JP6434237B2 - Method for producing hollow metal particles and hollow metal particles - Google Patents
Method for producing hollow metal particles and hollow metal particles Download PDFInfo
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Description
本発明は、微細気泡を用いた中空金属粒子の製造方法と中空金属粒子に関する。 The present invention relates to a method for producing hollow metal particles using fine bubbles and hollow metal particles.
中空金属粒子は、中実の金属粒子と比較して大きな比表面積、低密度、少ない金属量といった特性を有している。これらの特性を利用して、新規な高付加価値の機能性材料として期待されている。
中空金属粒子を製造するには、有機重合体からなる粒径１μｍ〜２ｍｍの芯材粒子表面に無電解メッキにより金属層を形成した後、芯材粒子を除去する方法が知られている（特許文献１参照）。この製造方法では、芯材粒子を除去する際に金属層の一部に開口部が生じるため、閉殻の中空金属粒子は得られない。
また、マイクロバブルを利用したポリマーやタンパク質の殻をもつ中空の有機微粒子の製造方法が提案されている。（特許文献２、非特許文献１参照）
Hollow metal particles have characteristics such as a large specific surface area, a low density, and a small amount of metal as compared with solid metal particles. Utilizing these properties, it is expected as a new high-value-added functional material.
In order to produce hollow metal particles, a method is known in which a metal layer is formed by electroless plating on the surface of a core material particle made of an organic polymer and having a particle diameter of 1 μm to 2 mm (patent). Reference 1). In this manufacturing method, when the core particles are removed, an opening is formed in a part of the metal layer, so that closed shell hollow metal particles cannot be obtained.
Further, a method for producing hollow organic fine particles having a polymer or protein shell using microbubbles has been proposed. (See Patent Document 2 and Non-Patent Document 1)
微細気泡を用いた簡便な中空金属粒子の製造方法を提供する。 Provided is a simple method for producing hollow metal particles using fine bubbles.
上記課題を解決するための手段は以下のとおりである。
１．微細気泡分散液中で、
金属微粒子を微細気泡の表面に吸着させる工程、
前記金属微粒子を凝集させて外殻を形成する工程、
を有することを特徴とする中空金属粒子の製造方法。
２．前記金属微粒子が、金属イオンと還元剤との還元反応により析出したものであることを特徴とする、１．に記載の中空金属粒子の製造方法。
３．前記微細気泡が還元剤を含有する気体からなることを特徴とする、２．に記載の中空金属粒子の製造方法。
４．前記気体が水素であることを特徴とする、３．に記載の中空金属粒子の製造方法。
５．前記金属微粒子が、数平均粒子径１ｎｍ〜２００ｎｍであることを特徴とする、１．〜４．のいずれかに記載の中空金属粒子の製造方法。
６．前記微細気泡分散液が塑性流体であり、
前記微細気泡の浮遊状態を、前記微細気泡に作用する前記降伏応力に基づいて制御することを特徴とする、１．〜５．のいずれかに記載の中空金属粒子の製造方法。
７．前記微細気泡分散液が、アガロース、ペクチン、カラギーナン、キサンタンガム、タマリンドガム、ジェランガム、グァーガム、アラビアガム、ゼラチン、にかわ、カルボキシメチルセルロース、プロピレングリコール、ポリビニルアルコール、ポリビニルピロリドンから選ばれる１種、または２種以上の増粘剤を、０．０１〜１０ｗｔ％有することを特徴とする、６．に記載の中空金属粒子の製造方法。
８．前記降伏応力と、前記微細気泡が発生する深さによって、前記中空金属粒子の外殻の厚さを制御することを特徴とする６．または７．に記載の中空金属粒子の製造方法。
９．前記金属微粒子が銀、銅、金のいずれかであることを特徴とする、１．〜８．のいずれかに記載の中空金属粒子の製造方法。
１０．上部に切欠き部を有する液槽を用い、
前記液槽の下部で微細気泡を発生させながら、または、前記液槽の下部に微細気泡分散液を供給しながら、
前記切欠き部から前記微細気泡分散液の上層を回収することを特徴とする、１．〜９．のいずれかに記載の中空金属粒子の連続製造方法。
１１．金属を外殻とし、数平均粒子径が０．１μｍ〜１０００μｍであることを特徴とする中空金属粒子。
１２．前記外殻が銀、銅、金のいずれかからなることを特徴とする、１１．に記載の中空金属粒子。
Means for solving the above problems are as follows.
1. In the fine bubble dispersion,
A step of adsorbing metal fine particles on the surface of fine bubbles,
A step of agglomerating the fine metal particles to form an outer shell;
A method for producing hollow metal particles, comprising:
2. The metal fine particles are precipitated by a reduction reaction between a metal ion and a reducing agent. The manufacturing method of the hollow metal particle as described in above.
3. 1. The fine bubbles are made of a gas containing a reducing agent, The manufacturing method of the hollow metal particle as described in above.
4). 2. the gas is hydrogen, The manufacturing method of the hollow metal particle as described in above.
5. The metal fine particles have a number average particle diameter of 1 nm to 200 nm. ~ 4. The method for producing hollow metal particles according to any one of the above.
6). The fine bubble dispersion is a plastic fluid;
The floating state of the fine bubbles is controlled based on the yield stress acting on the fine bubbles. ~ 5. The method for producing hollow metal particles according to any one of the above.
7). The fine bubble dispersion is one or more selected from agarose, pectin, carrageenan, xanthan gum, tamarind gum, gellan gum, guar gum, gum arabic, gelatin, glue, carboxymethylcellulose, propylene glycol, polyvinyl alcohol, polyvinylpyrrolidone. 5. Thickener of 0.01 to 10 wt%, The manufacturing method of the hollow metal particle as described in above.
8). 5. The thickness of the outer shell of the hollow metal particles is controlled by the yield stress and the depth at which the fine bubbles are generated. Or 7. The manufacturing method of the hollow metal particle as described in above.
9. The metal fine particles are any one of silver, copper, and gold. ~ 8. The method for producing hollow metal particles according to any one of the above.
10. Using a liquid tank with a notch on the top,
While generating fine bubbles in the lower part of the liquid tank, or supplying a fine bubble dispersion to the lower part of the liquid tank,
1. The upper layer of the fine bubble dispersion is recovered from the notch. ~ 9. The continuous manufacturing method of the hollow metal particle in any one of these.
11. Hollow metal particles having a metal as an outer shell and a number average particle diameter of 0.1 μm to 1000 μm.
12 10. The outer shell is made of any one of silver, copper, and gold. Hollow metal particles as described in 1.
本発明により、非常に簡便な方法で中空金属粒子を製造することができる。本発明の製造方法は、従来の芯材粒子を除去する工程が必要な方法と比較して、穏やかな条件下でシンプルな装置を用いた単純な工程により中空金属粒子を製造することができる。金属微粒子を金属イオンと還元剤との還元反応により析出させることにより、金属微粒子分散液が得られるので、金属微粒子を液中に分散させる工程を省くことができる。また、微細気泡中に還元剤を含有させることで、中空金属粒子を効率的に作成することができる。
微細気泡分散液として降伏応力を示す液を用いることにより、微細気泡の浮遊状態を制御することができ、中空金属粒子の粒径を調整することができる。また、降伏応力と微細気泡が発生する深さにより、中空金属粒子の外殻の厚さも制御することができる。さらに、本発明の製造方法によると、中空金属粒子を連続的に生産することもできる。
本発明の製造方法は、従来の製造方法と異なり芯材粒子を除去する工程が不要なので、閉殻である中空金属粒子が得られる。また、本発明の中空金属粒子は閉殻で、真球状であるため、強度、流動性に優れており潰れにくい。本発明の中空金属粒子は、電気伝導性、剛性、熱伝導性等の、金属が有する性能を維持しつつ、大きな比表面積、低密度等の中空構造に由来する特性を有するため、新規な機能性材料として用いることができる。
According to the present invention, hollow metal particles can be produced by a very simple method. The production method of the present invention can produce hollow metal particles by a simple process using a simple apparatus under mild conditions as compared with a conventional method that requires a process of removing core particles. By depositing the metal fine particles by a reduction reaction between metal ions and a reducing agent, a metal fine particle dispersion can be obtained, so that the step of dispersing the metal fine particles in the liquid can be omitted. Moreover, a hollow metal particle can be efficiently produced by containing a reducing agent in fine bubbles.
By using a liquid exhibiting yield stress as the fine bubble dispersion, the floating state of the fine bubbles can be controlled and the particle size of the hollow metal particles can be adjusted. Further, the thickness of the outer shell of the hollow metal particles can be controlled by the yield stress and the depth at which the fine bubbles are generated. Furthermore, according to the production method of the present invention, hollow metal particles can be produced continuously.
Unlike the conventional manufacturing method, the manufacturing method of the present invention does not require a step of removing the core particles, so that hollow metal particles having a closed shell can be obtained. Moreover, since the hollow metal particles of the present invention are closed shells and are spherical, they are excellent in strength and fluidity and are not easily crushed. The hollow metal particles of the present invention have characteristics derived from a hollow structure such as a large specific surface area and low density while maintaining the performance of the metal such as electrical conductivity, rigidity, and thermal conductivity, and thus have a novel function. It can be used as a material.
以下に、本発明を詳細に説明する。
本発明は、微細気泡分散液中で、金属微粒子を微細気泡の表面に吸着させる工程、前記金属微粒子を凝集させて外殻を形成する工程、を有することを特徴とする中空金属粒子の製造方法に関する。
The present invention is described in detail below.
The present invention has a process for adsorbing metal fine particles on the surface of fine bubbles in a fine bubble dispersion, and a process for agglomerating the metal fine particles to form an outer shell. About.
・微細気泡
本発明において、微細気泡とは、直径約０．１μｍ〜１０００μｍの気泡のことを意味する。微細気泡の中で、直径約０．１μｍ〜１μｍの気泡をウルトラファインバブル、直径約１μｍ〜１００μｍの気泡をマイクロバブル、直径約１００μｍ〜１０００μｍの気泡をサブミリバブルという。また、ウルトラファインバブルとマイクロファインバブルとを合わせた、直径約０．１μｍ〜１００μｍの気泡はファインバブルと総称される。（ＩＳＯ/ＴＣ２８１参照）
ここで、本発明において、ウルトラファインバブル、及びマイクロバブルの直径は、微細気泡分散液をレーザー回折式粒度分布計（株式会社島津製作所製、商品名：ＳＡＬＤ７１００）により測定した数平均径を意味し、サブミリバブルの直径は、写真撮影法で測定した数平均径を意味する。
-Fine bubble In this invention, a fine bubble means the bubble about 0.1 micrometer-1000 micrometers in diameter. Among the fine bubbles, bubbles having a diameter of approximately 0.1 μm to 1 μm are referred to as ultrafine bubbles, bubbles having a diameter of approximately 1 μm to 100 μm are referred to as microbubbles, and bubbles having a diameter of approximately 100 μm to 1000 μm are referred to as submillibubbles. Further, bubbles having a diameter of about 0.1 μm to 100 μm, which are a combination of ultrafine bubbles and microfine bubbles, are collectively referred to as fine bubbles. (See ISO / TC281)
Here, in the present invention, the diameters of the ultrafine bubbles and the microbubbles mean the number average diameter of the fine bubble dispersion measured by a laser diffraction particle size distribution meter (trade name: SALD7100, manufactured by Shimadzu Corporation). The diameter of the sub millibubble means a number average diameter measured by a photography method.
水中には、水分子が電離したＨ＋とＯＨ−とが存在している。ＯＨ−の水和エネルギーは、Ｈ＋の水和エネルギーよりも小さいため、微細気泡界面にＯＨ−が集まり、微細気泡は水中で負に帯電する。負に帯電した微細気泡同士は反発しあうため、微細気泡が合一して大きな泡となることはなく、微細気泡は水中で極めて安定している。 In water, H + and OH − in which water molecules are ionized exist. Since the hydration energy of OH − is smaller than the hydration energy of H + , OH − gathers at the microbubble interface, and the microbubbles are negatively charged in water. Since the negatively charged microbubbles repel each other, the microbubbles do not coalesce into large bubbles, and the microbubbles are extremely stable in water.
また、微細気泡は、上昇速度が極めて小さいという特徴を有する。微細気泡の上昇速度（ν）は下記式１に示す、Ｓｔｏｋｅｓの式で推定できる。
式１： ν＝ΔρｇｄＢ ２／１８μＬ
ここで、Δρは液と気泡内ガスとの密度差、ｇは重力加速度、ｄＢは微細気泡の直径、μＬは液粘度を示す。
Further, the fine bubbles have a feature that the rising speed is extremely small. The rising speed (ν) of the fine bubbles can be estimated by the Stokes equation shown in the following equation 1.
Equation 1: ν = Δρgd B 2 / 18μ L
Here, [Delta] [rho] is the density difference between the liquid and the bubble in the gas, g is the gravitational acceleration, d B is fine-bubble diameter, the mu L indicates a liquid viscosity.
上記式１から導かれるように、微細気泡の上昇速度は直径の２乗に比例するので、直径１ｍｍの気泡と比べると、直径１００μｍの気泡の上昇速度は１００分の１、直径１０μｍの気泡の上昇速度は１００００分の１となる。 As derived from Equation 1 above, the rising speed of the fine bubbles is proportional to the square of the diameter, so the rising speed of the 100 μm diameter bubble is 1 / 100th that of the 10 μm diameter bubble compared to the 1 mm diameter bubble. The rising speed is 1 / 10,000.
本発明において、微細気泡を形成する気体の種類は特に限定されない。例えば、窒素、酸素、水素、ヘリウム、二酸化炭素など汎用されている気体を使用することができる。この気体は混合して用いることもでき、混合物である空気を使用することもできる。また、ホルムアルデヒド、二酸化硫黄、水素、一酸化炭素等の還元能を有する気体を含ませることもできる。 In the present invention, the type of gas forming the fine bubbles is not particularly limited. For example, a widely used gas such as nitrogen, oxygen, hydrogen, helium, or carbon dioxide can be used. This gas can also be used by mixing, and air which is a mixture can also be used. Further, a gas having a reducing ability such as formaldehyde, sulfur dioxide, hydrogen, carbon monoxide and the like can be included.
・微細気泡発生装置
本発明において、微細気泡分散液の作成に使用する微細気泡発生装置の種類は特に限定されない。例えば、加圧溶解式、旋回液流式、スタティックミキサー式、エゼクター式、ベンチュリ式、極微細孔式、超音波付加中空針状ノズル式、蒸気凝縮式などの任意の微細気泡発生装置を用いることができる。
液中に上記微細気泡発生装置により微細気泡を発生させることにより、微細気泡分散液が得られる。上記したように、微細気泡は液中で極めて安定しているため、微細気泡分散液は、撹拌、加熱、混合等の通常の実験操作を施すことができる。
-Microbubble generator In this invention, the kind of microbubble generator used for preparation of a microbubble dispersion liquid is not specifically limited. For example, use any fine bubble generator such as pressure dissolution type, swirling liquid type, static mixer type, ejector type, venturi type, ultra fine hole type, ultrasonically added hollow needle nozzle type, vapor condensation type, etc. Can do.
A fine bubble dispersion is obtained by generating fine bubbles in the liquid using the fine bubble generator. As described above, since the fine bubbles are extremely stable in the liquid, the fine bubble dispersion can be subjected to normal experimental operations such as stirring, heating, and mixing.
なお、加圧溶解式、極微細孔式、超音波付加中空針状ノズル式、蒸気凝縮式などの微細気泡発生装置では、液回分式操作で微細気泡分散液を作製できる。 In addition, in a microbubble generator such as a pressure dissolution type, an ultrafine hole type, an ultrasonically added hollow needle nozzle type, or a vapor condensation type, a fine bubble dispersion can be produced by a liquid batch type operation.
（金属）
本発明の一次粒子である金属微粒子の製造方法は特に限定されず、熱プラズマ法、ＣＶＤ法等の気相法、固相合成法、乾式粉砕法、湿式粉砕法等の固相法、還元法、噴霧法等の液相法を使用することができる。これらの中で、還元法と湿式粉砕法とが、金属微粒子の分散液が得られ、そのまま中空金属粒子の製造に用いることができるため好ましい。金属の種類は限定されず、具体的には周期表の第３族から第１１族に含まれる遷移金属であれば特に制限することなく使用することができる。また、純金属だけでなく、酸化物、硫化物、炭化物、窒化物、塩化物、フッ化物等も用いることができる。
還元法により、金属イオンを金属微粒子に還元、析出させるならば、銀、銅、金が、析出した金属微粒子が凝集しやすいため好ましい。ここで、本発明において還元される金属イオンは単原子イオンに限定されず、錯イオン、多原子イオンでもよい。
なお、金属微粒子の数平均粒子径は、金属微粒子分散液をレーザー回折式粒度分布計（株式会社島津製作所製、商品名：ＳＡＬＤ７１００）により測定した値を意味する。
(metal)
The production method of the metal fine particles which are the primary particles of the present invention is not particularly limited, and a gas phase method such as a thermal plasma method and a CVD method, a solid phase synthesis method, a dry pulverization method, a solid phase method such as a wet pulverization method, and a reduction method. A liquid phase method such as a spray method can be used. Among these, the reduction method and the wet pulverization method are preferable because a dispersion of metal fine particles can be obtained and used as it is for the production of hollow metal particles. The type of the metal is not limited, and specifically, any transition metal included in Group 3 to Group 11 of the periodic table can be used without particular limitation. In addition to pure metals, oxides, sulfides, carbides, nitrides, chlorides, fluorides, and the like can be used.
If metal ions are reduced and deposited on metal fine particles by a reduction method, silver, copper, and gold are preferable because the deposited metal fine particles are likely to aggregate. Here, the metal ions to be reduced in the present invention are not limited to monoatomic ions, but may be complex ions or polyatomic ions.
The number average particle diameter of the metal fine particles means a value obtained by measuring the metal fine particle dispersion with a laser diffraction particle size distribution meter (trade name: SALD7100, manufactured by Shimadzu Corporation).
（還元剤）
還元法における、金属イオンの還元反応に使用する還元剤は、特に限定することなく使用することができる。例えば、グリオキサール、ホルムアルデヒド、アセトアルデヒド、二酸化硫黄、水素、一酸化炭素、アスコルビン酸、グルコン酸、グルコース、蟻酸、酒石酸、ハイドロキノン、ヒドラジン、亜硫酸ナトリウム、水素化ホウ素ナトリウム等が挙げられる。これらの中で、還元させる金属種や、還元反応の速度に応じて、適切な還元剤を選択すればよい。還元剤は、１種単独で用いてもよく、２種以上を用いることもできる。２種以上の還元剤は、反応開始時に液中に含有させておいてもよく、先の還元剤での反応が終了した後に、異なる還元剤を添加してもよい。
(Reducing agent)
The reducing agent used for the reduction reaction of metal ions in the reduction method can be used without any particular limitation. Examples include glyoxal, formaldehyde, acetaldehyde, sulfur dioxide, hydrogen, carbon monoxide, ascorbic acid, gluconic acid, glucose, formic acid, tartaric acid, hydroquinone, hydrazine, sodium sulfite, sodium borohydride and the like. Among these, an appropriate reducing agent may be selected according to the metal species to be reduced and the speed of the reduction reaction. A reducing agent may be used individually by 1 type, and 2 or more types can also be used for it. Two or more reducing agents may be contained in the liquid at the start of the reaction, or different reducing agents may be added after the reaction with the previous reducing agent is completed.
例えば、ジアンミン銀（Ｉ）イオン（［Ａｇ（ＮＨ３）２］＋）から銀を析出させるのであれば、グルコース、ホルムアルデヒド等が好適に用いられる。テトラアンミン銅（ＩＩ）イオン（［Ｃｕ（ＮＨ３）４］２＋）から銅を析出させるのであればアスコルビン酸等、テトラヨード金（ＩＩＩ）イオン（［ＡｕＩ４］−）や、テトラクロロ金（ＩＩＩ）イオン（［ＡｕＣｌ４］−）から金を析出させるのであればアスコルビン酸、シュウ酸等が好適に用いられる。 For example, if silver is precipitated from diammine silver (I) ions ([Ag (NH 3 ) 2 ] + ), glucose, formaldehyde and the like are preferably used. If copper is deposited from tetraammine copper (II) ions ([Cu (NH 3 ) 4 ] 2+ ), tetraiodogold (III) ions ([AuI 4 ] − ), tetrachlorogold (III), ascorbic acid, etc. Ascorbic acid, oxalic acid and the like are preferably used if gold is deposited from ions ([AuCl 4 ] − ).
還元反応は、金属イオン溶液と還元剤溶液とを別々に調製し、これらを混合して反応液として開始することが一般的であり、本発明においても、上記手法を採用することができる。さらに、本発明は、還元剤を含有する気体からなる微細気泡を発生させ、この微細気泡から液中に溶解した還元剤により還元反応を進行させることもできる。微細気泡に含有させられる還元剤としては、気体であるホルムアルデヒド、二酸化硫黄、水素、一酸化炭素などを挙げることができる。また、還元剤は、液中、微細気泡中の両方に含ませてもよい。 In the reduction reaction, it is common to prepare a metal ion solution and a reducing agent solution separately, and mix them to start as a reaction solution. In the present invention, the above method can also be adopted. Furthermore, the present invention can generate fine bubbles composed of a gas containing a reducing agent, and can proceed the reduction reaction with the reducing agent dissolved in the liquid from the fine bubbles. Examples of the reducing agent contained in the fine bubbles include gaseous formaldehyde, sulfur dioxide, hydrogen, carbon monoxide and the like. Further, the reducing agent may be included in both the liquid and the fine bubbles.
（中空金属粒子の形成）
本発明の中空金属粒子の製造方法を図１に示す。
微細気泡１が液中に分散している微細気泡分散液中に、一次粒子である金属微粒子２が存在すると、金属微粒子は濡れ性が悪いため微細気泡表面に吸着する。そして微細気泡表面で金属微粒子が凝集して外殻を形成することにより、中空金属粒子３が形成される。金属微粒子の数平均粒子径は１ｎｍ〜２００ｎｍが凝集しやすく外殻を形成しやすいため、好ましい。
なお、図１において、中空金属粒子はその断面が示されており、実際に製造される中空金属粒子は閉殻の球である。
(Formation of hollow metal particles)
The manufacturing method of the hollow metal particle of this invention is shown in FIG.
When the fine metal particle 2 as the primary particle is present in the fine bubble dispersion in which the fine bubble 1 is dispersed in the liquid, the metal fine particle is adsorbed on the surface of the fine bubble because the wettability is poor. Hollow metal particles 3 are formed by agglomeration of metal fine particles on the surface of fine bubbles to form an outer shell. The number average particle diameter of the metal fine particles is preferably 1 nm to 200 nm because it tends to aggregate and easily form an outer shell.
In FIG. 1, the cross-section of the hollow metal particles is shown, and the actually produced hollow metal particles are closed-shell spheres.
金属微粒子を還元法により製造するならば、微細気泡は、混合前の金属イオン溶液、混合前の還元剤溶液、または、混合後の反応液のいずれに分散させても良い。微細気泡を分散させる方法としては、上記液中に微細気泡を直接発生させてもよく、微細気泡分散液と混合してもよい。
金属微粒子を湿式粉砕法により製造するならば、粉砕後に得られる金属微粒子分散液中に微細気泡を直接発生させてもよく、微細気泡分散液と混合してもよい。
また、粉末状の金属微粒子であれば、予め金属微粒子分散液を調製し、この分散液中に微細気泡を直接発生させるか、微細気泡分散液と混合すればよい。
If the metal fine particles are produced by a reduction method, the fine bubbles may be dispersed in any of a metal ion solution before mixing, a reducing agent solution before mixing, or a reaction solution after mixing. As a method of dispersing fine bubbles, fine bubbles may be directly generated in the liquid, or may be mixed with a fine bubble dispersion.
If the metal fine particles are produced by a wet pulverization method, fine bubbles may be directly generated in the metal fine particle dispersion obtained after pulverization, or may be mixed with the fine bubble dispersion.
In the case of powdered metal fine particles, a metal fine particle dispersion may be prepared in advance, and fine bubbles may be directly generated in the dispersion, or mixed with the fine bubble dispersion.
なお、金属微粒子は、微細気泡表面だけでなく、液槽等の容器と微細気泡分散液との固液界面、微細気泡分散液の液面である気液界面にも集まり凝集する。固液界面での金属微粒子の凝集を防ぐために、容器、または容器内壁面は、疎水性の材料、例えば、ステンレス、アクリル、フッ素樹脂等から形成、または被覆されていることが好ましい。 The metal fine particles collect and aggregate not only on the surface of the fine bubbles but also on the solid-liquid interface between the container such as a liquid tank and the fine bubble dispersion and the gas-liquid interface which is the liquid surface of the fine bubble dispersion. In order to prevent agglomeration of metal fine particles at the solid-liquid interface, the container or the inner wall surface of the container is preferably formed or coated with a hydrophobic material such as stainless steel, acrylic, fluororesin or the like.
中空金属粒子を製造するためには、微細気泡表面全体に金属微粒子が吸着して、この金属微粒子が強固に凝集して外殻を形成しなければならない。中空金属粒子の形成中に、未完成の中空金属粒子である外殻片が微細気泡表面から離脱しないために、微細気泡が液中で激しく動くことは好ましくない。したがって、金属微粒子を吸着、凝集させる際に、微細気泡分散液の撹拌は行わない。 In order to produce hollow metal particles, metal fine particles must be adsorbed on the entire surface of fine bubbles, and the metal fine particles should be firmly aggregated to form an outer shell. During the formation of the hollow metal particles, it is not preferable that the fine bubbles move vigorously in the liquid because the outer shell pieces, which are incomplete hollow metal particles, do not leave the surface of the fine bubbles. Therefore, when the fine metal particles are adsorbed and aggregated, the fine bubble dispersion is not stirred.
上記したように、本発明において、還元剤を含有する気体からなる微細気泡を発生させることもできる。還元剤を含有する気体からなる微細気泡を利用した本発明の中空金属粒子の製造方法を図２に示す。
微細気泡１を形成する気体が還元剤を含有すると、微細気泡から液中に溶解した還元剤により還元反応が進行する。そのため、還元反応は微細気泡近傍のみで進行し、一次粒子である金属微粒子２は微細気泡近傍で析出する。析出した金属微粒子が、微細気泡表面で凝集して外殻を形成することにより、中空金属粒子３が形成される。
As described above, in the present invention, fine bubbles made of a gas containing a reducing agent can also be generated. FIG. 2 shows a method for producing hollow metal particles of the present invention using fine bubbles made of a gas containing a reducing agent.
When the gas forming the fine bubbles 1 contains a reducing agent, the reduction reaction proceeds by the reducing agent dissolved in the liquid from the fine bubbles. Therefore, the reduction reaction proceeds only in the vicinity of the fine bubbles, and the metal fine particles 2 that are primary particles are deposited in the vicinity of the fine bubbles. The deposited metal fine particles aggregate on the surface of the fine bubbles to form an outer shell, whereby the hollow metal particles 3 are formed.
微細気泡が還元剤を含有する製造方法では、金属微粒子は微細気泡に近い位置で析出するため、析出した金属微粒子はすぐ近くの微細気泡表面に吸着しやすい。容器との固液界面や、液面である気液界面よりも、微細気泡表面に金属微粒子が多く集まるため、中空金属粒子を効率的に製造することができる。 In the manufacturing method in which the fine bubbles contain a reducing agent, the metal fine particles are deposited at a position close to the fine bubbles, and therefore the precipitated metal fine particles are easily adsorbed on the surface of the nearby fine bubbles. Since a larger amount of metal fine particles are collected on the surface of the fine bubbles than the solid-liquid interface with the container or the gas-liquid interface that is the liquid surface, the hollow metal particles can be efficiently produced.
本発明では、微細気泡表面上で金属微粒子を凝集させることで中空金属粒子が製造されるので、製造される中空金属粒子の粒径は、微細気泡の直径に依存する。
微細気泡の直径が大きいと、微細気泡の表面全体を覆うのに必要な金属微粒子の量が多くなるため、金属微粒子が凝集して中空金属粒子を形成するのに必要な時間が長くなる。しかし、直径の大きな微細気泡は上昇速度が速く、液面に浮かび上がり気泡が弾けるまでの時間（以下、液中滞留時間という。）が短いため、金属微粒子の吸着が十分に行われない。さらに上昇速度が速いと液との摩擦によって吸着した金属微粒子が剥離しやすいため、中空金属粒子が形成されにくい。そのため、直径が大きな微細気泡表面で金属微粒子を凝集させ、大きな粒径の中空金属粒子を製造するには、液中滞留時間を長くすること、上昇速度を遅くすることが必要である。液中滞留時間を長くするには、液高を高くする、微細気泡の上昇速度を遅くするという方法が挙げられるが、液高を高くすると、製造設備が大規模になる、必要な液量が増える、という問題がありコストが増加してしまう。そのため、中空金属微粒子の生成に最も効果的なのは微細気泡の上昇速度を遅くして液中滞留時間を長くすることである。
In the present invention, hollow metal particles are produced by agglomerating metal fine particles on the surface of fine bubbles, and therefore the particle size of the produced hollow metal particles depends on the diameter of the fine bubbles.
When the diameter of the fine bubbles is large, the amount of metal fine particles necessary to cover the entire surface of the fine bubbles increases, and therefore the time required for the metal fine particles to aggregate to form hollow metal particles becomes long. However, fine bubbles having a large diameter have a high ascending speed, and the time until the bubbles rise to the surface of the liquid and blow off the bubbles (hereinafter referred to as the residence time in the liquid) is short, so that the metal fine particles are not sufficiently adsorbed. Further, when the rising speed is high, the metal fine particles adsorbed by friction with the liquid are easily peeled off, so that the hollow metal particles are hardly formed. Therefore, in order to agglomerate metal fine particles on the surface of fine bubbles having a large diameter and produce hollow metal particles having a large particle size, it is necessary to lengthen the residence time in the liquid and slow the ascent rate. In order to lengthen the residence time in the liquid, there are methods of increasing the liquid height and slowing the rising speed of the fine bubbles. However, if the liquid height is increased, the production equipment becomes large-scale, and the required liquid amount is increased. There is a problem that it increases, and the cost increases. Therefore, the most effective method for producing hollow metal fine particles is to slow the rising speed of the fine bubbles and lengthen the residence time in the liquid.
・降伏応力
上昇速度を遅くするには微細気泡分散液として、降伏応力を持つ塑性流体を使用すればよい。流体は、降伏応力を持つ塑性流体と、降伏応力を持たない粘性流体とに分類される。ずり速度により粘度が変わらない流体が粘性流体であり、水や低分子溶媒等が該当する。ずり速度により粘度が変わるものが非ニュートン流体であり、そのうち、特定の力（降伏応力）以上の力を加えないと流動しないものを塑性流体という。塑性流体とするための手法は特に制限されないが、増粘剤を添加する方法が、降伏応力の調整が容易であるため好ましい。増粘剤としては塑性流体が得られるものであれば特に制限することなく使用することができ、例えば、アガロース、ペクチン、カラギーナン、キサンタンガム、タマリンドガム、ジェランガム、グァーガム、アラビアガム、ゼラチン、にかわ、カルボキシメチルセルロース、プロピレングリコール、ポリビニルアルコール、ポリビニルピロリドンなどを挙げることができる。増粘剤の配合量は、特に制限されないが、通常、０．０１〜１０ｗｔ％である。
ここで、本発明の降伏応力は、２重円筒型回転式粘度計（デジタル粘度計（ＬＶ ＤＶ−ＩＩＩ Ｕｌｔｒａ，ＢＲＯＯＫＦＩＥＬＤ）を用いて測定した、液体がＨｅｒｃｈｅｌ−Ｂｕｌｋｌｅｙモデルに基づくと仮定した時の数値である。
-Yield stress A plastic fluid having a yield stress may be used as the fine bubble dispersion to slow the rate of increase. The fluid is classified into a plastic fluid having a yield stress and a viscous fluid having no yield stress. A fluid whose viscosity does not change depending on the shear rate is a viscous fluid, and water, a low molecular solvent, and the like are applicable. A non-Newtonian fluid whose viscosity changes depending on the shear rate is a non-Newtonian fluid, and a fluid that does not flow unless a force exceeding a specific force (yield stress) is applied. The method for forming the plastic fluid is not particularly limited, but a method of adding a thickener is preferable because it is easy to adjust the yield stress. As the thickener, any plastic fluid can be used without any particular limitation. For example, agarose, pectin, carrageenan, xanthan gum, tamarind gum, gellan gum, guar gum, gum arabic, gelatin, glue, carboxy Examples thereof include methyl cellulose, propylene glycol, polyvinyl alcohol, and polyvinyl pyrrolidone. Although the compounding quantity of a thickener is not restrict | limited in particular, Usually, it is 0.01-10 wt%.
Here, the yield stress of the present invention is measured using a double cylindrical rotary viscometer (digital viscometer (LV DV-III Ultra, BROOKFIELD)), assuming that the liquid is based on the Herchel-Bulkley model. It is a numerical value.
降伏応力を示す塑性流体中において、微細気泡の運動を阻止する力ＦＤは、下記式２で表される。
式２： ＦＤ＝τ０×π（ｄ／２）２
ここで、τ０は液の降伏応力［Ｎ／ｍ２］、ｄは微細気泡の直径［ｍ］を示す。
In the plastic fluid showing a yield stress, a force F D to prevent movement of the fine bubbles, is represented by the following formula 2.
Formula 2: F D = τ0 × π (d / 2) 2
Here, τ0 represents the yield stress [N / m 2 ] of the liquid, and d represents the diameter [m] of the fine bubbles.
また、微細気泡に加わる浮力ＦＵは、下記式３で表される。
式３： ＦＵ＝ＶΔρｇ
ここで、Ｖは微細気泡の体積［ｍ３］、Δρは液と微細気泡との密度差［ｋｇ／ｍ３］、ｇは重力加速度［ｍ／ｓ２］を示す。
Further, the buoyancy F U acting on the fine bubbles is represented by the following formula 3.
Formula 3: F U = VΔρg
Here, V represents the volume [m 3 ] of the fine bubbles, Δρ represents the density difference [kg / m 3 ] between the liquid and the fine bubbles, and g represents the gravitational acceleration [m / s 2 ].
降伏応力を示す液中の微細気泡には、運動を阻止する力が加わる。浮上する微細気泡に対して、この力が浮上を妨げるように加わるため、微細気泡が浮上する速度が遅くなり液中滞留時間が長くなる。直径の大きな微細気泡の液中滞留時間が長くなると、その表面で金属微粒子が吸着、凝集して外殻を形成することができるため、粒径の大きな中空金属粒子を製造することができる。 A force for preventing movement is applied to the fine bubbles in the liquid exhibiting the yield stress. Since this force is applied to the rising fine bubbles so as to prevent the rising, the speed of the rising of the fine bubbles is slowed and the residence time in the liquid is lengthened. When the residence time of fine bubbles having a large diameter in the liquid becomes long, metal fine particles can be adsorbed and aggregated on the surface to form an outer shell, so that hollow metal particles having a large particle diameter can be produced.
ここで、ＦＤ≧ＦＵとなる直径の微細気泡は、降伏応力由来の運動を阻止する力が浮力よりも大きいため浮上できない。ＦＤ＝ＦＵとなる直径（以下、限界直径という。）ｄ０は、上記式２、３より導くことができ、下記式４で表される。
式４： ｄ０＝（３τ０）／（２Δρｇ）
Here, the fine bubbles having a diameter satisfying F D ≧ F U cannot float because the force for preventing the movement derived from the yield stress is larger than the buoyancy. A diameter (hereinafter referred to as a limit diameter) d0 where F D = F U can be derived from the above formulas 2 and 3, and is represented by the following formula 4.
Formula 4: d0 = (3τ0) / (2Δρg)
上記式４より、限界直径は液の降伏応力により定まるため、微細気泡の浮遊状態を、微細気泡に作用する降伏応力に基づいて制御することができる。例えば、密度１０００ｋｇ／ｍ３、降伏応力τ０が０．３２７Ｎ／ｍ２である液中における微細気泡の限界直径ｄ０は約５０μｍと算出される。この液中では、直径が約５０μｍ未満の微細気泡は浮上することができず、直径が約５０μｍより大きな微細気泡のみが浮上できる。 From the above equation 4, since the critical diameter is determined by the yield stress of the liquid, the floating state of the fine bubbles can be controlled based on the yield stress acting on the fine bubbles. For example, the critical diameter d0 of fine bubbles in a liquid having a density of 1000 kg / m 3 and a yield stress τ 0 of 0.327 N / m 2 is calculated to be about 50 μm. In this liquid, fine bubbles having a diameter of less than about 50 μm cannot float, and only fine bubbles having a diameter of greater than about 50 μm can float.
この液中で、直径約０．１μｍ〜１０００μｍの微細気泡を用いて中空金属粒子の製造を行うと、限界直径以下の微細気泡（例えば、直径約０．１μｍ〜５０μｍ）は、浮上することができず、いわば液中滞留時間が無限であるため、その表面上で中空金属粒子が完成する。製造された粒径の小さな中空金属粒子は降伏応力により運動できないため、液中で浮上も沈殿もせずに漂い続ける。
十分な液中滞留時間を有する微細気泡（例えば、直径約５０〜１００μｍ）は、その表面に金属微粒子が吸着、凝集して外殻を形成して中空金属粒子が製造される。この中空金属粒子は、降伏応力よりも浮力が大きいため浮上することができ、また、内部に微細気泡を包含しており低密度であるため、液面に浮かび上がる。
上昇速度が速い微細気泡（例えば、直径約１００〜１０００μｍ）は、その表面で金属微粒子が吸着、凝集して中空金属粒子が完成する前に液面に浮上して弾けてしまうため、中空金属粒子ではなく外殻片が製造される。この外殻片は、微細気泡とともに液面に浮上する。
すなわち、本発明の製造方法によると、微細気泡の浮遊状態を降伏応力に基づいて制御することができ、限界直径よりも小さい直径の微細気泡からは液中に漂った状態の中空金属粒子を、限界直径よりも大きい直径の微細気泡からは液面に浮かび上がった状態の中空金属粒子を得ることができる。
なお、上記した微細気泡の直径は単なる一例であり、実際には液高や、反応速度等により、得られる中空金属粒子の粒径は異なる。
When hollow metal particles are produced using fine bubbles having a diameter of about 0.1 μm to 1000 μm in this liquid, fine bubbles having a diameter less than the limit diameter (for example, a diameter of about 0.1 μm to 50 μm) may float. In other words, since the residence time in the liquid is infinite, hollow metal particles are completed on the surface. The produced hollow metal particles having a small particle diameter cannot move due to the yield stress, and therefore continue to float without floating or settling in the liquid.
The fine bubbles having a sufficient residence time in the liquid (for example, a diameter of about 50 to 100 μm) are formed by adsorbing and agglomerating metal fine particles on the surface to form an outer shell to produce hollow metal particles. These hollow metal particles can float because they have a buoyancy greater than the yield stress, and also contain fine bubbles inside and have a low density, so they float on the liquid surface.
Fine bubbles (for example, a diameter of about 100 to 1000 μm) having a high ascending speed float and float on the liquid surface before metal particles are adsorbed and aggregated on the surface to complete the hollow metal particles. Rather, a shell piece is produced. This outer shell piece floats on the liquid surface together with fine bubbles.
That is, according to the production method of the present invention, the floating state of the fine bubbles can be controlled based on the yield stress, and the hollow metal particles in a state of floating in the liquid from the fine bubbles having a diameter smaller than the limit diameter, Hollow metal particles in a state of floating on the liquid surface can be obtained from fine bubbles having a diameter larger than the limit diameter.
Note that the diameter of the fine bubbles described above is merely an example, and the particle size of the obtained hollow metal particles actually varies depending on the liquid height, reaction rate, and the like.
上記したように、本発明の製造方法では、液の降伏応力を制御することにより、限界直径より略大きな粒径の中空金属粒子を選択的に液面に浮上させ、限界直径より略小さな粒径の中空金属粒子を選択的に液中に漂わせることができるため、特定の粒度分布を有する中空金属粒子を選り分けることができる。
液の降伏応力は、液面に浮上させる中空金属粒子の粒径に応じて、０．０５〜１．０Ｎ／ｍ２の範囲で適宜調整することができる。降伏応力は、増粘剤の種類、濃度、液温等により調製することができる。
また、中空金属粒子の外殻の厚さは、微細気泡表面に凝集する金属微粒子量に依存するため、液中滞留時間が長くなるほど外殻は厚くなる。すなわち、外殻の厚さは、降伏応力と微細気泡が発生する深さにより制御することができる。
As described above, in the production method of the present invention, by controlling the yield stress of the liquid, the hollow metal particles having a particle size substantially larger than the limit diameter are selectively levitated on the liquid surface, and the particle size substantially smaller than the limit diameter is obtained. Since the hollow metal particles can be selectively floated in the liquid, the hollow metal particles having a specific particle size distribution can be selected.
The yield stress of a liquid can be suitably adjusted in the range of 0.05-1.0 N / m < 2 > according to the particle size of the hollow metal particle which floats on the liquid level. The yield stress can be adjusted by the type, concentration, liquid temperature, etc. of the thickener.
Moreover, since the thickness of the outer shell of the hollow metal particles depends on the amount of metal fine particles aggregated on the surface of the fine bubbles, the outer shell becomes thicker as the residence time in the liquid becomes longer. That is, the thickness of the outer shell can be controlled by the yield stress and the depth at which fine bubbles are generated.
降伏応力を示す液中で中空金属粒子を製造した後の様子を図３に示す。
上記したように、製造終了後の液面には、限界直径よりも略大きな粒径の中空金属粒子３と、未完成の中空金属粒子である外殻片４が浮かんでいる。また、気液界面で凝集した板状の金属片５も浮かんでいる。すなわち、製造終了後に液面に浮かんでいる金属には、中空金属粒子３と外殻片４と板状の金属片５とが含まれている。限界直径よりも略小さな粒径の中空金属粒子６は浮上も沈殿もすることができないため、液中に漂っている。
FIG. 3 shows a state after the hollow metal particles are produced in the liquid showing the yield stress.
As described above, the hollow metal particles 3 having a particle diameter substantially larger than the limit diameter and the outer shell pieces 4 which are unfinished hollow metal particles are floating on the liquid surface after the production is finished. Further, a plate-shaped metal piece 5 aggregated at the gas-liquid interface also floats. That is, the metal floating on the liquid surface after the production is finished includes the hollow metal particles 3, the outer shell piece 4, and the plate-like metal piece 5. Since the hollow metal particles 6 having a particle size substantially smaller than the limit diameter cannot float and settle, they float in the liquid.
液面に浮かんでいる金属を回収して、洗浄した後のモデルを図４に示す。
中空金属粒子３は、閉殻であり粒子内部の中空部に水が侵入しないため低密度である。一方、外殻片４と板状の金属片５は、バルク金属であり密度が大きい。そのため、製造終了後には液面に浮かび上がっているが、本来は水に沈殿する。液面上に浮かんでいる金属を洗浄すると、外殻片４と板状の金属片５は沈殿するが、中空金属粒子３は浮かんだままなので、中空金属粒子を容易に選り分けることができる。
FIG. 4 shows a model after the metal floating on the liquid surface is collected and washed.
The hollow metal particle 3 has a closed shell and has a low density because water does not enter the hollow portion inside the particle. On the other hand, the outer shell piece 4 and the plate-like metal piece 5 are bulk metals and have a high density. Therefore, although it floats on the liquid surface after the production is finished, it is originally precipitated in water. When the metal floating on the liquid surface is washed, the outer shell piece 4 and the plate-like metal piece 5 are precipitated, but the hollow metal particles 3 remain floating, so that the hollow metal particles can be easily selected.
粒径の小さな中空金属粒子６は、増粘剤の濃度を低くする、液の温度を高める等により、液の降伏応力を小さくする、または、液をニュートン流体とすると、液面に浮上するため、容易に回収することができる。また、この中空金属粒子６は、降伏応力を示す液中で極めて安定して存在しているため、中空金属粒子の分散液のまま用いることもできる。なお、液中に分散している中空金属粒子６は、ろ過、遠心分離によっても回収できるが、潰れてしまうものがあるため、液面に浮上させてから回収することが好ましい。 The hollow metal particles 6 having a small particle size float on the liquid surface when the yield stress of the liquid is reduced by reducing the concentration of the thickener, increasing the temperature of the liquid, or when the liquid is a Newtonian fluid. Can be easily recovered. Moreover, since this hollow metal particle 6 exists very stably in the liquid which shows a yield stress, it can also be used with the dispersion liquid of a hollow metal particle. The hollow metal particles 6 dispersed in the liquid can be recovered by filtration and centrifugation, but some of them are crushed, and therefore, it is preferable to recover them after floating on the liquid surface.
上記したように、本発明の製造方法によると、限界直径よりも略大きな粒径の中空金属粒子は液面に浮かび上がる。そのため、中空金属粒子の製造に用いる液槽の上部に切欠き部等を形成し、水、原料、微細気泡等を供給しながら前記切欠き部等からの微細気泡分散液の上層を回収することで、中空金属粒子を連続的に製造することができる。連続生産する際には、微細気泡の液中滞留時間を長くするために、微細気泡は反応槽下部で発生させる、または、微細気泡分散液を反応槽下部から供給することが好ましい。微細気泡を発生させる、または、微細気泡分散液を供給する反応槽下部は、反応槽底面から液高の３分の１までが好ましく、５分の１までがより好ましく、反応槽底面が最も好ましい。
また、水を反応槽下部から供給しながら連続生産を行うと、液中に漂う限界直径よりも略小さな粒径の中空金属粒子も新たに供給される水に押し出されるように液の上層に移動するため、上層とともに回収することができる。
As described above, according to the production method of the present invention, hollow metal particles having a particle size substantially larger than the limit diameter emerge on the liquid surface. Therefore, a notch or the like is formed in the upper part of the liquid tank used for the production of the hollow metal particles, and the upper layer of the fine bubble dispersion liquid from the notch or the like is recovered while supplying water, raw materials, fine bubbles, etc. Thus, the hollow metal particles can be continuously produced. In continuous production, in order to increase the residence time of the fine bubbles in the liquid, it is preferable to generate the fine bubbles in the lower part of the reaction tank or supply the fine bubble dispersion from the lower part of the reaction tank. The lower part of the reaction tank for generating fine bubbles or supplying the fine bubble dispersion is preferably up to one third of the liquid height from the bottom of the reaction tank, more preferably up to one fifth, and most preferably the bottom of the reaction tank. .
In addition, when continuous production is performed while water is supplied from the bottom of the reaction tank, hollow metal particles having a particle size substantially smaller than the limit diameter floating in the liquid are also moved to the upper layer so that the newly supplied water is pushed out. Therefore, it can be recovered together with the upper layer.
・中空金属粒子
上記製造方法により、金属を外殻とし、粒径が０．１〜１０００μｍである中空金属粒子を製造することができる。なお、本発明において、中空金属粒子の粒径は、３Ｄリアルサーフィスビュー顕微鏡（株式会社キーエンス製、装置名：ＶＥ−８８００）で観察した画像を画像解析ソフト（日鐵住金テクノロジー株式会社、ソフト名：粒子解析ＩＩＩ）で解析した２００〜４００個の粒子の数平均粒子径を意味する。
本発明の製造方法により製造される中空金属粒子は、液中で微細気泡を包み込みながら形成されるため、閉殻であるという従来の中空金属粒子とは一見して区別できる外観を有している。これに対し、従来の製造方法では、芯物質を除去する際に、外殻に開口部が生じてしまうため、閉殻の中空金属粒子は得られない。
さらに、本発明の中空金属粒子は、真球である微細気泡表面で凝集して外殻を形成するため、真球状で、その内面が非常に平滑である。本発明の中空金属粒子は閉殻で、真球状であり、強度、流動性に優れているため、樹脂等と混合したり、分散液をポンプで循環させたりしても、潰れにくい。
Hollow metal particles Hollow metal particles having a metal as an outer shell and a particle size of 0.1 to 1000 µm can be produced by the above production method. In the present invention, the particle size of the hollow metal particles is the image analysis software (Nippon Sumikin Technology Co., Ltd., software name) observed with a 3D real surface view microscope (manufactured by Keyence Corporation, device name: VE-8800). : Means the number average particle diameter of 200 to 400 particles analyzed in Particle Analysis III).
The hollow metal particles produced by the production method of the present invention are formed while enclosing fine bubbles in a liquid, and thus have an appearance that can be distinguished from conventional hollow metal particles that are closed shells at a glance. On the other hand, in the conventional manufacturing method, when the core material is removed, an opening is generated in the outer shell, so that closed hollow metal particles cannot be obtained.
Furthermore, since the hollow metal particles of the present invention aggregate on the surface of fine bubbles, which are true spheres, to form an outer shell, they are true spheres and have very smooth inner surfaces. The hollow metal particles of the present invention are closed shells, have a spherical shape, and are excellent in strength and fluidity. Therefore, they are not easily crushed even when mixed with a resin or circulated with a pump.
次に、本発明を実施例に基づいて、さらに具体的に説明するが、本発明はこれらのみに限定されるものではない。 Next, the present invention will be described more specifically based on examples, but the present invention is not limited to these examples.
・銀鏡反応による銀析出を利用した中空金属粒子の製造
硝酸銀の０．３ｍｏｌ／Ｌ水溶液５．０ｍｌに、２．０ｍｏｌ／Ｌのアンモニア水を徐々に加えると、茶褐色の酸化銀（Ｉ）の沈殿が生じた。さらにアンモニア水を加えると、ジアンミン銀（Ｉ）イオン（［Ａｇ（ＮＨ３）２］＋）を形成して酸化銀（Ｉ）の沈殿が消失した。アンモニア水は、合計で２．２ｍｌ加えた。この液に、ｐＨ調整剤として１．０ｍｏｌ／Ｌの水酸化ナトリウム水溶液を０．４ｍｌ、増粘剤としてキサンタンガム（ＳＩＧＭＡ−ＡＬＤＲＩＣＨ株式会社製、商品名：Ｘａｎｔｈａｎ ｇｕｍ、製品番号：Ｇ１２５３−５００Ｇ、Ｂａｔｃｈ＃：０１４Ｋ０２１０）の０．６ｗｔ％水溶液を０．６ｍｌ加え、銀鏡反応溶液とした。
・ Production of hollow metal particles using silver precipitation by silver mirror reaction When 2.0 mol / L of ammonia water is gradually added to 5.0 ml of 0.3 mol / L aqueous solution of silver nitrate, brown silver (I) oxide precipitates Occurred. When ammonia water was further added, diammine silver (I) ions ([Ag (NH 3 ) 2 ] + ) were formed, and the precipitation of silver oxide (I) disappeared. A total of 2.2 ml of aqueous ammonia was added. To this solution, 0.4 ml of 1.0 mol / L sodium hydroxide aqueous solution as a pH adjuster and xanthan gum (manufactured by SIGMA-ALDRICH Co., Ltd., trade name: Xanthan gum, product number: G1253-500G, Batch) #: 0.6 ml of a 0.6 wt% aqueous solution of 014K0210) was added to obtain a silver mirror reaction solution.
銀鏡反応の還元剤であるグルコースの５ｖｏｌ％水溶液中に、加圧溶解式のマイクロバブル発生装置（株式会社オーラテック製、商品名：ＯＭ４−ＭＤＧ−０４５）を用いて、空気を気泡とする微細気泡を発生させて、微細気泡分散液とした。この分散液中の微細気泡の直径は１０〜４０μｍの範囲であり、数平均径は２２．９μｍであった。 Using a pressure-dissolving microbubble generator (product name: OM4-MDG-045, manufactured by Auratech Co., Ltd.) in a 5 vol% aqueous solution of glucose, which is a reducing agent for silver mirror reaction, fine air is used as bubbles. Bubbles were generated to obtain a fine bubble dispersion. The diameter of the fine bubbles in this dispersion was in the range of 10 to 40 μm, and the number average diameter was 22.9 μm.
上記銀鏡反応溶液８．２ｍｌと上記微細気泡分散液１６ｍｌとを混合した反応液を、試験管に液高３ｃｍとなるように入れ、５５℃の温浴中で１０分間静置した。反応液中のキサンタンガムの濃度は０．０１５ｗｔ％であり、この反応液の２０℃における降伏応力は０．１２３Ｎ／ｍ２であった。 A reaction solution obtained by mixing 8.2 ml of the silver mirror reaction solution and 16 ml of the fine bubble dispersion was placed in a test tube so as to have a liquid height of 3 cm, and allowed to stand in a warm bath at 55 ° C. for 10 minutes. The concentration of xanthan gum in the reaction solution was 0.015 wt%, and the yield stress of this reaction solution at 20 ° C. was 0.123 N / m 2 .
銀鏡反応の化学式は、以下のとおりであり、ジアンミン銀（Ｉ）イオンが鎖状構造のグルコース末端のアルデヒド基により還元され、金属銀が析出する。
Ｃ６Ｈ１２Ｏ６＋２［Ａｇ（ＮＨ３）２］＋＋２ＯＨ−
→Ｃ６Ｈ１２Ｏ７＋２Ａｇ＋４ＮＨ３＋Ｈ２Ｏ
The chemical formula of the silver mirror reaction is as follows. Diammine silver (I) ions are reduced by the aldehyde group at the glucose terminal of the chain structure, and metallic silver is deposited.
C 6 H 12 O 6 +2 [Ag (NH 3 ) 2 ] + + 2OH −
→ C 6 H 12 O 7 + 2Ag + 4NH 3 + H 2 O
加熱後に表面に浮かんでいる銀を網ですくい取り、純水で洗浄した。洗浄後も浮かんでいる銀を網ですくい取り、シャーレ上で乾燥させた。得られた銀をエポキシ樹脂中に包埋し、走査型電子顕微鏡で観察したところ、粒径１０〜２０μｍの中空銀粒子が得られたことが確認できた。得られた中空銀粒子の数平均粒子径は１４．８０μｍであった。 After heating, the silver floating on the surface was scooped with a net and washed with pure water. After washing, the floating silver was scooped with a net and dried on a petri dish. When the obtained silver was embedded in an epoxy resin and observed with a scanning electron microscope, it was confirmed that hollow silver particles having a particle diameter of 10 to 20 μm were obtained. The number average particle diameter of the obtained hollow silver particles was 14.80 μm.
図５に中空銀粒子の走査型電子顕微鏡画像、図６に中空銀粒子の外殻を拡大した走査型電子顕微鏡画像を示す。走査型電子顕微鏡による観察により、本発明の中空銀粒子が閉殻で、略真球状であること、一次粒子である金属微粒子が凝集して外殻が形成されていることが確認できた。
また、洗浄後に沈殿した銀に含まれる未完成の中空金属粒子である外殻片を回収して、同様の手法で走査型顕微鏡により観察した。図７に外殻片の走査型電子顕微鏡画像、図８に外殻片の内面を拡大した走査型電子顕微鏡画像を示す。図６、８より、本発明の中空銀粒子の内面が外面に比べて滑らかであることが確認できた。
FIG. 5 shows a scanning electron microscope image of the hollow silver particles, and FIG. 6 shows an enlarged scanning electron microscope image of the outer shell of the hollow silver particles. By observation with a scanning electron microscope, it was confirmed that the hollow silver particles of the present invention were closed shell and substantially spherical, and that the metal fine particles as primary particles were aggregated to form an outer shell.
Further, the outer shell pieces, which are incomplete hollow metal particles contained in the silver precipitated after washing, were collected and observed with a scanning microscope in the same manner. FIG. 7 shows a scanning electron microscope image of the outer shell piece, and FIG. 8 shows an enlarged scanning electron microscope image of the inner surface of the outer shell piece. 6 and 8, it was confirmed that the inner surface of the hollow silver particles of the present invention was smoother than the outer surface.
銀鏡反応溶液と微細気泡分散液とを混合した反応液を、試験管にそれぞれ液高１．４０ｃｍ、５．００ｃｍ、８．７０ｃｍとなるように入れた以外は、上記実施例１と同様にして中空銀粒子を製造した。
液高３．００ｃｍである実施例１と合わせて、得られた中空銀粒子の数平均粒子径を表１に示す。
The reaction solution obtained by mixing the silver mirror reaction solution and the fine bubble dispersion was put in a test tube so that the liquid heights were 1.40 cm, 5.00 cm, and 8.70 cm, respectively. Hollow silver particles were produced.
The number average particle diameter of the obtained hollow silver particles is shown in Table 1 together with Example 1 having a liquid height of 3.00 cm.
液高が高くなるにつれ、製造される中空銀粒子の数平均粒子径が大きくなることが確認できた。これは、液高が高くなると、上昇速度の早い、直径の大きな微細気泡でも液中滞留時間が長くなるため、直径の大きな微細気泡表面上でも中空銀粒子が完成したためである。 It was confirmed that the number average particle diameter of the hollow silver particles produced increased as the liquid height increased. This is because, as the liquid height increases, the retention time in the liquid becomes longer even for fine bubbles having a large diameter and a high rising speed, so that hollow silver particles are completed even on the surface of the fine bubbles having a large diameter.
銀鏡反応溶液を調製する際に加えるキサンタンガム水溶液の濃度を、それぞれ０．４ｗｔ％、１．８ｗｔ％、３．４ｗｔ％とした以外は、実施例１と同様にして中空銀粒子を作成した。反応液中のキサンタンガムの濃度はそれぞれ、０．０１０ｗｔ％、０．０４５ｗｔ％、０．０８５ｗｔ％であり、それぞれの反応液の２０℃における降伏応力は０．０９０６Ｎ／ｍ２、０．２４７Ｎ／ｍ２、０．４３４Ｎ／ｍ２であった。 Hollow silver particles were prepared in the same manner as in Example 1 except that the concentration of the xanthan gum aqueous solution added when preparing the silver mirror reaction solution was 0.4 wt%, 1.8 wt%, and 3.4 wt%, respectively. The concentrations of xanthan gum in the reaction liquid are 0.010 wt%, 0.045 wt%, and 0.085 wt%, respectively, and the yield stress of each reaction liquid at 20 ° C. is 0.0906 N / m 2 and 0.247 N / m. 2 and 0.434 N / m 2 .
反応液でのキサンタンガム濃度が０．０１５ｗｔ％である実施例１と合わせて、得られた中空銀粒子の数平均粒子径を表２に示す。 Table 2 shows the number average particle size of the hollow silver particles obtained in combination with Example 1 in which the xanthan gum concentration in the reaction solution was 0.015 wt%.
キサンタンガム濃度が０．０１０ｗｔ％では、中空銀粒子が得られなかった。これは、液の降伏応力が小さく、微細気泡の液中滞留時間が短かったため、中空銀粒子が完成しなかったためである。キサンタンガム濃度が０．０１０ｗｔ％、微細気泡の直径が１０〜４０μｍの条件下では、液高３．００ｃｍでは中空銀粒子が完成しなかったが、反応液の液高を高くして、液中滞留時間を長くすれば中空銀粒子が得られると予想される。
キサンタンガム濃度が高く、降伏応力が大きくなるにつれ、製造される中空銀粒子の数平均粒子径が大きくなることが確認できた。これは、降伏応力が大きくなると、限界直径が大きくなり、この限界直径より略大きな粒径の中空金属粒子が選択的に液面に浮かび上がったためである。なお、本実施例において、降伏応力の測定は２０℃、中空銀粒子の製造は５５℃で行っているため、上記式４に降伏応力の実測値を代入して算出される限界直径の値と、得られた中空銀粒子の粒子径とは一致していない。
When the xanthan gum concentration was 0.010 wt%, hollow silver particles were not obtained. This is because the hollow silver particles were not completed because the yield stress of the liquid was small and the residence time of the fine bubbles in the liquid was short. Under the conditions of xanthan gum concentration of 0.010 wt% and fine bubble diameter of 10 to 40 μm, hollow silver particles were not completed at a liquid height of 3.00 cm, but the liquid height of the reaction liquid was increased and the liquid stayed in the liquid. It is expected that hollow silver particles can be obtained if the time is increased.
It was confirmed that the number average particle diameter of the hollow silver particles produced increased as the xanthan gum concentration increased and the yield stress increased. This is because as the yield stress increases, the limit diameter increases, and hollow metal particles having a particle size substantially larger than the limit diameter are selectively raised on the liquid surface. In this example, since the yield stress was measured at 20 ° C. and the hollow silver particles were produced at 55 ° C., the value of the critical diameter calculated by substituting the measured value of the yield stress into the above equation 4 The particle diameter of the obtained hollow silver particles does not match.
・銅鏡反応による銅析出を利用した中空金属粒子の製造
硝酸銅の０．３ｍｏｌ／Ｌ水溶液５．０ｍｌに、３．０ｍｏｌ／Ｌのアンモニア水を２．２ｍｌ加えて硝酸銅を溶解し、テトラアンミン銅（II）イオン（［Ｃｕ（ＮＨ３）４］２＋）溶液とした。この液に、ｐＨ調整剤として１．０ｍｏｌ／Ｌの水酸化ナトリウム水溶液を０．４ｍｌ、増粘剤としてキサンタンガム（ＳＩＧＭＡ−ＡＬＤＲＩＣＨ株式会社製、商品名：Ｘａｎｔｈａｎ ｇｕｍ 製品番号：Ｇ１２５３−５００Ｇ Ｂａｔｃｈ＃：０１４Ｋ０２１０）の０．６ｗｔ％水溶液を６．０ｍｌ加え、銅鏡反応溶液とした。
・ Manufacture of hollow metal particles utilizing copper precipitation by copper mirror reaction To 5.0 ml of 0.3 mol / L aqueous solution of copper nitrate, 2.2 ml of 3.0 mol / L aqueous ammonia was added to dissolve the copper nitrate, and tetraammine copper (II) Ion ([Cu (NH 3 ) 4 ] 2+ ) solution was used. To this solution, 0.4 ml of a 1.0 mol / L sodium hydroxide aqueous solution as a pH adjuster and xanthan gum (manufactured by SIGMA-ALDRICH Co., Ltd., trade name: Xanthan gum Product No .: G1253-500G Batch #: 6.0 ml of a 0.6 wt% aqueous solution of 014K0210) was added to obtain a copper mirror reaction solution.
銅鏡反応の還元剤であるアスコルビン酸の５ｖｏｌ％水溶液中に、加圧溶解式のマイクロバブル発生装置（株式会社オーラテック製、商品名：ＯＭ４−ＭＤＧ−０４５）を用いて、空気を気泡とする微細気泡を発生させて、微細気泡分散液とした。この分散液中の微細気泡の直径は９０〜３００μｍの範囲であり、数平均径は１００μｍであった。 In a 5 vol% aqueous solution of ascorbic acid that is a reducing agent for the copper mirror reaction, air is made into bubbles using a pressure-dissolving microbubble generator (product name: OM4-MDG-045, manufactured by Auratech Co., Ltd.). Fine bubbles were generated to obtain a fine bubble dispersion. The diameter of the fine bubbles in this dispersion was in the range of 90 to 300 μm, and the number average diameter was 100 μm.
上記銅鏡反応溶液１３．６ｍｌと上記微細気泡分散液１６ｍｌとを混合した反応液を、試験管に液高３ｃｍとなるように入れ、５５℃の温浴中で１０分間静置した。反応液中のキサンタンガムの濃度は０．２６５ｗｔ％であった。 A reaction liquid obtained by mixing 13.6 ml of the copper mirror reaction solution and 16 ml of the fine bubble dispersion liquid was put in a test tube so that the liquid height was 3 cm, and was allowed to stand in a warm bath at 55 ° C. for 10 minutes. The concentration of xanthan gum in the reaction solution was 0.265 wt%.
銅鏡反応の化学式は、以下のとおりであり、テトラアンミン銅(ＩＩ)イオンがアスコルビン酸により還元され、金属銅が析出する。
［Ｃｕ（ＮＨ３）４］２＋＋アスコルビン酸＋２ＯＨ−
→デヒドロアスコルビン酸＋Ｃｕ＋４ＮＨ３＋２Ｈ２Ｏ
The chemical formula of the copper mirror reaction is as follows. Tetraammine copper (II) ions are reduced by ascorbic acid, and copper metal is deposited.
[Cu (NH 3 ) 4 ] 2+ + ascorbic acid + 2OH −
→ Dehydroascorbic acid + Cu + 4NH 3 + 2H 2 O
加熱後に表面に浮かんでいる銅を網ですくい取り、純水で洗浄した。洗浄後も浮かんでいる銅を網ですくい取り、シャーレ上で乾燥させた。得られた銅をエポキシ樹脂中に包埋し、走査型電子顕微鏡で観察したところ、９０〜３００μｍの中空銅粒子が得られたことが確認できた。得られた中空銅粒子の数平均粒子径は１００μｍであった。キサンタンガムの濃度が高く、降伏応力が大きいため、粒径の大きな中空銅粒子が得られた。
図９に中空銅粒子の走査型電子顕微鏡画像を、図１０にその拡大図を示す。走査型電子顕微鏡による観察により、本発明の中空銅粒子が閉殻であることが確認できた。
After heating, the copper floating on the surface was scooped with a net and washed with pure water. After washing, the floating copper was scooped with a net and dried on a petri dish. When the obtained copper was embedded in an epoxy resin and observed with a scanning electron microscope, it was confirmed that 90 to 300 μm hollow copper particles were obtained. The number average particle diameter of the obtained hollow copper particles was 100 μm. Since the concentration of xanthan gum was high and the yield stress was large, hollow copper particles having a large particle size were obtained.
FIG. 9 shows a scanning electron microscope image of the hollow copper particles, and FIG. 10 shows an enlarged view thereof. Observation with a scanning electron microscope confirmed that the hollow copper particles of the present invention were closed shells.
・金鏡反応による金析出を利用した中空金属粒子の製造
蒸留水７．６ｍｌに、ヨウ化カリウム０．６ｇ及びヨウ素０．１ｇを投入して攪拌溶解させた。この溶液に金を０．１ｇ投入して撹拌溶解させてテトラヨード金（ＩＩＩ）イオン（［ＡｕＩ４］−）溶液とした。さらに、増粘剤としてキサンタンガム（ＳＩＧＭＡ−ＡＬＤＲＩＣＨ株式会社製、商品名：Ｘａｎｔｈａｎ ｇｕｍ 製品番号：Ｇ１２５３−５００Ｇ Ｂａｔｃｈ＃：０１４Ｋ０２１０）の０．６ｗｔ％水溶液を４．０ｍｌ加え、金鏡反応溶液とした。
-Production of hollow metal particles utilizing gold precipitation by gold mirror reaction 0.6 g of potassium iodide and 0.1 g of iodine were added to 7.6 ml of distilled water and dissolved by stirring. To this solution, 0.1 g of gold was added and dissolved by stirring to obtain a tetraiodogold (III) ion ([AuI 4 ] − ) solution. Furthermore, 4.0 ml of a 0.6 wt% aqueous solution of xanthan gum (manufactured by SIGMA-ALDRICH Co., Ltd., trade name: Xanthan gum product number: G1253-500G Batch #: 014K0210) was added as a thickener to obtain a golden mirror reaction solution.
金鏡反応の還元剤であるアスコルビン酸の５ｖｏｌ％水溶液中に、加圧溶解式のマイクロバブル発生装置（株式会社オーラテック製、商品名：ＯＭ４−ＭＤＧ−０４５）を用いて、空気を気泡とする微細気泡を発生させて、微細気泡分散液とした。この分散液中の気泡の直径は５０〜２００μｍの範囲であり、数平均径は７０μｍであった。 In a 5 vol% aqueous solution of ascorbic acid, which is a reducing agent for the gold mirror reaction, using a pressure dissolution type microbubble generator (product name: OM4-MDG-045, manufactured by Aura Tech Co., Ltd.) Microbubbles are generated to form a fine bubble dispersion. The diameter of the bubbles in this dispersion was in the range of 50 to 200 μm, and the number average diameter was 70 μm.
上記金鏡反応溶液１１．６ｍｌと上記ファインバブル分散液１６ｍｌとを混合した反応液を、試験管に液高３．００ｃｍとなるように入れ、５５℃の温浴中で１０分間静置して、中空金粒子を製造した。反応液中のキサンタンガムの濃度は０．２０７ｗｔ％であった。 The reaction solution obtained by mixing 11.6 ml of the gold mirror reaction solution and 16 ml of the fine bubble dispersion is placed in a test tube so that the liquid height becomes 3.00 cm, and left in a warm bath at 55 ° C. for 10 minutes. Hollow gold particles were produced. The concentration of xanthan gum in the reaction solution was 0.207 wt%.
金鏡反応の化学式は、以下のとおりであり、テトラヨード金(ＩＩＩ)酸イオンがアスコルビン酸により還元され、金属金が析出する。
［ＡｕＩ４］−＋２アスコルビン酸
→２デヒドロアスコルビン酸＋Ａｕ＋４ＨＩ
The chemical formula of the gold mirror reaction is as follows. Tetraiodogold (III) acid ions are reduced by ascorbic acid, and metallic gold is deposited.
[AuI 4 ] − +2 ascorbic acid
→ 2 dehydroascorbic acid + Au + 4HI
加熱後に表面に浮かんでいる金を網ですくい取り、純水で洗浄した。洗浄後も浮かんでいる金を網ですくい取り、シャーレ上で乾燥させた。得られた金をエポキシ樹脂中に包埋し、観察した走査型電子顕微鏡画像を図１１に示す。走査型電子顕微鏡から、６０〜１３０μｍの中空金粒子が得られたことが確認できた。得られた中空金粒子の数平均粒子径は７０．０μｍであった。キサンタンガムの濃度が高く、降伏応力が大きいため、粒径の大きな中空金粒子が得られた。 After heating, the gold floating on the surface was scooped with a net and washed with pure water. After washing, the floating gold was scooped with a net and dried on a petri dish. The obtained gold was embedded in an epoxy resin, and an observed scanning electron microscope image is shown in FIG. From the scanning electron microscope, it was confirmed that hollow gold particles of 60 to 130 μm were obtained. The number average particle diameter of the obtained hollow gold particles was 70.0 μm. Since the concentration of xanthan gum was high and the yield stress was large, hollow gold particles having a large particle size were obtained.
・還元剤である水素からなる微細気泡を用いた中空金属粒子の製造
硝酸銀の０．９ｍｏｌ／Ｌ水溶液５０．０ｍｌに、６．０ｍｏｌ／Ｌのアンモニア水を徐々に加えると、茶褐色の酸化銀（Ｉ）の沈殿が生じた。さらにアンモニア水を加えると、ジアンミン銀（Ｉ）イオン（［Ａｇ（ＮＨ３）２］＋）を形成して酸化銀（Ｉ）の沈殿が消失した。アンモニア水は、合計で２５．０ｍｌ加えた。この液に、ｐＨ調整剤として１．５ｍｏｌ／Ｌの水酸化ナトリウム水溶液を４．０ｍｌ、増粘剤としてキサンタンガム（ＳＩＧＭＡ−ＡＬＤＲＩＣＨ株式会社製、商品名：Ｘａｎｔｈａｎ ｇｕｍ、製品番号：Ｇ１２５３−５００Ｇ、Ｂａｔｃｈ＃：０１４Ｋ０２１０）の０．６ｗｔ％水溶液を１０．０ｍｌ加え、反応液とした。この反応液８９．０ｍｌを、耐圧容器（ポリエチレンテレフタレート製、容量５００ｍｌ）に入れた。反応液中のキサンタンガムの濃度は０．０６７ｗｔ％であり、この反応液の２０℃における降伏応力は０．３３Ｎ／ｍ２であった。
Production of hollow metal particles using fine bubbles made of hydrogen as a reducing agent When 6.0 mol / L of ammonia water is gradually added to 50.0 ml of a 0.9 mol / L aqueous solution of silver nitrate, brown silver oxide ( Precipitation of I) occurred. When ammonia water was further added, diammine silver (I) ions ([Ag (NH 3 ) 2 ] + ) were formed, and the precipitation of silver oxide (I) disappeared. A total of 25.0 ml of aqueous ammonia was added. To this solution, 4.0 ml of a 1.5 mol / L sodium hydroxide aqueous solution as a pH adjuster and xanthan gum (manufactured by SIGMA-ALDRICH Co., Ltd., trade name: Xanthan gum, product number: G1253-500G, Batch) 10.0 ml of a 0.6 wt% aqueous solution of #: 014K0210) was added to prepare a reaction solution. 89.0 ml of this reaction liquid was put in a pressure vessel (made of polyethylene terephthalate, capacity 500 ml). The concentration of xanthan gum in the reaction solution was 0.067 wt%, and the yield stress of this reaction solution at 20 ° C. was 0.33 N / m 2 .
反応液を含む耐圧容器を水素ガスボンベに接続し、０．３ＭＰａまで加圧して弁を閉じた。耐圧容器をガスボンベから外して、１分間振とうして水素を溶解させた後、予め７０℃の恒温槽内に放置して調温しておいた反応容器に向けて弁を開放して反応液を勢い良く放出し、回分式の加圧溶解法により水素からなる微細気泡を発生させ、微細気泡分散液とした。この微細気泡分散液中の微細気泡の直径は１８〜８３μｍの範囲であり、数平均径は２９．９μｍであった。回分式加圧溶解法であったため、微細気泡の径にバラツキが大きかった。水素は燃焼・爆発しやすいため回分式加圧溶解法を用いたが、防爆仕様の適切な装置を用いれば、他の微細気泡発生方法を使用することができる。 The pressure vessel containing the reaction solution was connected to a hydrogen gas cylinder, pressurized to 0.3 MPa, and the valve was closed. After removing the pressure vessel from the gas cylinder and shaking for 1 minute to dissolve the hydrogen, the reaction solution was opened by opening the valve toward the reaction vessel that had been left in a constant temperature bath at 70 ° C. to adjust the temperature. Were released vigorously, and fine bubbles made of hydrogen were generated by a batch-type pressure dissolution method to obtain a fine bubble dispersion. The diameter of the fine bubbles in this fine bubble dispersion was in the range of 18 to 83 μm, and the number average diameter was 29.9 μm. Due to the batch-type pressure dissolution method, the diameter of the fine bubbles varied greatly. Since hydrogen is easy to burn and explode, the batch-type pressure dissolution method was used, but other fine bubble generation methods can be used if an appropriate explosion-proof device is used.
微細気泡分散液を、そのまま７０℃に設定した恒温槽内に１０分間静置して、微細気泡中の水素を還元剤として銀鏡反応を進行させた。なお、銀鏡反応は加熱しないと進行しないため、恒温槽内でしか銀鏡反応は進行していない。 The fine bubble dispersion was allowed to stand in a constant temperature bath set at 70 ° C. for 10 minutes as it was, and the silver mirror reaction was advanced using hydrogen in the fine bubbles as a reducing agent. Since the silver mirror reaction does not proceed unless heated, the silver mirror reaction proceeds only in the thermostat.
銀鏡反応の化学式は、以下のとおりであり、ジアンミン銀（Ｉ）イオンが水素により還元され、金属銀が析出する。
Ｈ２＋２［Ａｇ（ＮＨ３）２］＋＋２ＯＨ−
→２Ａｇ＋４ＮＨ３＋２Ｈ２Ｏ
The chemical formula of the silver mirror reaction is as follows, and diammine silver (I) ions are reduced by hydrogen to deposit metallic silver.
H 2 +2 [Ag (NH 3 ) 2 ] + + 2OH −
→ 2Ag + 4NH 3 + 2H 2 O
反応終了後、反応容器を恒温槽から取り出したところ、実施例１の方法と比較して反応容器の壁面に付着している銀の量が明らかに少なかった。これは、実施例６の製造方法では、微細気泡から溶解した水素のみが還元剤として働くため、銀鏡反応が微細気泡のごく近傍のみで起こり、析出した金属微粒子は微細気泡に素早く吸着し、反応容器の壁面に吸着した銀が少なかったためである。 After completion of the reaction, the reaction vessel was taken out of the thermostatic bath. As a result, the amount of silver adhering to the wall surface of the reaction vessel was clearly small as compared with the method of Example 1. This is because in the production method of Example 6, only hydrogen dissolved from the fine bubbles acts as a reducing agent, so the silver mirror reaction occurs only in the very vicinity of the fine bubbles, and the precipitated metal fine particles are quickly adsorbed to the fine bubbles and reacted. This is because there was little silver adsorbed on the wall of the container.
反応液の表面に浮かんでいる銀を網ですくい取り、純水で洗浄し、洗浄後も浮かんでいる銀を網ですくい取り、シャーレ上で乾燥させた。得られた銀をエポキシ樹脂中に包埋し、観察した走査型電子顕微鏡画像を図１２に示す。走査型電子顕微鏡画像から、粒径１８．４〜３７．７μｍの中空銀粒子が得られたことが確認できた。得られた中空銀粒子の数平均粒子径は２８．４μｍであった。また、得られた中空銀粒子の表面は、実施例１で得られた中空銀粒子と比較して滑らかであった。これは、実施例６で析出した金属微粒子は微細気泡に素早く吸着されるため、一次粒子が成長する時間が短かったためである。 The silver floating on the surface of the reaction solution was scooped with a net, washed with pure water, and the silver floating after washing was scooped with a net and dried on a petri dish. The obtained silver was embedded in an epoxy resin, and an observed scanning electron microscope image is shown in FIG. From the scanning electron microscope image, it was confirmed that hollow silver particles having a particle size of 18.4 to 37.7 μm were obtained. The number average particle diameter of the obtained hollow silver particles was 28.4 μm. Moreover, the surface of the obtained hollow silver particle was smooth compared with the hollow silver particle obtained in Example 1. This is because the metal microparticles precipitated in Example 6 are quickly adsorbed by the fine bubbles, so that the time for growing the primary particles is short.
１．微細気泡
２．金属微粒子
３．限界直径より略大きな粒径の中空金属粒子
４．外殻片
５．板状の金属片
６．限界直径より略小さな粒径の中空金属粒子
1. 1. Fine bubbles 2. Metal fine particles 3. Hollow metal particles having a particle size substantially larger than the limit diameter Outer shell piece5. 5. Plate-shaped metal piece Hollow metal particles with a particle size approximately smaller than the critical diameter
Claims (8)
数平均粒子径１ｎｍ〜２００ｎｍである金属微粒子を前記微細気泡の表面に吸着させる工程、
前記金属微粒子を凝集させて外殻を形成する工程、
を有し、
前記微細気泡の浮上可能な直径を、前記微細気泡に作用する降伏応力と前記微細気泡の浮力との関係に基づいて制御することを特徴とする中空金属粒子の製造方法。 In a fine bubble dispersion liquid which is a plastic fluid in which fine bubbles having a diameter of 0.1 μm to 1000 μm are dispersed ,
Adsorbing on the surface of the fine bubbles the metal fine particles is a number-average particle diameter 1 nm to 200 nm,
A step of agglomerating the fine metal particles to form an outer shell;
I have a,
A method for producing hollow metal particles , wherein the diameter of the fine bubbles that can float is controlled based on a relationship between a yield stress acting on the fine bubbles and a buoyancy of the fine bubbles .
前記液槽の下部で微細気泡を発生させながら、または、前記液槽の下部に微細気泡分散液を供給しながら、
前記切欠き部から前記微細気泡分散液の上層を回収することを特徴とする、請求項１〜７のいずれかに記載の中空金属粒子の連続製造方法。 Using a liquid tank with a notch on the top,
While generating fine bubbles in the lower part of the liquid tank, or supplying a fine bubble dispersion to the lower part of the liquid tank,
The continuous production method of hollow metal particles according to any one of claims 1 to 7 , wherein an upper layer of the fine bubble dispersion is recovered from the notch.
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