First, the content introduction
At the end of 1980s, China just introduced the flexible graphite production line. Expandable graphite, as the raw material of flexible graphite, not only meets the demand of domestic flexible graphite production, but also obtains a great market in the world. At that time, the technology of expandable graphite was chemical method and the technology was unstable. The residual sulfur content of many products after expansion is as high as 2000× 10-6.
Expandable graphite is a kind of residual graphite interlayer compound. In industry, sulfuric acid is usually used as intercalation agent to generate H2SO4-GIC, and then most of H2SO4 is removed by washing and drying to make expandable graphite. Expandable graphite is heated rapidly at high temperature, and graphite particles expand to form worm-like expanded graphite, which is rolled into strip or plate-like flexible graphite. Flexible graphite is a new generation of sealing material with the best performance at present, and it is the first choice for nuclear power plants. Widely used in power generation, petrochemical, automotive, chemical, aerospace and other industries to manufacture seals. The important index of flexible graphite is the residual sulfur content, which mainly depends on the residual sulfur content of expandable graphite. The more high-tech industries such as nuclear energy and fine chemicals, the lower the residual sulfur content is required.
When preparing H2SO4-GIC, sulfuric acid cannot be directly inserted into graphite. Common chemical methods must use strong oxidants such as potassium permanganate, nitric acid and hydrogen peroxide to insert H2SO4 between graphite layers. Once the chemical reaction begins, it will proceed spontaneously and the process is difficult to control. Therefore, once the ingredients deviate or the environmental conditions such as temperature, pressure and humidity change, the product quality will be problematic. Tsinghua University, a technical research institute, adopts electrochemical method to make graphite and sulfuric acid directly intercalate under anodic oxidation without using any oxidant. Power is supplied for the reaction, and the reaction is terminated by power failure, and the process is completely controllable. At the same time, the reaction degree is controlled by time and voltage (current), which ensures the product quality. The residual sulfur content of common expandable graphite is less than 800× 10-6, so it is difficult to prepare low-sulfur and sulfur-free expandable graphite for nuclear use by chemical methods. Because no additives are added, the recovery and reuse of residual acid in the process are easy, which reduces the cost and environmental pollution. From the comprehensive cost, the anodic oxidation method is lower than the traditional chemical method.
Second, popularization and application
This technology has been industrialized in Hebei, Inner Mongolia, Shandong and other enterprises, and most of the products are exported.
Three. Identification, awards and patents
This technology was developed and industrialized in 1989 ~ 1992. Three invention patents (patent number ZL91111825) have been obtained. x，ZL 9 1 1 1 1826.8，ZL92 165438+)。 This achievement won the third prize of 1993 national invention.