Synthesis of graphene oxide coated metal powders with improved flowability and reduced reflectance

Abstract

In this study, a method has been developed to coat metal powder particles (Fe, 316L stainless steel and Cu) with graphene oxide (GO). The method is based on using a pH window where opposite zeta potentials cause the GO sheets to be attracted to the passive oxide layer of the metal powder surface and a rotary evaporator mixing to achieve good dispersion and control the concentration of GO. The pH-dependent interactions of GO and Cu and Fe metal powders in solution have been investigated by mixing the metal powder with GO dispersions between pH 4.2 and 11.3, and it could be observed that GO attached to the metal powder surfaces up to pH ~8 for both Cu and Fe. At lower pH the zeta potential of GO becomes less negative and oxidation of the metal becomes more prominent. Based on these observations, a pH window just below the IEP of the surface metal oxides was used to adhere GO on metal powders in a rotary evaporator with controlled GO concentrations and good distribution of the GO sheets which was verified with SEM and Raman spectroscopy mapping. X-ray diffraction and Raman spectroscopy has been used to evaluate the GO and the metal oxides. Some relevant powder properties were investigated before and after coating of GO. The reflectance of Cu powders in the near-infrared 1070 nm wavelength range was reduced by up to 66 %, depending on the amount of GO coating. Flowability measurements showed that the flowability of the coated 316L powder could be improved significantly while the flowability of pure Fe powder was relatively unaffected by the coating. The results show that GO coated metal powder can be useful in additive manufacturing processes using a laser powder fusion technique where low reflectance and high flowability are important.