K. Rokosz i dr. SEM, EDS i XPS analiza nanostrukturirane prevlake koja se stvara na leguri od NiTi biomaterijala plasma elektrolitičkom oksidacijom (PEO) Tehnički vjesnik 24, 1(2017), 193-198 193 ISSN 1330-3651 (Print), ISSN 1848-6339 (Online) DOI:10.17559/TV-20151021112657 SEM, EDS AND XPS ANALYSIS OF NANOSTRUCTURED COATING FORMED ON NiTi BIOMATERIAL ALLOY BY PLASMA ELECTROLYTIC OXIDATION (PEO) Krzysztof Rokosz, Tadeusz Hryniewicz, Steinar Raaen Original scientific paper Plasma Electrolytic Oxidation (PEO) of NiTi alloy was studied in the electrolyte consisting generally of concentrated orthophosphoric acid with an addition of copper II nitrate. The PEO process was used to obtain a nanostructured coating on the Nitinol surface. The surface layer analyses methods, such as scanning electron microscopy (SEM) with the energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS), allowed determining the structure and composition of the most expected coatings and revealing the conditions for obtaining them. It was found that the porous PEO coating obtained in the electrolyte containing copper nitrate in an amount higher than 1,6 mol/L consists mainly of copper-titanium-nickel phosphates. Moreover, in comparison with matrix, the emergence of carcinogenic nickel appearing in the coating fortunately appears in very small quantities, i.e. below 1 at%. Keywords: biomaterials; coatings; electrochemical techniques; energy dispersive X-ray spectroscopy (EDS); NiTi alloy; X-ray photoelectron spectroscopy (XPS) SEM, EDS i XPS analiza nanostrukturirane prevlake koja se stvara na leguri od NiTi biomaterijala plasma elektrolitičkom oksidacijom (PEO) Izvorni znanstveni članak Plasma elektrolitička oksidacija (PEO) NiTi legure proučavana je u elektrolitu koji se uobičajeno sastojao od koncentrirane ortofosforične kiseline s dodatkom nitrata bakra II. Taj se PEO postupak primijenio za dobivanje nanostrukturirane prevlake na Nitinol površini. Metode analize površinskog sloja kao što su skeniranje elektronskim mikroskopom (SEM) s energetski disperzivnom rendgenskom spektroskopijom (EDS) i rendgenskom fotoelektronskom spektroskopijom (XPS), omogućile su određivanje strukture i sastava najočekivanijih prevlaka i otkrivanje uvjeta za njihovo dobivanje. Ustanovilo se da se porozna PEO prevlaka dobivena u elektrolitu koji je sadržavao bakreni nitrat u količini većoj od 1,6 mol/L sastoji uglavnom od fosfata bakra-titanija-nikla. Uz to, u usporedbi s matricom, karcinogeni nikal u prevlaci srećom se javlja u vrlo malim količinama, tj. ispod 1 at%. Ključne riječi: biomaterijali; prevlake; elektrokemijske metode; energetski disperzivna rendgenska spektroskopija (EDS); legura NiTi; rendgenska fotoelektronska spektroskopija (XPS) 1 Introduction Nitinol (nickel-titanium alloy), similar as other metals (titanium, tantalum, niobium, zirconium) and their alloys, can be treated inter alia by Electropolishing (EP) and Magnetoelectropolishing (MEP) [1÷7], as well as by Plasma Electrolytic Oxidation - PEO (Micro Arc Oxidation - MOA) [8÷23]. Concerning the nickel- titanium alloy surface treatment, our electrochemical experiments show that generally the electropolishing process is mostly run when using the voltage under 80 V. With increasing the voltage of the electrochemical treatment, the plasma in electrolyte is created and then the conditions for the plasma electrolytic oxidation (PEO) treatment are achieved. Another important feature of the PEO process is the electrolyte composition. In fact it is composed of a concentrated acid, usually orthophosphoric, and a salt of the bactericidal metals, e.g. silver [24÷26] or copper [27÷29]. These metals are important to cooperate and be compatible with the human being tissue. In present work, the study of nanostructured coating obtained on one of the intermetallic compounds used for biomaterials, known as Nitinol, is presented. The PEO process was studied to obtain the porous coating on NiTi surface. The analyses methods used in this work, such as SEM, EDS, and XPS, allowed determining the structure and composition of the most expected coatings and revealing the conditions for obtaining them. 2 Method The chemical composition of NiTi rectangular samples with dimensions 5 × 30 × 1 mm, which were used in experiments, is presented in Fig. 1. The PEO process was done at average voltage 450 V with pulsation of 300 Hz with amplitude of 92 V. The detailed description of the set up dedicated to PEO (MOA) process as well as to SEM, EDS and XPS equipment, is presented in references [18÷21]. Figure 1 EDS results of NiTi alloy before treatment (as received) 3 Results and discussion In Fig. 2, the SEM images of surface layer formed on NiTi alloy after the PEO treatment at voltage of 450 V in