Formation of graphite crystals at 1000–1200°C from mixtures of vinyl polymers with metal oxides

Abstract

The formation of graphite crystals from mixtures of different carbon precursors, poly(vinyl chloride) (PVC), poly(vinyl alcohol) (PVA) and poly(vinyl pyrrolidone) (PVP), with iron oxides Fe 3O 4 and Fe 2O 3, nickel oxide NiO, cobalt oxide Co 3O 4 and iron powder was studied at a temperature between 800 and 1200°C. The formation of flaky graphite crystals was confirmed from X-ray diffraction and transmission electron microscopy, and the reaction mechanism was studied by differential thermal analysis. From the powder mixtures of vinyl polymers, PVC, PVA and PVP, with Fe 2O 3, Fe 3O 4, Fe and Co 3O 4, graphite was obtained by the heat treatment at the temperature above 1000°C for 1 h, the higher temperature and the longer residence time giving the higher crystallinity of graphite. However, the mixture of NiO with PVA behaved a little different; well-developed turbostratic structure at 1000°C for 1 h and well-crystallized graphite at 1100°C for 24 h. The formation of graphite crystals was supposed to occur through the following steps; thermal decomposition and carbonization of vinyl polymers below 500°C, reduction of metal oxides to metal by carbonaceous products and then catalytic action of metals to precipitate graphite. Since carbons were consumed for the reduction of metal oxides, the mixing ratio of PVA to metal oxides suitable for the formation of graphite crystals was found to be related to the oxidation state of metals.