DE1671134C - Process for the production of shaped bodies made of graphite with isotropic thermal expansion - Google Patents

Description

The invention relates to a method for producing graphite, in particular shaped bodies made of graphite with a relatively high and essentially isotropic thermal expansion.

Moldings produced according to the invention can be used in the fields of space travel and nuclear technology be used. By covering with a heat-resistant Metal or with the carbide of such a metal can be effective against oxidation and surface erosion can be protected.

Refractory metal carbides are resistant to high temperatures and can therefore be used for the above-mentioned Purposes. Typical metal carbides of this type are silicon carbide and niobium carbide. Tungsten carbide and the like. Their use is due, for example, to their brittleness and their sensitivity handicapped to a thermal shock. Further application possibilities would arise if it were possible, coatings from these substances without cracks and without erosion on one to apply suitable carrier. These areas of application include, for example, the tips of Missiles and nuclear fuel elements in reactors.

For the same or similar purposes, refractory metals such as for example iridium, can be applied to suitable supports.

The successful application of refractory metals or metal carbides as a coating on one Carrier depends largely on the thermal expansions of the coatings and the carrier to match. If the coefficient of thermal expansion differs significantly, the coating will receive after repeated Heating and cooling jumps.

It is known to have coatings made of refractory metal carbides to be applied to shaped bodies made of graphite. However, such a graphite usually has one relatively low coefficient of thermal expansion. Further difficulties arise from the Anisotropy of graphite, usually one chooses shaped bodies made of graphite with a coefficient of thermal expansion that is similar to that of metal carbide. Then the parameters of the coating process are changed in order to obtain a compatible system to accomplish. However, these attempts have not yet led to complete success.

It is also known to use finely divided carbonaceous substances, e.g. B. coke, mix with a charring binder J.T1, to shape the mixture and then to heat it in an inert atmosphere so high, for example to 2600 to 300O ⁰ C, that it is converted into graphite. The production of carbon bodies from so-called soot coke is also known; The starting material here is a mixture of carbon black with small amounts of a carbon-containing binder, which ^{ve: cokes at 450 to 650 0} C, then calcined at 900 to 1500 ⁰ C, subsequently comminuted, mixed with binder, coked again and then in graphite by heating It was not known which starting materials should be used here in order to obtain moldings made of graphite with a high and essentially isotropic thermal expansion.

According to the invention, moldings are obtained au <graphite having an essentially isotropic thermal expansion coefficient.

Shaped bodies made of graphite according to the invention have a relatively high coefficient of thermal expansion, which is almost exactly the coefficient of thermal expansion of the metal used as a coating or Metal carbide.

The invention relates to a method for the production of shaped bodies from graphite with isotropy Thermal expansion by heating a shaped mixture of finely divided coke and a charable aromatic binder in an inert atmosphere at 2600 to 3000 "C. The procedure is characterized by the use of a coke made by mixing a petroleum residue at a Temperature above the melting point of this petroleum residue with 2 to 20 percent by weight of a carbon black with a particle diameter below 350 millimicrons. Coking the mixture at 450 to 650 C. Calcining the coke at 900 to 1500 C and crushing the calcined coke is obtained.

A mixture can also be used for the production of the coke, which in addition to the petroleum residue and carbon black additionally contains a non-coking diluent.

The carbon black used as the starting material has a surface area of 8 to 850 m ² / g or more. Suitable carbon blacks are split black and acetylene black. Kiln gas soot, deeply colored gas soot, long-flowing gas soot and furnace oil soot. Acetylene black, deeply colored gas black and long-flowing gas black are preferred.

The invention is based on the knowledge that when carbon black is added to a substance to be coked a coke is produced, which is converted into a graphite with a high isotropic thermal expansion and an excellent Flexural strength can be transferred. As stated earlier, the carbon black is used in amounts of 2 to 20 percent by weight added to the petroleum residue. This amount depends to some extent on that too Particle diameter and the surface of the soot. In general, lesser amounts will need one Small particle size and large surface area to be added, amounts of 2 to 10 percent by weight are usually used.

The expression "petroleum residues" means all hydrocarbons that are usually coked. Typical such substances are cracked tars and heavy, catalytically cracked oils. Residues from the distillation of crude oil under reduced pressure or at atmospheric pressure, catalytic or thermally cracked distillates and the like. Among these materials are particularly useful in the anosphärendruck d * »r distillation of crude oil under reduced pressure or at A remaining residues.

After mixing with the carbon black, the petroleum residues can be coked in a manner known per se in a continuous, semi-continuous or batch-wise manner. Typically carbonized at elevated pressures and at from 450 to 525 ° C, distortion, at 450 to 500 C. ^c If one wants to reduce the viscosity of the residue to 7 as to facilitate their pumps, one can not a verkokend j Add liquid of low viscosity and low boiling point, e.g. B. Kerosene, light oils or diesel oil. These substances can be mixed while warm with the molten petroleum residues before coking and before or after the addition of the carbon black. But you can also coke the pretreated petroleum residue in the liquid state, namely by passing it through a fluidized bed of coke particles at atmospheric or superatmospheric pressure and at temperatures of 450 to 650 ° C.

The resulting coke is then calcined at temperatures of 900 to 1500 "'C and adjusted to the desired temperature Crushed particle size. This particle size is generally dependent on the one to be used Molding method of the molded body.

Then the crushed coke is mixed with a charring aromatic binder. To this

ic include various charring pitches, such as coal tar pitch, Petroleum pitch or wood tar pitch. The choice of binder and its softening point depend on the size of the coke * particles used and the process used to manufacture the Moldings.

After the coke has been mixed with the binder, this mixture is shaped in the usual way, z. B. by pouring into molds or by extrusion.

The shaped body produced in this way is then heated to temperatures of usually 750 to 1000 C in an inert atmosphere, ο that the binder is coked and the volatile components be driven out. After the charring, the shaped body is heated in the usual way 2600 to 3000 C converted into graphite in an inert atmosphere.

example 1

Petroleum residues were mixed with soot in a mixer with a stirrer with four blades. Portions of 22 kg each were coked in an autoclave at 470.degree. During the coking, 75% of the petroleum residue evaporated. During the coking, an inert gas was kept in the autoclave at a pressure of about 3.5 kg / cm ² .

The crude coke thus obtained was calcined at 1000 ° C. in an inert atmosphere. Then crushed and the calcined coke was ground to a flour of which 55% had a particle diameter less than 0.075 mm.

This flour was then mixed with a coal tar pitch with a softening point of 110 C in mixed in such amounts that bolts 9 cm long and 1.5 cm in diameter are extruded or that cylinders 7.5 cm long and 7.5 cm in diameter could be formed. These parts were then packed in coke particles and heated to 1000 C in an inert atmosphere, so that the binder was carbonized. Then these parts were made inert by heating at 3000C. the atmosphere converted into graphite, and the physical properties were examined. A same one Shaped bodies made of graphite were also made from the oil residue, but without the addition of carbon black. manufactured. This body was used as a control body. Table I shows the properties of several Types of carbon blacks which can be successfully used in the process of the invention.

Table I.

soot

Deeply colored carbon black

Acetylene black

Long-flowing carbon black
Conductive oil furnace soot ..

soot

Carbon black

Soot

Average
Particle diameter

ΙΏμ

12th
50
28
29
29
80
347

Carbon black properties

surface
m ² g

850

64
295
190

85

23

Volatiles
Weight percent

13.0
1.0

12.0
2.0
1.0
1.0
1.0

Bound
carbon

Weight percent

87.0

99.0
88.0
98.0
99.0
99.0
99.0

Table II shows the results of an investigation of moldings produced according to the invention made of graphite.

Table II

Coke batch

Natural sound of the graphite obtained

in the direction
of the grain N 97 6th 215 6th 308 5 196 3 145 2 243 2 263 3

Flexural Strength kg / cm ²

in the direction
perpendicular
to the grain

Thermal expansion coefficient (cm / cnVC 10 ° (30 to 100 ° C)

in the direction perpendicular to the grain

in the direction
of the grain N 2.06 4th 5.40, 2 5.64 3 4.79 3 4.43 2 5.35 2 5.20 3

Residues from vacuum distillation of

Crude Oil 97 6

Residues from vacuum distillation of crude oil + 5.3 percent by weight deeper in color

Carbon black .... 215 6 200 6

Residues from vacuum distillation of

Crude oil + 5.3 percent by weight acetylene black 308 5 265 8

Residues from vacuum distillation of
Crude oil + 5.5 percent by weight of long-flowing carbon black 196 3 131 3

Residues from vacuum distillation of

Crude oil + 19.7 percent by weight Ga-soot ... 145 2 132 8

Residues from the distillation of thermally cracked oil + 3.6% by weight Acetylene black 243 2 158 3

Residues from the distillation of crude oil at atmospheric pressure + 3.9 percent by weight Acetylene black 263 3

N = number of patterns.
As the table shows, the isotropy of the shaped bodies are made of graphite

significantly improved by adding carbon black.

3.60

5.40 5.56

4.72 4.44

5.52

5.18 and their flexural strength

Example 2

The procedure of Example 1 was repeated, using a light cracking oil as a diluent for

Table III

various blends of petroleum residues and acetylene black were used. The results are included in Table III.

Ver yield acetylene
soot in Properties of the graphites obtained 1.5 cm 10O = C) Moldings of 7.5 cm C 10 " coking on calciner Extrudates with a Thermal expansion in
direction
of Diameter r 100 ⁰ C) pressure Raw coke tem coke diameter of coefficient, Kornes Thermal expansion in the direction
perpendicular cm / cm / ° C x 10 ⁶ more specific coefficient, to the grain Coke batch kg / cm ² Weight Weight more specific (30 to resistance cm / cm / percent percent resistance in
direction
of Ω cm 10 * (30 to ü-cm · 10 ⁴ Kornes in the direction
perpendicular in
direction
of in
direction
of 17.52 to the Koni Kornes Kornes 5.02 94.70 percent by weight 15th Residue from the vacuum 30.2 J 8.6 distillation of crude oil "he, 5.38 + 5.3 percent by weight ■ 18.00 5.02 Acetylene black 18.21 63.27 weight percent of one 15.22 Residue from the vacuum 5.33 distillation of crude oil 3.5 + 3.56 percent by weight 21.3 17.1 Acetylene black + 33.17 weight 5.48 percent of an easy one 20.57 5.10 Fission oil 18.43 54.66 weight percent of one ! 6.15 Residue from the vacuum 4.87 distillation of crude oil 3.5 + 3.07 percent by weight 19.0 17.1 Acetylene black + 42.27 weight 5.29 percent of an easy one 17.45 5.01 Fission oil 16.07 63.27 percent by weight iines 17.40 Residue from the vacuum 5.26 distillation of crude oil 3.5 + 3.56 percent by weight 25.8 12.7 Acetylene black + 33.17 weight 5.48 percent of an easy one 18.00 5.22 Fission oil 19.30

Claims (2)

Patent claims: 1. A process for the production of moldings axis graphite with isotropic Wärmeausdehnuflg by heating a shaped mixture of finely divided coke and a carbonizable aromatic binder in an inert atmosphere to 2600 to 3000 ° C, characterized by the use of a coke, which is obtained by mixing a petroleum residue at a Temperature above the melting point of this petroleum residue with 2 to 20 percent by weight of a carbon black with a particle diameter below 350 millimicrons, coking the mixture at 450 to 650 ° C, calcining the coke at 900 to 1500 ⁰ C and crushing the calcined coke is obtained. 2. The method according to claim 1, characterized in that one for the production of the coke a mixture is used which, in addition to the petroleum residue and soot, also contains a non-coking one Diluent ι rhalts.