Microwave mixed acid digestion method using HNO3-H2SO4 and HNO3 – HCl for determination of graphite impurities

The quality of graphite is determined by its physical and chemical properties. Characterization of graphite is carried out in a destructive and non-destructive examination consisting of crystallinity, morphology, surface area, porosity, density, purity and impurities. In elemental analysis, the non-destructive examination is a high-demand technique because of its safety issues, cost-effectiveness, short examination time and simplicity. However, the non-destructive examination has disadvantages such as the matrix effect, the higher limit of detection and non-conformity elements depending on the method. Therefore, the destructive examination is still performed and developed to obtain the method that results in high test accuracy and low detection limit. The method and solvent chosen are critical in the destructive examination, mainly for digestion. This study used a microwave-mixed acid digestion method using mixed HNO3 − H2SO4 and HNO3 − HCl to determine graphite impurities. Atomic Absorption Spectrometer performed the elemental analysis of the digestion solution. Evaluation of analysis was compared with non-destructive characterization methods, namely X-Ray Fluorescence (XRF) Spectroscopy and Neutron Activation Analysis (NAA). The morphology and crystallinity of graphite (before and after digestion) were characterized using Scanning Electron Microscopy-Energy Dispersive X-Ray Spectroscopy (SEM-EDS) and X-Ray Diffractometer (XRD). The characterization results showed that the microwave-mixed acid digestion method using HNO3 – HCl could extract more graphite impurities into the solvent, although the microwave-mixed acid digestion method using HNO3 − H2SO4 decreased the crystallinity of graphite but lowered the ability to dissolve impurities into the solvent.