Oxidative heat treatment of 316L stainless steel for effective catalytic growth of carbon nanotubes

Substrates consisting of stainless steel (SS) type 316L have been typically considered as non-responsive to catalytic formation of multi-walled carbon nanotubes (MW-CNTs) because of the protective chromium oxide layers on their surfaces. In current practices lengthy multi-step pretreatments are needed to break down these protective layers. This study oxidized 3161 SS wire mesh in air, at 800 degrees C, for time periods ranging from 1 to 20 min prior to its use as a substrate catalyst for CNT synthesis from pyrolyzate gases of polyethylene, i.e., a mixture of hydrocarbons and hydrogen. The shortest pretreatment of the substrate (1 min) produced the maximum yield of CNTs (0.0145 g/g of catalyst) in these experiments, whereas longer pretreatments resulted in progressively lower yields. The 10 min pretreatment produced MWCNT forests vertically growing in planes perpendicular to the substrate surface (the periphery of the cylindrical wires of the mesh), 20 mu m long and 21 nm in diameter on the average. Shorter (1-9 min) or longer (11-20 min) substrate heat treatments did not produce aligned CNTs at this temperature. Oxidative heat treatments of the substrate lengthier than 20 min did not produced any nanotubes. The results demonstrated an expedient and cost-effective method to activate the 316L SS substrate, and resulted in controllable CNT growth. (C) 2014 Elsevier B.V. All rights reserved.