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The term synthetic or natural graphite describes the origin of the graphite products. However, for the final application, the graphite material and surface properties are more important than the origin to distinguish between different graphite materials. The main categories of parameter that describe the graphite properties are purity, crystallinity, texture, particle size, and shape as well as the surface properties. As in all particle assemblies, these properties are distributive, and usually medium values are given to quantify the properties.
The purity of graphite can vary a lot depending on the origin. Natural graphite is generally of lower purity compared to synthetic graphite. The purity of graphite is generally assessed by measuring the ash residue after combustion (ASTM C 561-91). The ash composition depends on the deposit and usually contains large quantities of silica (SiO2), aluminosilicates, and other metal oxides commonly found in the Earth’s crust (Fe2O3, Al2O3, CaO, etc.). High-purity graphite is generally stable in corrosive environments and has good oxidation resistance, as especially metal impurities are known to catalyze graphite oxidation. For some polymer types, high-purity graphite is required (>99.9% C) as impurities may cause degradation of the polymer matrix.
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