Specialized metallurgical processes – compositions for use therei – Processes – Producing or purifying free metal powder or producing or...
Reexamination Certificate
2001-01-16
2003-04-01
Wyszomierski, George (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or purifying free metal powder or producing or...
C075S351000, C075S371000
Reexamination Certificate
active
06540811
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention concerns a method of producing alloy powders of high-purity, extremely small particle size, and excellent uniformity of composition. This invention also concerns alloy powders obtained by the abovementioned method and products, such as molding materials and electromagnetic shielding materials, that use these alloy powders.
2. Description of the Background
Metal powders are used as materials for powder metallurgy. For example, by dispersing a metal powder in a metal or resin, various materials with new characteristics can be obtained. In particular, metal powders of high magnetism can be dispersed in a resin and thereby be used as electromagnetic shielding material or as raw material for various molded objects aimed at shielding electromagnetic waves.
Also, an alloy (a solid solution of two or more metals, an intermetallic compound, or a mixture of such materials) often possesses new characteristics that cannot be obtained with a single type of metal or characteristics that are superior to those of a single type of metal. For example, a 20%Fe-80%Ni alloy (so-called permalloy) is extremely high in magnetic permeability, highly conductive, and thus excellent as an electromagnetic wave absorbing material. This permalloy can thus be made into a powder and dispersed in a resin to be used as the raw material for various molded objects aimed at shielding electromagnetic waves.
Methods of producing such alloy powders include, for example, (a) methods of producing alloy powders from the solid phase, such as by reduction of a solid metal salt (reduction method), etc., (b) methods of producing alloy powders from the liquid phase, such as the precipitation/deposition method, electrolysis method, molten metal atomization method, etc., and (c) methods of producing alloy powders from the gas phase, such as the chemical vapor thermal decomposition method, etc.
However, all alloy powders produced industrially by prior methods have a particle size of a few &mgr;m at the minimum. Presently, it is difficult to obtain alloy powders of extremely small particle size in the order of a few dozen to a few hundred nanometers on an industrial scale.
Meanwhile, with electromagnetic shielding materials that are obtained, for example, by dispersing a metal powder of high magnetism in a resin, it is known that by using a metal powder of smaller particle size, the gaps between particles can be narrowed (the metal powder can be filled more densely) and, as a result, increase the shield effect.
Also with electromagnetic shielding materials obtained by dispersing a metal powder in a resin, a smaller particle size facilitates processing of the material into a thin film, etc. and thereby meet the demands for making more compact and thin electronic equipment, which use such materials. Moreover, in the case where the metal powder is a material of high magnetic permeability, adequate absorption of electromagnetic waves can be anticipated even with a thin film.
The production of microparticles of the abovementioned permalloy and other alloy powders on an industrial scale is thus in demand for the above reasons.
Also, alloy powders of prior methods tend to cluster with contents rich of a specific element. It was thus difficult to obtain uniform composition and to obtain alloys of high purity. Such problems can inhibit the inherent characteristics of an alloy that can be obtained if the composition is uniform and the purity is high.
SUMMARY OF THE INVENTION
The first object of this invention is to provide a method of producing fine alloy powders that are high in purity and uniform in composition.
Other objects of this invention are to provide alloy powders made by the abovementioned method and provide application products, for example, molding materials, slurries, and electromagnetic shielding materials, that make use of these alloy powders.
As a result of continued active research towards achieving the above objects, the present inventors have made a completely new finding. By carrying out the process of mixing at least a trivalent titanium compound, which serves as a reducing agent, and a complexing agent, which binds with the trivalent titanium ion to form a coordination compound, in an aqueous solution containing two or more types of metal ion and thereafter causing the two or more types of metal to deposit simultaneously, an alloy powder comprised of the abovementioned two or more types of metal can be formed and the alloy powder thus formed can be made 1 to 100 nm, in other words, extremely small in particle size, high in purity, and uniform in composition. The present inventors have thus come to complete this invention.
The fine alloy powder production method by this invention is characterized in that after performing the process of mixing at least a trivalent titanium compound and a complexing agent, which binds with the trivalent titanium ion, in an aqueous solution containing two or more types of metal ion, the two or more types of metal are made to deposit simultaneously. With the trivalent titanium compound, which acts as the reducing agent in this invention, the potential difference (the potential difference based on the standard electrode potential, hereinafter referred to simply as the “potential difference”) of the oxidation of trivalent titanium [Ti(III)] to quadrivalent titanium [Ti(IV)] is 0.04V in a neutral aqueous solution. Meanwhile, for example, the potential difference of the reduction of bivalent nickel [Ni(II)] to metal nickel [Ni(0)] is 0.257V and the potential difference of the reduction of bivalent iron [Fe(II)] to metal iron [Fe(0)] is 0.440V. Since the potential difference of oxidation of trivalent titanium [Ti(III)] to quadrivalent titanium [Ti(IV)] is less than the potential difference of a reduction of bivalent nickel [Ni(II)] to metal nickel [Ni(0)] and less than the potential difference of a reduction of bivalent iron [Fe(II)] to metal iron [Fe(0)], when just a trivalent titanium compound is added to an aqueous solution containing bivalent nickel ions and bivalent iron ions, the reduction reactions will not progress and an Ni—Fe alloy will not deposit.
However, with the fine alloy powder production method by this invention, since the trivalent agent binds with a complexing agent to form a coordination compound, the stability of the ion changes, and as a result, the potential difference between Ti(III) and Ti(IV) becomes greater and thus produces a greater potential difference of oxidation of Ti(III) to Ti(IV). For example, when trivalent titanium ion is bound with citric acid as the complexing agent, the potential difference between Ti(III) and Ti(IV) in an aqueous solution of pH 9 becomes 1V or more. This value is extremely large, not only in comparison to the abovementioned potential difference of a reduction of Ni(II) to Ni(0) and the potential difference of a reduction of Fe(II) to Fe(0), but also in comparison to the potential difference of a reduction of other metal ions to zero-valence metal.
Thus by the production method of this invention, metal ions existing in aqueous solution can be reduced adequately and even in the case where two or more types of metal ion exist in a mixture, the two or more types of metal can be deposited without the deposition of just the metal of the lower potential difference and thus as an alloy of uniform composition.
Also, by the production method of this invention, the proportions of the component metals contained in the alloy can be adjusted as needed. For this purpose, the proportions of the two or more types of metal ion contained in the aqueous solution are simply adjusted as needed.
Normally when the potential differences of a reduction of the respective metals differ greatly, the more noble metal, which is lower in potential difference, deposits with priority. Even in such a case, by complexing the metal ions and shifting the potential difference of a redu
Hosoe Akihisa
Inazawa Shinji
Majima Masatoshi
Nishikawa Souji
Okazaki Hiroshi
McDermott & Will & Emery
Sumitomo Electric Industries Ltd.
Wyszomierski George
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