Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2001-12-14
2004-05-04
Le, H. Thi (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C075S371000, C075S373000, C075S374000, C075S770000, C427S220000
Reexamination Certificate
active
06730400
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for manufacturing ultrafine composite metal particles and more particularly to a method for manufacturing ultrafine composite metal particles that inexpensively mass-produces ultrafine composite metal particles that can be dispersed extremely well in an organic solvent and whose diameter can be controlled.
BACKGROUND ART
Ultrafine metal particles with a diameter under 100 nm have characteristics that are quite different from those of ordinary particles. In the case of gold (Au), for instance, one of the characteristics we see is a pronounced drop in the melting point when the particle diameter is 10 nm or less. These ultrafine metal particles also have high catalytic activity, among other features; and thus they are materials having much potential in various fields in the future.
In particular, these ultrafine metal particles have potential application to low-temperature sintering pastes and the like, used as wire forming materials in electronic devices and so forth by dry plating, which has virtually no adverse impact on the environment. Also, if the particle size is uniform, there is a possibility of two-dimensional orientation, allowing nano-structures to be formed, which holds promise for nonlinear optical effects, nano-electronic circuits, and so on.
However, problems were encountered with the methods typically employed to manufacture ultrafine metal particles. For instance, there is a known method for obtaining ultrafine metal particles in the vapor phase by evaporating the raw material metal in a vacuum or in the presence of a small amount of gas.
With this method, however, the amount of ultrafine metal particles that can be produced at one time is generally small because they are produced in a vacuum apparatus. Also, equipment is required for an electron beam, plasma, laser, inductive heating, or the like in order to evaporate the metal. This means that production costs are higher. Thus this method cannot truly be considered suitable for mass production. Furthermore, ultrafine metal particles obtained by one of these vapor phase methods tend to be in the form of clumps because they have no particle size uniformity and are relatively susceptible to agglomeration.
Methods in which ultrafine metal particles are prepared from the liquid phase have been proposed in an effort to make mass production feasible. For example, in a known method, ultrafine silver particles are manufactured by reducing an anmmoniac silver nitrate complex solution in a hydrophobic reaction tank. Unfortunately, ultrafine metal particles obtained by a liquid phase process also have no size uniformity and are relatively prone to agglomeration. In view of this, it has been proposed that a surfactant be subsequently added to this ultrafine metal particle solution to form a protective colloid in order to impart dispersion stability. Still, there are few applications for a protective colloid of ultrafine particles in a clumped state with poor dispersibility. Furthermore, almost nothing has been done about achieving uniform particle size.
In view of this, in Japanese Patent Application Laid-Open (Kokai) No. H10-183207, the inventors proposed ultrafine composite metal particles in which a sheath of an organic metal compound was formed around a metal core. A specific method for manufacturing these particles was also proposed therein. More specifically, when an organic metal compound is pyrolyzed at a temperature below its complete decomposition temperature in an inert gas atmosphere shut off from air, the organic component escapes as the compound decomposes, and the reduced metal agglomerates, forming a metal core at the center. This metal core is covered all around with a sheath of undecomposed organic metal compound, forming ultrafine composite metal particles in which the organic compound is situated as the outermost layer.
The property of these ultrafine composite metal particles is that their particle diameter is extremely uniform. Also, because the organic compound is situated as the outermost layer and organic groups protrude radially, even if numerous ultrafine composite metal particles agglomerate, they agglomerate with the organic groups facing each other. Therefore, even in a solid state, the powder form is maintained to a high degree and the particles tend not to clump. Also, if this powder is put in an organic solvent, the organic groups dissolve in the organic solvent, and as a result the ultrafine composite metal particles readily disperse individually in organic solvents.
Thus, the ultrafine composite metal particles proposed by the inventors have uniform size and good dispersibility. However, a drawback is that they are unsatisfactory in terms of being suited to mass production, their cost, and the ability to vary the particle size. In other words, since the above manufacturing method requires that an organic metal compound be pyrolyzed in an inert gas atmosphere shut off from air, the air inside of a sealed vessel must be replaced with the inert gas. Furthermore a sealed apparatus is needed in order to exhaust the pyrolyzed organic gas. Consequently, this method does not suit itself to mass production, and as a result the cost of the ultrafine composite metal particles is higher.
Also, this manufacturing method does not permit the size of the ultrafine composite metal particles to be varied. The individual ultrafine composite metal particles are substantially the same size, but it is very difficult to make the particles larger or smaller. This weak point limits their applications. A novel method for manufacturing ultrafine composite metal particles needs to be developed in order to solve these problems.
Furthermore, if the particle size is made variable, some technique needs to be developed for further enhancing dispersibility in order to ensure the stability of the ultrafine particles.
The present invention provides ultrafine composite metal particles characterized in that an organic compound sheath that originates from an organic metal compound and a surfactant sheath surround a metal core in which metal atoms obtained by reduction precipitation from an organic metal compound have agglomerated, and the particle diameter is 1 to 100 nm.
The present invention provides ultrafine composite metal particles characterized in that a surfactant sheath surrounds a metal core in which metal atoms obtained by reduction precipitation from an inorganic metal compound have agglomerated, and the particle diameter is 1 to 100 nm.
In the above ultrafine composite metal particles of the present invention, the metal core is made up of an alloy of a plurality of different metals.
In the above ultrafine composite metal particles of the present invention, the metal component is at least one type selected from among Cu, Ag, Au, Zn, Cd, Ga, In, Si, Ge, Sn, Pd, Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, V, Cr, Mn, Y, Zr, Nb, Mo, Ca, Sr, Ba, Sb, and Bi.
The present invention provides a method for manufacturing ultrafine composite metal particles, and the invention is characterized in that the method comprises a first step of forming an ultrafine particle precursor by producing a colloidal solution of an organic metal compound in a mixed solvent of a hydrophobic nonaqueous solvent and a hydrophilic nonaqueous solvent, and a second step of reducing the ultrafine particle precursor by adding a reducing agent to this colloidal solution, thereby forming ultrafine composite metal particles with a diameter of 1 to 100 nm and having an organic compound sheath around a metal core.
The present invention provides a method for manufacturing ultrafine composite metal particles, and the invention is characterized in that the method comprises a first step of forming an ultrafine particle precursor by producing a colloidal solution of an organic metal compound or an inorganic metal compound in a mixed solvent of a hydrophobic nonaqueous solvent and a hydrophilic nonaqueous solvent using a surfactant, and a second step of reducing the ultrafine particle precursor by adding a reduci
Komatsu Teruo
Nagasawa Hiroshi
Koda & Androlia
Komatsu Teruo
Le H. Thi
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