EP0743381A2 - Process for thermal stabilising of multi-layered products composed of polyacrylnitril fibres - Google Patents

Abstract

A process is claimed for the prodn. of multi-surfaced formed bodies consisting at least mainly of carbon fibres (CF) derived from polyacrylonitrile (PAN)-based starting material. The process comprises heating the corresp. body made of PAN fibres to 180-320 degrees C to convert the PAN into the infusible uncarbonised form and then passing gas contg. an oxygen-releasing substance through the body for 0.5-10 h, in amts. which are controlled so as to (a) maintain the necessary temp. for the chemical reactions required for thermal stabilisation of the fibres and (b) avoid overheating and consequent damage to the fibres. Also claimed are (i) formed bodies made of carbon fibres, obtd. by this process, and (ii) an appts. for the continuous thermal treatment of the above formed bodies made of PAN fibres.

Description

The invention relates firstly to a method for producing a multi-dimensional sheet-like structure composed of carbon or predominantly composed of carbon from a starting material consisting of polyacrylonitrile or essentially polyacrylonitrile, secondly a plant for carrying out the method and a felt produced by this method.

Mainly or entirely of carbon, multi-dimensional sheet-like structures made of fibers, such as woven fabrics, knitted fabrics, scrims, felts or nonwovens, which are based on organic polymers such as cellulose, wool, synthetic resins, pitch or polyacrylonitrile, are used in a wide variety of fields. They can be found, to name just a few applications, as flame-retardant textiles in vehicle seats or occupational safety agents, as insulating material that can be used under protective gas up to the highest temperatures, as corrosion-resistant filter material, depending on the quality, as electrically conductive or insulating substrates or as starting materials for Composites. A minimum requirement for the materials described here is that the fibers from which they are made have at some point been made infusible by thermal treatment and that the fiber structure has been retained despite the changes that have occurred in them. This thermal treatment is called oxidation or stabilization. It is carried out with the participation of oxidizing agents and should be conducted so that the fibers of the textile structure used have certain properties. For reasons of rational production, it would be desirable perform this stabilization process on entire webs of material in a continuous manner. With some types, such as textile materials made of cellulose, this is already possible today. In the case of multi-dimensional sheet-like structures based on polyacrylonitrile, hereinafter called PAN, which have been built up from fibers, web stabilization in continuous operation has so far not been able to be carried out economically and the discontinuous stabilization of material webs or pieces that are not quite thin is problematic. Thermally stabilized, multi-dimensional sheet-like structures based on polyacrylonitrile are therefore still produced today by a comparatively complex process, by first thermally stabilizing the PAN fibers as such, i.e. making them infusible, and then the stabilized fibers to form the various multi-dimensional sheet-like structures processed further. In the case of felts, the thermally stabilized fibers first have to be crimped, then cut into staple fibers and then a felt has to be made from the staple fibers in a last step. Such a process is cumbersome and time-consuming because the PAN fibers lose part of their textile properties during thermal stabilization and are then more difficult to process into the various textile structures. The application of the method is necessary, however, because during thermal stabilization, strongly exothermic reactions take place in the fiber and because of the hindrance of the heat transfer when stabilizing entire textile layers or webs, the fibers adiabatically overheat and as a result the fibers melt or burn off . These reactions, namely the dehydrogenation of the polymer under the action of oxidizing agents, especially oxygen, its cyclization to a heteroaromatic conductor polymer and further Chemical crosslinking and undesired but not completely suppressable unspecific oxidation of the polymer take place in parallel (see e.g. E. Fitzer, DJ Müller, Carbon, 13 (1975) pp. 63-69) and can only be influenced to a very limited extent by procedural measures. But even if it is possible to prevent the destruction of the fiber structure, the fibers will be damaged if the temperature is not optimal. Such damage can be, for example, excessive embrittlement or excessive oxygen uptake, which results in high oxidation and thus loss of quality in the subsequent carbonization step.

The invention was therefore based on the object of a method for the direct transfer of polyacrylonitrile or essentially polyacrylonitrile, multi-dimensional sheet-like structures composed of fibers, such as, for example, woven, knitted, knitted, laid, felted, nonwoven, into the infusible, non-carbonized form to provide in one process step. The task was, in particular, to provide a continuously operating method of this type, which offers the possibility of precisely regulating the reaction temperatures in the flat structures as a function of time. Another object was to provide a device or system by means of which the method according to the invention can be carried out. Finally, it was also an object of the invention to provide multidimensional flat structures made of infusible but not carbonized fibers, which were produced using the new method.

The object is achieved by a method having the characterizing features of claim 1. The others Claims contain the solution to the other stated objects or embodiments of the invention. They are hereby introduced into the text of the description.

The term "non-meltable, non-carbonized form" of fibers or of multi-dimensional sheet-like structures made of fibers used in the claims and in the description is synonymous with the term "thermally stabilized" or "stabilized" fibers or fiber-made multi-dimensional sheet-like structures and was used to clearly differentiate this thermal treatment stage of the fibers or flat structures from those stages which are reached at temperatures above 320 ° C. and which are either designated with “partially carbonized”, “carbonized” or with “graphitized”. For the term "multi-dimensional sheet-like structure constructed from fibers", the term "fabric web" is also used in the following due to the shorter spelling.

At the beginning of the stabilization process, the filaments in the fabric must be supplied with sufficient heat to start the reactions taking place during stabilization. From the time of the start, the total of the enthalpies of reaction is strongly exothermic and the reactions would go off with the consequence of the melting or burning of the material web, if this did not prevent the use of control measures. The essential feature of the method according to the invention is that the multi-dimensional sheet-like structures or fabric webs made up of PAN fibers are characterized by a gas or gas mixture which is tempered in an appropriately adapted manner during the entire thermal stabilization phase characterized by the initial heat requirement and the subsequent exothermic area is flowed through. In the start-up phase, such an amount of heat is applied to the fibers transferred that the stabilization reactions begin to take place. Thereafter, the gas cools the fibers to such an extent that the exothermic reactions take place at the specified temperatures and in the final phase, when the heat builds up in the fibers as the reactions subside, heat is optionally added again in order to maintain the desired reaction temperature and to finish stabilization quickly. During the entire stabilization phase, the gas flowing through also serves as a medium for mass transport. It transports oxygen or oxygen carriers to the fibers and leads gaseous reaction products such as H ₂ O, CO ₂ , CO or HCN away from the fibers. Since the material transitions to and from the fiber run in a diffusion-controlled manner, it is advantageous to work with comparatively high flow velocities in the fabric web in order to achieve thin phase interfaces on the fibers. This also meets the requirement for the best possible heat transfer conditions.

For the method according to the invention to be carried out successfully, the temperatures prevailing in the fabric web, which are control variables for the gases flowing through the fabric web and regulating the temperature in it, need to be recorded precisely. This is not a problem in discontinuous operation. Thermocouples can be arranged in the fabric by means of which measurement and control are carried out. The situation is different with the preferred continuous driving style. An indirect method must be used to adjust and maintain the temperatures in the fabric. The procedure is as follows: In a discontinuously operating test apparatus, in which an exact measurement of the temperature inside the multi-dimensional flat structure, for example by means of thermocouples is possible, the temperature range in which the desired quality of the multi-dimensional sheet-like structure consisting of fibers is obtained in the thermally stabilized state is first determined by varying the parameters composition, temperature and flow velocity of the gas. Thereafter, if this is still necessary, the given parameters, such as the temperature and the flow rate and, if necessary, the pressure of the flow-through, which are necessary for the correct and economical reaction management, can be provided by specifying the temperature curves which serve as a reference variable and which lie within the temperature range previously measured in the fabric web Gases are set. The apparatus for carrying out the experiments mentioned is described elsewhere in this document. Those parameters determined according to the method described above, which can be easily measured and controlled even in a continuously operating system and which are used to set and maintain the desired temperature profile in the fabric, are then transferred to the production system. The monitoring and fine control of the temperature of the fabric in this system can then, if necessary, be done, for example, by measuring the temperature difference between gas flowing in and out of the fabric or, in the case of thin fabrics, by measuring the surface temperature of the fabric. The temperature profile during the stabilization can be controlled isothermally after the start of the reactions involved in the stabilization, decreasing starting from a certain temperature level or increasing starting from such a temperature level. Where necessary, combinations of the three types of temperature profiles mentioned can also be used.

An important parameter, particularly influencing the economics of the process, is the time required for the stabilization reaction. Of course, the aim will always be to carry out this reaction in the shortest possible time. Since the stabilized fabric webs produced, depending on their later intended use, must have certain material properties and, as will be shown later, these depend strongly on the stabilization conditions, in many cases the shortest possible time, i.e. run at the highest possible temperature. The quality requirements, the temperature profile and the time required for the stabilization reaction must be optimized.

The method can be used to stabilize a wide variety of types of multidimensional flat structures produced using PAN fibers. The differences relate to the thickness of the flat structures - fabrics or nonwovens with a thickness in the range of tenths of a millimeter to felts in the range of 10 cm and above can be stabilized - also to the material composition - pure PAN or PAN with copolymers or Additions - the type of manufacture of the fibers and yarns - for example, yarns made from staple fibers or filaments - or the type of manufacture of the multidimensional flat structure and thus the fiber arrangement and the density or packing of the fibers in the structure such as weaving, knitting, knotting , Work, matting, confusion. Generally speaking, all multi-dimensional flat structures made of PAN fibers can be thermally stabilized, through which gas can flow.

Each of the qualities of flat structures has its own stabilization characteristics and accordingly the driving style must be determined for each of these qualities through tests. The following examples illustrate the necessity for this procedure: A fabric web, for example a felt, in which the fibers are arranged very close to one another, has a high energy density in the reactions taking place during the stabilization, its thermal insulation capacity is very good and it is comparatively difficult to flow through. Driving too fast at too high temperatures would damage the fabric until the reaction went through. At first glance, it seems that it is loose but made of very thick fibers or bundles of fibers, e.g. a fabric, scrim or knitted fabric, also has to be stabilized relatively slowly and at temperatures that are not too high, because here, despite good possibilities for heat transfer and removal, flowing gas overheating of the interior of the fibers or fiber bundles must be avoided and the stabilization reactions take a certain time because of their diffusion-controlled process. On the other hand, a thin fabric web of loose fiber structure made of thin threads, which can be stabilized in a relatively short time at a comparatively high temperature, is relatively unproblematic. Given the above, it is difficult to specify a preferred driving style. Because of the importance of the invention for high mass throughputs on fabric webs, however, the preferred method is that which has the shortest time for thermal stabilization if certain quality criteria are met for the fabric web.

Instead of using a gas or a gas mixture with a uniform composition, stabilization can also be carried out with gas mixtures are carried out, the composition of which changes during the stabilization reaction or an inert gas, for example nitrogen or argon, is used for part of the reaction and the gas containing an oxidizing agent is used for the other part. In this way you can, for example, delay the course of the reactions involved in the stabilization by initially suppressing the dehydrogenation and oxidation reactions and thus their shares in the enthalpy of reaction in the fibers under inert gas and making up for these reactions in the second stage under oxidizing conditions. In the opposite case, the fibers can first be pre-oxidized and loaded with oxygen under oxidizing conditions and the reactions can then be completed under inert gas in the manner envisaged.

The temperature range within which the stabilization is generally carried out is between 180 and 320, preferably between 220 and 260 ° C., these temperatures being defined as the temperatures which the gas flowing through the fabric web has on the upstream side. The temperatures of the individual fibers in the fabric web can be up to a maximum of 10 K above the temperatures of the inflowing gas when the specified gas temperatures and proper reaction sequence are used. Depending on the textile structure of the fabric web, dimensions and the shape and material composition of the fibers of the fabric web, the stabilization is carried out within a period in the range from 0.5 to 10 hours, preferably from 0.5 to 6 hours. Of course, the stabilization can also be carried out with considerably longer times, however, the process then becomes increasingly uneconomical and the flat structure or its fibers can suffer, for example due to excessive oxygen absorption, quality losses.

The presence of oxygen is necessary for the course of the dehydrogenation reaction of the PAN polymer, which is an integral part of the stabilization process. Suitable oxygen donors are all oxygen-releasing substances which can be converted into gas or vapor form, but especially molecular oxygen, ozone, sulfur trioxide, nitrogen dioxide or nitrous oxide, nitrous oxide or laughing gas and nitrogen monoxide. These substances are generally used in cases where this is possible, not in pure form, but in a mixture with an inert carrier gas. The proportion of substances consisting of or containing oxygen is preferably 20 percent by volume, based on the gas mixture, equal to 100%. The particularly preferred gas mixture used is air.

Partial carbonization, carbonization and graphitization can follow the stabilization process for further processing of the multi-dimensional flat structures as additional, subsequent process steps. For this purpose, one or more of these additional process steps can be carried out in plants which are coupled to the oxidation plant or which are part of this plant. The partial carbonization is carried out in a manner known per se in the temperature range from 320 to 800 ° C., preferably from 500 to 700 ° C., in an inert atmosphere. In this process step, which can also be carried out continuously, the carbon content of the material webs is further increased by releasing hydrogen, oxygen and heteroatoms, in particular nitrogen, and the degree of crosslinking of the carbon skeleton in the filaments is increased. At the same time, flame resistance, temperature and corrosion resistance increase, whereby the flexibility of the fibers in the Fabric web is largely preserved. Partially carbonized panels can be used, for example, for flame-retardant textiles, insulating linings, as filter material or for the production of composite materials.

Partial carbonization can be followed by carbonization, which is carried out in an inert atmosphere in the temperature range from 800 to 1800 ° C., preferably from 800 to 1400 ° C. In this process, which can also be carried out continuously, the fibers forming the multidimensional flat structure are completely converted into carbon. Such multi-dimensional flat structures can be used under protective gas up to the highest temperatures. They are extremely corrosion-resistant and have a comparatively high electrical resistance. Therefore, they can be used, for example, as filter material or as substrate material for catalytic or electrochemical applications. Felts so produced can e.g. can also be used as a high-temperature insulating material in a non-oxidizing atmosphere due to their heat-insulating properties. The main area of application for carbonized material webs, however, is the production of composite materials, in particular composite materials with a synthetic resin or carbon matrix.

The last thermal finishing stage to which the multi-dimensional sheet-like structures produced by the process according to the invention can be subjected is graphitizing, which is carried out in an inert atmosphere in the temperature range from 1800 to approximately 3000 ° C., preferably in the range above 2000 ° C. This process step can also be carried out continuously, for example with a system according to DE utility model 72 31 623.

Each of the multi-dimensional sheet-like structures produced by one of the methods described is suitable for the production of a wide variety of composite materials. By selecting the appropriate combination of fabric and matrix, suitable materials for a variety of applications can be produced in conjunction with appropriate further processing and / or finishing steps such as carbonizing, graphitizing, impregnating, coating, siliconizing or activating.

• Bei der Herstellung von aus thermisch stabilisierten Fasern auf Basis PAN bestehenden mehrdimensionalen flächigen Gebilden fällt der bisher notwendige Umweg, zuerst PAN-Fasern thermisch zu stabilisieren und dann diese thermisch stabilisierten Fasern, die im Vergleich zu den nicht stabilisierten Fasern aus PAN wesentlich steifer und damit mechanisch empfindlicher und textil schwerer verarbeitbar sind, zu Stoffbahnen zu verarbeiten, nunmehr weg. Dieser Vorteil ist besonders dort groß, wo die Fasern, wie dies beispielsweise bei der Herstellung von Filzen geschieht, zur Weiterverarbeitung gekräuselt oder/und zu Stapelfasern verarbeitet werden müssen, ehe daraus Stoffbahnen hergestellt werden. Stoffbahnen aus PAN-Fasern können jetzt direkt thermisch stabilisiert werden. Bei dieser Verfahrensweise ist es von Vorteil, daß die Herstellung von mehrdimensionalen flächigen Gebilden aus PAN-Fasern unproblematisch ist und letztere deshalb in einer Vielzahl von Qualitäten kommerziell verfügbar sind.
• Das Verfahren kann kontinuierlich durchgeführt werden. Dadurch ist es möglich, bezüglich der Verteilung ihrer Stoffeigenschaften gleichmäßigere und damit qualitativ bessere thermisch stabilisierte Stoffbahnen auf Basis PAN wirtschaftlicher herzustellen.
• Als Folge der gleichmäßigeren Verteilung der Stoffeigenschaften ergeben sich bei der Weiterverarbeitung der Stoffbahnen, insbesondere beim Teilcarbonisieren, Carbonisieren und Graphitieren Verarbeitungsvorteile. Die nach diesen Verarbeitungsstufen erhaltenen Stoffbahnen haben ebenfalls eine bessere Qualität.

The described method has the following advantages:

• In the manufacture of multi-dimensional sheet-like structures consisting of thermally stabilized fibers based on PAN, the previously necessary detour is to first thermally stabilize PAN fibers and then these thermally stabilized fibers, which are much stiffer and thus mechanically compared to the non-stabilized fibers made of PAN more sensitive and more difficult to process textile, to process into webs, now gone. This advantage is particularly great where the fibers, as is the case, for example, in the manufacture of felts, have to be crimped for further processing and / or processed into staple fibers before fabric webs are produced therefrom. Panels of PAN fibers can now be thermally stabilized directly. With this procedure, it is advantageous that the production of multi-dimensional flat structures from PAN fibers is unproblematic and the latter are therefore commercially available in a large number of qualities.
• The process can be carried out continuously. This makes it possible to distribute their Fabric properties more uniform and therefore better quality thermally stabilized panels based on PAN more economically.
• As a result of the more even distribution of the material properties, there are processing advantages in the further processing of the fabric webs, in particular in the case of partial carbonization, carbonization and graphitizing. The panels obtained after these processing stages are also of better quality.

In the following, the apparatus for determining the parameters with which the method is controlled in a continuous mode of operation and then the system for the continuous thermal stabilization of multidimensional flat structures based on PAN fibers are first described as examples.

• Zwei Stellen zum Messen der Strömungsgeschwindigkeit im Anströmbereich in Teilrohr 1, in Rohrmitte 10 und in Wandnähe 10',
• zwei Stellen zum Messen der Temperatur im Anströmbereich in Teilrohr 1, in Rohrmitte 11 und in Wandnähe 11',
• eine Stelle zum Messen des Gasdrucks 12 im Anströmbereich,
• zwei Stellen zum Messen der Temperatur in der, bzw. direkt an der Stoffbahn, in der Mitte 13 und im Randbereich 13',
• eine Stelle zum Messen des Gasdrucks 14 im Abströmbereich hinter der Stoffbahn,
• zwei Stellen zum Messen der Temperatur im Abströmbereich, in Rohrmitte 15 und in Wandnähe 15',
• eine Stelle zum Messen der Strömungsgeschwindigkeit 16 im Abströmbereich.

Fig. 1 shows a schematic representation of a flow tube consisting of two partial tubes 1, 1 'with an inner diameter of, for example, 12 cm made of a temperature and temperature change resistant device glass (Duran). Each of the partial tubes 1, 1 'has a flange 2, 2' on the side facing the center of the flow tube, by means of which the two partial tubes 1, 1 'have been clamped together by known means to form the flow tube. A graphite or a temperature-resistant PTFE seal 3 is clamped between the flanges 2, 2 'as a seal. At the other end of the partial pipes 1, 1 'is the inlet 4 (partial pipe 1) or outlet 5 (partial pipe 1'), not shown, for the gas flowing through the pipe. On the side of the gas supply there is also a delivery device 17, heating device 6 and control device for the gas flow which is only shown schematically. In the middle of the flow tube is a disc 7 from the testing fabric together with a comparatively coarse mesh 8 made of thin wire made of chrome-nickel steel (mesh size 3 to 5 mm, wire thickness approx. 0.2 mm) with the interposition of two rings of commercially available flexible graphite in the flange area between the flanges 2, 2 'clamped. The wire mesh 8 supports the fabric web 7 and prevents it from bending at higher flow pressures. A perforated plate 9 is provided in the first third of the partial tube 1 for uniform distribution of the gas entering the partial tube 1 at the inlet 4 over the cross section of the flow tube. The following measuring points are located in the flow tube to measure the values for the temperature, the flow rate and the gas pressure:

• Two points for measuring the flow velocity in the inflow area in partial pipe 1, in pipe center 10 and near wall 10 ',
• two points for measuring the temperature in the inflow area in partial pipe 1, in pipe center 11 and near wall 11 ',
• a point for measuring the gas pressure 12 in the inflow area,
• two points for measuring the temperature in or directly on the fabric web, in the middle 13 and in the edge area 13 ',
• a point for measuring the gas pressure 14 in the outflow area behind the fabric web,
• two points for measuring the temperature in the outflow area, in pipe center 15 and near wall 15 ',
• a location for measuring the flow velocity 16 in the outflow area.

At the end of the outflow area of the apparatus, after a gas cooling section (not shown), there is a speed-controllable fan 17 ', by means of which a differential pressure to the pressure in the inflow area can be regulated in order to improve the flow through the fabric web in the outflow area.

2 shows a system for the continuous thermal stabilization of multi-dimensional flat structures based on PAN fibers in a schematic representation, not to scale. A fabric web 18 is unwound from a web roll 20 located on an unwinding unit 19, on a grating 21, preferably a wire grating made of thin wires and with large open meshes, through an oven 23 consisting of at least one spatial section 22, in which the conditions for the thermal stabilization is maintained, transported and wound up on a winding device 24 after leaving the furnace 23. The grating 21 is expediently moved through the oven 23 in synchronism with the fabric web 18. For this purpose, it runs as an endless belt with the aid of driven rollers 25, 25 '. Another known method can also be used here. When passing through the furnace 23, which takes place during a certain predetermined time, the fabric web 18 is flowed through by a certain amount of gas, which has a predetermined composition and temperature and is coordinated with the respective stabilization task. To control and regulate the temperature and flow conditions in the furnace 23, measuring points for the are in the inflow area above the fabric web 18 and in the outflow area below the fabric web Temperature (T), for the gas pressure (p) and for the flow velocity (v) installed. Using correspondingly switched control loops, the heaters 26 for temperature control of the inflowing gas, the fans 27 in the inflow area for generating the desired gas flow and the fans 28 in the outflow area for the removal of the gases from the outflow area and for the maintenance are used by means of the values measured at these points of the differential pressure required for an effective flow through the fabric web 18. Grids or perforated plates 32 are provided for generating a gas flow which is uniform over the cross section of the respective department 22, 22 ', 22'',22''' of the furnace 23. In the case of thermal stabilizations which are not critical, for example in the case of thinner, easily flowable material webs, the fans 28 in the outflow area can also be omitted. The measurement of the gas temperatures in the inflow and outflow areas serves to control the temperature conditions in the fabric and allows important conclusions to be drawn about the correct course of the reaction and the quality of the fabric. In an isothermal mode of operation with a gas of constant composition, the subdivision of the furnace 23 into sections 22, 22 ', 22'',22''' can be omitted. However, if the stabilization reaction is to be carried out using certain temperature gradients or with gases of different compositions, the furnace must be divided into sections 22 in which the process parameters can be regulated independently of those of other sections 22. The number of four departments 22, 22 ', 22'',22''' has only been given here as an example. Depending on the procedural requirements, the system may also contain fewer or more departments 22. Since the fabric web 18 is always moved through the oven at a constant speed, the residence time of the fabric web 18 must be in the individual departments 22 are regulated by the extent, ie width, of the departments 22 in the direction of travel of the fabric web 18. Mixing of the gas streams of adjacent chambers 22 regulated at the same pressure level is avoided in addition to the partition walls of the departments 22 reaching down to just above the fabric web by maintaining a slight underpressure in the outflow chambers compared to the pressure in the inflow chambers. The gas pressures in the flow chambers should not differ too much from one another. Any gases escaping at the furnace inlet 29 or outlet 30 are collected in suction lock boxes 31, 31 'located there.

In the following, the invention is further explained on the basis of exemplary embodiments which are shown in the form of test overviews in Tables 1, 2 and 3.

All tests for thermal stabilization were carried out either with commercially available felts made from PAN fibers Dolanit® 10 or with fabrics made from PAN fibers based on Dolan® 25 or Dolanit® 12 in a pilot plant as shown in Figure 1 with air flowing Gas carried. The thermally stabilized multi-dimensional sheet structures thus obtained were subsequently carbonized under uniform inert conditions in a shaft furnace with a maximum temperature gradient of 10 K / h for 5 days. Tables 1, 2 and 3 above are the data characterizing the starting material (PAN felt or PAN fabric), then the temperature / time conditions under which the thermal stabilization was carried out, and then some characteristic data for the thermally stabilized flat structures recorded. This is followed by information on experiments which show that the multidimensional ones thermally stabilized by the process flat structures can be further refined by subsequent process steps, for example by carbonizing.

The test results show that webs of different qualities based on PAN can be thermally stabilized using different process conditions according to the process described above. It can further be seen from the test results that the properties of the stabilized fabric produced can be influenced by the choice of process conditions for thermal stabilization. This proves that with the method according to the invention, after carrying out simple preliminary tests, it is possible to produce multi-dimensional sheet-like structures with predetermined properties in a targeted manner from thermally treated PAN fibers.

Reference list

1, 1 '

Partial tubes made of glass

2, 2 '

Flanges on 1, 1 '

3rd

poetry

4th

Gas supply

5

Gas discharge

6

Heating and control device (schematic)

7

Disc made of multidimensional flat fiber structures

8th

Wire mesh

9

Perforated plate

10, 10 '

Locations for measuring the flow velocity in the inflow area

11, 11 '

Temperature measuring points in the inflow area

12th

Gas pressure measuring point in the inflow area

13, 13 '

Temperature measuring points in multi-dimensional flat fiber structures

14

Gas pressure measuring point in the outflow area

15, 15 '

Temperature measuring points in the outflow area

16

Point for measuring the flow velocity in the outflow area

17th

speed-controlled fan in the outflow area

17 '

speed-controlled fan in the inflow area

18th

Web from the multi-dimensional flat fiber structure

19th

Unwinding unit

20th

Roll from the multidimensional flat fiber structure

21

Grating

22, 22 ', 22' ', 22' ''

Departments of the furnace

23

oven

24th

Take-up device

25, 25 '

Rollers for the circulation of the supporting grate

26, 26 ', 26' ', 26' ''

Heaters for the gas

27, 27 ', 27' ', 27' ''

Fans in the inflow area

28, 28 ', 28' ', 28' ''

Fans in the outflow area

29

Oven entrance

30th

Furnace exit,

31, 31 '

Lock boxes on 29 and 30

32, 32 ', 32' ', 32' ''

Grid to equalize the gas flow

Claims (18)

Process for the production of a multi-dimensional sheet-like structure consisting of carbon or predominantly of carbon and made of fibers from a starting material consisting of polyacrylonitrile or essentially of polyacrylonitrile,
characterized in that
the multi-dimensional sheet-like structure consisting of fibers of polyacrylonitrile or essentially of polyacrylonitrile for conversion into the non-meltable, non-carbonized form while maintaining its textile structure with a gas containing an oxygen-releasing substance heated to temperatures in the range from 180 to 320 ° C. is flowed through for a time of at least 0.5 and at most 10 hours, the amount of gas flowing through the flat structure being regulated such that, on the one hand, the temperatures in the flat structure are always maintained which are essential for the course of the thermal stabilization of the polyacrylonitrile or essentially Fibers consisting of polyacrylonitrile are necessary chemical reactions are necessary and on the other hand, a harmful overheating of these fibers does not occur in the flat structure. Method according to claim 1,
characterized in that
a gas containing an oxidizing agent from the group consisting of oxygen, ozone, SO ₃ , NO ₂ , N ₂ O, NO is used to flow through the multidimensional flat structure composed of fibers. Method according to claim 1,
characterized in that air is used as the oxidizing agent for converting the multi-dimensional sheet-like structure consisting of the organic polymer into the non-meltable, non-carbonized form. Method according to one of claims 1, 2 or 3,
characterized in that
the multidimensional sheet made of the organic polymer for conversion into the non-meltable, non-carbonized form first with an inert gas heated to temperatures in the range from 180 to 320 ° C. and then with a gas containing an oxidizing agent, the temperatures in the range of Has 180 to 320 ° C, is flowed through. Method according to one of claims 1, 2 or 3,
characterized in that
the multi-dimensional sheet-like structure consisting of the organic polymer for conversion into the non-meltable, non-carbonized form first with a gas containing an oxidizing agent heated to temperatures in the range from 180 to 320 ° C. and then with an inert gas having temperatures in the range of Has 180 to 320 ° C, is flowed through. Method according to one of claims 1 to 5,
characterized in that
the multi-dimensional sheet-like structure consisting of the organic polymer is flowed through when being converted into the non-meltable, non-carbonized form with at least one gas which has temperatures in the range from 220 to 260 ° C. Method according to one of claims 1 to 6,
characterized in that
the multi-dimensional sheet-like structure consisting of the organic polymer is flowed through for at least one gas heated to temperatures in the range from 180 to 320 ° C. for a period in the range from 0.5 to 6 hours when it is converted into the non-meltable, non-carbonized form. Method according to one of claims 1 to 7,
characterized in that
it is carried out continuously. Method according to one of claims 1 to 8,
characterized in that
the multidimensional flat structure converted into the non-meltable, non-carbonized form is additionally partially carbonized at temperatures in the range from 320 to 800 ° C. under non-oxidizing conditions. Method according to claim 9,
characterized in that
the multidimensional flat structure converted into the non-meltable, non-carbonized form is partially carbonized at temperatures in the range from 500 to 700 ° C. Method according to one of claims 1 to 10,
characterized in that
the multidimensional flat structure converted into the non-meltable, non-carbonized form is additionally carbonized in the temperature range from 800 to 1800 ° C after passing through the temperature range from 320 to 800 ° C. Method according to claim 11,
characterized in that
carbonization is carried out in the temperature range from 800 to 1400 ° C Method according to one of claims 1 to 12,
characterized in that
as a multi-dimensional flat structure, a fabric web produced by a weaving, knitting or knitting method is used. Method according to one of claims 1 to 12,
characterized in that
a fleece or a felt is used as a multi-dimensional flat structure. Multi-dimensional flat structure made of carbon or predominantly made of carbon,
characterized in that
it has been produced by one of the methods according to claims 1 to 13. Device for the continuous thermal treatment of multi-dimensional sheet-like structures (18) consisting of fibers made of polyacrylonitrile or essentially made of polyacrylonitrile with a
Unwinding (19) and winding device (24),
a gas-permeable transport path (21) arranged between the unwinding (19) and the winding device (24) for a multi-dimensional sheet-like structure (18) consisting of fibers
and
one around part of the transport path (21) for the multi-dimensional sheet-like structure (18) consisting of fibers arranged furnace (23), through which the multi-dimensional sheet-like structure (18) consisting of fibers can be transported on the transport path (21),
characterized in that
the furnace (23) has at least one chamber-like section (22) through which the multi-dimensional sheet-like structure (18) consisting of fibers can be transported,
that devices (27) are present, by means of which gases can be conveyed through the at least one chamber-like section (22),
that devices (26) are present, by means of which the gases flowing through the at least one chamber-like section (22) can be heated in a controlled manner,
that the at least one chamber-like section (22) is equipped (32) such that the tempered gases flow as uniformly as possible in the direction of the multi-dimensional sheet-like structure (18) consisting of fibers and flow through it,
that, viewed in the direction of the gas flow, devices (28) are present behind the multi-dimensional sheet-like structure (18) consisting of fibers for the removal or suction of the gases which have flowed through the multi-dimensional sheet-like structure (18) consisting of fibers,
and that, viewed in the direction of the gas flow, devices (T, p, v) are present in the at least one chamber (22) for measuring and regulating the gas temperature and the state of flow of the gas at least in front of the multi-dimensional sheet-like structure (18) which regulates the temperature and / or the gas flow of the flowing gas in the at least one chamber-like section (22) to specific, predetermined values. Device according to claim 16,
characterized in that
Seen in the direction of the gas flow, devices (T, p, v) for measuring and regulating the gas temperature and the state of flow of the gas are present in the at least one chamber-like section (22) before and after the multi-dimensional sheet-like structure (18) consisting of fibers. Device according to one of claims 16 and 17,
characterized in that
for monitoring and regulating the flow state of the gas, measuring and regulating devices for the gas pressure (p) and the gas velocity (v) are present.

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