PREPARATION AND CHARACTERIZATION OF CARBON-COATED W AND Si BASED COMPOSITE POWDERS BY POLYMER PYROLYSIS METHOD

In this study, carbon coated W and Si based composite powders were produced by polymer pyrolysis method. For this purpose Si and W powders were selected as starting materials and two different polymers namely, poly (vinyl alcohol) and poly (vinyl chloride) being used as carbon source. Following the preparation of powder and polymer mixtures in SPEX dual mixer, all mixtures were heated up to 700 degrees C in argon atmosphere. After pyrolysis, morphologies and crystal structures of the carbon-coated samples were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), Roman Spectrometer and specific surface area measurement (BET). From BET, the increase in specific surface area was observed after coating, irrespective of carbon source. Under certain circumstances formation of WC and SiC phases were observed during pyrolsis. Decomposition products evolved during thermal degradation of poly (vinyl alcohol) and poly (vinyl chloride) plays an important role for the formation of new phases and the structure of the composite powder. During pyrolysis initial powders lost their integrity and microstructural refinement leading particle formation around 100 nm were observed in Si powders.