JPS60264316A - Production of molded article of expanded graphite - Google Patents

Abstract

PURPOSE:To obtain the titled molded article with a low residual sulfur content useful for gaskets, etc., by dipping graphite particles in a mixed solution of concentrated sulfuric acid and a strong oxidizing agent, washing the resultant intercalation compound with water and aqueous solution of sodium hydroxide and then water, and expanding and molding the washed compound. CONSTITUTION:Graphite particles, preferably natural scaly graphite from the viewpoint of ready availability is dipped in a mixed solution of concentrated sulfuric acid and strong oxidizing agent to form an intercalation compound. Various oxidizing agents including nitric acid may be used as the above-mentioned oxidizing agent, but a system of sulfuric acid and nitric acid is cited as a preferred example. 10pts.wt. graphite particles is treated with a mixed acid of 20- 50pts. wt. concentrated sulfuric acid and 5-20pts.wt. concentrated nitric acid, and then the treated graphite is separated in a suitable deacidifying apparatus. The separated graphite is then washed with 50-200pts.wt. 1-5wt% aqueous solution of sodium hydroxide and then with 100-200pts.wt. water and dehydrated to give a graphite intercalcation compound, which is subjected to the well- known expanding and molding steps to afford the desired expanded molded graphite article.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing an expanded graphite molded body suitable as a gasket, a backing, or a molding material thereof.

(Prior art) Graphite has a layered structure in which six-membered carbon ring network planes are piled up, and the bonds within the 9-layer plane are very strong, forming a dense network plane, but in the direction perpendicular to the 1-layer plane. The bonding is weak, leaving a relatively wide space within one layer.

Therefore, under appropriate conditions, other types of chemical species such as acids, alkali metals, and halides easily enter the interlayers of graphite and combine with carbon atoms to form graphite interlayer compounds. When this graphite intercalation compound is heated to an appropriate temperature, the compound instantly decomposes, the interstitial chemical particles become vapor and dissipate, and the graphite expands 10 to 400 times in the C-axis direction of the crystal. Graphite is obtained. This expanded graphite molded body is mainly used as a molding material for high-performance gaskets and backings.
Due to the inherent properties of expanded graphite, it has excellent heat resistance, chemical resistance, and sealing properties.

Concentrated sulfuric acid, nitric acid, fuming nitric acid, and potassium chlorate are used as reactive agents to form graphite intercalation compounds.

Many combinations based on concentrated sulfuric acid are known, such as mixtures with potassium dichromate, perchloric acid, phosphoric acid, and their compounds.

However, in the expanded graphite molded body obtained by expanding and molding the graphite intercalation compound formed by the above method, the sulfur content used during the formation of the intercalation compound remains, and this is difficult to use when used as an actual backing or gasket. Predisposes the material to electrochemical corrosion.

As a method for reducing the sulfur content, the graphite intercalation compound is washed with a large amount of water, and the expanded graphite molded body is
Although the former method uses a large amount of water and time, the desulfurization effect is small, and the latter method has a large desulfurization effect, but a small amount of oxidation consumption occurs during heating.
As a result, there are drawbacks such as a decrease in strength.

(Objective of the Invention) An object of the present invention is to provide a method for manufacturing an expanded graphite molded body that eliminates the above-described drawbacks.

(Structure of the Invention) In the present invention, a graphite intercalation compound formed by immersing graphite particles in a mixed solution of concentrated sulfuric acid and a strong oxidizing agent is washed with an aqueous sodium hydroxide solution, then with water, and then expanded.

The present invention relates to a method for manufacturing an expanded graphite molded body, which is characterized by molding.

As the graphite particles used in the present invention, in addition to the generally known natural flaky graphite, graphite particles such as Quiche graphite and pyrolyzed 1:[graphite can be used, but natural flaky graphite is preferred because it is easily available.

The treatment liquid is mainly concentrated sulfuric acid, and the various oxidizing agents mentioned above including nitric acid can be used, but a sulfuric acid-nitric acid system will be described below as an example.

10 parts by weight of graphite particles and 20 to 50 parts by weight of concentrated sulfuric acid.

The graphite is treated with a mixed acid containing 5 to 20 parts by weight of concentrated nitric acid, and the treated graphite is separated using a suitable deoxidizer such as a filter press or a centrifugal dehydrator. This is washed with 50 to 200 parts by weight of an aqueous solution of 1 to 5 wt. This is known as expansion,
An expanded graphite molded body is obtained by the molding process.

To quantify the residual sulfur content in a molded object, use JIS G
It is best to use the 1215 combustion neutralization titration method, but
It is also easy to compare the sulfur content counts using a fluorescent X-ray analyzer.

(effect) After forming a graphite intercalation compound in this way.

By washing this with sodium hydroxide, the chemical reaction of formula (1) occurs, thereby producing water-soluble sodium thiosulfate and sodium sulfide. Next, by washing with water, these can be eluted and desulfurization can be performed.

This greatly reduces the residual sulfur content in the expanded graphite molded product, reducing the rusting effect on the mating contact material and backing.

It is thought that the lifespan of Kaskerato will also be longer.

6 Na OH+48 = 3H20+N a, S*O
a+2Na2S ・” ”・・・(11 (Example)) Next, the present invention will be explained in detail.

Example 1 100 g of natural scaly graphite with a fixed carbon content of 97% by weight, ash content of 2% by weight, and a peak at 42 meshes was immersed for 1 hour in a mixed acid of 98% hydrogen sulfuric acid aoog and 62% hydrogen nitrate and 1009%. Deoxidized using a centrifugal dehydrator. A portion of this treated graphite is 2% industrial hydroxide) IJum aqueous solution 5kg
It was treated with water, washed with water, and dehydrated. Then, it was heated for 30 seconds in a Matsufuru furnace heated to 1,000°C to form worm-shaped expanded graphite.

This was further molded using a press to obtain an expanded graphite molded body with a thickness of 0.38 mm and a density of 1.0 g/am.The residual sulfur content of these was measured by JI8 G 1215 combustion neutralization titration method. However, the residual sulfur content of the molded product not treated with sodium hydroxide was 0.38% by weight, but the residual sulfur content of the molded product treated with IJium hydroxide was as low as 0.08% by weight.

Example 2 A part of the acid-treated graphite obtained in the same manner as in Example 1 was treated with 5% by weight of industrial hydroxide) IJum 5 to 9. This was expanded and molded in the same manner as in Example 1 to obtain an expanded graphite molded body. As a result of analyzing this expanded graphite molded body with a fluorescent X-ray analyzer, it was found that the sulfur content count number of the untreated molded body by fluorescent X-ray was 1 sooo counts/10 seconds. In the molded body treated with sodium, it decreased to 7500 counts/10 seconds9.

(Effects of the invention) The expanded graphite molded product obtained by the production method of the present invention has an extremely low residual sulfur content compared to that obtained by the conventional method without sodium hydroxide treatment, and the backing produced from this sheet is It reduces the rusting effect of moving materials and provides a long life.6-

Claims (1)

[Claims] (1) Hydroxification of a graphite intercalation compound formed by immersing graphite particles in a mixed solution of concentrated sulfuric acid and a strong oxidizing agent) Expansion characterized by expanding and molding after washing with IJum aqueous solution 1 and water A method for producing graphite molded bodies.