DE1469489A1 - Carbon wires with improved resistance to oxidation and methods of making the same - Google Patents

Description

PATENTANWÄLTE _{η STuTTGART λ} IJ. Nov. 1964 DR.-ING. WOLFF, BARTELS, DR.BRANDES 48 / ^ 9 long street 51

TELEPHONE: »« 10 and 2972 «TELEX: 0722312

ReK. No. 119 516

H. I. Thompson Fiber Glass Co., 1600 West 135th Street, Qardena, State of California, United States of America

Carbon threads with improved resistance to oxidation and methods of making the same.

The invention relates to carbon threads of improved resistance to oxidation and to a method for making the same.

Amorphous carbon filaments have various uses has better properties than the threads made of other materials that were mostly used in the past. Carbon thread are therefore recently used to a large extent in the art of rockets and missile weapons, since they the have excellent wear properties of graphite and, moreover, a much lower one Thermal conductivity than graphite are excellent.

Carbon threads are particularly suitable for use

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It is used in places where high temperatures occur, because the sublimation point of carbon is very high (over 3600 ° C) and because its strength increases with decreasing temperature. In addition, carbon fibers are resistant to chemical attack except that they can be attacked by strong oxidizing substances at elevated temperatures, for example at temperatures above 427 ° C (800 ⁰ P). In addition, the electrical resistance of carbon threads is variable and depends on their diameter, their surface area and the like, so that carbon threads can also be used either as insulators or as, electrical conductors, special resistance for special purposes.

Since carbon threads are often flexible and easily malleable and since they do not smear or rub off, as is the case with graphite threads and graphite fabric, so can they are easily processed into a wide variety of products, such as fabrics or weaving, bougier cane, for roving, ribbon, felt, wadding and loose threads, using threads of the same or different lengths can be. Carbon filaments are in diameters up to about 0.127 mm (0.005 ") or larger high purity available.

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The analysis of a common thread made of amorphous carbon shows, for example:

95.2 carbon 2 pounds? 1 wt .- *

Hydrogen 1.0 wt

Oxygen 3 »3 wt .-%

Impurities 0.5 wt -.% (The impurities are made in this case mainly made of nickel, copper and tin, with traces of calcium, iron, silicon, magnesium and titanium).

in the

Carbon threads can be exemplified / in the US patent No (U.S. patent application Ser.Wo.

l60 $ 05) described above. This patent describes how non-thermoplastic cellulose threads, such as rayon threads, wool threads and the like, are cleaned of their production materials, how the washing liquid is then rinsed off, the threads are dried and then heated in a closed atmosphere by being auegesetzt immenhöheren temperatures in succession to the volatiles expel from them and coals the threads ohnff that its thread Nature was destroyed by this treatment the temperature is not approximately 149 ° C (300 ⁰ F) to over about 538 ° C

increased
(1000 ⁰ FK at a temperature gradually increased by 11.11 to 27.78 ° C (20 to! 50 ⁰ F), with each temperature increment

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Takes 8 to 30 hours. This is followed by a sudden heating i ("flash" firing) to a much higher temperature under non-oxidizing conditions, such as about 982 to 1092 ° C (18OO-2OOO ° F) to drive off the remaining volatile constituents and e.a heat shrinkage to carry out the threads. The filaments in non-oxidizing conditions to less than 149 ° C (300 ⁰ F) to be cooled. If this step-by-step heat treatment, carried out under close supervision, with subsequent, sudden, high heating were to be omitted, then the carbon threads would tend to split into separate parts and the lamellar shapes formed would tend to split apart when used at elevated temperatures. In addition, the sudden heating to high temperature ("flash" firing) reduces the tendency of the carbon threads to react.

Although the carbon threads produced in accordance with the method described above are resistant to most chemical Attacks are resistant, they are wear-resistant and maintain their structure if they are not heated to temperatures above their Sublimation Point® such carbon threads are then very strongly attacked and suffer a great loss of weight.

lust if you have higher temperatures than approx. 427 ° C 809901/0754 bad OBIG «*« ·

(800 ° P) in the presence of oxygen. Under such conditions, the carbon in the filaments tends to react with oxygen (e.g. the oxygen in the atmosphere) and thereby carbon monoxide and carbon dioxide to build. The basic constituent of the threads evaporates and the thread mass is lost as a result a.

The invention is therefore based on the object to provide carbon fibers improved resistance to oxidation, which in säuerstoffreicher environment are stable even at temperatures above about 427 ⁰ C (800 ° F) and the flexural properties, the uniform structure, their lower thermal conductivity, wear thereof - and removal properties as well as their strength properties and other desirable properties inherent in carbon threads are unchanged.

This object is according to the invention by means of carbon filaments dissolved, which have a carbide coating on their surface with zirconium or titanium or chromium or Nickel or a mixture of these metals, " which surrounds the threads and is linked to them * ■ · ■■■ -

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The fact that the carbide coating encloses the threads and is linked to them / is achieved that the Carbon background of the threads is protected against oxidation by a permanent coating, while at the same time the desired properties of carbon filaments are fully preserved.

The invention is also based on the further object of providing a method for treating carbon threads create, by means of which carbide coatings can be produced on the threads in a particularly advantageous manner. This object is achieved according to a further feature of the invention in that the surface of the threads with both carbon and zirconium or chromium or nickel or titanium or mixtures of these Heat-emitting substance is covered and that this substance under non-oxidizing conditions at increased Temperature is converted into a carbide. It is thereby achieved that the carbide coating essentially over the entire surface of each carbon filament distributed and thus protects it excellently. In addition, the carbide coating soaks the surface of the thread, i.e. it spreads out

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into the surface irregularities of the threads and will permanently chained with the threads. When the threads coated with carbide are exposed to an oxidizing atmosphere such as air, at temperatures above 427 ° C (800 ° F), then the carbide of each thread will be incorporated into the

corresponding heat-resistant oxide transferred. This ^ refractory oxide does not react with the atmosphere and therefore forms a permanent, effective protective coating, which covers the threads and protects them against oxidation. This will destroy the otherwise quickly occurring Prevents carbon threads in a strongly oxidizing atmosphere. In addition, the refractory oxide doesn't just work as a chemical protective wall against oxidation but also as a heat shield, which increases the general resistance the carbon threads improved. |

As a typical example, the following may be mentioned: A carbon fabric that has been manufactured by cleaning, rinsing and drying rayon fabric that has been stored in a closed atmosphere from 149 ° C (300 ⁰ F) to 538 ⁰ C (1000 ⁰ F) in 27 , 8 ° C (50 ⁰ F) draw forming temperature steps · was heated 8 hours duration, and thereafter (2200 ⁰ F) was heated for 10 seconds abruptly at about 12O6 ° C (* flash firing), the subject described in the following treatment:

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The carbon fabric is placed in an impregnation solution immersed, which contains 175 g of chromium acetate, i.e. an amount sufficient to apply a

To form a chromium / carbide coating, the proportion of which is about 5% by weight of the finished fabric. The carbon fabric absorbs approximately 0.8 ml of impregnation solution per gram of the fabric. The carbon fabric is left in the solution for 20 minutes, then removed from the solution, after draining the solution, dried in air at about 121 ° C (250 ° P) and roasted in a non-oxidizing atmosphere, which in this case consists of nitrogen, although a noble gas such as argon, krypton, neon or the like could also be used. The Röstaauer is one hour at 1200 ⁰ C. This temperature is sufficient to form from the Chrorakarbid acetate. The carbide layer formed on the threads of the fabric includes any carbon thread gänzlih and close a, is concatenated with the surface of the threads $ and fills the surface irregularities and pores of the CARBON twine. The treated fabric is then cooled to ambient temperature in the non-oxidizing atmosphere.

In the more detailed description that follows, the invention will be described explained in detail.

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The single figure shows a graph in which the resistance to oxidation of carbon filaments according to the invention is illustrated.

According to the method steps of the invention, Koh can μ

fabric threads in any suitable form, e.g. in the form of Mats, cotton balls, felt, fabric, bougier tube, roving, strips, or as loose threads or the like. Treated to increase their resistance to oxidation.

The sutures to be treated can in any suitable manner, such as in the specific manner described in that previously mentioned US. Patent specification No. (US application "

A.
3rd No. 16O 605) is described. In any case, the carbon threads to be treated should already be in their finished form, ie they should already have been subjected to flash firing to high temperatures or a comparable treatment so that essentially all volatile constituents have been swept up from them and they are already heat shrunk.

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This is necessary because when the invention. Treatment is carried out on threads that still have moisture or other comparable volatile components that i. Expulsion takes place of these moisture or other volatiles during the Röstschrit · tes thereby. (In the case of moisture) a. Hydrolysis effect occurs or that on the surface of the. The carbide formed by the threads is attacked in some other way, as a result of which carbide loss occurs on the thread surface. occurs. For the process according to the invention, only carbon threads are used which have already been heat-treated (flash fired), have been subjected to heat shrinkage and from which essentially all volatile constituents have already been expelled.

According to the method according to the invention, such carbon threads are brought into contact with a selected agent which essentially consists of a $ t <6 substance which, when heated, gives off carbon and a metal such as nickel, chromium, zirconium, titanium or mixtures of these metals. It has been shown that these metals produce particularly effective protective coatings made of carbide, which can be produced in the desired manner even at low temperatures.

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1469488

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It is particularly important to note that the treatment material should be selected so that it gives off carbon at the roasting temperature, so that the carbon required for carbide formation does not have to be taken from the carbon filament, which has a relatively small diameter, but comes from the treatment material . As a result, the fine carbon threads remain intact, while a carbide layer is formed on their surface at the same time. If, on the other hand, the carbon of the threads is used as the carbon source for a carbide formation, the surface of the thread is attacked by the carbide formation and a loss of thread mass occurs. Since the carbon threads usually have a relatively small diameter and accordingly a relatively large surface area, a considerable part of the total mass of the carbon threads would be used for carbide formation in this case. Upon subsequent use of such a yarn in an oxidizing atmosphere at elevated temperature, for example at a temperature above iJ27 ° C (8OQ ⁰ F), a substantial portion of the yarn mass would be lost by the fact that the carbide is converted to the corresponding refractory oxide, while carbon in the form of carbon oxides would not volatilize from aar carbide. this

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However, this would not correspond to the purpose of the invention, which is to prevent the thread mass from being oxidized protect and prevent a loss of thread mass in the form of volatile charcoal oxides.

Therefore, according to the method according to the invention, an external carbon source is provided which is contained in the treatment substance is mixed with the selected metal and brought into intimate contact to ensure that the components of the treatment agent effectively into a carbide coating associate.

The chosen metals nickel, titanium, zirconium and chromium have the property that they are easily with relatively low temperatures from organic compounds, in which they are contained, can be split off under Formation of a protective layer of carbide that gives the desired | Properties of the carbon threads are not affected, too ' react. With organic compounds that when heated deposit the selected metals, the carbide protective layer can be created on the filaments without the carbon of threads are weakened. In addition, the relatively low temperatures reduce the treatment costs kept low. If organic compounds are used for the process according to the invention, then can

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disassembly of the treatment substances are carried out at temperatures in the Größenordniing of approximately 1000 ⁰ C, while in contrast, be die.gewöhnlichen Kohlungstemperaturen at least about 150o C to 2000 ^{0 0} C. .

Any suitable compound containing carbon can be used, which also, metals such as nickel, .- chromium, .zircon, titanium and mixtures of these can be used. However, preference is given to those connections that are easy to get into a suitable, inexpensive solvent such as: water are soluble. Such compositions are also preferable, which to one; viscous syrup, be concentrated can lead to a glaze-like, essentially, smooth coating dries up, in contrast to those compounds which crystallize easily and thereby tend to form an irregular coating with "islanding" form, especially on threads of small diameter as is the case with carbon threads.

Organic substances or compounds are therefore preferably used, such as ζ · .Β * acetates or formates, such as chromium- '^; acetate, Zirkonäc'etat, ^{Zirkanförmi'at:} Nickelacetät, nickel formate, titanium oxide in an emulsion, which is stabilized with acetic acid and the like ..

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Chromium acetate and zirconium acetate are generally considered to be acetate complexes rather than true compounds. They can be concentrated to viscous syrups, which can be applied as a smooth, even coating to the entire outer surface of the carbon filaments that are to be treated, which can easily penetrate the pores of the carbon filaments and their surface irregularities can fill, so that .the coating is intimately linked with the threads. In other words, such compounds wet the carbon threads in the desired manner and adhere to them. This is also in from _die--: erzeugten- sen connections on the thread surface carbides the case. · ■ _ .. ■. ".- .: ^

Nickel acetate is common, crystalline ^ can_ however:, in. a suitable solvent, such as. B-. Water again -. .: ■ can be solved in this. Shape, to be used. :,. An emulsion of titanium oxide j .stab by acetic acid - ^{the first} is lized, represents a colloid. Which in limited; ..;. Areas is stable and that turns out to be aiLles when heated; trapping hydrogel settles. Also, special. Formiaibe can preferably be used, such as z -.- B. IJ-ickjel.-.-; -: 'forraiat-mit-der. Formula. ■ -; ......, · -, .- ■. ■ .-. y, -. ■ - »? - ■■; - ■■

Ni (HCOO) "· 2H" 0

■ ■ -

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that is water soluble. Chromium formate with the formula

Cr (OH) (HCOO) ₂

is a dark green, tanning liquid which can also be used for the method according to the invention can. It is clear that any other suitable organic compound which, when heated, is nickel carbide or chromium carbide or zirconium carbide or titanium carbide or a mixture of these forms »also for that method according to the invention can be used, such as B. selected organometallic compounds such as metal chelates

The treatment agent is usually in a suitable one Medium, e.g., a dispersant, a solvent or the like so that it can effectively and evenly contact the carbon filaments to be treated and can penetrate into it. For example, they are water-soluble Zirconium acetate, chromium acetate, hickel acetate, nickel formate, Chromium formate and certain other organic compounds. The water can then be removed by evaporation, e.g. when drying the with the impregnation coating provided threads. If a different solvent or dispersing agent is used, that of the carbon does not respond, such as. Ethyl alcohol and the like.

thus, depending on the type of treatment substance, a drying step can also be carried out in order to remove such Remove solvent from the coating.

The treatment material is in the impregnation medium in göeig- W neter concentration. The lowest concentration suitable here is that which results in an essentially uninterrupted refractory carbide coating over the entire outer surface of the carbon threads to be treated when the threads are immersed once or several times in the soaking medium. It has been found that the surface area of the surface of the threads, the nature of the surface irregularities of the filaments and other factors min _h least concentration of the treating material and thus the strength of the filaments subsequent Karbidüberzugs is dependent variable. Gwöhnlich is a Karbidüberzug whose metal content is at least about 0.5 wt -.% Of the finished product is (carbide plus carbon fibers) sufficiently thick and forms coating SchutzÜ-uninterrupted, the underlying carbon filaments so effectively against oxidation at temperatures above 427 ° C (800 ° F) are protected. It can be used Karbidüberzüge to a metal content of 10 wt -.% Of the finished product. Concentrations greater than about 10 wt.

809901/0 7 54 BADORlGfNAl.

however, bring about significant changes in the properties of the carbon threads, such as changes in the general appearance and structure of carbon fabrics. It has been found that carbide coatings with a metal content of about 2 to 4 wt .- $ are preferable because they provide the greatest possible protection against oxidation at M

offer the smallest possible change in the thread properties.

Carbide concentrations of more than about # 6 wt. % Result in only slightly improved protection against oxidation, compared to carbide concentrations of a little less than 6 wt. % * In addition, the filaments show when the concentration is higher than 6 wt. % some tendency to crumble during treatment.

H
This increased stiffness and friability of the carbon filaments is apparently due, in at least some examples, to the vitreous nature of the selected dehydrated metal complex used as the treating agent. This crumbling or fragility of the threads disappears again when the metal complex is converted into the carbide by heating. However, it is easier, more convenient, and more economical to use lower concentrations, thereby reducing the inconvenience and the possibility of mechanical destruction.

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% may occur, to avoid - in the stiffness and brittleness of the threads at concentrations above 6 wt.. For most applications, the maximum concentration of the carbide is therefore about 6 wt ..-- ^ ■ of the metal content, based on the weight of the finished ^! Product, limited.

According to the method according to the invention, the carbon fabric is brought into contact with the treatment substance in any suitable manner, such as, for example, by being thawed in. the treatment substance or in a mixture, _dispersion:; - _{; Γ} > · \ ?. ■ or solution or the like from the treatment substance and ei-- -. · ■ ^r nem suitable medium. The carbon threads can too. · .- .:

with one with the treatment substance or i »/ the treatment substance -, - .. ■■

.Containing medium are sprayed or they can be passed through a zone in which the treatment substance or a mixture of the treatment substance evaporates
the medium -iörderHö-wird or the like, or the ..

Treatment substance can also be painted, poured over or otherwise applied to the threads. That Application of the treatment substance is carried out in such a way that the carbon threads are impregnated and coated and that essentially all of the outer surfaces of the yarns are enclosed by the treatment fabric.

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After the desired amount of the carbon threads If the treatment agent has been absorbed, the carbon residues will be removed from the excess treatment agent removed, e.g. by pulling out the carbon threads from an aqueous solution or a bath containing the treatment substance. Then the ™

Carbon threads subjected to a treatment to remove excess To remove treatment material from them, e.g. by allowing them to drain and then the carbon threads dries or otherwise removed from the excess treatment material. This treatment is carried out in such a way that the treatment substance with the pad surface linked under Y formation of a protective layer and that the treatment substance settles on the threads. So will

at
eg ve "use of zirconium acetate as a treatment substance, etc. serving as a solvent water from the end on the yarn surface treatment material expelled by the fact that they are dried in air at temperatures of about 121 ° C (25O ° F) and a drying time of about half Hour with moving air. The treatment substance settles on the carbon threads as a solid, vitreous coating made of zirconium acetate. .

Thus-impregnated carbon fibers, covered with a, t 'completely enclosing coating of the treatment agent

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are then heat treated (roasted) to get the. Treatment substance into the desired carbide or ind the. desired carbides by breaking down the treatment material to be converted into carbide-forming constituents containing carbon and metal. In the present case it will be the dried carbon threads that. on their surface, have a uniform coating of the treatment substance distributed on them, under non-oxidizing conditions roasted, e.g. in nitrogen, in hydrogen, in helium, in argon or the like at a temperature higher than this

duration

than about lOQirc, with the roasting «* being chosen long enough is to completely decompose the carbon-containing treatment substance and the desired, selected carbide or the carbides on the surface of the To form threads. The roasting temperature can be significantly lower than the temperature that would be necessary to get the pure Refractory metal or metal hydride or oxide to react with the carbon to form carbide («« £ carburizing temperature). It should be noted that the roasting temperature at which the carbide according to the invention Process formed on the thread surface is kept below the temperature at which the Carbon is converted into graphite because of its thermal conductivity of graphite threads is much higher than that

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of carbon threads and da dl · · if 41 · P & den both elevated temperatures should not be used »nioht is desirable.

The carbon threads treated in this way and provided with a selected carbide layer are then cooled to ambient temperature and are ready for use be carried out, e.g. under non-oxidizing conditions or under oxidizing conditions, since the K & rbldechutechicht protects the carbon threads effectively against oxidation at elevated temperatures. The abbreviation «» - step can therefore either be in a setmtiataosphire from hydrogen, nitrogen, argon »xenon, krypton, helium or dergi. or in a vacuum, or in the presence

of oxygen or an oxygen-containing atomic 4 '\

take place · e.g. air /. Oils are prepared "with a"

Carbide-coated carbon filaments are now ready for use · They are particularly well suited as thermal insulation and can be exposed to high temperatures in oxidizing conditions , in which unprotected carbon filaments would be oxidized quickly and would lose mass without it and would therefore be unsuitable. The continuous carbide coating that blends with the surface of the

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Carbon threads are chained together and the pores and surface imperfections fills the threads, acts both as a protective wall against oxidation and as a heat child for the carbon threads. The · is achieved that the Karbidüberzug having an even lower thermal conductivity than the Kohlenetoffäden itself. In addition, zirconium carbide, titanium carbide, chromium carbide and Nickelkarbid when they are exposed to Teaperaturen above 427 ⁰ C (80O ⁰ F) an oxidizing atmosphere associated in their refractory oxides transferred. The refractory oxide superimpositions, which are insensitive to oxidation, are formed on the threads and are coated with the carbon fibers. These oxides, too, have a lower thermal conductivity such as hUftetöffä ^ e "unu act as demgeaäß Hltseechlld.

the desired protection of the carbon threads is achieved and a permanent concatenation of the refractory oxides on the surface of the carbon threads itself is possible Before and effective use is achieved, while, in contrast, usually refractory in the formation and chaining of oxides on substrates at temperatures below the Combination temperature of the oxides, difficulties f occur.

The following examples illustrate treatments in accordance with the method according to the invention.

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- 23 Example I.

A carbon fabric is made according to the present method treated. The carbon fabric has the following chemical composition:

. . Carbon · 95 * 2 wt ..-?

Hydrogen 1.0 % by weight

Oxygen 3.3 wt .- #

Ash 0.5% by weight .

An aqueous solution that contains sufficient zirconium acetate to form "Ηβ to zirconium carbide with 4 wt -.% Zirconium, based on aas total weight of the carbon cloth is used as the treatment solution. <& The carbon fabric is immersed in the solution for impregnation and the fabric absorbs approximately 0.8 ml of solution per g of carbon fabric with a soaking time of 30 minutes. Therefore, in this case, each 800 ml of the solution contains approximately 192 g of zirconium acetate of the formula

The tissue is then pulled out of the solution and left Drain off the excess aqueous zirconium acetate solution and then sends the fabric through a dryer at a temperature of about 135 ° C (275 ° F) where it dries in about 20 minutes. In doing so, the excess Water is removed from the zirconium acetate and the compound is dried to a glassy, solid state in which it as a continuous smooth layer with the outer

- 2k -

Surfaces of the carbon threads is chained and thereby the threads are impregnated and all pores and surface

fills. regularity of the threads ausfitüfcx

The dried fabric coated with the treating agent is then placed in an oven which has a nitrogen atmosphere. ^{Here it is slowly heated to a temperature of 1000 °} C. over a period of approximately 5 hours and is left at this temperature for approximately 8 hours. When this time has elapsed, the heating elements of the oven are switched off and the fabric is allowed to cool to ambient temperature in the nitrogen atmosphere. In έ this taking place at 1000 ⁰ C in the oven heat treatment the volatile components are expelled from the zirconium acetate and the zirconium acetate is converted to zirconium carbide. The zirconium carbide formed on the threads is linked to the surfaces of the carbon threads by filling their pores and surface irregularities, effectively protecting the threads against wear caused by oxidation. The carbon used to form the carbide is essentially taken from the carbon of the acetate and not from the carbon of the carbon threads. Therefore the mass of the carbon threads remains essentially untouched, while a carbide

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layer is formed * A review of the so-made Threads ze ^ j; that they are much better resilience have anti-oxidation and slightly reduced thermal conductivity Carbon threads of the same kind. All others Properties of the negotiated carbon threads correspond essentially those of untreated threads. ™

Example II

A carbon fabric is subjected to the treatment described in Example III, with the exception that an aqueous solution of zirconium formate is used instead of the aqueous zirconium acetate solution. The concentration of the zirconium formate is chosen so that there is a concentration of ί approximately 2 Om in the finished carbon fabric. <~% Zirconium in the form of the desired zirconium carbide coating. In other words, the weight of the egg in the zirconium carbide coating is approximately 2% of the total weight of the fabric.

In a parallel series of experiments, a Treatment according to Example I, a chromium carbide coating on j flashed heating (flash

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Carbon threads formed, but using a aqueous solution of chromium acetate of such a concentration that in the chromium carbide coating of the finished treated Threads 2% by weight of chromium, based on the total weight of the finished threads.

The coated with zirconium carbide carbon filaments (2 wt .- ^ zirconium) as well as the coated chromium carbide filaments (2 wt -.% Chromium) show the same general appearance and the same other characteristics as unüberzogene carbon fibers, except that it has a substantially greater Have resistance to oxidation at temperatures above 80 ° C. *

The single figure shows the oxidation resistance of threads treated according to the present method, determined in tests. The oxidative image level was determined in the experiment by taking samples weighing one gram from the threads, which were heated to approximately 900 to 1000 ° C., with a temperature increase of 10 ^° C. per minute. The filaments were exposed to an air flow of 0.02832 m ^ (1 standard cubic foot) per hour.

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The weight loss of the threads was measured at various times during this test. The curve A shows the increasing weight loss of carbon threads without a protective coating during the test Curve B shows the weight loss occurring during the test from being provided with a zirconium carbide coating.

nen carbon threads and the curve C the corresponding ^

Shows weight loss of chromium carbide coated threads. As is apparent from the figure clear, e & newspaper gene which are provided with zirconium carbide carbon fibers (curve B) has a substantially increased resistance to

as
Oxidation, w4e the carbon threads without a coating (curve A).

This significantly increased resistance to oxidation is particularly evident at temperatures above approximately 900 ^° C. The carbon filaments provided with a chromium carbide coating (curve C) have an even better resistance to oxidation over essentially the entire temperature range of the experiment. The figure clearly shows that the resistance of carbon filaments to oxidation can be significantly improved by coating them with a coating of a selected carbide.

Similar attempts have been made with carbon threads that

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a Nickelkarbidüberzug of about 5 wt -.% nickel and having with carbon filaments with Chromkarbidüberzug of about 6 wt .- /? Chromium, carbon filaments with Titankarbidüberzug of about 2 wt -..% Titanium and untreated carbon cloth, that is, carbon cloth "from uncoated carbon fibers These experiments were the same criteria as previously described

ben carried out, that is, by 1 g of heavy samples of the various yarns were heated at an air flow of 0.02832 nr * (1 SCP) per hour of about ambient temperature to about 1000 ° C at a temperature increase of 10 ⁰ C per minute. At the end of the test, it was determined how much percent by weight of the samples had remained. It was found that carbon fabric, which was not protected by a carbide layer, had only 2.15 wt .- ^ of its original mass. Kohlenstoffäaen with Titankarbidüberzug (with 2.8 wt -.% Titanium, based on the total weight of the filaments) exhibited a much better oxidation resistance in that the residue is about 33.2 wt -% of the original yarn was weight.. When carbon filaments with Nickelkarbidüberzug 32.0 percent remained -.% And carbon fibers with Chromkarbidüberzug remained even 37.4 percent -.%.

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Example III

An aqueous solution of nickel formate is produced into which a ready-made, heat-treated (flash fired) carbon fabric is immersed. The solution containing the Nickelfamiat in such a large concentration that look in the finished product so treated about 5 wt -.% Nickel yield. Therefore, the solution per liter is approximately

Gram
264 nickel formate. 30 liters of this solution are used and a 10,000 g sample of carbon tissue is immersed in it. The carbon fabric is immersed in the nickel formate for about half an hour.

BXi,

solution and left / closing pulled out of it, after dripping the solution at approximately L43 ° C (29o ⁰ P) and then dried at about 1200 ⁰ C for about roasted in a nitrogen atmosphere for 2 hours. It is then cooled to ambient temperature in the nitrogen atmosphere for 3 hours.

When testing the carbon fabric with a nickel carbide coating, it is found that the carbide coating completely encloses and is tightly interlinked with all of the outer surfaces of the carbon threads of the fabric. The carbide fills the pores, f

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Depressions and surface irregularities of the carbon unload. When the carbide-coated fabric is exposed to an atmosphere containing oxygen is, like e.g. air, at temperatures above 427 ° C (800 ° P) then it is shown that the carbide has changed into nickel oxide and that the nickel oxide coating is coherent and a good protective coating on the surface of the carbon threads represents. The oxide coating is essentially in the oxygen containing state at such elevated temperatures Environment unreactive and also acts as a heat shield.

In parallel "test series, samples of Carbon threads made with a coating of titanium carbide and checked. They were completely heat-treated (flash fired) carbon filaments in the form of a fabric immersed in a bath containing an emulsion of titanium oxide stabilized by acetic acid as a treatment substance. 0

The Titanoxydemulsion is obtained by reacting <& Äthylorthotitanat to an agitated, unheated, v / aqueous solution of 25 wt -% is acetic acid and an emulsion of.

80990 1/07 54

about 1OS? To obtain titanium oxide. If this emulsion is heated to a temperature noticeably above room temperature, then it forms an all-encompassing gel.

will
Bgxnata The emulsion / on its titanium oxide content thereby

investigates that a sample is taken from it and that it is dried and annealed to form titanium oxide. Then, the emulsion 255 is aqueous acetic acid solution so diluted that a TiOg content of 4.25 wt -.% Results, the 2.5 wt? iiBallic titanium corresponds. If this emulsion is subsequently used to impregnate carbon fabric, then such a treatment material produces a coating, acetate-stabilized

which as XS «£ & $ x» «ä & SX £ S £ gli £ $ g Oxyd 2 wt. 5? Contains Ti.

The dipped fabric is drawn out, and after about 1 hour from the solution dried by dripping of the solution at a temperature of about 121 ⁰ C (25O ⁰ P). When it dries, the treatment substance forms a gelatinous coating on the fabric, which contains acetic acid until it is roasted έ . The roasting is performed in a hydrogen atmosphere at a temperature of more than 1000 ° fyjedoch below 1100 ⁰ C ^, is performed at a roasting time of about 8 hours, a time period in which substantially all of the treatment material in titanium carbide having a continuous protective layer on the Surface of the carbon filaments of the tissue. The finished product

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Reg.-Ur. 119

This is then cooled to ambient temperature in hydrogen. It turns out that the titanium carbide coating (2 f titanium, based on the weight of the finished product) is evenly and firmly linked to the carbon thread surface and that this coating protects the entire surface of the carbon thread of the fabric. Such a carbide coating effectively increases the strength of the fabric against oxidation.

The above examples clearly show that carbon threads are produced by the process according to the invention, which have a higher resistance to oxidation, especially at elevated temperatures. the Threads can be produced in a simple, effective and fast manner using readily available raw materials getting produced. The finished filaments have an outer carbide coating interlinked with them made of titanium carbide, zirconium carbide, chromium carbide, nickel carbide and the like or mixtures thereof. This carbide coating protects the underlying carbon threads effective against loss of mass when the threads are exposed to oxidizing conditions. This forms from the carbide the corresponding oxide, that against oxidation is constant and that has a heat shield

, BAD ORIGINAL

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around the threads represents »

In accordance with the invention, a new, improved product and method is provided. The method according to the invention is primarily directed to the treatment of carbon threads and differs from other possible ways of forming carbides in that the small diameter carbon threads remain undamaged during the carbide formation taking place on the threads, in that d. t according to the present method, a separate carbon source is provided. In addition, when an organic compound is used, the carbide-forming reaction takes place at relatively low temperatures. Further advantages that can be achieved by the invention emerge from the foregoing.

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Claims (20)

_ 34 - claims 1. Carbon threads with improved resistance to oxidation, characterized in that they are on their surface have a carbide coating with zirconium or titanium or chromium or nickel or with a Mixture of this metal is formed so that the carbide coating surrounds the threads and is linked to them. 2. Carbon threads according to claim 1, characterized in that zirconium carbide is provided. 3 · carbon threads according to claim 1, characterized in that chromium carbide is provided. 4. carbon threads according to claim 1, characterized in that Titanium carbide is provided. ., ...-... 5. carbon threads according to claim 1, characterized in that Nickel carbide is provided. . . BATH ORIGINAL 809901/0754 6. carbon threads according to one of claims 1 to 5 * the
characterized in that the carbon threads forming the substrate for the carbide coating consist of amorphous carbon. ^c 7. carbon threads according to one of claims 1 to 6, characterized in that the metal content of outer protective coating is between about 0.5% to about 10 $ t of the yarn weight is. 8. carbon threads according to one of claims 1 to 7 »characterized in that the outer coating between about 2% to. is about k% of the thread weight. 9. Method of treating carbon threads for improvement the resistance of the same to oxy- (dation), characterized in that the surface of the Threads made with a both carbon and zirconium or chromium or nickel or titanium or mixtures this substance, which is emitted when heated, is covered and that this substance under non-oxidizing conditions elevated temperature is converted into a carbide, whereby the carbon filaments have an increased resistance to oxidation at temperatures above (800 ° F) obtain. BATH ORIGINAL 809901/0754 10. The method according to claim 9, characterized> that the fibers heat-treated at below about 537 ° C (1000 ⁰ F) and subsequently at about 982 ⁰ C (l800 ° F) to 12O6 ° C (2200 ⁰ F) heat shrunk. 11. The method according to claim 9 or 10, characterized in that that amorphous carbon is used as thread material. 12. The method according to any one of claims 9 to 11, characterized in that the coating is converted into carbide ^{at a temperature of over approximately 1000 ° C.} 13. The method according to any one of claims 9 to 12, characterized characterized in that the filaments are essentially entirely of the carbon and at least one when heated Metal releasing substance can be included. 14. The method according to any one of claims 9 to 13, characterized characterized in that the threads with the by heating the decomposable substance / distributed in a suitable impregnation body we uy are impregnated so that the threads are removed from the impregnation medium after impregnation and that the impregnation substance is linked to the threads. 15. The method according to claim 14, characterized in that aaß the 3toff zirconium acetate, which can be decomposed by heating BATH ORIGINAL 809901 / C754 shows that water is used as the impregnation medium and that the impregnated threads are kept at less than approximately 149 ° C (300 ° F) and that the filaments are then used to form a zirconium carbide coating which the Including the thread surface in its entirety and is chained to it, to be roasted. 16. The method according to claim 14, characterized in that (j the decomposable by heating material comprises chromium acetate, that water is used as the impregnation medium, that the impregnated threads ^{are dried at less than about 149 ° C (300 0} F) and that the threads then roasted to produce a protective coating made of chromium carbide, which essentially completely encloses the thread surface and is linked to it. 17. The method according to Anapruch 14, characterized in that the material which can be dismantled by heating has formed nickel that is used as the impregnation medium V / water, that the impregnated threads ^{are dried at less than about 149 ° C (300 0} F) and that the threads then to produce a protective coating of nickel carbide, which essentially completely encloses the surface of the thread and is linked to it, 0 can be roasted. 18. The method according to claim 14, characterized in that the substance, which can be dismantled by heating, made of a vinegar BATH ORIGINAL 809901/0754 '^ - 1469469 acid-stabilized emulsion consists of a titanium oxide that is used as the impregnation medium V / water, that the impregnated threads ^{are dried at less than about 149 C (300 0} P) and that the threads are then used to produce a protective coating of titanium carbide, which the thread surface in essential to be roasted completely and is linked to it. 19. The method according to any one of claims 9 to l8, characterized in that as a proportion of the metal approximately between one to ten percent by weight of the threads is chosen. 20. The method according to any one of claims 9 to 19, characterized characterized in that approximately two to four percent by weight of the B'äaen wira selected as the proportion of the metal. ■ BADORiGlNAL 80990 1/07 54