DE2602341B2 - Process for making graphite articles - Google Patents

Description

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The invention relates to a method for the production of graphite objects according to the preamble of Claim 1, in particular for use in nuclear reactors.

Graphite articles are usually made by extruding or pressing a graphitizable mixture sches made of graphite or coal particles (coke) and a binder (pitch binder). The molded Objects are then fired, cooled, impregnated with additional pitch, and fired again This re-impregnation is repeated several times until> above the desired final density is reached. The impregnated article will eventually be at sufficiently higher Graphitized temperature

When manufacturing nuclear reactor fuel elements, refractory graphite bodies are required whose properties match one another. This is particularly true for those areas of application in which graphite with a low content of impurities, in particular sulfur, is required. In fact, sulfur causes some problems. If it is present, the graphitization must namely be carried out at temperatures of up to 3000 ^° C. in order to drive it out of the object to be graphitized. In the absence of sulfur sufficient temperatures 2200-2600 ^0C sulfur catalytic t> 5 Siert probably the graphitization. Therefore, when the sulfur diffuses through the article at elevated temperatures, which has a different graphitization door consequence In this way, localized stress areas are created in the graphitized article

The one from the _; DE-OS 14 71 507 known method, graphite objects for nuclear reactors are made from coal tar This coal tar diehi as a common starting material for the production of the coke, the binding agent and the impregnating agent.

From GB-PS 875114 it is known that the Use of coal tar in view of the impurities cause difficulties in the manufacture of binders and impregnating agents. In this connection, GB-PS 8 75 114 lists earlier proposals using mineral oils as starting materials to use.

The graphite bodies produced by this known method were, however, according to the findings of the aforementioned GB-PS due to the irregular evolution of gas during graphitization brittle.

In order to avoid these difficulties when using mineral oils, the GB-PS describes 8 75 114 a procedure in which the oraphite body is made from petroleum pitch produced by oxidation treatment.

DE-AS 10 27 580 is known as the filler in a process for the production of coke used for coal bodies from the same hydrocarbons or to produce pitches, which are also used as binders.

The object of the invention is therefore to provide a method of the type mentioned at the beginning for producing graphite objects with high mechanical strength, relatively low porosity with consistent quality Provide carbon precursors (pitch) of consistent quality. The task is thereby solved that as starting material for the production of the coke, the binding agent and the impregnating agent each non-oxidized, thermal petroleum pitch is used. This can reduce the graphing temperature varied within certain limits and kept below the temperature required for expulsion the sulfur impurities is required.

Petroleum coke has long been known in the petrochemical industry as a starting material for manufacture of petroleum pitch, a refinery hydrocarbon stream is commonly used, which is high Has aromatic content. B. Decanting oil or a solvent exfcakl of decanting oil. When processing these pitch materials different procedures are used. Each of these processes begins with that from the pitch feedstock the low-boiling oils are removed by fractionation. In the manufacture of Thermal pitch, the high-boiling fraction is then further heated so that the aromatic Compounds condense further and polymerize to polynuclear aromatics. The product obtained is a high quality pitch with a softening point of usually 54.5 to 143 ° C in one Another process, the so-called air oxidation process, is used to produce pitch through the air heated high-boiling fraction blown, but this creates unfavorable relationships between the softening point and adjust the coking value or the viscosity that the production of graphitized Making bad luck more difficult and expensive.

Pss thermal petroleum peeh is a common refinery product, its softening point is usually about 54.5 to 143-C. The one also available oxidized petroleum pitch is not included in the invention. In the following table are some properties of some typical ones useful in the present invention Petrol pitch compiled,

Softening point (R&B) C. 116 77 149 Brockfield Viscosity, Pa · s at 0.140 190.5 C 0.030 0.390 0.275 177 C 0.045 0.780 0.700 163 C 0.086 1,600 51 Coking wide (ASTM D-2416) 38 63 5.0 Benzene insolubles (% by weight) 4th 28 - Quinoline insolubles (% by weight) - 0.5 1.22 Specific weight (25 C / 25 C) 1.19 1.24 1.3 Sword (weight- ⁰ / ») 1.3 1.3 487 Mean Molecular weight 380 530 93.1 Carbon (wt%) 92.4 94.0 5.4 Water content (% by weight) 5.7 4.4

The petroleum coke produced according to the invention is produced from the same pitch that is used as the binder pitch is used. Typical properties of a petroleum needle coke, which has been made from pitch samples with a softening point of 77 to 116 ° C, are summarized below:

Pen softening 116 point (R&B), C 60 77 Carbon yield. % ') 49 0.3358 X-ray diffraction, nm 86 Layer spacing 0.336 100 Lc 52 La 51 83 Coke microstructure,% 17th acicular 77 finely structured, isotropic 23

') In a closed graphite boat at 2800 C in Argon carbonized.

Suitable processes for the production of needle coke from petroleum pitch are known. For the production of graphite objects, certain amounts of thermal petroleum pitch and powdery !! or particulate! Coke made from the same pitch is placed in a suitable mixer. The mixing is 20 to 120 minutes at a temperature of 70 to 200 ⁰ C, depending on the melting point of the pitch binder. The mixture is then pressed or extruded into the desired shape and fired for 5 to 60 days at temperatures of about 600 to 1000 ° C. in order to carbonize the binder. Of the

The object obtained in this way is then impregnated with a further amount of the same pitch originally used, the temperature and pressure conditions being chosen so that the liquid pitch penetrates into the pores of the object. The object is then fired again at temperatures of 600 to 1000 * C long enough to carbonize the added pitch. The impregnation and heating are repeated as often as necessary. Finally, the impregnated and fired article is at a temperature of 2200 ° C or higher, e.g. B. 2800 to 3000 ⁰ C and preferably 2200 to 2600 ⁰ C, graphitized.

When using a thermal petroleum pitch with a low level of impurities, in particular The binder produced by graphitizing coke from the same pitch has a low sulfur content The subject also necessarily has a low sulfur content. Objects of this kind are suitable particularly suitable for thermonuclear applications.

The thermal petroleum pitches used according to the invention have a softening point of, for. B. about 54.5 to 143 ° C, preferably about 77 to 116 ° C.

Except through repeated impregnation with pitch and Burning, the objects can also be compacted by the fact that they are in the green state subjected to isostatic pressure before molding and before subsequent firing and graphitization.

Claims (1)

Claims; U Process for the production of graphite objects by pressing a coke-binder mass, Carbonization of the binder, impregnation and graphitization of the fired! Body, where the same starting material is used to produce the coke, the binder and the impregnating agent is used, thereby marked ι « draws that the starting material is non-oxidized, thermal petrol pitch used Z method according to claim 1, characterized! Characterized, that you have a thermal petroleum pitch with a softening point of about 54.5 to 143 "C, ιϊ preferably 77 to Π 6 "C, used, 3. The method according spoke 1 or 2, characterized in that a thermal petroleum pitch is used with a sulfur content of less than about $ 1 percent by weight 4. The method according to any one of claims 1 to 3, characterized in that the impregnated body is fired prior to graphilation and impregnated again with the starting material, and that there ·; Impregnate and burn like that repeatedly until the desired density is reached 5. Use of the method according to any one of claims 1 to 4 produced graphite articles as components of nuclear reactors m tor-fuel assemblies.