Preparation from Natural Graphite to Expandable, Expanded & Flexible Graphite

Today, in the rapid developing of science field, graphite, as an important inorganic non-metallic material, is widely used in the fields of metallurgy, chemical, electronic semiconductor, new energy, etc. In this article, we will introduce something about expandable graphite, expanded graphite and flexible graphite as well as their preparation methods, and hope our customers can have a better understanding of these graphite categories.

The detailed step of how to make flexible graphite from natural graphite

Preparation of expandable graphite-expanded graphite-flexible graphite

Preparation of Expandable Graphite

Natural flake graphite is a mineral that is formed through long-term geological metamorphism of carbonaceous rocks. It is a kind of natural crystalline graphite with a fish scale like appearance. It belongs to hexagonal crystal system and presents a layered structure. While expandable graphite is an unexpanded graphite interlayer compound that is obtained by treating natural crystalline flake graphite with an acidic oxidizing agent. It is also known as graphite acid, acidized graphite or graphite oxide.

The preparation of expandable graphite mainly includes chemical method, electrochemical method, microwave method, explosion method and gas phase volatilization method. These physical or chemical methods allow non-carbon reactants to be inserted into the interlayers of graphite, while maintaining the layered structure of graphite and bonding with the hexagonal network plane of carbon. Among them, chemical oxidation and electrochemical methods are the most commonly used methods and both methods have been industrialized.

Chemical Oxidation Method

Since graphite is a non-polar material, it is difficult to intercalate layers using organic or inorganic acids with low polarity alone. Therefore, strong oxidants are needed to open the graphite layers. Among them, the most commonly used oxidants are nitric acid and potassium permanganate.

Under the action of strong oxidants, oxygen-containing functional groups are formed on the surface and edges of graphite layers. These functional groups can react with intercalator to allow them to enter into the interlayers of graphite. The reaction products are then filtered, washed and dried to obtain expandable graphite.

Electrochemical Method

Put the graphite in the electrolyte and then apply an external voltage to allow electrons to transfer between the graphite surface and the electrolyte, thus causing the redox reaction. The reaction products are then filtered, washed and dried to obtain expandable graphite.

A pile of graphite powder is placed on the desk.
Preparation of Expanded Graphite

When expandable graphite is heated rapidly at high temperatures, the expansion force generated by the thermal vaporization of the interlayer insert can overcome the intermolecular forces that bind the graphite layers together, causing the graphite flakes to expand along the c-axis direction by tens to hundreds of times, and completely expand at 1000 °C. The expanded graphite has a worm-like shape and exhibits a large number of unique network-like microporous structures, showing a fibrous, worm-like shape. It is usually called expanded graphite (EG) or worm-like graphite.

Evenly placed expanded graphite
Preparation of Flexible Graphite

Expanded graphite is pressed or calendered, and the worms mesh together, forming graphite rolls or sheets. These rolls or sheets are flexible graphite, also known as graphite paper/foil. This material adds its unique flexibility, resilience, and sealing properties and can be made into flexible graphite products and graphite sealing products.

2 methods for flexible graphite preparation

Pressed forming (left) & calendered forming (right)

Flexible graphite papers are displayed in a fan-shape.