SEM and EDX study of Stainless Steels, Suggested as Biomaterials EUROPEAN UNION EUROPEAN SOCIAL FUND OPERATIONAL PROGRAMME SCIENCE AND EDUCATION FOR SMART GROW Green Technologies Innovative Materials Research network GreTInMat Four-day working meeting Starosel, Bulgaria, June 18 – 21, 2018 SEM and EDX study of Stainless Steels, Suggested as Biomaterials Rositza Simitchiiska, Dimka Ivanova, Ludmil Fachikov Department of Inorganic and Electrochemical Production University of Chemical Technology and Metallurgy 1

The work presents the results obtained in the comparative study of corrosion behavior of two austenitic stainless steels (Cr18Ni9 and Cr18Mn12N) in Artificial Saliva Fusayma/Meyer at two values of Ph. This solution is standardized for testing biodegradability of dental and orthodontic metal alloys.

Results and discussions SEM – analyses shows that the main form of corrosion on the steel surfaces after electrochemical treatment of the samples is basically pitting corrosion. In order to establish the type and size of the pits appeared on the surfaces of both investigated steels, the samples were observed by scanning electron microscopy. The microphotographs for both steels are presented for saliva-1 and on for saliva-2. The microscopy observations indicate more numerous pits on Cr18Ni9 steel surfaces which are larger in comparison to these on the surface of the Cr18Mn12N samples in both solutions. The pits occurring at the nitrogen steel surface are spherical in shape and could be divided formally into two groups: small pits with diameters in the rage 20-60 μm and large pits with diameters of about 200 μm. The pits on the nickel steel surface are also spherical in shape, but in contrast to the nitrogen steel samples they are larger (with 200-250 μm in diameter) and deeper. Some of the pits are open and the others are under surfaces types. EDX analyses of the surfaces on the bottom of the pits were performed after electrochemical treatment of the samples in two solutions: saliva-1 and saliva-2. Surface analysis provides information, besides altering the content of metal alloy components Fe, Cr, Mn, Ni, the content of corrosion products where high levels of oxygen, phosphorus and chlorine are visible. This shows that during the surface dissolution, besides the formation of oxides, there are metal chlorides and phosphates.

Conclusions At the time of comparative investigation the corrosion behavior of two austenitic stainless steels (Cr18Ni9 and HNS Cr18Mn12N), suggested for the orthodontic appliances, in two model artificial saliva were defined the character (pitting corrosion, with different in size spherical pits) and the probable composition of the corrosion products. The results manifested that the nitrogen-containing steel possess higher résistance in model media and more suitable for orthodontic appliances.

E-mail: fachikov@uctm.edu EUROPEAN UNION EUROPEAN SOCIAL FUND OPERATIONAL PROGRAMME SCIENCE AND EDUCATION FOR SMART GROW Supervisor : Assoc. Prof. Dr. Eng. Ludmil Fachikov - Head of Department E-mail: fachikov@uctm.edu Department of Inorganic and Electrochemical Production University of Chemical Technology and Metallurgy Bulgaria, Sofia 1756, 8, Kliment Ohridsky, Blvd. The Department conducts research in the following major fields: environment protection in inorganic production; use of biotechnologies in inorganic production; preparation of mixed fertilizers; new materials and coatings, including nanomaterials and thin films; testing the quality of inorganic products; new inorganic and electrochemical technologies; corrosion protection of materials; technology strategy formulation of chemical and electrochemical processes. Eng. Rositza Nikolaeva Simitchiiska PhD student e-mail: simitchiiska@uctm.edu Research interests keywords: electrochemical corrosion, stainless steels, body implants Project: Corrosion behavior of stainless steels, suggested as biomaterials Acknowledgment: „The research network has been financially supported by the Operational Programme "Science and education for smart growth" 2014-2020 of the European Union cofounded by the European Social Fund through the project BG05M2ОP001-2.009-0015 “Support for the development of capacity of doctoral students and young researchers in the field of engineering, natural and mathematical sciences” 6

Thank you for your attention! EUROPEAN UNION EUROPEAN SOCIAL FUND OPERATIONAL PROGRAMME SCIENCE AND EDUCATION FOR SMART GROW Thank you for your attention! Acknowledgment: „The research network has been financially supported by the Operational Programme "Science and education for smart growth" 2014-2020 of the European Union cofounded by the European Social Fund through the project BG05M2ОP001-2.009-0015 “Support for the development of capacity of doctoral students and young researchers in the field of engineering, natural and mathematical sciences” 7