Note: Descriptions are shown in the official language in which they were submitted.
CA 02708830 2010-06-09
FP08-0470-00
DESCRIPTION
POWDER AND METHOD FOR PRODUCING THE SAME
Technical Field
[0001] The present invention relates to a powder suitable as a starting
_powder for production of a low iron loss powder magnetic core.
Background Art
[0002] A large variety of familiar products exist that utilize
electromagnetism, including transformers, electric motors, generators,
speakers, induction heaters, actuators and the like. For higher
performance and size reduction, it is essential to improve the
performance of the magnetic core, which is a green compact of a soft
magnetic material.
[0003] Conventionally, the magnetic core is produced by alternately
layering a plurality of silicon steel thin-films and insulating layers, and
punching the stack with a die (magnetic steel sheet). However, this
method is often inconvenient for product downsizing and unsuitable for
forming complex shapes, while reduced eddy current loss has also been
a problem.
[0004] These problems have been examined with recent research and
development focused on powder magnetic cores obtained by
compression molding soft magnetic metal powder, as magnetic cores
with high moldability and low production cost.
[0005] Such powder magnetic cores are required to increase magnetic
permeability to increase the flux density. Magnetic cores for motors,
in particular, are usually used in an alternating field, and since high iron
loss impairs the energy conversion efficiency they are required to have
1
CA 02708830 2010-06-09
FP08-0470-00
low iron loss.
[0006] Iron loss includes hysteresis loss, eddy current loss and residual
loss, with hysteresis loss and eddy current loss mainly constituting the
problems.
[0007] Increased hysteresis loss in a powder magnetic core is due to
application of a large degree of working strain to the soft magnetic
metal powder when the soft magnetic metal powder is compression
molded into a powder magnetic core. In order to reduce hysteresis loss,
therefore, it is effective to anneal the obtained compact after
compression molding to relieve the strain on the soft magnetic metal
powder, for which an annealing temperature of 600 C or higher is
considered preferable.
[0008] On the other hand, covering the soft magnetic metal powder
with an insulating material is effective for reducing eddy current loss.
Insulating materials commonly used in the prior art, however,
decompose when annealed to reduce hysteresis loss, because of the low
heat resistance of the insulating material, and the insulating property is
markedly impaired as a result. It has therefore been a primary goal to
achieve both reduced eddy current loss and reduced hysteresis loss.
[0009] Insulating materials with excellent heat resistance are being
developed toward reaching this goal. In particular, the use of iron
powder as soft magnetic metal powder is a target of much research and
development, as it allows production of powder magnetic cores with
low cost and high flux density. Patent document 1, for example,
proposes a method of employing silica particles as an insulating film
with excellent heat resistance. The document discloses a method in
2
CA 02708830 2012-05-11
27986-96
which iron powder with a phosphated surface is mixed with a silica
particle-containing suspension, and the mixture is dried to obtain metal
powder coated with silica powder.
[0010] However, when it is attempted to produce a powder magnetic
core using such iron powder coated with silica particles, it has been
necessary to use a higher annealing temperature than the ordinary
temperature of around 600 C (for example, 800 C or higher) to obtain
sufficient bonding force between the metal powder. An excessively
high annealing temperature can lower the magnetic properties of the
powder magnetic core because the Curie temperature of iron is 769 C.
[0011] Patent document 2 proposes a method in which an oxide layer
and an insulating layer are formed on the surface of soft magnetic metal
powder and subjected to bond-strengthening treatment in a reducing
atmosphere under high-temperature conditions, to form a monolayer
with an excellent insulating property on the surface of the soft magnetic
metal powder.
[Patent document 1] Japanese Unexamined Patent Publication HEI No.
9-180924
[Patent document 2] Japanese Unexamined Patent Publication No.
2007-194273
Disclosure of the Invention
[0012] Soft magnetic metal powder produced by the method disclosed
in Patent document 2 can be used to provide a powder magnetic core
with excellent heat resistance. However, because of the high energy
cost associated with annealing in this method and the fact that the
3
CA 02708830 2012-05-11
27986-96
method is not suitable for mass production, more simple methods for obtaining
coated soft magnetic metal powder with excellent heat resistance have been
considered.
[0013] Yet, although flux density can be effectively increased by forming a
very
thin and broad insulating layer on soft magnetic metal powder, no simple and
low-
cost method for doing this has been known.
[0014] The present invention provides a soft magnetic metal starting powder
that can both reduce hysteresis loss and reduce eddy current loss in powder
magnetic cores, while also having low iron loss and high flux density.
[0015] The invention provides a powder comprising a metal powder, an apatite
layer covering the metal powder and silica particles attached to at least the
apatite
layer.
[0016] According to the invention, metal powder is covered with an apatite
layer and silica particles are attached to at least the apatite layer, to
allow forming an
insulating film on the metal powder surface that can withstand annealing
temperatures of 600 C or higher. The use of this construction and its effect
is based
on knowledge of the present inventors that formation of a satisfactory heat-
resistant
insulating film that can withstand annealing temperatures of 600 C or higher
is
effective for reducing hysteresis loss.
[0017] According to the invention, the apatite layer preferably contains a
compound represented by the following formula (I-a) or (I-b).
4
CA 02708830 2012-05-11
27986-96
Caio(PO4)6X2 (I-a)
Ca(ia(m . n)/2)M.(P04)6X2 (I-b)
(In the formulas, M represents a cation-donating atom or group of atoms,
in represents the valency of the cation donated by M, n is greater than 0
and not greater than 5, and X represents an atom or group of atoms that
donates a monovalent anion.)
[0018] The silica particles are preferably silica particles that have been
surface-modified with an organic group.
[0019] The silica particles that have been surface-modified with an
organic group are preferably silica particles that have been
surface-modified using a compound represented by the following
formula (II) or (III).
R1nSi(OR2)4_n (II)
R1nSiX4-n (i)
(In the formulas, n is an integer of 1-3, R1 and R2 represent monovalent
organic groups, and X represents a halogen.)
[0020] The metal powder is preferably a soft magnetic material powder.
[0021] The powder of the invention is suitable as a powder for a
powder magnetic core.
[0022] The invention provides a method for producing powder which
comprises a first step of covering a metal powder with apatite, a second step
of
attaching silica powder to at least the apatite surface obtained in the first
step,
and a third step of pre-curing the powder obtained in the second step at not
greater than 350 C to obtain a powder comprising the metal powder, the apatite
layer covering the metal powder, and silica particles attached to at least the
5
CA 02708830 2010-06-09
FP08-0470-00
apatite layer.
[0023] The metal powder provided in the first step is preferably
phosphated metal powder.
Effect of the Invention
[0024] The powder of the invention is covered with an insulating layer
comprising an apatite layer and silica particles attached thereto, and the
insulating layer has excellent insulating properties and heat resistance.
Annealing can therefore be carried out at high temperature without
destruction of the insulating layer during production of powder
magnetic cores. The insulating property of the insulating layer is thus
maintained, and a powder magnetic core with sufficiently high magnetic
permeability can be obtained.
Brief Description of the Drawings
[0025] Fig. 1 is a photograph showing a scanning electron microscope
(SEM) image of a cross-section of the hydroxyapatite-covered iron
powder obtained in Example 1 (magnification: 2500x).
Fig. 2 is a photograph showing an SEM image of a cross-section of the
hydroxyapatite-covered iron powder obtained in Example 1
(magnification: 50000x).
Fig. 3 is a photograph showing an SEM image of a cross-section of the
nanosilica-attached hydroxyapatite-covered iron powder obtained in
Example 1 (magnification: 1000x).
Fig. 4 is a photograph showing an SEM image of a cross-section of the
nanosilica-attached hydroxyapatite-covered iron powder obtained in
Example 1 (magnification: 100000x).
Best Mode for Carrying Out the Invention
6
CA 02708830 2012-05-11
27986-96
[0026] One mode of the powder of the invention is a powder
comprising metal powder, an apatite layer covering the metal powder
and silica particles attached to at least the apatite layer. Each
of the constituent elements of the powder of the invention will now be
explained.
[0027] (Metal powder)
The metal powder used for the invention is not particularly restricted so
long as it is metal powder with ferromagnetism and exhibiting high
saturated flux density, and as specific examples there may be mentioned
soft magnetic materials such as iron powder, silicon-steel powder,
sendust powder, amorphous powder, permendur powder, soft ferrite
powder, amorphous magnetic alloy powder, nanocrystal magnetic alloy
powder and permalloy powder, which may be used alone. or in mixtures
of two or more. Iron powder is preferred among these from the
viewpoint of strong magnetism and low cost.
[0028] Among iron powders, pure iron powder is especially preferred
from the standpoint of excellent magnetic properties including saturated
flux density and magnetic permeability, and excellent compressibility.
As specific examples of such pure iron powders there may be
mentioned atomized iron powder, reduced iron powder and electrolytic
iron powder, such as 300NH by Kobe Steel, Ltd.
[0029] The metal powder used may be the metal powder with a
modified element composition in a range that does not adversely affect
the compressibility or the magnetic properties of the powder magnetic
core. Specifically, elemental phosphorus may be added to prevent
oxidation of the metal powder, or an element such as cobalt, nickel,
7
CA 02708830 2010-06-09
FP08-0470-00
manganese, chromium, molybdenum or copper may be added to
improve the magnetic properties.
[0030] There are no particular restrictions on the particle size of the
metal powder, and it may be appropriately selected according to the
purpose and properties required for the powder magnetic core.
Generally speaking, it may be selected so that the size of the particles as
observed under a scanning electron microscope (SEM) is in the range of
1 gm-300 gm. A particle size of 1 gm or greater will tend to facilitate
molding during production of the powder magnetic core, while a
particle size of 300 pm or smaller will help prevent increased eddy
current of the powder magnetic core and tend to facilitate coating of the
apatite layer. The mean particle size (the mean secondary particle size
determined by screening) is preferably 50-250 pm.
[0031] The form of the metal powder is not particularly restricted and
may be spherical or globular, or flat powder obtained by flattening
treatment by a known process or machining method.
[0032] (Apatite layer)
The apatite layer covering the surface of the powder of the invention
functions as an insulating film for the metal powder. From this
viewpoint, the apatite layer preferably has a coating film structure
covering the surface of the metal powder in a laminar fashion.
[0033] An apatite layer is a layer composed of a substance with an
apatite structure. As specific preferred examples of substances with
apatite structures for the apatite layer there may be mentioned
compounds represented by the following formula (I-a) or (I-b).
Calo(PO4)6X2 (I-a)
8
CA 02708830 2010-06-09
FP08-0470-00
Ca(lo-(m = n)/2)Mn(1 O4)6X2 (I-b)
(In the formulas, M represents a cation-donating atom, m represents the
valency of the cation donated by M, n is greater than 0 and not greater
than 5, and X represents an atom or group of atoms that donates a
monovalent anion.)
[0034] In formula (I-b), the cation-donating atom M is preferably a
metal that can replace calcium. As such metals there may be
mentioned, specifically, metals with ion radii of 0.80-1.40 A, such as
sodium, magnesium, potassium, calcium, scandium, titanium,
chromium, manganese, iron, cobalt, nickel, zinc, strontium, yttrium,
zirconium, ruthenium, rhodium, palladium, silver, cadmium, indium, tin,
antimony, tellurium, barium, lanthanum, cerium, praseodymium,
neodymium, promethium, samarium, europium, gadolinium, terbium,
dysprosium, holmium, erbium, thulium, ytterbium, lutetium, hafnium,
platinum, gold, mercury, thallium, lead or bismuth. M in formula (I-b)
may be of a single type or two or more types. The range for n in
formula (I-b) is greater than 0 and not greater than 5, more preferably
greater than 0 and not greater than 2.5, and even more preferably greater
than 0 and not greater than 1Ø Also, each X in formula (I-a) and (I-b)
is preferably hydroxyl (OH) or a halogen (such as F, Cl, B or I) and is
more preferably hydroxyl or fluorine. X is preferably a hydroxyl
group from the viewpoint of excellent coatability onto metal powder,
and it is preferably fluorine from the viewpoint of excellent strength.
[0035] The substance with an apatite structure for the apatite layer is
more preferably a compound represented by formula (I-a), and
especially preferably hydroxyapatite (Cajo(PO4)6(OH)2) or fluoroapatite
9
CA 02708830 2010-06-09
FP08-0470-00
(Calo(PO4)6F2), from the viewpoint of excellent insulating properties,
heat resistance and dynamic properties when made into a powder
magnetic core.
[0036] The term "covering the metal powder with the apatite layer" in
regard to the powder of the invention means that at least a portion of the
metal powder is covered by the apatite layer. The term
"apatite-covered metal powder" used below, therefore, includes not only
metal powder completely covered with apatite but metal powder that is
partially exposed. The extent of coverage of the metal powder by the
apatite layer is preferably to a higher coverage factor from the
viewpoint of facilitating adhesion of silica, described hereunder, and
resulting in improved transverse strength. Specifically, preferably at
least 90% of the surface, more preferably at least 95% and even more
preferably all (essentially 100%) of the metal powder is covered by the
apatite layer.
[0037] The apatite layer in the powder of the invention has a thickness
of preferably 10 nm-1000 nm and more preferably 20-500 nm. A
,thickness of 10 nm or greater will tend to provide an insulating effect,
while a thickness of not greater than 1000 nm will tend to provide a
density-improving effect.
[003 8] The method of forming the apatite layer on the metal powder
may be a method in which an aqueous solution containing calcium ion
or additionally the ion of the cation-donating atom or group of atoms M
of formula (1-b) in a prescribed ratio is reacted with an aqueous solution
containing phosphate ion, to deposit a substance that adopts an apatite
structure on the metal powder surface. In order to obtain a layer with
CA 02708830 2010-06-09
FP08-0470-00
an apatite structure, it is essential to control the reaction mixture to
between the neutral and basic range (pH = 6.0 or higher). In the acidic
range, a calcium phosphate layer may sometimes be deposited in
addition to the substance with an apatite structure.
[0039] When hydroxyapatite is deposited as the apatite layer, a method
using a calcium nitrate aqueous solution and ammonium
dihydrogenphosphate aqueous solution may be employed. The
stoichiometric composition of the hydroxyapatite obtained in this
manner is Ca10(PO4)6(OH)2, but it may be a nonstoichiometric
composition so long as the majority is an apatite structure and it can be
maintained, and for example, a portion may be
Caio-z(HI'O4)z(PO4)6-z(OH)2-z (0 < Z < 1, 1.50 < Ca/P (atomic weight
ratio) < 1.67).
[0040] The amount of apatite layer starting material added is preferably
0.1-1.0 part by mass, more preferably 0.4-0.8 part by mass and even
more preferably 0.5-0.7 part by mass with respect to 100 parts by mass
of the metal powder. An amount of at least 0.1 part by mass will tend
to result in adequate resistivity when the powder is formed into a
powder magnetic core. A uniform insulating layer can also be formed
on the powder, and an effect of improved insulation can be satisfactorily
obtained. An amount of not greater than 1.0 part by mass will help
prevent reduction in the compact density when the powder is formed
into a powder magnetic core. The mass of apatite layer can be
determined by quantifying the amount of calcium (and metal M) by
elemental analysis of the obtained powder.
[0041] (Silica particles)
11
CA 02708830 2010-06-09
FP08-0470-00
The silica particles used for the powder of the invention may be any that
are known in the prior art, among which fumed silica and colloidal
silica may be mentioned specifically, but colloidal silica is preferred
from the viewpoint of easy manageability. There are no restrictions on
the shapes of the silica particles.
[0042] The particle size of the silica particles may be any of various
sizes, but silica particles having a submicron particle size are preferred
for film formability. Specifically, the mean primary particle size of the
silica particles is preferably not greater than 50 nm, more preferably not
greater than 30 nm and even more preferably not greater than 20 nm.
[0043] The silica particles are preferably dispersed without aggregation
in an organic solvent. For improved dispersibility of the silica
particles, the silica particle surfaces may be modified with an organic
group. As examples of organic groups there may be mentioned
cyclohexyl, phenyl, benzyl, phenethyl and C l -C6 (1-6 carbon atoms)
alkyl groups.
[0044] The method of modifying the silica particle surfaces with the
organic group may be a method of reacting the silica particle surfaces
with a silane compound having an organic group in the molecular
structure. This can increase the transverse strength and often improve
the resistivity, when the powder is formed into a powder magnetic core.
[0045] Specific silane compounds include alkoxysilanes represented by
the following formula (II) and halogenosilane compounds represented
by the following formula (III).
R1nSi (OR)4-n (II)
R11SiX4-n (III)
12
CA 02708830 2010-06-09
FP08-0470-00
(In the formulas, n is an integer of 1-3, R1 and R2 represent monovalent
organic groups, and X represents a halogen.)
[0046] R1 in formulas (II) and (III) is the organic group that is to
modify the silica particles, and specifically there may be mentioned
cyclohexyl, phenyl, benzyl, phenethyl and Cl-C6 (1-6 carbon atoms)
alkyl groups. R2 may be a monovalent organic group, and specifically
methyl, ethyl or the like. X may be chloro, bromo, iodo or the like.
[0047] Specific examples of alkoxysilanes represented by formula (II)
include trimethoxysilanes such as methyltrimethoxysilane,
ethyltrimethoxysilane, n-propyltrimethoxysilane,
iso-propyltrimethoxysilane, n-butyltrimethoxysilane,
tert-butyltrimethoxysilane, n-pentyltrimethoxysilane,
n-hexyltrimethoxysilane, cyclohexyltrimethoxysilane,
phenyltrimethoxysilane, benzyltrimethoxysilane and
phenethyltrimethoxysilane;
triethoxysilanes such as methyltriethoxysilane, ethyltriethoxysilane,
n-propyltriethoxysilane, iso-propyltriethoxysilane,
n-butyltriethoxysilane, tert-butyltriethoxysilane, n-pentyltriethoxysilane,
n-hexyltriethoxysilane, cyclohexyltriethoxysilane, phenyltriethoxysilane,
benzyltriethoxysilane and phenethyltriethoxysilane;
dimethoxysilanes such as dimethyldimethoxysilane,
ethylmethyldimethoxysilane, methyl-n-propyldimethoxysilane,
methyl-iso-propyldimethoxysilane, n-butylmethyldimethoxysilane,
methyl-tert-butyldimethoxysilane, methyl-n-p entyldimethoxysilane,
n-hexylmethyldimethoxysilane, cyclohexylmethyldimethoxysilane,
methylphenyldimethoxysilane, benzylmethyldimethoxysilane and
13
CA 02708830 2010-06-09
FP08-0470-00
phenethylmethyldimethoxysilane;
and diethoxysilanes such as dimethyldiethoxysilane,
ethylmethyldiethoxysilane, methyl-n-propyldiethoxysilane,
methyl-iso-propyldiethoxysilane, n-butylmethyldiethoxysilane,
methyl-tert-butyldiethoxysilane, methyl-n-pentyldiethoxysilane,
n-hexylmethyldiethoxysilane, cyclohexylmethyldiethoxysilane,
methylphenyldiethoxysilane, benzylmethyldiethoxysilane and
phenethylmethyldiethoxysilane.
[0048] Specific examples of halogenosilane compounds represented by
formula (III) include:
trichlorosilanes such as methyltrichlorosilane, etyltrichlorosilane,
n-propyltrichlorosilane, iso-propyltrichlorosilane, n-butyltrichlorosilane,
tert-butyltrichlorosilane, n-pentyltrichlorosilane, n-hexyltrichlorosilane,
cyclohexyltrichlorosilane, phenyltrichlorosilane, benzyltrichlorosilane
and phenethyltrichlorosilane;
and dichlorosilanes such as dimethyldichlorosilane,
etylmethyldichlorosilane, methyl-n-propyldichlorosilane,
methyl-iso-propyldichlorosilane, n-butylmethyldichlorosilane,
methyl-tert-butyldichlorosilane, methyl-n-pentyldichlorosilane,
n-hexylmethyldichlorosilane, cyclohexylmethyldichlorosilane,
methylphenyldichlorosilane, benzylmethyldichlorosilane and
phenethylmethyldichlorosilane.
[0049] These silane compounds may be used alone or in combinations
of two or more.
[0050] The surface modification of the silica particles can generally be
accomplished by adding the alkoxysilane compound or halogenosilane
14
CA 02708830 2010-06-09
FP08-0470-00
compound to a dispersion of the silica particles and stirring the mixture.
In this case, it is preferably added in a range of 0.4-0.6 part by weight to
1 part by solid weight of the silica particles. Limited to not greater
than 0.6 part by weight, there will be no residual unreacted silane
compound added, and in an amount of at least 0.4 part by weight a
sufficient effect of organic group modification of the silica particles can
be achieved. The silica particles may be dispersed in water or
dispersed in an organic solvent.
[0051 ] To promote rapid modification reaction of the organic group
onto the silica particle surfaces under mild conditions, it is preferred to
use an acid catalyst such as an inorganic acid, organic acid or acidic ion
exchange resin. In this case it is particularly preferred to use
hydrochloric acid, nitric acid, acetic acid, citric acid, formic acid, oxalic
acid or the like. Common acids can react with apatite and impair its
properties, and therefore hydrochloric acid and acetic acid are especially
preferred for their high volatility to escape from the system. The
amount of acid catalyst added is preferably 0.05-0.1 part by weight to 1
part by solid weight of the silica particles.
[0052] The temperature for the modification reaction is preferably
0-50 C and more preferably 10-40 C, to prevent aggregation of the
silica particles. Also, the silica particles are preferably dispersed in an
organic solvent such as isopropyl alcohol, polyethyleneglycol
monomethyl ether acetate, toluene or xylene.
[0053] (Production method)
The method for producing the powder of the invention comprises a first
step of covering metal powder with apatite to form metal powder
CA 02708830 2010-06-09
FP08-0470-00
covered with an apatite layer (hereunder referred to as "apatite-covered
metal powder"), a second step of attaching silica powder to the metal
powder or apatite layer of the apatite-covered metal powder obtained in
the first step, and a third step of pre-curing the powder obtained in the
second step at not greater than 350 C to obtain powder comprising the
metal powder, the apatite layer covering the metal powder, and silica
particles attached to the metal powder or apatite layer.
[0054] (Phosphating treatment of metal powder)
The metal powder provided in the first step is preferably phosphated
metal powder, from the viewpoint of preventing oxidation of the metal
powder. In the method for producing powder according to the
invention, the phosphating treatment may be carried out before the first
step, or a commercially available metal powder that has been subjected
to phosphating treatment may be used. The phosphating treatment
may be carried out by a method known in the prior art.
[0055] (Formation of apatite layer)
The method of forming the apatite layer on the metal powder may be a
method in which an aqueous solution containing calcium ion (if
necessary with the ion of a cation-donating atom or group of atoms M
other than calcium) is reacted with an aqueous solution containing
phosphate ion, as explained above, to deposit apatite on the metal
powder surface. Specifically, the aqueous solution used as the calcium
source may be placed in a flask together with the metal powder and
stirred therewith while adding the aqueous solution as the phosphate
source in a dropwise manner. Alternatively, water and the metal
powder may be placed in a flask and stirred while adding the aqueous
16
CA 02708830 2010-06-09
FP08-0470-00
solution as the calcium source and the aqueous solution as the
phosphate source in a dropwise manner, either simultaneously or
successively. In the case of successive dropwise addition, they may be
added in either order.
[0056] The calcium source is not particularly restricted so long as it is a
water-soluble calcium compound, and as specific examples there may
be mentioned calcium salts of inorganic bases such as calcium
hydroxide, calcium salts of inorganic acids such as calcium nitrate,
calcium salts of organic acids such as calcium acetate, and calcium salts
of organic bases. As phosphate sources there may be mentioned
phosphoric acid, and phosphoric acid salts such as ammonium
dihydrogenphosphate and diammonium hydrogenphosphate.
[0057] In order to obtain a layer with an apatite structure, the reaction
mixture is preferably in the neutral range to basic range, with a pH of
preferably 7 or higher, more preferably 8 or higher, even more
preferably 9 or higher and especially preferably 10 or higher. Because
a layer of calcium phosphate other than apatite may be deposited in the
acidic range, the aqueous solution as the calcium source and the
aqueous solution as the phosphate source is preferably preadjusted to a
pH of 7 or higher with a base such as ammonia water.
[0058] The reaction temperature may be room temperature, but it is
preferably 50 C or higher, more preferably 70 C or higher and even
more preferably 90 C or higher to promote the reaction. If the solvent
is water, the upper limit for the temperature will be the reflux
temperature of the reaction mixture, i.e. near 100 C.
[0059] The reaction time will depend on the concentrations of the
17
CA 02708830 2010-06-09
FP08-0470-00
aqueous solution as the calcium source and the aqueous solution as the
phosphate source, with a shorter reaction time being sufficient for
higher concentrations and a longer reaction time preferred for lower
concentrations. The concentrations of the aqueous solution as the
calcium source and the aqueous solution as the phosphate source in the
production method of the invention are preferably each in the range of
0.003-0.5M, in which case the reaction time is preferably 1-10 hours.
[0060] (Attachment of silica powder)
Silica particles are attached to the apatite-covered metal powder
obtained in the manner described above. The method may involve
adding a dispersion of the silica particles to the apatite-covered metal
powder and shaking and stirring the mixture. If a commercially
available organosilica sol is used, it may be diluted to an appropriate
concentration. When the surfaces of the silica particles are
surface-modified with an organic group such as a silane compound in a
commercially available organosilica sol as described above, the reaction
mixture used for the surface modification may be used directly. The
silica particles used in this case may be attached to an apatite layer or
they may be attached to the exposed metal powder surface at defect
sections where the apatite layer covering is lacking.
[0061] The solvent used to disperse the silica particles is not
particularly restricted, and as specific examples there may be mentioned
alcohol-based solvents such as isopropyl alcohol, ketone-based solvents
such as methyl ethyl ketone, and aromatic-based solvents such as
toluene. Particularly preferred are aromatic solvents that allow the
colloidal solution state of the silica particles in the organosilica sol to be
18
CA 02708830 2010-06-09
FP08-0470-00
maintained more easily.
[0062] (Pre-curing)
The apatite-covered metal powder having silica particles attached to the
surface is then pre-cured at not greater than 350 C. This can cure the
apatite layer to form a strong heat-resistant coating. Without
pre-curing, the silica particles on the surface will become embedded in
the apatite layer when the starting powder is compression molded to
produce a powder magnetic core, tending to result in an insufficient
insulating property. The temperature for pre-curing is preferably
100-300 C.
[0063] The amount of silica particles used for the invention is
preferably 0.05-1.0 part by mass with respect to 100 parts by mass of
the metal powder used. An amount of at least 0.05 part by mass will
allow uniform coverage of the metal powder by the silica particles,
tending to produce an effect of improving the insulating property. An
amount of not greater than 1.0 part by mass will help prevent reduction
in the compact density when the powder is formed into a powder
magnetic core, as well as prevent reduction in the transverse strength of
the obtained powder magnetic core.
[0064] (Production of powder magnetic core)
The powder for a powder magnetic core according to the invention may
be formed into a powder magnetic core by compression molding a
mixed powder with admixture of a lubricant if necessary. The
lubricant may also be used by coating and drying a dispersion thereof
onto the die wall face. As lubricants there may be used metal soaps
such as zinc stearate, calcium stearate and lithium stearate, long-chain
19
CA 02708830 2010-06-09
FP08-0470-00
hydrocarbons such as waxes, and silicone oils. The molding pressure
is preferably 500-1500 MPa. The obtained powder magnetic core may
be annealed to lower the hysteresis loss. The annealing temperature in
this case is preferably selected within the range of 500-800 C. The
annealing is preferably carried out in an inert gas such as nitrogen or
argon.
[0065] The powder magnetic core produced by this method exhibits
high compact density and insulating properties. The mechanism by
which these properties are exhibited has not been fully elucidated, but
the present inventors conjecture that it is the following. Specifically,
when the apatite layer covers the metal powder, the high adsorptive
power of the apatite facilitates attachment of the silica particles to the
metal powder. It is believed that the attached silica particles
effectively fill the fissures in the apatite layer created during molding,
thereby allowing a high compact density (for example, 7.0 g/cm3 or
greater) and high heat resistance and insulation to be maintained. The
reason that a particle size below the submicron level is preferred for the
silica particles may be that smaller silica particles move more easily and
the silica particles therefore more effectively fill in the fissures of the
apatite layer.
[0066] The compact density of the powder magnetic core formed from
the powder of the invention is preferably 7.0 g/cm3 or greater and more
preferably 7.4 g/cm3 or greater. A density of at least 7.4 g/cm3 will
tend to improve the flux density of the powder magnetic core.
[0067] The electrical resistance value of the surface of the powder
magnetic core is preferably at least 30 fhn, more preferably at least 50
CA 02708830 2010-06-09
FP08-0470-00
12m and even more preferably at least 90 12m. An electrical
resistance of at least 30 12m will tend to produce an effect of reducing
the eddy current loss of the powder magnetic core.
Examples
[0068] The present invention will now be explained in greater detail
through the following examples, with the understanding that these
examples are in no way limitative on the invention.
[0069] [Example 1]
In a 300 mL 4-necked flask there were placed 75 mL (1.79 mmol, 0.024
M) of a calcium nitrate aqueous solution prepared to pH 11 or higher
with 25% ammonia water, and 30 g of iron powder (pure iron powder
300NH, by Kobe Steel, Ltd.). Also, 75 mL (1.07 mmol, 0.014 M) of
an ammonium dihydrogenphosphate aqueous solution prepared to pH
11 or higher with 25% ammonia water was placed in a dropping funnel
with a bypass line and the funnel was attached to the 4-necked flask.
The contents of the 4-necked flask were stirred at room temperature
(25 C) while adding the ammonium dihydrogenphosphate aqueous
solution in the dropping funnel dropwise over a period of 10 minutes.
[0070] Next, the 4-necked flask was reacted for 2 hours while stirring in
an oil bath at 90 C. The obtained slurry was suction filtered and the
filtered product was dried in an oven at 110 C to obtain a gray powder
(yield: 96 mass%). Upon analyzing the atomic abundance ratio near
the surface of the obtained powder by X-ray photoelectron spectroscopy
(XPS), the atomic abundance ratio was Fe: 4.58%, Ca: 15.7% and the
CaiP ratio (molar ratio) was 1.64, and the iron powder was confirmed to
be covered with hydroxyapatite.
21
CA 02708830 2010-06-09
FP08-0470-00
[00711 Next, 20 g of the obtained apatite-covered iron powder and 2 g
of an organosilica sol-toluene solution (solid concentration: 3.0 mass%)
were mixed and shaken for 10 minutes in a polypropylene bottle with a
maximum internal volume of 50 mL, and the contents were removed
into a stainless steel dish and pre-cured at 200 C for 30 minutes. The
pre-cured powder was passed through a 250 m sieve to remove the
giant aggregate particles, to obtain nanosilica-attached apatite-covered
iron powder.
[0072] Figs. 1 and 2 show SEM photographs of the cross-sections of
apatite-covered iron powder obtained in this manner, and Figs. 3 and 4
show SEM photographs of the cross-sections of nanosilica-attached
apatite-covered iron powder. It was confirmed that a hydroxyapatite
layer and nanosilica layer had been formed on the particle surfaces.
[0073] After packing 5.92 g of the obtained nanosilica-attached
apatite-covered iron powder into a die with an inner diameter of 14 mm,
it was molded into a cylindrical tablet with a molding pressure of 1000
MPa. The thickness of the obtained tablet was approximately 5 mm.
The surface of the molded tablet was polished, and the volume
resistivity (resistivity) was measured with a four-terminal resistivity
meter to be 296 pf2m. The density was 7.48 g/cm3. The tablet was
annealed under a nitrogen atmosphere, at 600 C for 1 hour, and after
repolishing the surface, the volume resistivity (resistivity) was measured
with a four-terminal resistivity meter to be 91 p Im. The density was
7.47 g/cm3.
[0074] [Comparative Example 1]
Hydroxyapatite-covered iron powder was prepared as follows, partly in
22
CA 02708830 2010-06-09
FP08-0470-00
the same manner as Example 1. Specifically, in a 300 mL 4-necked
flask there were placed 75 mL (1.79 mmol, 0.024 M) of a calcium
nitrate aqueous solution prepared to pH 11 or higher with 25% ammonia
water, and 30 g of iron powder (pure iron powder 300NH, by Kobe
Steel, Ltd.). Also, 75 mL (1.07 mmol, 0.014 M) of an ammonium
dihydrogenphosphate aqueous solution prepared to pH 11 or higher with
25% ammonia water was placed in a dropping funnel with a bypass line
and the funnel was attached to the 4-necked flask. The contents of the
4-necked flask were stirred at room temperature (25 C) while adding
the ammonium dihydrogenphosphate aqueous solution in the dropping
funnel dropwise over a period of 10 minutes.
[0075] Next, the 4-necked flask was reacted for 2 hours while stirring in
an oil bath at 90 C. The obtained slurry was then suction filtered and
the filtered product dried in an oven at 110 C to obtain a gray powder.
(Yield: 96 mass%). The obtained powder was passed through a 250
gm sieve to obtain apatite-covered metal powder. After packing 5.95 g
of the obtained apatite-covered metal powder into a die with an inner
diameter of 14 mm, it was molded into a cylindrical tablet with a
molding pressure of 1000 MPa. The thickness of the obtained tablet
was approximately 5 mm. The surface of the molded tablet was
polished, and the volume resistivity (resistivity) was measured with a
four-terminal resistivity meter to be 144 jL m. The density was 7.54
g/cm3. The polished tablet was annealed under a nitrogen atmosphere,
at 600 C for 1 hour, and after repolishing the surface, the volume
resistivity (resistivity) was measured with a four-terminal resistivity
meter to be 0.54 gDm. The density was 7.53 g/cm3.
23
CA 02708830 2010-06-09
FP08-0470-00
[0076] [Comparative Example 2]
Nanosilica was attached to iron powder by the method of attaching
nanosilica used in Example 1, but without providing an apatite layer.
Specifically, 20 g of iron powder (pure iron powder 3 OONH by Kobe
Steel, Ltd.) and 2 g of a nanosilica-toluene solution (solid concentration:
3.0 mass%) were mixed and shaken for 10 minutes in a polypropylene
bottle with a maximum internal volume of 50 mL, and pre-cured at
200 C for 30 minutes. The pre-cured powder was passed through a
250 pm sieve to remove the giant aggregate particles, to obtain.
nanosilica-attached metal powder. A 5.99 g portion of the obtained
powder was molded at 1000 MPa into a cylindrical tablet with a
diameter of 1.4 cm and a thickness of 5.145 mm. The surface of the
molded tablet was polished, and the volume resistivity (resistivity) was
measured with a four-terminal resistivity meter to be 79 tS m. The
density was 7.57 g/cm3. The polished tablet was annealed and fired
under a nitrogen atmosphere, at 600 C for one hour, and after
repolishing the surface, the volume resistivity (resistivity) was measured
with a four-terminal resistivity meter to be 20 m. The density was
7.57 g/cm3.
[0077] The results of measuring the density and resistivity of the
powder magnetic core obtained in this manner are shown in Table 1.
[0078] [Table 1]
24
CA 02708830 2010-06-09
FP08-0470-00
Hydroxy- Silica Density Resistivity
2
(g/cm) after Resistivity (gS2m)
Compact apatite particle 600 C (i 1m) after 600 C
covering attachment annealing annealing
Example 1 Occurred Occurred 7.47 296 91
Comp. Ex. 1 Occurred None 7.53 144 0.54
Comp. Ex. 2 None Occurred 7.57 79 20
[0079] Judging from Table 1, hydroxyapatite covering and silica
particle attachment are both essential for obtaining high resistivity.
Also, the compact density in Example 1 did not lower than the compact
densities in Comparative Example 1 and Comparative Example 2, even
though the powder in Example 1 was subjected to hydroxyapatite
covering and silica particle attachment. This is attributed to
destruction during compression molding, and embedding of the silica
particles in the pores at the fissures of the produced apatite layer.
[0080] Next, in order to estimate the adsorptive strength between the
apatite layer and silica particles, silica particles were attached to pure
iron powder having a different surface form, and apatite-covered iron
powder, and the degree of silica particles remaining on the surface was
compared by quantitative analysis. As the method, 3.0 g of each
powder was added to 5.0 g of organosilica sol solution (medium:
toluene) containing silica particles with a mean particle size of 20 nm
measured by dynamic light scattering using an HPPS by Malvern Co.
(solid concentration: 3.0 mass%), that had been placed in a glass screw
tube with a maximum volume of 10 mL. The screw tube was stirred
for 3 hours with a mix rotor set to a rotational speed of 105 rpm. The
stirred solution was suction filtered using No.5B (JIS P3801) filter
CA 02708830 2010-06-09
FP08-0470-00
paper for quantitative analysis, and the filtered product was rinsed with
toluene and vacuum dried to obtain each powder.
The obtained powder was subjected to elemental analysis by ICP-OES,
and the silica particles attached to the powder were quantified based on
the quantity of silicon atoms. The results are shown in Table 2.
[0081] [Table 2]
No. Powder Si adsorption (ppm by mass)
1 Pure iron powder (300NH) 160
2 Apatite-covered iron powder 360
[0082] According to the results shown in Table 2, the quantity of silicon
atoms quantified from the apatite-covered iron powder was
approximately twice that of the pure iron powder. Since the silicon
atoms derive only from the silica particles, this indicated an increased
degree of silica particle attachment, and stronger adsorptive power of
the silica particles with the apatite layer than with the pure iron powder
surface layer.
[0083] [Example 2]
After adding the iron powder to the calcium nitrate aqueous solution as
in Example 1, an additional step of stirring for 15 minutes in an oil bath
at 30 C was carried out.
[0084] Specifically, in a 300 mL 4-necked flask there were placed 75
mL (1.79 mmol, 0.024 M) of a calcium nitrate aqueous solution
prepared to pH 11 or higher with 25% ammonia water and 30 g of iron
powder (pure iron powder 300NH, by Kobe Steel, Ltd.), and the
mixture was stirred for 15 minutes in an oil bath at 30 C. Next, 75 mL
26
CA 02708830 2010-06-09
FP08-0470-00
(1.07 mmol, 0.014 M) of an ammonium dihydrogenphosphate aqueous
solution prepared to pH 11 or higher with 25% ammonia water was
placed in a dropping funnel with a bypass line and the funnel was
attached to the 4-necked flask. The contents of the 4-necked flask
were stirred in the oil bath at 30 C, while adding the ammonium
dihydrogenphosphate aqueous solution in the dropping funnel dropwise
over a period of 10 minutes.
[0085] The oil bath temperature was then raised from 30 C to 90 C
over a period of 10 minutes, and reaction was conducted at 90 C for 2
hours while stirring. The obtained slurry was suction filtered and the
filtered product was dried in an oven at 110 C to obtain a gray powder.
Upon analyzing the atomic abundance ratio near the surface of the
obtained powder by XPS, the atomic abundance ratio was Fe: 3.31%,
Ca: 17.1% and the Ca/P ratio (molar ratio) was 1.63, and the powder
was confirmed to be covered with hydroxyapatite.
[0086] Next, 20 g of the obtained apatite-covered powder and 2 g of an
organosilica sol-toluene solution (solid concentration: 3.0 mass%) were
mixed and shaken for 10 minutes in a polypropylene bottle with a
maximum internal volume of 50 mL, and then the mixture was dried for
5 minutes at a pressure of not greater than 1 MPa and the removed
powder was pre-cured at 200 C for 25 minutes. The pre-cured powder
was passed through a 250 m sieve. A 6 g portion of the sifted iron
powder was packed into a die with an inner diameter of 14 mm, and
molded into a cylindrical tablet at a molding pressure of 1000 MPaJcm2.
The thickness of the obtained tablet was approximately 5 mm. The
surface of the molded tablet was polished, and the volume resistivity
27
CA 02708830 2010-06-09
FP08-0470-00
(resistivity) was measured with a four-terminal resistivity meter to be
236 [tQm. The compact density was 7.50 g/cm2. The polished tablet
was fired under a nitrogen atmosphere, at 600 C for 1 hour, and after
polishing the surface, the volume resistivity (resistivity) was measured
with a four-terminal resistivity meter to be 75 m. The compact
density was 7.50 g/cm2.
[0087] [Example 3]
After adding an ammonium dihydrogenphosphate aqueous solution
dropwise to the contents of the 4-necked flask as in Example 2, an
additional step of stirring for 1.5 hours in an oil bath at 30 C was
carried out.
[0088] Specifically, in a 300 mL 4-necked flask there were placed 75
mL (1.79 mmol, 0.024 M) of a calcium nitrate aqueous solution
prepared to pH 11 or higher with 25% ammonia water and 30 g of iron
powder (pure iron powder 30ONH, by Kobe Steel, Ltd.), and the
mixture was stirred for 15 minutes in an oil bath at 30 C. Next, 75 mL
(1.07 mmol, 0.014 M) of an ammonium dihydrogenphosphate aqueous
solution prepared to pH 11 or higher with 25% ammonia water was
placed in a dropping funnel with a bypass line and the funnel was
attached to the 4-necked flask. The contents of the 4-necked flask
were stirred in the oil bath at 30 C, while adding the ammonium
dihydrogenphosphate aqueous solution in the dropping funnel dropwise
over a period of 10 minutes, after which the mixture was stirred for 1.5
hours while keeping the temperature of the oil bath at 30 C.
[0089] The oil bath temperature was then raised from 30 C to 90 C
over a period of 10 minutes, and reaction was conducted at 90 C for 2
28
CA 02708830 2010-06-09
FP08-0470-00
hours while stirring. The obtained slurry was suction filtered and the
filtered product was dried in an oven at 110 C to obtain a gray powder.
Upon analyzing the atomic abundance ratio near the surface of the
obtained powder by XPS, the atomic abundance ratio was Fe: 5.56%,
Ca: 14.85% and the Ca/P ratio (molar ratio) was 1.63, and the powder
was confirmed to be covered with hydroxyapatite.
[0090] Next, 20 g of the obtained apatite-covered powder and 2 g of an
organosilica sol-toluene solution (solid concentration: 3.0 mass%) were
mixed and shaken for 10 minutes in a polypropylene bottle with a
maximum internal volume of 50 mL, and then the contents were
removed into a stainless steel dish and dried for 5 minutes at a pressure
of not greater than 1 MPa, and the removed powder was pre-cured at
200 C for 25 minutes. The pre-cured iron powder was passed through
a 250 m sieve.
After packing 6 g of the obtained nanosilica-attached apatite-covered
iron powder into a die with an inner diameter of 14 mm, it was molded
into a cylindrical tablet with a molding pressure of 1000 MPa/cm2.
The thickness of the obtained tablet was approximately 5 mm. The
surface of the molded tablet was polished, and the volume resistivity
(resistivity) was measured with a four-terminal resistivity meter to be
111 [LQm. The compact density was 7.51 g/cm2. The polished tablet
was annealed under a nitrogen atmosphere, at 600 C for 1 hour, and
after repolishing the surface, the volume resistivity (resistivity) was
measured with a four-terminal resistivity meter to be 55 LQm. The
compact density was 7.51 g/cm2.
[0091 ] [Example 4]
29
CA 02708830 2010-06-09
FP08-0470-00
The 90 C reaction time in Example 3 was changed from 2 hours to 10
minutes.
[0092] Specifically, in a 300 mL 4-necked flask there were placed 75
mL (1.79 mmol, 0.024 M) of a calcium nitrate aqueous solution
prepared to pH 11 or higher with 25% ammonia water and 30 g of iron
powder (pure iron powder 300NH, by Kobe Steel, Ltd.), and the
mixture was stirred for 15 minutes in an oil bath at 30 C. Next, 75 mL
(1.07 mmol, 0.014 M) of an ammonium dihydrogenphosphate aqueous
solution prepared to pH 11 or higher with 25% ammonia water was
placed in a dropping funnel with a bypass line and the funnel was
attached to the 4-necked flask. The contents of the 4-necked flask
were stirred in the oil bath at 30 C, while adding the ammonium
dihydrogenphosphate aqueous solution in the dropping funnel dropwise
over a period of 10 minutes, after which the mixture was stirred for 1.5
hours while keeping the temperature of the oil bath at 30 C.
[0093] The oil bath temperature was then raised from 30 C to 90 C
over a period of 10 minutes, and reaction was conducted at 90 C for 10
minutes while stirring. The obtained slurry was then suction filtered
and dried in an oven at 110 C to obtain a gray iron powder. Upon
analyzing the atomic abundance ratio near the surface of the obtained
powder by XPS, the atomic abundance ratio was Fe: 6.79%, Ca: 12.77%
and the Ca/P ratio (molar ratio) was 1.44.
[0094] Next, 20 g of the obtained apatite-covered powder and 2 g of an
organosilica sol-toluene solution (solid concentration: 3.0 mass%) were
shaken for 10 minutes in a polypropylene bottle with a maximum
internal volume of 50 mL, and then the contents were removed into a
CA 02708830 2010-06-09
FP08-0470-00
stainless steel dish and dried for 5 minutes at a pressure of not greater
than 1 MPa, and the removed powder was pre-cured at 200 C for 25
minutes. The pre-cured iron powder was passed through a 250 m
sieve. After packing 6 g of the obtained nanosilica-attached
apatite-covered iron powder into a die with an inner diameter of 14 mm,
it was molded into a cylindrical tablet with a molding pressure of 1000
MPa/cm2.. The thickness of the obtained tablet was approximately 5
mm. The surface of the molded tablet was polished, and the volume
resistivity (resistivity) was measured with a four-terminal resistivity
meter to be 214 t! m. The compact density was 7.50 g/cm2. The
polished tablet was annealed under a nitrogen atmosphere, at 600 C for
1 hour, and after repolishing the surface, the volume resistivity
(resistivity) was measured with a four-terminal resistivity meter to be 53
pSZm. The compact density was 7.49 g/cm2.
[0095] [Example 5]
The reaction time at 90 C in Example 3 was changed from 2 hours to 5
hours.
[0096] Specifically, in a 300 mL 4-necked flask there were placed 75
mL (1.79 mmol, 0.024 M) of a calcium nitrate aqueous solution
prepared to pH 11 or higher with 25% ammonia water and 30 g of iron
powder (pure iron powder 300NH, by Kobe Steel, Ltd.), and the
mixture was stirred for 15 minutes in an oil bath at 30 C. Next, 75 mL
(1.07 mmol, 0.014 M) of an ammonium dihydrogenphosphate aqueous
solution prepared to pH 11 or higher with 25% ammonia water was
placed in a dropping funnel with a bypass line and the funnel was
attached to the 4-necked flask. The contents of the 4-necked flask
31
CA 02708830 2010-06-09
FP08-0470-00
were stirred in the oil bath at 30 C, while adding the ammonium
dihydrogenphosphate aqueous solution in the dropping funnel dropwise
over a period of 10 minutes, after which the mixture was stirred for 1.5
hours while keeping the temperature of the oil bath at 30 C.
[0097] The oil bath temperature was then raised from 30 C to 90 C
over a period of 10 minutes, and reaction was conducted at 90 C for 5
hours while stirring. The obtained slurry was suction filtered and dried
in an oven at 110 C to obtain a gray iron powder. Upon analyzing the
atomic abundance ratio near the surface of the obtained powder by XPS,
the atomic abundance ratio was Fe: 6.07%, Ca: 13.98% and the Ca/P
ratio was 1.67, and the powder was confirmed to be covered with
hydroxyapatite.
[0098] Next, 20 g of the obtained apatite-covered powder and 2 g of an
organosilica sol-toluene solution (solid concentration: 3.0 mass%) were
shaken for 10 minutes in a polypropylene bottle with a maximum
internal volume of 50 mL, and then the contents were removed into a
stainless steel dish and dried for 5 minutes at a pressure of not greater
than 1 MPa, and the removed powder was pre-cured at 200 C for 25
minutes. The pre-cured iron powder was passed through a 250 m
sieve. After packing 6 g of the obtained nanosilica-attached
apatite-covered iron powder into a die with an inner diameter of 14 mm,
it was molded into a cylindrical tablet with a molding pressure of 1000
MPa/cm2. The thickness of the obtained tablet was approximately 5
mm. The surface of the molded tablet was polished, and the volume
resistivity (resistivity) was measured with a four-terminal resistivity
meter to be 218 42m. The compact density was 7.47 g/cm2. The
32
CA 02708830 2010-06-09
FP08-0470-00
polished tablet was annealed under a nitrogen atmosphere, at 600 C for
1 hour, and after repolishing the surface, the volume resistivity
(resistivity) was measured with a four-terminal resistivity meter to be 93
[d2m. The compact density was 7.47 g/cm2.
[0099] [Example 6]
The reaction temperature of 90 C in Example 3 was changed to 30 C.
[0100] Specifically, in a 300 mL 4-necked flask there were placed 75
mL (1.79 mmol, 0.024 M) of a calcium nitrate aqueous solution
prepared to pH 11 or higher with 25% ammonia water and 30 g of iron
powder (pure iron powder 300NH, by Kobe Steel, Ltd.), and the
mixture was stirred for 15 minutes in an oil bath at 30 C. Next, 75 mL
(1.07 mmol, 0.014 M) of an ammonium dihydrogenphosphate aqueous
solution prepared to pH 11 or higher with 25% ammonia water was
placed in a dropping funnel with a bypass line and the funnel was
attached to the 4-necked flask. The contents of the 4-necked flask
were stirred in the oil bath at 30 C, while adding the ammonium
dihydrogenphosphate aqueous solution in the dropping funnel dropwise
over a period of 10 minutes, after which the mixture was stirred for 3.5
hours while keeping the temperature of the oil bath at 30 C.
[0101] The obtained slurry was then suction filtered and dried in an
oven at 110 C to obtain a gray iron powder. Upon analyzing the
atomic abundance ratio near the surface of the obtained powder by XPS,
the atomic abundance ratio was Fe: 7.84%, Ca: 11.67% and the Ca/P
ratio (molar ratio) was 1.65, and the iron powder was confirmed to be
covered with hydroxyapatite.
[0102] Next, 20 g of the obtained apatite-covered powder and 2 g of an
33
CA 02708830 2010-06-09
FP08-0470-00
organosilica sol-toluene solution (solid concentration: 3.0 mass%) were
shaken for 10 minutes in a polypropylene bottle with a maximum
internal volume of 50 mL, and then the contents were removed into a
stainless steel dish and dried for 5 minutes at a pressure of not greater
than 1 MPa, and the removed powder was pre-cured at 200 C for 25
minutes. The pre-cured iron powder was passed through a 250 pm
sieve. After packing 6 g of the obtained nanosilica-attached
apatite-covered iron powder into a die with an inner diameter of 14 mm,
it was molded into a cylindrical tablet with a molding pressure of 1000
MPa/cm2. The thickness of the obtained tablet was approximately 5
mm. The surface of the molded tablet was polished, and the volume
resistivity (resistivity) was measured with a four-terminal resistivity
meter to be 119 pQm. The compact density was 7.53 g/cm2.
The polished tablet was annealed under a nitrogen atmosphere, at 600 C
for 1 hour, and after repolishing the surface, the volume resistivity
(resistivity) was measured with a four-terminal resistivity meter to be 31
pDm. The density was 7.53 g/cm2.
[0103] [Example 7]
The reaction temperature of 90 C in Example 3 was changed to 50 C.
Specifically, in a 300 mL 4-necked flask there were placed 75 mL (1.79
mmol, 0.024 M) of a calcium nitrate aqueous solution prepared to pH 11
or higher with 25% ammonia water and 30 g of iron powder (pure iron
powder 30ONH, by Kobe Steel, Ltd.), and the mixture was stirred for 15
minutes in an oil bath at 30 C. Next, 75= mL (1.07 mmol, 0.014 M) of
an ammonium dihydrogenphosphate aqueous solution prepared to pH
11 or higher with 25% ammonia water was placed in a dropping funnel
34
CA 02708830 2010-06-09
FP08-0470-00
with a bypass line and the funnel was attached to the 4-necked flask.
The contents of the 4-necked flask were stirred in the oil bath at 30 C,
while adding the ammonium dihydrogenphosphate aqueous solution in
the dropping funnel dropwise over a period of 10 minutes, after which
the mixture was stirred for 1.5 hours while keeping the temperature of
the oil bath at 30 C.
[0104] The oil bath temperature was then raised from 30 C to 50 C
over a period of 5 minutes, and reaction was conducted at 90 C for 2
hours while stirring. The obtained slurry was suction filtered and dried
in an oven at 110 C to obtain a gray iron powder. Upon analyzing the
atomic abundance ratio near the surface of the obtained powder by XPS,
the atomic abundance ratio was Fe: 7.08%, Ca: 13.24% and the Ca/P
ratio (molar ratio) was 1.77, and the iron powder was confirmed to be
covered with hydroxyapatite.
[0105] Next, 20 g of the obtained apatite-covered powder and 2 g of an
organosilica sol-toluene solution (solid concentration: 3.0 mass%) were
shaken for 10 minutes in a polypropylene bottle with a maximum
internal volume of 50 mL, and then the contents were removed into a
stainless steel dish and dried for 5 minutes at a pressure of not greater
than 1 MPa, and the removed powder was pre-cured at 200 C for 25
minutes. The pre-cured iron powder was passed through a 250 im
sieve.
[0106] After packing 6 g of the obtained nanosilica-attached
apatite-covered iron powder into a die with an inner diameter of 14 mm,
it was molded into a cylindrical tablet with a molding pressure of 1000
MPa/cm2. The thickness of the obtained tablet was approximately 5
CA 02708830 2010-06-09
FP08-0470-00
mm. The surface of the molded tablet was polished, and the volume
resistivity (resistivity) was measured with a four-terminal resistivity
meter to be 176 R9 m. The compact density was 7.46 g/cm2. The
polished tablet was annealed under a nitrogen atmosphere, at 600 C for
1 hour, and after repolishing the surface, the volume resistivity
(resistivity) was measured with a four-terminal resistivity meter to be 53
Qm. The compact density was 7.47 g/cm2.
[0107] [Example 8]
The reaction temperature of 90 C in Example 3 was changed to 30 C,
and firing at 110 C was not carried out.
[0108] Specifically, in a 300 mL 4-necked flask there were placed 75
mL (1.79 mmol, 0.024 M) of a calcium nitrate aqueous solution
prepared to pH 11 or higher with 25% ammonia water and 30 g of iron
powder (pure iron powder 300NH, by Kobe Steel, Ltd.), and the
mixture was stirred for 15 minutes in an oil bath at 30 C. Next, 75 mL
(1.07 mmol, 0.014 M) of an ammonium dihydrogenphosphate aqueous
solution prepared to pH 11 or higher with 25% ammonia water was
placed in a dropping funnel with a bypass line and the funnel was
attached to the 4-necked flask. The contents of the 4-necked flask
were stirred in the oil bath at 30 C, while adding the ammonium
dihydrogenphosphate aqueous solution in the dropping funnel dropwise
over a period of 10 minutes, after which the mixture was stirred for 3.5
hours while keeping the temperature of the oil bath at 30 C.
[0109] The obtained slurry was then suction filtered, removed into a
stainless steel dish and dried for 5 minutes at a pressure of not greater
than 1 MPa to obtain a gray iron powder. Upon analyzing the atomic
36
CA 02708830 2010-06-09
FP08-0470-00
abundance ratio near the surface of the obtained powder by XPS, the
atomic abundance ratio was Fe: 5.53%, Ca: 13.63% and the Ca/P ratio
(molar ratio) was 1.52.
[0110] Next, 20 g of the obtained apatite-covered powder and 2 g of an
organosilica sol-toluene solution (solid concentration: 3.0 mass%) were
shaken for 10 minutes in a polypropylene bottle with a maximum
internal volume of 50 mL, and then the contents were removed into a
stainless steel dish and dried for 5 minutes at a pressure of not greater
than 1 MPa, and the removed powder was pre-cured at 200 C for 25
minutes. The pre-cured iron powder was passed through a 250 m
sieve.
After packing 6 g of the obtained nanosilica-attached apatite-covered
iron powder into a die with an inner diameter of 14 mm, it was molded
into a cylindrical tablet with a molding pressure of 1000 MPa/cm2.
The thickness of the obtained tablet was approximately 5 mm. The
surface of the molded tablet was polished, and the volume resistivity
(resistivity) was measured with a four-terminal resistivity meter to be
168 Ii m. The compact density was 7.50 g/cm2. The polished tablet
was annealed under a nitrogen atmosphere, at 600 C for 1 hour, and
after polishing the surface, the volume resistivity (resistivity) was
measured with a four-terminal resistivity meter to be 56 pQm. The
compact density was 7.49 g/cm2.
[0111] [Example 9]
The reaction temperature of 90 C in Example 3 was changed to 50 C,
and firing at 110 C was not carried out.
[0112] Specifically, in a 300 mL 4-necked flask there were placed 75
37
CA 02708830 2010-06-09
FP08-0470-00
mL (1.79 mmol, 0.024 M) of a calcium nitrate aqueous solution
prepared to pH 11 or higher with 25% ammonia water and 30 g of iron
powder (pure iron powder 300NH, by Kobe Steel, Ltd.), and the
mixture was stirred for 15 minutes in an oil bath at 30 C. Next, 75 mL
(1.07 mmol, 0.014 M) of an ammonium dihydrogenphosphate aqueous
solution prepared to pH 11 or higher with 25% ammonia water was
placed in a dropping funnel with a bypass line and the funnel was
attached to the 4-necked flask. The contents of the 4-necked flask
were stirred in the oil bath at 30 C, while adding the ammonium
dihydrogenphosphate aqueous solution in the dropping funnel dropwise
over a period of 10 minutes, after which the mixture was stirred for 1.5
hours while keeping the temperature of the oil bath at 30 C.
[0113] The oil bath temperature was then raised from 30 C to 50 C
over a period of 5 minutes, and the contents of the 4-necked flask were
reacted at 90 C for 2 hours while stirring. The obtained slurry was
then suction filtered, removed into a stainless steel dish and dried for 5
minutes at a pressure of not greater than 1 MPa to obtain a gray iron
powder. Upon analyzing the atomic abundance ratio near the surface
of the obtained powder by XPS, the atomic abundance ratio was Fe:
4.89%, Ca: 15.54% and the Ca/P ratio (molar ratio) was 1.77, and the
powder was confirmed to be covered with hydroxyapatite.
[0114] Next, 20 g of the obtained apatite-covered powder and 2 g of an
organosilica sol-toluene solution (solid concentration: 3.0 mass%) were
shaken for 10 minutes in a polypropylene bottle with a maximum
internal volume of 50 mL, and then the contents were removed into a
stainless steel dish and dried for 5 minutes at a pressure of not greater
38
CA 02708830 2010-06-09
FP08-0470-00
than 1 MPa, and the removed powder was pre-cured at 200 C for 25
minutes. The pre-cured iron powder was passed through a 250 m
sieve. After packing 6 g of the obtained nanosilica-attached
apatite-covered iron powder into a die with an inner diameter of 14 mm,
it was molded into a cylindrical tablet with a molding pressure of 1000
MPa/cm2. The thickness of the obtained tablet was approximately 5
mm. The surface of the molded tablet was polished, and the volume
resistivity (resistivity) was measured with a four-terminal resistivity
meter to be 137 pfIm. The compact density was 7.50 g/cm2. The
polished tablet was annealed under a nitrogen atmosphere, at 600 C for
1 hour, and after repolishing the surface, the volume resistivity
(resistivity) was measured with a four-terminal resistivity meter to be 44
S2m. The compact density was 7.50 g/cm2.
[0115] [Example 10]
The firing at 110 C in Example 3 was not carried out.
[0116] Specifically, in a 300 mL 4-necked flask there were placed 75
mL (1.79 mmol, 0.024 M) of a calcium nitrate aqueous solution
prepared to pH 11 or higher with 25% ammonia water and 30 g of iron
powder (pure iron powder 300NH, by Kobe Steel, Ltd.), and the
mixture was stirred for 15 minutes in an oil bath at 30 C. Next, 75 mL
(1.07 mmol, 0.014 M) of an ammonium dihydrogenphosphate aqueous
solution prepared to pH 11 or higher with 25% ammonia water was
placed in a dropping funnel with a bypass line and the funnel was
attached to the 4-necked flask. The contents of the 4-necked flask
were stirred in the oil bath at 30 C, while adding the ammonium
dihydrogenphosphate aqueous solution in the dropping funnel dropwise
39
CA 02708830 2010-06-09
FP08-0470-00
over a period of 10 minutes, after which the mixture was stirred for 1.5
hours while keeping the temperature of the oil bath at 30 C.
[0117] The oil bath temperature was then raised from 30 C to 90 C
over a period of 10 minutes, and reaction was conducted at 90 C for 2
hours while stirring. The obtained slurry was suction filtered and
vacuum dried at 0 MPa to obtain a gray iron powder. Upon analyzing
the obtained iron powder by XPS, the atomic abundance ratio was Fe:
3.85%, Ca: 16.63% and the Ca/P ratio (molar ratio) was 1.56.
[0118] Next, 20 g of the obtained apatite-covered powder and 2 g of an
organosilica sol-toluene solution (solid concentration: 3.0 mass%) were
shaken for 10 minutes in a polypropylene bottle with a maximum
internal volume of 50 mL, and then the contents were removed into a
stainless steel dish and dried for 5 minutes at a pressure of not greater
than 1 MPa, and the removed powder was pre-cured at 200 C for 25
minutes. The pre-cured iron powder was passed through a 250 m
sieve. After packing 6 g of the obtained nanosilica-attached
apatite-covered iron powder into a die with an inner diameter of 14 mm,
it was molded into a cylindrical tablet with a molding pressure of 1000
MPa/cm2. The thickness of the obtained tablet was approximately 5
mm. The surface of the molded tablet was polished, and the volume
resistivity (resistivity) was measured with a four-terminal resistivity
meter to be 137 pQm. The compact density was 7.50 g/cm2. The
polished tablet was annealed under a nitrogen atmosphere, at 600 C for
1 hour, and after repolishing the surface, the volume resistivity
(resistivity) was measured with a four-terminal resistivity meter to be 30
p,, m. The compact density was 7.50 g/cm2.
CA 02708830 2010-06-09
FP08-0470-00
[0119] [Example 11 ]
In Example 3, the calcium nitrate charging amount was changed from
1.79 mmol to 0.60 mmol and the ammonium dihydrogenphosphate
charging amount was changed from 1.07 mmol to 0.36 mmol.
[0120] Specifically, in a 300 mL 4-necked flask there were placed 75
mL (0.60 mmol, 0.008 M) of a calcium nitrate aqueous solution
prepared to pH 11 or higher with 25% ammonia water and 30 g of iron
powder (pure iron powder 300NH, by Kobe Steel, Ltd.), and the
mixture was stirred for 15 minutes in an oil bath at 30 C. Next, 75 mL
(0.36 mmol, 0.005 M) of an ammonium dihydrogenphosphate aqueous
solution prepared to pH 11 or higher with 25% ammonia water was
placed in a dropping funnel with a bypass line and the funnel was
attached to the 4-necked flask. The contents of the 4-necked flask
were stirred in the oil bath at 30 C, while adding the ammonium
dihydrogenphosphate aqueous solution in the dropping funnel dropwise
over a period of 10 minutes, after which the mixture was stirred for 1.5
hours while keeping the temperature of the oil bath at 30 C.
[0121] The oil bath temperature was then raised from 30 C to 90 C
over a period of 10 minutes, and reaction was conducted at 90 C for 2
hours while stirring. The obtained slurry was suction filtered and dried
in an oven at 110 C to obtain a gray iron powder. Upon analyzing the
atomic abundance ratio near the surface of the obtained powder by XPS,
the atomic abundance ratio was Fe: 7.29%, Ca: 13.14% and the Ca/P
ratio (molar ratio) was 1.52.
[0122] Next, 20 g of the obtained apatite-covered powder and 2 g of an
organosilica sol-toluene solution (solid concentration: 3.0 mass%) were
41
CA 02708830 2010-06-09
FP08-0470-00
shaken for 10 minutes in a polypropylene bottle with a maximum
internal volume of 50 mL, and then the contents were removed into a
stainless steel dish and dried for 5 minutes at a pressure of not greater
than 1 MPa, and the removed powder was pre-cured at 200 C for 25
minutes. The pre-cured iron powder was passed through a 250 m
sieve. After packing 6 g of the obtained nanosilica-attached
apatite-covered iron powder into a die with an inner diameter of 14 mm,
it was molded into a cylindrical tablet with a molding pressure of 1000
MPa/Cm2. The thickness of the obtained tablet was approximately 5
mm. The surface of the molded tablet was polished, and the volume
resistivity (resistivity) was measured with a four-terminal resistivity
meter to be 122 [ Qm. The compact density was 7.56 g/cm2. The
polished tablet was annealed under a nitrogen atmosphere, at 600 C for
1 hour, and after repolishing the surface, the volume resistivity
(resistivity) was measured with a four-terminal resistivity meter to be 30
d2m. The compact density was 7.56 g/cm2.
[0123] [Example 12]
In Example 3, the calcium nitrate charging amount was changed from
1.78 mmol to 2.98 mmol and the ammonium dihydrogenphosphate
charging amount was changed from 1.07 mmol to 1.78 mmol.
[0124] Specifically, in a 300 mL 4-necked flask there were placed 75
mL (2.98 mmol, 0.040 M) of a calcium nitrate aqueous solution
prepared to pH 11 or higher with 25% ammonia water and 30 g of iron
powder (pure iron powder 300NH, by Kobe Steel, Ltd.), and the
mixture was stirred for 15 minutes in an oil bath at 30 C. Next, 75 mL
(1.78 mmol, 0.024 M) of an ammonium dihydrogenphosphate aqueous
42
CA 02708830 2010-06-09
FP08-0470-00
solution prepared to pH 11 or higher with 25% ammonia water was
placed in a dropping funnel with a bypass line and the funnel was
attached to the 4-necked flask. The contents of the 4-necked flask
were stirred in the oil bath at 30 C, while adding the ammonium
dihydrogenphosphate aqueous solution in the dropping funnel dropwise
over a period of 10 minutes, after which the mixture was stirred for 1.5
hours while keeping the temperature of the oil bath at 30 C.
[0125] The oil bath temperature was then raised from 30 C to 90 C
over a period of 10 minutes, and reaction was conducted at 90 C for 2
hours while stirring. The obtained slurry was suction filtered and dried
in an oven at 110 C to obtain a gray iron powder. Upon analyzing the
atomic abundance ratio near the surface of the obtained powder by XPS,
the atomic abundance ratio was Fe: 2.76%, Ca: 17.59% and the Ca/P
ratio (molar ratio) was 1.67.
[0126] Next, 20 g of the obtained apatite-covered powder and 2 g of an
organosilica sol-toluene solution (solid concentration: 3.0 mass%) were
shaken for 10 minutes in a polypropylene bottle with a maximum
internal volume of 50 mL, and then the contents were removed into a
stainless steel dish and dried for 5 minutes at a pressure of not greater
than 1 MPa, and the removed powder was pre-cured at 200 C for 25
minutes. The pre-cured iron powder was passed through a 250 m
sieve. After packing 6 g of the obtained nanosilica-attached
apatite-covered iron powder into a die with an inner diameter of 14 mm,
it was molded into a cylindrical tablet with a molding pressure of 1000
MPa/cm2. The thickness of the obtained tablet was approximately 5
mm. The surface of the molded tablet was polished, and the volume
43
CA 02708830 2010-06-09
FP08-0470-00
resistivity (resistivity) was measured with a four-terminal resistivity
meter to be 213 gf 2m. The compact density was 7.44 g/cm2. The
polished tablet was annealed under a nitrogen atmosphere, at 600 C for
1 hour, and after repolishing the surface, the volume resistivity
(resistivity) was measured with a four-terminal resistivity meter to be 88
am. The compact density was 7.44 g/cm2.
[0127] [Example 13]
Hydroxyapatite-covered iron powder with a hydroxyapatite layer
composed of a single layer was prepared in the same manner as
Example 11, and the same treatment was also repeated to prepare
hydroxyapatite-covered iron powder with a hydroxyapatite layer
composed of a two-layer structure.
[0128] Specifically, in a 300 mL 4-necked flask there were placed 75
mL (0.60 mmol, 0.008 M) of a calcium nitrate aqueous solution
prepared to pH 11 or higher with 25% ammonia water and 30 g of iron
powder (pure iron powder 300NH, by Kobe Steel, Ltd.), and the
mixture was stirred for 15 minutes in an oil bath at 30 C. Next, 75 mL
(0.36 mmol, 0.005 M) of an ammonium dihydrogenphosphate aqueous
solution prepared to pH 11 or higher with 25% ammonia water was
placed in a dropping funnel with a bypass line and the funnel was
attached to the 4-necked flask. The contents of the 4-necked flask
were stirred in the oil bath at 30 C, while adding the ammonium
dihydrogenphosphate aqueous solution in the dropping funnel dropwise
thereto over a period of 10 minutes, after which the mixture was stirred
for 1.5 hours while keeping the temperature of the oil bath at 30 C.
[0129] The oil bath temperature was then raised from 30 C to 90 C
44
CA 02708830 2010-06-09
FP08-0470-00
over a period of 10 minutes, and the contents of the 4-necked flask were
reacted at 90 C for 2 hours while stirring. The obtained slurry was
suction filtered and dried in an oven at 110 C to obtain a gray iron
powder (yield: 96 mass%).
[0130] Next, 28.8 g of the obtained apatite single-layer-covered powder
and 72 mL (0.57 mmol, 0.008 M) of a calcium nitrate aqueous solution
prepared to pH 11 or higher with 25% ammonia water were placed in a
300 mL 4-necked flask, and the mixture was stirred for 15 minutes in an
oil bath at 30 C. Next, 72 mL (0.34 mmol, 0.005 M) of an ammonium
dihydrogenphosphate aqueous solution prepared to pH 11 or higher with
25% ammonia water was placed in a dropping funnel with a bypass line
and the funnel was attached to the 4-necked flask. The contents of the
4-necked flask were stirred in the oil bath at 30 C, while adding the
ammonium dihydrogenphosphate aqueous solution in the dropping
funnel dropwise thereto over a period of 10 minutes, after which the
mixture was stirred for 1.5 hours while keeping the temperature of the
oil bath at 30 C.
[0131] The oil bath temperature was then raised from 30 C to 90 C
over a period of 10 minutes, and reaction was conducted at 90 C for 2
hours while stirring. The obtained slurry was suction filtered and dried
in an oven at 110 C to obtain a gray iron powder. Upon analyzing the
atomic abundance ratio near the surface of the obtained powder by XPS,
the atomic abundance ratio was Fe: 7.05%, Ca: 13.84% and the Ca/P
ratio (molar ratio) was 1.59.
[0132] Next, 20 g of the obtained apatite two-layer-covered powder and
2 g of an organosilica sol-toluene solution (solid concentration: 3.0
CA 02708830 2010-06-09
FP08-0470-00
mass%) were shaken for 10 minutes in 'a polypropylene bottle with a
maximum internal volume of 50 mL, and then the contents were
removed into a stainless steel dish and dried for 5 minutes at a pressure
of not greater than 1 MPa, and the removed powder was pre-cured at
200 C for 25 minutes. The pre-cured iron powder was passed through
a 250 gm sieve. After packing 6 g of the obtained nanosilica-attached
apatite-covered iron powder into a die with an inner diameter of 14 mm,
it was molded into a cylindrical tablet with a molding pressure of 1000
MPa/cm2. The thickness of the obtained tablet was approximately 5
mm. The surface of the molded tablet was polished, and the volume
resistivity (resistivity) was measured with a four-terminal resistivity
meter to be 131 gf2m. The compact density was 7.53 g/cm2. The
polished tablet was fired under a nitrogen atmosphere, at 600 C for 1
hour, and after repolishing the surface, the volume resistivity
(resistivity) was measured with a four-terminal resistivity meter to be 59
LQm. The compact density was 7.53 g/cm2.
[0133] [Example 14]
Hydroxyapatite-covered iron powder with a hydroxyapatite layer
composed of two layers was prepared in the same manner as Example
13, and the same treatment was also repeated to prepare
hydroxyapatite-covered iron powder with a hydroxyapatite layer
composed of a three-layer structure.
[0134] Specifically, in a 300 mL 4-necked flask there were placed 75
mL (0.60 mmol, 0.008 M) of a calcium nitrate aqueous solution
prepared to pH 11 or higher with 25% ammonia water and 30 g of iron
powder (pure iron powder 3 0ONH, by Kobe Steel, Ltd.), and the
46
CA 02708830 2010-06-09
FP08-0470-00
mixture was stirred for 15 minutes in an oil bath at 30 C. Next, 75 mL
(0.36 mmol, 0.005 M) of an ammonium dihydrogenphosphate aqueous
solution prepared to pH 11 or higher with 25% ammonia water was
placed in a dropping funnel with a bypass line and the funnel was
attached to the 4-necked flask. The contents of the 4-necked flask
were stirred in the oil bath at 30 C, while adding the ammonium
dihydrogenphosphate aqueous solution in the dropping funnel dropwise
over a period of 10 minutes, after which the mixture was stirred for 1.5
hours while keeping the temperature of the oil bath at 30 C.
[0135] The oil bath temperature was then raised from 30 C to 90 C
over a period of 10 minutes, and reaction was conducted at 90 C for 2
hours while stirring. The obtained slurry was suction filtered and dried
in an oven at 110 C to obtain a gray iron powder.
[0136] Next, 29.5 g of the obtained apatite single-layer-covered iron
powder and 74 mL (0.59 mmol, 0.008 M) of a calcium nitrate aqueous
solution prepared to pH 11 or higher with 25% ammonia water were
placed in a 300 mL 4-necked flask, and the mixture was stirred for 15
minutes in an oil bath at 30 C. Next, 74 mL (0.35 mmol, 0.005 M) of
an ammonium dihydrogenphosphate aqueous solution prepared to pH
11 or higher with 25% ammonia water was placed in a dropping funnel
with a bypass line and the funnel was attached to the 4-necked flask.
The contents of the 4-necked flask were stirred in the oil bath at 30 C,
while adding the ammonium dihydrogenphosphate aqueous solution in
the dropping funnel dropwise over a period of 10 minutes, after which
the mixture was stirred for 1.5 hours while keeping the temperature of
the oil bath at 30 C.
47
CA 02708830 2010-06-09
FP08-0470-00
[0137] The oil bath temperature was then raised from 30 C to 90 C
over a period of 10 minutes, and the contents of the 4-necked flask were
reacted at 90 C for 2 hours while stirring. The obtained slurry was
suction filtered and dried in an oven at 110 C to obtain a gray iron
powder.
[0138] A 29.5 g portion of the obtained apatite two-layer-covered iron
powder and 74 mL (0.59 mmol, 0.008 M) of a calcium nitrate aqueous
solution prepared to pH 11 or higher with 25% ammonia water were
placed in a 300 mL 4-necked flask, and the mixture was stirred for 15
minutes in an oil bath at 30 C. Next, 74 mL (0.35 mmol, 0.005 M) of
an ammonium dihydrogenphosphate aqueous solution prepared to pH
11 or higher with 25% ammonia water was placed in a dropping funnel
with a bypass line and the funnel was attached to the 4-necked flask.
The contents of the 4-necked flask were stirred in the oil bath at 30 C,
while adding the ammonium dihydrogenphosphate aqueous solution in
the dropping funnel dropwise over a period of 10 minutes, after which
the mixture was stirred for 1.5 hours while keeping the temperature of
the oil bath at 30 C.
[0139] The oil bath temperature was then raised from 30 C to 90 C
over a period of 10 minutes, and reaction was conducted at 90 C for 2
hours while stirring. The obtained slurry was suction filtered and dried
in an oven at 110 C to obtain a gray iron powder. Upon analyzing the
atomic abundance ratio near the surface of the obtained powder by XPS,
the atomic abundance ratio was Fe: 10.33%, Ca: 10.95% and the Ca/P
ratio (molar ratio) was 1.69.
[0140] Next, 20 g of the obtained apatite three-layer-covered iron
48
CA 02708830 2010-06-09
FP08-0470-00
powder and 2 g of an organosilica sol-toluene solution (solid
concentration: 3.0 mass%) were shaken for 10 minutes in a
polypropylene bottle with a maximum internal volume of 50 mL, and
then the contents were removed into a stainless steel dish and dried for 5
minutes at a pressure of not greater than 1 MPa, and the removed
powder was pre-cured at 200 C for 25 minutes. The pre-cured iron
powder was passed through a 250 m sieve. After packing 6 g of the
obtained nanosilica-attached apatite three-layer-covered iron powder
into a die with an inner diameter of 14 mm, it was molded into a
cylindrical tablet with a molding pressure of 1000 MPa/cm2. The
thickness of the obtained tablet was approximately 5 mm. The surface
of the molded tablet was polished, and the volume resistivity
(resistivity) was measured with a four-terminal resistivity meter to be 95
Dm. The compact density was 7.494 g/cm2. The polished tablet
was annealed under a nitrogen atmosphere, at 600 C for 1 hour, and
after repolishing the surface, the volume resistivity (resistivity) was
measured with a four-terminal resistivity meter to be 31 iS m. The
compact density was 7.50 g/cm2.
[0141] [Example 15]
The amount of iron powder charged in Example 3 was changed to a
33-fold amount, the reactor volume and amount of solvent were
correspondingly changed 33-fold, and the time for stirring in the 30 C
oil bath after dropwise addition of the ammonium dihydrogenphosphate
aqueous solution to the 4-necked flask contents was changed from 1.5
hours to 2 hours.
[0142] Specifically, 250 mL (5.95 mmol, 0.024 M) of a calcium nitrate
49
CA 02708830 2010-06-09
FP08-0470-00
aqueous solution prepared to pH 11 or higher with 25% ammonia water
and 100 g of iron powder (pure iron powder 300NH, by Kobe Steel,
Ltd.) were placed in a 1000 mL 4-necked flask, and the mixture was
stirred for 15 minutes in an oil bath at 30 C. Next, 250 mL (3.57
mmol, 0.014 M) of an ammonium dihydrogenphosphate aqueous
solution prepared to pH 11 or higher with 25% ammonia water was
placed in a dropping funnel with a bypass line and the funnel was
attached to the 4-necked flask. The contents of the 4-necked flask
were stirred in the oil bath at 30 C, while adding the ammonium
dihydrogenphosphate aqueous solution in the dropping funnel dropwise
over a period of 30 minutes, after which the mixture was stirred for 2
hours while keeping the temperature of the oil bath at 30 C.
[0143] The oil bath temperature was then raised from 30 C to 90 C
over a period of 10 minutes, and reaction was conducted at 90 C for 2
hours while stirring. The obtained slurry was suction filtered and dried
in an oven at 110 C to obtain a gray iron powder. Upon analyzing the
obtained iron powder by XPS, the atomic abundance ratio was Fe:
3.85%, Ca: 15.30% and the Ca/P ratio was 1.76, and the iron powder
was confirmed to be covered with hydroxyapatite.
[0144] Also, 60 g of the obtained apatite-covered iron powder and 6 g
of an organosilica sol-toluene solution (solid concentration: 3.0 mass%)
were shaken for 10 minutes in a polypropylene bottle with a maximum
internal volume of 50 mL, and then the contents were removed into a
stainless steel dish and dried for 5 minutes at a pressure of not greater
than 1 MPa, and the removed powder was pre-cured at 200 C for 25
minutes. The pre-cured iron powder was passed through a 250 m
CA 02708830 2010-06-09
FP08-0470-00
sieve. After packing 6 g of the obtained nanosilica-attached
apatite-covered iron powder into a die with an inner diameter of 14 mm,
it was molded into a cylindrical tablet with a molding pressure of 1000
MPa/cm2. The thickness of the obtained tablet was approximately 5
mm. The surface of the molded tablet was polished, and the volume
resistivity (resistivity) was measured with a four-terminal resistivity
meter to be 193 tS m. The compact density was 7.51 g/cm2. The
polished tablet was annealed under a nitrogen atmosphere, at 600 C for
1 hour, and after repolishing the surface, the volume resistivity
(resistivity) was measured with a four-terminal resistivity meter to be 41
Dm. The compact density was 7.51 g/cm2.
[0145] The evaluation results for the hydroxyapatite-covered iron
powders and nanosilica-attached hydroxyapatite-covered iron powders
obtained in Examples 1-15 are summarized in Tables 3 to 5.
51
CA 02708830 2010-06-09
FP08-0470-00
[0146] [Table 3]
Apatite starting Synthesis conditions
material Nanosilica-attached
charging Apatite-covered iron powder synthesis step apatite-coated iron
Examples amount powder synthesis step
(with respect to
iron powder) Iron Synthesis Synthesis time
(mass%) powder time @30 C @T C Di Drying
mass (g) (min) (min) @110-C @200 C
Example 1 0.6 30 0 120(T=90) Conducted Conducted
Example 2 0.6 30 25 120(T=90) Conducted Conducted
Example 3 0.6 30 115 120(T=90) Conducted Conducted
Example 4 0.6 30 115 10(T=90) Conducted Conducted
Example 5 0.6 30 115 300(T=90) Conducted Conducted
Example 6 0.6 30 235 0 Conducted Conducted
Example 7 0.6 30 115 120(T=50) Conducted Conducted
Example 8 0.6 30 25 0 None Conducted
Example 9 0.6 30 115 120(T=50) None Conducted
Example 10 0.6 30 115 120(T=90) None Conducted
Example 11 0.2 30 115 120(T=90) Conducted Conducted
Example 12 1.0 30 115 120(T=90) Conducted Conducted
Example 13 0.6(x2) 30 115(x2) 120(T=90)(x2) Conducted Conducted
Example 14 0.6(x3) 30 115(x3) 120(T=90)(x3) Conducted Conducted
Example 15 0.6 100 165 120(T=90) Conducted Conducted
52
CA 02708830 2010-06-09
FPO8-0470-00
[0147] [Table 4]
XPS data (atomic ratios, %) Coverage factor
Examples Ols+Ca2p+P2p Ca/P
Cis Nis Ols Ca2p Fe2p P2p /(Ols+Ca2p+Fe2p+P2p) x 100
Example 1 16.7 0 53.5 15.7 4.6 9.6 94.5 1.67
Example 2 13.9 0 55.2 17.1 3.3 10.5 96.2 1.63
Example 3 14.1 0 56.4 14.9 5.6 9.1 93.5 1.63
Example 4 14.5 0 57.0 12.8 6.9 8.9 92.1 1.43
Example 5 14.0 0 57.6 14.0 6.1 8.4 92.9 1.67
Example 6 16.3 0 57.1 11.7 7.8 7.1 90.6 1.65
Example 7 15.1 0 57.2 13.2 7.1 7.5 91.7 1.77
Example 8 16.8 0 55.1 13.6 5.5 8.9 93.4 1.52
Example 9 12.3 0 58.5 15.5 4.9 8.8 94.4 1.77
Example 10 11.0 0 57.9 16.6 3.9 10.6 95.7 1.56
Example 11 15.7 0 55.2 13.1 7.3 8.7 91.4 1.52
Example 12 11.1 0 58.0 17.6 2.8 10.5 96.9 1.67
Example 13 13.6 0 56.8 13.8 7.1 8.7 91.8 1.59
Example 14 14.6 0 57.7 11.0 10.3 6.5 87.9 1.69
Example 15 16.3 0 55.9 15.3 3.9 8.7 95.4 1.76
[0148] [Table 5]
53
CA 02708830 2010-06-09
FP08-0470-00
Powder magnetic core properties
Examples Compact density Resistivity ( m)
(g/cm)
Example 1 7.47 91
Example 2 7.50 75
Example 3 7.51 55
Example 4 7.49 53
Example 5 7.47 93
Example 6 7.53 31
Example 7 7.47 53
Example 8 7.48 56
Example 9 7.50 44
Example 10 7.50 30
Example 11 7.56 30
Example 12 7.44 88
Example 13 7.53 59
Example 14 7.50 31
Example 15 7.51 41
[0149] Judging from Table 4, hydroxyapatite layers could be formed on
the metal powders with the similar coverage factor regardless of the
synthesis method. Also, judging from Tables 3 and 5, powder
magnetic cores of the nanosilica-attached hydroxyapatite-covered iron
powders obtained using a step of pre-curing at 100-300 C in the
production process exhibited high resistivity and compact density.
54
