CS268609B1 - Process for producing expandable carbon - Google Patents

Abstract

Carbon particles, preferably natural flake graphite, are leached with a mixture of nitric acid and boric acid or its salt together with a salt of manganous acid. The thus prepared expandable carbon particles are washed with water to the desired pH value, dried and subjected to thermal expansion, thereby obtaining expandable carbon. From this, flexible carbon foils are prepared by compression and pressing.

Description

The invention relates to a process for the production of expandable carbon, in particular for the production of flexible carbon.

Conventional processes for preparing expandable carbon use the leaching of carbon particles, most often graphite, with an oxidizing mixture consisting of various combinations of acids, for example sulfuric acid, nitric acid, hydrochloric acid, chloric acid, chromic acid and the like. After this leaching, the carbon particles are washed with water to the desired pH, and thus the so-called expandable carbon is prepared. This product can be further heat treated to expanded carbon. It can be used to make final products from flexible carbon by pressure forming. In the prior art processes, undesirable impurities of sulfur and chlorine compounds from the leaching agents used remain in both expandable and flexible carbon. Expandable and consequently flexible carbon also exhibits undesirable corrosive effects in industrial use.

These disadvantages are eliminated by a process for the production of expandable carbon using leaching with an oxidizing mixture according to the invention, the essence of which consists in leaching carbon particles, preferably natural flake graphite, with a mixture of nitric acid and boric acid or its salt together with a manganese acid salt. after which these carbon particles are washed with water.

Natural flake graphite with a size of more than 0.1 mm and high purity, as well as artificially prepared carbons, for example pyrolytic carbon, can preferably be used as starting material for this production process.

The concentration of nitric acid in said production process may range from 40 to 95 weight percent, preferably 65 to 75 weight percent. The ratio of the weight of nitric acid to the weight of carbon is not critical, but it is necessary to form a mixture of a thin slurry consistency which can be stirred with sufficient intensity. This is achieved at a weight ratio of nitric acid to carbon of 3 to 10: 1. The amount of the manganese acid salt, preferably its alkali salt, may be 3 to 25 weight percent, preferably 10 to 15 weight percent of the carbon used. The amount of boric acid or its salt, preferably its alkali salt, may be 3 to 30 weight percent, preferably 10 to 15 weight percent of the carbon used. The temperature used in the above leaching with the oxidizing mixture can range from 15 ° C to the boiling point of the oxidizing mixture used. The time for which the oxidizing mixture is applied to the carbon particles can range from 10 minutes to 6 hours, preferably from 1 to 4 hours.

After leaching the carbon particles with the oxidizing mixture, they are washed with water to remove residual oxidizing mixture. The washing is carried out until the pH of the material to be washed reaches at least 2, preferably 5. This produces expandable carbon which, due to its non-corrosive properties, is suitable for further use in industry.

In the further production of expanded carbon, the washed expandable carbon particles are dried and subjected to rapid heating to a temperature in the range of 400 ° C to 1500 ° C, preferably 800 ° C to 1200 ° C. The heating time depends on the temperature used and ranges from 3 seconds to 10 hours.

This procedure gives a gray-black feathery mass - expanded carbon. Residual contents of manganese and boron compounds are present in the expanded carbon thus prepared. This fact has a very favorable effect in terms of further processing of the expanded carbon into flexible carbon, since the resulting glassy structures of boron and manganese oxides are firmly fixed in the mass of the resulting carbon structure and give flexible carbon products high resistance to oxidation.

The expanded carbon is further processed by compression and molding into the final product - a flexible carbon film - at a pressure of 5 to 20 MPa. Flexible carbon films with a specific gravity of about 1 g ^/ cm 3 can be used, for example, as seals, electrodes and the like.

Example 1

To 100 mL of nitric acid (65 weight percent) was added 15 g of natural flake graphite with stirring. Then 2 g of boric acid and then 2 g of potassium permanganate were added portionwise. The resulting mixture was stirred at 60 ° C for 4 hours.

-2OS 268 609 Bl

The resulting expandable carbon was washed with water until pH = 5. After drying, it was subjected to thermal expansion for 10 seconds at 1200 ° C. The expanded carbon thus obtained was successively pressed on a stationary press at a pressure of 10 MPa on a flexible carbon film.

Example 2

To 100 mL of nitric acid (65 weight percent) was added 15 g of natural flake graphite with stirring. Then 3 g of crystalline sodium tetraborate and 2 g of potassium permanganate were added portionwise. The resulting mixture was stirred at 65 ° C for 4 hours. The resulting expandable carbon was washed with water to pH = 5. After drying, it was subjected to thermal expansion for 10 seconds at 1200 ° C. The expanded carbon thus obtained was successively pressed on a stationary press at a pressure of 10 mPa on a flexible carbon film. ·

Claims (1)

OBJECT OF THE INVENTION Process for the production of expandable carbon using leaching with an oxidizing mixture, characterized in that carbon particles, preferably natural flake graphite, are leached with a mixture of nitric acid and boric acid or its salt together with a manganese acid salt, after which these carbon particles are washed with water.