Investigation of surface and thermogravimetric characteristics of carbon-coated iron nanopowder

Demand for high-density press and sinter components is increasing day by day. Of the different ways to improve the sinter density, the addition of nanopowder to the conventional micrometer-sized metal powder is an effective solution. The present investigation is aimed at studying the surface chemistry of iron nanopowder coated with graphitic carbon, which is intended to be mixed with the conventional iron powder. For this purpose, iron nanopowder in the size range of 30 nm to submicron (less than 1 micron) was investigated using thermogravimetry at different temperatures: 400 degrees C, 600 degrees C, 800 degrees C, 1000 degrees C, and 1350 degrees C. The X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and high-resolution scanning electron microscopy (HR-SEM) were used for characterizing the powder as well as samples sintered at different temperatures. The presence of iron, oxygen, carbon, chromium, and zinc were observed on the surface of the nanopowder. Iron was present in oxide state, although a small metallic iron peak at 707 eV was also observed in the XPS spectra obtained from the surface indicating the oxide scale to be maximum of about 5 nm in thickness. For the sample treated at 600 degrees C, presence of manganese was observed on the surface. Thermogravimetry results showed a two-step mass loss with a total mass loss of 4 wt.% when heated to 1350 degrees C where the first step corresponds to the surface oxide reduction