Expandable graphite refers to that under appropriate conditions, a variety of chemical substances such as acid, alkali metal and salt can be inserted between graphite layers and combine with carbon atoms to form a new chemical phase graphite intercalation on compounds (GIC). This graphite intercalation compound is expandable graphite. When the interlayer compound is heated to an appropriate temperature, it can decompose rapidly and generate a large amount of gas, which makes the graphite expand in the axial direction into a worm like new material, i.e. expanded graphite.
Expandable graphite can expand rapidly when heated at high temperature. The expansion factor is as high as tens to hundreds or even thousands of times. The apparent volume of expanded graphite is 250-300ml / g or more. The expanded graphite is worm like, with a size of 0.1mm to a few millimeters. It has a large number of unique network like microporous structures inside and is called expanded graphite or graphite worm. In addition to the excellent properties of natural graphite such as cold and heat resistance, corrosion resistance and self lubrication, expanded graphite also has the characteristics of softness, compression resilience, adsorption, ecological environment coordination, biocompatibility and radiation resistance that natural graphite does not have.
Expandable graphite and its expanded graphite can be used in iron and steel, metallurgy, petroleum, chemical machinery, medical, aerospace, atomic energy and other departments, with a wide range of applications.
Methods for preparing expandable graphite include chemical oxidation method, electrochemical method, gas phase diffusion method (two chamber method), mixed liquid phase method, melting method, pressure method, explosion method, catalyst method, photochemical method, etc. among them, chemical oxidation method and electrochemical method are the most widely used preparation methods. Electrochemical method, with the advantages of low environmental pollution, low cost, large processing capacity and recyclable acid solution, has attracted much attention in recent years. Other synthesis methods have their own advantages and disadvantages, and the synthesis objects are not the same, so they are rarely used.
Chemical oxidation method: chemical oxidation method is a traditional method for preparing expandable graphite. This method uniformly mixes natural flake graphite with an appropriate amount of oxidant and intercalation agent, controls a certain temperature, keeps stirring, and obtains expandable graphite through water washing, filtration and drying. There are many kinds of oxidants. Generally, the oxidants used are solid oxidants (such as potassium permanganate, potassium dichromate, chromium trioxide, potassium chlorate, etc.) or some liquid oxidants (such as hydrogen peroxide, nitric acid, etc.). In recent years, it has been found that potassium permanganate is the main oxidant used to prepare expandable graphite. The intercalation agent is mainly acid. In recent years, the researchers mainly focus on sulfuric acid, nitric acid, phosphoric acid, perchloric acid, mixed acid and glacial acetic acid.
Electrochemical method: the electrochemical method is to form a composite anode with graphite and metal materials (stainless steel material, platinum plate, lead plate, titanium plate, etc.) under a constant current, with the aqueous solution of the insert as the electrolyte, and insert metal materials into the electrolyte as the cathode to form a closed circuit; Or the graphite is suspended in the electrolyte, the cathode and anode plates are inserted in the electrolyte at the same time, and the anode oxidation is performed by energizing the two electrodes. In recent years, electrochemical method has gradually become the preferred method for preparing expandable graphite by many enterprises with many advantages.