WO2006122736A2

WO2006122736A2 - Nanotube composite systems, method for producing the same and use of the same in heating elements

Info

Publication number: WO2006122736A2
Application number: PCT/EP2006/004557
Authority: WO
Inventors: Walter Von Wirth; Klaus Hying; Ivica Kolaric; Dominik Nemec
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2005-05-19
Filing date: 2006-05-15
Publication date: 2006-11-23
Also published as: WO2006122736A3

Abstract

The invention relates to a nanotube composite system. The inventive system is an especially flat system comprising nanotubes and fibers, the nanotubes being substantially adsorbed to the fibers. The invention also relates to a method for producing a nanotube comprising system, whereby the nanotubes and fibers are dispersed in a dispersant. The invention finally relates to the use of the inventive composite materials in heating elements.

Description

Nanotube's comprehensive composite systems, their method of manufacture and their use in heating elements

The present invention relates to systems comprising nanotubes, in particular planar systems, as well as methods of their production and the use of systems comprising nanotubes in heating elements.

Nanotubes have a variety of interesting properties such as high thermal conductivity and excellent mechanical and electrical properties, which is why they are being investigated for a variety of applications. A direct conversion from electrical to mechanical energy is possible (actor), so that a wealth of applications up to an artificial muscle are conceivable. In. In combination with suitable dielectric materials, powerful capacitors can be produced. It is also possible to use it as a biological nutrient medium.

To date, the production of planar structures that consist entirely or to a large extent of nanotubes, in particular carbon nanotubes, is laborious, fraught with great difficulty and limited to small flat bodies.

In the previously known methods, the carbon nanotube raw material is first dispersed using ultrasound and using a surfactant. The hydrophobic nature of the carbon nanotubes and the strong van der Waals interactions between the individual tubes cause poor dispersibility. The carbon nanotube concentration is therefore limited to about 0.1% in an aqueous surfactant solution. To remove impurities, particles and amorphous carbon, the suspension is centrifuged and then decanted off. Subsequently, the suspension is filtered off through a microliter, forming the flat Bucky paper. To accelerate the filtration process, the filtrate is either sucked through the filter with negative pressure or forced through the filter by means of overpressure. To remove the surfactant, the Bucky paper must be rinsed several times with distilled water. Finally, it is carefully separated from the filter and dried.

The authors are not aware that with the hitherto known method Bucky-paper with a diameter of more than 90 mm and thicknesses of more than 0.3 mm could be realized. The production of large areas fails in these known methods also because over large areas in the batch process no uniform layer thickness and density can be obtained.

In addition, the known method is very labor-intensive and time-consuming. Typically, for example, the production of a 90 mm diameter 90 mm diameter Bucky paper from a 0.04% carbon Nanotube suspension in 1% sodium dodecylsulfate with a 0.4 mm ) about two to three hours. A large-scale application based on these processes is therefore unlikely, especially as the realized unit is too small for a technical application or not yet reproducible in sufficient numbers.

The use of surfactants requires the rinsing of the surfactant with distilled water in a further step.

Depending on the type and quality of the raw material and the applied filtration process (underpressure or overpressure), it is difficult to separate the Bucky paper from the filter without damaging it.

A continuous manufacturing process is also not possible with this method. In addition, parameters such as the tensile strength of the Bucky paper can hardly be influenced.

For coating surfaces or for forming planar structures, carbon nanotubes can also be applied specifically to surfaces by deposition from the gas phase by the CVD method (chemical vapor deposition). The use of this technology for targeted coating in a continuous process is currently unknown. Also, the production of a self-supporting planar structure, for example by separation of the carbon Nanotubes layer of a surface is currently not known.

The object of the present invention is to provide a Nanotubes comprehensive, in particular flat system, which is relatively easy and can be produced in larger quantities.

This object is solved by the features of claim 1 and claim 8. The nanotube-containing system of the present invention is a composite system comprising nanotubes and fibers wherein the nanotubes are substantially adsorbed to the fibers.

This composite system is in particular a planar system.

Surprisingly, much larger planar structures can be produced from these fibers with adsorbed nanotubes in a relatively simple manner, since the nanotubes adsorbed on the fibers can be combined with the known production processes for producing planar structures, for example on the usual devices and processes known from the paper industry planar composite of macroscopic fibers and nanotubes are further processed.

The production of composites from nanotubes and foreign fibers makes it possible to specifically influence and control the mechanical properties of the planar structures. It has also been shown that the e-electromechanical properties of carbon nanotubes, such as the actuation, are also retained in cellulose fiber-reinforced papers.

The nanotubes can be adsorbed on the fibers by dispersing the nanotubes together with the fibers, preferably by means of ultrasound, in a dispersion medium.

A significant advantage of the present invention is that the use of foreign fibers and taking advantage of the transfer process, in which the nanotubes draw on the foreign fiber, an industriefähiger process for mass production of composites of Bucky papers with foreign fibers is possible, the largely classical Processes in the paper industry.

The adsorption of the nanotubes on the fibers can be determined in various ways, for example by means of SEM images or by resistance measurements.

In addition, the prerequisite of "essentially adsorption" is also present if the majority of the fibers on the SEM image show the adsorbates, even if nanotubes as agglomerates and / or fibers with few or no adsorbed nanotubes are present in addition to these adsorbates. Another indication for the adsorption of the nanotubes on the fibers is the fact that from a concentration - the limit concentration - of nanotubes, which is sufficient for example to form a monolayer on the fiber surface, a clear effect on the electrical resistance of the composite of fibers and nanotubes is available. The limiting concentration depends on the geometry of the nanotube and the surface of the fibers used. If the mass fraction of nanotubes is sufficient to fully occupy the fiber surface, the conductivity increases abruptly, that is, the resistance drops.

The unambiguous influence on the resistance lies with a calculated degree of coverage of the nanotubes on the surface of 50%. The surfaces of various cellulose fibers at which the degree of coverage is calculated are shown in Table 5.

A clear indication of the stability of the fiber composition could be drawn from a first machine trial on a pilot paper machine. A material according to the invention was produced with a grammage of 100 g / m ² . The corresponding resistance of the material was 220 ohms / cm (equivalent to 1700 ohms / sq). The committee was, as usual in the paper industry, taken up with water and processed into a pulp. During the subsequent use of this material, the same ohmic resistance was achieved with the same basis weight.

In principle, the fiber occupancy can be achieved as follows: Either a pulp is mixed with the nanotubes, in particular the solid carbon nanotubes substance, and ultrasonicated (variant A) or the pulp is adjusted to a desired degree of grinding and then a pre-dispersed mother solution of nanotubes in water was added (variant B).

Variant A is particularly suitable for relatively high carbon nanotube concentrations. The minimum concentration of carbon nanotubes for this process variant should preferably be 10%, based on the solids content in the pulp, since a uniform coverage of the fibers is more difficult to achieve below this concentration. It should be noted that the ultrasonic treatment causes an additional grinding effect, so that the mass is therefore to be checked exactly to the degree of grinding.

The occupation of the fibers by the addition of a predispersed mother solution of carbon nanotubes (variant B) is in a wide range of Ratio of carbon nanotubes to fibers used. Thus, controlled concentrations of 1% carbon nanotubes relative to the fiber can be reproducibly realized with this method. Furthermore, the solids content of the carbon nanotubes in water, which is achieved with this mother solution, is very well suited for the fiber concentration of the individual laid paper. While 2 to 3% are common in a mixed tank, the concentration can drop to 0.3% down to the machine chest.

This is the preferred concentration range for the mother solution according to the invention (or mother dispersion) of the carbon nanotube, since the mother solution can be adjusted to the particular concentration of the chest without causing disadvantageous changes in the concentration of the pulp.

Another advantage of variant B is that it is also customary in the paper industry to dose additives of polymer dispersions or pigment slurries inline, which is why the concept of the mother solution ideally fits the procedures customary in the paper industry.

The concentration range of at least 0.3% nanotubes, in which the mother liquor should preferably be prepared, also results from the fact that an approach below the concentration of the machine chest would not make sense because of an undesirable dilution of the pulp.

After dispersions of carbon nanotubes in water show a strong increase in viscosity - the viscosity increase can also be used to check the progress of dispersion - dispersions with more than 3% carbon nanotubes in water are extremely viscous and therefore less preferred.

In the range of 1 to 3%, optimum results are obtained in terms of time and energy yield, with possibly the impact events of the particles additionally supporting the dispersing effect.

For the application of variant A (direct use of solid carbon nanotubes in the pulp) is analogous. A use of solid components in the machine chest is not common. Although in principle a pulp in the Mischbütte be set at 0.3 to 0.5% and are brought into the paper machine after appropriate treatment. However, such a process is very costly for the grinding of the pulp and technically difficult to control, which is why for the Variant A is a range of 1 to 3% solids, that is, carbon nanotubes and fibers is recommended.

Compared to the processes known from the prior art, in the production according to the invention of the laminar layers comprising nanotubes according to variant B with a mother solution in a conventional concentration range of 1 to 3 wt.% Nanotubes or according to variant A in a conventional paper industry Dispersion worked preferably with 1 to 3 wt.% Solid, that is, it is a more concentrated suspension of nanotubes used from which the ultrasonically dispersed nanotubes then adsorb to the surface of the fibers. These concentrations are common for the preparation of pulp in the paper industry and facilitate economical production.

It is assumed that the adsorption is based on the following transfer mechanism: By using ultrasound, at least some of the nanotubes are dispersed. The dispersed nanotubes have an affinity for the surface of the fibers and are adsorbed thereto, further nanotubes are dispersed and subsequently adsorbed and so on until the nanotubes are substantially adsorbed to the surface.

According to the invention, the use of anionic surfactants such as sodium dodecyl sulfate should be avoided, since these compete with the negative potential of the paper fibers and hinder or reverse the retention on the fibers.

In contrast to the conventional processes, which require amounts of anionic surfactants of about 1% in relation to the amount of nanotubes used, the process cited here does not contain any surface-active substances.

In particular, it has been found that the adsorption of the nanotubes on the fiber surface is promoted by the fact that the anionic surfactants, such as sodium dodecyl sulfate, which are customarily used as dispersants for the preparation of the nanotube dispersion, are not used to prepare the dispersion. This is attributed to the fact that nanotubes without anionic surfactants are not stabilized in the dispersion as negatively charged particles which are repelled by the likewise partially negatively charged fiber surface.

The surface potential of the cellulose, measured with a PCD 03 from Mütek, should preferably be between -500 mV and -1400 mV. The preferred freedom of anionic surfactants such as sodium dodecylsulfate not only effective adsorption of the nanotubes is achieved on the fibers, but it also eliminates the multiple rinsing, which is required in the known production of Bucky paper to the surfactants added as a dispersant to remove.

If desired, a transfer of the paper fibers or the nanotube suspension in the positive area can be achieved by means of cationic surfactants. As a result, the adsorption can be facilitated and a time savings in the preparation of the dispersion can be achieved by means of ultrasound. However, reloading is ultimately not required for the process.

In principle, auxiliaries can be used in the preparation of the mother liquor or the direct adsorption, as they are usually used for the preparation of dispersions. Substances which increase the negative surface potential of the carbon nanotubes are of course not advantageous since the cellulose inherently has a negative surface potential. However, if one has produced a positive potential by pretreatment of the cellulose, this can be advantageous.

On the other hand, leaving aside the negative surface potential of cellulose, it is helpful to positively pre-charge the carbon nanotubes. For this purpose, well-known substances, such as, for example, quaternary ammonium compounds having an acrylate skeleton, can be used in the paper industry.

A neutral polymer such as polyvinyl alcohol can also be used.

The neutralization of existing charges or transhipment can, as previously described, be used occasionally.

In addition, the entire range of measures customary in the paper industry is possible:

1. Neutral or acid sizing.

2. Use of wet strength agents.

3. Use of fillers or pigments in the mixing tank or online in the form of slurries.

The solids concentration in the pulp for the process for producing the pulp should be about 0.01% to 10% by weight, preferably between 0.1 to 5% by weight, and more preferably between 0.2 to 2% by weight. The solids concentration in the pulp for the process of production within the paper machine should be between about 0.1 to 1 wt.%.

The ratio of fiber to nanotube can be varied within wide limits, depending on which properties the laminar composite material should have.

Although a material with a proportion of 10% fibers can be realized, the pleasant strength properties of paper fiber composites are not very pronounced here. In addition, these high concentrations do not cause any noticeable improvement in the properties for which the carbon nanotubes are responsible.

If conductivity and strength are desired at the same time, the range of 10 to 20% carbon nanotube is highly recommended. At the same time, this area is also optimal from a cost point of view.

In the lower area, the occupancy of the fibers with carbon nanotubes is the limiting factor. It may be assumed that there should be a minimal amount of monomolecular layer on the fibers to achieve significant conductivity.

It has been found that the calculated coverage of the fibers clearly correlates with the degree of conductivity or electrical resistance range achieved. The following rule applies here: a) Apaser * dcNT ⁼ VcNT, mono

AFaser = surface fiber dcNT = diameter of carbon nanotube

VcNτ, mono = volume of a single-layer CNT layer on the fiber b) Vα \ | T, mono X PcNT = nicNT.mono

PCNT = specific gravity CNT mcNτ, mono = mass of CNT adsorbed on the fiber for a single layer

C) α = m _C NTmoπo / fTlcNTmono α = degree of coverage mcNTmono = mass of CNT adsorbed on the fiber for a single layer

The surface area of the fibers was calculated according to Table 5, assuming that the fiber forms a nearly cylindrical body. If a degree of coverage of 0.4 is fallen below, a sudden increase in the electrical resistance was found in all cases. An erratic increase means an increase of at least two orders of magnitude. Thus, resistivities for a 120 gm thick material range from 1 to 5 kOhm / cm (corresponding to 7.7 to 38.5 kOhms / sq), while when the underfill level falls below 0.4, it is a typical range of resistance for paper from 10 ⁶ to 10 ⁹ ohms / cm (corresponding to 7.7 x 10 ⁶ to 7.7 x 10 ⁹ ohms / sq).

The degree of coverage was calculated in practice between 0.4 and 1.2 and ranges in the majority of cases between 0.5 and 0.9.

Table 6 shows the experimental results on three different CNT types, all of which have a different average diameter.

In fact, using 1% multi-walled carbon nanotubes with a mean diameter of 15 nm on a long fiber pulp, a resistance limit of 2.7 kOhm / cm (corresponding to 20.8 kOhm / sq) was achieved. For 0.8%, ie a coverage of 51%, the value jumps to the mega-ohm range.

At a concentration of 1% by weight of multi-walled carbon nanotubes with a mean diameter of 15 nm, a resistance of one to a few kilo-ohms is already achieved. At 10% by weight, the material already falls below the 10 ohm limit. An economical range is in the range of 10 to 25 wt.%. Although in principle a further increase in the conductivity is possible, but this can only be achieved with a high cost of materials and resulting in loss of strength.

Basically, a range of 0.8 to 95% by weight of nanotubes can be realized. Particularly advantageous in terms of material costs and achieved effect are 2 to 30%, and an optimum can be seen in the range of 10 to 20%.

In the context of the present invention, it is possible in principle to use all known fibers, ie elongate aggregates whose molecules or crystallites are rectified in the molecular longitudinal direction or a lattice straight line, be it finite-length fibrous structures or virtually endless filaments, either individually or in groups. or in a bundled form.

The fibers used may be cellulose, modified cellulose, polyamide, polyacrylonitrile, polyolefin, teflon, silicate fibers, or other natural or synthetic fibers. Liehe fibers are used, depending on the mechanical or electrical properties of the composite material should have.

Preference is given to using cellulose, cellulose derivatives, wool, chitin or polyamide as fibers, inter alia, since particularly stable adsorbates of nanotubes, in particular carbon nanotubes, have been obtained on these fibers.

It is particularly preferred to use as fibers cellulose fibers. In addition to the long-chain cellulose fibers, for example from softwoods, which are characterized by greater mechanical stability and strength, of course, short-chained fibers such as poplar fibers can be used.

In a preferred embodiment, the cellulose fibers to be used are pretreated, in particular ground and spliced, as is customary in papermaking.

In principle, all possible nanotubes can be used to produce the composite according to the invention, be it single-, double- or multi-walled nanotubes, be it carbon, gold or boron nitride, silicon nanotubes, substituted carbon nanotubes (for example with BN ), Nanotubes of metal dichalcogenides MX ₂ with M = Mo, W and X = S, Se, Te, the metal chlorides MCI ₂ and metal sulfides MS ₂ such as the nanotubes of WS ₂ , MoS ₂ and NiCl ₂ .

In order to slurry the fibers and the nanotubes, a multiplicity of dispersants can be used, for example water, preferably deionized, but also aqueous cationic surfactant solutions or polyvinyl alcohol solution. In addition, it is also possible to use aprotic, polar or nonpolar solvents, for example dimethyl sulfoxide, vinylpyrrolidone or kerosene.

Water is the preferred solvent for the process according to the invention. Surfactants are not necessary and are in the case of anionic surfactants - as already explained - even with a negative effect on the process.

Experiments show that the nanotubes from the suspension adsorb not only on the conventional cellulose fibers with a slightly negative surface charge, but also on fibers with a slightly positive surface charge. A positive potential of the fibers or a positive potential of the nanotubes is advantageous and reduces the process times. Another embodiment provides for orienting the nanotubes in the composite. This can be achieved according to the invention in that the fibers on which the nanotubes are adsorbed are oriented.

The rather parallel orientation of the fibers to one another, in particular of the cellulose fibers, has been well studied, since this effect, which is precisely counteracting the desired statistical arrangement, should be avoided in papermaking.

Basically, the paper industry wants turbulent flow conditions when the substance casseroles onto the sieve. This avoids flocculation on the one hand and supports a disorientation of the fibers, which are usually oriented in the direction of flow of the substance (longitudinal / transverse ratio).

The following parameters are normally used for these purposes and thus, conversely, are also suitable for reinforcing orientation of the fibers relative to one another.

1. exit speed. Low flow velocities and laminar flow conditions lead to a strong longitudinal orientation.

2. Use of perforated rollers in the headbox. These rotating perforated rollers are located before the material exits and can support a laminar flow due to reduced speed or standstill.

3rd stage diffuser block. Parallel diffusers lead to micro-turbulences in the area of the transition zones. Abandoning this constructive element also helps to keep the flow laminar.

4. Schüttelbock. One of the most important elements for adjusting the longitudinal / transverse ratios. The element is the first part of the wire section and puts the screen in vibrations of adjustable frequency and amplitude.

5. Three-layer headbox. This element is often used on high-speed paper machines. The principle is based on the fact that the material from three slot nozzles instead of one exits. To generate turbulence, all three streams have different concentrations. If the concentration is set to the same value, then a strong longitudinal orientation can be achieved with such a machine.

It is also possible to use fibers comprising nanotubes by means of high-voltage fields or by movement of the liquid phase through electro-magnetic fields. magnetic or magnetic fields or by calendering under the influence of strong magnetic or electromagnetic fields.

In this embodiment, which maintains the orientation of the nanotubes in the composite, a non-statistic alignment of the nanotubes to one another is ultimately achieved by aligning the fibers with the nanotubes also oriented in a preferred direction on the surface thereof.

When using cellulose fibers, a subsequent removal of the cellulose components by thermal or chemical decomposition is possible, so that in a further process step, a bucky paper is available which consists exclusively of Carboπ nanotubes. Due to the biocompatibility of pure carbon nanotube structures, applications in tissue engineering are possible.

If desired, the composite according to the invention can then be subjected to a subsequent refinement. For example, a polymer coating of an aqueous phase is possible, wherein the deposition preferably takes place on the surface of the adsorbates, ie on the nanotubes, on account of their hydrophobic nature, so that a system of one conductive and two dielectric layers (capacitor) can be built up ,

It is also possible to achieve a strong penetration into the microstructure by means of a polymer coating made of a suitable solvent, so that a three-phase composite material cellulose, nanotubes, in particular carbon nanotubes, polymer can be produced.

Within the scope of the composite according to the invention, mechanical and electrical properties can be set within wide limits and produced in close manufacturing tolerances. Reduced manufacturing costs allow a wide dissemination of the advantageous properties of nanotube systems, in particular carbon nanotube systems.

The composite according to the invention can be used in a variety of ways, for example as an actuator, sensor, substrate (medicine), tissue engineering, electrical conductors, as a heat conductor (cooling elements), as a resistance heater, as a filter, as a cell substrate, as a reinforcing material, as a flame retardant, etc.

A particularly preferred variant of the invention consists in the use of the composite system according to the invention in heating systems, which following are described in more detail:

Heating element, in particular as Spieqelheizunq

The heating element comprises a planar composite system comprising nanotubes, which is electrically conductive and generates heat when current flows, as well as the electrical contacts required for the current flow. Particularly preferred as Nanotubes comprehensive composite system is a flat, especially paper-thin, composite system with a thickness between 20 microns and 10 mm and in particular a thickness between 100 microns and 500 microns.

After the heat is generated in the entire planar composite system during current flow, the heating element is a surface heating element, which causes heating over its entire current-carrying surface. With a suitable arrangement of the electrodes, current flows through the entire composite system.

After the heat generation in the composite system as such is done and the composite system is available as such, the heating element is also easy to manufacture, since only an adaptation to the required size and contacting are required. The complex, the application of the electrical lines on the heating element concerned manufacturing steps of the conventional heating elements (etching) thus eliminated.

Another significant advantage is that the heating element is far less susceptible to interference than the previously known heating elements, as a power line in the entire composite material and thus heating takes place even if the material is damaged at one or the other point.

Depending on the type of bonding, the type and composition of the nanotube comprehensive composite system and its thickness, the material has a different resistance in current flow. These parameters can thus be used to set the resistance and thus the heat generated when current flows through.

When used as a mirror heater, the Nanotube composite system, which is often paper-like, is adhered to one side to the back of the mirror, preferably with power supply connectors attached to the other side of the composite system. When current flow is due to the electrical resistance of the composite system generates heat in the composite material, which then, for example, on passing a mirror adjacent to the heating element to de-ice it.

In principle, the heating element according to the invention can be operated with DC and AC voltage, in particular with the 12V DC voltage provided in automobiles, so that it can be used for the field of application in automobiles as exterior mirror heating and seat heating. Also, an operation with AC voltage, in particular 220 V, is possible, for example, for use as a mirror heater in the bathroom.

Preferably, the electrical contacts are all mounted on one side of the composite material, since the electrical resistance and thus the heat generated in the one-sided contacting is greatest.

In general, the resistivity of the composite comprising nanotubes at room temperature should be approximately between 600 and 7500 Ωmm ² / m, and more preferably between 75 Ωmm ² / m and 3,750 Ωmm ² / m.

Insofar as the specific resistance of the composite system is specified in this embodiment, the area A in the YZ direction in FIG. 5 [mm ² ] and the length L [mm] in the X direction enter into the same in accordance with the distance between the electrodes.

As part of the use in heating elements, carbon nanotubes adsorbed on cellulose fibers with a layer thickness of about 200 μm were used as the composite material, which have distinguished themselves by the required stability, easy processability and good thermal performance.

A change in the desired heat generation of the heating element can also be achieved simply by selecting a thicker or thinner sheet-like composite material, since the heating power achieved is also dependent on the layer thickness of the sheet-like composite material. The resistance and thus the recoverable heat can also be adjusted via the composition of the composite material or for a given composite material on the arrangement of the electrodes and their shape. The more contacts are provided on the composite material and the shorter their distance from each other, the lower the resistance.

Another advantage of the heating element according to the invention over the conventional is its lower susceptibility to corrosion. Also, the heat-generating composite material can be well attached, and it can be easily adapted to a variety of shapes, for example, by simply cutting with a pair of scissors. If desired, it can also be rolled or folded.

When used as a vehicle exterior mirror heater (12V voltage), the resistivity of the laminated composite should be between 600 and 7,500 Ωmm ² / m, preferably between 75 and 3,750 Ωmm ² / mm.

The resistance of the heating element according to the invention is in the temperature range between - 20 ⁰ C and + 20 ⁰ C substantially constant and slightly higher than in the conventional mirror heating.

Heating element, for example for use as a heat exchanger

A further variant of the present invention provides for the use of the composite material according to the invention in a heating element, wherein the composite material is formed as a planar layer and on each side of the sheet-like layer electrically conductive elements are provided which have a contact surface and abut the sheet-like layer, wherein the at least one composite system is received under at least light pressure between the elements.

As a result, a heating element is formed which is compact in its construction and can deliver the heat generated in the composite system to a solid, liquid or gaseous medium via the electrically conductive elements. By applying a voltage heat is generated in the composite system, with increasing heat, the resistance in the composite system is increased, which in turn a higher heat output can be achieved. As a result, a relatively high temperature can be achieved in a very short time.

As with the heating elements described above, this embodiment also has the advantage that the heat is not emitted at points, but distributed over the entire surface of the composite system evenly distributed to the contact surfaces. In addition, the composite system generates heat even when individual spots or areas should be damaged. This heating element is also adaptable to various shapes and geometries, so that in addition to a compact design, the use in different applications is possible. Advantageously, one or both contact surfaces can be pressurized. This reduces the contact resistance and increases the heat yield.

According to a preferred embodiment, it is provided that the contact surfaces of the electrically conductive elements are flat and plane parallel. This is preferably used with plate-shaped elements. This allows easy manufacture and assembly with the composite system. Alternatively, it can be provided that a corrugated or flat V-shaped shape of the O berfläche is provided to increase the contact surfaces. The opposing contact surfaces are formed congruent to each other, so that a uniform surface pressure of the sheet-like composite system between the two electrically conductive elements is given.

According to a further advantageous embodiment, it is provided that the electrical elements are formed of thermally conductive material. This allows a quick removal of the heat to the outside, ie away from the contact surfaces, carried out, whereby a transition of the heat energy is made possible in a solid, liquid or gaseous medium. For example, copper, silver, aluminum or the like can be used.

According to one embodiment, the electrically conductive elements are plate-shaped, half-shell-shaped, wave-shaped or formed by arbitrary free-forms, and have connection sections or heat-conducting elements opposite the contact surface. For example, slats may be provided as heat-conducting elements, which project into a flow channel, so that the flow of liquid and gaseous medium is heated. Likewise, the terminal portions may be formed as solid body portions which are to be heated or receive solid media for heating or have contact surfaces for heating solid media, liquid or gas-filled units.

According to a preferred embodiment of the invention, the electrically conductive elements take on the connection sections on chambers, which are flowed through by a liquid or gas. As a result, a heating of the liquid or of the gas can be achieved, the use of which is manifold. For example, such an arrangement may be provided in a boiler or hot water tank to heat the water or other liquid. Similarly, surface sections or volume of space can be heated. The heating element is preferably adjustable with respect to its maximum heating temperature by the preselected voltage. The composite system can be heated to a maximum temperature depending on its thickness, its design and its surface pressure acting thereon. By applying a specific voltage, the maximum heating temperature can be determined and limited.

According to a further advantageous embodiment of the invention, it is provided that a composite system in the form of a liquid or a gel is sprayed or applied to the contact surfaces of the electrically conductive elements. With the spraying or attachment of the composite system, the contact surfaces and the electrically conductive elements are optimally prepared and then positioned and fixed to each other.

Advantageously, it is provided that the at least one composite system has a layer thickness in a range of 50 to 1000 microns. With such a layer thickness, in particular in a range between 150 and 200 microns, a particularly rapid heating was made possible. For example, a temperature of about 110 ⁰ C was beginning with a starting temperature of about 28 ⁰ C within about 170 sec. Attained.

The invention will be described in more detail below with reference to exemplary embodiments.

I. Exemplary embodiments and experimental results on carbon nanotube cellulose adsorbates

1. Examples for Producing a Compound of Adsorbed Carbon Nanotubes According to the Invention

The nanotube / fiber composite systems according to the invention can be produced in various ways.

On the one hand, it is possible that the nanotubes according to variant A are dispersed directly with dry fibers in water (see the following experiment)

1).

Furthermore, the nanotubes according to variant B can be dispersed as a stock solution (cf., subsequent experiments 2 and 6) and added to a prepared pulp (cf subsequent experiments 3, 4, 5 and 7). For sheet formation, the suspensions can be used both on a professional sheet former, for example, the company Haage, as well as a standard laboratory filter slide.

The resistances quoted in ohms / cm were measured with the measuring cell of an Hewlett Packard LCR meter. The measuring cell consists of a circular contact in the center and an annular second contact, which is located at an exactly equal distance of 1 cm from the center. The digital LCR meter used uses a measuring voltage of 3 V for resistance determination.

The surface charges of the dispersions were measured using a PCD 03 from Mira Mütek.

1. The following example illustrates the direct use of carbon nanotubes and dispersion together with the pulp:

1 g of multi-walled carbon nanotubes (MWCNT) from Nanocyl Thin Multi Wall CNT and 4.0 g of eucalyptus cellulose from Ceasa are mixed in 250 g of water for 15 minutes with an ultrasound machine from Banelin with a power of 100% corresponding to 200 W dispersed. 100 g are diluted to a solids content of 0.5% and produced in a sheet former from Haage with a basis weight of 120 g / m ² . The resulting material has a resistance of 3.5 ohms / cm (corresponding to 27 ohms / sq). The covering is complete.

The material was additionally tested for actuation: Volt actuation resistance

0.4 0.1 μm 3.5 ohms

0.8 0.2 μm 3.5 ohms

Example 2 demonstrates the preparation of a mother suspension without the use of dispensing aids.

Preparation of a mother suspension of Ahwahnee Multi Wall CNT bundled (Ml): 2.5 g of nanotubes are slurried with 247.5 g of water. The material is dispersed with an ultrasonic device from Bandelin with 10% power corresponding to 20 W, duration: 1 hour. The re- sultϊerende stock solution contains nanotubes with a concentration of 1%.

3. In the following example, a mother liquor is used to prepare a material with a total content of 10% CNT: 15 g suspension from example 2 (ml) are diluted with 85 g deionized water with stirring. This suspension is added slowly with stirring to 135 g of suspension of a 1% suspension of Norland pulp. The resulting mixture is aspirated on a 50 micron mesh metal screen. The material has an ohmic resistance of 8.5 ohms / cm (corresponding to 65.5 ohms / sq). The composite contains nanotubes at a concentration of 10%, the coverage is complete.

4. This example shows the use of wool as a pulp: 0.3 g of a 19 micron roving wool is mixed with 50 ml of deionized water. 1 g of the mother liquor according to Example 2 are added. The wool threads are removed after a contact time of 30 minutes from the solution and felted by heating in boiling water. The wool composite has a resistance of 8 kΩhm / cm (corresponding to 61.6 kΩhm / sq).

5. In this example, a material is prepared which demonstrates the conductivity limit: 1.5 g suspension from Example 2 (Ml) are diluted with stirring with 80 g deionized water. This suspension is slowly stirred into 148.5 g of a suspension

1% suspension of Norland pulp. The resulting mixture is aspirated on a 50 micron mesh metal screen. The material has an ohmic resistance of 2.7 kOhm / cm (corresponding to 20.8 kOhm / sq). The composite contains nanotubes at a concentration of 1%. The calculated coverage is 0.83.

6. In this example, a strong cationic conductive resin is used to facilitate the deposition of CNTs on the fibers. Preparation of a mother suspension of nanotubes (M2): 1.5 g of nanotubes are slurried with 148.1 g of water. Thereafter, 1 g of Induquat 69L (Indulor Chemie) is added. The material is dispersed with an ultrasonic device from Bandelin with 10% power corresponding to 20 W, duration: 1 hour. The resulting stock solution contains nanotubes at a concentration of 1%. 7. This example demonstrates that the conductivity achieved is higher by using the cationic excipients than in Reference Example 3: 15 g suspension of Example 6 (M2) are diluted with stirring 85 g deionized water. This suspension is added slowly with stirring to 135 g of suspension of a 1% suspension of Norland pulp. The resulting mixture is aspirated on a 50 micron mesh metal screen. The material has an ohmic resistance of 3.4 ohms / cm (corresponding to

26.2 ohms / sq). The composite contains nanotubes at a concentration of 10%, the coverage is complete.

8. The following example shows the use of polyvinyl alcohol (PVA) as an aid. Although PVA is a very good dispersing agent for CNTs, it is also used for CNT compound materials. However, there are no advantages for the invention as a result of the addition of PVA, especially since the results without dispersing assistant according to test 3 are even better:

Preparation of a mother suspension (M3): 2 g of multi-walled carbon nanotubes (MWCNT) from the company Ahwahnee are slurried with 196.5 g of water. Thereafter, 1.5 g Mowiol 24/88 solution (10% in water, manufacturer Clariant) was added. The material is added with an ultrasonic device from Bandelin with 10% power accordingly. The material is dispersed with an ultrasonic device from Bandelin with 10% power corresponding to 20 W. Duration: 1 hour. The resulting stock quench contains nanotubes at a concentration of 1%.

9. 15 g suspension of Example 8 (M3) are diluted with stirring with 85 g of deionized water. This suspension is added slowly with stirring to 135 g suspension with 1% suspension of Norland pulp. The resulting mixture is carried on a metal screen

Sucked out 50 micrometers mesh size. The material has an ohmic resistance of 8.9 cm (corresponding to 68.5 ohms / sq). The composite contains nanotubes at a concentration of 10%. 2. Resistances of Naπotube adsorbates according to the above embodiments (measured with standard cell fHP)

Example CNT Surface Finish Resistance Pretreatment Area Content (%) Charge (mV) Ohm / cm Treatment CNT Weight

(Ohms / sq) g / m ² (mean)

20% - 230 3.5 Ohm / cm No 120

(27 ohms / sq)

10% - 150 8.35 ohms / cm No 120 (64.3 ohms / sq)

3.3% 50 8,000 ohms / cm None na (61600 ohms / sq)

1% - 280 2675 ohms / cm No 120 (20598 ohms / sq)

7 10% 360 3.4 ohms / cm ECR 120

(26.2 ohms / sq)

10% - 110 8.9 ohms / cm PVA 120

(68.5 ohms / sq)

3. Experimental results on the ratio of carbon nanotube molecules: fibers

In a series of experiments according to the invention resistances of various 150 g test specimens were measured, which differ in the ratio of carbon nanotubes: fibers. 10% carbon nanotube 8.4 ohms / cm (equivalent to 64.7 ohms / sq), 15% carbon nanotubes 2.9 ohms / cm (equivalent to 22.3 ohms / sq), 20% carbon nanotubes 2.4 Ohms / cm (equivalent to 18.5 ohms / sq), 30% 2.2 ohms / cm (equivalent to 16.9 ohms / sq). It is not difficult to see that only small increases in conductivity are achieved with further increase in concentration. In addition, as of 30% carbon nanotube content, increasing strength losses occur. This loss was made with nanocyl-multi-walled carbon nanotubes. 4. Calculation of the Coverage of Fibers with Carbon Nanotubes

Assuming cylindrical shape of the fibers, using conventional sources from the fiber diameter d and the lengths I, a ratio of surface A to mass m calculated that for long fiber pulps between 300 and 350 mrπ ² / mg corresponding to 3,000 cm ² / g. Thus, 1% carbon nanotube = 10 micrograms evenly distributed over the area of the pulp would have to reach a height of 10 mm ² /300,000 mm ² 30 nm. Even assuming a density of carbon nanotubes smaller than 1, this is close to monolayers.

5. Table

Surfaces of cellulose fibers and their mass are shown in the following table:

Column column

Density A / VA / md (mm) I (mm) AA ((rmr m ² ) V (mm ³ ) (g / cm ³ ) mm ² / mm ³ mm ² / mg

Example 0.1 1 0.33 0.0079 1 42.00 42.00

Lanqfasern

Fir 0.05 4.3 0.68 0.0084 0.41 80.47 196.26

Spruce 0.03 2.9 0.27 0.0020 0.43 134.02 311.68

Pine 0.03 3.1 0.29 0.0022 0.49 133.98 273.43

short fibers

European beech 0,0175 0,95 0,05 0,0002 0,68 230,68 339,23

Oak 0.018 1/1 0.06 0.0003 0.65 224.04 344.68

Poplar _{0.03 1/2 0.11 0.0008 0.4 135.00} 337.50

Mean 0.0293 2.2583 0.2661 0.0023 0.5100 156.36 300.46

d: diameter of the fiber A: surface of the fiber m: mass of the fiber I: length of the fiber V: volume of the fiber "Ullmann, Encyclopedia of Industrial Chemistry, 4th Edition

6. Table

Bedeckunqsqrad in the border region of the conductivity of three types of

Carbon nanotubes

No. Quality Surface Manufacturer Type Φ mm ³ spec.

Fiber Fiber CNT d CNT (mm) CNT / mg Density mm ² / mg Fiber

1. Spruce 312 Ahwahnee MWCNT 0.000035 0.010909 1.8

2. Spruce 312 Nanocyl MWCNT 0.000015 0.004675 1.8

3. Spruce 312 na SWCNT 0.000002 0.000623 0.9

mg mass conc. Experim. CNT (Theoret.) Corresponding

CTN / mg for Mono Limit Number of Beds Resistance

Fiber layer concentrate. (theoretical) degree

1. 0.0196 1.96% 1% 0.51 51% 2,700 ohms

2. 0.0084 0.84% 0.70% 0.83 83% 2.200 ohms

MWCNT: multi-walled carbon nanotubes SWCNT: single-walled carbon nanotubes

II. Process for the preparation of dispersions of nanotubes in dissolved polymers

In addition to the occupancy of cellulose fibers in the macroscopic range, attempts have also been made to use cellulose at the molecular level, that is, dissolved. The nanotubes are dissolved in the volume of the polymer and not just adsorbed on the surface. In the field of so-called rayon, two methods are generally known to bring cellulose into a soluble form: 1. The viscose process dissolves cellulose by using carbon disulfide.

2. The copper silk process uses the property of copper tetraarπine complexes to dissolve cellulose.

Since the technical literature describes the process as the one with the higher-grade results, only this process was used.

Since only a basic suitability should be tested, was dispensed with the use of spinnerets. In principle, however, this principle opens up possibilities for producing fibrous structures based on carbon nanotubes.

In the following Examples 1 and 2, the resulting dispersions are concentrated and the cellulose is re-precipitated by means of dilute sulfuric acid.

The polymers comprising the nanotubes can then be further processed, for example, into planar structures.

1st example:

8.3 g of copper sulfate with 5 mol of water of crystallization are dissolved in 200 ml of deionized water. A solution of 2.7 g of sodium hydroxide in 50 ml of water is added. The precipitated copper (II) hydroxide is filtered off and washed with deionized water. The still moist copper hydroxide is dissolved in 60 ml of 20% ammonia solution. This solution is mixed with 0.8 g of finely comminuted long-fiber pulp (manufacturer Bohemia). This mixture is kept for 12 hours in a closed PE container. Thereafter, the cellulose solution is mixed with 0.2 g of nanotubes and treated with 10% ultrasound for 45 minutes. In order to avoid a strong heating of the solution this happens in 3 stages of 15 minutes each. 15 g of this dispersion are strongly concentrated in a Petri dish. In a 1 l beaker, the mixture is mixed with a 3% sulfuric acid. The resulting, still soft product is washed three times with water and pressed between filter paper. The product has a resistance of 600 ohms / cm (equivalent to 4620 ohms / sq). 2nd example:

8.3 g of copper sulfate with 5 mol of water of crystallization are dissolved in 200 ml of deionized water. A solution of 2.7 g of sodium hydroxide in 50 ml of water is added. 31 g of the solution according to Example 3 are added to this solution. The copper hydroxide formed is filtered off together with the cellulosic / nanotube dispersion. The filter cake is taken after washing three times with 60 ml of 20% ammonia solution and subjected with stirring to a ten-minute sonication. 15 g of this dispersion are strongly concentrated in a Petri dish. In a 1 l beaker, the mixture is mixed with a 3% sulfuric acid. The resulting, still soft product is washed three times with water and pressed between filter paper.

The product has a resistance of 1,300 ohms / cm (equivalent to 10010 ohms / sq).

III. SEM images of different samples

SEM images of various samples are shown in Figures 1 to 4.

FIGS. 1 and 2 show an SEM image of a sample with a carbon nanotube content of 10% by weight on cellulose, FIGS. 3 and 4 the SEM images of a sample with a carbon nanotube content of 1% on cellulose.

Figures 1 and 2 and 3 and 4 differ in each case in the magnification.

The SEM images of the sample with a carbon nanotube content of 10% by weight on cellulose (FIGS. 1 and 2) could be made without sputtering with gold since they are already electrically conductive. Due to the low conductivity of the sample with a share of only 1 wt.% Carbon nanotubes was sputtered in this sample with gold.

In Fig. 1, the composite of carbon nanotubes and cellulose fibers can be seen, the cellulose is clearly visible in the surface topography. The cavities in the cellulosic structure are largely filled by carbon nanotubes.

In Fig. 2 it can be clearly seen how the surface of the cellulose fibers is covered with the carbon nanotubes. Also individual particles can be seen. In Fig. 3, the cellulose fibers and the unfilled voids between the fibers are shown.

In Fig. 4 can be seen on the surface very well individual nanotubes, not completely cover the surface of the cellulose fiber.

IV. Use of the nanotube comprehensive composite system according to the invention in heating elements

The use of the composite material according to the invention in heating elements is explained in more detail below using the example of a mirror heater and a heat exchanger. Show it :

5 shows a schematic representation of a mirror heater with the heating element according to the invention (exploded view),

6 shows the side of the inventive (a) and a conventional (b) heating element adhered to the mirror, FIG.

FIG. 7 various possible contacts (a, b) of the mirror heater,

8 shows comparison of the temperature at the mirror surface of the mirror when heated with an inventive "CNT mirror" and a conventional ( "Original mirror") heating at a temperature from - 10 ⁰ C (no ice),

9 shows comparison of the temperature at the mirror surface of the mirror when heated with an inventive ( "CNT-mirror) and a conventional (" Original mirror ") heating at a temperature from - 10 ⁰ C and Eiströpfchen at the mirror,

FIG. 10 shows temperature measurements on a device according to the invention

Heating element at different supply voltages as a function of time,

11 is a perspective view of another variant of the heating element for liquid and gaseous media,

FIG. 12 shows a diagram of a heating element in which the temperature is plotted as a function of the voltage, 13 shows a warm-up curve of a heat exchanger with the composite material according to the invention and FIG

Figure 14 is a perspective view of a heating element as a water heater.

A mirror heating with the composite material according to the invention is shown schematically in FIG. The planar, nanotube composite system 12 in this embodiment is a composite of carbon nanotubes adsorbed on the surface of cellulosic fibers. The composite material 12 is paper-like. With the side facing in the + z direction (in the xy plane), the composite material is adhered to the back of a mirror 16. On the in-z direction side of the composite material 12, which is also shown in Fig. 6 (a), the contacts 13, 14 (positive and negative electrodes) are attached to apply the voltage required for the current flow.

The application of the contacts can be done, for example, that they are glued directly to the surface of the composite material, the adhesive must of course be electrically conductive. Also, the contact strips can be glued to a foil and aligned with the contacting side on the surface of the composite system and all laminated together.

Further possibilities for the arrangement of the contacts on the in-z-direction facing surface are shown in Figure 7 a and b. FIG. 7a shows the simplest and most cost-effective arrangement of the electrodes. 7b shows "toothed" electrodes, because of the larger electrode area and the small distance between the electrodes, the resistance decreases.

The subsequent experiments with the heating element according to the invention as a mirror heating were carried out with DC voltage (low voltage), since this corresponds to the conditions in the automobile. For comparison, the experiments were also carried out with the conventional mirror heaters based on wound electric wires.

Widerstandsmessunqen

First, the nanotube composite material consisting of carbon nanotubes substantially adsorbed on cellulosic fibers was investigated and the following measurements were obtained: approx. 6,000 Ωmm ² / m - without power connection at ambient temperature + 20 ⁰ C, approx. 4,200 Ωmm ² / m - with a connection of 13.8 V and an ambient temperature of -10 ⁰ C

The investigated composite material of adsorbed carbon nanotubes was 200 μm thick (its surface was approximately 14,000 mm ² ).

For conventional heating the following values were determined: approx. 18 Ω (for the system with a connection of 13.8 V and an ambient temperature of -10 ⁰ C).

Measurement of the Spieqeltemperatur at ambient temperature of -10 ⁰ C with and without Eiwöpfchen on the mirror

In order to compare the inventive mirror heater with the conventional one, temperature measurements were made on the surface of the mirror when heated with the composite system according to the invention and heating with the conventional system.

The study of both systems was carried out under the following same conditions: air chamber (-10 ⁰ C), network supply 13.8 V, the mirrors were positioned vertically (as it is in the installed position as mirrors for cars the case), the decrease of temperature took place on the mirror surface.

In the first experiment, the results of which are shown in Figure 8, both mirror surfaces were free of ice or water droplets.

In the second experiment, the results of which are shown in Figure 9, the mirror surface was iced.

Since two different temperature sensors were used in the experiments, there is a slight deviation of 1.2 ⁰ C when comparing the measurements in the diagrams.

The measurements in FIGS. 8 and 9 show that with the heating elements according to the invention a faster heating takes place than with the conventional heating elements. In particular, in the heating element according to the invention, the temperature of 0 ⁰ C (melting temperature of the ice) is reached faster in the mirror with the heating element according to the invention than in the conventional heating element. The further temperature rise after The melting of the ice is also faster with the heating element according to the invention than in the conventional mirror heaters, which also brings a faster evaporation of thawed ice and condensation with it.

FIG. 10 shows the temperature increase (and thus the heating) as a function of the applied voltage in the low-voltage region on a heating element with the composite material according to the invention. The results show that temperatures of 100 ^° C. can be achieved with the heating element according to the invention.

The highest temperature increase (of about 100 ^° C.) is observed at the lowest voltage of 3V and the lowest temperature increase is observed at a voltage of 6V. The strongest temperature increase / time unit, ie the largest slope, is observed at the lowest voltage of 3V examined.

This makes it possible to limit the maximum temperature of the composite material by the applied voltage. This effect ensures thermal protection and safe operation.

FIG. 11 shows in perspective a further variant of the heating element 111 according to the invention, which can serve for heating liquid or gaseous media. Between two electrically conductive elements 112, a composite system 114 is provided which comprises nanotubes. Each of these electrically conductive elements 112 has contact surfaces 116 facing and resting against the composite system 114 and holding it between the elements 112. An unspecified fastening system, for example, by a detachable screw, clamping or clamping connection, an adjustable pressure on the elements 112 and their contact surfaces 116 can act on the sheet-like composite system 114. Alternatively, an adhesive connection may be provided. On one side of the heating element 111, a positive electrode 118 is connected to the one element 112 and, opposite to the element 112, a negative electrode 119 is provided. In addition, sealing or shielding elements can be provided between the two electrically conductive elements 112 in order to protect the laminar composite system 114 from external influences. The composite system 114 may be formed equal to or smaller than the contact surfaces 116. Several composite systems 114 may also be provided to form a large-scale composite system 114.

The heating of the composite system 114 as a function of the voltage is shown in FIG. When applying a voltage such as 6 volts, the heating element according to Figure 11 can be heated to a temperature of for example 125 ⁰ C. This temperature was tapped on the composite system 114. When applying a voltage of, for example 9 volts, a temperature of 150 ⁰ C can be achieved.

In FIG. 13, a warm-up curve of the heating element 111 shown in FIG. 11 is recorded by way of example. At a starting temperature of, for example, about 28 ^° C., a temperature of about 120 ^° C. is reached in less than about 180 seconds. In the above diagrams, a composite system 114 was used between two electrically conductive elements 112 made of aluminum, with the composite system 114 having a layer thickness in the range of 100 to 200 μm. A further increase in the temperature is not given at a constant voltage, so that over the preselected voltage with respect to a particular composite system 114, a temperature setting is possible.

In Figure 14, the heating element 111 of the invention is shown in an application as a water heater. On the respective outside of the electrically conductive elements 112, chambers 122 are provided at connection sections, each having a connection 123 for a supply line 124 and a discharge line 125. For example, a cool medium is supplied to the lower chamber 122 via the supply line 124. In the chamber 122, the heat transferred from the composite system 114 to the electrically conductive elements 112 is transferred to the chamber 122. Subsequently, the liquid is removed from the lower chamber 122 and fed to the upper chamber 122. From there, the heated liquid is supplied to the intended use.

The electrically conductive elements 112 and chambers 122 can in principle also be a unit.

To determine the efficiency of such a heating element 111, a measurement at the embodiment according to Figure 14 was carried out in the fresh water having a temperature of 22.3 ⁰ C the water heater according to FIG supplied fourteenth With an applied current of 10 ampere at a voltage of 15 volts initially at the outlet of the water heater, a temperature of 23.3 ⁰ C was measured. After a test period of 270 sec., A water temperature of 29.8 ⁰ C was measured. On the basis of this data and the experimental setup, the calculations yielded an efficiency of 0.92. Under the same conditions and water temperature and energy introduced, a comparative measurement was carried out with an immersion heater. Such a system yielded an efficiency of only 0.71 according to the calculations.

In the heating element 111 according to the invention, the length I of the resistivity in the Z direction is measured and thus corresponds to the thickness of the sheet-like layer and the area A corresponds to the area of the composite system which bears against the contact surface 116 of the electrically conductive element 112.

Thus, a powerful heating element 111 is provided, which is also designed to be robust in function and allows a variety of applications due to the optional geometric design. The laminar composite system 114 may be adapted to different geometries so as to enable different geometries of the electrically conductive elements 112 adapted to installation situations.

Claims

claims

1. Nanotubes comprehensive system, characterized in that the system is a Nanotubes and fibers comprehensive, in particular two-dimensional composite system and the nanotubes are adsorbed to the fibers substantially.

2. Nanotube comprehensive system according to claim 1, characterized in that the calculated degree of coverage of the nanotubes on the fibers is between 0.1 and complete coverage.

3. Nanotube comprehensive system according to claim 1 or 2, characterized in that the proportion of nanotubes in the composite system between 0.8 wt.% And 95 wt.%, Preferably between 2 and 30 wt.% And particularly preferably between 10 and 20 % By weight.

4. Nanotube comprehensive system according to one of claims 1 to 3, characterized in that the resistance at an increase in the calculated degree of coverage of 0.3 to 1, in particular from 0.4 to 0.9, leaps and bounds, that is by at least two orders of magnitude , decreases.

5. Nanotubes comprehensive system according to one of claims 1 to 4, characterized in that the fibers of the cellulosic, modified cellulose, cellulose derivatives, chitin, polyamide, polycrinonitrile, polyolefin, Teflon, silicate fibers, wool group consisting to be selected.

6. Nanotubes comprehensive system according to one of claims 1 to 5, characterized in that the nanotubes are carbon nanotubes, gold, boron nitride, silicon, substituted Carbonnanotubes, nanotubes of metal chalcogenides, metal chlorides or metal sulfides.

7. Nanotube comprehensive system according to one of claims 1 to 6, characterized in that the adsorbed on the fibers Na Notubes are aligned in the composite by orientation of the fibers in the composite in a preferred direction.

8. A method for producing a system comprising nanotubes, in particular according to one of claims 1 to 7, characterized in that nanotubes and fibers are dispersed in a dispersion medium.

9. A method for adsorbing nanotubes to fibers, in particular according to one of claims 1 to 7, characterized in that the nanotubes and the fibers are dispersed in a dispersion medium.

10. The method according to any one of claims 8 or 9, characterized in that the dispersion medium is subsequently separated and in particular filtered off.

11. The method according to any one of claims 8 to 10, characterized in that a pulp is mixed with the nanotubes and subjected to an ultrasonic treatment or the pulp is added a predispersed mother solution or dispersion of nanotubes.

12. The method according to claim 11, characterized in that the mother solution (or dispersion) and / or the pulp to which the nanotubes are added, between 0.1 and 5 wt.% Nanotubes, preferably between 0.3 and 4 wt. % and in particular between 1 and 3 wt.% Nanotubes.

13. The method according to any one of claims 8 to 12, characterized in that the solids content in the dispersion between 0.01 and 10 wt.%, Preferably between 0.1 and 5 wt.% And particularly preferably between 0.2 and 2 wt .% is.

14. The method according to any one of claims 11 to 13, characterized in that the mother solution or mother dispersion and / or the dispersion comprising the fibers and the nanotubes is substantially free of anionic surfactants.

15. The method according to any one of claims 8 to 14, characterized in that the dispersion medium is water, preferably deionized, an aqueous cationic surfactant solution, Polyvinylalkohollö- solution, dimethyl sulfoxide, vinyl pyrrolidone or kerosene.

16. The method according to any one of claims 8 to 15, characterized in that the fibers are aligned with the adsorbed nanotubes in the production of the composite.

17. The use of a system comprising nanotubes according to one of claims 1 to 7 in a heating element which comprises heat-generating means (12) and electrical contacts (13, 14) when current flows through, the heat-generating means (12) being a planar, Nanotube's comprehensive composite system that is electrically conductive.

18. Use of a system comprising nanotubes in a heating element according to claim 17, characterized in that the specific resistance of the composite system is between 600 and 7,500 Ωmm ² / m and more preferably between 750 and 3,750 Ωmm ² / m.

19. Use of a nanotube comprehensive system in a heating element according to any one of claims 17 or 18, characterized in that the Nanotubes comprehensive composite system a paper-thin composite system, in particular with a thickness between 20 microns and 10 mm and more preferably with a thickness between 100 microns and 500 microns, is.

20. Use of a system comprising nanotubes in a heating element according to one of claims 17 to 19, characterized in that the electrical contacts (13, 14) are each arranged on the same side of the composite material (12).

21. Use of the nanotube comprehensive system according to one of claims 1 to 7 in a heating element, which heating element at least one Nanotubes comprehensive composite system (114), which is designed as a sheet-like layer, and on each side of the sheet-like layer of the composite system (114) electrically conductive elements (112) having a contact surface (116) and abutting the sheet-like layer of the composite system (114), the at least one composite system (114) being received between the electrically conductive elements (112) at least under light pressure.

22. Use of the system comprising nanotubes according to claim 21, characterized in that the contact surfaces (116) of the conductive elements (112) planar and plane-parallel or congruent shaped surfaces, in particular corrugated or flat V-shaped forms have.

23. Use of the system comprising nanotubes according to one of claims 21 or 22, characterized in that the electrically conductive elements (112) are plate-shaped, half-shell-shaped, wave-shaped or by any free-form and the contact surface (116) opposite terminal portions o- the Wärmeleitelemeπte arranged are to heat directly or indirectly solid, liquid or gaseous media.

24. Use of the nanotube comprehensive system according to one of claims 21 to 23, characterized in that in particular liquid-flow-through chambers (122) can be attached to the electrically conductive elements (112).

25. The use of the system comprising nanotubes according to claim 24, characterized in that the electrically conductive element (112) and the chamber (122) are formed as a unit.