DE1178765B - Carbon material - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY DEUTSCHES ÄTflSiS PATENTAMT Internat. Class: C 04 b

EDITORIAL

Number: File number: Filing date:
Display day:

German KL: 80 b -8/12

U7295VIb / 80b

July 2nd , 1960

September 24, 1964

The present invention relates to the use of carbon or graphite fiber material as a carrier for fission products in moldings or structures. The term "carbon" is intended to include both types of fiber in the following.

There are various proposals for molded bodies or structures made of porous carbon or graphite known with fissile material dispersed therein, for example from "Introduction to Pile Theory" (The Science and Engineering of Nuclear Power), 1956, pp. 302-304. This reference refers based on solid fuel mixtures produced by dispersing uranium metal or compounds in a refractory solid such as graphite.

According to "Nuclear Fuels" 1956, pp. 252/253, uranium compounds can also be found in porous artificial Graphite, made in the form of solid blocks, can be dispersed.

Finally, US Pat. No. 2,835,606 discloses a method of manufacturing an article described, which consists of graphite with uranium oxide distributed in it, with aqueous solutions of Uranyl nitrate hexahydrate can be used as an impregnating agent for the porous graphite. It will Uranyl nitrate hexahydrate converted to uranium oxide dispersed in the object.

The prior art has dealt with the use of carbon or graphite in the form of porous solids or blocks with fissile material dispersed therein. The usual Porous solid graphite have been used so far because they are known in powder form only Raw material could be produced.

The present invention now relates to the use of a different type of Graphite as a carrier for an object which contains fissile material dispersed therein.

Compared to the known use of carbonaceous material, especially porous Carbon, as a carrier for fissile material that may be dispersed in this body, the Carrier and the fissile material form a shaped body, the invention is characterized in that one moldings or structures made of fibrous carbon or graphite as a carrier for fissile Material used.

The fissile material can be present in the article as a precipitate from solution or from steam or dispersed in the form of particles. The individual fibers can have a carbon skin on or around them or outer layer bearing the fissile carbon material

Applicant:

United Kingdom Atomic Energy Authority,

London

Representative:

Dipl.-Ing. R. Beetz, patent attorney,

Munich 22, Steinsdorfstr. 10

Named as inventor:
Robert Lewis Bickerdike,
Anthony Reginald George Brown,
Garyth Hughes,
William Johnson,

William Watt, Farnborough, Hampshire
(Great Britain)

Claimed priority:

Great Britain July 2, 1959 (22747,

22748, 22 749, 22 750, 22 751)

Material and the fibers wrapped. This skin or top layer can be made of a liquid impregnating agent, such as a synthetic resin that has been converted to carbon; she can also called carbon by pyrolytic deposition of carbon from the vapor of a Be deposited carbon compound. The skin or outer layer can also be practically impermeable be.

In some cases, the new carbon molded body is impermeable as a whole or at least in the essential impermeable; the impermeability is achieved by a long lasting or multiple repeated deposition of the skin or top layer; this can be continued for so long or repeat several times to fill in the spaces between the fibers until a satisfactory one Degree of impermeability is reached.

The carbon body according to the invention can take the form of objects with areas of different, have a predetermined fiber density.

The particularly dense areas can optionally be made impermeable, so that they a Partition opposite the passage of

409 688/350

3 4

Form fission products. For example, leaf-shaped

tubular object a ring or cylinder bubbles or the appearance of cracks and crevices

shaped area to be avoided with opposite to the adjoining.

Have areas of greater density, so the in the pyrolytic precipitation of The passage or diffusion of 5 carbon can in between the carbon fission products by the pipe wall to prevent. subject to graphitization, The process for the preparation of according to the invention by heating it to a high temperature, according to the example Carbon articles with fibrous wise at 2000 to 2800 ° C in a non-oxidizing structure is, for example, that one heats up the atmosphere. Then a fibrous structure made of synthetic or natural io further pyrolytic deposition of organic carbon fibers joins or -presses, then made of material; in this way a body is created the assembled structure under non-oxidizing with a "duplex structure", which is partially made of the conditions up to the charring temperature soft graphitic material and partially heated, it being held in the desired shape by hard, pyrolytically precipitated carbon and - if necessary - there is external carbon. Optionally, the graphitization can be done after coating be carried out on or around the individual carbon ends of the precipitate, fibers of the mass precipitate. After the pyrolytic precipitation, one works again For example, after a pyrolytic range of amounts of carbon, the Precipitation method in which the carbon mass is a carbon object if it is still porous in an atmosphere or stream of a 20 with a furan derivative such as furfuryl alcohol in Gas, which is a gaseous carbon compound treated in the manner described above, contains, is heated to more than 500 ° C. The furfuryl alcohol is in the pores of the counter-total pressure can be about 1 atm. amount, but polymerized to a solid resin and this state Higher pressures can also be used, then solid resin - right down to the inside in order to increase the rate of precipitation 25 pores in - encircle carbon or graphite. The partial pressure of the carbon compound is converted by touching the object or the must be set appropriately so that material heats up to a temperature that is not low The formation of soot in the furnace is below 950 ° C.

ligen process conditions is avoided. The mass of the original substance on the fibrous organic fibers forming the carrier or the carbon fibers, the carbon is preferably carried out, can arise from these natural fibers under pressure before the deposition of carbon or vacuum with a synthetic resin providing carbon in its skin or covering layer around the fibers by thermal decomposition; In this way, the skin is enveloped or the fibers are soaked, preferably with a furander coating, it also binds adjacent like furfuryl alcohol, which is then polymerized and carbonized on the bare fibers and finally also covers the soaking. A final graphitizing substance can cause the reactive movement brought on or between the fibers.
treatment at more than 2000 ° C. In the process of producing a mold

The pyrolytic deposition of carbon 40 body or structure of carbon according to the

can be continued until a high present invention can make the mass more organic

The density and strength of the carbon body are fixed in a compression mold before the fibers are carbonized

is enough or the body is completely, at least compressed, at least during

on the surface, is impermeable. But you can rend the period of time in which the crowd is on

the carbon body is also brought to a very considerable temperature at which a decomposition

lichen residual porosity that a settlement or transformation of the fibers in the first

favorable effect on the physical own stage of their conversion into carbon takes place,

has shafts of the product, and indeed for some time

turn wise, because then an unusually charring temperature will be continued, with

large deformation occurs before a complete 50 one the pressure and / or the other conditions

The piece breaks under load. The pyro- the pyrolytic precipitation either con-

lyse can hold on a free-standing object or stationary, remove the pressure or remove the

in the case of an object in a form or under conditions in the most favorable way

Printing can be carried out. can. Preferably, the pyrolysis is only after one

The fibers 55 used as the starting material can reduce the temperature considerably as a loose, confusedly mingled mass, that value is made that is used during the process how, for example, raw tree charcoal had to be complied with. Under these wools; They can also be spun and / or woven or any other treatment of lower moldings when the molding pressure is above are thrown to give them a desired orientation- 60 a most favorable temperature in the charring process or a desired cohesion is maintained, sudden shrinkage give. the fiber mass occur, whereby the fiber mass

If loose fibers, such as cotton fibers, are separated from the walls of the mold and the mold is turned, these fibers are expediently bent or even torn,
pressed before charring; preferably their 65. In the event that the method of manufacturing expansion during the charring process of the carbon article impregnation of a be limited, for example, by holding them together in bulk of organic, natural or synthetic a clamp or press, so as to allow the table fibers with a thermosetting adhesive resin

comprises, the mass can be heated to initially bond or cohesive the
Reach fibers and harden the adhesive resin.
Then the mass will be during at least the last
Section of polymerizing or curing the
Resin compressed in a compression mold to get on this
Way to obtain the object with sufficient strength and rigidity; further compression can occur during the charring process
be performed. The adhesive resin is preferably a cylinder of high density within a cylinder which, when decomposed by heat in the actual entire pipe or its wall effect, results in a high carbon content. Furfuryl alcohol and phenol formaldehyde resins are particularly suitable.

In the production of

stand from the fibrous carbon material used in the invention, which is in its final
Form a substantially impermeable layer
or have an impermeable area, for example an annular or cylindrical impermeable area, if they are used for the surface layers of the sigen area, the original fiber material can be arranged in such a way that there is a tube with pipes
forms at least one cylindrical intermediate zone,
in which the density of the fibers is greater than in the
inner and outer peripheral zones of the tube; 25th
here too the fibers are charred and then
Coatings, layers or skins of carbon
the charred fibers produced by pyrolytic deposition or by impregnation with a liquid artificial resin.

The tubes can generally by hydrostatic pressure on a fiber mass in a Rubber containers are molded. In order to achieve the desired high density of the char in the mitt

hol or a phenol-formaldehyde resin, arranged in a mold and then a slight axial Compressive stress while being heated to polymerize the resin. 5 If necessary, further pressure can be applied during all or part of the process stage in which the heating is then carried out takes place for the purpose of charring the fibers.

The zones or areas of high density er

manure. Then the pipe made of fibrous carbon material after the pyrolytic Process can be treated or it can be an in-tube counter-impregnation and charring treatment in the

Learned manner described above, whereby the tight inner cylinder quickly a substantially forms impermeable cylindrical barrier. Normal commercial cotton is good

example 1

A solid cylinder is made of carbon with a dispersion in its central part of uranium and completely enclosed in an outer coating pyrolytically sealed with carbon while the whole forms a single coherent mass.

A second, smaller diameter disk was placed on a disk of woven cellulosic material and laid out of finer spun and woven material that contains a dispersion of uranium

To achieve a leren area of the pipe wall, a 35 is held; the uranium dispersion was a precipitate

loose layer of fibrous material around the perimeter of a solution of uranyl nitrate; the precipitation took place

arranged thin-walled rubber tube. Outside by ammonia. Around the edge of the smaller ones

Over this first layer a tube or washer was woven a ring of the coarser

Tube made of tightly woven material (woven from material laid that has the same outer diameter

natural or artificial yarn). The 40 had like the lower disk. Then a white

woven tubing is made with a furfuryl alcohol, tere disk made of the coarse material with the

is added to the acid, soaked and outside the same diameter as the first disc on top.

this hose is put another layer of. This stacking was repeated several times

arranged loose fiber material. The whole thing is repeated by. In this way a column and

surrounded by an outer rubber tube. The two 45 by arranging some panes made of uranium-free

Rubber pipes are then pressurized into material at the top and bottom of the column

(The one from an appropriate source for hydrosta- was the dispersed uranium in the inner area

table pressure is taken) to the fiber tube of the column completely encased by a uranium-free

pressed on. Zone or envelope. All discs were before

After releasing the pressure and removing 5 °, slightly add acid for hardening of the pressed tube, this is moistened in a prepared furfuryl alcohol; the pillar Clamping device fitted to a radial extent was held under slight axial pressure, while stretching the outer surface or a composite of the alcohol was polymerized and through avoid dragging the inner surface; its bonding and hardening solidified the column and this is followed by the charring of the pipe. This charred them for the charring treatment Rohr will eventually get a treatment. During the charring the column was under subjected to pyrolytic deposition in which light axial pressure is maintained; also at made of carbon. the first part of the pyrolytic process

The processing of the pipe down to its final deposition of carbon. The charring

valid dimensions may have been made between 60 by heating in a non-oxidizing atmosphere

two stages of pyrolytic precipitation sphere carried out up to 1000 ° C; after setting done before the material has become too hard
is to be easily machined on a lathe too
will.

Optionally, rings made of woven textile with a pressure of 8 cm Hg can be put through the oven.

material passing through in a circular or cylindrical center, with a precipitate of coals

or lowering the temperature to 860 ° C was a nitrogen stream, which at a total pressure of an atmosphere of benzene vapor with a partial

central zone has an increased density, after impregnation with an adhesive resin such as furfuryl alcohol

fabric was formed in the pulp. The outer uranium-free areas, which are made up of coarser fibers

were more easily penetrated by the gas diffusing into the body than the gas inside Area, with the result that the uranium-containing zone inside the body by pyrolytically deposited Carbon was sealed before the outer zone or shell became impermeable. That Pyrolytic deposition of carbon was continued until the surface layer was also complete closed or sealed.

When using fabric, a uniform pore size is obtained; there are no unusual occurrences large pores, so that it is relatively easy to treat a large workpiece so that it becomes impermeable.

15 Example 2

Approximately 20 grams of cotton linters were added Immersed in a 10% solution of uranyl acetate in water at room temperature. The excess Liquid was removed by gently squeezing and draining; then the Put cotton in a 10% ammonia solution. After decanting and washing it became Material dried in an oven at 120 ° C. Three discs of 3 g each were made in the manner that 2.25 g of uncolored linters and 0.75 g of that colored by the uranyl acetate Material took and pressed in a metal mold of 20 mm diameter. The cotton was in placed in the mold in such a way that the "colored" material is completely surrounded by the uncolored was.

The disks were then placed in a graphite clamping device to prevent peeling, packed in soot inside a quartz tube with a graphite end cap and carbonized by slowly heating to 1000 ° C. for a period of 2 days. After cooling and removing the soot, the test pieces received a treatment to deposit carbon in a stream of nitrogen and benzene vapor at 860 ° C. in a quartz tube furnace. In between, the pieces were removed from the oven and ground flat or thin. The total gas pressure was 1 atm. and the partial pressure of benzene 8 cm Hg. Two of the specimens received a further treatment with pyrolytic deposition of carbon, one for 7/2 days and the other for 1/2 day, in the nitrogen-benzene vapor atmosphere. The original density (ie, after carbonization) was approximately 0.5 g / cm ³ and the final density (after the carbon was deposited) was approximately 1.46 g / cm ³ . During or after their irradiation in a nuclear reactor, the specimens showed a good retention capacity for fission products of the uranium 235 with which they had been impregnated.

Example 3

60

In a different embodiment of Example 2, 100 g of cotton linters were ^{moistened or soaked with 280 cm 2 of} a solution of uranyl nitrate in water (total uranyl nitrate content 5 g) by kneading the liquid on the cotton and kneading the cotton until it was evenly soaked was. The damp cotton was then exposed to ammonia fumes by passing a stream of nitrogen containing ammonia over it. After a few hours, the ammonia content of the gas entering the treatment vessel was brought to zero and the temperature increased to 120 ° C. to dry the cotton. The cotton was then pressed into a disc shape, both with and without particularly undyed linters, in order to then proceed as described in Example 2.

If the shaped bodies or structures contain carbon which has been precipitated by pyrolysis, so the oriented structure of carbon can be used to advantage. The base level of the The crystal of the precipitated coal forms only a small angle with the one below it lying precipitation surface, which causes the movement of foreign atoms, such as. B. fission products, is hindered or prevented at all in a direction normal to the axis of the fiber. Consequently The nuclear fission products are precipitated to a large extent within the skin Carbon retained or captured.

Another advantage that is particularly evident when introducing reactive substances into the fibrous Material results in that there is a uniform and finely divided dispersion of reactive elements can be obtained within the entire carbon block. This still has to do with the Reaction potential has the advantage that corresponds to the use of a fine powder of reactive material, but the physical disadvantages of treating and evenly distributing the powder in any medium.

Claims (5)

Patent claims: 1. Use of molded bodies or structures made of fibrous carbon or graphite as a carrier for fissile material. 2. A method for the production of molded bodies or structures according to claim 1, characterized in that characterized in that the fissile material in the fibrous carbon or Graphite dispersed by making the fissile material from one through the fibrous Carbon or graphite absorbed solution falls or from a vapor in the fibrous Carbon or graphite precipitates or particles of this material with the carbon or graphite mixes. 3. A method for the production of molded bodies or structures according to claim 1 or 2, characterized in that characterized in that the fibrous carbon or graphite before or after it Charring impregnated with a carbon-forming synthetic resin, the resin polymerizes and in situ to form an outer carbon layer or skin around the fibers and charred around the fissile material. 4. A method for the production of shaped bodies or structures according to one of claims 1, 2 or 3, characterized in that the fibrous carbon or graphite is treated subjected to a pyrolyzable carbon compound with steam and the reaction temperature and adjusts the partial pressure of the connection so that an external carbon 9 ίο Substance cover layer or skin from the steam Publications considered: precipitates on the fibers. German Patent No. 873,386; 5. The method according to any one of claims 2, 3 Austrian Patent No. 165 311; or 4, characterized by U.S. Patent No. 2,835,608; Carbon layer or skin around the fibers so 5 Introduction to Pile Theory, 1956, pp. 302 to 304; long precipitates until the moldings or Ge Nuclear Fuels 1956, pp. 252 and 253; are essentially impermeable. At the. Ceramic Soc. Bull., 1957, p. 101. 409 688/350 9.64 © Bundesdruckerei Berlin