Selection of Carbon Seal Material
The original inventor used concentrated sulfuric acid as oxidant and intercalating agent. However, after being applied to the seal of a metal component, a small amount of sulfur remaining in the flexible graphite was found to corrode the contact metal after long term use. In view of this point, some domestic scholars have tried to improve it, such as Song Kemin who choosed acetic acid and organic acid instead of sulfuric acid. acid, slow in nitric acid, and lower the temperature to room temperature, made from a mixture of nitric acid and acetic acid. By using the mixture of nitric acid and acetic acid as the inserting agent, the sulfur free expanded graphite was prepared with potassium permanganate as oxidant, and acetic acid was slowly added to nitric acid. The temperature is reduced to room temperature, and the mixture of nitric acid and acetic acid is made. Then the natural flake graphite and potassium permanganate are added to this mixture. Under constant stirring, the temperature is 30 C. After reaction 40min, the water is washed to neutral and dried at 50~60 C, and the expanded graphite is made after high temperature expansion. This method achieves no vulcanization under the condition that the product can reach a certain volume of expansion, so as to achieve a relatively stable nature of the sealing material.