Preparation and Microstructure of Graphite-encapsulated Iron Sphere

It is known that dissolved carbon in the molten Iron (Fe) crystalizes out as graphite on cooling. Graphite-encapusulated Fe sphere was prepared by using this process.Mixture of carbon black and 45 atm % Fe powder was heat-treated at 2500°C and then the magnetic product was separated from the residure. The product was α-Fe sphere wrapped in graphite. The sphere was 0.25-100 μm in diameter and contained 92 wt % of Fe. The thermogravimetric analysis of the sphere in oxidative atmosphere showed thata weight loss sets in at 730°C, as well as a natural graphite. Magnetization curve did not exhibit the hysteresis loop and saturation magnetization was 189emu/g corresponding to Fe content. From those results, it was concluded that the graphite-encapsulated Fe sphere is ferromagnetic and stable in oxidative atmosphere.