Formation of graphite crystals at 1000-1200 degrees C from mixtures of vinyl polymers with metal oxides

The formation of graphite crystals from mixtures of different carbon precur sors. poly(vinyl chloride) (PVC)I poly(vinyl alcohol) (PVA) and poly(vinyl pyrrolidone) (PVP), with iron oxides Fe3O4 and Fe2O3, nickel oxide NiO, cob alt oxide Co3O4 and iron powder was studied at a temperature between 800 an d 1200 degreesC. The formation of flaky graphite crystals was confirmed fro m X-ray diffraction and transmission electron microscopy, and the reaction mechanism was studied by differential thermal analysis. From the powder mix tures of vinyl polymers, PVC, PVA and PVP, with Fe2O3, Fe3O4, Fe and Co3O4, graphite was obtained by the heat treatment at the temperature above 1000 degreesC for 1 h, the higher temperature and the longer residence time givi ng the higher crystallinity of graphite. However, the mixture of NiO with P VA behaved a little different; well-developed turbostratic structure at 100 0 degreesC for 1 h and well-crystallized graphite at 1100 degreesC for 24 h . The formation of graphite crystals was supposed to occur through the foll owing steps: thermal decomposition and carbonization of vinyl polymers belo w 500 degreesC, 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 t o metal oxides suitable for the formation of graphite crystals was found to be related to the oxidation state of metals. (C) 2001 Elsevier Science Ltd . All rights reserved.