Tailoring the surface of NiTi alloy using PIRAC nitriding followed by anodization and phosphonate monolayer deposition

Gilad Zorn, Racheli Adadi, Reuven Brener, Vladimir A. Yakovlev, Irena Gotman, Elazar Y. Gutmanas, Chaim N. Sukenik

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Nickel titanium (NiTi, nitinol) shape memory alloy was nitrided using a powder immersion reaction assisted coating (PIRAC) method to modify its surface properties. PIRAC nitriding is based on annealing the samples in an atmosphere of highly reactive nitrogen supplied by decomposition of unstable nitride powders or, alternatively, by selective diffusion of atmospheric nitrogen to the sample surface. Since it is not line of sight limited, PIRAC nitriding of nitinol alloys allows uniform treatment of complex shapes (e.g., surgical implants). It results in the formation of a Ni-free TiN film and considerably improves the corrosion behavior of the underlying NiTi alloy. The usefulness of PIRAC nitrided nitinol could be significantly enhanced by attaching to its surface a phosphonate anchored self-assembled monolayer (SAM). Phosphonate-anchored SAMs on PIRAC nitrided nitinol and on thin films of TiN sputtered onto a silicon wafer have been characterized by FTIR, contact angle measurements, and XPS analysis. The SAM was only weakly attached to the nitride surface. However, when anodization was used to add an oxide layer on top of the TiN, a robust, uniform phosphonate-anchored SAM could be formed. Thus, anodization of the nitride surface allows it to continue functioning as a corrosion barrier while still being able to take advantage of the range of surface chemistries offered by SAM films. The composition and morphology of the nitrided TiNi surface, before and after anodization, are reported, along with an analysis of phosphonate-anchored SAM formation on these surfaces.

Original languageEnglish
Pages (from-to)5368-5374
Number of pages7
JournalChemistry of Materials
Issue number16
StatePublished - 26 Aug 2008


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