title: Assessment of nickel titanium and beta titanium corrosion resistance behavior in fluoride and chloride environments.
abstract: OBJECTIVE
  To assess the influence of fluoride concentration on the corrosion behavior of nickel titanium (NiTi) superelastic wire and to compare the corrosion resistance of NiTi with that of beta titanium alloy in physiological solution with and without addition of fluoride.
  
  
  METHODS
  NiTi corrosion resistance was investigated through electrochemical impedance spectroscopy and anodic polarization in sodium chloride (NaCl 0.15 M) with and without addition of 0.02 M sodium fluoride (NaF), and the results were compared with those associated with beta titanium. The influence of fluoride concentration on NiTi corrosion behavior was assessed in NaCl (0.15 M) with and without 0.02, 0.04, 0.05, 0.07, and 0.12 M NaF solution. Galvanic corrosion between NiTi and beta titanium were investigated. All samples were characterized by scanning electron microscopy.
  
  
  RESULTS
  Polarization resistance decreased when NaF concentration was increased, and, depending on NaF concentration, NiTi can suffer localized or generalized corrosion. In NaCl solution with 0.02 M NaF, NiTi suffer localized corrosion, while beta titanium alloys remained passive. Current values near zero were observed by galvanic coupling of NiTi and beta titanium.
  
  
  CONCLUSIONS
  There is a decrease in NiTi corrosion resistance in the presence of fluoride. The corrosion behavior of NiTi alloy depends on fluoride concentration. When 0.02 and 0.04 M of NaF were added to the NaCl solution, NiTi presented localized corrosion. When NaF concentration increased to 0.05, 0.07, and 0.12 M, the alloy presented general corrosion. NiTi corrosion resistance behavior is lower than that of beta titanium. Galvanic coupling of these alloys does not increase corrosion rates.
authors: Department of Metallurgy and Materials Science, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil. elisajk@metalmat.ufrj.br
authors: Elisa J
authors: EJ
authors: Kassab
authors: José Ponciano
authors: JP
authors: Gomes
mesh_terms: D003343:Corrosion; D003722:Dental Alloys / Q000737:chemistry*; D058266:Dielectric Spectroscopy; D008422:Materials Testing; D009532:Nickel / Q000737:chemistry*; D009969:Orthodontic Wires; D012965:Sodium Chloride; D012969:Sodium Fluoride; D014025:Titanium / Q000737:chemistry*
chemical_list: D003722:Dental Alloys; C023988:beta titanium; D012965:Sodium Chloride; D009532:Nickel; D012969:Sodium Fluoride; D014025:Titanium