The graphite gasket is made of the flexible graphite,also called expandable graphite,it’s one of the new type carbon materials since 1960s,and it first come from the patent of Union Carbine Co USA. After that,with the development of petroleum chemical industry and nuclear power industry,the need for sealing material is also more strict,and the flexible graphite sealing material replace the asbestos material.
The flexible graphite has the similar properties with the natural graphite on the structure.and it has many good properties such as high thermal resistance,corrosion resistance,resilience, radiation resistance,high purity etc.
The purity of the flexible graphite has a big influence to the sealing property,the Sulpher in the graphite will separate out and make the surface corrosion of the metal,and weak the sealing effect,and to the nuclear industry,the Sulpher content is more important to control,or it will make the pollution to the reaction medium and lead to the system paralysis,so the low S and even no S products are more and more popular,many scholars around the world do this research. Now the main technique to process flexible graphite is : chemical oxidation process, electrochemical method, microwave method, explosive method and gas diffusion method etc.The way to get low S: the key point is to reduce the dosage of sulfuric acid in the intercalation agent and use the organic acid as the intercalator. By this way,it can reduce the content of the sulpher.
The way to get no S: it’s use the nitric acid, sulfuric acid, perchlorate or mixed acid as the intercalation. By this way,it can get the no S flexible graphite. And we should also pay attention on the raw graphite powder, it should be no S content raw material, so we could get the 100% no S flexible graphite. Then we could get the low S or no S flexible graphite gasket.