Common preparation methods
1. The initial raw material used in the preparation of chemical intercalation method is high-carbon flake graphite
, and other chemical reagents such as concentrated sulfuric acid (above 98 ), hydrogen peroxide (above 28), potassium permanganate, etc. all use industrial grade reagents.
The general steps of preparation are: at appropriate temperatures
, add different proportions of hydrogen peroxide solution, natural flake graphite and concentrated sulfuric acid in different adding procedures while stirring continuously. React for a certain period of time, then wash with water until neutral, centrifuge, dehydrate and dry under vacuum at 60
℃.
2. Electrochemical method: Treat graphite powder in a strong acid electrolyte to make expandable graphite, hydrolyze, clean and dry. As strong acids, sulfuric acid or nitric acid is mainly used. The expandable graphite produced by this method has low sulfur content.
3. Ultrasonic oxidation method. In the process of preparing expandable graphite, the anodized electrolyte is subjected to ultrasonic vibration. The time of ultrasonic vibration is the same as the time of anodization.
Because the vibration of the electrolyte caused by ultrasonic waves is beneficial to the polarization of the cathode and anode, it speeds up the anodization and shortens the oxidation time.
4. The vapor phase diffusion method places the graphite and the intercalated material at both ends of a vacuum sealed tube, heats the end of the intercalated material, and uses the temperature difference between the two ends to form the necessary reaction pressure difference, so that the intercalated material It enters into the layers of flake graphite in the form of small molecules to produce expandable graphite. The number of layers of expandable graphite produced by this method can be controlled, but its production cost is high.
5. Molten salt method: Several inserts are mixed and heated with graphite to form expandable graphite.
Extended information:
Graphite crystal has a hexagonal network planar layered structure composed of carbon elements. The carbon atoms on the layer plane are bonded by strong *** valence bonds, while the layers are bonded by van der Waals forces. The bonding is very weak, and the distance between layers is large.
Therefore, under appropriate conditions, various chemical substances such as acids, alkali metals, and salts can be inserted into the graphite layers and combine with carbon atoms to form a new chemical phase - graphite interlayer compounds ( Graphite
Intercalation on Compounds, referred to as
GIC).
When heated to an appropriate temperature, this interlayer compound can decompose rapidly in an instant, producing a large amount of gas, which causes the graphite to expand along the axial direction into a new worm-like substance, namely expanded graphite. This unexpanded graphite interlayer compound is expandable graphite.
Reference: Baidu Encyclopedia----Expandable Graphite