▎ 摘　　要

NOVELTY - Multi-walled carbon nanotubes comprise tubes of a graphene sheet where carbon atoms are arranged in a hexagonal honeycomb form, coaxially, where a diameter of an outermost wall is 3-15 nm, and a length of 1.0 mm or more. USE - Multi-walled carbon nanotubes used for composite material. ADVANTAGE - The multi-walled carbon nanotubes provides composite material having excellent purity, strength, conductivity, and thermal conductivity. DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for preparation of multi-walled carbon nanotubes, which involves forming a support film for supporting the metal catalyst, on a surface of a smooth plate, supporting a metal catalyst formed from manganese, iron, cobalt, nickel, molybdenum, palladium, indium, tin, or an alloy containing these metals, on the support film, disposing the substrate containing a catalyst film formed of the metal catalyst formed on a surface of the support film, in the reaction vessel, bringing an inside of the reaction vessel under an atmosphere of inert gas or oxidizing gas, heating the inside of the reaction vessel to a synthesis temperature of the multi-walled carbon nanotubes, granulating the catalyst film by exposing the catalyst film to an atmosphere of gas having reducing activity, and thermally decomposing the hydrocarbon to grow multi-walled carbon nanotubes on the surface of the catalyst film of the substrate, as introducing raw material gas containing at least hydrogen and hydrocarbon from one end of the substrate to another end to contact the raw material gas to a surface of the catalyst film while preheating the raw material gas to a temperature capable of promoting thermal decomposition of the hydrocarbon on the catalyst film and lower than the synthesis temperature, and exhausting the inside of the reaction vessel unidirectionally by a non-circulation method to generate a current in a direction from the one end of the substrate to the other end in the reaction vessel.