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

Beginning of the patent period; 15, August 1969.

The invention relates to a process for the production of fibers, textiles and molds from elemental metal.

Until now, elemental metal fibers have been made by various methods, but all have significant limitations. So z. For example, in the scraping or peeling method, a wire passes a large number of blades to peel off small fibers. This method is severely limited by the fact that the base metal must have a high tensile strength, and it is not possible to peel fibers with less than about 20 μ diameter in the production machines.

In the whisker method, fibers are formed from the vapor phase or by electrolysis of a molten salt. This process is too expensive for large-scale production.

Processes for the production of metal oxide fibers are known in which, starting from preformed fibers, by allowing them to be allowed to burn off or by annealing, ie in each case with a high temperature increase, the organic starting material is decomposed. If the organic material is exposed to high temperatures during decomposition, a product with only low mechanical strength results. This will be discussed later in detail.

None of the previously known processes produce continuous elemental metal fibers in lengths that can be processed into coiled yarns or wipes. If the fibers z. B. manufactured according to the widespread Drahtziehmethode must follow such a rotation and shaping after fiber formation. This is a time consuming and expensive process that is often rendered impossible by lack of tensile strength or shear strength.

The object of the invention is a new cryogenic process for the production of elemental metal fibers, textile molds or shaped metal articles, which does not have the disadvantages and limitations of the previously known methods. The fibers should consist predominantly of one or more elemental metals, with diameters of 3 μ or less, length / diameter ratios of over 400, tensile strengths of over 2800 kg / cm² and have high flexibility.

The textile forms produced according to the invention include staple fibers, continuous tow and yarn, woven fabrics, wadding and felts made of elemental metal fibers. The molded metal articles include films, pipes, shells, and other forms made of elemental metal. The novel fibers, textiles and shapes consist of one or more metals of the

Group IB (copper, silver and gold), VIB (chromium, molybdenum and tungsten), VIII of the Periodic Table (iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum), technetium,

Rhenium and zinc. All of these metals have a melting point above 350 ° C, and the corresponding ones

Metal oxides have a free energy of formation (AF) at 350 ° C of up to 73 kcal / gram atom of oxygen as seen in Table I.

No. 280464

Table I;

<td>elemental metal</td><td>melting point (° C)</td><td>oxide form</td><td>ΔΓ of the oxide at 350 ° C</td>

<td>Cu</td><td>1083</td><td>Cu₂O</td><td>29</td>

<td>Ag</td><td>960</td><td>Agio</td><td>0</td>

<td>Au</td><td>1063</td><td>Au₂O</td><td>0</td>

<td>Cr</td><td>1890</td><td>C^r2 ° 3</td><td>73</td>

<td>Mo</td><td>2625</td><td>MoO₂</td><td>53</td>

<td>W</td><td>3410</td><td>Where₂</td><td>55</td>

<td>tc</td><td>2700</td><td>TcO₂</td><td>39</td>

<td>re</td><td>3170</td><td>ReO₂</td><td>38</td>

<td>Fe</td><td>1539</td><td>FeO</td><td>53</td>

<td>Co</td><td>1495</td><td>CoO</td><td>44</td>

<td>Ni</td><td>1455</td><td>NiO</td><td>44</td>

<td>Ru</td><td>2500</td><td>RuO₂</td><td>13</td>

<td>rh</td><td>1966</td><td>K *&gt;₂° 3</td><td>7</td>

<td>Pd</td><td>1550</td><td>PdO</td><td>7</td>

<td>os</td><td>2700</td><td>OsO₂</td><td>18</td>

<td>Ir</td><td>2454</td><td>Fri.₂O₃</td><td>10</td>

<td>Pt</td><td>1774</td><td>pto</td><td>3</td>

<td>Zn</td><td>419</td><td>ZnO</td><td>68</td>

Metal compounds, such as metal oxides, may be included in the elemental metal fibers, textiles, and molds made in accordance with the present invention, but in amounts less than 20 percent by weight.

The elemental metal fibers may be in the form of a large number of textile forms, such as in staple fibers of 1.6 to 75 mm in length and more, in continuous tow and yarn, rovings, woven fabric, knits, edgings, felts, papers and the like.

The inventive method is that

a) a preformed organic polymeric material is impregnated with a compound of one or more metals of groups IB, VIB or VIII of the periodic table, technetium, rhenium or zinc in a manner known per se in order to obtain an impregnated material,

b) heating said impregnated material to a temperature high enough to carbonize and then volatilize said organic polymeric material, wherein said step b) is carried out under conditions which inhibit the ignition of said organic polymeric material prevent and

c) the product of step b) is heated in a manner known per se in the presence of a reducing gas to a temperature which is high enough to reduce the product from step b) to the elemental form.

As used herein, the term "preformed" means that the organic polymeric material would be formed into a fibrous or non-fibrous form prior to being impregnated with the metal compound.

The physical form and shape of the elemental metal product is substantially the same as that of the preformed organic starting material, although significant shrinkage occurs. During conversion of impregnated organic fibers to elemental metal fibers, both the diameter and length of the fiber shrink to about 40 to 60 percent of the original dimensions. A similar shrinkage of all dimensions also occurs in the non-fibrous forms.

When a yarn is desired from a variety of elemental-metal fibers of continuous length, an organic continuous-fiber yarn is used as the starting material for the process of the present invention. If a woven fabric or a felt of elemental metal fibers is to be produced, an organic pulp or felt may be used as the starting material. Of course, textiles woven from metal can also be obtained by starting from metal staple fibers or yarns produced according to the invention and processing them by the usual textile production processes.

Theory and method mechanism of the method according to the invention should be as follows;

Microscopically, organic, polymeric materials, such as cellulose, are extremely small crystallites

No. 2809464 of polymeric chains (micelles or microfibrils) held together in a matrix of amorphous polymers.

If the organic material is immersed in a solvent, such as. As in water, aqueous solutions or organic solvents, it swells, which open the cavities between the crystallites. The amorphous areas and the distance between the crystallites increase. The dissolved metal compound, for. As a salt, penetrates into the swollen amorphous areas, which are generally about 50 to 90 vol. -% of the swollen organic material and remains trapped in the amorphous areas between the crystallites when the solvent is removed from the material.

The metal compounds do not crystallize during drying of the organic material, as would normally be the case when drying most of the solutions, since they are effectively suspended and separated as islands of about 50 Å in size in the case of cellulose between the polymer crystallites.

The organic polymeric material may be impregnated with two or more metal compounds from the same solvent so that fibers, textiles, or molds containing more than one elemental metal may be prepared. In a first approximation, most metal compounds will enter the cavities in proportion to their solution concentration whereby the relative loading of the metal compound organic material can be easily controlled. Because of the blocking effect of the organic crystallites, the metal compounds and later the oxides and elemental metals can not separate or crystallize during the following steps.

Any polymeric organic material may be used as the starting material for the process of the present invention, provided that it has the above-described structure of extremely small crystallites held together in a matrix of amorphous regions which increase upon immersion in the solvent and which Allow metal compounds to penetrate. Also, materials composed of long-chain molecules held together by chemical crosslinking can be used, provided that these materials are capable of swelling and of absorbing the solvent, and provided that the organic polymeric material does not melt on heating. Any cellulosic material may be used, for example, rayon, saponified cellulose acetate, cotton, ramie, wood, and the like. similar. Other suitable organic materials are e.g. Proteinaceous materials (such as wool and silk) and the artificially prepared acrylics, polyesters, vinyls and polyurethanes. Certain organic materials, e.g. Polyethylene and polypropylene, are not suitable for use in the process of the invention because they do not swell and therefore do not soak up the metal compounds and / or melt during pyrolysis and lose their structure. A preferred pyrolysis material is rayon because it has structural integrity, good wicking properties, and high purity.

The impregnation or impregnation of the organic material can take place in various ways. If the element to be formed in the finished metal article forms salts which are readily soluble in water, impregnation can be carried out by immersing the organic material in a concentrated aqueous solution of such a salt. If z. For example, when a nickel fiber is desired, an organic fiber may be prepared by immersion in an aqueous solution of nickel nitrate (Ni (NO₃)₂) or nickel chloride (NiCl₂) are impregnated at concentrations of 2.0 to 4.4 moles salt / l. For salts which hydrolyze when dissolved in water (acid reaction), the acidity of the impregnating solution is preferably not greater than 1.0 molar (hydrogen ion) in order to prevent degradation of the organic material during immersion. The acid can be neutralized with ammonia if desired.

In order to obtain adequate strength for the elemental metal end product, cellulosic materials are soaked to the extent of at least 1/4 mole and preferably from 1.0 to 2.0 moles of metal compound (s) per mole of cellulose. As used herein, the term base mole refers to the molecular weight of a glycoside unit of the cellulose chain (molecular weight 162). For non-cellulose containing materials, the concentration should be at least 0.1 and preferably 0.5 to 1.0 gram equivalent metal in the solution containing the metal compound / gram be organic material. After that z. B. at least 0.1 x 183.9 / 58.7 or 0.31 g of tungsten metal in a solution to be absorbed by 1 g of a non-cellulosic fiber. At lower concentrations of the metal compound (s), too little elemental metal remains in the organic material residue to form a mechanically strong article and the process becomes less productive in terms of elemental metal yield per unit weight of the organic starting material.

No. 280464

It is preferred to pre-swell the organic cellulosic materials in water prior to immersion in the concentrated impregnating solutions to increase the extent and rate of salt impregnation. For acrylic and polyester materials, aromatic alcohols are suitable swelling agents, and the ketones are useful for the same purpose for swelling vinyl and polyurethane materials.

For the impregnation of cellulosic materials in metal compounds, water is the preferred solvent. Other solvents, such as alcohols, do not cause such effective swelling and solubility for the chosen metal compound to be highly soaked. For vinyl and polyurethane materials, esters and ketones are suitable solvents, e.g. B, normal butyl acetate or methyl ethyl ketone, For acrylic and polyester materials z. B. aromatic alcohols and amines such as aniline, nitrophenol, meta-cresol and paraphenylphenol, suitable solvents for the metal compound.

At room temperature (21 to 23 ° C) a dipping time of a few minutes to several days, depending on the used. Salt (salts) and organic material to achieve adequate impregnation. An immersion time of more than three days in concentrated salt solutions is unfavorable to cellulosic materials because the material may degrade, resulting in a decrease in the amount of salt absorbed. In the case of fibers, a sticking together of these is caused.

To illustrate the impregnation step, it should be noted that Viscoserayon swells rapidly and ZnCl₂ absorbed to a great extent from concentrated solutions. Within 15 minutes, water-swollen viscose rayon absorbs 3.4 moles of ZnCl₂/ Base molar rayon from a 6.8 molar solution at 21 ° C. However, the rayon impregnated by this treatment practically swells into a gel and becomes sticky. In this swollen state, the rayon is too weak for treatment and the fibers can not be separated. The preferred method of impregnating rayon with ZnCl₂In the case where the salt-loaded rayon does not decompose and the fibers do not stick together, immersing water-swollen rayon in a 3.6 to 4.0 molar solution for 1 to 3 hours. In this treatment Viskoserayon absorbed 0.6 to 1.0 moles of ZnCl₂ / Base mole rayon.

If the rate of penetration of the metal compounds into the organic materials is to be increased in order to shorten the immersion time, the solution of the metal compound may be heated up to 100 ° C. Thus, for example, the immersion time of salts, which are absorbed only slowly by cellulose fibers, can be shortened by raising the temperature of the salt solution to 50 ° C. However, care should be taken at elevated temperatures because many salts strongly decompose the organic material at high temperatures.

After soaking up the metal compound (s) from a solution, it is necessary to remove the excess solution from the space between the organic fibers prior to drying so that the fibers are not joined together by salt and to remove them from the surface of the non-fibrous forms to avoid salt deposits on it. Leaving unswept salt or hydrolysis product on the fibers results in reduced strength and increased brittleness in the final elemental metal product. For the removal of excess solution from the organic material, it is convenient to thoroughly wipe it with absorbent paper or tissue under moderate pressure. In addition, washing, the use of high velocity gas streams, vacuum filtration and centrifugation to remove the excess solution have proven useful. For solutions with viscosities greater than about 10 cP, increasing the temperature of the organic material to 50 to 60 ° C helps to remove the excess solution,

Then, the impregnated organic material is removed by suitable methods, e.g. B. by air drying or heating in a warm gas stream, carefully dried. It is desirable to rapidly dry the impregnated fibers (within 1 hour or less) to prevent the salt from migrating from the interior of the organic material to its surface.

When a product containing two or more elemental metals is desired, the organic material is impregnated with two or more salts or hydrolysis products. When two or more water-soluble salts are used, the impregnation can be carried out by simply immersing in an aqueous solution containing both salts. When two metals are desired, one of which is introduced from an aqueous solution into the organic material and the second by hydrolysis of the metal halide or oxyhalide from organic solution, a preferred method is to add first with the hydrolysis product and then with the water-soluble salt impregnate.

No. 280464

In the next major step of the process of the invention (the decomposition of the preformed organic polymeric material), the impregnated organic material is heated under controlled conditions. This heating must be sufficiently long so that the organic structure is destroyed and a carbonaceous residue is formed which contains the metal compound in finely dispersed form, with at least one part of the carbon removed simultaneously and / or subsequently.

The controlled conditions must be such that ignition of the organic material is avoided. In the impregnated organic materials used in the process of the present invention, combustion tends to take the form of an uncontrolled increase in temperature within the material rather than the shape of a flame. An uncontrolled temperature rise is a rapid increase substantially different from the heating of the impregnated organic material and its environment , If the pyrolysis conditions are properly controlled, the temperature rise in the impregnated organic corresponds^-Material is almost exactly the temperature of the environment (atmosphere, furnace wall and the like,), although the exact temperature of the organic material in comparison with the nominal temperature of the environment has small deviations. When the organic material ignites or burns instead of charring, the temperature of the metal compound excessively increases because of the close proximity to the organic material. Under such circumstances, it is impossible to control the temperature, whereby the melting point of the intermetallic compounds formed can be exceeded. In addition, the metal compound can be suspended in the pyrolysis product vapors and thus lost to the environment, thereby failing to form the desired residue. If ignition is prevented, the products have smoother surfaces and are stronger because of the more ordered arrangement of the metal compound particles.

In practice, a convenient way to determine whether a fire has occurred during the heating steps is to determine the degree of shrinkage or the degree of compaction of the organic starting material. Namely, if no ignition has taken place, the impregnated organic material is subjected to a significant shrinkage along its longest extent, which is generally on the order of 40 to 60%. (Shrinkage of 10 cm length to 5 cm length is a 50% shrinkage.) The intermediate metal oxide product is strong and microcrystalline and very flexible in the case of fiber products. However, if undesirable ignition has taken place during the heating steps, the amount of shrinkage is significantly less and the resulting metal oxide intermediate is more crystalline than microcrystalline, brittle and of low strength. If ignition occurs towards the end of the charring step, the amount of shrinkage can still be considerable the physical properties of the product will be less favorable. In general, the amount of shrinkage is inversely proportional to the loading of the metal compound organic material. It has proven convenient to adjust the process conditions so that maximum shrinkage occurs for the particular metal compound loading of the impregnated organic polymeric material.

It has been found that in practice, ignition can be prevented by employing controlled reaction conditions, in particular conditions which can cause harsh temperature fluctuations and variations in atmospheric composition and the like. similar. be avoided. Severe changes of conditions usually lead to the uncontrolled temperature increases in the impregnated organic material, which lead to a flaming as defined above.

As an example of such controlled conditions, cellulose fibers impregnated with metal salts were heated to a temperature between about 350 and 900 ° C in an atmosphere containing between 5 and about 25% by volume of oxidizing gas at a rate of not more than 100 ° C. h heated. (It is of course clear that if the metal compound intermediate is an oxide such as Ni₂O₃ or co₂O₃with a decomposition or melting point lower than 900 ° C, the organic impregnated material should not be heated above this temperature.) At present, since the impregnated fiber is heated to 350 ° C and higher under the conditions described above, the most of the cellulose fibers have been pyrolyzed (carbonized) to carbon and the carbon has been removed in the form of a carbon-containing gas, while most of the metal compound in the impregnated fiber will disintegrate and / or be oxidized to the metal oxide form.

After the first slow heating to a temperature above 350 ° C., it is no longer necessary to keep the content of oxidizing gas at 25% by volume or less, although in general there is no significant advantage in using an atmosphere exceeding 25% Vol. -% oxidizing gas contains. The preferred oxidizing gas is oxygen, although other oxidizing as desired

No. 280464

Gases such as nitrogen dioxide and sulfur trioxide can be used. The rest of the gas atmosphere contains gases that are chemically unreactive at temperatures up to 900 ° C and more, eg nitrogen, helium, argon, neon u. similar. In the first heating cycle, it is in many cases not essential to use an oxidizing gas.

In the process of the present invention, it is important to control the process variables so as to prevent ignition and / or burning of the organic part of the impregnated organic material. This can be achieved in many ways, ζ. By controlling the temperature, limiting the amount of oxidizing agent present for the impregnated material, or using vacuum or an inert atmosphere. It should be remembered that in many organic materials, such as ζ. B, in cellulose, a part of the chemical structure consists of oxygen, so that in the impregnated material itself a certain amount of an oxidizing agent is present. Here it is recommended to use smaller batches of the impregnated material or relatively low heating rates, especially at temperatures up to 350 ° C, to prevent unwanted ignition. However, it has been found that in many systems, particularly impregnated cellulosic fibers from which excess solvent has been removed, and which have been carefully dried, rapid heating is possible in a vacuum or inert atmosphere without causing ignition.

Control of flammability conditions is generally easier with fibers or fibrous materials, such as textiles, than with non-fibrous forms, such as organic foams or sponges, which have been impregnated with metal compounds. In such non-fibrous forms it is generally preferred to use non-oxidizing atmospheres in the first part of the carbonation-oxidation process and to keep the heating rate below 50 ° C / hr. After a substantial part of the carbonation step is over, an oxidant can be introduced into the atmosphere. It is also possible to carry out the entire carbonation treatment of non-fibrous forms by heating at rates between 10 and 50 ° C / h in atmospheres containing 5 to 25% by volume of oxygen.

With fibrous and non-fibrous materials it is rarely necessary to use temperatures above 1000 ° C.

The precise choice of reaction conditions will of course depend on the shape and chemical composition of the organic starting material and the metal compound (dea) used in the impregnating step).

The carbonation of the impregnated organic material and the removal of this carbon by volatilization (usually to CO or CO₂) are not separate steps. When the heating of the soaked organic material is started, pyrolysis of the organic portion to carbon is the predominant chemical reaction. The carbonated organic material contains predominantly carbon, but may also contain small amounts of residual hydrogen. However, there is usually little oxidation of the carbon formed and the metal present in the impregnated fiber. As heating proceeds, while virtually all organic material is converted to carbon, the oxidation of the carbon, and often of the metal soaked in the fiber, becomes the predominant reaction.

In this first heating step, in which the organic polymer is first carbonated and then oxidized, the metal compound is also usually oxidized to the metal oxide. However, it is not essential to produce metal oxide in this step as long as the metal remains in the form of a compound which

a) is reducible to elementary form last, and

b) is relatively non-volatile so that the metal compound is not volatilized during the heating steps.

As the carbon is volatilized, microscopic voids are formed in the fibrous or non-fibrous form. Maximum densification is achieved by limiting the concentration of the oxidizing gas and the temperature of the mold below about 500 ° C during the first heating oxidation step. This step usually comes to an end after 1 to 48 hours, depending on the metal compound (s) and the resulting intermediates, ζ, B, the metal oxide, or the metal oxide mixture. Many metal compounds, such as iron oxide, copper oxide and chromium oxide, increase the rate of carbon oxidation from the organic material; With the presence of these metal oxides in the fiber, relatively lower temperatures are normally used.

The volatilization of the carbon at a higher rate (evoked either

No.280464 by increased concentration of the oxidizing gas or relatively higher temperatures in the early stages of this step) results in a less dense and weaker elemental metal form, due to the voids remaining in the mold. Relatively high temperatures above 500 ° C also induce crystallite formation in the mold, which weakens the final product, causes rough surfaces, and increases the difficulty of reducing fiber residue in the second heat reduction step to the elemental metal form. Higher temperatures and / or more reducing atmospheres must be used in the case of crystalline fibers. For these reasons, the first heating step is carried out under conditions which suppress the crystallite formation as much as possible. The compression of the metal fiber is z. B. observed as shrinkage of diameter and length of the fiber during the oxidation. The length / diameter ratio as well as the geometry of the fiber cross section remains substantially the same as that of the organic starting material during the transformation.

In the last step of the process according to the invention, the remainder of the first heating step is further heated to at least 300 ° C. in the presence of a reducing gas. As indicated previously, the metals that have been incorporated into the elemental fibrous or non-fas fibrous form in accordance with the invention have a free energy of formation in the oxide form of less than about 73 kcal / gram atom of oxygen in the oxide at 350 ° C (see Table I) ). Also, most of the remnants from the first heating step are usually at least partially in the oxide form. Because of their relatively low free energy of formation, they can be easily reduced to elemental form at temperatures between about 300 to 1400 ° C. The following table contains suitable temperatures for the reduction of the oxides of the various metals to the elemental form in a hydrogen atmosphere:

Table II:

<td>Temperature ° C</td><td>metal</td>

<td>300 - 400</td><td>Gu Ag Au Ru rh Pd os Ir Pt</td>

<td>400 - 500</td><td>Ni Co Fe tc re</td>

<td>500 - 700</td><td>Mo W Fe</td>

<td>1200 - 1400</td><td>Cr</td>

It should be noted that chromium oxide is rather difficult to reduce to elemental form but can be reduced under less severe conditions when alloyed with other metals. So z. For example, chromium oxide (Cr₂O₃) alone a temperature of 1200 to 1400 ° C for reduction with hydrogen, but it is reduced together with iron oxide or nickel oxide in hydrogen, the reduction at about 900 ° C can be achieved.

For the second heating reduction step there is no actual upper temperature limit, but, as can be seen from Table II, all elemental metal forms can be reduced by reduction in

Hydrogen atmospheres are produced at temperatures below about 1400 ° C.

No. 280464

Hydrogen gas is the preferred reducing atmosphere, although other known reducing agents such as carbon monoxide and ammonia may be used. For carbon monoxide, the reduction temperature should be at least 600 ° C, in the case of ammonia temperatures of at least 800 ° C are the most suitable.

The duration of the second heating-reduction step depends on the metal compound to be reduced, the temperature and the reducing agent. In general, this step is completed at the temperatures indicated in Table II in 2 to 6 hours. The reduction step is preferably monitored by the condensation of the water from the escaping gas. When no more water is formed, the reaction is complete. In the production of elemental tungsten fibers, it is preferred to keep the fibers at 600 ° C for 4 hours so that virtually all of the carbon is removed. Of course, in a continuous process, it is not appropriate to track the progress of the reaction by the presence of water in the exhaust gas.

It should be noted that the elemental metal forms produced according to the invention are highly crystalline.

In a preferred embodiment of the invention wherein a partial yarn containing a plurality of elemental metal fibers is desired, the impregnated organic fiber yarn is kept taut during the first and second heating steps. To keep 3300 denier / 1440 fiber rayon yarns taut during these steps, stresses between 10 and 40 g have been found to be satisfactory.

In another useful embodiment of the invention, elemental tungsten fibers are prepared by first adding enough ammonium paratungstate at about 50 to 70 ° C to an aqueous solution containing about 30 to 40 weight percent hydrogen peroxide, about 700 to 1000 grams of dissolved tungsten / 1 solution to receive. The solution is immediately cooled to about room temperature once the ammonium paratungstate is completely dissolved, and the rayon fiber is immersed in the solution at room temperature within 72 hours after the cooling step. The rayon fibers swell, and the cavities open, so that the tungsten compound is absorbed. The unswept tungsten compound is removed from the outer surface of the rayon fiber and the tungsten compound impregnated fiber is dried. Then, the impregnated fiber is at least partially heated in an oxygen-containing atmosphere to temperatures of 350 to 500 ° C at a rate of not more than 100oc / h to decompose the rayon fiber and allow at least most of the carbonaceous material to escape, thereby forming a tungsten oxide fiber residue becomes. This is further heated in the presence of a reducing gas at 350 to 1000 ° C to reduce the tungsten to its elemental form. This further heating step lasts at least 3 hours at a temperature of at least 500 ° C.

It seems that hydrogen peroxide affects the amount of ammonium paratungstate which can be dissolved in an aqueous solution. Experiments have shown that only insufficient tungsten saturation of the organic fibers occurs when the same tungsten compound is simply dissolved in ammonium hydroxide solutions. That is, the resulting solution contains only about 100 grams of dissolved tungsten / 1 solution, and this concentration is too low to produce strong elemental tungsten fibers from rayon.

It has been found that an aqueous solution containing 30 to 40% by weight of hydrogen peroxide at about 50 to 70 ° C is capable of dissolving 700 to 1000 g of tungsten / 1 solution, and this concentration range is from the standpoint of effective impregnation the fiber spaces optimally in minimum time. Higher concentration solutions are too tough to effectively penetrate the tungsten compound. So you reached z. B. using 745 g of tungsten / 1 with a pH of 1.2, an equilibrium soaking of 1.3 kg of tungsten compound / kg of rayon in less than 30 minutes.

Dissolution of the ammonium paratungstate at 50 to 70 ° C is necessary for a rapid reaction to form a readily soluble but unstable peroxy tungsten compound which (NH₃)₃OW₂O₇, 2H₂O can be. The rapid dissolution of the ammonium paratungstate in hydrogen peroxide starts at about 60 ° C, which heats the mixture to 80 to 90 ° C when not cooled. The resulting reaction product is relatively unstable at this temperature, and therefore the solution is cooled to room temperature immediately upon complete dissolution. During the dissolution process, oxygen is released due to the decomposition of the peroxy tungsten compound reaction product. If the solution is not cooled, the pH rises to 3.0-4.0 over 1 h, and the tungsten precipitates out of the solution as a yellow solid. In this form, it is not usable for rayon fiber impregnation.

Using this method, strong, shiny fibers of 99.6% tungsten and less were used

No. 280464, prepared as 0.04% carbon, which had remarkably high specific gravity, eg 17.5 to 18.1 g / cm³ or 91 to 94% of the theoretical density of tungsten.

By means of this process, a woven ribbon of elemental tungsten was produced which had the utmost smoothness and high gloss by starting from a rayon ribbon as sold in many stores. The properties of the rayoriband from which one starts and the tungsten tape product are the following;

<td></td><td>rayon band</td><td>tungsten band</td>

<td>Width in cm</td><td>3.8</td><td>1.6</td>

<td>Length, normalized</td><td>2.5</td><td>1.0</td>

<td>Strip thickness in cm</td><td>0.02</td><td>0,015</td>

<td>Weight in g / m²</td><td>90.0</td><td>283</td>

<td>Yarn count, weft / cm</td><td>21</td><td>58</td>

<td>Yarn count, chain / cm</td><td>49</td><td>118</td>

<td>Threads / yarn</td><td>40</td><td>40</td>

<td>Diameter of the threads in μ</td><td>10</td><td>3</td>

Fibers, textiles, and shaped articles of elemental tungsten and molybdenum can also be made by hydrolyzing suitable organic solvent compounds. These metals form compounds that hydrolyze or react with water to form metal oxide products that are substantially water-insoluble. This chemical property is used to achieve impregnation of organic materials with these metal oxides, as described below. Suitable hydrolyzable and / or water-reactive compounds are, for. The following metal halides and oxyhalides;

1. Mo₂O₃C1₆ and MoC1₅, the MoO_2Depending__3J0hydrate and give

Second WCl_G and WC1_B, the WO₃hydrate (wolft; amic acid).

The above-mentioned metal halides or oxyhalides are dissolved in a water-immiscible organic liquid such as carbon tetrachloride, chloroform, carbon disulfide, ethyl ether or benzene to the extent of 5 to 50 g of metal halide or oxyhalide per 100 ml of organic liquid, rayon or others Organic material is exposed to air with a relative humidity of 50 to 90% to swell the material by adding 5 to 30 wt. -% water absorbed. When swollen and containing the absorbed water, the organic material is immersed in the organic metal halide or oxyhalide solution. As the metal halide or oxyhalide penetrates into the wet organic material, it reacts with the water and an oxide precipitate forms directly in the organic structure. This hydrolysis reaction usually takes 20 to 30 minutes. The remaining steps for producing elemental fibers, textiles or shaped articles are those previously described.

The elemental fibers and fiber compositions of the invention are widely used. So they can z. B. for reinforcing plastics for use at relatively low temperatures and of metals, porcelains and other ceramic articles for use at high temperatures.

Some of the elements that can be made in the form of very small diameter fibers in accordance with the present invention are well-known catalysts for chemical reactions. So z. B, elemental platinum and palladium are widely used as hydrocarbon conversion catalysts. The fibers of the present invention can be used for this purpose with the advantage of providing close contact with the hydrocarbon material because of the large fiber surface area.

Certain elemental metal fibers are characterized by a relatively high thermal conductivity and are useful where this property is desired. So z. B. flexible fabric, which consists of Nikkei, silver or tungsten fibers in woven form, as special clothing, for. For astronauts.

Certain of these elemental metal fibers are characterized by high electrical conductivity, e.g. As silver, copper, nickel and tungsten. These fibers can be made into fabrics to dissipate static electricity or into materials for electrical heating.

Elemental tungsten is widely used as a glow material, and the tungsten fibers of the present invention are suitable for this purpose. An inventive yarn of elemental tungsten was

No. 280464 heated to glow by passing current through, and the yarn behaved almost like a thread, in a light bulb.

The elemental tungsten fibers, especially in bulk form, are suitable as resistance heating elements in high-temperature furnaces. In manufacturing, their flexibility offers an important advantage over tungsten wire.

The metal forms of the invention are widely used. The thin films can be used as conductive arcs. The metal molds according to the invention can be used as lightweight structural parts u. similar. be used. Metal molds made from organic foams or sponges are also useful as filters.

For use as filters, the metal molds of the invention are preferably made from cellulosic foams or sponges that are characterized by open porosity, uniform cell size, and low density.

The metal films according to the invention can be used as films whose thickness is very uniform and can be 10 μ,

The following examples are intended to illustrate the invention and its advantages in more detail.

Example 1: tungsten material

The solution used for impregnation was prepared by dissolving 249 g of ammonium paratungstate in 200 ml of 30% hydrogen peroxide. The solution was heated to 60 to 70 ° C, at which temperature the ammonium paratungstate reacted and dissolved within 5 to 10 minutes. Then, the solution was rapidly cooled to room temperature and contained 745 g of tungsten / 1 with a specific gravity of 1.89 and a pH of 1.0. The rayon was a 5-binder Atlas fabric in weft and warp direction of one Textile grade viscose yarn (1650 denier / 720 fibers in yarn / l layer), fabric being 357 g / m² weighed. A 15 x 46 cm piece of fabric weighing 35.6 g was immersed in the tungsten salt solution for 3 hours. Then, the cloth was centrifuged to remove the excess solution and dried in warm air.

The dried fabric contained 1.30 g tungsten salt / g rayon.

The fabric was converted to the elemental tungsten metal mold by first heating it in air at a rate of 20 ° C / hr to 300 ° C and maintaining that temperature for 4 hrs. Then, the fabric was further heated to 350 ° C at a rate of 50 ° C / hr and maintained at this temperature for 4 hours. Then the air in the tube furnace was purged with gaseous nitrogen before hydrogen reduction was begun. Hydrogen gas was passed through the oven at a rate of 4 l / min. The fabric was exposed to the following temperatures: 550 ° C for 1/2 h, 600 ° C for 4 h, 700 ° C for 1 h and 1000 ° C for 1 h. During the heat treatment at 1000 ° C, the hydrogen was carefully dried by passing it through a pipeline into a trap with liquid nitrogen. The reduced fabric had uniform metallic luster, the flexibility of the metal cloth was almost that of the original rayon, and the metal cloth had a tear strength of 5.3 kg / cm width. An X-ray diffraction study of the powder revealed a highly crystalline tungsten phase as the only phase in the fabric. The complete absence of a W.₂C phase indicated that less than 0.4% carbon was present. The tungsten fibers in the fabric had a spec. Weight of 18.1 g / cm³, which corresponds to a density of 93.8% of theoretical. The fibers had a diameter of 4 to 5 μ.

Example 2; Tungsten felt ·

A portion of a rayon felt of 5.0 denier rayon fibers weighing 3.7 g and measuring approximately 6.5 x 15 x 0.64 cm was dipped in a solution containing 500 g of tungsten / l whose spec. Weight 1.69 and its pn value was 0.9. After two hours of immersion, the felt was centrifuged and dried at 54 ° C in air. The impregnated felt was converted to tungsten metal felt by heating it in air at a rate of 50 ° C / hr to 300 ° C and maintaining that temperature for 4 hrs. Then it was heated at a rate of 50 ° C / h to 350 ° C and held at this temperature for 4 h. The resulting black felt was then placed in a tube furnace and rapidly heated to 640 ° C (in a 4 liter / minute stream of hydrogen) and held at that temperature for 25 minutes. Then it was heated to 900 ° C and held at this temperature for 2 h. The resulting felt made of elemental tungsten had high gloss, shiny metallic appearance and was both flexible and strong (minimum tear 0.36 kg / cm width). A yield of 53.2% (wt) was obtained, based on the initial weight of the rayon (0.532 g elemental tungsten / g rayon). The felt area was 14.1% and the thickness was 0.25 cm. The felt had a bulk density of 0.58 g / cm³ or a 97% porosity. The elementary tungsten fibers in the felt had diameters of 7 to 8 μ.

No. 280464

Example 3: Tungsten yarn and tungsten fibers

The rayon yarn used was 18 meters long, of high tensile strength and of the viscose type (1650/4000/1) with a nominal denier value of the fibers of 0.4. The cross section was almost round and had a diameter of 56.3 μ. Although the yarn consisted of only one layer, it was easy to separate two layers from the zero machine yarn. One layer of the chamois was 800 deniers, the other about 870 deniers. The impregnation of the Gams in tungsten solution was carried out in the same manner as described in Example 1. After centrifuging off the excess solution from the yarn but before drying, the length of the yarn was divided into 10 parts, talking part was hung by itself and tensioned by means of 100g weights to allow the fibers in the yarn to be parallel during drying just stayed. The conversion of the yarn to the elemental metal was carried out in a vertically oriented tube furnace while weights of 40 grams were hung on the yarns to keep them straight during the transformation. They were first heated in air at a rate of 50 ° C / h to 350 ° G and then held at this temperature for 4 h. Then the air was purged with a nitrogen gas stream before hydrogen was introduced into the tube furnace. Pre-purified hydrogen was passed through the furnace at a rate of 11 / min. The yarns were heated rapidly to 400 ° C and then to 600 ° C at a rate of 100 ° C / hr. The temperature was maintained at 600 ° C for 2 hours and then heated to 985 ° C at a rate of 200 ° C / hour and held at this temperature for 3/4 hours. During this heat haul, the piece of yarn in the oven shrank to half the original length.

A 7.6 cm long piece of 1015 denier elemental tungsten metal yarn was removed from the central portion of the yarn for tear tests. The ends of the yarn were bonded to metal strands with epoxy resin and the tear strength of the yarn was measured by means of an instrument provided with a transducer cell to indicate the tension to which the sample was subjected at the moment of rupture. The yarn had a tear strength of 0.32 kg. Based on the fiber area, the tenacity of the yarn was 5500 kg / cm², A single tungsten fiber (1.27 cm long) was removed from the torn yarn and its tear strength measured similarly using a modified analytical balance. The fiber, which had a diameter of 2.0 μ, held a weight of 0.53 g, giving a tear strength of 17,700 kg / cm² results.

Example 4: Silver Cloth

A piece of atlas fabric (identical to that of Example 1) weighing 21.1 g, measuring 11.4 x 30.5 cm, was immersed in a saturated silver nitrate solution for 15 minutes. (The specific weight of the solution at 22 ° C was 2.22.) The salt immediately penetrated the rayon, causing it to swell. The fibers were very swollen and stretchy, but not degraded. After centrifuging off the solution from the fabric and drying, it contained 1.83 g of silver nitrate / gm of material,

Conversion of the silver-loaded rayon to the elemental metal was easy because of the reactivity of the nitrate in the rayon when reaching 130 ° C in the heating scheme (50 ° C / hr to 350 ° C and holding this temperature for 4 hrs). The reaction between nitrate and the rayon took place and heated the fibers to sufficiently high temperature in air to cause complete disintegration and volatilization of the rayon and to produce metallic silver fibers, although this transformation was carried out in the presence of air. A sufficiently reducing atmosphere or environment has been created in the fibers to reduce the silver salt to metallic silver. The resulting silver fibers were very white.

The fibers and the fabric had high strength, although no quantitative measurements were made. When viewed under the microscope at 25x magnification, the metallic luster appeared. The fibers were very elastic. The weight yield of the silver fibers was 1.20 g metal / g rayon.

Example 5: Nickel yarns of a 0.4 denier rayon yarn were immersed in 100 ml of 3.0 M nickel chloride solution (NiCip) After 18 hours of residence, the fibers were centrifuged to remove excess solution and dried in warm air , 5 g nickel chloride / g rayon.

The fibers were oxidized by heating them in air at a rate of 10 ° C / h to 375 ° C and leaving them at this temperature for 24 hours. After this oxidation treatment, the fibers retained their high gloss and were uniformly gray. At that time, the fibers showed no signs of splitting but were quite weak. Then they were reduced to elemental nickel by keeping them in a dry stream of hydrogen at 400 ° C for 1/2 h, then the temperature was slow

No.280464 increased to 800 ° G, and they held 1/2 hour at this value. The reduced nickel fibers were shiny metallic in color, flexible and ductile. They had diameters of 1.8 i 0.3 μ, which was found at 1500x magnification by means of a calibrated Filarokulartr. Some of these fibers were further heated in hydrogen at 900 ° C. There was essentially no change in the fibers; but when they were further heated to 1000 ° C, the fibers easily sintered together, ie metallurgical bonds formed at the points of contact of the fibers. These fibers were attracted by a magnet. X-ray diffraction patterns of powders indicated that a well crystallized face centered phase was the only structure present in the fibers. The metal yield of the above sample was low, compared to optimum conditions, low x 0.17 g nickel / g starting rayon. Using 4.3m of nickel chloride and pre-swelling in water followed by 24 hours of impregnation gave weight yields of 0.41g of elemental nickel / g of starting rayon.

Example 6; Nickel iron alloy

The solution used for this impregnation contained 1.4 m nickel chloride solution (NiCl₂The solution had an iron / nickel atomic ratio of 1.81, the pH was 0.5, and the fabric used for the impregnation was a 2 longitudinal fibers x 2 transverse fibers basket weave rayon fabric A 25.4 X 25.4 cm piece weighing 36.0 g was dipped in the solution, the excess solution was centrifuged off and the cloth dried at 47 ° C. The dried fabric contained 0.65 g of mixed salt / g of rayon with a nickel content of 5.12% and an iron content of 8.8%. This fabric was rapidly heated to 350 ° C in air and held at this temperature for 22 hours. Then it was placed in a tube furnace and heated in a hydrogen stream in about 2 hours at 800 ° C and then further heated to 1000 ° C at a rate of about 50 ° C / h. After removal from the oven, the element of elemental nickel-iron alloy had a shimmering metallic luster. The fabric was stiff due to a slight sintering of the yarn.

Although no chemical analysis was performed, it was important that the fabric contain little residual oxygen and carbon because it was ductile and could be hammered into a thin film with no evidence of brittleness. X-ray diffraction analysis of the powder revealed that the fabric was a single metallic phase contained.

Example 7: Nickel-chromium alloy

The impregnating solution used was prepared by adding 20 ml of conc. Chromic acid solution added to 100 ml of 4.4 M nickel chloride solution. The resulting solution should have a relative chromium / nickel content of 20 × 80% by weight; the pH of the solution was 0.3. The material used was identical to that used in Example 6. A piece of cloth (13.5 g) was immersed in the solution for 19 hours. After centrifuging off the excess solution and drying overnight, the salt content of the fabric was 0.25 g / g rayon. Then the substance was oxidized by heating it in air in about 1 h at 400 ° C and lh kept at this temperature. The resulting oxide was dark green to black. The reduction of the deoxidized substance was carried out by heating it in a dry hydrogen stream at 900 ° C in a tube furnace and maintaining it at that temperature for 15 minutes. The resulting fabric had a shiny metallic appearance, was ductile and could be hammered into a thin film with no signs of brittleness. X-ray diffraction analysis of the powder revealed that the fabric was completely metallic and composed of a chromium and nickel rich phase. This example demonstrates that the invention facilitates the production of nickel-chromium fibers at relatively low temperatures (880 to 900 ° C),

Example 8: Tungsten films

The organic film used to make the tungsten film was commercially available, smooth cellophane (33μ thick), cellophane is a clear cellulose film of viscose and is essentially of the same composition as rayon.

A piece of cellophane with an area of ​​26 cm² was immersed in a 3.7 molar aqueous solution of ammonium metatungstate for 20 hours. The film was removed from the solution, cleaned of excess solution by wiping and allowed to dry.

Then it was pyrolyzed by heating it in air at a rate of 50 ° C / h to 350 ° C and held at this temperature for 4 h. Then, the carbonized film was placed in a tube furnace and heated in a stream of hydrogen each at 450 ° C, 550 ° C, 700 ° C, 800 ° C and 1000 ° C in 1/2 hour.

The product of the above treatment was a smooth, highly reflective metallic film with an area of ​​15.5 cm², The film thickness was 20 to 21 μ. A metallographic section of the film revealed that the metal was completely dense and with no apparent crystal incoordination. X-ray diffraction, however, indicates that the film consisted of crystalline tungsten. The purity of the film was greater than 99% elemental tungsten.

In a preferred embodiment of the invention, tungsten fibers are produced by means of a continuous process in the form of a continuous fiber yarn.

As a preformed, organic, polymeric material strongly oriented rayon yarn is used. The impregnating or impregnating solution is an aqueous solution of ammonium metatungstamate, a compound of the formula (NH 4) 2 O 3₂O.

At a temperature of 23 ° C and a dipping time of 22 h, different rayon yarns from this solution (specific, weight 1.66 to 1.76) absorb between 0.58 and 2.64 g / g Ray10 on depending on the type of yarn ,

After impregnation, the excess solution is removed, for example by centrifuging and subsequent air drying. Then, the impregnated yarn is subjected to the heating steps to convert it into tungsten yarn of continuous length. For this purpose, a continuous process can be used.

In an example of such a continuous process, a 2.3 meter laboratory reactor with a 1.3 cm diameter reaction tube is used The reaction tube is divided into four 40 cm heating zones where the steps of the process are carried out 200 ° C, Zone 2 to about 500 to 600 ° C, Zone 3 to about 800 ° C and zone 4 to about 800 to 900 ° C. In zones 1 and 2, the carbonation of the rayon takes place and (predominantly in zone 2) the ammonium metatungstate is decomposed into tungsten oxide. In heating zones 3 and 4, the carbon is removed by volatilization and the tungsten oxides are reduced to tungsten metal. Hydrogen is passed countercurrently through the reactor, creating a hydrogen atmosphere for all heating steps. In heating zones 1 and 2, hydrogen is not needed, but its presence is not detrimental, and therefore it is passed through the reactor for convenience. It is convenient to add an inert gas (e.g., argon) to the flow of hydrogen between zones 2 and 3 to flush out the gaseous decomposition products formed in zones 1 and 2. The decomposition of the rayon and the volatilization of the carbon are achieved without the use of an oxidizing atmosphere in any part of the reactor.

In this continuous process it has been found that it is sometimes beneficial to have some carbon left in the yarn when it reaches the high temperature zone (zone 3). In this case, the volatilization of the last carbon content is achieved simultaneously with the reduction of tungsten oxides to elemental tungsten. It has been found to be beneficial if some moisture is present in the hydrogen to facilitate the volatilization of the carbon.

For example, B. at a Garndurchgangsgeschwindigkeit of 46 m / h, a content of 6 Voi. -%H₂O in the hydrogen to be optimal for the conditions described above. (The water can be supplied to the hydrogen simply by blowing it through water.) At the said throughput rate of 46 m / h, the yarn remains in each 40 cm heating zone for about 20 seconds.