Surface and Coatings Technology 183 (2004) 216–223 0257-8972/04/$ - see front matter  2003 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2003.08.088 RBS and XRD analyses of carbon-coated stainless steel plates N. Cunningham , J.P. Dodelet , D. Guay , G.G. Ross *, A.R. Hlil , A.S. Hay a a a a, b b INRS-EMT, C.P. 1020, Varennes, Quebec, Canada J3X 1S2 a ´ Department of Chemistry, McGill University, Montreal, PQ, Canada H3A 2K6 b Received 2 April 2003; accepted in revised form 13 August 2003 Abstract This study focused on understanding the strong adhesion between coatings, up to 20 mm thick, made from a pyrolyzed polymer (M2-48) and a stainless steel plate (316L). Using X-ray diffraction, no carbide phase was detected in the coating. However, iron was detected by Rutherford backscattering spectroscopy throughout the entire thickness of the carbon coating and even on their surface. The linear relationship between the logarithm of the Fe concentration and the number of layers sprayed to make the coatings would tend to indicate that diffusion is occurring during the pyrolysis procedure. It is assumed that the presence of Fe in the carbon coating, and therefore the lack of a discrete interface between the carbon coating and the stainless steel substrate, is responsible for the good adhesion properties. The structure of unsupported carbon films and fibres has been identified as turbostratic, typical structure found in carbon blacks and heat-treated phenolic resins.  2003 Elsevier B.V. All rights reserved. Keywords: Stainless steel; 316L; Pyrolysis; Polymer coating; Rutherford backscattering spectroscopy 1. Introduction More than 40 years ago, researchers at General Electric synthesized poly(m-diethynylene benzene). At the time, this polymer was studied in order to produce high modulus, high strength carbon fibres w1–3x. It was proven that upon slow heating to more than 600 8C at (1 8Cymin) w4,5x over 90% of the polymer could be transformed into a black carbonaceous residue contain- ing more than 95% carbon w6x. More interestingly, it was also reported that poly(m-diethynylene benzene) could be cast into uniform films w5,6x that could be pyrolyzed to produce carbon coatings with minimal weight loss and little dimensional changes. Poly(m-diethynylene benzene) is not very soluble even in very aggressive solvents. To reduce the com- plexity in handling this polymer, several copolymers containing poly(m-diethynylene benzene) were there- fore, synthesized w7x. Among them, the M2-48 polymer (Fig. 1) was found to be particularly useful to obtain the first layer of a multi-layer protective carbon coating for 316L stainless steel. This carbon coating was used *Corresponding author. Tel.: q1-450-929-8108; fax: q1-450-929- 8102. E-mail address: ross@inrs-emt.uquebec.ca (G.G. Ross). to protect 316L bipolar plates against corrosion in a proton exchange membrane fuel cell w7x. It was assumed at the time that the role of pyrolyzed M2-48 in the multi-layer approach was to create a first layer that adhered strongly to the stainless steel substrate. However, looking at the coefficient of thermal expan- sion of 19.9 mmy(mK) for stainless steel w8x and of 1–3 mmy(mK) for carbon (artificial graphite w9x), it is difficult to imagine that a pyrolyzed carbon film would stay on top of steel without shattering during heating or cooling cycles. Also to be noted is the fact that a pyrolyzed M2-48 coating adheres well to stainless steel but does not adhere well to glassy carbon, quartz, platinum, copper or niobium. The pyrolyzed M2-48 coating shows adhesion to copper only if the substrate is roughened using 1200-grit (1.5–5 mm) sandpaper. There is an abundant literature on the interaction between carbon and stainless steels at high temperature. For example, it is well known that stainless steels such as 316L are susceptible to carbide precipitation at grain boundaries at temperatures between 427 and 871 8C w10x. Various other high-temperature effects have also been extensively studied. However, this is mainly based on studies conducted for the petroleum industry more precisely in the presence of hydrocarbons or CO w10x.