The chemical properties of graphite and carbon materials

Carbon materials are chemically inert in non-oxidizing media. Under normal temperature and pressure, no chemical changes will occur. Except for long-term immersion in nitric acid, hydrofluoric acid or in fluorine, bromine and other strong oxidizing atmospheres, interlayer compounds will slowly form, and it is not affected by other acids and alkalis. Corrosion with salt does not interact with any organic compounds. Graphite has no significant oxidation phenomenon within 450℃ in the air. It starts to react with water vapor above 700℃, and reacts with CO and CO2 above 900℃. The temperature at which graphite can produce carbides with certain metals and oxide powders Most of them are above 1000°C.

The chemical reactions of carbon materials can be divided into the following three types: 

(1) gasification reaction and high-temperature oxidation reaction; 

(2) solid-solid phase reaction with metals and ceramics; 

(3) interlayer compound formation reaction.

Factors affecting the gasification reaction of carbon materials

(1) Graphitization degree: As the graphitization degree of carbon material increases, its activity to gas decreases. The higher the final heat treatment temperature of the carbon material, the higher the temperature at which it starts to oxidize, so the initial oxidation temperature of graphite products is higher than that of carbon products.

(2) Structural state: The carbon material with loose and porous surface is easy to react with gas. For example, pyrolytic graphite with dense surface heat-treated at 3200°C starts to oxidize in the air at a temperature of 850°C, while charcoal with a porous surface starts to burn at 360°C.

(3) Catalytic effect of impurities: The impurities contained in carbon materials have a great influence on its gasification reaction, and its catalytic effect is large or small. For example, iron, cobalt, nickel, copper, manganese, etc. are the oxidation of carbon materials. Impurities such as boron, titanium, and tungsten can inhibit oxidation. Alkali metals and transition metals show great catalytic effects on any gasification reaction of carbon materials.