US3803056A

US3803056A - Heat resistant black fibers and fabrics derived from regenerated cellulose,containing certain heavy metals

Info

Publication number: US3803056A
Application number: US00221832A
Authority: US
Inventors: M Hart
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1968-06-28
Filing date: 1972-01-27
Publication date: 1974-04-09
Anticipated expiration: 1991-04-09

Abstract

Black, essentially amorphous, electrically conducting, carbonaceous fiber materials containing about 0.5 to 6 percent by weight of nitrogen, from 1 to 50 percent by weight of a heavy metal and about 40 to 95 percent by weight of carbon, the said heavy metal being present in a form other than the carbide, and being chemically bound to the said fiber, are obtained by the pyrolysis of regenerated cellulose fibers which are impregnated with certain salts under conditions in which exotherm is prevented and below the temperature at which any substantial reaction of the heavy metal with carbon occurs to form refractory carbide. An intermediate non-conducting carbonaceous fiber material can also be obtained.

Description

United States Patent Hart [ Apr. 9, 1974 [75] Inventor: Marvin L. Hart, Stillwater Township, Washington County, Minn.

[73] Assignee: Minnesota Mining and Manufacturing Company, St. Paul, Minn.

[22] Filed: Jan. 27, 1972 [2]] Appl. No.: 221,832

Related 0.8. Application Data [62] Division of Ser. No. 740,987, June 28, I968,

abandoned.

[52] US. Cl. 252/478, 117/46 CC, 252/30l.l R, 264/.5, 264/29, 423/439, 423/440 [51] Int. Cl C09k 3/00 [58] Field of Search 252/478, 301.1 R; 264/.5,

264/29; 423/439, 440; Il7/46 CC [56] References Cited UNITED STATES PATENTS 3.242.000 3/1966 Lynch 264/.5 UX

HEAT RESISTANT BLACK FIBERS AND FABRICS DERIVED FROM REGENERATED CELLULOSE, CONTAINING CERTAIN I-IEAVY METALS 3,403,008 9/ 1 968 Hamling 264/.5

Primary ExaminerLeland A. Sebastian fittorney, Agent, or FirmAlexander, Sell, Steldt & DeLaHunt I I I [57] ABSTRACT Black, essentially amorphous, electrically conducting. carbonaceous fiber materials containing about 0.5 to 6 percent by weight of nitrogen, from 1 to 50 percent by weight of a heavy metal and about 40 to 95 percent by weight of carbon, the said heavy metal being present in a form other than the carbide, and being chemically bound to the said fiber, are obtained by the pyrolysis of regenerated cellulose fibers which are impregnated with certain salts under conditions in which exotherm is prevented and below the temperature at which any substantial reaction of the heavy metal with carbon occurs to form refractory carbide. An intermediate non-conducting carbonaceous fiber material can'also be obtained.

22 Claims, No Drawings HEAT RESISTANT BLACK FIBERS AND FABRICS DERIVED FROM REGENERATED CELLULOSE, CONTAINING CERTAIN HEAVY METALS This is a division of application Ser. No. 740,987, filed June 28, 1968 now abandoned.

BACKGROUND OF THE INVENTION Fibers of carbon or graphite are known, and have been produced by carbonization of a number of materials, with or without subsequent heat treatments to bring about crystallization of the carbon. Likewise, fibers which are essentially metal carbides have been prepared, as have metallic nitride fibers and the like. Such fibers, however, are not the same as nor do they have the same properties as fibers of the instant invention. Furthermore, the presently claimed processes for making fibers containing heavy metals are likewise novel. Typical disclosures of the fibers of the prior art can be found in patents to Peters, U.S. Pat. No. 3,235,323; Cross et al., U.S. Pat. Nos. 3,116,975; 3,281,261; British Pat. specification No. 1,012,878 and the like. The Peters U.S. Pat. No. 3,235,323 shows a process similar to that of the present invention, but the inclusion of heavy metals in that process is not suggested. It might have been expected that inclusion of heavy metals would catalyze combustion so as to render pyrolysis uncontrollable. but surprisingly it has been found that this is not the case.

Carbonized acrylic or rayon textile products including refractory metal oxides are disclosed in U.S. Pat. No. 3,242,000. Such materials, while they contain refractory metals as oxides, are different from the fibers produced in the process of the present invention in that they do not contain combined nitrogen and in that they apparently contain the refractory metals as oxide coatings. These materials, as well as those made by longcontinued heating of carbonizable fabrics, are not the same as or even closely similar to applicants amorphous materials, made by extremely rapid heating with short dwell time, in which the heavy metals are somehow bound into a residual, amorphous polymer chain which is composed chiefly of carbon with a small percentage of combined nitrogen.

The present invention contemplates providing carbonized fibers produced by pyrolysis of regenerated cellulose fibers, containing by weight from about /z to 6 percent of nitrogen and from 1 to about 50 percent of heavy metal combined with the said carbonized fiber, the amount of carbon contained in said fiber being from about 40 to about 95 percent (depending upon the amount of heavy metal present). Possibly very minor amounts of other constituents (totaling not more than percent) can also be present in the carbonized fibers. Preferably these final carbonized fibers of the present invention contain /2 to 4 percent of nitrogen and l to 35 percent of heavy metal with the remainder (except for very minor amounts of other constituents) being carbon. Also within the purview of the invention are processes for producing such fibers containing heavy metals.

The novel fibrous materials of the invention are produced by the thermochemical transformation of corresponding regenerated cellulose, e.g. rayon, fabrics and fibers, which retain their fibrous identity but are changed to a flexible black state having an entirely different chemical composition and radically different chemical and physical properties. In the process, a regenerated cellulose precursor material is impregnated with a nitrogenous salt and with a heavy metal salt or a combination of salts of' two or more heavy metals, dried to remove substantially all of the solvent (e. g. water), and then heated in a process comprising either one or two stages of pyrolysis. In the two stage pyrolysis, the first stage is carried out in the presence of air at about 200-300C. and the second stage is carried out in an inert atmosphere at a final temperature of at least about 700 C., preferably in the range of 1,200l,500 C. In the one stage pyrolysis, the lower temperature step is eliminated. Thus the impregnated precursor material is heated rapidly in a non-oxidizing environment at a temperature of at least 700 C., preferably in the range of 1,200-l,500 C.

The final product of the processes is a black, carbonaceous material which is electrically conductive, amorphous, highly heat resistant and which has significant capability for absorption of x-radiation.

In the first stage of heating in the two step pyrolysis process (which is presently preferred as giving a stronger final product), the impregnated fibers are not only changed by pyrolysis but by an accompanying chemical reaction wherein nitrogen atoms become chemically combined in some way in the stable polymeric oxygen-containing carbon compound molecules of the black fibers produced. The thermochemical transformation is rapid, requiring not more than about 1 to 10 minutes at temperatures in the range of about 200-300C., and is accomplished in the presence of oxygen under conditions controlled to prevent rapid and destructive exotherm from taking place. These include control of the flow of the atmosphere as well as close control of final temperature. Under the preferred conditions, a dwell time of as little as 2 minutes or less is employed. The regenerated cellulose fibers are rapidly brought to the oven temperature as they are conveyed directly into the zone heated to pyrolysis temperature. The process is therefore quite different from those processes previously employed in producing partially carbonized fibers and carbon fibers, by lengthy heating of cellulose fibers at gradually increased temperatures.

During this stage of the chemical transformation, water, carbon dioxide, carbon monoxide and other materials, such as decomposition products of nitrogen salts which may be present, are evolved. The result is an intermediate fibrous product which contains (in percent by weight exclusive of the heavy metal) at least A percent and preferably not more than 15 percent of nitrogen, 50 to 65 percent of carbon (from the fiber), the remainder including hydrogen, oxygen and other residuals, e.g. from the impregnating salts. The total amount of heavy metal in the intermediate product is essentially the same as in the original impregnated fiber, none having been lost in the first pyrolysis step.

While as noted hereinabove, dwell times of from 1 to 10 minutes at temperaturesin the range of about 200-350 C. are employed in the first stage of the process, higher temperatures and shorter dwell times may be employed. Thus, for example, if the temperature is raised to the order of 400500 C. or even somewhat higher, a dwell time which is considerably shorter, even of the order of seconds, can be employed. It will of course be apparent that such short dwell times will be most useful in the case of conversion of fibers having small mass, i.e. single ply or two ply yarns of small denier, in that the pyrolytic conversion occurs throughout the cross-section of the fibers during the short dwell time. In such instances, however, it may be necessary to adjust the ambient atmosphere to prevent uncontrolled combustion. This can be done by restricting the flow of air, whereupon the oxygen content of the atmosphere surrounding the fibers is lowered.

ln the second stage of pyrolysis in the two step process, the intermediate product is heated in a nonoxidizing atmosphere, preferably argon, other rare gases or the like, although nitrogen, or mixtures of nitrogen and argon, etc. can be employed. The essential consideration is to permit evolution of gases from the fibers during continued pyrolysis, without reaction with the ambient atmosphere. The temperature of the fiber is rapidly brought to the range of about l,200-l,500 C., and even somewhat higher, but below the temperature at which any substantial amount of reaction of the heavy metal employed with carbon would take place to produce heavy metal carbide. Heating of the fiber in this stage is also rapid, from 5 seconds to minutes being required, and dwell periods of 10 to 60 seconds being the preferred condition.

In the processes of the present invention, it appears that the regenerated cellulose is first degraded, apparently by decomposition and ring-cleavage of the cellulose molecules; the result being liberation of water vapor and other gases. As the reaction progresses, the decomposed molecules recombine to form a new type of polymeric molecule, containing carbon-bonded nitrogen atoms and also apparently containing carbon or nitrogen-bonded heavy metal to the extent that this was present in the originally impregnated fiber.

As noted previously, the lower temperature stage in the pyrolysis can be simply eliminated and the higher temperature stage carried out in the manner explained above.

The water-soluble nitrogenous salt which is employed to impregnate the regenerated cellulose fibers and/or fabric is a non-oxidant, water-soluble salt of a strong acid and nitrogenous base, e.g., ammonium chloride, methyland ethyl-amine salts of phosphoric acids, and mixtures thereof. To this may be added boric acid or an equivalent boron compound, if desired. The salts useful for this process of the invention are those disclosed in the US. Pat. No. 3,235,323, for making carbonized rayon fibers and fabrics which do not contain heavy metals.

The material to be pyrolyzed is impregnated with about 5 to about 45 percent of the salt, on a dry weight basis for the best results. This may be accomplished by immersion for about 5 minutes or less in a nearly boiling salt solution, the excess solution then being removed. The wet pickup of salt solution is about 200 percent by weight.

The heavy metal salts employed for impregnation are salts of carbide-forming heavy metals, which have carbides stable at high temperatures. They are to be distinguished from the metals which reject carbon, for example, copper, silver, tin, germanium, lead and so on. Reference is made to Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 4, 1964, pages 75-91, also to page 71 of that publication, wherein the binary compounds of carbon are classified. Included within the heavy metals therein shown and categorized with respect to carbide formation are tungsten, titanium, tantalum, niobium, chromium, molybdenum, vanadium, hafnium, zirconium, uranium and thorium. Fissionable actinides can also be used. The soluble salts of these metals useful for the purpose of the invention include salts with strong and weak acids, preferably those which have high solubility in water.

Where the solubility of the heavy metal salt is great enough, this can be included in the solution of salt of strong acid and nitrogenous base previously referred to. However, particularly where larger amounts of heavy metal are to be included in the fiber, it is necessary to introduce the heavy metal salt in a separate step (drying the fiber between the impregnations). Introduction of the heavy metal salt preferably precedes but may follow the impregnation with nitrogenous salt. Again dependent upon whether larger percentages of salt are to be introduced into the regenerated cellulose, the solutions can be warmed or even heated to boiling, to facilitate impregnation of the fibers.

The amount of salt to be added to the fiber on a wet or dry basis is of course dependent upon the desired concentration of heavy metal in the final product. As a guideline, 5 percent by weight of heavy metal introduced into the initial fiber (on a dry weight basis) normally results in a concentration of about 20 percent of heavy metal in the final product.

It is considered to be quite unexpected that the presence of the heavy metal does not interfere with the chemical transformation of the regenerated cellulose in the presence of nitrogenous salts.

Typical heavy metal salts which can be employed are zirconium tetracetate, tungstic oxide (in ammoniacal solution), tungstosilicic acid, uranium nitrate, thorium nitrate, molybdenum oxalate, tantalum fluoride, titanium tetrachloride, titanium oxalate, tungsten tetrachloride, chromium acetate, molybdenum chloride, hafnium tetrachloride, and the like. Mixtures of these salts can be used so that the ultimate carbonaceous material contains two or more heavy metals.

The damp, salt-treated fibrous material is then heated until dry, preferably at about to 200 C. It is found that the dry fibers are impregnated with the salts used, not merely coated. If the impregnation treatment has caused the fibers to stick together, processing is improved by flexing, rubbing, tumbling and the like to loosen and free the individual fibers so they will be fully exposed to the ambient atmosphere during heatmg.

The dried, salt-impregnated regenerated cellulose fibers are then heated in a suitable oven to bring about the transformation of the fibers.

EXAMPLE 1 The following procedure, in which all parts are by weight unless otherwise specified, illustrates a presently preferred procedure for making carbonized regenerated cellulose fiber or cloth containing heavy metals. The material used is first cleaned by the usual methods, e.g., by scouring, washing, detergent treatment or the like, to remove sizings, lubricants, etc. This step may be omitted if the material is clean as received from the supplier.

Two-ply rayon yarn (regenerated cellulose, denier 1,650 per end, 720 filaments per end) is thoroughly impregnated by passing it through a dip tank containing a solution including ammonium chloride or sulfate and a soluble salt of the metal to be introduced into the fibers. A useful solution of this type is the following:

Ammonium chloride parts Zirconium tetraacetate 10 parts Acetic acid (glacial) 3 parts Wetting agent 0.3 parts Water 66.7 parts The wetting agent used is not critical. It may be omitted if desired; any compatible wetting agent can be used, in small amounts as known to the art, to facilitate wetting of the fibers and penetration of the solution.

Conveniently, the yarn is handled in long lengths which are stored on rolls. The yarn is usually passed through tube-like ovens, electrically heated, having suitable control means. These are located so that the process steps are performed sequentially, the length of the heated zones being such as to provide the requisite dwell time with the yarn travelling at constant speed of, e.g., l to 2 feet per minute.

The impregnated yarn is passed through a drying oven which is supplied with heated air at 140 C. flowing at a rate of 30 CPI-I, the temperature of the drying tube being maintained at about 155 C. After substantially all of the water has been removed from the yarn, which is accomplished by a dwell time of about one minute, it is conveyed into and through an oven which is supplied with heated air at about 200 C. which is flowing at the rate of about 30 CFI-I. The temperature in this oven is maintained at about 245 C. The yarn is exposed to the oven temperature for 2 minutes. The yarn, transformed by the heating to a black, lustrous condition, emerges from the oven into ambient air. At this point, the material is electrically non-conductive and quite strong. The weight percent of heavy metal originally present has increased about 50 percent, and the yarn itself has decreased to about 80 percent of its original weight. However, owing to the presence of the heavy metal, which is strongly incorporated into the rayon, so that it can no longer be washed out, the material exhibits excellent absorption of x-ray or gamma radiation. The yarn is also heat resistant and can be heated to 400 C. for short periods of time in air without loss of integrity.

The yarn thus obtained may be used as such for various purposes, being heat resistant and x-ray absorbent, but it is preferred to treat the material by further pyrolysis, to obtain a material having a greatly increased proportion of carbon and which is electrically conductive. For this purpose, the yarn is passed into and through an oven which is provided with an argon atmosphere, flowing at the rate of about 12 CFH (cubic feet per hour), and which is maintained at l,370 C. The yarn is exposed to the oven temperature for 40 seconds. 1mmediately after emerging from the oven, the yarn is exposed to ambient temperature and atmosphere.

The yarn thus produced (impregnated with the above solution) contains 12.7 percent zirconium, 84.6 percent carbon and 1.9 percent nitrogen. About 0.6 percent of hydrogen is also present. The material is completely amorphous and is found to have a breakingstrength of 3,405 grams, denier 1,755 and tenacity 1.98. The conductivity of this material is about ohms/ft. The yarn is very heat-resistant, and strongly absorbs x-radiation.

A similar procedure is used with other heavy metals which it is desired to incorporate into the rayon yarn. In the event that the heavy metal is not soluble to the extent desired in the solution containing the ammonium compound, it is preferred that the heavy metal be first deposited in the rayon fibers by way of a solution, preferably aqueous but which may also contain organic solvents, followed by drying and then impregnating with the ammonium compound-containing solution. In this way, heavy metals, salts of which are relatively less soluble in the solution of ammonium compound, can be incorporated in larger amounts.

The atmosphere in the first heatingstage, where the rayon yarn is heated to approximately 250 C., is carefully controlled so as to prevent exotherm, glowing and uncontrolled combustion of the rayon yarn. This can be done visually if desired, or by using sensitive thermometric devices. The atmosphere in this stage consists of decomposition products of the rayon yarn together with air. If desired, ammonia or inert gas can be introduced to reduce or prevent exotherm, or the flow of fresh gas into the oven can be reduced'to permit the percentage of atmosphere contributed by the off-gases to be increased. It will be recognized that some of the heavy metals are more likely to catalyze exotherm and decomposition than others, and appropriate precautions can be taken, following simple experimental runs to determine empirical values for atmosphere, temperature and flow. The inclusion of boric acid or equivalent boron compound in the impregnating composition to provide 0.5 to 2.5 percent boron content in the yarn also inhibits combustion and glowing.

The following Table I shows the results obtained when rayon yarns impregnated with various heavy metals of the kind used in making the carbonized materials according to the invention were treated by the above First heating Second heating Drying section stage stage Impregnating solution Atrn./ Atn1./ Atm/ Analysis, percent Break Te- Heavy metal Temp., flow, Temp., flow, Temp, flow, stren th I )enac- Run compound/parts Other additive 0. 0.1.11. C. c.f.h. "C. c.l'.h. C N Metal g.) mer ity 1 Uranyl nitrate/10 Air/50... 242 Air/30." 1,426 Nz/S 84.4 1.4 12.1 1,635 1,590 1.03

2 'Ietrabutyl (Ethanol 165 Air/50.-. 220 Air/50.-. 1,426 Ni/8 11.1 3,360 1,404 2.39

titanate/30. solution).

3 Nizrabiumoxalatel (Oxa'c acid/5L... Air/50. 210 N2/30 1,426 Nz/B 77.3 1.3 14.6 545 1,623 0.34 4 Hafnium tetra- (Ethanol Air/50. 93 Air/30-.. 1,426 Ni/B 78.0 1.6 19.7 1,635 1,819 0.90 chloride/10. solution).

5 Tungstic aeid/5.4 (fioglihmllzo 155 Air/30." 260 Air/30..- 1,426 N7/8 82.7 1.0 15.3 1,405 1,431 0.98

y o e 6 Thorium nltrate/ 150 Air/15 230 Air/15... 1,426 N1/8 76.1 1.1 21.3 2,344 1,891 1.24

10. 7 Tantlalurrli (Oxalic acid/5) NHa/IL. 242 Air/40... 1,426 Nz/8 85.3 0.9 13.6 1,362 1,503 0.91

oxa ate 4. 8 Ammonium (Ammonium 165 Air/20.-. 238 Air/11L 1,426 Nz/8 79.7 0.9 15.0 2,270 1,813 1.25

molybdate/fi.5. hydroxide/7).

In addition to ammonium chloride. "Not determined.

procedure. The impregnating solutions contained 20-25 parts of ammonium chloride and the number of parts of heavy metal containing compounds as indicated. Dwell time in the drying section was one minute, in the first heating stage 2 minutes, and in the second heating stage, 30-40 seconds, in each instance.

These yarns can be used to make fiber-reinforced plastic sheets, as by laying up the fibers with epoxy resin prepolymer and curing agent, followed by curing, as known to the art. The sheets thus produced can be used for x-ray shielding.

EXAMPLE 2 A similar procedure is used for treating rayon cloth EXAMPLE 3 Ammonium chloride 19.6 parts Tungstic acid 5.4 parts Ammonium Hydroxide 19,6 purt (concentrated) Wetting agent 2.1 parts Water 53.3 ports to produce carbonized cloth containing heavy metals. 'hp f y f is passed throughca 'y Samples of rayon (square weave approximately OZ- Whlch 1S Supplled Wlth heated all at C., flowing at /yd cloth about 12 inches wide and 12 inches long are a fate the temperature of the drymg tube used. The ovens provided have cross-section adequate belhg mamtamed at about 155 After substahhahyi to receive h l h i h f ldi all of the water has been removed from the yarn, which To aid in increasing the take-up of heavy metal salt, i f p f y a dwell time of about 01:16 h the impregnation is optionally conducted in two steps, 15 f y i and through 01/511 whlch P the cloth being dried between the steps. Excess solution Vlded Wlth a nitrogen m p flqwlhg at the fate is removed running the cloth through a hand Of about and WhlCh IS maintained at 1,426 wringen The yarn is exposed to the oven temperature for 40 sec- When heavy closely-woven fabrics are used, the heat ohds- Immediately after g g from the 01/611, the treatments are preferably conducted in such a way as yarn is exposed to ambient temperature and atmoto avoid excessively rapid temperature rise in the interphereior of the fabric, such as may be caused by the exother- The yarn thus produced contains 16.0 percent tungmic nature of the chemical transformation and the relasten, 82.5 percent carbon and about 1 percent nitrotively poor thermal conductivity of the fabric. This can gen. About 0.4 percent hydrogen is also present. The be done by heating in successive stages at increasingly material is completely amorphous and is found to have high temperatures. a breaking strength of 1,545 grams, denier 1,588 and The fabric thus produced can be used, 6g 88 tape tenacity 0.97. The conductivity of this material is about backings, or to wrap cables, or in the form of multiple 152 ohms/ft. The yarn is very heat-resistant, and layers sewn together, as x-ray shielding material. The strongly absorbs x-radiation. fabric can also be used to form reinforced plastic sheet laminates. EXAMPLE 4 Table 11 shows the results obtained. Two-ply rayon yarn (denier 1,650/end, 720 fila- TABLE 11" First Second Analysis Drying Section Heating Stage Heating Stage impregnating Solution Time/Temp Time/Temp Time/Temp Atm/ Atml Atml me- Run (aqueous) min C Flow min C Flow sec "C Flow C N tal CFH can CFH 9 1st solution:

ammonium sulfate, 10% 8/120 air/50 10/260 air/50 /1345 N,/8 l0 boric acid, 4% cyanoguanidine, 2% zirconium acetate. 10% glacial acetic acid, 6% 2nd solution: ammonium sulfate, 10% boric acid, 4% cyanoguanidine, 2% ammonium phosphate, 4% 10 1st solution: 8/120 air/ 10/260 air/50 40/1345 N2/8 62.2 4.4 19 thorium nitrate, 10% (2.8 0.4

B, P) boric acid, 4% cyanoguanidine, 2% 2nd solution: ammonium sulfate, 10% boric acid, 4% cyanoguanidine, 2% ammonium phosphate, 4% 11 tungstic acid, 5% 10/110 air/50 10/232 air/50 40/1350 N,/8 73.5 0.9 22.8

ammonium chloride. 25%

' not determined ments/ply) is thoroughly impregnated by passing it through a dip tank containing a solution having the following composition:

Ammonium chloride l9.6 parts Tungstic acid 4 parts Ammonium hydroxide (35%) 19.6 parts Wetting agent 2 1 parts Water 53.3 pans Conveniently, the yarn is handled in long lengths which are stored on rolls.

The impregnated yarn is passed through a drying oven as described in Example 1, which is supplied with heated air at 120 C. flowing at a rate of 40 CFl-l, the temperature of the drying tube being'maintained at about 145 C. After substantially all of the water has been removed from the yarn, which is accomplished by a dwell time of about one minute, it is conveyed into and through an oven which is supplied with heated air at about 215 C., which is flowing at the rate of about 6 CFl-l. The temperature in this oven is maintained at about 265 C., and the yarn is exposed to the oven temperature for about 2 minutes. The yarn, transformed by the heating to a black, lustrous condition, emerges from the oven into ambient air.

The yarn thus produced contains 8.2 percent tungsten, 54.1 percent carbon, 4.4 percent nitrogen and 3.5 percent of hydrogen. The material is completely amorphous and is found to have a breaking strength of 2,180 grams, denier 2,599 and tenacity 0.84. The material is electrically non-conductive and quite heat-resistant.

I claim:

1. A process of thermochemically converting regenerated cellulose fiber starting material to corresponding black, conductive, heavy metal-containing fiber material, which consists essentially in impregnating clean starting material with a solution of acetate, nitrate, oxalate, oxide, fluoride or chloride salt of heavy metal which is capable of reacting with carbon to form a refractory high-temperature stable carbide, and water-soluble ammonium, methylamine or ethylamine salt with strong acid that is capable of rendering the fibers nonflammable, drying and heating the dry saltimpregnated fiber material for about 1 to minutes at an effective temperature of about 200 to 350 C. and in the presence of air, the conditions being controlled so as to cause the fiber material to pass through a pyrolytic stage, while avoiding destructive exotherm, to result in a flexible, black, electrically non-conducting fiber material having a fiber carbon content in the range of about 50 to 65 percent and a nitrogen content of at least about 1 percent, both exclusive of heavy metal; and subsequently carbonizing this fiber material by rapidly heating for about 5 seconds to 10 minutes in an essentially non-oxidizing environment to a final temperature in the range of l,200 to 1,500 but below the temperature at which reaction of the said heavy metal with carbon occurs to form the heavy metal carbide, to produce electrically conductive, x-rayabsorbent, heat-stable, nitrogen-containing fibers having a fiber carbon content of about 40 to 95 percent and a nitrogen content of about 6 to 6 percent, and containing from 1 to 50 percent by weight of heavy metal chemically bound to said fiber in other than carbide form.

2. A process according to claim 1, in which the heavy metal is a fissionable actinide.

3. A process according to claim 1, in which the fiber is first impregnated with a heavy metal salt and then impregnated with a salt of a strong acid and a nitrogenous base.

4. A process according to claim '1, in which the fiber is first impregnated with a salt of a strong acid and a nitrogenous base and then is impregnated with a heavy metal salt.-

5. A process according to claim 1, in which the fiber is simultaneously impregnated with a heavy metal salt and a salt of a strong acid and a nitrogenous base.

6. A process according to claim 5, in which the salt of a strong acid and a nitrogenous base is ammonium chloride.

7. A process according to claim 1, in which both heating steps are less than 2 minutes in duration.

8. A process according to claim 1, in which a mixture of two or more heavy metal salts is used.

9. A process according to claim 1, in which the water-soluble salt of a strong acid and a nitrogenous base is impregnated in the fiber to the extent of 5 to 45 percent by weight.

10. In the process according to claim 1 for thermochemically converting regenerated cellulose fiber starting material to corresponding heavy metal-containing fibrous material without loss of fiber identity, the step which consists essentially in heating dry saltimpregnated fiber for about 1 to 10 minutes at an effective temperature of at least about 200 C. up to 350 C. and in the presence of air, the conditions being so controlled as to cause the fiber material to pass through a pyrolytic stage while avoiding destructive exotherm to result in a flexible, black, electrically non-conducting, x-ray-absorbent fiber material having a fiber carbon content in the range of about 50 to 65 percent and a nitrogen content of at least about 1 percent, the remainder of the material being essentially only oxygen and hydrogen exclusive of heavy metal; and containing substantially all of the heavy metal with which it was originally impregnated, in amount of about 1 to 50 percent by weight.

11. A process according to claim 10, in which the fiber is first impregnated with the heavy metal salt and then with the salt of a strong acid and a nitrogenous base.

12. A process according to claim 10, in which the fiber is simultaneously impregnated with the heavy metal salt and the salt of a strong acid and a nitrogenous base. g

13. A process according to claim 10, in which the salt of a strong acid and a nitrogenous base is ammonium chloride.

14. A process according to claim 10, in which a mixture of two or more heavy metal salts is used.

15. A process according to claim 10, in which the heavy metal is fissionable actinide.

16. A process according to claim 1, in which the heavy metal is tungsten.

17. A process according to claim 1, in which the heavy metal is uranium.

18. A process according to claim 1, in which the heavy metal is tantalum.

19. A process according to claim 1, in which the heavy metal is thorium.

20. A process according to claim 1, in which the heavy metal is zirconium.

21. A process according to claim 1, in which the heavy metal is molybdenum.

22. A process of thermochemically converting regenerated cellulose fiber starting material to corresponding black, conductive, heavy metal-containing fibrous material which consists essentially in impregnating clean starting material with acetate, nitrate, oxalate, oxide, fluoride or chloride salt of heavy metal which is capable of reacting with carbon to form a refractory high-temperature stable carbide, and water-soluble ammonium. methylamine or ethylamine salt with strong acid that is capable of rendering the fibers nonflamma- 12 ble, drying and carbonizing the dry salt-impregnated fiber material by rapidly heating for about 5 seconds to 10 minutes in a non-oxidizing environment to a final temperature in the range of 1,200 to l,500 C., but below the temperature at which reaction of the said heavy metal with carbon occurs to form the heavy metal carbide, to produce electrically conductive, xray-absorbent, heat-stable nitrogen-containing fibers having a carbon content of about 40 to percent and nitrogen content of about 1% to 6 percent and containing from 1 to 50 percent by weight of heavy metal chemically bound to said fibers in other than carbide form.

Claims

2. A process according to claim 1, in which the heavy metal is a fissionable actinide.
3. A process according to claim 1, in which the fiber is first impregnated with a heavy metal salt and then impregnated with a salt of a strong acid and a nitrogenous base.
4. A process according to claim 1, in which the fiber is first impregnated with a salt of a strong acid and a nitrogenous base and then is impregnated with a heavy metal salt.
5. A process according to claim 1, in which the fiber is simultaneously impregnated with a heavy metal salt and a salt of a strong acid and a nitrogenous base.
6. A process according to claim 5, in which the salt of a strong acid and a nitrogenous base is ammonium chloride.
7. A process according to claim 1, in which both heating steps are less than 2 minutes in duration.
8. A process according to claim 1, in which a mixture of two or more heavy metal salts is used.
9. A process according to claim 1, in which the water-soluble salt of a strong acid and a nitrogenous base is impregnated in the fiber to the extent of 5 to 45 percent by weight.
10. In the process according to claim 1 for thermochemically converting regenerated cellulose fiber starting material to corresponding heavy metal-containing fibrous material without loss of fiber identity, the step which consists essentially in heating dry salt-impregnated fiber for about 1 to 10 minutes at an effective temperature of at least about 200* C. up to 350* C. and in the presence of air, the conditions being so controlled as to cause the fiber material to pass through a pyrolytic stage while avoiding destructive exotherm to result in a flexible, black, electrically non-conducting, x-ray-absorbent fiber material having a fiber carbon content in the range of about 50 to 65 percent and a nitrogen content of at least about 1 percent, the remainder of the material being essentially only oxygen and hydrogen exclusive of heavy metal; and containing substantially all of the heavy metal with which it was originally impregnated, in amount of about 1 to 50 percent by weight.
11. A process according to claim 10, in which the fiber is first impregnated with the heavy metal salt and then with the salt of a strong acid and a nitrogenous base.
12. A process according to claim 10, in which the fiber is simultaneously impregnated with the heavy metal salt and the salt of a strong acid and a nitrogenous base.
13. A process according to claim 10, in which the salt of a strong acid and a nitrogenous base is ammonium chloride.
14. A process according to claim 10, in which a mixture of two or more heavy metal salts is used.
15. A process according to claim 10, in which tHe heavy metal is fissionable actinide.
16. A process according to claim 1, in which the heavy metal is tungsten.
17. A process according to claim 1, in which the heavy metal is uranium.
18. A process according to claim 1, in which the heavy metal is tantalum.
19. A process according to claim 1, in which the heavy metal is thorium.
20. A process according to claim 1, in which the heavy metal is zirconium.
21. A process according to claim 1, in which the heavy metal is molybdenum.
22. A process of thermochemically converting regenerated cellulose fiber starting material to corresponding black, conductive, heavy metal-containing fibrous material which consists essentially in impregnating clean starting material with acetate, nitrate, oxalate, oxide, fluoride or chloride salt of heavy metal which is capable of reacting with carbon to form a refractory high-temperature stable carbide, and water-soluble ammonium, methylamine or ethylamine salt with strong acid that is capable of rendering the fibers nonflammable, drying and carbonizing the dry salt-impregnated fiber material by rapidly heating for about 5 seconds to 10 minutes in a non-oxidizing environment to a final temperature in the range of 1,200* to 1, 500* C., but below the temperature at which reaction of the said heavy metal with carbon occurs to form the heavy metal carbide, to produce electrically conductive, x-ray-absorbent, heat-stable nitrogen-containing fibers having a carbon content of about 40 to 95 percent and nitrogen content of about 1/2 to 6 percent and containing from 1 to 50 percent by weight of heavy metal chemically bound to said fibers in other than carbide form.