Process for production of ultrafine nickel powder

Details Process for production of ultrafine nickel powder Process for production of ultrafine nickel powder

2001-01-23

2002-12-31

Wyszomierski, George (Department: 1742)

Specialized metallurgical processes, compositions for use therei

Processes

Producing or purifying free metal powder or producing or...

C075S369000, C075S374000

Reexamination Certificate

active

06500227

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a process for production of ultrafine nickel powder in which ultrafine nickel powder having an average particle diameter of 1.0 &mgr;m or less can be produced by reducing raw material gas including nickel chloride vapor with hydrogen, and in particular, relates to a technique in which the quality of the ultrafine nickel powder can be improved while the productivity thereof is maintained at a high level.
BACKGROUND ART
Conductive metal powders such as nickel, copper, silver, palladium, etc., are useful for internal electrodes in multilayer ceramic capacitors, and in particular, since nickel powder, which is a base metal, is inexpensive, such application has recently attracted attention. As a process for production of such a nickel powder, a process in which nickel chloride vapor is generated and is reduced with hydrogen charged into a reducing furnace is known. In addition, multilayer ceramic capacitors generally have a construction such that ceramic dielectric layers and metallic layers used for internal electrodes are alternately laminated. Recently, reduced thickness and reduced resistance in the internal electrode, etc., are required for miniaturization and capacity increase of the capacitors, and therefore, the average particle diameter of the ultrafine powders is preferably 1.0 &mgr;m or less, more preferably 0.5 &mgr;m or less, and most preferably 0.1 to 0.4&mgr;m.
In order to reduce the particle diameter of the nickel powder, it is necessary that the residence time of the nickel chloride vapor in hydrogen be shortened, and in addition, it is necessary that the nickel powder be formed so as to be as spherical as possible, that the particle diameter thereof be made uniform, and that the desired particle diameter be obtained. Furthermore, in order to increase the production yield of the nickel powder, it is effective for the flow rate of raw material gas fed into the reducing furnace to be increased or for the partial pressure of the nickel chloride vapor in the raw material gas to be increased; however, stabilization of quality and further improvement thereof are then difficult.
Therefore, an object of the present invention is to provide a process for production of ultrafine nickel powder in which the following targets can be met.
{circle around (1)} Ultrafine nickel powder is produced in which the average particle diameter thereof is preferably 1.0 &mgr;m or less, and more preferably 0.1 to 0.4 &mgr;m.
{circle around (2)} Qualities such as uniformity of shape and particle diameter of the ultrafine nickel powders are improved, while manufacturing efficiency is maintained at a high level.
DISCLOSURE OF THE INVENTION
The inventors have performed intensive research with regard to the conditions under which the raw material gas is fed into the reducing furnace. As a result, they have discovered suitable conditions which can meet the above targets. That is, a first process for production of ultrafine nickel powder, in which ultrafine nickel powders are produced by vapor-reducing nickel chloride vapor, is characterized in that raw material gas having a partial pressure of nickel chloride vapor within a range from 0.2 to 0.7 is fed into a reducing furnace, and the nickel chloride vapor is reduced with hydrogen while flowing the raw material gas in this reducing furnace at a space velocity (SV) within a range from 0.02 to 0.07 sec
−1
.
In addition, a second process for production of ultrafine nickel powder, in which ultrafine nickel powders are produced by vapor-reducing nickel chloride vapor, is characterized in that hydrogen is discharged from a first outlet nozzle provided at an inlet nozzle of a reducing furnace, raw material gas having a partial pressure of nickel chloride vapor within a range from 0.2 to 0.7 is simultaneously discharged from a second outlet nozzle provided so as to surround the first outlet nozzle, and the nickel chloride vapor is reduced with hydrogen while flowing the raw material gas in this reducing furnace at a space velocity (SV) within a range from 0.02 to 0.07 sec
−1
.
More preferred embodiments of the above first or second production processes are as follows.
{circle around (1)} Raw material gas having a partial pressure of nickel chloride vapor within a range from 0.3 to 0.7 is fed into a reducing furnace and the nickel chloride vapor is reduced with hydrogen while flowing the raw material gas in the reducing furnace at a space velocity (SV) within a range from 0.025 to 0.07 sec
−1
.
{circle around (2)} In order to obtain ultrafine nickel powders having an average particle diameter within a range from 0.1 to 0.2 &mgr;m, raw material gas having a partial pressure of nickel chloride vapor within a range from 0.25 to 0.6 is fed into a reducing furnace and the nickel chloride vapor is reduced with hydrogen while flowing the raw material gas in this reducing furnace at a space velocity (SV) within a range from 0.03 to 0.07 sec
−1
, and it is preferable that raw material gas having a partial pressure of nickel chloride vapor within a range from 0.3 to 0.55 be fed into a reducing furnace and that the nickel chloride vapor be reduced with hydrogen while flowing the raw material gas in the reducing furnace at a space velocity (SV) within a range from 0.035 to 0.07 sec
−1
.
{circle around (3)} In order to obtain ultrafine nickel powders having an average particle diameter within a range from 0.25 to 0.4 &mgr;m, raw material gas having a partial pressure of nickel chloride vapor within a range from 0.3 to 0.7 is fed into a reducing furnace and the nickel chloride vapor is reduced with hydrogen while flowing the raw material gas in the reducing furnace at a space velocity (SV) within a range from 0.02 to 0.06 sec
−1
, and it is preferable that the raw material gas having a partial pressure of nickel chloride vapor within a range from 0.3 to 0.7 be fed into the reducing furnace and that the nickel chloride vapor be reduced with hydrogen while flowing the raw material gas in the reducing furnace at a space velocity (SV) within a range from 0.03 to 0.06 sec
−1
.
{circle around (4)} Raw material gas is discharged from a second outlet nozzle to a reducing furnace at a linear velocity within a range from 0.5 to 5.0 m/second.
{circle around (5)} Hydrogen is discharged from a first outlet nozzle provided at an inlet nozzle of a reducing furnace, and raw material gas is discharged from a second outlet nozzle provided around the first outlet nozzle. At this time, hydrogen at 30 to 100 mol % of the theoretical amount required to reduce nickel chloride vapor is discharged from the first outlet nozzle.
In the following, preferred embodiments of the present invention will be explained in detail. Terms used in the present description are defined as follows.
{circle around (1)} “Raw material gas” refers to a gas in which nickel chloride vapor is diluted with inert gas and/or halogen gas such as chlorine gas and which is a mixture as a raw material to be reduced. Inert gas or halogen gas acts to dilute the nickel chloride vapor and/or as a carrier thereof. As the inert gas, nitrogen gas or argon gas is generally employed, and in addition, the gas can also be employed with halogen gas in combination.
{circle around (2)} The “partial pressure of nickel chloride vapor” refers to the mole percentage of the nickel chloride vapor occupied in a mixture of nickel chloride vapor with inert gas and/or halogen gas.
{circle around (3)} “Space velocity” is indicated by SV (space velocity; units: sec
−1
) and refers to a ratio of feeding speed (liter/second; conversion at reduction temperature and at 1 atm) of nickel chloride vapor fed into a reducing furnace to volume V (liters) of a reacting portion in the reducing furnace (volume of a space from an inlet nozzle portion of raw material gas to a cooling portion for cooling formed ultrafine nickel powder). Although the nickel chloride vapor is fed as a mixture of inert gas and/or halogen gas, SV is the value for nickel chloride excepting the

Affiliated with

Also associated with

Rating

Process for production of ultrafine nickel powder does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Process for production of ultrafine nickel powder, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for production of ultrafine nickel powder will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2992948