DE1646588C3 - Process for reducing the metal content of carbon fiber material - Google Patents

Description

. escaping metallic impurities to the essence of the cellulosic material

remove. This treatment reduced the entire borrowed amount completely to amorphous carbon. ^ calcium metal content of the sample by over 70 weight- lead, while the fiber integrity is essentially percent The sodium content of the sample was retained by. The amorphous it about 3800 reduced to 135 ppm. The initially 5 carbon fiber material has a relatively high tensile strength Contents of potassium, calcium, magnesium strength and flexibility and low thermal and end lithium in the sample were retained or electrical conductivities. Usually that has further reduced so that the sample after the final material has a sodium concentration of more than Treatment with a very low level of sodium, 1000 ppm. Most uses where Possessed potassium, calcium, magnesium and lithium. If a low sodium content is desired, the pie thermal conductivity of the treated sample was sodium concentration essentially below 500 ppm the same as a control sample, which will be reduced in the same way, while the amorphous nature of the Way carbonized and heated, however, material had tensile strength and flexibility as well not the metallic cleaning treatment ucter- thrown the thermal and electrical conductivities would. The tensile strength and flexibility must be maintained 15.

the control sample and the test sample were identical. In the method according to the invention that

Both the control sample and the test sample were carbon fiber material, either before or after one, consisting essentially of amorphous carbon. optional heat treatment, which was, for example, at a second Reyongewebeprobe treated in the same about 820 to about 1150 ⁰ C in an inert gas durchchen manner, but was at S: elle 20 is guided, comparable to the hydrocarbons to verflüchvon hydrobromic hydroiodic and turn the material to shrink in the heat. The same advantageous results were obtained with an aqueous solution of hydrogen iodide, ie a low sodium content and acid, hydrochloric acid or a mixture of the other advantageous properties. brought this into contact. The acids react with

In a third sample, sodium bromide and / or sodium iodide was used instead of bromine in the material to form hydrochloric acid (1 percent by weight). The treats. In this experiment, however, the sodium lung with the acids can, by spraying and the like, be five times as high as in the experiment with Jem, preferably the hydrobromic acid solution is used. Only cloth fiber material, however, immersed in the acid. The when the internal temperature was increased to 1200 ⁰ C 3 ° acid is comparable at an appropriate concentration and longer time was maintained at this temperature, turns, for example with a concentration of, for example, half an hour or more, then fell from about 0.5 to 5 weight percent, preferably with the sodium content down to a level that with that with a concentration of about 1 to 2 weight percent. Hydrobromic acid and hydriodic acid. A suitable contact time is, for example, comparable with treated samples. That means 35 about 1 to 5 minutes. The treatment is preferable to the treatment with hydrochloric acid significantly wise agitating the solution and the material is more disadvantageous and promoted and facilitated in comparison with the treatment by ultrasound, with hydriodic acid and hydrobromic acid then the material comes out of the solution

is unsuitable. taken out, dried and placed in an inert

According to the method of the invention, carbon gas such as argon, krypton, xenon or fabric fiber material that contains sodium and is burned with a helium or in a vacuum, namely conventional carbonization processes, is pretreated above the temperature which is sufficient to approx has been, treated with an aqueous solution of iodine - essentially rapid volatilization of the salts which are to be removed from the carbon fiber from hydrochloric acid or hydrobromic acid until the fibers are completely removed from the solution. Although the boiling point of sodium bromide are permeated and impregnated. The reaction at 139O ⁰ C and the boiling point of sodium iodide between the treatment agent and the metal should be 1300 ° C, it is not necessary to bring the carbon dioxide to a temperature above the start-up to form volatile bromides and / or iodide fiber material. Then the carbon fiber material is heated to the given boiling point, dried and fired at a temperature to remove 50 salts from it. Instead, the temperature is below the temperature at which the thermal heating is carried out at a temperature below about 1200 C conductivity and the electrical conductivity is increased, ie below the temperature at which the thermal conductivity is, however, the temperature must be chosen The carbon fiber strongly indicates that the desired reaction between the hand increases due to the conversion of the carbon dioxide and the metal to the formation of volatile 55 from the amorphous to the crystalline form. However, bromides and / or iodides takes place and the heating in an inert gas such as bromides and / or iodides of the metals volatilized nitrogen, argon, helium, krypton or xenon can be carried out in a satisfactory manner, namely at one temperature That out-amount This significantly reduces the sodium content and the sufficient to an essentially rapid volatilization content of other metals in the carbon fibers 6 ° of the sodium bromide and / or the sodium iodide. to achieve the carbon fiber. This temperature

The carbon fiber material is made from cotton, is at least about 815 C and not higher than Rayon or similar cellulosic materials at about 1150 ° C and preferably at about 930 to 1040 C. produced, which are preferably particularly advantageous results with a before carbonization are essentially free of impurities. 65 reached a temperature of about 980 C. Suitable for

The carbonization can be, for example, from about 1 to about a suitable heating time Period of time at a suitable rate in 20 minutes, preferably at about 5 to 10 minutes, carried out in a certain temperature range. This treatment process removes the sodium

content in the carbon fiber greatly reduced. From Table I is closed

Quality and better g
Example 1 Thermal conductivity and electrical conductivity

Two samples of carbon fiber fabric that showed at
about 1090 ⁰ C has been heat treated and off

Reyna fiber fabric by step-wise heating her- io B e i s ρ i e 1 2

had been made and over 96 percent by weight
Carbon is essentially in the amorphous form

A series of ^^^^^^^.

to reduce. The samples were prepared and treated as in Example 1 in the acid solutions indicated in Table 1, with the acid solutions being immersed, but subjected to ultrasound for 5 minutes 15 after impregnation of the samples with 1 or long ultrasound, 5% aqueous hydrogen bromide solutions from the solutions or taken out dried about 93 ° C and then hydriodic acid solutions for 5 minutes! Burned for 5 minutes in helium at 820 ^° C. The 1090 ^° C. was burned.

Samples were after cooling to room temperature with the 1 and 5% HBr and HJ solutions

examined for their metal content. The results *> similar results were obtained. All cases are summarized in Table I. became the calcium content and the magnesium content

of samples greatly reduced. The samples tested and

Table I, the control samples examined were

iSte treatment for tensile strength, flexibility, appearance and heat

(p _pm) a ₅ conductivity essentially identical.
^ - Further investigations were carried out,

(1) Control 3800 in which carbon fiber fabric samples as in the

(2) 1% HJ 250 game 1 were treated, however, the m Table II

(3) l% HBr 135 parameters specified were used:

Table II Sample treatment heating impurities (ppm) resistance

temperature Na K Ca Mg Li Ω per 6.5 cm *

( ⁰ Q

(1) control - 1050 24 34 36 <1 0.61 (2) HBr 930 275 16 12th 36 <1 0.60 (3) HBr 980 4th 6th 1 5 <1 0.64 (4) HJ 980 13th 2 1 22nd <1 0.64 (5) HBr 1090 21 11th 10 36 <1 0.60

Example 3

From Table II it can be seen that the sodium content was greatly reduced in further series of tests carried out according to the procedure described in the two samples by treatment with hydrobromic acid and hydroiodic acid. Bales of carbon fiber fabric were 5 minutes, in some cases to negligible values. For a long time in a 1% aqueous hydrobromic acid, the potassium and calcium solution was immersed in most of the samples and during this time an ultra and magnesium content was also reduced while being subjected to sonication. The impregnated the lithium content at a very low level 60 samples were then stayed at for 5 minutes. The resistance or the electrical conductivity- 980 ⁰ C heated. Samples taken from the bales remained very low and about the same level as before the acid bath treatment, after the acid control sample. The electrical conductivity of the carbon treatment and after burning on its fuel is directly proportional to the thermal conductivity. Metal content examined. It should be noted that low thermal conductivity is desirable. The whether the aqueous acid bath itself without the firing tensile strength and flexibility of the control sample treatment had any effect on the reduction of the test samples were about the same. All treated metal content exercised. The results obtained are: the third samples were of consistently high quality. summarized in Table III.

7th before the 16 46 588 r 590 24 8th before the after Table III Burn 22nd 7th Burn Burn Bale 1 598 Bale 2 48 41 Bale 3 570 25th before 20th after before before after 32 38 before 22nd 6th Acid bath 40 Burn Acid bath burn burn <1 <1 Acid bath 39 37 Sodium (ppm) 872 33 29 770 693 111 793 43 43 Potassium (ppm) 25th <1 7th 25th 30th <1 <1 Calcium (ppm) 59 692 38 45 697 113 57 665 110 Magnesium (ppm) 42 38 41 43 Lithium (ppm) <1 691 <1 <1 <1 676 115 Average 999 113 882 924 Total alkalinity (ppm) Maximum total 1028 121 900 934 alkalinity [highest individual sample (ppm]

Table III (continued)

Bale 4

before before after
Acid bath burn burn

Bale 5

before before after

Acid bath burn burn

Bale 6

before before after after

Acid bath burn burn

Sodium (ppm) 673 520 23 Potassium (ppm) 21 22nd 7th Calcium (ppm) 42 37 31 Magnesium (ppm) 43 43 43 Lithium (ppm) <1 <1 <1 Average 776 613 100 Total alkalinity (ppm) Maximum total 881 626 100 alkalinity [highest individual sample (ppm)]

845 580 27 1018 610 29 23 21 6th 27 21 7th 61 41 47 52 48 39 41 39 33 43 43 38 <1 <1 1 1 1 1 971 682 114 1141 723 114

748

119

1186 795

132

Table III (continued)

Bale 7

before before

Acid bath burning

after
Burn

Sodium (ppm) 1143 640 37 Potassium (ppm) 25th 14th 7th Calcium (ppm) 58 29 33 Magnesium (ppm) 47 31 41 Lithium (ppm) <1 <1 <1 Average 1274 715 108 Overall quality (ppm) Maximum total 1357 768 108 alkalinity [highest individual sample (ppm)]

From Table III it can be seen that the sodium content of the carbon fiber fabric was determined before Burning was reduced by treatment with hydrobromic acid. This reduction in sodium content is apparently caused by extraction. The further strong reduction in the sodium content is achieved by firing after treatment with hydrobromic acid. In the In most cases, the potassium, calcium, and magnesium levels go along with the sodium levels reduced so that the final product was found to have a total alkalinity of less than about 150 ppm could be. The starting materials had a total alkalinity that was five to ten times as high. The method according to the invention is simple, quick and economical to carry out Method for reducing the sodium content in carbon fiber materials. The tensile strength, the flexibility and the low thermal conductivity and electrical conductivity of the carbon fiber material remain with this procedure. In the method according to the invention other metals such as calcium, magnesium, lithium and potassium effectively removed from the carbon fiber. The metals are to a small extent by extraction and to an xr larger part due to volatilization of the bromides and / or iodides of the metals during firing ii Removed the presence of an inert gas

Claims (4)

material are expelled. Due to the high temperatures required, a partial 1. Process for reducing the metal content white graphitization and thus increasing the heat of the carbon fiber material, thereby making the carbon fiber material conductive. indicates that a sodium contains 5 From US-PS 26 57 118 it is already known, of the, essentially amorphous carbon fiber coke and coal with chlorine gas at a temperature material with an aqueous solution of bromine of about 1400 ⁰ C to treat, whereby some of the hydrochloric acid, hydriodic acid or medium carbon reacts with chlorine gas. This entanglement thereof treated and then driven at a temperature above that for the removal of io is not suitable for treating carbon fiber material, since due to the reaction between sodium impurities, carbon and chlorine gas, the strength properties are significantly reduced below the one substantial increase and the amorphous character, thermal conductivity and crystallinity of the would be impaired. Carbon fiber material causing temperature The invention is based on the task of providing a is burned until the sodium 15 drive to create the metal content of content of the carbon fiber material is substantially amorphous carbon fiber material effectively reduced. can be gert without doing any essential 2. The method according to claim 1, characterized in that graphitization and thus an increase in heat show that the carbon fiber material occurs at a conductivity of the amorphous carbon fiber material temperature between about 820 to about 1150 ⁰ C ao. is burned. This problem is solved by a method for 3. The method according to claim 1, characterized in reducing the metal content of KoMenstoffaser, that the carbon fiber material about material which is characterized in that a Substantially amorphous, in an aqueous solution containing sodium for 1 to 5 minutes an acid concentration of about 1 to 5 Ge 35 carbon fiber material with an aqueous solution weight percent is immersed, the aqueous solution of hydrobromic acid, hydroiodic acid or Solution treated during immersion by means of ultrasound mixtures thereof and then with a is moved to remove the carbon fiber material according to temperature which is above that for removal of Na from the aqueous solution at a temperature lying at trium impurities, however Temperature dried below about 150 ° C and thereafter a substantial increase in thermal conductivity for about 1 to 20 minutes in an inert state and the crystallinity of the carbon fiber gas is at a temperature of about 980 ° C, the temperature causing the material to be fired, as long as is burned until the sodium content of the carbon 4. The method of claim 3, characterized in that the fiber material is significantly reduced. records that a 1 weight percent bromine water 35 The method according to the invention enables one Substantial acid or hydriodic acid containing substantial reduction in particular of the sodium aqueous solution is used and in a content of the amorphous carbon fiber material without Nitrogen existing purge gas flow for 5 minutes that its amorphous character is of major importance is burned. is impaired. One according to the procedure of the Er-40 treated amorphous carbon fiber material thus retains its low thermal conductivity, Amorphous carbon fiber material is characterized by car- low electrical conductivity, tensile strength as well Rating of cellulosic fibrous material flexibility and also has a verrinherufactured and is characterized by its low metal content. conductivity and electrical conductivity as well as through 45 Preferred design features of the process high tensile strength and flexibility. For according to the invention are certain in the subclaims Applications, for example, to claim. position of ablation cooling devices, is an amor- To prove that only one treatment with phes carbon fiber material with a hydrobromic acid or hydroiodic acid if possible low metal content required. 50 desired beneficial results guaranteed, To reduce the metal content of coal, the following experiments were carried out, Fabric fiber material has usually been used in the past. Carbon fiber material heated so high that the loan amorphous carbon produced by metallic impurities to about 180 can be up to about 54O ⁰ C in helium with stepwise current removed from the fiber washed Reyongewebe volatilize at temperatures of material and with the aid of a Sprühgas- 55th Have been carbonized at this encryption temperature increase of about 1O ⁰ C go high temperatures required, wherein the sample to increase the thermal conductivity of the temperature level was maintained for about 2 hours at any however. The carbonized carbon fiber material as a result, since the carbon sample was immersed in an aqueous solution, the pulp fiber material is partially graphitized. In addition, about 1 percent by weight hydrobromic acid was allowed to release it to form undesirable carbides. Good contact between the fibers and the coming. Solution was ensured that during To reduce the metal content of coal- the immersion was moved with ultrasound. The fabric fibers have already been tried, carbon contact time was 5 minutes. The sample was then taken out of the solution by fibers with chlorine gas at temperatures of 2200 to 65, ^{to be treated at about 276O 0} C, the metallic fibers 12O ⁰ C being dried in air and then for 5 minutes the impurities converted into the corresponding halides burnt 1040 ⁰ C, wherein a beeeführt of nitrogen and this was then used in the carbon fiber standing purge stream to the from the