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The growth of multi-walled carbon nanotubes (MWNTs) with a large diameter of 200 nm on nickel (Ni) coated silicon wafer at different growth times up to 30 min was investigated. CNT cobwebs were found after a short growth time (7 min) and developed into ordered forests at higher growth times (t t 10 min). One of the important formation features of the CNTs in this study was the coaxial structure of the nanotubes, ie. a MWNT within a MWNT. Its formation was due to secondary nanostructures of Ni particles. Unexpected growth of carbon micro-balloons occurred when high flow rates of carbon feedstock was used or when growth time exceeded 15 min.