Note: Descriptions are shown in the official language in which they were submitted.
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NEW COMPOSITE IRON- BASED POWDER COMPOSITION, POWDER
COMPONENT AND MANUFACTURING METHOD THEREOF
Field of the invention
The present invention concerns a soft magnetic composite powder material for
the
preparation of soft magnetic components as well as the soft magnetic
components
which are obtained by using this soft magnetic composite powder. Specifically
the
invention concerns such powders for the preparation of soft magnetic
components
materials working at high frequencies, the components suitable as inductors or
reactors for power electronics.
Background of the invention
Soft magnetic materials are used for various applications, such as core
materials in
inductors, stators and rotors for electrical machines, actuators, sensors and
transformer cores. Traditionally, soft magnetic cores, such as rotors and
stators in
electric machines, are made of stacked steel laminates. Soft magnetic
composites
may be based on soft magnetic particles, usually iron-based, with an
electrically
insulating coating on each particle. By compacting the insulated particles
optionally
together with lubricants and/or binders using the traditionally powder
metallurgy
process, soft magnetic components may be obtained. By using the powder
metallurgical technique it is possible to produce such components with a
higher
degree of freedom in the design, than by using the steel laminates as the
components can carry a three dimensional magnetic flux and as three
dimensional
shapes can be obtained by the compaction process.
The present invention relates to an iron-based soft magnetic composite powder,
the
core particles thereof being coated with a carefully selected coating
rendering the
material properties suitable for production of inductors through compaction of
the
powder followed by a heat treating process.
An inductor or reactor is a passive electrical component that can store energy
in form
of a magnetic field created by the electric current passing through said
component.
An inductors ability to store energy, inductance (L) is measured in henries
(H).
Typically an inductor is an insulated wire winded as a coil. An electric
current flowing
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through the turns of the coil will create a magnetic field around the coil,
the field
strength being proportional to the current and the turns/length unit of the
coil. A
varying current will create a varying magnetic field which will induce a
voltage
opposing the change of current that created it.
The electromagnetic force (EMF) which opposes the change in current is
measured
in volts(V) and is related to the inductance according to the formula;
v(t)=L di(t)/dt
(L is inductance, t is time, v(t) is the time-varying voltage across the
inductor and i(t)
is the time-varying current.)
That is; an inductor having an inductance of 1 henry produces an EMF of 1 volt
when
the current through the inductor changes with 1 ampere/second.
Ferromagnetic- or iron- core inductors use a magnetic core made of a
ferromagnetic
or ferrimagnetic material such as iron or ferrite to increase the inductance
of a coil by
several thousand by increasing the magnetic field, due to the higher
permeability of
the core material.
The magnetic permeability, , of a material is an indication of its ability to
carry a
magnetic flux or its ability to become magnetised. Permeability is defined as
the ratio
of the induced magnetic flux, denoted B and measured in newton/ampere*meter or
in
vorsecond/meter2, to the magnetising force or field intensity, denoted H and
measured in amperes/meter, A/m. Hence magnetic permeability has the dimension
volt*second/ampere*meter. Normally magnetic permeability is expressed as the
relative permeability 11r = 11/ 1_10, relative to the permeability of the free
space, 0 =
4*rl*1 0-7Vs/Am.
Permeability may also be expressed as the inductance per unit length,
henries/meter.
Magnetic permeability does not only depend on material carrying the magnetic
flux
but also on the applied electric field and the frequency thereof. In technical
systems it
is often referred to the maximum relative permeability which is maximum
relative
permeability measured during one cycle of the varying electrical field.
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An inductor core may be used in power electronic systems for filtering
unwanted
signals such as various harmonics. In order to function efficiently an
inductor core for
such application shall have a low maximum relative permeability which implies
that
the relative permeability will have a more linear characteristic relative to
the applied
.. electric field, i.e. stable incremental permeability, pp (as defined
according to
AB=pA*AH), and high saturation flux density. This enables the inductor to work
more
efficiently in a wider range of electric current, this may also be expressed
as that the
inductor has "good DC- bias". DC- bias may be expressed in terms of percentage
of
maximum incremental permeability at a specified applied electrical field, e.g.
at 4 000
.. A/m. Further low maximum relative permeability and stable incremental
permeability
combined with high saturation flux density enables the inductor to carry a
higher
electrical current which is inter alia beneficial when size is a limiting
factor, a smaller
inductor can thus be used.
.. One important parameter in order to improve the performance of soft
magnetic
component is to reduce its core loss characteristics. When a magnetic material
is
exposed to a varying field, energy losses occur due to both hysteresis losses
and
eddy current losses. The hysteresis loss is proportional to the frequency of
the
alternating magnetic fields, whereas the eddy current loss is proportional to
the
square of the frequency. Thus at high frequencies the eddy current loss
matters
mostly and it is especially required to reduce the eddy current loss and still
maintaining a low level of hysteresis losses. This implies that it is desired
to increase
the resistivity of magnetic cores.
In the search for ways of improving the resistivity different methods have
been used
and proposed. One method is based on providing electrically insulating
coatings or
films on the powder particles before these particles are subjected to
compaction.
Thus there are a large number of patent publications which teach different
types of
electrically insulating coatings. Examples of published patents concerning
inorganic
coatings are the U.S. Pat. No. 6,309,748, U.S. Pat. No. 6,348,265 and U.S. No.
6,562,458. Coatings of organic materials are known from e.g. the U.S. Pat. No.
5,595,609. Coatings comprising both inorganic and organic material are known
from
e.g. the U.S. Pat. Nos. 6,372,348 and 5,063,011 and the DE patent publication
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3,439,397, according to which publication the particles are surrounded by an
iron
phosphate layer and a thermoplastic material. European Patent EP1246209B1
describes a ferromagnetic metal based powder wherein the surface of the metal-
based powder is coated with a coating consisting of silicone resin and fine
particles of
.. clay minerals having layered structure such as bentonite or talc.
US6,756,118B2 reveals a soft magnetic powder metal composite comprising a
least
two oxides encapsulating powdered metal particles, the at least two oxides
forming at
least one common phase.
The patent application JP2002170707A describes an alloyed iron particle coated
with
a phosphorous containing layer, the alloying elements may be silicon, nickel
or
aluminium. In a second step the coated powder is mixed with a water solution
of
sodium silicate followed by drying. Dust cores are produced by moulding the
powder
and heat treat the moulded part in a temperature of 500-1000 C.
Sodium silicate is mentioned in JP51-089198 as a binding agent for iron powder
particles when producing dust cores by moulding of iron powder followed by
heat
treating of the moulded part.
In order to obtain high performance soft magnetic composite components it must
also
be possible to subject the electrically insulated powder to compression
moulding at
high pressures as it is often desired to obtain parts having high density.
High
densities normally improve the magnetic properties. Specifically high
densities are
needed in order to keep the hysteresis losses at a low level and to obtain
high
saturation flux density. Additionally, the electrical insulation must
withstand the
compaction pressures needed without being damaged when the compacted part is
ejected from the die. This in turn means that the ejection forces must not be
too high.
Furthermore, in order to reduce the hysteresis losses, stress releasing heat
treatment
of the compacted part is required. In order to obtain an effective stress
release the
heat treatment should preferably be performed at a temperature above 300 C and
below a temperature where the insulating coating will be damaged, in an
atmosphere
of for example nitrogen, argon or air, or in vacuum.
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The present invention has been done in view of the need for powder cores which
are
primarily intended for use at higher frequencies, i.e. frequencies above 2 kHz
and
particularly between 5 and 100 kHz, where higher resistivity and lower core
losses
are essential. Preferably the saturation flux density shall be high enough for
core
downsizing. Additionally it should be possible to produce the cores without
having to
compact the metal powder using die wall lubrication and/or elevated
temperatures.
Preferably these steps should be eliminated.
In contrast to many used and proposed methods, in which low core losses are
desired, it is an especial advantage of the present invention that it is not
necessary to
use any organic binding agent in the powder composition, which powder
composition
is later compacted in the compaction step. Heat treatment of the green compact
can
therefore be performed at higher temperature without the risk that any organic
binding agent decomposes; a higher heat treatment temperature will also
improve the
.. flux density and decrease core losses. The absence of organic material in
the final,
heat treated core also allows the core to be used in environments with
elevated
temperatures without risking decreased strength due to softening and
decomposition
of an organic binder, and improved temperature stability is thus achieved.
Objects of the invention
An object of the invention is to provide a new iron- based composite powder
comprising a core of an iron based powder the surface thereof coated with a
new
composite electrical insulated coating. The new iron based composite powder
being
especially suited to be used for production of inductor cores for power
electronics.
Another object of the invention is to provide a method for producing such
inductor
cores.
Still another object of the invention is to provide an inductor core having
"good" DC-
bias, low core losses and high saturation flux density.
The present invention provides an iron powder mixture and process methods for
treating said mixture which can be used to prepare e.g. inductors having high
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saturation flux density, lower core loss, and the manufacturing process
thereof can be
simplified.
Summary of the invention
At least one of these objects is accomplished by:
- A coated iron-based powder composition, the coating comprising a first
phosphorous containing layer and a second layer containing a combination of
alkaline silicate and particles of clays containing defined phyllosilicates,
wherein the
iron-based powder composition comprises a mixture of iron-powder and sendust.
According to an embodiment the coating is constituted of the above two layers
alone.
- A method for producing a inductor core comprising the steps of:
a) providing a coated iron powder composition as above,
b) compacting the coated iron and sendust powder mixture, optionally mixed
with a
lubricant, in a uniaxial press movement in a die at a compaction pressure
between
400 and 1200 MPa
c) ejecting the compacted component from the die.
d) heat treating the ejected component at a temperature up to 800 C.
- A component, such as an inductor core, produced according to above.
There is further provided a composite iron-based powder composition comprising
core particles, wherein the core particles are a mixture of (a) iron alloy
particles
consisting essentially of 7% to 13% by weight silicon, 4% to 7% by weight
aluminium,
the balance being iron, and (b) atomized iron particles, wherein said core
particles
are coated with a first phosphorous containing layer, and wherein the atomized
iron
particles have a second layer comprising: (i) an alkaline silicate combined
with a clay
mineral containing a phyllosilicate, the combined silicon-oxygen tetrahedral
layer and
hydroxide octahedral layers thereof being electrical neutral, or (ii) a metal
organic
layer.
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Detailed description of the invention
The composition may be a composite iron-based powder composition comprising
core particles coated with a layer containing an alkaline silicate combined
with a clay
mineral containing a phyllosilicate, wherein the combined silicon- oxygen
tetrahedral
layer and hydroxide octahedral layers thereof preferably are electrically
neutral,
wherein the core particles is a mixture of
(a) iron alloy particles consisting essentially of 7% to 13% by weight
silicon, 4% to 7%
by weight aluminium and the balance being iron, and
(b) atomized iron particles.
.. The iron alloy particles may also be refered to as "sendust" or "sendust
particles".
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In one embodiment, the sendust particles are coated with a phosphorous
containing
layer prior to coating with said alkaline silicate combined with a clay
mineral
containing a phyllosilicate. For brevity, this coating may be termed "alkaline
silicate-
coating", or "clay-coating". This coating may be e.g. kaolin- or talc-based.
In another embodiment, both the iron alloy particles and the atomized
particles are
coated with a phosphorous containing layer prior to coating with said alkaline
silicate
coating.
Throughout the text, the terms "layer" and "coating" may be used
interchangeably.
The iron particles may be in the form of a pure iron powder having low content
of
contaminants such as carbon or oxygen. The iron content is preferably above
99.0%
.. by weight, however it may also be possible to utilise iron- powder alloyed
with for
example silicon. For a pure iron powder, or for an iron- based powder alloyed
with
intentionally added alloying elements, the powders contain besides iron and
possible
present alloying elements, trace elements resulting from inevitable impurities
caused
by the method of production. Trace elements are present in such a small amount
that
.. they do not (or only marginally) influence the properties of the material.
Examples of
trace elements may be carbon up to 0.1 %, oxygen up to 0.3%, sulphur and
phosphorous up to 0.3 % each and manganese up to 0.3%.
The particle size of the iron- based powder is determined by the intended use,
i.e.
which frequency the component is suited for. The mean particle size of the
iron-
based powder, which is also the mean size of the coated powder as the coating
is
very thin, may be between 20 to 300 pm. Examples of mean particle sizes for
suitable iron-based powders are e.g. 20-80 pm, a so called 200 mesh powder, 70-
130 urn, a 100 mesh powder, or 130-250 pm, a 40 mesh powder.
The iron alloy particles may consist essentially of 7% to 13% by weight
silicon, 4% to
7% by weight aluminium, the balance being iron, the remainder being
impurities.
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Such a powder is known in the field as sendust. Typically, sendust essentially
contains 84-86 A.Fe, 9-10%Si and 5-6%Al, on a weight basis.
The iron particles may be water atomized or gas atomized. Methods for
atomizing
iron are known in the literature.
The phosphorous containing coating which is normally applied to the bare iron-
based
powder may be applied according to the methods described in US patent
6,348,265.
This means that the iron or iron- based powder is mixed with phosphoric acid
dissolved in a solvent such as acetone followed by drying in order to obtain a
thin
phosphorous and oxygen containing coating on the powder. The amount of added
solution depends inter alia on the particle size of the powder; however the
amount
shall be sufficient in order to obtain a coating having a thickness between 20
and 300
nm.
Alternatively, it would be possible to add a thin phosphorous containing
coating by
mixing an iron-based powder with a solution of ammonium phosphate dissolved in
water or using other combinations of phosphorous containing substances and
other
solvents. The resulting phosphorous containing coating cause an increase in
the
phosphorous content of the iron-based powder of between 0.01 to 0.15%.
The alkaline silicate coating is applied to the phosphorous coated iron-based
powder
by mixing the powder with particles of a clay or a mixture of clays containing
defined
phyllosilicate and a water soluble alkaline silicate, commonly known as water
glass,
followed by a drying step at a temperature between 20-250 C or in vacuum.
Phyllosilicates constitutes the type of silicates where the
silicontetrahedrons are
connected with each other in the form of layers having the formula (Si2052),.
These
layers are combined with at least one octahedral hydroxide layer forming a
combined
structure. The octahedral layers may for example contain either aluminium or
magnesium hydroxides or a combination thereof. Silicon in the
silicontetrahedral
layer may be partly replaced by other atoms. These combined layered structures
may
be electroneutral or electrically charged, depending on which atoms are
present.
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It has been noticed that the type of phyllosilicate is of vital importance in
order to fulfill
the objects of the present invention. Thus, the phyllosilicate shall be of the
type
having uncharged or electroneutral layers of the combined silicontetrahedral-
and
hydroxide octahedral - layer. Examples of such phyllosilicates are kaolinite
present in
the clay kaolin, pyrophyllite present in phyllite, or the magnesium containing
mineral talc.
The mean particle size of the clays containing defined phyllosilicates shall
be below
15, preferably below 10, preferably below 5 pm, even more preferable below 3
pm.
The amount of clay containing defined phyllosilicates to be mixed with the
coated
iron-based powder shall be between 0.2-5%, preferably between 0.5-4%, by
weight
of the coated composite iron- based powder.
The amount of alkaline silicate calculated as solid alkaline silicate to be
mixed with
the coated iron-based powder shall be between 0.1-0.9% by weight of the coated
composite iron- based powder, preferably between 0.2-0.8% by weight of the
iron-
based powder. It has been shown that various types of water soluble alkaline
silicates can be used, thus sodium, potassium and lithium silicate can be
used.
Commonly an alkaline water soluble silicate is characterised by its ratio,
i.e. amount
of SiO2 divided by amount of Na2O, K20 or Li2O as applicable, either as molar
or
weight ratio. The molar ratio of the water soluble alkaline silicate shall be
1.5-4, both
end points included. If the molar ratio is below 1.5 the solution becomes too
alkaline,
.. if the molar ratio is above 4 S102 will precipitate.
It may be possible to omit the second kaolin ¨ sodium silicate coating on the
Sendust
particles and still achieve excellent magnetic properties. However, in order
to further
enhance the magnetic properties the second coating layer should cover both the
Sendust and the iron powder.
In an alternative embodiment, the alkaline silicate (or clay) coating may be
replaced
by a metal-organic coating (second coating)
In this case, at least one metal-organic layer is located outside the first
phosphorous-
based layer. The metal-organic layer is of a metal-organic compound having the
general formula:
Ri[(Ri)x(R2)y(MOn-1)11
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wherein:
M is a central atom selected from Si, Ti, Al, or Zr;
0 is oxygen;
Ri is a hydrolysable group;
R2 is an organic moiety and wherein at least one R2 contains at least one
amino
group;
wherein n is the number of repeatable units being an integer between 1 and 20;
wherein x is an integer between 0 and 1; wherein y is an integer between 1 and
2 (x
may thus be 0 or 1 and y may be 1 or 2).
The metal-organic compound may be selected from the following groups: surface
modifiers, coupling agents, or cross-linking agents.
R1 in the metal-organic compound may be an alkoxy-group having less than 4,
preferably less than 3 carbon atoms.
R2 is an organic moiety, which means that the R2-group contains an organic
part or
portion. R2 may include 1-6, preferably 1-3 carbon atoms. R2 may further
include one
or more hetero atoms selected from the group consisting of N, 0, S and P. The
R2
group may be linear, branched, cyclic, or aromatic.
R2 may include one or more of the following functional groups: amine, diamine,
amide, imide, epoxy, hydroxyl, ethylene oxide, ureido, urethane, isocyanato,
acrylate,
glyceryl acrylate, benzyl-amino, vinyl-benzyl-amino. The R2 group may alter
between
any of the mentioned functional R2-groups and a hydrophobic alkyl group with
repeatable units.
The metal-organic compound may be selected from derivates, intermediates or
oligomers of silanes, siloxanes and silsesquioxanes or the corresponding
titanates,
aluminates or zirconates.
According to one embodiment at least one metal-organic compound in one metal-
organic layer is a monomer (n=1).
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According to another embodiment at least one metal-organic compound in one
metal-
organic layer is an oligomer (n=2-20).
According to another embodiment the metal-organic layer located outside the
first
layer is of a monomer of the metal-organic compound and wherein the outermost
metal-organic layer is of an oligomer of the metal-organic compound. The
chemical
functionality of the monomer and the oligomer is necessary not same. The ratio
by
weight of the layer of the monomer of the metal-organic compound and the layer
of
the oligomer of the metal-organic compound may be between 1:0 and 1:2,
preferably
.. between 2:1-1:2.
If the metal-organic compound is a monomer it may be selected from the group
of
trialkoxy and dialkoxy silanes, titanates, aluminates, or zirconates. The
monomer of
the metal-organic compound may thus be selected from 3-aminopropyl-
trimethoxysilane, 3-aminopropyl-triethoxysilane, 3-aminopropyl-methyl-
diethoxysilane, N-aminoethy1-3-aminopropyl-trimethoxysilane, N-aminoethy1-3-
aminopropyl-methyl-dimethoxysilane, 1,7-bis(triethoxysilyI)-4-azaheptan,
triamino-
functional propyl-trimethoxysilane, 3-ureidopropyl-triethoxysilane, 3-
isocyanatopropyl-
triethoxysilane, tris(3-trimethoxysilylpropy1)-isocyanurate, 0-(propargyloxy)-
N-
(triethoxysilylpropyI)-urethane, 1-aminomethyl-triethoxysilane, 1-aminoethyl-
methyl-
dimethoxysilane, or mixtures thereof.
An oligomer of the metal-organic compound may be selected from alkoxy-
terminated
alkyl-alkoxy-oligomers of silanes, titantes, aluminates, or zirconates. The
oligomer of
the metal-organic compound may thus be selected from methoxy, ethoxy or
acetoxy-
terminated amino-silsesquioxanes, amino-siloxanes, oligomeric 3-aminopropyl-
methoxy-silane,
3-aminopropyl/propyl-alkoxy-silanes, N-aminoethy1-3-aminopropyl-alkoxy-
silanes, or
N-aminoethy1-3-aminopropyl/methyl-alkoxy-silanes or mixtures thereof.
The total amount of metal-organic compound may be 0.05-0.6 %, preferably 0.05-
0.5
%, more preferably 0.1-0.4%, and most preferably 0.2-0.3% by weight of the
composition. These kinds of metal-organic compounds may be commercially
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obtained from companies, such as Evonik Ind., Wacker Chemie AG, Dow Corning,
etc.
The metal-organic compound has an alkaline character and may also include
coupling properties i.e. a so called coupling agent which will couple to the
first
inorganic layer of the iron-based powder. The substance should neutralise the
excess acids and acidic bi-products from the first layer. If coupling agents
from the
group of aminoalkyl alkoxy-silanes, -titanates, -aluminates, or -zirconates
are used,
the substance will hydrolyse and partly polymerise (some of the alkoxy groups
will be
hydrolysed with the formation of alcohol accordingly). The coupling or cross-
linking
properties of the metal-organic compounds is also believed to couple to the
metallic
or semi-metallic particulate compound which may improve the mechanical
stability of
the compacted composite component.
Metal or semi-metallic particulate compound
The coated soft magnetic iron-based powder may also contain at least one
metallic
or semi-metallic particulate compound. The metallic or semi-metallic
particulate
compound should be soft, having Mohs hardness less than 3.5, and constitute
fine
particles or colloids. The compound may preferably have an average particle
size
below 5 pm, preferably below 3 pm, and most preferably below 1 pm. The
metallic or
semi-metallic particulate compound may have a purity of more than 95%,
preferably
more than 98%, and most preferably more than 99% by weight. The Mohs hardness
of the metallic or semi-metallic particulate compound is preferably 3 or less,
more
preferably 2.5 or less. SiO2, A1203, MgO, and TiO2 are abrasive and have a
Mohs
hardness well above 3.5 and is not within the scope of the invention. Abrasive
compounds, even as nano-sized particles, cause irreversible damages to the
electrically insulating coating giving poor ejection and worse magnetic and/or
mechanical properties of the heat-treated component.
The metallic or semi-metallic particulate compound may be at least one
selected from
the group: lead, indium, bismuth, selenium, boron, molybdenum, manganese,
tungsten, vanadium, antimony, tin, zinc, cerium.
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The metallic or semi-metallic particulate compound may be an oxide, hydroxide,
hydrate, carbonate, phosphate, fluorite, sulphide, sulphate, sulphite,
oxychloride, or a
mixture thereof.
According to a preferred embodiment the metallic or semi-metallic particulate
compound is bismuth, or more preferably bismuth (III) oxide. The metallic or
semi-
metallic particulate compound may be mixed with a second compound selected
from
alkaline or alkaline earth metals, wherein the compound may be carbonates,
preferably carbonates of calcium, strontium, barium, lithium, potassium or
sodium.
The metallic or semi-metallic particulate compound or compound mixture may be
present in an amount of 0.05-0.5%, preferably 0.1-0.4%, and most preferably
0.15-
0.3% by weight of the composition.
The metallic or semi-metallic particulate compound is adhered to at least one
metal-
organic layer. In one embodiment of the invention the metallic or semi-
metallic
particulate compound is adhered to the outermost metal-organic layer.
The metal-organic layer may be formed by mixing the powder by stirring with
different
amounts of first a basic aminoalkyl-alkoxy silane (DynasylaneAmeo) and
thereafter
with an oligomer of an aminoalkyl/alkyl-alkoxy silane (Dynasylane1146), e.g.
by
using a 1:1 relation, both produced by Evonik Inc. The composition may be
further
mixed with different amounts of a fine powder of bismuth(III) oxide (>99wtcYo;
D50 -0.3
This good saturation flux density achieved by the material according to the
invention
makes it possible to downsize inductor components and still maintain good
magnetic
properties.
Compaction and Heat Treatment
Before compaction the coated iron-based composition may be mixed with a
suitable
organic lubricant such as a wax, an oligomer or a polymer, a fatty acid based
derivate
or combinations thereof. Examples of suitable lubricants are EBS, i.e.
ethylene
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bisstearamide, Kenolube available from Hogands AB, Sweden, metal stearates
such as zinc stearate or fatty acids or other derivates thereof. The lubricant
may be
added in an amount of 0.05-1.5% of the total mixture, preferably between 0.1-
1.2%
by weight.
Compaction may be performed at a compaction pressure of 400-1200 MPa at
ambient or elevated temperature.
After compaction, the compacted components are subjected to heat treatment at
a
temperature up to 800 C, preferably between 600-750 C. Examples of suitable
atmospheres at heat treatment are inert atmosphere such as nitrogen or argon
or
oxidizing atmospheres such as air.
The powder magnetic core of the present invention is obtained by pressure
forming
an iron-based magnetic powder covered with a new electrically insulating
coating.
The core may be characterized by low total losses in the frequency range 2-100
kHz,
normally 5-100 kHz, of about less than 12W/kg at a frequency of 20kHz and
induction of 0.05T. Further a resisitivity, p, more than 1000, preferably more
than
2000 and most preferably more than 3000 pc2m, and a saturation magnetic flux
density Bs above 1.1, preferably above 1.2 and most preferably above
1.3T.Further,
the coercivity shall be below 210A/m, preferably below 200A/m, most preferably
below 190A/m and DC- bias not less than 50% at 4000A/m.
Examples
The following examples are intended to illustrate particular embodiments and
should
not be construed as a limitation of the scope of the invention.
Example 1
Two types of iron powder have been used as core particles; a pure water
atomized
iron powder having a content of iron above 99.5% by weight and a pure sponge
iron
having a content of iron above 99.5% by weight. The mean particle size of both
types
of powder was about 45pm. The core particles have been mixed with grinded
Sendust (typically 85c/oFe, 9,5 /cSi and 5,5%Al) and the powder mix was then
treated
with a phosphorous containing solution according to W02008/069749¨Briefly, the
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coating solution was prepared by dissolving 30 ml of 85 A weight of
phosphoric acid
in 1 000 ml of acetone, and 40 ml ¨ 60 ml of acetone solution was used per
1000
gram of powder. After mixing the phosphoric acid solution with the metal
powder, the
mixture is allowed to dry.
The obtained dry phosphorous coated iron ¨ sendust mix powder was further
blended with kaolin and sodium silicate according to the following table 1.
After drying
at 120 C the powder was mixed with 0.6% Kenolube and compacted at 800MPa
into rings with an inner diameter of 45mm, an outer diameter of 55mm and a
height of
5mm. The compacted components were thereafter subjected to a heat treatment
process at 700 C in a nitrogen atmosphere for 0.5 hours.
The specific resistivities of the obtained samples were measured by a four
point
measurement. For maximum permeability, pmõ, and coercivity measurements the
rings were "wired" with 100 turns for the primary circuit and 100 turns for
the
secondary circuit enabling measurements of magnetic properties with the aid of
a
hysteresisgraph, Brockhaus MPG 100. For core loss the rings were "wired" with
30
turns for the primary circuit and 30 turns for the secondary circuit with the
aid of
Walker Scientific Inc. AMH-401POD instrument.
When measuring incremental permeability, the rings were wounded with a third
winding supplying a DC- bias current of 4 000A/m. DC-bias was expressed as
percentage of maximum incremental permeability.
Unless otherwise stated all tests in the following examples were performed
accordingly.
In order to show the impact of using sponge or atomized iron together with
grinded
sendust, the impact of a phosphorous coating layer and the impact of the
presence of
kaolin and sodium silicate in the second coating on the properties of the
compacted
and heat treated component, samples A-H, were prepared according to table 1
which
also shows results from testing of the components. In table 1, the invention
has also
been compared with the use of sponge iron without a first phosphorous coating
layer
(sample D) according to US4177089.
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Table 1
Additives on the iron - Sendust mix Component properties
Sample
Phosporous Wt-% Wt-% Resistivit pmax Coercivity Core
loss at .. Bs
coating Kaolin Sodium [-] [A/m] 0.051 20kHz [T]
[Pa=ml
y
silicate [W/kg]
100%Atomized iron A
A Yes 2% 0.4% 20000 97 222 13.5 1.98
Comp
100% Sendust B
Yes 2% 0.4% 70000 55 70 5,0 0.88
Comp
50%Sponge iron + 50% Sendust C-E
Yes 4 140 249 67.8 1.42
Comp
No 2% 0.4% 41 87 209 44.0 1.32
Comp
Yes 2% 0.4% 468 76 202 9.8 1.33
Comp
50%Atomized iron + 50% Sendust F-H
Yes 40 145 180 55.2 1.52
Comp
No 2% 0.4% 6013 79 149 9.2 1.35
Comp
H Inv Yes 2% 0.4% 77394 66 138 8.2 1.35
As can be seen from table 1, the combination of atomized iron, sendust, a
primary
phosphorous coating layer and a second coating layer consisting of kaolin and
sodium silicate considerably improves resistivity and hence lowers core
losses. It
also gives a good saturation flux density in comparison with 100% sendust.
Example 2
To illustrate the possibility to dope pure phosphorous and kaolin ¨ sodium
silicate
coated atomised iron powder with Sendust with only the first phosphorous
coating
layer and considerably enhance the magnetic properties of the compacted
component the following samples were prepared. Table 2 also shows results from
testing of the components.
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Table 2
Additives on Sendust Component properties
Sample Phosporous Wt-% Wt-% Resistivity [pfl m] Coercivity
IA/m] Core loss at
coating Kaolin Sodium 0.05T
silicate 20kHz
[W/kg]
50%Atomized iron phosphorous and kaolin ¨ sodium silicate coated + 50% Sendust
I-L
I Comp No 2531 169 9.5
J Comp No 2% 0.4% 4587 140 9.0
K Inv Yes 50354 137 8.7
L Inv Yes 2% 0.4% 77394 138 8.2
As can be seen from table 2, it is beneficial to have a first phosphorous
coating layer
on the sendust particles.
Example 3
It is possible to control the magnetic properties of the compacted and heat
treated
component by varying the content of sendust in the atomized iron powder. The
following samples have all been treated in the same way ¨ a first layer of
phosphorous coating and a second layer coating consisting of 2%kaolin clay and
0.4%sodium silicate, compacted to 800MPa and heat treated in 700 C for 0.5h in
a
nitrogen atmosphere. The difference between the samples is that the sendust
content
in the atomized iron powder has been varied. Table 3 also shows results from
testing
of the components.
Table 3
Wt-% Component properties
Sample Sendust Resistivity [pfl-m] pmax [-] Coercivity [A/m] Core
loss at 0.05T 20kHz Bs [T]
[W/kg]
Atomized iron + Sendust ¨ different compositions, phosphorous coated and a
second coating layer with 2%kaolin
and 0.4%sodium silicate M-U
20000 97 222 13.5 1.98
Comp
N Inv 2.5% 24588 91 216 13.0 --
1.95
0 Inv 5% 52794 87 210 12.5 1.90
P Inv 10% 51438 85 202 11.1
1.85
10 Inv 20% 113513 79 179 10.6 1.63
IR Inv 30% 103656 75 167 9.8 1.52
S Inv 40% 686475 67 153 9.4 --
1.42
U Inv 60% 430569 61 125 7.7
1.22
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As can be seen from table 3, even a small amount of sendust in the atomized
iron
powder enhances the magnetic properties of the compacted and heat treated
component.
Example 4
This example shows that the phosphorous- clay- silicate coating concept
according to
the invention may be applied to different particle sizes of the iron powder -
the
Sendust powder has a fixed particle size of approximately 45pm. For sample V)
an
iron powder having a mean particle size of -45pm has been used, for sample W)
an
iron powder having a mean particle size of -100pm has been used and for sample
X)
an iron powder having a mean particle size of -210pm has been used. The iron -
Sendust powder mix was coated with a first phosphorous containing layer.
Thereafter
some samples were further treated with 1% kaolin and 0.4% sodium silicate as
earlier described. Heat treatment was performed for 0.5h at 700 C in nitrogen.
Results from testing of samples V-X) according to table 4
Table 4
Powder mix properties Component properties
Sample Mean Wt-% Wt-% Wt-% Resistivity Coercivity
Core
particle size Kaolin Sodium [PQATI] [A/m] loss at
[pm] silicate Sendust 0.05T
20kHz
[W/kg]
All samples have a first phosphorous coating layer V-X
V Inv 45 1% 0.4% 40% 72850 134 7.5
Sample 45 1% 0.4% 15000 226 15.0
V Comp
W Inv 100 1% 0.4% 40% 88187 105 9.9
Sample 100 1% 0.4% 19000 177 25.2
W Comp
X Inv 210 1% 0.4% 40% 114479 83 11.1
Sample 210 1% 0.4% 35000 140 30.1
X Comp
Table 4 shows that regardless of the particle size of the iron powder clear
improvements of resistivity and core losses are obtained for components
according to
the present invention.
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Example 5
Example 5 illustrates that it is possible to use different types of water
glass and
different types of clays containing defined phyllosilicates. The 60% atomized
iron ¨
40% sendust powder mixes were coated as described above with the exception
that
various silicates (Na, K and Li) and various clays (kaolin and talc)
containing
phyllosilicates having electroneutral layers were used. In comparative
examples clays
containing phyllosilicates having electrical charged layer, Veegume and a
mica, were
used. Veegum is a trade name of clay from the smectite group. The mica used
was
muscovite. The second layer in all the tests contained 1% of clay and 0.4wt-%
of
water glass. Heat treatment was perform-ed for 0.5h at 700 C in nitrogen.
The following table 5 shows results from testing of the components.
Table 5
Additives on the iron ¨ Sendust mix Component properties
Sample Type of Type of Mol ratio Resistivity pmax Coercivity
[Aim] Core loss
clay silicate silicate [-] at 0.051
20kHz
[W/kg]
60%Atomized iron + 40% Sendust ¨ phosphorous coated with a second coating
layer consisting of 1%clay and
0.4%silicate Y-e
Y Inv Kaolin Na 2.5 72850 80 134 7.5
Z Inv Talc Na 2.5 72321 94 131 7.4
a Veegume Na 2.5 97 91 135 19.9
Comp
Mica Na 2.5 389 106 138 15.4
Comp
c Inv Kaolin Na 3.37 72569 84 136 7.3
d Inv Kaolin K 2.5 84992 86 140 8.4
e Inv Kaolin Li 2.5 77403 85 147 8.2
As evident from table 5, various types of water glass and clays containing
defined
phyllosilicates can be used provided the phyllosilicate is of the type having
electroneutral layers.
Example 6
Example 6 illustrates that by varying the amounts of clay and alkaline
silicate in the
second layer the properties of the compacted and heat treated component can be
controlled and optimized. The samples were prepared and tested as described
earlier. Heat treatment was performed for 0.5h at 700 C in nitrogen.
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The following table 6 shows results from testing
Table 6
Additives on the iron - Sendust
Component properties
Sample mix
Wt-% Wt-% Resistivity [pilm]
Coercivity [Aim] Core loss at
Kaolin Sodium silicate
0.05T 20kHz
[W/kg]
60%Atomized iron + 40% Sendust, phosphorous coated f-n
f Comp - 0.4% 100 151 15.8
g Inv 0.5% 0.4% 2956 155 10.2
h Inv 1% 0.4% 172850 154 9.6
i Inv 2% 0.4% 686475 153 9.4
j Inv 3% 0.4% 732463 157 10.0
k Inv 5% 0.4% 179478 164 11.6
I Inv 2% 0.2% 136795 157 10.1
m Inv 2% 0.6% 88309 156 10.1
n Inv 2% 0.8% 3359 164 10.3
As can be seen from table 6, resistivity will decrease if the content of
sodium silicate
in the second layer exceeds 0.7% by weight. Resistivity will also decrease as
the
content of sodium silicate is decreased thus the content of silicate shall be
between
0.2-0.7% by weight, preferably between 0.3-0,6 A) by weight of the total
60%atomized iron ¨ 40% Sendust powder mix. Further increased clay content in
the
second layer up to about 4% will increase resistivity but decrease core loss
due to
increased Coercivity. Thus, the upper limit of clay in the second layer is 5
%,
preferably 4%, by weight of the iron- based composite powder. The lower limit
for
content of clay is 1%, preferably 3% as a too low content of clay will have a
detrimental influence of resistivity and core loss.
Example 7
The following example 7 illustrates that powder produced according to the
invention
can be compacted to different compaction pressures and at different compaction
die
temperatures. The samples below have been treated as described above,
60%atomized iron and 40% Sendust has been phosphorous and clay ¨ sodium
silicate coated, the content of kaolin in the second layer was 2% and the
content of
sodium silicate was 0.4% by weight of the composite iron - Sendust powder.
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The samples o-v) were compacted to between 400¨ 1200MPa either at 20 C or
60 C compaction die temperature and heat treated for 0.5h at 700 C in
nitrogen.
Results from testing according to table 7;
Table 7
Compaction properties Component properties
Compaction Compaction Density Resistivity pmax Coercivity Core
Bs
Sample Pressure die Nix] [PO [-] [A/m] loss at
[T]
[MPa] temperature 0.05T
[CC] 20kHz
[W/kg]
60%Atomized iron + 40% Sendust ¨ phosphorous coated with a second coating
layer consisting of
2%kaolin and 0.4%sodium silicate o-v
o Inv 400 20 5.86 25441 56 167 10.0
1.30
p Inv 600 20 6.15 52357 65 166 9.3
1.36
g Inv 800 20 6.27 686475 67 153 9.4
1.42
r Inv 1000 20 6.41 773125 79 166 8.6
1.41
s Inv 1000 60 6.42 720625 86 156 8.3
1.42
t Inv 1100 20 6.43 796750 83 165 8.4
1.43
u Inv 1100 60 6.45 101250 86 166 8.3
1.44
v Inv 1200 60 6.50 96875 90 162 8.1
1.44
Table 7 shows that high resistivity and low core losses are obtained for
components,
according to the invention, compacted to different compaction pressures and
compacted at different compaction die temperatures. A rise of the density and
a
lowering of the losses can be observed when raising the compaction pressure
from
400 to 800MPa, further increasing the compaction pressure however gives just
little
effect. The compaction die temperature only increases the resistivity slightly
and
does not give any further improvements of the magnetic properties.
Example 8
The following example 8 illustrate that components produced from powder
according
to the invention can be heat treated in different atmospheres and different
temperatures. The samples below have been treated as described above,
60%atomized iron and 40% Sendust has been phosphorous- and clay ¨ sodium
silicate coated, the content of kaolin in the second layer was 2% and the
content of
sodium silicate was 0.4% by weight of the composite iron - Sendust powder.
The samples w-Dd) were heat treated at between 550 ¨ 750 C in nitrogen and air
respectively. Results from testing according to table 8;
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Table 8
Sample Heat treatment parameters Component properties
Heat treatment Heat treatment Resistivity pmax Coercivity
Core loss at
temperature [ C] atmosphere [PO-11 [-] IA/m] 0.05T 20kHz
[W/kg]
60%Atomized iron + 40% Sendust ¨ phosphorous coated with a second coating
layer consisting of 2%kaolin and
0.4%sodium silicate w-Dd
w Comp 550 C Nitrogen 190574 54 283 22.8
x Comp 600 C Nitrogen 184382 61 228 16.6
y Inv 650 C Nitrogen 178613 69 183 12.1
z Inv 700 C Nitrogen 686475 67 153 9.4
Aa Inv 750 C Nitrogen 566356 70 150 8.9
Bb Inv 700 C 90%Nitrogen + 561917 69 165 9.2
10%Air
Cc Inv 700 C 50%Nitrogen + 429138 66 250 10.5
50%Air
Dd 700 C Air 17400 64 303 12.1
Comp
Table 8 shows that high resistivity and low core losses are obtained for
components
according to the invention heat treated at between 650 C ¨ 750 C in nitrogen
atmosphere or in a mixed atmosphere with nitrogen and air.
Example 9
The following example 9 illustrates that it is possible to boost the magnetic
properties
of components produced from powder according to the invention by adding gas
atomized FeSi to the mix. The iron ¨ Sendust powder mixes have a first
phosphorous
coating layer and a second layer consisting of 2%kaolin and 0.4%sodium
silicate.
The powder mixes have been compacted to 800MPa and heat treated at 700 C, for
30minutes in a nitrogen atmosphere.
Table 9
Mixture composition Component properties
Sample
Wt-% Wt-%Gas Resistivity pmax [- Coercivity Core
loss at 0.05T
Sendust atomized FeSi [PO'rri] [A/m] 20kHz [W/kg]
Atomized iron powder ¨ the powder mixtures have a phosphorous coating and a
second coating layer consisting
of 2%kaolin and 0.4%sodium silicate Ee-Gg
Ee Inv 30% 103656 75 167 9.8
Ff Inv 40% 686475 67 153 9.4
Gg Inv 30% 10% 704380 55 149 8.7
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As can be seen in table 9 an adding of 10 /0FeSi in the phosphorus and kaolin
¨
sodium silicate coated iron ¨ Sendust mix enhances the resistivity and lowers
the
Coercivity and the core losses.
Example 10
A pure water atomized iron powder having a content of iron above 99.5% by
weight
has been used as core particles. The mean particle size of the powder was
about
45pm. The core particles have been mixed with Sendust (typically 85%Fe, 9%Si
and
6 /0A1) and the powder mix was treated with a phosphorous containing solution
according to W02008/069749. The obtained dry phosphorous coated iron powder ¨
sendust mix was further treated with a second (metal organic) coating layer as
described in W02009/116938, namely mixing the powder by stirring with
different
amounts of first a basic aminoalkyl-alkoxy silane (Dynasylan Ameo) and
thereafter
with an oligomer of an aminoalkyl/alkyl-alkoxy silane (Dynasylan 1146), using
a 1:1
relation, both produced by Evonik Inc. The composition was further mixed with
different amounts of a fine powder of bismuth(III) oxide (>99wt%; D50 --0.3
pm).
After coating the powder was mixed with 0.4% amide wax and compacted to 800
MPa into rings with an inner diameter of 45mm, an outer diameter of 55mm and a
height of 5mm. The compacted components were thereafter subjected to a heat
treatment process at 700 C in a nitrogen atmosphere for 0.5 hours.
Unless otherwise stated all tests in the following examples were performed
accordingly.
Samples Hh-li) were prepared according to table 10 which also shows results
from
testing of the components.
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Table 10
Additives on the iron ¨
Component properties
Sendust mix
Heat
Sample
Phosphorous Metal treatment Resistivity pmax Coercivity
Core DC
coating organic [-] [A/m] loss at
Bias
temperature
layer 0.05T [%]
20kHz
[W/kg]
100%Atomized Iron Hh
Hh Yes Yes 650 C 19923 226 195 10,0 40
Comp
60%Atomized Iron + 40% Sendust Ii
li Inv Yes Yes 700 C 125000 113 151 6.7 60
As can be seen from table 10 the combination of atomized iron, Sendust, a
primary
phosphorous coating layer and a second (metal organic) coating layer
considerably
improves resistivity, DC-bias and lowers core losses and Coercivity compared
to
using 100%atomized iron powder.
Example 11
It is possible to control the magnetic properties of the compacted and heat
treated
component by varying the content of sendust in the atomized iron powder. The
following samples have all been treated in the same way ¨ a first layer of
phosphorous coating and a second (metal organic) coating layer. The difference
between the samples is that the sendust content in the atomized iron powder
has
been varied. The samples have all been compacted to 800MPa and heat treated
for
0.5h at 700 C in a nitrogen atmosphere. Table 11 also shows results from
testing of
the components.
Table 11
Sample Composition Component properties
Wt-% Wt-% pmax [-] Coercivity Core loss at
0.051 DC-Bias Bs
Sendust Iron [A/m] 20kHz [W/kg] ro] [T]
Atomized iron + Sendust - different compositions - phosphorous coated with a
second layer metal organic coating
Jj 100% 226 195 10 40 1.99
Comp
Kk Inv 20% 80% 135 176 6.9 51 1.72
LI Inv 30% 70% 123 164 6.8 55 1.61
Mm Inv 40% 60% 113 151 6.7 60 1.48
Nn Inv 50% 50% 104 139 6.6 63 1.35
As for the clay/sodium silicate coated atomized iron- and sendust-powder-mix
an
increased share of sendust considerably improves resistivity and DC-bias and
hence
lowers core losses and Coercivity.
