JPH066510B2 - Manufacturing method of artificial graphite electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a graphite electrode which reduces puffing and improves the bulk specific gravity of the graphite electrode when producing an artificial graphite electrode using coal tar needle coke as a raw material. The present invention relates to a manufacturing method.

(Prior Art) An artificial graphite electrode used for an electrode of an electric furnace for steelmaking is generally made of easily graphitizable coke and a binder such as pitch and an impregnating agent, and (1) crushing coke, blending particle size, (2) )
Manufactured through the steps of kneading with binder, (3) molding, (4) primary firing, (5) impregnation with impregnating agent, (6) secondary firing, (7) graphitization, and (8) elimination processing. .

In the graphitization process, the secondary fired electrode is heated to 2500-3000 ° C in an electric furnace in an inert atmosphere of nitrogen, argon, etc., or in a state in which air is shut off by using packing powder, and coke is converted to graphite. In the process of changing, the graphitization using the conventional Acheson furnace has been changed to the method using the rapid graphitizing furnace for the purpose of rationalization in recent years.

It is known that when a rapid graphitizing furnace is used, graphitization is carried out for, for example, several tens of hours, so that the temperature rises rapidly during graphitization, and irreversible expansion, so-called puffing, occurs in the electrodes during the temperature rise. If the degree of puffing is large, the bulk specific gravity of the graphite electrode becomes small and the strength becomes weak.
This puffing becomes more remarkable as the rate of temperature rise during graphitization becomes faster, which is a particular problem when graphitizing the electrode in a rapid graphitization furnace.

Conventionally, coke made from heavy petroleum oil has been used as a raw material for this graphite electrode. Petroleum-based coke contains about 0.4 to 2.0% of sulfur. The cause of puffing of petroleum coke begins to form graphite structure 17
It is said that it occurs due to the rapid volatilization of sulfur at temperatures of 00 to 2000 ° C. (For example, E. Fitzer, High Temperature
-High Pressure, Vol.19, P, 243-250, 1977). Therefore, as a conventional anti-puffing agent, there has been proposed a method of adding a compound that reacts with sulfur in coke to form a sulfide and prevents volatilization as sulfur. For example, compounds such as iron oxide, calcium fluoride, and titanium oxide are said to be effective as anti-puffing agents (U.S. Pat.Nos. 3,338,993, 3,563,705, 4,140,623, 4,312,745, and 4,312,745. 4,334,980 each specification).

Puffing also occurs when coal tar type needle coke is used as a raw material for graphite electrodes, but coal tar type needle coke has a feature that it has a lower sulfur content than petroleum type needle coke,
It is unlikely that puffing will occur for the same reason.

Therefore, the anti-puffing agent is also proposed to be different from the case of petroleum-based needle coke, and iron oxide and the like, which are considered effective for petroleum-based needle coke, have no effect on coal tar-based needle coke, As an anti-puffing agent for coal tar-based needle coke, for example, chromium oxide is reported to be effective.

(16 th, Biennial Conference on Carbon.Extended Abs
tract July 18-22, 1983, see page 595).

The present inventors have found that nickel and cobalt compounds, and further iron compounds having an average particle size of 3 μm or less are suitable as anti-puffing agents for coal tar-based needle coke, and have already filed a patent application (Japanese Patent Application No. 59-129671).
No. 60-54284).

The present inventors have conducted various studies on the cause of puffing during graphitization when producing a graphite electrode from a coal tar needle coke as a raw material, and in the case of coal tar needle coke, an extremely small amount is included. Although the puffing caused by sulfur is slightly generated, it was found that a large part is caused by the volatilization of nitrogen in the raw coke at 1700 to 1800 ℃, at which the growth of graphite crystal starts to grow rapidly.

From these facts, although there is a difference in sulfur and nitrogen between petroleum-based needle coke and coal tar-based needle coke, in all cases, elements other than carbon contained in the raw coke are gas at a temperature at which graphite crystals develop at 1700 ° C or higher. Turn into
It was estimated that this gas pressure causes puffing.

Based on the above assumptions, the inventors of the present invention smoothly prevent hydrogen sulfide, carbon disulfide, or nitrogen gas derived from sulfur or nitrogen from being diffused from the raw material coke, and the pressure due to the gas is reduced to prevent or reduce puffing. Based on the idea that it is possible, various studies were carried out on the production of a graphite electrode using coal tar needle coke as a raw material, and the present invention was completed.

(Problems to be Solved by the Invention) The present invention provides a method for producing a graphite electrode in which puffing that occurs during production of a graphite electrode using coal tar-based needle coke as a raw material is prevented, and the bulk specific gravity of the obtained electrode is increased. It is provided.

(Means for Solving Problems) In producing an artificial graphite electrode using coal tar-based needle coke as a raw material, the present invention comprises an iron compound having an average particle size of 3 μm or less and calcium, magnesium, cerium and lanthanum as a puffing inhibitor. One or more oxides or carbonates are used.

The present invention will be described in detail below.

As the coal tar-based needle coke, which is a raw material for the artificial graphite electrode, used in the present invention, any one having a needle-like anisotropic fine structure can be used.

Such coke is produced, for example, by producing a raw coke from a coal tar pitch from which quinoline insoluble matter is removed by a delayed coker and then calcining the coke with a calcineer. Usually, this coke has a sulfur content of about 0.05 to 0.3% and 0.3 to 0.6.
% Of nitrogen is contained. Coal tar needle coke is as described above (1) crushing, particle size blending, (2) kneading with binder, (3) molding, (4) primary firing, (5) impregnation with impregnating agent, (6) secondary An artificial graphite electrode is obtained through the steps of firing, (7) graphitization, (8) removal processing and the like. In the present invention, the anti-puffing agent is added at least in the step before the graphitization step.

Examples of the iron compound used in the present invention include iron oxide, iron hydroxide and iron carbonate. It is preferable that these particles have a fine particle size.
The particle size of the iron compound greatly affects the puffing prevention effect, and the effect is small even if the iron compound having a particle size of more than 3 μm is added.

In the present invention, oxides or carbonates of calcium, magnesium, cerium and lanthanum are used in addition to the iron compound, and the role of the iron compound is considered as follows.

The iron compound acts as an anti-puffing agent, and has an effect of increasing the bulk specific gravity of the graphite electrode in addition to the anti-puffing effect.

That is, it is known that the iron compound serves as a carbonization catalyst, and improves the carbonization yield of the pitch serving as the binder.
Therefore, the bulk specific gravity of the electrode after the primary firing is increased by adding the iron compound. As described above, one of the objects of the present invention is to increase the bulk specific gravity of the graphite electrode, so it is necessary to add an iron compound that increases the carbonization yield of pitch.

Compounds such as oxides or carbonates of calcium, magnesium, cerium and lanthanum have an effect of preventing puffing, but they do not have a carbonization catalytic ability, and therefore graphite electrodes having high bulk specific gravity can be used even if used alone. I can't get it.

The present inventors have found that the above-mentioned compounds of calcium, magnesium, cerium and lanthanum are very effective in preventing puffing of coal tar type needle coke.

The reason why puffing can be prevented by adding these compounds is not clear so far. As the compounds of calcium, magnesium, cerium and lanthanum, any one kind or two or more kinds of compounds are used.

The calcium, magnesium, cerium, or lanthanum compound used as the anti-puffing agent in the present invention preferably has a fine particle size, but there is no particular limitation and an industrially available compound can be used as it is.

The addition amount of the compound of iron compound and calcium, magnesium, cerium and lanthanum is not particularly limited, if the amount is too small, the effect is not significantly exhibited, and if the amount is too large, the coefficient of thermal expansion of the manufactured graphite electrode becomes large, And because it is economically disadvantageous, iron compound and calcium, magnesium, relative to the total amount of coke and binder pitch,
The total amount of cerium and lanthanum compounds is 0.
The range of 2 to 3% by weight is desirable, and more preferably 0.2.
~ 2% by weight.

The mixing ratio of the iron compound and the compound of calcium, magnesium, cerium or lanthanum is not particularly limited, but a weight ratio of 1: 1 to 0.2 is usually used. When the compounding ratio of the iron compound is small, the function as a carbonization catalyst is insufficient and the bulk specific gravity of the graphite electrode does not increase. If the amount of the compound of calcium, magnesium, cerium, or lanthanum is small, the effect of preventing puffing is small. If the amount of these compounds is too large, so-called secondary puffing at around 2500 ° C. increases, which is not preferable.

Examples of the present invention will be shown below.

(Example) A test piece was prepared using a coal tar needle coke containing a nitrogen content of 0.43% and a sulfur content of 0.20%.
The puffing was measured.

The anti-puffing agent was added at the time of kneading the coke and the binder pitch.

The conditions for producing the test piece are as follows.

Needle coke particle size: 16-60 mesh 20wt% 60-200mesh 45wt% 200mesh or less 35wt% Binder pitch compounding amount: 35wt% Kneading condition: 145 ° C, 20 minutes Molding method: Molding test piece: 200mm ^φ x 100mm ^L The test piece created under the above conditions is fired at 900 ° C and then 150
The test piece was impregnated with the impregnated pitch at a temperature of 5 ° C. and a pressure of 5 kg / cm ² , and the test piece was baked again at 900 ° C. to measure the puffing.
After the puffing measurement was completed, the size and weight were measured at room temperature to calculate the bulk specific gravity.

The puffing measurement conditions are as follows.

Rapid heating up to 1000 ℃ in argon atmosphere, then 10 ℃
The temperature was raised at a rate of / min and the amount of linear expansion from room temperature to 2600 ° C was measured.

The measurement results are shown in the table. It can be seen that the puffing is small and the bulk specific gravity after graphitization is high in the example in which the particle size of the iron compound and the calcium compound is adjusted as compared with the comparative example in which the particle size is not adjusted. In the comparative example, the particle size of the compound used was 30 μm for the iron compound and 40 μm for the calcium compound.
In all the examples, the iron compound was 1.5 μm, and the compounds such as calcium were 3 μm or less.
In addition, as a reference example, an example in which an iron compound alone with a particle size adjusted to 1.5 μm is added is shown.

(Effects of the Invention) As described above, according to the present invention, it is possible to prevent puffing during graphitization in a method for producing a graphite electrode using coal tar-based needle coke as a raw material, and an electrode having a high bulk specific gravity is obtained, A high quality artificial graphite electrode can be advantageously manufactured.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hisayuki Nagino 46-51 Nakahara-Sonohama, Tobata-ku, Kitakyushu, Fukuoka Prefecture, Research Institute, Nippon Steel Chemical Co., Ltd. (72) Ryo Yamashita, Tobata-ku, Kitakyushu, Fukuoka Nakahara Sen no Hama 46-51 Nippon Steel Chemical Co., Ltd. Technical Research Laboratory (56) References JP-A-54-66360 (JP, A) JP-A-59-162175 (JP, A)

Claims (1)

[Claims] 1. A group consisting of an iron compound having an average particle size of 3 μm or less and an oxide or carbonate of calcium, magnesium, cerium and lanthanum as an anti-puffing agent in producing an artificial graphite electrode using coal tar needle coke as a raw material. A method for producing an artificial graphite electrode, comprising adding one or more compounds selected from the above.