Metallurgical apparatus – Means for treating ores or for extracting metals – By means applying heat to work – e.g. – furnace
Utility Patent
1998-07-31
2001-01-02
Wyszomierski, George (Department: 1742)
Metallurgical apparatus
Means for treating ores or for extracting metals
By means applying heat to work, e.g., furnace
C266S905000, C075S359000, C075S360000, C075S365000, C075S369000
Utility Patent
active
06168752
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to processes for producing metallic powders such as Ni, Cu and Ag or the like fit for various uses, for example, conductive paste fillers used for electric parts, Ti materials for cladding and catalysts. The invention further relates to apparatuses for producing the metal powders such as above.
2. Background Art
Conductive metallic powders such as Ni, Cu and Ag are useful for internal electrodes of multi-layer ceramic capacitors, particularly, Ni powders are recently closed up for such uses. Of those powders, ultrafine Ni powders produced by a chemical vapor deposition are known to be promising. According to a tendency of smaller size and larger capacity in capacitors, internal electrodes are required to be thin and have low resistance, whereby ultrafine powders of diameters of not only 1 &mgr;m or less, but also 0.5 &mgr;m or less are required.
Up to now, various kinds of processes have been proposed for producing the above mentioned metal powders. For example, Japanese Patent Publication No. S59 (84)-7765 proposes a production method for Ni powders by reducing nickel chloride gas with hydrogen gas, thereby injecting hydrogen gas at a high flow rate to the nickel chloride vapor, then nucleating nickel particles at an interfacial unstable region between the nickel chloride vapor flow and the hydrogen gas flow. Furthermore, Japanese Unexamined Patent Publication (Kokai) No. H4 (92)-365806 proposes a method for producing ultrafine nickel powders with a partial pressure of nickel chloride vapor (hereinafter referred to NiCl
2
gas) obtained by heating solid nickel chloride in the range of 0.05 to 0.3, and the reducing method by hydrogen gas at a temperature ranging from 1004 to 1453° C. According to the above processes, ultrafine powders of average particle diameters ranging from 0.1 &mgr;m to a few &mgr;m are formed.
However, the above proposals with respect to the producing process for metallic ultrafine powders imply the following problems since the solid nickel chloride is employed as a primary raw material in the each process.
{circle around (1)} As heating solid NiCl
2
is an inevitable step for obtaining NiCl
2
vapor, it is difficult to stably produce metal chloride vapor. As a result, the partial pressure of NiCl
2
gas varies, whereby the produced Ni powders are not uniform in particle diameter.
{circle around (2)} The amount of the solid NiCl
2
in a vaporizing portion varies during the operation, so that the generation rate of NiCl
2
vapor varies, whereby stable operation will not be expected.
{circle around (3)} The solid NiCl
2
contains crystal water, so that the process requires a dehydration step to eliminate the oxygen contamination prior to the vaporization step.
{circle around (4)} As vaporization is a slow process in general, a large amount of carrier gas (inert gas such as nitrogen gas or the like) is required for carrying NiCl
2
gas to a reducing step and additional energy is also required for heating carrier gas.
{circle around (5)} And hence, the partial pressure of NiCl
2
gas during the reducing step can not be increased, whereby the reaction rate for producing Ni powders is very slow and a large reactor chamber is required.
Therefore, the invention is completed for solving the above problems, thereby providing processes for producing metal powders and apparatuses for producing the same which can accomplish the following objectives:
1) Stable production of Ni, Cu or Ag powders (ultrafine powders) or the like having average particle diameters ranging from 0.1 to 1.0 &mgr;m.
2) Easy control of the reaction rate.
3) Controlling the entire process by regulating the chlorine gas flow rate, thereby arbitrarily producing metal powders having desired particle diameters.
4) Low energy consumption.
SUMMARY OF THE INVENTION
The present invention provides a method and apparatus for producing ultrafine metal powders, comprising the steps of a chlorination step for continuously producing chloride gas of the metal by reacting the metal with chlorine gas, and a reduction step for continuously reducing the chloride gas directly fed from the chlorination step.
In the moment of contacting the chloride gas with the reducing gas, the metallic particles can be generated in a gas phase reaction. Thus ultrafine particles are generated and grow by virtue that the metallic atoms come into contact with each other and precipitate particles. The particle diameters will vary depending on the conditions such as the partial pressure of the chloride gas and the reduction temperature. According to the invented process for producing the metallic powders, the chloride gas of the metal is produced according to the feed rate of the chlorine gas. Therefore, regulating the feed rate of the chlorine gas can control the amount of the chloride gas of the metal to the reduction step. Moreover, since the chloride gas of the metal is produced by the reaction between the chlorine gas and the metal, the process can eliminate carrier gas for transporting the metal chloride gas when the process condition permits, unlike the process in which the chlorine gas of the metal is produced by heating solid chloride of the metal. Thus, the invention can reduce the cost of the production since the carrier gas and the heating energy are not required.
By mixing inert gas with the chloride gas of the metal produced in the chlorination step, the partial pressure of the chloride gas of the metal in the reduction step can be controlled. Thus, by regulating the feeding rate of the chlorine gas or the partial pressure of the chloride gas of the metal in the reduction step, the particle diameters of the metal powders can be controlled, thereby stabilizing the particle diameter of the metal powders and arbitrarily controlling the mean particle diameter.
The invention also provides an apparatus for producing metallic powders comprising a chlorination furnace for chlorinating the metal filled therein and a reduction furnace for reducing the metal chloride gas produced in the chlorination step. The chlorination furnace comprises a nozzle for feeding raw material therein, a nozzle for feeding the chlorine gas therein, a nozzle for transporting the chloride gas of the metal into the reduction furnace and a nozzle for feeding inert gas which dilutes the chloride gas of the metal into the chlorination furnace. The reduction furnace comprises a nozzle for injecting the metal chlorine gas of the metal into the reduction furnace, a nozzle for feeding the reducing gas into the reduction furnace and a nozzle for feeding the inert gas which can cool the metallic powders as reduced. The chlorination furnace is located at the upper stream of the reduction furnace, the chlorination furnace and the reduction furnace are directly connected, and whereby the chlorination and reduction reaction can substantially proceed simultaneously and continuously.
In the above apparatus for producing metallic powders, the chloride gas of the metal can be generated corresponding to the feed rate of the chlorine gas. Moreover, as the chlorination furnace and the reduction furnace are directly connected, regulating the feed rate of the chlorine gas can control the amount of the chloride gas of the metal supplied to the reduction furnace. The chlorination furnace equips the inert gas feeding nozzle, thereby controlling the partial pressure of the chloride gas of the metal in the chlorination furnace. Therefore, the invented apparatus for producing metallic powders also can control the particle diameters by regulating the feed rate of the chlorine gas or the partial pressure of the chloride gas of the metal fed to the reduction furnace. And hence, the apparatus has the same advantages as above, thereby producing the metallic powders and arbitrarily controlling the particle diameters stably.
REFERENCES:
patent: 2556763 (1951-06-01), Maddex
patent: 3649242 (1972-03-01), Arias
patent: 4086084 (1978-04-01), Oliver et al.
patent: 4383852 (1983-05-01), Yoshizawa
patent: 5853451 (1998-12-01),
Irie Takefumi
Kagohashi Wataru
Takatori Hideo
Oliff & Berridg,e PLC
Toho Titanium Co., Ltd.
Wyszomierski George
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