Application of nano-structured copper-polymer catalyst for activation of gas nitriding of steels

In the paper forming of nanostructured catalytic systems of nitriding and their precursors on the basis of copper nanoparticles is discussed. Recent investigation has discovered the catalytic effect of  copper oxide film applied at the surface of low-carbon and  medium-carbon steels before nitriding. It accelerates the growth of the diffusion layer and mainly of the compound zone. It is known that the effect of catalytic systems is higher when nano-structured catalysts are used. It is the result of high reactivity of nano-particles having huge overall specific surface.  

An attempt was undertaken to increase the dispersion of particles of CuO-catalyst by synthesis of its precursor (metallic copper film)  with usage of polymers such as poly-N-vinilpirrolidone (PVP). Specimens of low-carbon steel (DC04 grade by  EN 10139) were treated in CuSO₄ water solution with addition of PVP. After 1 hour of treatment a coating of violet-brown color typical for copper sol was observed at the steel surface. Investigation in AFM discovered nano-dimensional particles of composite structure formed as a result of reduction process of copper at the iron surface from copper sulfate. It was shown by high-resolution TEM that composite consists of copper nano-particles (about 20 nm) surrounded by polymeric shell. According to the theory of  pseudo-matrix synthesis the macromolecules of PVP act as the protectors by screening of metal surface and by preventing of growth of copper particles.

Catalytic activity of thermo-oxidized product (CuO) formed from such nanocomposite is higher than of oxide received from copper not modified by PVP. Nitriding of DC04 steel samples with nano-structured catalytic oxide film at 590°С during 120 minutes gives the compound zone in 1,5 times thicker comparing to the nitride layer formed under non-modified CuO-film.  The regulating parameters of the catalytic nitriding process are: reacting time of deposition of nano-structured precursor, and molecular weight of used polymer influencing the morphology of nanocomposite.