Metal Nitride Fibers, Textiles and Shapes and Process for Producing them

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PATENTS AND REGISTRATION OFFICE

PUBLISHING POSITION NO 3Ö9? 45

Int Ci ^{C 04 b} 3S / S &amp; κι. ^{SO b} 8/11

Patent Application. No. 98E / 67 Received on 23 I 1967

Validity Day on 23 In 1967

Ans. generally available on 1 vii 196g

Ans. Exhibition and Excerpt published on March 31, 1969

Priority received from 24 ooh 28 I same 19

ΏΕΙ 1966 (United States, 522,380, 523,549,

602 571) tJBION CABBIDE CORBOBATION, NEW YORK, NY, USA

Inventor BH Hraaling

Ombuds G Ernerot

Methods of Making Crystalline Metallic Silk Fibers, Textiles and Fiberglass Bodies

Oh.

The present invention relates to a method of making crystalline metal carbide fibers, textiles and molds.

. The characteristics of the method are evident from the following mortgage requirements. ·

Hitherto, certain metal carbide fibers have been produced by a variety of methods, but each of them is characterized by important limitations. For example, silicon carbide has been crystallized in a liquid system, but this approach requires high pressures and / or high temperatures. According to the whipping method, fibers are formed from steam phase or by electroDupP.kl. 80 bs9 / 20 light of smll; salt. This method produces fibers that are often irregularly wrinkled, twisted and very much lying. close together. In addition, metal carbide fibers made by the whipping method are characterized by distortions and are relatively short (below 6.3 mm). It has hitherto been impossible to reproducibly produce flexible metal carbide fibers with a length-to-dimieter-Jöhholdleuide over 400, characterized by high strength at high temp.

On the other side is ^da clear att ^sthese fibers would. imply an approximation to the upper limit of strength-to-weight ratio of a given material, depending on the cohesive forces of adjacent atoms. It has been calculated that the weight of pressure vessels reinforced with high-strength metal carbide fibers could be on the order of one-seventh more than that of conventional pressure vessels intended for high-temperature use.

Thus far, there has been no completely satisfactory method for producing metal carbide objects of predetermined irregular or compressed forms. Previous methods have included machining or other molding techniques, or in the case of foam material ·, the use of various blowing agents. The methods were either difficult and complicated, or they were too difficult to control accurately the final shape of the object.

It is an object of the present invention to provide molded metal carbide articles. Another object of the invention is to provide a method for producing such objects from non-fibrous organic materials. Yet another object is to provide a variety of molding bodies such as films, tubes, bowls and others which are the same as those of mikkokkistallin metal carbides.

Another object of the invention is to provide a method of making small carbide carbide fibers. diameters of less than about 30 microns, which is reproducible.

Another purpose · is to make a coma in one way. production of uniform diameter carbide fibers which are straight and have a smooth surface and are free from distortions.

Yet another object is to make carbonated metal carbide fibers of more than approx. 30 microns in diameter with a length-to-diameter ratio above UOO, which are flexible and characterized by high strength at high temperatures.

Yet another object is to fabricate a variety of textile shapes, including staple fibers, cohesive blue and yarns, woven fabrics, wadding and blankets, the co-nonsant of non-carbide fibers.

These and other objects and advantages of the present invention will become apparent from the following description and appended claims. . . .

One aspect of the new method involves first combining a compound dissolved in a solvent, and immersing a pre-formed organic polymeric material in the resulting solution to thereby swell and. open the organic medium in the medium

- 4 that the metal compound is sucked in or absorbed in

The non-suction medium compound is then removed from the outer surfaces of the organic material and the material impregnated with the metal compound is dried. Thereafter, the material is first heated to a temperature of at least 250 ° C^d one ^hrsAstig^hrsa ti ^ 'Llä ^ &lt;3klå ^ g^t low to release volatile decomposition products of the organic material without destroying the integrity of this polymeric material. This pyrolysis step is continued for a sufficient period of time, to decompose the organic culture of the polymeric material and to form a carbonaceous one. residue (leaving) containing the mealie in finely dispersed form. In the final carbonization step, the residue is further heated from the pyrolysis step to a temperature of about 1000-2000^OC in a non-oxidizing atmosphere to cause the aspirated teat to react with the carbonaceous organic polymer residue to form a metal carbide mold body, fiber or textile. The non-oxidizing atmosphere of the carbonization step may be, for example, an inert gas, hydrogen or hydrocarbon reducing gas, vacuum or a combined ion of any of these atmospheres. As a result, one obtains a T^,t ^ c ^ -fomk ^ 3? c ^ pp which has substantially the same physical form as the original i. preformed organic polymer material, although the dimensions may. have decreased as much as about M-0b0

However, without the invention being fixed by any particular theory, the theory and mechanism of the method of the invention would be as follows: Microscopically, organic polymeric materials, such as rayon fibers, composed of extremely small crystallites of cellulose chains (micelles or microfibrils) are held together in a matrix of amorphous cellulose. The crystallites ,. · About UO A in diameter and 250 'A long in high-strength rayon yarn, are parallel to the axis of the rayon fiber and are spaced about 20 · Å in the dry state. A 1-denier fiber (· tg weight per 9000 m length) has several million crystallites in its cross-section. When the fiber is dipped in a solvent such as water or aqueous solutions,. it swells sideways and opens the gaps, the amorphous regions are enlarged and the crystallite end becomes about 50 Å (in the case of rayon). The selected dissolved metal compound in the form of a salt enters the swollen amorphous regions, which constitute about 85% of the volume of the swollen rayon, and become entrapped in the amorphous regions between the crystallites as the solvent is evaporated from the fibers.

Met all compounds do not crystallize when drying the organic polymer, which would normally occur when drying a solution, since they are effectively suspended and seo pared as islands about 50 Å in size between crystallites.

The. the organic polymers can be impregnated with two or more metal compounds from the same solution, so that carbides of more than one milliliter can be prepared, for example tungsten carbide and zirconium carbide. At the first approach, most of the metal compounds in the polymer enter directly in proportion to their solution concentration, which allows for precise control of them. The relative interferences of the metal compound in the pre-formed organic polymer. Due to the segment action of the organic crystallites, the metal compounds can. not understand. from each other or crystallize during the drying and heat-curing steps, since they are finely dispersed, the 'intermediate gamma and, later, the oxides and carbides are extremely reactive and can be subjected to the necessary chemical reactions to form the desired multi-carbon alloyed product at lower temperature. which is normally required by ordinary co-precipitation or by powder blending methods for preparing such mixtures.

Any organic polyethylene material can be used as a starting material according to the present invention provided that it is characterized by the above-described structure with extremely small crystallites held together in a matrix of amorphous regions which are enlarged and release metal compounds upon immersion in the solvent. Any class of material that is assembled from long chain molecules held together by chemical bridging can also be used. Any cellulose material can be used including rayon, cellophane, saponified cellulose acetate, cotton, wood and nettle grass (ramie). Midra suitable organic materials include protligible fibers (H.1 and silk) and synthetic fibers of acrylics, polyesters, vinyls and. polyurethanes. Some organic matter! such as polyethylene and polypropylene are not suitable for use in accordance with the present invention because they cannot be swelled for suction of well compound and / or

- 7 ~ the material contaminate and lose its structure during pyrolysis.

A preferred cellulose material is rayon due to its structural uniformity, good absorbency and low contaminant content.

The physical shape and design of the product of elemental metal carbide is substantially the same as, and is determined by, the physical shape of the pre-formed organic polymeric starting material. During conversion, they agreed. metal compound impregnated the organic fibers, e.g. to the pure metal carbide fiber, the length of the fiber usually shrinks to about Η&gt; -6θ $ and the diameter to 25-35 $ of the original dimensions. Similar shrinkage in all dimensions Also occurs with the non-fibrous molds. When one wants a yarn composed of a plurality of continuous lengths of metal carbide fibers, one uses a continuous organic yarn as the starting material of the present invention. In particular, when you want a woven fabric or a blanket assembled from -meal carbide fibers, an organic woven fabric or blanket can be used as starting woven metal textiles. fibers or yarns prepared according to the method of the present invention.

In order to obtain a suitable tensile strength in the finished product of flour carbide fibers, the cellulose material is submerged with the flour compounds to an extent of at least one quarter mole and preferably 1.0-2.0 moles of the metal compound (s) in each base mole of cellulose. The term base mole used herein refers to the mole molecular weight of a cellulose chain glycoside unit (mole molecular weight 162). For non-cellulose materials, the degree of impregnation should be at least 0.1 and preferably 0.5-1.0 grams equivalent of millionion in the medium compound impregnation solution per gram of organic; polymer.

With lower concentrations of meal compound (s), insufficient amount of salt is available in the residual (leaving) of the organic matter to obtain a static body and the method is less effectively expressed in exchange of medium carbide per unit weight of pre-formed organic matter. polymeric starting A Another disadvantage of a low concentration of methyl compound is that more drastic oxidation states are necessary to achieve pyrolysis.

Impregnation, or ingestion or soaking, of the organic substance can be accomplished by several methods. When the mill element, which will be present in the finished metal carbide fiber, has salts which are highly soluble in water, the impregnation step can be carried out by reopening the organic material in a concentrated aqueous solution of such salt. When, for example, a ZrC fiber is desired, the organic fiber can be impregnated by dipping into a water-soluble solution of zirconyl chloride or zirconyl nitrate having concentrations in a range of 2.5-3.0 mol per liter. For salts which hydrolyze to a large extent (acidic reaction) when dissolved in water, the acidity of the impregnation solution is preferably not greater than 1.0 molar (in hydrogen ion) in order to prevent degradation of the organic fiber during immersion. Acid can possibly be neutralized with ammonia.

Pre-swelling of the organic cellulose polymers in water prior to immersion in concentrated soaking solutions is preferably used to increase both the rate and extent of salt entry. Water is also suitable for swelling of protein material. For acrylic and polyester polymers, aromatic alcohols are suitable swelling agents and ketones are useful in the swelling of vinyl and polyurethane polymers for the same purpose.

Water is the preferred solvent for metal compound simpregnation of cellulose and synthetic materials such as wool and silk. Other solvents such as alcohols offer a similar • efficient swelling of polymer emma or solubility to the selected metal compound for a high degree of soaking.

For vinyl and polyurethane silicone polymers. are esters and ketones suitable solvents, e.g. usually butyl acetate or methyl ethyl ketone. For acrylic and polyester polymers, including solvents suitable for multi-compound impregnation aromatic alcohols and amines such as aniline, nitrophilic, methacresol, and paraphenylpheniol. .

Neddoopninisides at normal roost temperatures (21-23 ° C) · required to provide suitable impregnation vary from 30 · minutes to several days depending on the salt used or

- the salts and the type of organic polymer used. Immersion times greater than about 3 days in concentrated saline solutions are. undesirable for fibers since the organic fiber can be degraded, resulting in a reduction in the amount of metal compound absorbed in the organic polymer and causing the polymers to bond to each other. When it is desirable to increase the extent of impregnation of the mealyl compound in the organic polymer to shorten the impregnation time, the metal compound solution can be heated to as high as 100 ° C.

One way to impregnate rayon fibers and other cellulose fibers and films with certain important alleles is to absorb water in rayon and then contact the rayon with a compound of the metal so that dn penetrates the fiber and is hydrolyzed. or reacts with the absorbed water to form insoluble metal oxide products. The meeal oxide product remains in the fiber mass without significantly disrupting the fibrous character of the rayon. The amount or amount of precipitated inside the fiber is directly a function of the amount of water absorbed in the rayon. Typical hyraol3a^,octisner is described by the following

<td colspan="7">reactions</td>

<td>SiCl</td><td> +</td><td>3H.₂O</td><td></td><td>hrs₂SiO₃</td><td> +</td><td>Uici</td>

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The amount of water absorbed into the rayon fibers is easily controlled by exposing the fibers to air containing the desired amount of moisture. For maximum water absorption can

309743 The rayon fibers are dipped directly into flowing water. Amount of water absorbed in textile quality of viscose rayon in equilibrium with moisture in air and liquid water^d 24 ° C ⁽75 ° F) is shown ne^dan:

Relative Humidity Moisture;% by weight of 2b- ° C_ dry fiber

<td> 10</td><td>M</td>

<td> 30</td><td> 8</td>

<td> 50</td><td> 10</td>

<td> 70</td><td>M</td>

<td> 80 .</td><td> 17</td>

<td> 90</td><td> 23</td>

<td> 9$</td><td> 30</td>

100 (dipped in water) 80-110 Some hydrolyzable metal compounds are liquid under normal conditions and the H 2 O strained rayon can be dipped directly into the intermediate compound to cause the hydrolysis product to form in the fiber. Examples of liquids are SiCl 2, TiCl 2 WOOC 3, VCC However, many of the hydrolysis reactions proceed very quickly with the growth of worms. The resulting hardened states can degrade or break up the fibers; in this case, the metal compound is preferably diluted with a non-reactive, miscible liquid to avoid such conditions. Many non-polar organic liquids, such as benzene, toluene, hexane, carbon tetrachloride, chloroform, are suitable non-reactive liquids. These organic liquids, when used as diluents for the singlet compounds, slow down the rate of hydrolysis and help to dissipate the heat from the reaction. Hcke-rea309745

- 12 ferrous metal compound liquid (as well as any diluent) can be removed from the intermediate fibers by evaporation, as they have high vapor pressures.

Other compounds which can be incorporated into fibers, films and. similarly by hydrolysis reaction, but normally liquids are best dissolved in a non-reactive liquid which is immiscible with water. Such metal compounds include, for example, SaCl ^, NbCl ^, ZrCl ^, UCC ^. Suitable solvents are bromoform, carbon tetrachloride, diethyl ether and nitrobenzene.

After impregnation with. metal compound (s) from a solvent solution, it is necessary to remove excess solution from. the positions between the organic fibers before drying in order to avoid the bonding of fibers by salt cakes. If excess of the non-suctioned meal or hydrolysis product is allowed to remain on the fibers, this results in reduced strength and increased brittleness in the finished product of meal carbide fibers. In most cases, it is sufficient to dry up the excess with an absorbent paper or cloth using moderate pressure. In addition, vacuum filtration and nitrification have been shown. are effective methods for removing excess solution from the positions between the fibers.

Increase in temperature. of the wet fibers to 50 ° -6 ° C contributes to the removal of excess shot solution from the fibers during drying with absorbent apertures, vacuum cleaners, or centrifugation.

?

- 13 309745

The one with. metal compound impregnated organic polymer is then thoroughly dried in any convenient manner, such as air drying or heating in a hot gas stream at a temperature not exceeding 70 ° C. It is desirable to dry the polymer quickly (within about 1 inch or less) to prevent the extrusion of the metal compound from the interior of the organic polymer to its surface.

When a product containing two or more metal carbides is desired, the organic polymer is impregnated with compounds containing all of the desired - alleles · When, for example, two or more water-soluble salts are used, the impregnation can be carried out with a single dip in an aqueous solution containing both salts · When two mills are desired, one of which is sucked into the organic polymer from aqueous solution and the other. is introduced by hydrolysis of methyl halide or oxyhalide from organic solution^- a preferred way to first impregnate with the hydrolysis product and then with the water-soluble salt.

In the next step of the process of the present invention (decomposition of the organic polymer structure), the organic polymer impregnated with the metal compound is heated under controlled conditions, namely: (1) to a temperature of at least 2 ° C, (2) at a rate sufficiently low to dispense volatile decomposition products of the polymer without destroying polymer integrity; (3) for a sufficient period of time to decompose the organic structure of the polymer; and

- ιΑ to form a carbonaceous residue (leaving) containing the metal compound in fine dispersed form. with

It is necessary to heat the polymer to impregnate the impregnated polymer at a rate sufficiently low to avoid ignition of the polymer. If the organic polymer burns instead of being carbonized, the temperature of the mealyl compound rises too sharply, due to its intimate relationship with the organic structure. In such circumstances, it is impossible to control the temperature, even the melting point of formed / intermediate compounds may be exceeded or excessive crystallization or nucleation will occur. Also, the metal compound may be suspended, in the organic compound, vapors, and so on, and lost to the environment and may not be available to form the desired residue (leaving). When ignition is avoided, the finished foam bodies, fibers and textiles have smoother surfaces, are more flexible. oeh are stronger. Ie very rapid heating and extrusion of decomposing gases cause the polymer continuity to break or result in excessive crystallization of. the metal salt or oxide within the polymer residue which, as a final result, does not result in as smooth, flexible and strong merall carbide products as the non-ignited amorphous or low crystalline, more dense intermediate metal oxide.

The first annealing step is usually carried out in an oxidizing inert atmosphere, e.g. it sown ^^ - but fellow

Nitrogen, helirai, argon, neon and the like, or a vacuum. However, if it is desirable to reduce the amount of carbon remaining from the polymer's pyrolysis step, some or all of this first heating step may. is carried out in an oxygen-containing atmosphere, preferably with about 5 to 25% by volume of oxidizing gas. The rest of the gaseous atmosphere consists of gases that are chemically non-reactive with the environment, e.g. aforementioned inert gases. Before an oxygen-containing gas is used, a portion of the carbon is removed as a carbonaceous gas by reaction with the oxidizing gas (volatile gas). The oxidation provides a means of reducing the carbon content of the polymer residue, and an adjustment of the carbon-to-metal ratio for the subsequent carbonization reaction occurs. Generally, the cellulose pyrolysis yields about b moles of carbon per mole of cellulose as a residue, and the carbon-to-metal molar ratio required for a stoichiomeric carbonization reaction is about 3/1 to 7/4.

Thermal heat is affected by the alloy whether it is inert or oxidizing, the latter being more difficult to control. In an oxidizing atmosphere, the velocity of velocity may be at least¹⁰⁰° C ^pis thne or ^haycomb, so. ^lthan^ge as ignition ignition is avoided. It is preferred to heat the polymer at a rate of between 10 ° C and 100 ° C per hour in an atmosphere containing 5-25% by volume of oxygen, although higher heating rates may be satisfactory with effective measures for ventilating the carbonaceous gas. Higher oxygen concentrations may be appropriate, especially during the latter part of it

- 16 first heating step ·. The preferred oxidizing gas is oxygen, although other oxidizing gases such as nitrogen dioxide and sulfur trioxide may be used if desired.

When wetting of the impregnated polymer is first started (even in an oxidizing atmosphere), the pyrolysis of the polymer to carbon is the predominant chemical reaction. The carbonized organic polymer is predominantly carbon but may also include small amounts of residual acid and hydrogen. If heating is continued and in an oxidizing atmosphere, oxidation of the carbon becomes the predominant reaction.

In the final process step according to the invention, the residue (leaving) from the first heating pyrolysis step is further heated to a temperature between about 1000 ° C and 2000 ° C in a non-oxidizing atmosphere to cause the reaction to react with the carbonaceous residue to form a metal carbide fiber, textile or mold body. The non-oxidizing atmosphere may be a vacuum, an inert gas such as nitrogen, helium or argon, or alternatively a reducing gas such as hydrogen or a hydrocarbon.

A carbonization temperature of at least about 1000 ° C is necessary to form a crystalline structure, which in turn produces a high-strength solid product. Ie that the tensile strength of the metal carbide products according to the present invention is^sthaw^rre than 7O^,3 ^kg/ nm ^{(100 000} psi). It is desirable to limit the carbonization temperature and time period to achieve minimum grain size in the product. In the preparation of

- 17 fibers preferred crystal grain sizes of less than 0.2 of the fiber diameter. Larger crystal grain sizes reduce fiber strength and flexibility. The speed of heating in the car boniserin^gsste^git is not critical; ^hrsAsti^ghether from approx ²⁰⁰° C to 10Ö0 ° C per hour has proved suitable, although higher speeds can be used. Similarly, the total duration of the carbonization step is not critical, and periods of between about 1 and 4 hours can be used for one. batch process, while shorter times can. used in a continuous. process.

As stated above, any metal forming a stable carbide can be used in the practice of the present invention. The preferred carbon: iron content expressed in reaction temperature and molar ratio will vary somewhat depending on the selected carbon-to-metal molar ratio. for a stoichiomeric reaction the mean is about 3/1 and 7/4. It is preferred to carry out the carbonization under approximately stoichiometric conditions when desiring a substantially pure metal carbide product. However, non-stoichiometric states can be used. For example, excess carbon can be used if the desired product is a metal larbide / lol mixture.

One of the outstanding characteristics of the microcrystalline single-crystal biller products of the invention is their retention of high temperature flexibility and strength. For this reason, the products are preferably prepared using etals which form carbides having relatively high salt patches of at least 188 ° C (3300 ° C?)

300745

This base includes preferred metals from those of group ba, (titanium, zirconium and hafnium), group 5a (vanadium, niobium and tantalum). and group 6a (chromium, molybdenum and tungsten) of the periodic table, as well as boron, aluminum, silicon, toriim, uranium and plutonium. In the following Table 1, preferred impregnation methods and carbonization temperatures for the preparation of these metal carbides using rayon fibers are listed.

The millicarrid fibers of the present invention are useful for many purposes. For example, they can be used for reinforcing plastics to be used at relatively low temperatures, and reinforcing metal and ceramic bodies for use at high temperatures, especially where high strength, high Yotmg's modulus and low weight are desirable. To coat plastics, the fibers belong to / find spikes on and / or be interconnected within the glomerular fairness of the plastic body since the loading of the embedded fibers is carried out via a shear transfer process at the intermediate surface between the matrix and the fiber. Since the shear strength of polymers is low, a greater transfer length (i.e., on the fibers) is necessary if the fibers are to carry the bulk of the load. Plastics reinforced with short fibers generally show tensile strengths of about 35 kg / mm (350 kg / cm), while the same polymers reinforced with continuous (continuous fibers) may exhibit tensile strengths of Γ / 5 ^kg/ m^{2 (1}75OO kg / cm²) Or p^thawRRE. Continuous fiber yarns according to the present invention made from boron carbide (B 2 C) and silicon carbide (SiC) are particularly suitable for reinforcing plastic bodies.

Since these metal carbide fibers can be made in the form of fabric and continuous yarn, they can be used to be wound as fiber wires in and around composite drops.

The metal carbide fibers, textiles, and mold bodies of the present invention are generally useful as insulating materials in high temperature applications, as corrosion resistant articles and the like.

According to the method of the present invention, a pre-formed organic polymeric material is used. The term preformed means that the organic polymeric material has been fabricated into a fibrous or non-fibrous mold body prior to impregnation with the intermediate compound.

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US

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CM OO

CM

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CM

- 21 309745

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- 22 . '1

The metal carbide mold bodies of the present invention have a wide field of application. Metal carbide bodies made from organic foam material or sponge material are also useful as filters.

For use as a filter, it is preferred that the all-carbide bodies of the present invention be prepared from foam or sponge material on eellulose-based canned food of open porosity, uniform pore size and low. density. '

Metal carbide films inherited from the present invention are sheets having high uniformity in thickness and which may be 10 microns.

The following Examples 1-6 illustrate the process for preparing crystalline mlcalcarbide products according to the present invention.

Example 1: UC fibers

7.1 g of 1.5 denier ordinary viscose fiber was swollen by dipping in water for 1 hour, and then dipping in 100 ml of a uranyl chloride (W 2 C 2) aqueous solution having a temperature of 4.20 and After a 10 minute immersion in the solution, the fibers were removed and centrifuged for a specific weight of 2.11. After the water in the swollen area diluted the solution, it was later replaced with a new 100 ml of 4.2 molar UO to remove excess solution. The fibers contained 3.3 grams of solution per gram of rayon. They were dried in₍a hot air stream and after drying they weighed 22.2 g, including 1.57 g

- 23 absorbed uranium per gram of rayon. These fibers were then placed in a tube-type oven and heated in a vacuum of about 1 micron Hg at a heating rate of 10 ° C / hour to 900 ° C. The oven was then allowed to cool to room temperature under vacuum. The resulting carbonaceous fiber residue weighed IU, 9 g, and contained finely dispersed uranium with a carbon-to-uranium atomic ratio of 3.7 · The fibers were black, glossy and strong and there was no fiber breakage.

fiberThese carbonaceous / residues had about the proper carbon-to-uranium ratio to produce mono-uranium, carbide fibers by heating to temperatures of about 15002000 ° C in a non-oxidizing atmosphere. For example, through the reaction UO, g + 3C-hUC + 2CO, UC fibers could be prepared by heating uranium-impregnated rayon fibers to about 1700 ° C and maintaining this temperature level for a period of 1 hour in an argon atmosphere.

Example 2: WC fabric sheet

The solution used for impregnation was prepared by dissolving MOO g of ammonium paraffinate in b-00 ml of 30 $ hydrogen peroxide solution. The solution was warmed to 60-70 ° C at which temperature the ammonia volume of vol: fi ammonium reacted with the hydrogen peroxide and dissolved within 5-10 minutes. The clear solution was then quickly cooled to pestle temperature and contained 655 g of tungsten per hter, with a^pECI^got weight of 1^,82 ^g/ cm^hrs and one ^pH of 1.1. The rayon fabric was of 5-shaft satin weave in both warp and weft directions using the textile fabric of

- 24 viscose rayon yarns (1650 denier / 720 fiber threads), the weight of the fabric being 5X0 g / m A fabric piece of 154 x 462 mm weighing 35? 6 g was dipped in the tungsten salt solution for 17 hours. From chewed, excess solution was then eventrifuged and the fabric dried in warm air. The dried fabric contained 1.2g tungsten salt / g rayon.

The fabric was converted to tungsten carbide by first heating in air at a rate of 20 ° C / hour to 300 ° C and kept at this temperature for 4 hours. The fabric ·· was then further heated at a rate of 50 ° C / hour until 35θ ° θ was reached and this temperature was maintained for 4 hours, thereby forming the carbonaceous fiber residue containing finely divided tungsten in dispersed form. The air in the tube furnace was then expelled with nitrogen before the carbonization reaction began. Dry hydrogen was brought through the furnace at a rate of 4 liters / minute (SPT) when the fabric was heated to 600 ° C within 30 minutes and held at 600 ° C for 1 hour, then heated to 1000 ° C and kept there for 1 hour. During the pyrolysis and carbonization steps, the fabric shrank from 154 x 462 mm to 77 x 254 mm.

The weight of the tungsten carbide fabric was 73% by weight of the starting material, ie. rayontyget.

The carbonized fabric had the following physical and chemical properties:

1st Looks: glossy and metallic gray.

2nd Flexibility: could be folded without weighing or breaking.

- 25 309745

3 · Tear strength strength 1,4 1.4-5-2.50 kg / cm width.

4th Composition: by X-ray powder diffraction analysis, the fabric was found to be composed mainly of highly crystalline tungsten carbide (WC) (ie at least 80% by weight) and traces of tungsten number.

5th Coholt's 4.98% by weight;

6th - Specific weight: 1^4,7 ^{g /}cm 2 determined ^genom the bromoform pycnometer method.

7 · Electric power: 0.43 ohms per 1 cm wide

15.4 cm in length (in the length dimension).

Eighth Fiber diameter: 5-6 microns.

9 · Crystal grain size: 1 micron.

Example 3: ZrC fibers

The wall material was a blend of viscose rayon fibers

1.5 denier (133,000 continuous fiber threads in the blend) ·. The 6.8 g film was swollen in water for 15 minutes prior to dipping in 2.84 moles of ZrOCl 2 solution for 4 hours. Then, the non-suction solution was centrifuged from the interstitial fibers and the air dried. The screened rayon mixture weighed 12.5 grams and contained 0.84 grams of zirconium salt per gram of rayon.

The well was placed in a tube furnace and heated under a vacuum of 1-10 microns Hg at a rate of 50^ο0 / ϊΡπ ^ to 4⁰⁰° C ^dlibel^ft^eRV^{id 100}C / T^pNME ^- to 1⁰⁰⁰° C. The^pyrolysera^dthe fibers were black,. had a high gloss and weighed 6.0 g. The fiber residue contained 33.7 wt.% carbon and 43.0 wt.

-26 percent zirconium.

In order to carry out the carbonization reaction between the carbon and the zirconium, the fiber residue was placed in a graphite crucible and heated at 1900 ° C for 2 hours in a hydrogen atmosphere using a high frequency induction furnace. The resultant fibers weighed 4.2 g, had a black-gray color, showed no signs of sintering and had a diameter of 4-5 microns. The fibers were very flexible and had a tensile strength of between 7⁰ oc^{h 10}5 ^kg/ mm². The fibers for electrically conductive and X-ray diffraction patterns showed that the fibers were co-assembled from polycrystalline surface centered cubic zirconium carbide (ZrC). Some gafit lines were not observed in the X-ray island site. The fibers were over 305 mm long with a crystal grain size of less than 0.2 microns.

Example 4; Tk fibers

A 305 mm length of 9 µm of dernier viscose rayon blue (22,000 continuous fiber wires in the blue) was dipped in a 1.6 ml TiCl 3 aqueous solution for 4 hours. The blister was freed from the non-suction solution by means of blotting paper technique and. dried. The rayon blister containing the TiCl 2 salt was pyrolyzed and carbonized in the same manner as described in Example 3. The fiber product was greyish-black, flexible and had a diameter of 12-15 microns. The only crystalline phase present in the fibers, such as X-ray diffraction powder analysis, was the surface-centered cubic titanium carbide (T ± C). The crystal grain size was less than 0.5 micron and

Thus less than 0.2 of the fiber diameter. Fibers of TiC with lengths of 15 m have been produced by the same method.

Example, 5 t Bt_|C: fLb.re.r

A 305 mm length of 20 denier viscose rayon blue (10,000 continuous filaments in the blue) was dipped in an aqueous solution containing 25 wt% boric acid for one hour. The solution was kept at 90 ° C during the impregnation to keep the boric acid in solution. The bladder was then centrifuged while the fortfarinide was kept warm to remove the non-aspirated boric acid.

from the fiber between the fibers. After drying the blister in air, it was subjected to the same pyrolysis and carbonization treatment described in Example 3 ·

The finished fibers were black, free from each other and had considerable flexibility and strength. X-ray diffraction analysis showed that the fibers consisted of crystalline boron carbide (B ^C). The diameter of the fibers was about 20 microns and the crystal size was less than 0.2 of said diameter.

Example 6; SiC fibers

A 5δθ mm length of 20 denier viscose rayon blue (10,000 · continuous fiber filaments in the blue), weighing 13.3 g, was dipped in silica tetrachloride liquid for 30 minutes. Prior to dipping, the blister contained 1, + g of absorbed lattice. After 30 minutes dipping, the reaction with the silicon tetrachloride and the water in the rayon was complete, as evidenced by the cessation of HCC gas evolution from the fibers. The blister was freed from excess silicon tetrachloride by evaporation. The towel then weighed 15 g and contained 3&gt; 1 g of silicic acid. The silicon rayon blend

- 28 were pyrolyzed and carbonigrated in the same manner as described in Example 3 · The finished fibers had a metallic sheen, weighed 3.9 g, and were characterized by considerable flexibility and strength. X-ray diffraction samples showed a mixture of crystalline SiC and graphite. The fiber diameter was about 20 microns and the crystal grain size was less than 0.5 microns.

Although preferred embodiments of the invention are described in detail herein, it will be apparent that modifications to the method and composition may be made and that certain known characters may be used without others, but fall within the scope of the invention.