Large Scale Carbon Coating on Cohesive Particles by a Chemical Vapour Deposition Process in a Fluidized Bed Reactor

摘要

The coating of particles by very thin functional carbonaceous layers in the range of a few nanometers is a very helpful tool when it comes to the development of conductive or antistatic and transparent paints/coatings. In order to meet the requirements of the commercial production on a large scale of homogenously carbon coated particles, an efficient coating process and a suitable reactor design have to be developed. Thin carbon layers of a thickness of about 2 to 5 nm are obtained on the surface of the particles by conducting a Chemical Vapour Deposition (CVD) process at elevated temperatures starting from 500 °C. Precursors of different carbon content, e. g. acetone and 3-methyl-2-butin-2-ol were used in the CVD process and their influence on the final carbon coating concerning conductivity was investigated. Furthermore the deposition time of the carbon precursors was varied in order to achieve different quantities of carbon deposited on the particle surface. The resulting carbon content obtained by the CVD process was determined by thermo gravimetric analysis (TGA). In order to study the influence of the carbon coating on the electrical conductivity of the particles the specific resistance of the bulk material consisting of the carbon coated particles was measured as well. As the carbon content on the particle surface increases to 1,5 weight percent, the specific resistance decreases dramatically from about 50 Mficm for the uncoated material to nearly 60 Qcm for the carbon coated material. RAMAN spectroscopy measurements of the carbon layers which have been deposited on top of the particle surface reveal a nanocrystalline graphite (nc) structure. Transmission electron microscopy (TEM) images show a homogenous coating of every single particle; the layer thickness ranges from 3 to 5 nm.