U.S. patent application number 11/841196 was filed with the patent office on 2009-02-26 for homogeneous granulated metal based and metal-ceramic based powders.
This patent application is currently assigned to HERAEUS INC.. Invention is credited to Carl Derrington, Bernd Kunkel, Fenglin YANG.
Application Number | 20090053089 11/841196 |
Document ID | / |
Family ID | 40246131 |
Filed Date | 2009-02-26 |
United States Patent
Application |
20090053089 |
Kind Code |
A1 |
YANG; Fenglin ; et
al. |
February 26, 2009 |
HOMOGENEOUS GRANULATED METAL BASED and METAL-CERAMIC BASED
POWDERS
Abstract
A method of making a homogeneous granulated metal-based powder,
comprises steps of: providing preselected amounts of at least one
metal element or metal alloy, at least one ceramic compound, and/or
at least one non-metallic element; forming a homogeneous
slurry/suspension or wet mixture comprising the preselected amounts
of metal element(s) and/or metal alloys, ceramic compound(s),
and/or non-metallic element(s), a liquid phase comprising at least
one liquid, and at least one binder material; drying the
slurry/suspension or mixture to remove at least a portion of the
liquid phase and form a powder mixture comprising partially or
completely dried granules; and subjecting the granules to a thermal
de-binder process for effecting: additional removal of any
remaining liquid phase, if necessary; removal of the at least one
binder material; reduction of carbon content; reduction of oxygen
on the surfaces or interior of the metal or metal alloy phases in
the granules; and optional partial sintering for strengthening for
withstanding subsequent processing. The resultant granules are
useful in fabricating magnetic sputtering targets employed in the
manufacture of magnetic data/information storage and retrieval
media.
Inventors: |
YANG; Fenglin; (Gilbert,
AZ) ; Derrington; Carl; (Tempe, AZ) ; Kunkel;
Bernd; (Phoenix, AZ) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
18191 VON KARMAN AVE., SUITE 500
IRVINE
CA
92612-7108
US
|
Assignee: |
HERAEUS INC.
Chandler
AZ
|
Family ID: |
40246131 |
Appl. No.: |
11/841196 |
Filed: |
August 20, 2007 |
Current U.S.
Class: |
419/13 ; 419/19;
419/20; 419/21; 419/22; 419/5 |
Current CPC
Class: |
B22F 9/026 20130101;
C22C 1/05 20130101 |
Class at
Publication: |
419/13 ; 419/19;
419/20; 419/21; 419/22; 419/5 |
International
Class: |
B22F 7/00 20060101
B22F007/00; C22C 32/00 20060101 C22C032/00 |
Claims
1. A method of making a homogeneous granulated metal-based powder,
comprising steps of: (a) providing a preselected amount of at least
one metal element or metal alloy and a preselected amount of at
least one ceramic compound and/or at least one non-metallic
element; (b) forming a homogeneous slurry/suspension or wet mixture
comprising said preselected amounts of said at least one metal
element or metal alloy and said at least one ceramic compound
and/or said at least one non-metallic element, and a liquid phase
comprising at least one liquid, at least one binder material, and
at least one optional additive; (c) drying said slurry/suspension
or said mixture to remove at least a portion of said liquid phase
and form a powder mixture comprising partially or completely dried
granules; and (d) subjecting said partially or completely dried
granules to a thermal de-binder process for effecting: (i)
additional removal of any liquid phase, if required; (ii) removal
of said at least one binder material; (iii) reduction of carbon
content; (iv) reduction of oxygen on the surfaces or interior of
the metal constituent(s); and optional (v) partial sintering for
strengthening the particles for withstanding subsequent
processing.
2. The method according to claim 1, wherein: step (a) comprises
providing a preselected amount of a powder containing said at least
one metal element or metal alloy, a preselected amount of another
powder containing said at least one ceramic compound, and/or a
preselected amount of another powder containing the at least one
non-metallic element.
3. The method according to claim 2, wherein: step (a) comprises
providing preselected amounts of a plurality of powders containing
respective metal elements and/or metal alloys, respective ceramic
compounds, and/or respective non-metallic elements.
4. The method according to claim 3, wherein: step (a) comprises
providing preselected amounts of two powders respectively
containing first and second metal elements and/or alloys and/or
preselected amounts of two powders respectively containing first
and second ceramic compounds and/or non-metallic elements.
5. The method according to claim 1, wherein: step (a) comprises
providing a preselected amount of a compound of said at least one
metal or metal alloy and a preselected amount of a sol-gel of said
at least one ceramic compound or said at least one non-metallic
element.
6. The method according to claim 1, wherein: step (a) comprises
providing a preselected amount of at least one metal element or
metal alloy comprising metals selected from the group consisting
of: Co, Cr, Fe, Pt, Pd, Ru, Re, Ta, Al, Sm, and Nd, a preselected
amount of at least one non-metallic compound selected from the
group consisting of: TiO.sub.2, SiO.sub.2, MgO, Ta.sub.2O.sub.5,
Nb.sub.2O.sub.5, A1.sub.2O.sub.3, TaC, BN, ZrO.sub.2, HfO.sub.2,
ZnO, CaO, La.sub.2O.sub.3, WO.sub.3, CoO, Co.sub.2O.sub.3,
Y.sub.2O.sub.3, Cr.sub.2O.sub.3, MnO.sub.2, NiO, CuO, CeO.sub.2,
Eu.sub.2O.sub.3, V.sub.2O.sub.5, Sm.sub.2O.sub.3, Sb.sub.2O.sub.5,
BeO, BaO, B.sub.2O.sub.3, IrO.sub.2, PbO, MoO.sub.3, ReO.sub.2,
RuO.sub.2, Ag.sub.2O, SrO, TaC, NbC, BN, B, and C.
7. The method according to claim 6, wherein: step (a) comprises
providing preselected amounts of a plurality of metal elements
and/or metal alloys, ceramic compounds, and/or non-metallic
elements selected from said groups.
8. The method according to claim 1, wherein: step (b) comprises
forming said homogeneous slurry/suspension or wet mixture to
comprise a liquid phase comprising at least one of water, an
alcohol, and at least one organic solvent, and further comprising
at least one inorganic or organic binder material.
9. The method according to claim 8, wherein: step (b) comprises
forming said homogeneous slurry/suspension or wet mixture to
comprise a liquid phase comprising at least one of water, an
alcohol, and at least one organic solvent selected from the group
consisting of: acetone, toluene, hexane, heptane, xylene, and
decane.
10. The method according to claim 8, wherein: step (b) comprises
forming said homogeneous slurry/suspension or wet mixture to
further comprise at least one organic binder material selected from
the group consisting of: polyvinyl alcohol (PVA), polyethylene
glycol (PEG), gum arabic, other natural gums, methyl cellulose,
acrylic resin emulsions, ethylene oxide polymers, water soluble
phenolics, alginates, natural or synthetic waxes, flour, starches,
or at least one inorganic binder material selected from the group
consisting of: carbonates, nitrides, oxylates, and
oxychlorides.
11. The method according to claim 8, wherein: step (b) comprises
forming said homogeneous slurry/suspension or wet mixture to
further comprise at least one of a deflocculating agent, wetting
agent, de-foaming agent, plasticizer, and suspending agent.
12. The method according to claim 1, wherein: step (c) comprises
spray drying.
13. The method according to claim 1, wherein: step (d) comprises
performing said thermal de-binder process to reduce said carbon
content of said granules to less than about 500 ppm.
14. The method according to claim 13, wherein: step (d) comprises
performing said thermal de-binder process in an atmosphere
comprising at least one reducing gas.
15. The method according to claim 14, wherein: step (d) comprises
performing said thermal de-binder process in an atmosphere
comprising at least one reducing gas selected from the group
consisting of: H.sub.2, NH.sub.3, CO, forming gas, dissociated
NH.sub.3, H.sub.2/N.sub.2 mixtures, and reformed hydrocarbon
gases.
16. The method according to claim 14, wherein: step (d) comprises
performing said thermal de-binder process in an atmosphere further
comprising at least one weak oxidizing agent.
17. The method according to claim 16, wherein: step (d) comprises
performing said thermal de-binder process in an atmosphere
comprising at least one weak oxidizing agent selected from the
group consisting of: H.sub.2O, CO.sub.2, air, O.sub.2, and air or
O.sub.2 diluted in an inert gas or a weakly oxidizing or
non-oxidizing gas.
18. The method according to claim 14, wherein: step (d) comprises
performing said thermal de-binder process in an atmosphere
comprising said at least one reducing gas only in a latter portion
of said thermal de-binder process, and at a same or different
temperature than in an earlier portion of said process.
19. A homogeneous granulated metal based or metal-ceramic based
powder formed by the method according to claim 1.
20. A homogeneous granulated metal-based powder as in claim 19,
comprising at least one metal element or metal alloy comprising
elements selected from the group consisting of: Co, Cr, Fe, Pt, Pd,
Ru, Re, Ta, Al, and Sm, and at least one ceramic compound or
non-metallic element selected from the group consisting of:
TiO.sub.2, SiO.sub.2, MgO, Ta.sub.2O.sub.5, Nb.sub.2O.sub.5,
Al.sub.2O.sub.3, TaC, BN, ZrO.sub.2, HfO.sub.2, ZnO, CaO,
La.sub.2O.sub.3, WO.sub.3, CoO, Co.sub.2O.sub.3, Y.sub.2O.sub.3,
Cr.sub.2O.sub.3, MnO.sub.2, NiO, CuO, CeO.sub.2, Eu.sub.2O.sub.3,
V.sub.2O.sub.5, Sm.sub.2O.sub.3, Sb.sub.2O.sub.5, BeO, BaO,
B.sub.2O.sub.3, IrO.sub.2, PbO, MoO.sub.3, ReO.sub.2, RuO.sub.2,
Ag.sub.2O, SrO, TaC, NbC, BN, B, and C.
21. A magnetic sputtering target fabricated from a homogeneous
granulated metal-based magnetic powder of claim 20.
22. The method according to claim 1, wherein: step (a) comprises
providing only a fraction of the requisite metal or metal alloy
powders and a fraction or all of the requisite ceramic, oxide,
and/or non-metallic element powders; and the method further
comprises a step of: (e) blending the resultant granulated powder
with the balance of requisite metal or metal alloy powders and
ceramic, oxide, and/or non-metallic element powders for
consolidation therewith.
Description
FIELD OF THE DISCLOSURE
[0001] The present disclosure generally relates to highly
homogeneous metal based and metal-ceramic based powders and methods
of making same, and, in particular, to metal based and
metal-ceramic based powders utilized in consolidated form as
sputtering targets for thin film deposition processes, e.g., as in
manufacture of magnetic recording media, in powder form in other
applications, e.g., plasma spray coating, and precursors for PM
consolidation.
BACKGROUND OF THE DISCLOSURE
[0002] Metal based and metal-ceramic based powders and powder
mixtures enjoy utility in a number of industrially useful
applications, including use in consolidated form as sputtering
targets for various thin film deposition processes, such as in the
manufacture of thin film magnetic recording media, and in powder
form in other coating applications, such as plasma spraying, and as
precursors for PM consolidation, etc.
[0003] More specifically, the ever increasing demand for data
storage requires higher areal recording density magnetic recording
media than currently available. In this regard, efforts are
continually made with the aim of increasing the areal recording
density, i.e., bit density of the magnetic media. Conventional thin
film thin-film type magnetic media, wherein a fine-grained
polycrystalline magnetic alloy layer serves as the active recording
layer, are generally classified as "longitudinal" or
"perpendicular", depending upon the orientation of the magnetic
domains of the grains of magnetic material.
[0004] Perpendicular recording media have been found to be superior
to longitudinal media in achieving very high bit densities without
experiencing the thermal stability limit associated with the
latter. In perpendicular magnetic recording media, residual
magnetization is formed in a layer of a magnetic material in a
direction ("easy axis") perpendicular to the surface of the
layer.
[0005] In either instance, it is important that the magnetic grains
of the recording layer be mutually separated, i.e., segregated, in
order to physically and magnetically de-couple the grains and
provide improved media performance characteristics. Segregation of
the grains of magnetic media with Co-based alloy magnetic recording
layers (e.g., CoCr alloys) can occurs when oxides, nitrides, and/or
carbides are present at the boundaries between adjacent magnetic
grains to form so-called "granular" media. One currently practiced
method for manufacturing such granular-type thin film magnetic
recording media involves sputtering a target comprised of a
ferromagnetic material (typically a Co-based alloy) and an oxide,
nitride, or carbide material. The sputtering target is typically
fabricated by consolidating a granular powder or powder mixture
comprised of the magnetic metal or alloy and an oxide, nitride, or
carbide material.
[0006] Uniform mixing of the component ("raw") powders prior to
consolidation is critical for obtaining homogeneous sputtering
targets, target performance, and, ultimately, performance of the
resultant magnetic media. Typically, fine metal or metal alloy
particles (i.e., 200 .mu.m or less) and ultra-fine oxide, nitride,
or carbide particles (i.e., 30 .mu.m or less) are required as
starting materials for forming products with fine grain sizes.
However, homogeneous mixing of the ultra-fine oxide, nitride, or
carbide particles in the metal or metal alloy matrix is a very
challenging task. Specifically, if the fine oxide, nitride, or
carbide particles agglomerate, or if the distribution of the
ultra-fine oxide, nitride, or carbide particles on the surfaces of
the fine metal or metal alloy particles is not homogeneous, poor
performance of the resultant sputtering target results, including
particle "spitting" leading to target cratering, non-uniform thin
film formation, and degraded magnetic performance
characteristics.
[0007] Current practice of the powder metallurgy industry is to
utilize dry blending or grinding methodology for forming such
sputtering targets via powder/granule consolidation techniques.
However, such methodology is disadvantageous because of the
tendency for agglomeration of cohesive fine particles and
segregation of powders of different densities and/or particle
sizes.
[0008] Accordingly, there exists a need for improved methodology
for making high homogeneity granulated metal based and
metal-ceramic based powders and powder mixtures useful as
precursors in a number of industrially significant processes,
including without limitation, thin film deposition processes such
as dc, rf, and magnetically enhanced (magnetron) sputtering,
cathode arc deposition, ion plating, as well as plasma
spraying.
[0009] More specifically, there exists a need for improved
methodology for making high homogeneity granulated metal powders
comprising at least one magnetic metal element or an alloy thereof,
e.g., CoCr, CoCrPt, CoPt, FePt, and at least one ceramic compound,
such as an oxide, nitride, or carbide, or at least one non-metallic
element. Suitable oxides include, for example, and without
limitation: TiO.sub.2, SiO.sub.2, MgO, Ta.sub.2O.sub.5,
Nb.sub.2O.sub.5, and Al.sub.2O.sub.3; suitable carbides include,
for example, and without limitation: TaC and NbC; suitable nitrides
include, for example, and without limitation: BN; and suitable
non-metallic elements include, for example, and without limitation:
B and C.
SUMMARY OF THE DISCLOSURE
[0010] An advantage of the present disclosure is improved methods
of making homogeneous granulated metal based and metal-ceramic
based powders.
[0011] Another advantage of the present disclosure is improved
methods of making homogeneous granulated metal based and
metal-ceramic based powders useful in the manufacture of sputtering
targets, particularly magnetic sputtering targets.
[0012] Further advantages of the present disclosure include
improved homogeneous granulated metal based and metal-ceramic based
powders, particularly magnetic powders, and sputtering targets
fabricated from the improved homogeneous granulated metal-based
powders, particularly magnetic sputtering targets.
[0013] Additional advantages and features of the present disclosure
will be set forth in the disclosure which follows and in part will
become apparent to those having ordinary skill in the art upon
examination of the following or may be learned from the practice of
the present disclosure. The advantages may be realized and obtained
as particularly pointed out in the appended claims.
[0014] According to an aspect of the present disclosure, the
foregoing and other advantages are achieved in part by an improved
method of making a homogeneous granulated metal based or
metal-ceramic based powder, comprising steps of:
[0015] (a) providing a preselected amount of at least one metal
element or metal alloy and a preselected amount of at least one
ceramic compound and/or at least one non-metallic element;
[0016] (b) forming a homogeneous slurry/suspension or wet mixture
comprising the preselected amounts of the at least one metal
element or metal alloy and the at least one ceramic compound and/or
the at least one non-metallic element, and a liquid phase
comprising at least one liquid, at least one binder material, and
at least one optional additive;
[0017] (c) drying the slurry/suspension or mixture to remove at
least a portion of the liquid phase and form a powder mixture
comprising partially or completely dried granules; and
[0018] (d) subjecting the partially or completely dried granules to
a thermal de-binder process for effecting: [0019] (i) additional
removal of any liquid phase, if present; [0020] (ii) removal of the
at least one binder material; [0021] (iii) reduction of carbon
content; [0022] (iv) reduction of oxygen on the surfaces and/or
interior of the metal constituent(s); and optional [0023] (v)
partial sintering for strengthening of the particles for
withstanding subsequent processing.
[0024] According to embodiments of the present disclosure, step (a)
comprises providing a preselected amount of a powder containing the
at least one metal element or metal alloy, a preselected amount of
another powder containing the at least one ceramic compound, and/or
a preselected amount of another powder containing the at least one
non-metallic element.
[0025] In accordance with other embodiments of the present
disclosure, step (a) comprises providing preselected amounts of a
plurality of powders containing respective metal elements and/or
metal alloys, respective ceramic compounds, and/or respective
non-metallic elements. For example, according to certain
embodiments of the present disclosure, step (a) comprises providing
preselected amounts of two powders respectively containing first
and second metal elements and/or alloys and/or preselected amounts
of two powders respectively containing first and second ceramic
compounds and/or non-metallic elements.
[0026] According to still other embodiments of the present
disclosure, step (a) comprises providing a preselected amount of a
compound of the metal or metal alloy and a preselected amount of a
sol-gel of the ceramic compound or non-metallic element.
[0027] In accordance with embodiments of the present disclosure,
step (a) comprises providing a preselected amount of at least one
metal element or metal alloy comprising metal elements selected
from the group consisting of: Co, Cr, Fe, Pt, Pd, Ru, Re, Ta, Al,
Sm, Nd, etc., and a preselected amount of at least one ceramic
compound and/or at least one non-metallic element selected from the
group consisting of: TiO.sub.2, SiO.sub.2, MgO, Ta.sub.2O.sub.5,
Nb.sub.2O.sub.5, Al.sub.2O.sub.3, TaC, BN, ZrO.sub.2, HfO.sub.2,
ZnO, CaO, La.sub.2O.sub.3, WO.sub.3, CoO, Co.sub.2O.sub.3,
Y.sub.2O.sub.3, Cr.sub.2O.sub.3, MnO.sub.2, NiO, CuO, CeO.sub.2,
Eu.sub.2O.sub.3, V.sub.2O.sub.5, Sm.sub.2O.sub.3, Sb.sub.2O.sub.5,
BeO, BaO, B.sub.2O.sub.3, lrO.sub.2, PbO, MoO.sub.3, ReO.sub.2,
RuO.sub.2, Ag.sub.2O, SrO, TaC, NbC, BN, B, and C.
[0028] According to preferred embodiments of the present
disclosure, step (a) comprises providing preselected amounts of a
plurality of metal elements and/or metal alloys, ceramic compounds,
and/or non-metallic elements selected from the above groups; and
step (b) comprises forming the homogeneous slurry/suspension or wet
mixture to comprise a liquid phase comprising at least one of
water, an alcohol, and at least one organic solvent, and further
comprising at least one inorganic or organic binder material.
[0029] Embodiments according to the present disclosure include
those wherein step (b) comprises forming the homogeneous
slurry/suspension or wet mixture to comprise a liquid phase
comprising at least one of water, an alcohol, and at least one
organic solvent selected from the group consisting of: acetone,
toluene, alkanes such as hexane, heptane, xylene, decane, etc., and
forming the homogeneous slurry/suspension or wet mixture to further
comprise at least one organic binder material selected from the
group consisting of: polyvinyl alcohol (PVA), polyethylene glycol
(PEG), gum arabic, other natural gums, methyl cellulose, acrylic
resin emulsions, ethylene oxide polymers, water soluble phenolics,
alginates, natural or synthetic waxes, flour, starches, and
inorganic binders such as carbonates, nitrides, oxylates, and
oxychlorides. In addition, step (b) may comprise forming the
homogeneous slurry/suspension or wet mixture to further comprise
one or more of a deflocculating agent, wetting agent, de-foaming
agent, plasticizer, and suspending agent.
[0030] Preferably, step (c) comprises spray drying, and step (d)
comprises performing the thermal de-binder process to reduce the
carbon content of the granules to less than about 500 ppm.
[0031] According to preferred embodiments of the present
disclosure, step (d) comprises performing the thermal de-binder
process in an atmosphere comprising at least one reducing gas,
e.g., selected from the group consisting of: H.sub.2, NH.sub.3, CO,
forming gas, dissociated NH.sub.3, H.sub.2/N.sub.2 mixtures, and
reformed hydrocarbon gases, and when an organic binder material is
used, performing the thermal de-binder process in an atmosphere
further comprising at least one weak oxidizing agent, e.g.,
selected from the group consisting of: H.sub.2O, CO.sub.2, air,
O.sub.2, and air or O.sub.2 diluted in an inert gas or a
non-oxidizing or weakly oxidizing gas.
[0032] According to another embodiment of the present disclosure,
step (d) comprises performing the thermal de-binder process in an
atmosphere comprising the at least one reducing gas only in a
latter portion of the thermal de-binder process, and at the same or
a different temperature than in an earlier portion of the
process.
[0033] Another aspect of the present disclosure is homogeneous
granulated metal based and metal-ceramic based powders formed by
the above method, e.g., comprising at least one metal element or
metal alloy comprising metal elements selected from the group
consisting of: Co, Cr, Fe, Pt, Pd, Ru, Re, Ta, Al, Sm, and Nd and
at least one ceramic compound or non-metallic element selected from
the group consisting of: TiO.sub.2, SiO.sub.2, MgO,
Ta.sub.2O.sub.5, Nb.sub.2O.sub.5, Al.sub.2O.sub.3, TaC, BN,
ZrO.sub.2, HfO.sub.2, ZnO, CaO, La.sub.2O.sub.3, WO.sub.3, CoO,
Co.sub.2O.sub.3, Y.sub.2O.sub.3, Cr.sub.2O.sub.3, MnO.sub.2, NiO,
CuO, CeO.sub.2, Eu.sub.2O.sub.3, V.sub.2O.sub.5, Sm.sub.2O.sub.3,
Sb.sub.2O.sub.5, BeO, BaO, B.sub.2O.sub.3, IrO.sub.2, PbO,
MoO.sub.3, ReO.sub.2, RuO.sub.2, Ag.sub.2O, SrO, TaC, NbC, BN, B,
and C.
[0034] Yet another aspect of the present disclosure is magnetic
sputtering targets fabricated from a homogeneous granulated metal
based magnetic or metal-ceramic based powder formed by the above
method.
[0035] Additional advantages of the present disclosure will become
readily apparent to those skilled in this art from the following
detailed description, wherein only the preferred embodiments of the
present disclosure are shown and described, simply by way of
illustration of the best mode contemplated for practicing the
present disclosure. As will be realized, the disclosure is capable
of other and different embodiments, and its several details are
capable of modification in various obvious respects, all without
departing from the spirit of the present invention. Accordingly,
the drawings and description are to be regarded as illustrative in
nature, and not as restrictive.
DETAILED DESCRIPTION OF THE DISCLOSURE
[0036] The present disclosure addresses and effectively solves, or
at least mitigates, the above-described difficulties and drawbacks
associated with conventional dry techniques for forming high
homogeneity granulated metal based powders and metal-ceramic based
powders and powder mixtures, thereby facilitating subsequent
utilization of such powders in industrially significant
applications, e.g., in consolidated form in thin film deposition
processing and PM parts, and in granular form, e.g., as in plasma
spraying.
[0037] Briefly stated, according to the present disclosure, wet
processing is utilized to form a homogeneous slurry/suspension or a
wet mixture of the constituent powders. Mixing of the particles at
an individual particle level is achieved by proper mixing
techniques and the addition of binder material(s) and other
additives such as deflocculating agents, wetting agents, de-foaming
agents, plasticizers, suspending agents, etc.
[0038] The homogeneous slurry/suspension is dried, e.g., as by
spray drying, to remove the solvent. Because the slurry/suspension
is dried very quickly, e.g., in about 2-20 sec.), the homogeneous
mixing pattern obtained in the slurry is essentially maintained
(preserved) upon drying. The particle size of the resultant
granules can be in the range from about 10 to about 650 .mu.m when
formed by spray drying. Other methods for drying are applicable in
the context of the present disclosure, and the particle sizes of
the resultant particles can be larger or smaller, provided the
homogeneous mixing pattern of the slurry/suspension is maintained
(preserved) upon drying.
[0039] Alternatively, the constituent metal and ceramic and/or
non-metallic compounds or elemental powders can be homogeneously
mixed by wetting the particle surfaces by addition thereto of a
small amount of a suitable liquid solvent and binder material(s),
e.g., at least one organic binder material, followed by drying of
the well-mixed and wetted blend of powders to remove the solvent
therefrom. The shape of the powder granules can be spherical, as
when spray drying is utilized, or irregular.
[0040] In either instance, the slurry/suspension or wetted powder
blend or mixture can be dried to cake or lump form and then crushed
to yield appropriately small size particles or granules.
[0041] The binder material(s) is (are) then removed after drying
via a thermal treatment, which thermal de-binder treatment lightly
sinters the powder granules in order to maintain their integrity
upon binder removal. Any oxygen absorbed or otherwise picked up by
the granules during previous processing is reduced during the
thermal de-binder treatment. However, oxides such as TiO.sub.2,
SiO.sub.2, MgO, Ta.sub.2O.sub.5, Nb.sub.2O.sub.5, Al.sub.2O.sub.3,
etc., are unaffected at the temperatures utilized for the thermal
de-binder treatment.
[0042] In this regard, a challenge typically encountered when
organic binder materials or other additives are used in making the
slurry/suspension or wetted powder is removal of the organic binder
materials and additives from dried, granulated powders without the
presence of air or O.sub.2 as utilized in typical "binder bum-off",
in order to avoid presence of a high amount of residual carbon from
the organic binder materials and other additives. As a consequence,
wet blending with addition of organic binder materials, followed by
drying (e.g., spray drying) is rarely employed for granulation of
high purity metal based and metal-ceramic based powders.
[0043] Further in this regard, another challenge encountered in
granulation processing for making high purity metal based and
metal-ceramic based powders is the tendency for surface oxidation
of the metal particles to occur when water-based
slurries/suspensions are processed and then dried in an air
atmosphere, resulting in significant oxygen incorporation
("pickup") in the metal-based phases.
[0044] In contrast with prior methodologies, the presently
disclosed process is capable of producing high homogeneity
granulated metal based and metal-ceramic based powders and powder
mixtures without significant carbon content or oxygen pickup. A key
feature of the presently disclosed process is subjecting partially
or completely dried granules, formed as by spray drying, to a
thermal de-binder process for effecting additional removal of any
liquid phase (if required), removal of the at least one binder
material, reduction of carbon content, reduction of oxygen on the
surfaces of the metal constituent(s), and optionally partial
sintering for strengthening of the granules for withstanding
subsequent processing.
[0045] Further, the presently disclosed methodology can be employed
for uniform mixing of multi-component powders or to coat/distribute
one or more ultra-fine powders on the surfaces of other powders of
equivalent or larger particle size.
[0046] Notable examples of the utility of the present disclosure
include coating/distributing micron- or nano-sized non-metallic
powder materials, e.g., oxides and ceramics, such as TiO.sub.2,
SiO.sub.2, MgO, Ta.sub.2O.sub.5, Nb.sub.2O.sub.5, Al.sub.2O.sub.3,
TaC, BN, etc., on the surfaces of metal or metal alloy based
particles, such as magnetic metals and powders of "master" alloys
(via gas atomization or melting followed by crushing), including,
for example but not limited to, Co, Cr, Pt, Fe, CoPt, CrCo, FePt,
and CoCrPt to make high homogeneity granulated powders and powder
mixtures with uniform distribution of the oxide or ceramic
particles. The granulated powders afforded by the present
disclosure may be consolidated and processed into targets suitable
for thin film deposition processing, e.g., sputter deposition
processing used in the manufacture of thin film magnetic recording
media, including high areal recording density granular
perpendicular media. In addition, the methodology afforded by the
present disclosure is useful in the fabrication of all manner of
targets, etc., required for future applications.
[0047] For example, the present disclosure provides methodology for
forming precursor granulated powders and powder mixtures suitable
for forming sputtering targets to be used in fabricating the
upcoming generation of granular perpendicular magnetic recording
media, e.g., CoCrPt--TiO.sub.2, CoCrPtSiO.sub.2, and other
CoCrPt-oxides. In addition, the methodology of the present
disclosure is useful in preparing precursor granulated powders and
powder mixture useful in fabricating sputtering targets
contemplated for future generation thermally assisted perpendicular
magnetic recording media, e.g., FePt-oxides and CoPt-oxides, where
the oxides include, without limitation, TiO.sub.2, SiO.sub.2, MgO,
Ta.sub.2O.sub.5, Nb.sub.2O.sub.5, and Al.sub.2O.sub.3. The present
methodology is also useful in the preparation of precursor
granulated powders or powder mixtures comprised of at least one
metal and at least one ceramic material, including, for example and
without limitation, carbides and nitrides such as TaC and BN. Other
examples include CoPd oxides and Fe oxides.
[0048] The present methodology is also useful for making granulated
precursor powders utilizing only a fraction of the requisite metal
or metal alloy powders together with a fraction or all of the
requisite ceramic, oxide, and/or non-metallic element powders. The
resultant granulated powder is blended with the balance of
requisite metal or metal alloy powders and ceramic, oxide, and/or
non-metallic element powders for consolidation therewith.
[0049] The methodology afforded by the present disclosure will now
be described in additional detail.
[0050] Mixing or blending of constituent powders is a critical step
prior to consolidation for obtaining homogeneously composed solid
materials. Dry blending or grinding processing for mixing or
blending incur disadvantages such as agglomeration of the fine
particles of the constituent powders which are naturally cohesive.
Moreover, segregation in dry blending processing can be worsened
when the particle size distribution, density, and shapes of the
constituent particles are different.
[0051] In this regard, powder particles having sizes less than
about 20-30 .mu.m are typically classified as "cohesive" in the
powder processing industry. When particle sizes are in the micron
or sub-micron range, they are more cohesive and easily agglomerate
during dry mixing. Particle-level mixing is therefore not possible.
However, the current trend in the magnetic data/information storage
industry (i.e., manufacture of magnetic recording media) requiring
sputtering targets with ever finer grain sizes (e.g., <.about.20
.mu.m) with high homogeneity poses significant problems to
sputtering target manufacturers.
[0052] In a first step according to embodiments of the presently
disclosed methodology, a wet mixing technique is utilized,
employing either water, an alcohol, alcohol-water, or at least one
organic solvent as the liquid phase. At least one binder material
(inorganic or organic) is added and a homogeneous slurry/suspension
of the constituent powders or a wetted homogeneous mixture of the
constituent powders is formed. The choice of liquid phase material
depends upon the desired microstructure of the ultimate product.
For example, sputtering targets generally require an ultra-fine
microstructure. Depending upon the final metal particle size and
the chemical properties (e.g., reactivity) of the metal(s),
compatibilities of the constituent powders with the solvents,
either water, an alcohol, or at least one organic solvent, e.g.,
acetone, toluene, hexane, etc., is used for the liquid phase.
[0053] When ultra-fine microstructure is required (as with some
types of sputtering targets), wet milling or grinding of the
constituent ("raw") powders or coarse components can be employed
for forming homogeneous slurries/suspensions. When super-fine
microstructure is required (as in some types of sputtering
targets), the metal powder(s) may be replaced with compound(s)
containing the metal, e.g., an oxalate, carbonate, or hydroxide of
the metal and the ceramic powder(s) replaced with a sol-gel to form
a homogeneous solution/suspension. In such instances, the metal
compound(s) in the solvent is (are) either soluble or form a
suspension comprising super-fine entities. After drying, the
granulated mixture is subjected to thermal processing in a reducing
atmosphere to decompose or reduce the metal-containing compounds to
metal form.
[0054] In general, the raw powders may have a particle size
distribution (PSD) ranging from a few nanometers (mn) to hundreds
of microns, e.g., .about.300 .mu.m. The powder particles can be of
any shape or density, and the resultant (mixed) compositions can
vary over a wide range, depending upon the requirements of the
intended target or alloy application.
[0055] Conventional inorganic or organic binders can be added to
the slurry/suspension or wetted powder mixture, with 0.5-5 wt. % of
the dry mixture being typical. However, >.about.5 wt. % is also
possible. Additives such as deflocculating agents, wetting agents,
plasticizers, de-foaming agents, suspending agents, etc., can also
be utilized for forming homogeneous solutions/suspensions.
[0056] The raw powders and binder material(s) are added to the at
least one solvent (liquid phase) according to an optimized
sequence, with appropriate mixing tools/devices (e.g., high shear
mixers) being utilized for effecting homogeneous mixing of all of
the ingredients. If finer particles sizes are required which are
not available in raw powder form, a wet grinding or milling step in
slurry/suspension form can be added to the process. The solids
content of the slurry/suspension can be in the range from about 20
to about 80 wt. % when spray drying is the method of solvent
removal. Alternatively, the wetted powder (where the solvent and at
least one binder material only wet the surfaces of the particles)
can have a solids content as high as about 99 wt. %.
[0057] In the next step according to the present methodology, the
homogeneous slurry/suspension or wetted powder is dried to remove
at least a portion of the liquid phase (i.e., solvent) and form a
powder mixture comprising partially or completely dried granules.
Any suitable drying technique can be utilized for removing bulk
solvent(s). Typically, the binder material(s) is (are) not removed
during the drying step. However, when the temperature utilized for
the drying step exceeds the thermal stability limit of the binder
material, the binder material may be partially removed. The amount
of remaining (i.e., residual) solvent can be controlled to be in a
wide range as long as the dried powder maintains the homogeneous
mixing achieved during the wet mixing step. Drying may comprise
spray drying when the wet mix is in slurry/suspension form and the
particle size of all powders present in the slurry/suspension is
less than about 45 .mu.m.
[0058] When organic solvent(s) is (are) used as the liquid phase,
or when the metal particles after milling are highly flammable, an
inert gas, e.g., N.sub.2, Ar, Ne, etc., should be used as the
drying gas. In addition, a closed loop spray dryer is preferably
employed when organic solvent(s) is (are) used as the liquid
phase.
[0059] Following the drying step, the partially or completely dried
powder is subjected to a thermal de-binder process for effecting
additional removal of the liquid phase (if necessary), removal of
the at least one binder material, reduction of carbon content,
reduction of oxygen on the interior and/or exterior surfaces of the
metal constituent(s), and optional partial sintering for
strengthening of the granules for withstanding subsequent
processing. In particular, when organic binder material(s) is (are)
used in initial mixing processing of the constituent powders to
form a slurry/suspension or wetted powder mixture, removal of the
binder material(s) from the partially or completely dried powder is
necessary to reduce the carbon content. Typically, the carbon
content of the final granulated powder is expected to be less than
about 1000, ppm, preferably less than about 500 ppm. The thermal
de-binder process typically comprises heating the partially or
completely dried powder at a temperature ranging from ambient to
about 1400.degree. C. for from about 30 min. to about 24 hrs., in
an atmosphere comprising at least one strong reducing gas (e.g.,
H.sub.2, NH.sub.3, CO, dissociated NH.sub.3, H.sub.2/N.sub.2
mixtures, reformed hydrocarbon gases, etc.), to which at least one
weak oxidizing agent (H.sub.2O, CO.sub.2, etc.) is added. The weak
oxidizing agent serves to selectively oxidize the organic binder
agent(s) and any other carbon present in the partially or
completely dried powder and convert them to gases which are readily
removed from the solid material. The presence of the at least one
strong reducing gas ensures that the metal(s) or metal alloy
components of the partially dried powder is (are) not oxidized
during the thermal treatment. When the partially dried powder
contains an inorganic binder material, the thermal treatment may be
conducted in an atmosphere comprising at least one reducing gas, in
the absence of any weak oxidizing agent.
[0060] When water is utilized as the solvent for the liquid phase
in forming the slurry/suspension or wetted powder, or air is used
as a media for drying or present in the drying atmosphere, the
outer and/or inner surface(s) of the metal constituent(s) of the
powder may become oxidized. Therefore, another function of the
thermal de-binder treatment is to reduce any oxygen present on the
outer and/or inner surfaces of the metal particles. This may be
accomplished during the thermal de-binder treatment (with the weak
oxidizing agent present) or by switching to reducing gas(es) only
at the latter portion of the treatment (in the absence of any weak
oxidizing agent).
[0061] In addition to the above, the thermal de-binder treatment
may serve to pre-sinter the particles, thereby increasing the
strength of the granulated powder upon removal of the binder
material(s). The extent of sintering is variable by appropriate
regulation of the thermal de-binder treatment temperature.
[0062] The utility of the present disclosure will now be
demonstrated with reference to the following illustrative, but
non-limitative, examples.
EXAMPLE 1
[0063] Co-15.56 wt. % TiO.sub.2 Granulated Powder
[0064] A homogeneous slurry/suspension having the following
composition was prepared. [0065] Raw Co particle size: 1.4-8.5
.mu.m [0066] TiO.sub.2 particle size: <2 .mu.m [0067] Total
solids (Co+TiO.sub.2): 60 wt. % [0068] Binders (dry basis): 1.5 wt.
% polyvinyl alcohol (PVA) [0069] 1.5 wt. % polyethylene glycol
(PEG) [0070] Balance H.sub.2O (solvent/liquid phase)
[0071] The slurry/suspension was stirred/mixed to a homogeneous
state and spray dried in a spray drier having a diameter of 20 ft.
The slurry/suspension was constantly stirred during spray drying,
with hot air employed as drying gas at an air inlet temperature of
about 210.degree. C. and air outlet temperature of about
110.degree. C. The moisture content after spray drying was about
0.2 wt. %. The spherical, spray dried particles were then thermally
de-bindered/reduced in a muffle furnace for about 8 hrs. at a peak
temperature of about 800.degree. C. under a wet H.sub.2 atmosphere.
Any oxygen picked up by the metal constituent was reduced by
switching to dry H.sub.2 at a latter portion of the de-binder
treatment conducted at about 800.degree. C. for about 1 hr. The
latter temperature is sufficient to reduce oxygen present on the
surfaces of the metal particles but will not reduce the TiO.sub.2.
The thus-produced granulated powder contained spherically shaped
particles with sizes ranging from about 15 to about 100 .mu.m. The
residual carbon in the final granulated powder was extremely low,
as may be evident from the following: [0072] Carbon content of the
raw powder: 198 ppm [0073] Carbon content of the spray-dried powder
(containing binder): 15308 ppm [0074] Carbon content after
de-binder treatment: 87 ppm
EXAMPLE 2
[0075] Co-12.80 wt. % SiO.sub.2 Granulated Powder
[0076] A homogeneous slurry/suspension having the following
composition was prepared. [0077] Raw Co particle size: 1.4-8.5
.mu.m [0078] SiO.sub.2 particle size: <5 .mu.m [0079] Total
solids (Co+SiO.sub.2): 50 wt. % [0080] Binder (dry basis): 2 wt. %
polyethylene glycol (PEG) [0081] Balance H.sub.2O (solvent/liquid
phase)
[0082] The slurry/suspension was stirred/mixed to a homogeneous
state and spray dried in a spray drier having a diameter of 20 ft.
The slurry/suspension was constantly stirred during spray drying,
with hot air employed as drying gas at an air inlet temperature of
about 210.degree. C. and air outlet temperature of about
110.degree. C. The moisture content after spray drying was about
0.3 wt. %. The spherical, spray dried particles were then thermally
de-bindered/reduced in a muffle furnace for about 8 hrs. at a peak
temperature of about 800.degree. C. under a wet H.sub.2 atmosphere.
Any oxygen picked up by the metal constituent was reduced by
switching to dry H.sub.2 at a latter portion of the de-binder
treatment conducted at about 800.degree. C. for about 1 hr. The
latter temperature is sufficient to reduce oxygen present on the
surfaces of the metal particles but will not reduce the SiO.sub.2.
The thus-produced granulated powder contained spherically shaped
particles with sizes ranging from about 15 to about 150 .mu.m. The
residual carbon in the final granulated powder was extremely low,
as may be evident from the following: [0083] Carbon content of the
raw powder: 206 ppm [0084] Carbon content of the spray-dried powder
(containing binder): 11216 ppm [0085] Carbon content after
de-binder treatment: 72 ppm
EXAMPLE 3
[0086] Fe-15.31 wt. % SiO.sub.2 Granulated Powder
[0087] A homogeneous slurry/suspension having the following
composition was prepared. [0088] Raw Fe particle size: 3-12 .mu.m
[0089] SiO.sub.2 particle size: <5 .mu.m [0090] Total solids
(Co+SiO.sub.2): 67 wt. % [0091] Binder (dry basis): 3 wt. %
polyethylene glycol (PEG) [0092] Balance H.sub.2O (solvent/liquid
phase)
[0093] The slurry/suspension was stirred/mixed to a homogeneous
state and spray dried in a spray drier having a diameter of 20 ft.
The slurry/suspension was constantly stirred during spray drying,
with hot air employed as drying gas at an air inlet temperature of
about 210.degree. C. and air outlet temperature of about
110.degree. C. The moisture content after spray drying was about
0.2 wt. %. The spherical, spray dried particles were then thermally
de-bindered/reduced in a muffle furnace for about 9 hrs. at a peak
temperature of about 700.degree. C. under a wet H.sub.2 atmosphere.
Any oxygen picked up by the metal constituent was reduced by
switching to dry H.sub.2 at a latter portion of the de-binder
treatment conducted at about 700.degree. C. for about 1 hr. The
latter temperature is sufficient to reduce oxygen present on the
surfaces of the metal particles but will not reduce the SiO.sub.2.
The thus-produced granulated powder contained spherically shaped
particles with sizes ranging from about 15 to about 120 .mu.m. The
residual carbon in the final granulated powder was extremely low,
as may be evident from the following: [0094] Carbon content of the
raw powder: 276 ppm [0095] Carbon content of the spray-dried powder
(containing binder): 14530 ppm [0096] Carbon content after
de-binder treatment: 40 ppm
EXAMPLE 4
[0097] Co-14.31 wt. % Cr-13.50 wt. % TiO.sub.2 Granulated
Powder
[0098] A homogeneous slurry/suspension having the following
composition was prepared. [0099] Raw Co particle size: 1.4-8.5
.mu.m [0100] Raw Cr particle size: <37 .mu.pm [0101] TiO.sub.2
particle size: <2 .mu.m [0102] Total solids (Co+Cr+SiO.sub.2):
62 wt. % [0103] Binder (dry basis): 1.4 wt. % polyvinyl alcohol
(PVA) [0104] 1.4 wt. % polyethylene glycol (PEG) [0105] Balance
H.sub.2O (solvent/liquid phase)
[0106] The slurry/suspension was stirred/mixed to a homogeneous
state and spray dried in a spray drier having a diameter of 20 ft.
The slurry/suspension was constantly stirred during spray drying,
with hot air employed as drying gas at an air inlet temperature of
about 210.degree. C. and air outlet temperature of about
110.degree. C. The moisture content after spray drying was about
0.2 wt. %. The spherical, spray dried particles were then thermally
de-bindered/reduced in a muffle furnace for about 8 hrs. at a peak
temperature of about 900.degree. C. under a wet H.sub.2 atmosphere.
Any oxygen picked up by the metal constituent was reduced by
switching to dry H.sub.2 at a latter portion of the de-binder
treatment conducted at about 900.degree. C. for about 1 hr. The
latter temperature is sufficient to reduce oxygen present on the
surfaces of the metal particles but will not reduce the TiO.sub.2.
The thus-produced granulated powder contained spherically shaped
particles with sizes ranging from about 15 to about 180 .mu.m. The
residual carbon in the final granulated powder was extremely low,
as may be evident from the following: [0107] Carbon content of the
raw powder: 202 ppm [0108] Carbon content of the spray-dried powder
(containing binder): 12916 ppm [0109] Carbon content after
de-binder treatment: 110 ppm
EXAMPLE 5
[0110] Co-8.37 wt. % Cr-20.68 wt. % Fe-10.28 wt. % TiO.sub.2
Granulated Powder
[0111] A homogeneous slurry/suspension having the following
composition was prepared. [0112] Raw Co particle size: <7 .mu.m
[0113] Raw Cr particle size: <20 .mu.m [0114] Raw Fe particle
size: <12 .mu.m [0115] TiO.sub.2 particle size: <2 .mu.m
[0116] Total solids (Co+Cr+Fe+TiO.sub.2): 68 wt. % [0117] Binder
(dry basis): 1.5 wt. % polyvinyl alcohol (PVA) [0118] 1.5 wt. %
polyethylene glycol (PEG) [0119] Deflocculating agent: Darvan
C.RTM.--0.5 wt. % [0120] De-foaming agent: Foam
Blaster-327.RTM.--0.02 wt % [0121] Balance H.sub.2O (solvent/liquid
phase)
[0122] The slurry/suspension was stirred/mixed to a homogeneous
state and spray dried in a spray drier having a diameter of 20 ft.
The slurry/suspension was constantly stirred during spray drying,
with hot air employed as drying gas at an air inlet temperature of
about 210.degree. C. and air outlet temperature of about
110.degree. C. The moisture content after spray drying was about
0.2 wt. %. The spherical, spray dried particles were then thermally
de-bindered/reduced in a muffle furnace for about 9 hrs. at a peak
temperature of about 750.degree. C. under a wet H.sub.2 atmosphere.
Any oxygen picked up by the metal constituent was reduced by
switching to dry H.sub.2 at a latter portion of the de-binder
treatment conducted at about 750.degree. C. for about 1 hr. The
latter temperature is sufficient to reduce oxygen present on the
surfaces of the metal particles but will not reduce the TiO.sub.2.
The thus-produced granulated powder contained spherically shaped
particles with sizes ranging from about 15 to about 160 .mu.m. The
residual carbon in the final granulated powder was extremely low,
i.e., 98 ppm.
EXAMPLE 6
[0123] Co-7.88 wt. % Cr-25.25 wt. % Mo-9.69 wt. % TiO.sub.2
Granulated Powder
[0124] A homogeneous slurry/suspension having the following
composition was prepared. [0125] Raw Co particle size: <7 .mu.m
[0126] Raw Cr particle size: <15 .mu.m [0127] Raw Mo particle
size: <10 .mu.m [0128] TiO.sub.2 particle size: <2 .mu.m
[0129] Total solids (Co+Cr+Mo+TiO.sub.2): 67 wt. % [0130] Binder
(dry basis): 2 wt. % polyvinyl alcohol (PVA) [0131] 1 wt. %
polyethylene glycol (PEG) [0132] Deflocculating agent: Darvan
C.RTM.--0.3 wt. % [0133] De-foaming agent: Foam
Blaster-327.RTM.--0.02 wt % [0134] Balance H.sub.2O (solvent/liquid
phase)
[0135] The slurry/suspension was stirred/mixed to a homogeneous
state and spray dried in a spray drier having a diameter of 20 ft.
The slurry/suspension was constantly stirred during spray drying,
with hot air employed as drying gas at an air inlet temperature of
about 210.degree. C. and air outlet temperature of about
110.degree. C. The moisture content after spray drying was about
0.2 wt. %. The spherical, spray dried particles were then thermally
de-bindered/reduced in a muffle furnace for about 9 hrs. at a peak
temperature of about 750.degree. C. under a wet H.sub.2 atmosphere.
Any oxygen picked up by the metal constituent was reduced by
switching to dry H.sub.2 at a latter portion of the de-binder
treatment conducted at about 900.degree. C. for about 1 hr. The
latter temperature is sufficient to reduce oxygen present on the
surfaces of the metal particles but will not reduce the TiO.sub.2.
The thus-produced granulated powder contained spherically shaped
particles with sizes ranging from about 15 to about 150 .mu.m. The
residual carbon in the final granulated powder was extremely low,
i.e., 115 ppm.
[0136] In summary, notable advantages provided by the process
methodology according to the present disclosure vis-a-vis
conventional dry powder processes include:
[0137] (1) significantly better mixing uniformity than possible
with dry mixing techniques;
[0138] (2) absence of micro and/or micro segregations;
[0139] (3) reduced processing cost;
[0140] (4) extremely low amount of residual carbon in ultimate
granulated metal powder products; and
[0141] (5) mixing at particle level achievable within a wide range
of particle sizes of the constituent powders.
[0142] In the previous description, numerous specific details are
set forth, such as specific materials, structures, reactants,
processes, etc., in order to provide a better understanding of the
present disclosure. However, the present disclosure can be
practiced without resorting to the details specifically set forth.
In other instances, well-known processing materials and techniques
have not been described in detail in order not to unnecessarily
obscure the present disclosure.
[0143] Only the preferred embodiments of the present disclosure and
but a few examples of its versatility are shown and described in
the present disclosure. It is to be understood that the present
disclosure is capable of use in various other combinations and
environments and is susceptible of changes and/or modifications
within the scope of the disclosed concept as expressed herein.
* * * * *