DE2204749A1 - Isotropic carbon bodies prodn - by pyrolysing aromatic resins of high glass temperature - Google Patents

Abstract

Materials or components of cpd. bodies consisting of isotropic C are produced by thermal breakdown, in a non-oxidising atmos., of a linear polymer, with at least partly aromatic structure, with a Tg >500 degrees C. Such polymers combine the advantages of the thermoplastic binders and the hard, cross-linked duroplasts. C yields are >50%. C bodies reinforced with C fibres are made by pyrolysing moulded polymer bodies contg. not 10 vol.% C fibres or fabric. C-glass bodies are made by pyrolysing a mixt. of a polyimide and is not 10 vol. % of glass powder, fibre or fabric; similarly, C-bonded ceramic bodies are produced by shaping a polyimide binder contg. ceramic granules, and pyrolysing this body.

Description

Patent description Process for the production of materials from isotropic carbon The invention relates to a method of production of materials or material components in composite materials made of isotropic carbon by pyrolysis of organic compounds.

It is known to make isotropic carbon bodies by thermal To produce degradation of preformed polymers that are not liquid during pyrolysis or go through plastic phase. These polymers are highly cross-linked Thermodure, for example around polyfurfuryl alcohols and phenol-formaldehyde resins. It is also known for the production of polycrystalline carbon bodies to use thermoplastic binders, especially pitch, softening and shrinking of the binder is determined by the granulometry of the filler and the use of support masses Burning is taken into account, which, however, complicates the combustion process and the properties (in particular the pore distribution) and shapes of the products to be produced Bodies are tightly limited. There has therefore been no lack of experiments using chemical methods or other hardening measures for the binder to overcome these disadvantages, which finally leads to the already mentioned use of Thermoduren. To the current state of the art is not aware of any universally usable binder that on the one hand can be processed with a simple technology and on the other hand is not limited to certain areas of application.

It has now surprisingly been found that VCrWendwr of essentially linear polymers, which are at least partially aromatic Contain structural elements and whose glass transition temperature is above 500 ° C, dissolved can be. This twus-surprising effect namely the non-flatulent standardized Pyrolysis with the formation of a coherent, very solid isotropic coke, has not yet been clarified in detail.

Certainly the previous assumption applies that to achieve more coherent strongly cross-linked isotropic carbon bodies while ensuring a high coke yield Use polymers as raw materials for thermal degradation, not to. According to the invention essentially linear and at least partially aromatic structural elements containing polymers with glass transition temperatures above 500 0C are apparently not at all or networked only to a subordinate extent.

Furthermore, it has hitherto been assumed that a to be pyrolyzed Binder should thermally degrade over a wide temperature range in order to the removal of volatile products and the secondary effects caused by them such as heat effects, secondary pyrolysis, reactions with filler substances, etc. over one to distribute a large temperature and time range. The firing treatment takes place in almost all cases with a continuous rise in temperature. Also this one so far Measure deemed necessary for the essentially linear and at least Polymers partially consisting of aromatic structural elements with glass transition temperatures not to above 5000C because they are relatively temperature resistant. It is in On the contrary, an additional feature of the invention that there is thermal degradation below 5000C as far as possible.

By using polymers according to the invention with r, last Temperaturona 50G0C will almost ideally combine the benefits of thermal application with the benefits the use of thermoplastic binders. By the inventive Vererdung, of polymers with at least partially aromatic structural elements coke yields are achieved after thermal degradation, although not quite that of the best thermal treatment, but are still above 50%. Most notably Polymers from the group of polyimides, such as those below, have proven useful Examples are explained in detail. Despite the relatively high manufacturing price of these Polymers is their use in the production of KflWrprrn according to the invention made of isotropic carbon because of the very simplified procedure thermal Degradation and because of the extraordinary properties of the substances produced in this way justified.

A certain upper limit only exists for the thickness for such Body made of isotropic carbon, obtained by pyrolysis from pure polymers without any further Additives are made.

Such a limitation also applies to the raw materials known up to now for molded bodies made of isotropic carbon. This limitation of dimensions in one Dimension can analogously also be applied to a.rerbrmdkörper, whereby 8 Maximum sizes of the polymer areas between the embedded materials result.

This dimension limitation has no meaning for the external ones Dimensions of the composite body.

How the polymer works during thermal degradation in composite bodies is not exactly clarified. The transport route for volatile products is not safe solely decisive for this, but presumably the shrinkage behavior during the Pyrolysis. When dismantling, it is self-supporting and free of any reinforcement component Body is guaranteed isotropic shrinkage.

In composite bodies or machnically in molds during pyrolysis fixed polymer bodies must have a certain deflection of the pyrolysis shrinkage In a preferred direction take place. Obviously this is only in a certain unifang, i.e. possible with limited thickness. It is a special feature of this invention, as a reinforcement component temporarily and reversibly in thermoplastically deformable verb body components to use.

Silicate glass has proven particularly useful for this. Through the plasticity de glass at elevated temperature, shrinkage stresses in the carbon matrix degraded, which means that the thickness of the body can be considerably greater than that of bodies without the addition of glass can be increased without cracks occurring. The plastic glass phase improves in addition, mechanical and thermal shock resistance at elevated temperatures.

It has been shown that preformed bodies from the invention selected polymers are retained in their shape during thermal degradation. However, this form of preservation by mechanical means has proven successful to support e.g. f3. by using mechanical aids such as support surfaces, Dies or dies made of different materials. Carbon proved its worth particularly good because of its low coefficient of thermal expansion.

It was found that the caking of the polymers on the support surface must be prevented, for example by known release agents and coatings such as e.g. by spreading graphite suspensions. It is a feature of this invention that it is particularly advantageous to use commercially available graphite foil for this purpose can.

The heating of the polymers in a non-oxidizing atmosphere up to 500 ° C can take place as quickly as you like, since it is mostly in a non-oxidizing atmosphere thermostable polymers.

The heating rate in this area can, however, depend on the properties other components forming a composite with the polymers of a composite are limited. It has been found that pyrolysis works above 500 ° C. with heating rates of <50 ° C./h must be done. It can also be carried out by switching on isothermal pyrolysis areas will.

The production of materials or material components according to the invention within composite bodies made of isotropic carbon through thermal degradation of an essentially linear structure, at least partially composed of aromatic structural elements Existing polymers in a non-oxidizing atmosphere are shown in the examples below explained in more detail.

Example 1 In a manner known per se, pyromelitic anhydride became and 4,4-diaminodiphenlether in a two-stage process a 'r it from polydiphenyloxydpyromelithimid 0.1 mm thick.

The foil was stored flat between graphite foils and in one oven preheated to 5000C under a nitrogen atmosphere with a Heating rate heated from 20 ° C / h to 1100 ° C. After cooling to room temperature, a linear Shrinkage of the film of 18.5 and a weight loss of 46.5% based on the polmere bus> ansfolie, determined. The isotropic film obtained in this way Carbon had a smooth, 2 shiny surface. The tensile strength was too high 15 kp / mrn Example 2 2 Made of a commercially available polyimide film (Kapton (R) H 500 from Du Pont) a helix was turned and the ends of the helix were clamped in fixed a device made of graphite.

The device was purged in an inert gas and heated to 500 ° C given preheated oven and left at this temperature for an hour. The temperature was then increased at intervals of 50 ° C. with a holding time from 1 hour to 8S ° C and finally in a last step to 1100 ° C increased and held at this temperature for a further hour. The specific one the electrical resistance of the carbon winding thus obtained was 6.10-3 # .cm .

Example 3 From a sintered body made from the polyimide polymer SP and 30 total% <R) of chopped glass fiber (Vespel SP-5 from Du Pont) was made by mechanical Machining a bearing bush made. This was in a graphite crucible in an oven preheated to 4oo0c, flushed with inert gas and with a Heating rate from 12 ° C / h to 1000 ° C. The obtained shrinkage linearly by 9.5% The socket consisted of a continuous carbon matrix with embedded glass fibers.

Example 4 There were composite bodies with a content of 35 vol. the endless carbon fiber thornel 50! R) of the Union Carbide Corpora tion according to the Wet winding process produced under the same conditions once with a Phenol-formaldehyde matrix tPhenodur 373 U from Chemische Werke Albert) and once with a polyimide matrix (QX-13 from ICI). After curing the obtained Laminates under mechanical pressure at elevated temperature were made from the laminates Sawed test rods and inserted it into a r; raphite device, which prevented the rods from warping during thermal degradation.

The degradation takes place under inert gas, starting at 200 ° C with a heating rate from 120C / h up to a temperature of 1000 C.

Under these gentle conditions it is possible to get out of the pure Phenol-formaldehyde resin without reinforcement component crack-free grains all isotropic To preserve carbon. After cooling, the Verhundkörper were at room temperature the following properties were measured: density, flexural strength, interlaminar strength, shear strength g / cm3 kp / mm2 kp / mm phenol 1.43 2 0.1 formaldehyde resin polyimide as 1.50 30 2.6 Matrix precursor 9A microscopic examination showed those with the Polyimide resin made composite bodies in contrast to those made from phenol-formadehyde resin completely free of pyrolysis cracks.

Claims (1)

Patent applications 1. Process for the production of materials or material components within composite bodies made of isotropic carbon through thermal degradation of organic compounds in a non-oxidizing atmosphere, thereby identified, that as a raw material for their production an essentially linear, at least partially Polymer made up of aromatic structural elements with a glass transition temperature is used above 500 C. 2. The method according to claim 1, characterized in that polyimides be used as raw material. 9. The method according to claim 1 or 2, characterized in that the pure polymer areas are smaller than 1 mm in at least one dimension. 4. Method according to claim 1 or one of the following claims, characterized in that the body from the raw material taking into account the linear shrinkage to be preformed according to the final shape and the shape of the Body is preserved during pyrolysis. 5. The method according to 4. z; iir production of shaped bodies, characterized in that that one can preserve the final shape, e.g. the curvature of the one to be made from the polymers Carbon parts by mechanical devices during pyrolysis until at least 700 ° C supported. 6. The method according to 1 or one of the claims which follow thereafter, characterized characterized in that the blanks or composite bodies produced from the polymers from the support surface or from the mechanical forming device during the pyrolysis treatment separated by graphite foils. 7. The method according to 1 or the following claims, characterized in that that the thermal degradation of the polymer; hstoffs by temperature control essentially in Temp: for areas above the gas temperature is shifted and --e heating Takes place in a non-oxidizing atmosphere. 8. Process naser 1 and the following claims, characterized in that that the pyrolysis by increasing the temperature above 500 ° C with speeds <500C / h takes place. 9. The method according to claim 1 and the following claims for production of foils made of isotropic carbon with thicknesses down to 10, characterized in that daF made of polydiphenyloxydpyromelithimide prefabricated foils in non-oxidizing Atmosphere can be pyrolyzed. 10. Process for the production of composite bodies made of carbon fiber reinforced Carbon, characterized in that one polymer moldings with a proportion of at least 10% by volume of endless or crimped carbon fibers or carbon braids or carbon felts preform and then the thermal degradation treatment subject. 11. Process for the production of carbon-glass composite bodies with continuous carbon matrix, characterized in that a starting mixture of polyimide with at least 10% by volume glass in the form of powder, fibers or braids is preformed and then pyrolyzed. 12. Process for the production of ceramic bodies with carbon bond. ,, characterized in that they are granular in a manner known per se, as ceramic Substances, hard materials or materials consisting of carbon with a polyimide binder preformed and then pyrolyzed.