U.S. patent application number 10/173085 was filed with the patent office on 2003-05-29 for anticorrosive magnetic nanocolloids protected by precious metals.
Invention is credited to Bonnemann, Helmut, Brijoux, Werner, Brinkmann, Rainer, Wagener, Michael.
Application Number | 20030098437 10/173085 |
Document ID | / |
Family ID | 7857782 |
Filed Date | 2003-05-29 |
United States Patent
Application |
20030098437 |
Kind Code |
A1 |
Bonnemann, Helmut ; et
al. |
May 29, 2003 |
Anticorrosive magnetic nanocolloids protected by precious
metals
Abstract
The invention relates to new single- or multi-metallic magnetic
colloid particles (for example, Fe, Co, Ni, Fe/Co) having a size of
up to 20 nm, the surface of which is protected against corrosion by
precious metals, such as Pd, Ag, Pt or Au. The invention also
relates to a method for producing such materials. In isolated form
or in solution said materials are used among other things as
sealing media against dust and gas in magnetic fluid seals (liquid
O ring), for lubricating and mounting rotating shafts (magnetic
levitation bearing), for the magnetooptic storage of information as
well as for the magnetic marking of cells and their separation in
biological samples or for the local administration of
medicines.
Inventors: |
Bonnemann, Helmut; (Essen,
DE) ; Brijoux, Werner; (Oberhausen, DE) ;
Brinkmann, Rainer; (Mulheim an der Ruhr, DE) ;
Wagener, Michael; (Bremen, DE) |
Correspondence
Address: |
KURT G. BRISCOE
NORRIS McLAUGHLIN & MARCUS
30TH FLOOR
220 EAST 42ND STREET
NEW YORK
NY
10017
US
|
Family ID: |
7857782 |
Appl. No.: |
10/173085 |
Filed: |
June 17, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10173085 |
Jun 17, 2002 |
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09622081 |
Aug 11, 2000 |
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6491842 |
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09622081 |
Aug 11, 2000 |
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PCT/EP99/00835 |
Feb 9, 1999 |
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Current U.S.
Class: |
252/62.55 |
Current CPC
Class: |
B03C 1/01 20130101; B82Y
25/00 20130101; B01J 13/0008 20130101; H01F 1/0054 20130101; H01F
1/442 20130101 |
Class at
Publication: |
252/62.55 |
International
Class: |
H01F 001/04 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 14, 1998 |
DE |
198 06 167.6 |
Claims
1. A process for the preparation of precious-metal protected,
anticorrosive metal and alloy colloids, characterized in that
previously prepared or in situ prepared magnetic nanocolloids are
treated with strong reductants in a solvent, and precious metal
salts are added to the resulting mixtures.
2. The process according to claim 1, wherein Fe, Co, Ni or Fe/Co
colloids are employed as said previously prepared or in situ
prepared magnetic nanocolloids.
3. The process according to claim 1, wherein hydrides of elements
from main groups 1 to 3 of the Periodic Table or complex hydrides
of these elements or of tetraalkylammonium are employed as said
strong reductants.
4. The process according to claim 1, wherein reducing
organometallic compounds of main groups 1 to 4 of the Periodic
Table are employed as said strong reductants.
5. Magnetic nanocolloids having a particle size of smaller than 20
nm, characterized in that said magnetic particles are provided with
a precious-metal coating and are stable towards corrosion for more
than 3 hours as seen from their magnetogram and their UV/Vis
spectra.
6. The magnetic nanocolloids according to claim 5, wherein Au is
employed as said precious metal, and Fe as said magnetic particles,
and said nanocolloids are stable towards corrosion for more than
100 hours.
7. The magnetic nanocolloids according to claim 5, wherein Au is
employed as said precious metal, and Co as said magnetic particles,
and said nanocolloids are stable towards corrosion for more than 20
hours.
8. Use of the magnetic nanocolloids according to claims 5 to 7 as a
magnetic fluid having a high saturation magnetization and at the
same time a low filler content in a magnetic fluid seal.
9. Use of the magnetic nanocolloids according to claims 5 to 7 as a
magnetic cell label after applying an additional cell-compatible
coating.
10. Use of the magnetic nanocolloids according to claims 5 to 7 for
magnetic cell separation.
11. Use of the magnetic nanocolloids according to claims 5 to 7 for
magnetooptical storage of information.
Description
[0001] The present invention relates to novel mono- and
polymetallic magnetic colloid particles (e.g., Fe, Co, Ni, Fe/Co)
of a size of up to 20 nm the surface of which is protected from
corrosion by precious metals, e.g., Pd, Ag, Pt or Au, and a process
for the preparation of these materials.
[0002] Various methods are known for the preparation of unprotected
colloidal magnetic metals, especially Fe, Co and Ni, e.g., salt
reduction (G. Schmid (Ed.), Clusters and Colloids, VCH, 1994, EP
423 627, DE 44 43 705 and U.S. Pat. No. 5,620,584), thermal,
photochemical and sonochemical decomposition of metal carbonyls and
nitrosyl complexes (K. S. Suslick, T. Hyeon, M. Fang, A. A.
Cichowlas in: W. Moser (Ed.), Advances Catalysts and Nanostructured
Materials, Chapter 8, p. 197, Academic Press, 1996), and the
reduction of salts or the decomposition of carbonyl compounds in
micellar solutions (O. A. Platonova, L. M. Bronstein, S. P.
Solodovnikov, I. M. Yanovskaya, E. S. Obolonkova, P. M. Valetsky,
E. Wenz, M. Antonietti, Colloid Polym. Sci. 275, 1997, 426). The
long-term stability of such previously proposed colloidal magnetic
metals against atmospheric oxygen is unsatisfactory, however (see
Comparative Examples: Table 1, Nos. 2, 3 and 5, FIGS. 1a, 2 and
4).
[0003] Therefore, it has been the object of the present invention
to provide a process for the preparation of corrosion-stable
colloidal magnetic nanometals of a size of up to 20 nm by
protecting the particle surface against corrosive attack by means
of precious metal coatings.
[0004] Japanese Patent JP 0727 2922 AZ describes the preparation of
anticorrosive, resin-bound Fe magnets protected by three coatings
with, inter alia, precious metals. However, they are exclusively
coated magnetic bulk materials which are not suitable for
nanotechnology and magnetic fluids. A process for the preparation
of precious-metal protected magnetic nanocolloid particles of a
size of up to 20 nm has not been known. Toshima et al. describe the
preparation of Pd--Pt bimetal colloids (1.5-5.5 nm) with a
controllable core-shell structure (Y. Wang and N. Toshima, J. Phys.
Chem. B, 1997, 101, 5301). Schmid et al. describe the preparation
of gold-coated Pd particles of a size of from 20 to 56 nm having a
layer structure (G. Schmid, H. West, J.-O. Malm, J.-O. Bovin, and
C. Grenthe, Chem. Eur. J. 1996, 1099). However, the mentioned
processes cannot be transferred to a combination of magnetic metal
(Fe, Co, Ni) and precious metal coating. J. Sinzig tried to protect
the particle surface of an N(octyl).sub.4-stabilized Co colloid
from corrosion by chemical plating with elemental gold (J. Sinzig,
Proefschrift, p. 74, Rijksuniversiteit te Leiden (NL) 1997). The
following redox process occurs at the Co surface: 12 Co.sup.(0)+2
AuCI.sub.3.fwdarw.Co.sub.9Au.sub.2+3 CoCl.sub.2. Although the
oxidation stability of the materials can be enhanced in this way,
it is still insufficient for the mentioned applications (see
Comparative Example: Example No. 8, Table 1 No. 6, FIGS. 1b and
6).
[0005] It has now surprisingly been found that corrosion-stable
magnetic nanocolloids can be obtained by preparing, e.g., Fe, Co,
Ni or Fe/Co alloy colloids by methods known from the literature
(see above) or generating them in situ, treating them, under
extremely strict exclusion of atmospheric oxygen in organic
solvents, with strong reductants, e.g., hydrides of elements from
main groups 1 to 3 of the Periodic Table, complex hydrides of these
elements or of tetraalkylammonium, or reducing organometallic
compounds of main groups 1 to 4 of the Periodic Table, and adding
precious metal salts, e.g., of Pd, Ag, Pt or Au, preferably in
solution in a molar ratio (Colloid:precious metal salt) of >1:1,
preferably 1:0.3, to the resulting mixture. Suitable solvents
include aliphatic and aromatic solvents and ethers, and suitable
reductants include, e.g., the above mentioned hydrides and
organometallic compounds in a molar ratio (reductant:colloid) of at
least 1:1, preferably >3:1.
[0006] The thus obtained precious-metal protected anticorrosive
magnetic nanocolloids of a size of up to 20 nm have long-term
stability; for example, in the Au-protected Fe colloid, a decrease
of magnetization J by corrosion cannot be detected until the
measurement is terminated after 100 hours. The materials can be
employed in isolated form or in solution, without intending to
limit their use, e.g., as a sealing medium against dust and gases
in magnetic fluid seals (liquid O ring), for the lubrication and
bearing of rotating shafts (magnetic levitation bearing), for
magnetooptical storage of information, e.g., in compact disks and
minidisks, and further, after applying an additional
cell-compatible coating, for the magnetic labeling of cells and
their magnetic separation in biological samples, or for the topical
application of medicaments. The superior corrosion stability of the
new materials as compared to unprotected magnetic nanocolloids of
similar size will be illustrated by the following Examples
(Examples 1 to 7, Table 2, FIGS. 1a, 1b, 3 and 5).
EXAMPLE 1
[0007] Under argon as a protective gas, 1.3 g (1.43 mmol Fe) of Fe
colloid (identification symbol: MK2) is dissolved in 50 ml of THF
in a 500 ml flask, and a solution of 2.61 g (4.61 mmol) of
(C.sub.8H.sub.17).sub.4NBE- t.sub.3H in 27 ml of THF is added.
Under exclusion of light, a solution of 0.146 g (0.48 mmol) of
AuCl.sub.3 in 185 ml of THF is added dropwise at room temperature
within 14 h. Any precipitated reaction products are removed by
filtration through a D4 glass frit, and the resulting solution is
concentrated. After 3 h of drying in vacuo (0.1 Pa) at 40.degree.
C., 5.5 g of brown-black, wax-like, Au-protected Fe colloid is
obtained (Table 2, No. 3, FIGS. 1a and 3).
[0008] For determining the magnetization, 1 g of a dried metal
colloid is redispersed in 2 ml of solvent (toluene, THF) and placed
on a magnetic scale in an open cylindrical glass jar having a
diameter of 2 cm. When an NdFeB magnet having a high magnetic field
strength of B.sub.R=1.1 T and a low distance of magnet to metal
colloid of 5 mm is used, it can be considered that the colloid
particles are magnetically saturated in the liquid. Therefore, the
weight ratio of G.sub.0/G(t), measured at time t, is equal to the
ratio of the magnetization at time t to the initial magnetization,
J(T)/J.sub.0.
EXAMPLE 2
[0009] The same procedure as in Example 1 is used, except that
0.287 g (3 mmol Fe) of Fe colloid (identification symbol: MK3) in
100 ml of THF and 5.55 g (9.8 mmol) of
(C.sub.8H.sub.17).sub.4NBEt.sub.3H in 58 ml of THF are used, 0.3 g
(1 mmol) of AuCl.sub.3 dissolved in 377 ml of THF is added dropwise
within 14 h, and 13.5 g of brown-black, viscous, Au-protected Fe
colloid is obtained (Table 2, No. 9, FIG. 1a).
EXAMPLE 3
[0010] The same procedure as in Example 1 is used, except that 0.9
g (1 mmol Fe) of Fe colloid (identification symbol: MK2) in 40 ml
of THF is used, 0.55 g (1.5 mmol) of Al(octyl).sub.3 is added, and
0.1 g (0.33 mmol) of AuCl.sub.3 dissolved in 94 ml of THF is added
dropwise within 16 h, and 2.2 g of brown-black, Au-protected Fe
colloid is obtained (Table 2, No. 7).
EXAMPLE 4
[0011] The same procedure as in Example 1 is used, except that 2.9
g (3.2 mmol Fe) of Fe colloid (identification symbol: MK2) in 80 ml
of THF and 6.0 g (10.6 mmol) of (C.sub.8H.sub.17).sub.4NBEt.sub.3H
dissolved in 32 ml of THF are used, and 0.37 g (1.1 mmol) of
PtCl.sub.4 dissolved in 306 ml of THF is added dropwise within 16 h
to obtain 14.5 g of Pt-protected Fe colloid (Table 2, No. 13).
EXAMPLE 5
[0012] The same procedure as in Example 1 is used, except that 0.9
g (1.1 mmol Fe) of Fe colloid (identification symbol: MK4) in 40 ml
of THF and 0.18 g (1.7 mmol) of LiBEt.sub.3H dissolved in 2 ml of
THF are used, and 0.11 g (0.36 mmol) of AuCl.sub.3 dissolved in 112
ml of THF is added dropwise within 16 h to obtain 1.3 g of
Au-protected Fe colloid (Table 2, No. 11).
EXAMPLE 6
[0013] The same procedure as in Example 1 is used, except that 3.1
g (3 mmol Co) of Co colloid (identification symbol: MK5) in 300 ml
of THF and 5.43 g (9.6 mmol) of (C.sub.8H.sub.17).sub.4NBEt.sub.3H
dissolved in 33 ml of THF are used, and 0.3 g (1 mmol) of
AuCl.sub.3 dissolved in 500 ml of THF is added dropwise within 18 h
to obtain 13.5 g of dark brown, wax-like, Au-protected Co colloid
(Table 2, No. 16, FIGS. 1b and 5).
EXAMPLE 7
[0014] The same procedure as in Example 1 is used, except that 0.83
g (5 mmol Co) of Co colloid (identification symbol: MK7) in 300 ml
of THF and 5.43 g (9.6 mmol) of (C.sub.8H.sub.17).sub.4NBEt.sub.3H
dissolved in 33 ml of THF are used, and 0.3 g (1 mmol) of
AuCl.sub.3 dissolved in 300 ml of THF is added dropwise within 16 h
to obtain 7.2 g of black-brown, viscous, Au-protected Co colloid
(Table 2, No. 17).
EXAMPLE 8
(Comparative Example: Gold Plating of Co Colloid)
[0015] Under argon as a protective gas, 6.5 g (6 mmol Co) of Co
colloid (identification symbol: MK6) is dissolved in 250 ml of
toluene in a 500 ml flask, and 0.3 g (1 mmol) of solid AuCl.sub.3
is added at room temperature. Within 16 h, the AuCl.sub.3
dissolves, and a brown-black solution containing low amounts of a
finely dispersed gray-black precipitate forms. This is removed by
filtration through a D4 glass frit, and after concentrating and 3 h
of drying in vacuo (0.1 Pa) at 30.degree. C., 6.8 g of black solid
Co-Au colloid is obtained (FIGS. 1b and 6).
1TABLE 1 Magnetic metal colloids employed Mean Identifi- Metal
colloid particle cation No. Metal Stabilizer size [nm] symbol 1 Fe
(C.sub.8H.sub.17).sub.4NC- l 2-3 MK1 2 Fe
(C.sub.8.sub.H17).sub.4NBr 3-4 MK2 3 Fe N-lauroylsarcosine Na salt
5-6 MK3 4 Fe 2-(dimethyldodecylammonio)- ace- -- MK4 tate Rewoteric
AM DML 5 Co (C.sub.8H.sub.17).sub.4NCl 2-3 MK5 6 Co
(C.sub.8H.sub.17).sub.4NBr 2-3 MK6 7 Co Korantin SH (BASF) 7-11 MK7
8 Ni (C.sub.8H.sub.17).sub.4NCl 2-3 MK8 9 Fe.sub.2Co
(C.sub.8H.sub.17).sub.4NBr 2-3 MK9
[0016]
2TABLE 2 Synthesis of precious-metal protected magnetic
nanocolloids Metal colloid Reductant Precious metal salt Product
No. Metal Ident. mmol THF, ml Formula mmol THF, ml Formula mmol
THF, ml Time [h] [g] 1 Fe MK1 3 173
(C.sub.8H.sub.17).sub.4NBEt.sub.3H 9.6 48 AuCl.sub.3 1 370 16 12.8
2 Fe MK2 1 50 (C.sub.6H.sub.13).sub.4NBEt.sub.3H 3.2 16 AuCl.sub.3
0.33 160 14 3.5 3 Fe MK2 1.43 50 (C.sub.8H.sub.17).sub.4NBEt.sub.3H
4.61 27 AuCl.sub.3 0.48 185 14 5.5 4 Fe MK2 1 50
(C.sub.12H.sub.25).sub.4NBEt.sub.3H 3.2 16 AuCl.sub.3 0.33 160 14
4.5 5 Fe MK2 2.9 100* (C.sub.8H.sub.17).sub.4NBEt.sub.3H 9.3 24
AuCl.sub.3 1 303 16 12.7 6 Fe MK2 2.9 100 LiBEt.sub.3H 4.4 22*
AuCl.sub.3 1 303 18 8.8 7 Fe MK2 1 40 Al(octyl).sub.3 1.5 --
AuCl.sub.3 0.33 94 16 2.2 8 Fe MK2 1 40 Al(octyl).sub.3 1.5 --
Au[(octyl).sub.4N].sub.3Br.sub.3Cl.sub.3 0.33 94 16 2.4 9 Fe MK3 3
100 (C.sub.8H.sub.17).sub.4NBEt.sub.3H 9.8 58 AuCl.sub.3 1 377 16
5.8 10 Fe MK3 1.64 57.5 (C.sub.8H.sub.17).sub.4NBEt.sub.3H 5.62 17
AuBr.sub.3 0.55 250 16 3.1 11 Fe MK4 1.1 40 LiBEt.sub.3H 1.7 2
AuCl.sub.3 0.36 112 16 1.3 12 Fe MK2 3.1 80
(C.sub.8H.sub.17).sub.4NBEt.sub.3H 9.6 29 Pd(CH.sub.3COO).sub.2 1
278 16 12.2 13 Fe MK2 3.2 80 (C.sub.8H.sub.17).sub.4NBEt.sub.3H
10.6 32 PtCl.sub.4 1.1 306 16 14.5 14 Fe MK2 2.9 80
(C.sub.8H.sub.17).sub.4NBEt.sub.3H 9.6 29 Ag neodecanoate 1 278 16
13.2 15 Fe MK2 2.9 100 (C.sub.8H.sub.17).sub.4NBEt.sub.3H 9.3 24 Ag
neodecanoate 1 323* 18 12.9 16 Co MK5 3 300
(C.sub.8H.sub.17).sub.4NBEt.sub.3H 9.6 33 AuCl.sub.3 1 500 18 13.5
17 Co MK7 5 300 (C.sub.8H.sub.17).sub.4NBEt.sub.3H 9.6 33
AuCl.sub.3 1 300 16 7.2 18 Co MK7 5 300
(C.sub.8H.sub.17).sub.4NBEt.sub.3H 19.2 66 AuCl.sub.3 2 600 16 12.6
19 Co MK7 5 300 (C.sub.8H.sub.17).sub.4NBEt.sub.3H 28.8 99
AuCl.sub.3 3 900 16 18.0 20 Ni MK9 2.76 97
(C.sub.8H.sub.17).sub.4NBEt.sub.3H 8.83 26.7 AuCl.sub.3 0.92 340 16
12.2 21 Fe.sub.2Co MK10 3.2 100 (C.sub.8H.sub.17).sub.4NBEt.sub.3H
10.6 27.8 AuCl.sub.3 1.1 300 16 12.1 *Solvent toluene
* * * * *