Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Description
Component with a layer into which CNT (carbon nanotubes) are
incorporated and a method for the manufacture of said
component
The invention relates to a component with a layer with CNT
incorporated into the grains thereof.
A layer with CNT, as mentioned above, can typically be
produced on a contact element as described in WO 2007/118337
Al. This electrical contact element is used for closing and
opening an electrical contact and is subject to great stress
during this process. This stressing is attributable to the
transmission of the electrical switching current, wherein, in
accordance with WO 2007/118337 Al, an increase in the service
life of the contact is to be achieved by the fact that carbon
nanotubes (referred to below as CNT) are present in the
contact layer. The increase in the service life is
attributable to the fact that the CNT on the one hand improve
the electrical conductivity of the layer and on the other hand
also bring about improved heat dissipation during the
switching process. The thermal stress during the switching
process is reduced by this method and the contact layer is
subject to less of a strain.
The object of the invention is thus to bring about a further
improvement in the wear behavior of coated components,
especially electrical contact elements.
This object is inventively achieved with the component
mentioned at the start by a dry lubricant being incorporated
into the grains in addition to the CNT particles. The
background of the inventive measure is that the incorporation
of CNT, contrary to the widely-held belief among those skilled
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in the art, only inadequately improves the wear behavior of a
coating. CNT does actually improve the hardness of the
coating, but the tribological behavior of surfaces is not
solely influenced by their hardness. Instead the lubricating
properties of the coating during frictional stress are also of
primary importance. This is the starting point of the
invention, in that the particles of a dry lubricant are also
incorporated in addition to the CNT. Dry lubricants belong to
a material group characterized by its ability to improve the
lubricating properties of the surfaces involved. This
advantageously reduces wear, which enables the component into
the grains of which CNT and particles of a dry lubricant are
incorporated to achieve a better service life. In this case
the grains of the layer form a matrix in which the particles
of the dry lubricant and the CNT, which can also be regarded
as particles, are distributed dispersed. Because of their
dimensions, the CNT represent nanoparticles. The particles of
the dry lubricant can be embodied as nanoparticles but can
also have dimensions in the micrometer range.
In accordance with an advantageous embodiment of the invention
there is provision for at least one of the dry lubricants
used, molybdenum sulfide, tungsten sulfide, tantalum sulfide,
graphite, hexagonal boron nitride, graphite fluoride and
silver niobium selenide, to be contained in the particles. The
particles of the dry lubricant can thus consist of one or more
of the dry lubricants listed and also be mixed with other dry
lubricants which are not specified here. It is also possible
to use particles of differing compositions, i.e. to mix
particles of a dry lubricant with particles of another dry
lubricant, with both types of dry lubricant being incorporated
into the grains of the layer. Through a suitable mixture and
choice of dry lubricants the layer can advantageously be
optimized to a specific application in respect of its wear
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behavior. In such cases the circumstances of the application
are to be taken into account, whereby it should be noted that
the tribological behavior of two components generally can only
be predicted to a restricted extent so that trials are
necessary for an optimization, i.e. a selection of suitable
dry lubricants. The dry lubricants specified generally exhibit
good lubrication properties however, which is why they are the
preferred choices in order to arrive at satisfactory results.
A further embodiment of the invention is obtained if the layer
has metallic grains, especially made of a nickel-cobalt alloy.
The metallic grains of the layer make it possible to conduct
the electrical current with advantageously low electrical
resistance. Nickel-cobalt alloys in particular are suitable
for electrical switching elements since they combine
comparatively good electrical and thermal conductivity with a
satisfactory wear behavior. Thus the optimization potential
through the incorporation of CNT and dry lubricant particles
can advantageously be used especially well.
In accordance with another embodiment of the invention there
is provision for the layer to have a ceramic grain or at least
ceramic grain proportions, especially made of oxidic or
nitridic ceramics such as titanium nitride. This
advantageously enables very hard layers, for coating a tool
for example, to be produced, with their tribological behavior
able to be optimized by embedding of the dry lubricant
particles. This enables the service life to be advantageously
improved. At the same time the thermal conductivity of the CNT
can be used in order for example to effectively dissipate the
heat from cutting tools. The reduction in thermal stress
advantageously simultaneously leads, at high cutting speeds of
the tool, to an improved service life, or makes it possible to
cut at higher speeds with the same service life.
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It is also conceivable for only specific grain proportions to
be ceramic while other grain proportions are metallic. An
electrical conductivity of the layer is thus retained, with
the ceramic grain proportions predominantly being employed to
optimize the service life. Finally, electrically-conductive
ceramics can also be used with which, even with purely ceramic
layers, it is possible to establish electrical contact layers.
This is especially the case with titanium nitride.
The invention further relates to a method for electrochemical
coating of a component in which the component is placed in an
electrolyte, where a layer of elements of the electrolyte is
deposited, with CNT being dispersed in the electrolyte which
are incorporated into the layer.
A method of the stated type is known for example in accordance
with US 2007/0036978 Al, with CNT being dispersed in the
electrolyte for the purposes of incorporation into an
electrochemical layer to be produced. During the fabrication
of the electrochemical layer these CNT will thus also be
incorporated into the layer.
The object of the invention is to specify a method for
electrochemical coating while incorporating CNT with which
layers can be created with an enhanced functional scope.
This object is achieved inventively with the said method in
that particles of a dry lubricant which will also be
incorporated into the layer are also dispersed in the
electrolyte in addition to the CNT. This enables layers to be
created which advantageously meet requirement profiles, as
have already been illustrated above in connection with the
inventive layers.
Advantageously an aqueous electrolyte can be used for coating,
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with the CNT and the particles of a dry lubricant being
dispersed using a wetting agent in the electrolyte. In such
cases it is advantageously possible to draw on a plurality of
available electrolytes, with use also able to be made of the
wetting agents specified in US 2007/0036978 Al.
Another especially advantageous form of embodiment of the
inventive method is obtained if an ionic fluid is used as an
electrolyte for the coating. Fluid salts in which the salt is
not dissolved in a solvent (preferably water) are referred to
as ionic liquids. This involves organic liquids which are
composed of cations and anions. In the present case alkalized
imidazolium, pyridinium, ammonium or phosphonium ions are used
as cations. Simple halogenides, tetrafluorborate,
hexafluorphosphate, Bi(trifluoromethylsulfonyl)imide or
Tri(pentafluoroethyl)trifluorphosphate can typically be used
as anions. The effect of choosing these cations and anions is
that the ionic fluids are available in the fluid state at
temperatures of below 100 C, preferably even at room
temperature. Because of their chemical structure, ionic fluids
possess surfactant-type properties, which is why these fluids
are excellently well suited to the production of dispersions.
The ionic fluid acts in such cases as a means of dispersion,
with the dispersants to be dispersed able to be microparticles
or nanoparticles and being formed in the invention by the CNT
and the particles of the dry lubricant. Advantageously this
enables wetting agents for dispersal to be dispensed with,
which avoids the properties of the particles incorporated into
the electrochemically-fabricated layer being adversely
affected by built-in wetting agents. In addition comparatively
high concentrations of dispersed particles can be achieved in
ionic fluids, whereby higher incorporation rates into the
layer to be created are also advantageously achieved.
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In addition the metals can also be deposited from the ionic
fluid as nano crystalline metal layers. In this regard the
parameters in accordance with WO 2006/061081 A2 or information
provided by F. Endres, "Ionische Flussigkeiten zur
Metallabscheidung (Ionic fluids for metal deposition)",
Nachrichten aus der Chemie, 55, May 2007, Pages 507 to 511,
should be taken into account. The structure of nano
crystalline metal layers is advantageously especially well
suited to the incorporation of CNT as well as the particles of
the dry lubricant, so that advantageously especially high
incorporation rates can be achieved.
The deposition from aqueous electrolytes and also deposition
from ionic liquids can be undertaken both in direct current
mode and also in pulsed mode. This advantageously makes it
possible to vary the deposited proportions of CNT and
particles of the dry lubricant. Copper and gold can also
typically be used, in addition to those metals already
mentioned, as possible metals for depositing the metallic
layer. The CNT used can likewise have different
characteristics. In particular the use of single wall CNT,
multi-wall CNT or double-wall CNT is possible. Furthermore the
CNT can feature functional groups which influence their
characteristic profile.
An exemplary embodiment of the inventive method will be
described below. In this exemplary embodiment the following
steps are performed:
1. In an ionic fluid, such as 1-Butyl-3-
methylimidazoliumtetrafluorborate, the appropriate
salts for the ionic salts, such as nickel
tetrafluoroborate and cobalt sulfamate, are dissolved
as ion carriers.
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2. Subsequently molybdenum or tungsten sulfide are
dispersed in these electrolytes as nano particles or
micro particles.
3. Once the said dispersants are distributed homogenously
in the electrolyte, an anode consisting of nickel and
cobalt is introduced into the bath. Such electrodes are
soluble electrodes in order to achieve a constant Ni
and Co concentration.
4. The tool which is to be coated and which is
electrically-conductive is then immersed the
electrolyte and connected to a power source as the
cathode.
5. With a current of 0.5 to 20 A/dm2, Ni/Co is deposited
with the said sulfides and the CNT.
Further details of the invention are described below with
reference to the drawing. Elements of the drawing which are
the same or which correspond to one another are provided in
the individual figures with the same reference signs in each
case and are only explained more than once where there are
differences between the individual figures. The figures show:
Figure 1 an exemplary embodiment of the inventive component as
an electrical contact element,
Figure 2 the detail identified in Figure 1 and
Figure 3 an exemplary embodiment of the inventive method in a
schematic diagram.
A component 11 in accordance with Figure 1 is embodied as an
electrical switching element. In its contact area this has a
layer 12 into which, as can be seen from Figure 2, on the one
hand CNT 13 and on the other hand particles 14 of a dry
lubricant are embedded. This advantageously gives a contact
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surface 15 formed by the layer 12 an increased resistance to
wear, an increased ability to carry the switching current and
thereby an enhanced service life.
In the method in accordance with Figure 3 a container 17 is
filled with an electrolyte 16 embodied as an ionic fluid.
Dispersed in the electrolyte 16 are CNT and particles 14 of a
dry lubricant. The component 11 to be coated as the working
electrode and an opposing electrode 18 are in contact with a
power source 19, enabling a layer to the produced on the
component 11 by embedding the CNT 13 and the particles 14 of
the dry lubricant.
