Expandable graphite is manufactured by general natural graphite or flake graphite with other chemicals such as acids, alkalis, and salts. Graphite Intercalation Compounds (GIC) inserted inside by acid treatment vaporize quickly at a specific temperature, and the interlayer distance of graphite is instantaneously widened by the pressure of the released gas.
Due to the expansion characteristics at a specific temperature, expandable graphite is mainly used in various industries related to fire fighting and flame-retardant, and is mainly used as a material for making internal insertion gaskets, insulation pads, and flame-retardant composites. In addition, it has excellent material properties such as high adsorption properties, corrosion resistance, and strong resistance to high and low temperatures, implying the possibility of being used in more diverse industries.
The expansion performance of expandable graphite varies depending on the type and mixing ratio of GIC used in the manufacturing process and differs depending on the temperature of the heat exposed during the expansion process. In this study, SEM photographs of expanded graphite were performed at 200°C intervals from 300°C to 900°C to check the heat treatment temperature, which shows the maximum expansion temperature of expandable graphite. As the temperature increases, the interlayer spacing of expanded graphite becomes growing and the destruction points caused by weakened structure gradually increase. In addition, through the change in pore volume and pore diameter according to the degree of expansion of expanded graphite by temperature was measured by BET analysis, and the total pore volume increased by about 200 times from 3.9061×10-5(cm3g-1) to 7.9928×10-3(cm3g-1) at 900°C, and the average pore diameter increased by 0.357 times.
Thereafter, the amount of sulfuric acid for expanding a predetermined amount of natural graphite (10g) based on sulfuric acid-nitric acid (H2SO4-HNO3) was increased at 100g intervals from 100g to 500g to prepare a mixed solution, and the expansion rate of the expandable graphite was measured to determine the amount of sulfuric acid most suitable for preparing the reference amount (10g). Based on the determined amount, three additional mixtures of sulfuric acid-ammonium sulfate (H2SO4-(NH4)2S2O8), hydrochloric acid-Nitric acid (HCl-HNO3), and potassium perchloric acid-permanganate (HClO4-KMnO4) were prepared, and expandable graphite was prepared through different GICs. As a result, it was confirmed that graphite prepared with hydrochloric acid-nitric acid did not expand at all, and the most excellent expansion performance was a sample of sulfuric acid-ammonium sulfate (H2SO4-(NH4)2S2O8), and the maximum expansion rate was measured to be about 5400% of the original volume. Here, as a result of calculating and measuring the interplanar distance through XRD analysis, it was confirmed that the interplanar distance also tends to increase as the acid weight increases. Based on the data obtained in this way, the expansion magnification was measured by increasing the Particle size from 80 mesh to 50 mesh and 30 mesh, and the expansion magnification generally increased as the Particle size increased.
Finally, TGA analysis confirmed the thermal characteristics and expansion initiation temperature of expandable graphite manufactured by GIC type, and check the weight loss occurred at different times depending on the acid mixture type used respectively, which confirm that this check can adjust the expansion initiation temperature and expansion rate.