法と組み合わせれば、粒径等の制御性に優れた合金粒子製造方法となる。優れた制御性は、合金粒子の量産に重視される特徴である。 When the production method of the present invention is combined with a known liquid phase precipitation method such as an alcohol reduction method, it becomes an alloy particle production method having excellent controllability such as particle size. Excellent controllability is a feature that is important for mass production of alloy particles.
本発明を適用すれば、従来は均一な固溶が困難と考えられてきた金属の組み合わせにおいても、原子レベルでの固溶を実現できる。水素吸収／放出サイクルによる結晶構造における変化のメカニズムは、現段階ではその詳細が明らかではないが、水素原子の結晶格子への侵入と結晶格子からの放出との繰り返しが金属粒子に内在するドメインの再構成を促していると考えられる。 By applying the present invention, it is possible to realize solid solution at the atomic level even in the case of a metal combination that has been conventionally considered difficult to form a uniform solid solution. The mechanism of the change in the crystal structure due to the hydrogen absorption / release cycle is not clear at this stage, but the repetition of the entry of hydrogen atoms into the crystal lattice and the release from the crystal lattice is the domain in which the metal particles are inherent. It is thought that it is promoting the reconstruction.
新たな合金粒子からは、従来知られていなかった触媒活性やより優れた諸特性が得られる可能性がある。現時点で明らかになっているだけでも、パラジウムと白金とが均一に固溶した合金粒子は、従来のパラジウム／白金二元系コア・シェル型金属微粒子よりも優れた水素吸蔵特性を発揮する。 From new alloy particles, there is a possibility that catalyst activity and various other characteristics that were not conventionally known can be obtained. Even now, it is clear that alloy particles in which palladium and platinum are uniformly solid solution exhibit hydrogen storage characteristics superior to conventional palladium / platinum binary core / shell type metal fine particles.
本発明の製造方法を適用する金属粒子には、２種以上の金属原子が２種以上の結晶格子を形成するように混在していればよく、その構造に制限はないが、少なくとも、これら金属がコア・シェル構造を形成している金属粒子は本発明による合金化に適している。コア・シェル構造を有する金属粒子のＸ線回折チャートからは、通常、コア金属の結晶格子に由来する回折ピークと、シェル金属の結晶格子に由来する回折ピークとが観察される。これに対し、コア・シェル型金属粒子に本発明を適用して得た合金粒子からは、コア金属とシェル金属とから構成された新たな結晶格子に由来する回折ピークが観察される。 The metal particles to which the production method of the present invention is applied are not limited as long as two or more kinds of metal atoms are mixed so as to form two or more kinds of crystal lattices. Are suitable for alloying in accordance with the present invention. From the X-ray diffraction chart of a metal particle having a core / shell structure, a diffraction peak derived from the crystal lattice of the core metal and a diffraction peak derived from the crystal lattice of the shell metal are usually observed. On the other hand, from the alloy particles obtained by applying the present invention to the core-shell type metal particles, a diffraction peak derived from a new crystal lattice composed of the core metal and the shell metal is observed.
２種以上の金属原子の種類に制限はないが、これら金属には遷移金属が適しており、２種以上の金属原子の少なくとも１種が、白金族元素（ルテニウム、ロジウム、パラジウム、オスミウム、イリジウム、白金）および金から選ばれる金属原子であることが好ましい。パラジウム原子および白金原子を含み、パラジウム原子と白金原子とが単一種の結晶格子を形成するように固溶した合金粒子、は、本発明により製造が可能となった代表的な合金粒子である。 There are no restrictions on the types of two or more metal atoms, but transition metals are suitable for these metals, and at least one of the two or more metal atoms is a platinum group element (ruthenium, rhodium, palladium, osmium, iridium). , Platinum) and gold are preferred. Alloy particles containing palladium atoms and platinum atoms, in which palladium atoms and platinum atoms form a single type crystal lattice, are typical alloy particles that can be produced by the present invention.
ただし、本発明により得られる合金粒子は、パラジウム／白金系に限られるわけではない。本発明の適用により、優れた特性の発揮が期待できる合金粒子には、パラジウムと白金との組み合わせに加え、例えばパラジウムとニッケル、白金とニッケル、白金とロジウム、銅とパラジウム、銀とパラジウムが挙げられる。金属粒子および合金粒子は、３以上の金属原子を含んでいても構わない。 However, the alloy particles obtained by the present invention are not limited to the palladium / platinum system. In addition to the combination of palladium and platinum, alloy particles that can be expected to exhibit excellent properties by applying the present invention include, for example, palladium and nickel, platinum and nickel, platinum and rhodium, copper and palladium, silver and palladium. It is done. The metal particles and alloy particles may contain 3 or more metal atoms.
金属粒子の粒径、および合金粒子の粒径は、特に制限はないが、１００ｎｍ以下、例えば０．５ｎｍ〜１００ｎｍ、さらには１ｎｍ〜１００ｎｍ、特に２ｎｍ〜５０ｎｍ、とりわけ２ｎｍ〜２０ｎｍが好適である。本発明の製造方法は、例えば１０ｎｍ以下のナノ粒子についても適用が可能であり、この程度に微細な粒子を原子レベルで均一化できるという点に本発明の製造方法の特長の一つがある。 The particle size of the metal particles and the particle size of the alloy particles are not particularly limited, but 100 nm or less, for example, 0.5 nm to 100 nm, further 1 nm to 100 nm, particularly 2 nm to 50 nm, especially 2 nm to 20 nm are suitable. The production method of the present invention can be applied to, for example, nanoparticles of 10 nm or less, and one of the features of the production method of the present invention is that such fine particles can be made uniform at the atomic level.
金属粒子の製造方法に制限はないが、金属粒子は、アルコール還元法に代表されるように、液相において形成することが好ましい。アルコール還元法は、従来から知られているように、有機高分子の存在下、アルコールを含む溶液中で金属イオンを還元することにより行えばよい。 Although there is no restriction | limiting in the manufacturing method of a metal particle, It is preferable to form a metal particle in a liquid phase so that it may be represented by the alcohol reduction method. The alcohol reduction method may be performed by reducing metal ions in a solution containing an alcohol in the presence of an organic polymer as conventionally known.
有機高分子としては、水溶性のポリマーが好ましく、具体的にはＰＶＰのような環状アミド構造を有するポリマーが好適であるが、これに限らず、目的とする金属粒子の種類等に応じ、例えばポリビニルアルコール、ポリビニルエーテル、ポリアクリレート、ポリ（メルカプトメチレンスリレン−Ｎ−ビニル−２−ピロリドン）、ポリアクリロニトリルを用いてもよい。 As the organic polymer, a water-soluble polymer is preferable, and specifically, a polymer having a cyclic amide structure such as PVP is preferable. However, the organic polymer is not limited to this. Polyvinyl alcohol, polyvinyl ether, polyacrylate, poly (mercaptomethylenethrylene-N-vinyl-2-pyrrolidone), polyacrylonitrile may be used.
アルコールは、溶液中で還元剤として作用する。アルコールも、金属や有機高分子の種類等に応じて適宜選択するとよく、例えばエタノール、プロパノールや、エチレングリコール、グリセリン等の多価アルコールを用いればよい。 Alcohol acts as a reducing agent in solution. The alcohol may be appropriately selected according to the type of metal or organic polymer, and for example, polyhydric alcohols such as ethanol, propanol, ethylene glycol, and glycerin may be used.
溶液中における有機高分子の量を相対的に増やすと、析出する金属粒子の粒径は小さくなる。これを利用すれば金属粒子の粒径を制御できる。添加する金属塩の濃度を調整することによっても、析出する金属の量、ひいては金属粒子の粒径を制御できる。得られる粒子の組成の均一性も高い。このように、アルコール還元法は、粒径等の制御性に優れており、金属粒子の製造方法として適している。本発明の製造方法は、金属粒子を液相において生成させる工程、特にアルコール還元法による金属粒子生成工程、をさらに含むことが好ましい。 When the amount of the organic polymer in the solution is relatively increased, the particle size of the deposited metal particles becomes smaller. If this is utilized, the particle size of the metal particles can be controlled. By adjusting the concentration of the metal salt to be added, it is possible to control the amount of the deposited metal, and hence the particle size of the metal particles. The uniformity of the composition of the obtained particles is also high. Thus, the alcohol reduction method is excellent in controllability such as particle size, and is suitable as a method for producing metal particles. The production method of the present invention preferably further includes a step of generating metal particles in a liquid phase, particularly a step of generating metal particles by an alcohol reduction method.
後述する実施例のように、アルコール還元法に代表される液相析出法では、金属の種類ごとに準備した溶液を用い、コアを形成した後にシェルを形成することにより、コア・シェル構造を実現してもよい。コア形成工程、またはシェル形成工程を所定回数繰り返すことにより、所望の径のコアもしくは所望の厚さのシェルの形成、または所望のコア金属／シェル金属重量比、とすることもできる。 In the liquid phase deposition method represented by the alcohol reduction method as in the examples described later, a core / shell structure is realized by using a solution prepared for each type of metal and forming a shell after forming a core. May be. By repeating the core forming step or the shell forming step a predetermined number of times, it is possible to form a core having a desired diameter or a shell having a desired thickness, or a desired core metal / shell metal weight ratio.
水素吸収／放出サイクルは、金属粒子を構成する複数種の金属が原子レベルで固溶するまで所定回数を繰り返して行うとよい。この所定回数は、諸条件、例えば温度、により影響を受ける。本発明者が確認した限りにおいて、完全な合金化に必要な繰り返し回数は温度が高くなるにつれて少なくなるが、パラジウム／白金系においては少なくとも２回の繰り返しが必要であった。一方、水素吸収／放出サイクルを適用する温度が高すぎると粒子同士が凝集するおそれがある。水素吸収／放出サイクルの適用は、金属粒子を２０℃以上４００℃以下、特に５０℃以上１００℃以下に保持しながら行うことが好ましい。 The hydrogen absorption / release cycle may be repeated a predetermined number of times until a plurality of types of metals constituting the metal particles are dissolved at the atomic level. This predetermined number of times is affected by various conditions such as temperature. As far as the present inventors have confirmed, the number of repetitions required for complete alloying decreases as the temperature increases, but in the palladium / platinum system, at least two repetitions are necessary. On the other hand, if the temperature at which the hydrogen absorption / release cycle is applied is too high, the particles may aggregate. The application of the hydrogen absorption / release cycle is preferably performed while holding the metal particles at 20 ° C. or higher and 400 ° C. or lower, particularly 50 ° C. or higher and 100 ° C. or lower.
本発明により得られる合金粒子は、特に粒径が小さい場合には、有機高分子で被覆された状態で使用することが好ましい。この状態は微粒子の酸化防止に有効である。保護剤となる有機高分子は、特に制限されず、アルコール還元法で用いる各種ポリマーをそのまま用いればよい。 The alloy particles obtained by the present invention are preferably used in a state of being coated with an organic polymer, particularly when the particle size is small. This state is effective for preventing oxidation of fine particles. The organic polymer used as the protective agent is not particularly limited, and various polymers used in the alcohol reduction method may be used as they are.
図１に、ポリマー２で被覆された合金粒子１を例示する。ポリマー２が被覆した状態、例えばアルコール還元法により得たそのままの状態、で、合金粒子１に水素吸収／放出サイクルを適用することもできる。ポリマー２が存在しても、本発明の効果が得られる程度に、合金粒子１に水素を作用させることは可能である。 FIG. 1 illustrates an alloy particle 1 coated with a polymer 2. The hydrogen absorption / release cycle can also be applied to the alloy particles 1 in a state where the polymer 2 is coated, for example, as it is obtained by an alcohol reduction method. Even if the polymer 2 is present, it is possible to cause hydrogen to act on the alloy particles 1 to the extent that the effects of the present invention can be obtained.
以下、実施例により本発明をさらに具体的に説明するが、以下の実施例は、本欄における上記記載と同様、本発明の実施形態の例示に過ぎず、本発明を限定するものではない。 EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the following examples are only examples of the embodiments of the present invention, as described above in this section, and do not limit the present invention.
（Ｐｄナノ粒子の合成）
塩化パラジウム（ＰｄＣｌ2）を希塩酸に溶解し、２ｍＭのＨ2ＰｄＣｌ4水溶液を調製した。この水溶液８０ｍｌ（１６０μｍｏｌ）に保護剤としてＰＶＰ１７７．７ｍｇ（モノマーユニットで１．６ｍｍｏｌ）および超純水５６０ｍｌを加えた溶液に、還元剤としてエタノール１６０ｍｌを撹拌しながら加えた。この溶液を１００℃で３時間還流することにより、ＰＶＰ保護Ｐｄナノ粒子（以下「Ｐｄ−ＰＶＰナノ粒子」という）を調製した。
(Synthesis of Pd nanoparticles)
Palladium chloride (PdCl 2 ) was dissolved in dilute hydrochloric acid to prepare a 2 mM H 2 PdCl 4 aqueous solution. To a solution obtained by adding 177.7 mg of PVP (1.6 mmol as a monomer unit) and 560 ml of ultrapure water as a protective agent to 80 ml (160 μmol) of this aqueous solution, 160 ml of ethanol as a reducing agent was added with stirring. The solution was refluxed at 100 ° C. for 3 hours to prepare PVP-protected Pd nanoparticles (hereinafter referred to as “Pd-PVP nanoparticles”).
このＰｄ−ＰＶＰナノ粒子分散液を出発粒子としＰｄ粒子の段階成長を行った。まず、Ｐｄ−ＰＶＰナノ粒子分散液２００ｍｌにＨ2ＰｄＣｌ4水溶液６０ｍｌ（１２０μｍｏｌ）、超純水４２０ｍｌおよびエタノール１２０ｍｌを撹拌しながら加え、１００℃で３時間還流を行って第二段階合成を行い、Ｐｄ−ＰＶＰナノ粒子を得た。さらに同様の手順による第三段階合成により、Ｐｄ−ＰＶＰナノ粒子（この最終粒子を、以下「Ｐｄナノ粒子」という）を得た。 Using this Pd-PVP nanoparticle dispersion as starting particles, Pd particles were grown in stages. First, 60 ml (120 μmol) of an H 2 PdCl 4 aqueous solution, 420 ml of ultrapure water and 120 ml of ethanol were added to 200 ml of a Pd-PVP nanoparticle dispersion with stirring, and the mixture was refluxed at 100 ° C. for 3 hours to perform the second-stage synthesis. Pd-PVP nanoparticles were obtained. Furthermore, Pd-PVP nanoparticles (this final particle is hereinafter referred to as “Pd nanoparticle”) were obtained by a third-stage synthesis according to the same procedure.
（Ｐｄ／Ｐｔコア・シェル型ナノ粒子の合成）
Ｐｄナノ粒子０．４７ｇに超純水５０ｍｌおよびエタノール１００ｍｌを加え、これを保持するフラスコ内の空気を窒素置換して除去した。次いで、このＰｄナノ粒子分散液を水素雰囲気下で２時間撹拌を行った。引き続き、Ｐｄナノ粒子分散液の液温を７５℃に保持しながら、Ｈ2ＰｔＣｌ6・６Ｈ2Ｏ０．２１ｇ（０．４ｍｍｏｌ）を超純水１００ｍｌに溶解したものを３時間かけて等圧滴下ロートを用いて滴下した。さらに、反応を十分に進行させるために、Ｐｄナノ粒子分散液を７５℃に保持しながら８時間撹拌した。こうして、Ｐｄ／Ｐｔコア・シェル型ナノ粒子を得た。
(Synthesis of Pd / Pt core / shell type nanoparticles)
50 ml of ultrapure water and 100 ml of ethanol were added to 0.47 g of Pd nanoparticles, and the air in the flask holding this was purged with nitrogen and removed. Subsequently, this Pd nanoparticle dispersion was stirred for 2 hours in a hydrogen atmosphere. Subsequently, while maintaining the temperature of the Pd nanoparticle dispersion at 75 ° C., 0.21 g (0.4 mmol) of H 2 PtCl 6 .6H 2 O dissolved in 100 ml of ultrapure water was dropped at an equal pressure over 3 hours. It was dripped using a funnel. Furthermore, in order to advance reaction sufficiently, it stirred for 8 hours, hold | maintaining Pd nanoparticle dispersion liquid at 75 degreeC. Thus, Pd / Pt core / shell type nanoparticles were obtained.
（Ｐｄ／Ｐｔコア・シェル型ナノ粒子の水素吸収／放出処理による合金化）
Ｐｄ／Ｐｔコア・シェル型ナノ粒子を３７３Ｋで３０分間真空乾燥させた後、１気圧の水素圧下に放置し、ナノ粒子への水素吸収を約３０分行った。この時間は、ナノ粒子の水素吸蔵が終了し、系が定常状態になるのに十分な時間である。その後３７３Ｋで真空脱気し、ナノ粒子からの水素放出を行った。水素放出は、真空ポンプを停止しても圧力の増加がおこらなくなる十分な時間、具体的には約３０分間行った。これを１サイクルとして、合計３サイクルの水素吸収／放出処理（以下、「水素処理」という）を繰り返し実施し、Ｐｄ／Ｐｔ完全固溶型ナノ粒子を得た。
(Alloying Pd / Pt core / shell nanoparticles by hydrogen absorption / release treatment)
The Pd / Pt core / shell type nanoparticles were vacuum-dried at 373 K for 30 minutes, and then left under a hydrogen pressure of 1 atm to absorb hydrogen into the nanoparticles for about 30 minutes. This time is sufficient for the nanoparticles to occlude hydrogen and the system is in a steady state. Thereafter, vacuum deaeration was performed at 373 K, and hydrogen was released from the nanoparticles. The hydrogen release was performed for a sufficient period of time during which the pressure did not increase even when the vacuum pump was stopped, specifically about 30 minutes. With this as one cycle, a total of three cycles of hydrogen absorption / release treatment (hereinafter referred to as “hydrogen treatment”) were repeatedly performed to obtain Pd / Pt complete solid solution type nanoparticles.
（透過型電子顕微鏡（ＴＥＭ）を用いた観察）
電子顕微鏡用炭素被服銅グリッド上に、Ｐｄ／Ｐｔコア・シェル型ナノ粒子のエタノール分散液をパスツールピペットで６滴落とし、乾燥させた。ＴＥＭ観察は、加速電圧１００ｋＶ、倍率１０万倍として行った。平均粒径は、ＴＥＭ写真中の任意エリアから約２００個の粒子を選出して直径を測定し、その統計結果から、平均粒径および標準偏差を算出した。
(Observation using transmission electron microscope (TEM))
Six drops of an ethanol dispersion of Pd / Pt core / shell nanoparticles were dropped on a carbon-coated copper grid for an electron microscope using a Pasteur pipette and dried. The TEM observation was performed at an acceleration voltage of 100 kV and a magnification of 100,000 times. For the average particle size, about 200 particles were selected from an arbitrary area in the TEM photograph, the diameter was measured, and the average particle size and standard deviation were calculated from the statistical results.
Ｐｄ／Ｐｔコア・シェル型ナノ粒子の平均粒径は８．１ｎｍ、標準偏差は０．９ｎｍであった。Ｐｄナノ粒子の平均粒径が５．９ｎｍであったことから、Ｐｔシェルは４原子層に相当することが確認できた。水素処理後の粒子についても測定を行ったが、粒子の粒径および形状に変化はなかった。 The average particle diameter of the Pd / Pt core-shell type nanoparticles was 8.1 nm, and the standard deviation was 0.9 nm. Since the average particle diameter of the Pd nanoparticles was 5.9 nm, it was confirmed that the Pt shell corresponds to a 4-atomic layer. Measurement was also performed on the particles after hydrogen treatment, but there was no change in the particle size and shape of the particles.
（粉末Ｘ線回折による分析）
０．５ｍｍφのガラスキャピラリーに試料とする粒子を封入した。測定は波長０．０８４９３９ｎｍの放射光を用いて行った。Ｘ線回折チャートを図２に示す。また、このＸ線回折チャートから算出した格子定数を図３に示す。
(Analysis by powder X-ray diffraction)
Sample particles were encapsulated in a 0.5 mmφ glass capillary. The measurement was performed using synchrotron radiation having a wavelength of 0.084939 nm. An X-ray diffraction chart is shown in FIG. Moreover, the lattice constant calculated from this X-ray diffraction chart is shown in FIG.
水素吸収／放出サイクルを経ていないＰｄ／Ｐｔコア・シェル型ナノ粒子（処理回数０回）は、それぞれｆｃｃ構造をとるＰｄコアとＰｔシェルからの回折の足し合わせで再現される。１回の水素処理の適用により回折パターンはやや変化したが、この回折パターンもＰｄコアとＰｔシェルからの回折の足し合わせである。 Pd / Pt core / shell type nanoparticles that have not undergone the hydrogen absorption / release cycle (the number of treatments is 0) are reproduced by the addition of diffraction from the Pd core and Pt shell each having an fcc structure. Although the diffraction pattern slightly changed by one application of hydrogen treatment, this diffraction pattern is also an addition of diffraction from the Pd core and the Pt shell.
これに対し、２回以上の水素処理を適用すると、１つのｆｃｃ格子からの回折パターンのみが観察できた。これは、Ｐｄ／Ｐｔコア・シェル型ナノ粒子が、ＰｄとＰｔとが完全に混合した固溶体型のナノ粒子に変化したことを示している。 In contrast, when two or more hydrogen treatments were applied, only the diffraction pattern from one fcc grating could be observed. This indicates that the Pd / Pt core-shell type nanoparticles were changed to solid solution type nanoparticles in which Pd and Pt were completely mixed.
（水素吸蔵能力の確認）
試料とする粒子に対し、上記水素処理と同様の処理を行ってＰＣＴ（Hydrogen Pressure−Composition−Isotherms）曲線を得た。結果を図４に示す。２回の水素処理を経て得たＰｄ／Ｐｔ完全固溶型ナノ粒子から、最も優れた水素吸蔵特性が観察された。
(Confirmation of hydrogen storage capacity)
The particle | grains used as a sample were processed like the said hydrogen treatment, and the PCT (Hydrogen Pressure-Composition-Isotherms) curve was obtained. The results are shown in FIG. The most excellent hydrogen storage characteristics were observed from Pd / Pt completely solid solution type nanoparticles obtained through two hydrogen treatments.
参考のため、図５として、バルクＰｄ−Ｐｔ合金の水素固溶度を、バルクＰｄの水素固溶度とともに示す（出典；黄燕清他、日本金属学会会報、（１９７９）、Ｐ６９４）。バルクＰｄ−Ｐｔ合金では、上記実施例とは逆に、Ｐｔとの合金化によって水素固溶度は低下している。これは、バルク合金ではＰｄとＰｔとが相分離しているためであると考えられる。 For reference, FIG. 5 shows the hydrogen solubility of the bulk Pd—Pt alloy together with the hydrogen solubility of the bulk Pd (Source: Kiyoshi Huang et al., Journal of the Japan Institute of Metals, (1979), P694). In the bulk Pd—Pt alloy, contrary to the above example, the hydrogen solid solubility is lowered by alloying with Pt. This is probably because Pd and Pt are phase separated in the bulk alloy.
本発明の製造方法は、特に粒径が小さい合金微粒子の製造において有用であり、合金粒子が用いられている技術分野、例えば導電性ペースト、触媒、水素吸蔵体の分野、において利用価値が高い。本発明によれば、従来の製造方法では得られなかった新しい合金粒子も提供できる。本発明の適用により得られる合金粒子は、原子レベルで金属原子が固溶しており、上記各分野において、優れた特性を発現するに適した構造を有する。 The production method of the present invention is particularly useful in the production of alloy fine particles having a small particle diameter, and has high utility value in technical fields in which alloy particles are used, for example, in the fields of conductive pastes, catalysts, and hydrogen storage materials. According to the present invention, new alloy particles that could not be obtained by the conventional manufacturing method can also be provided. The alloy particles obtained by application of the present invention have metal atoms in a solid solution at the atomic level, and have a structure suitable for expressing excellent characteristics in each of the above fields.
１ 合金粒子
２ ポリマー
1 Alloy particle 2 Polymer
Claims (10)
水素を吸収させ、前記水素の少なくとも一部を放出させる水素吸収／放出サイクルを所定回数適用することにより、
前記２種以上の金属原子を含み、単一種の結晶格子が内在する合金粒子を得る、
合金粒子の製造方法。 For metal particles containing two or more kinds of metal atoms and having two or more kinds of crystal lattices,
By applying a hydrogen absorption / release cycle that absorbs hydrogen and releases at least a portion of the hydrogen a predetermined number of times,
Obtaining an alloy particle containing two or more kinds of metal atoms and having a single kind of crystal lattice;
A method for producing alloy particles.
The alloy particles according to claim 8 or 9, coated with an organic polymer.
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