Nature of surface layer and electrochemical behavior of NaOH hydrothermally treated NiTi alloy

P. Shi, F. T. Cheng, Hau Chung Man

Research output: Journal article publicationJournal articleAcademic researchpeer-review

5 Citations (Scopus)


NiTi samples were hydrothermally treated in NaOH at 200°C with different soaking times. The morphology of the surface layer formed was studied by scanning electron microscopy (SEM). The composition of the layer and the major phases presented were determined by energy-dispersive spectroscopy (EDS) and X-ray diffractometry (XRD), respectively. In contrast to the results reported by some authors, the surface layer was essentially Ni(OH)2instead of being TiO2. The electrochemical behavior of the samples was studied by electrochemical impedance spectroscopy (EIS) in 3.5%NaCl solution at 23°C, and analyzed using a simplified Randle circuit consisting of a resistance R and a capacitance C in parallel. After hydrothermal treatment, R was increased by a factor ranging from 1.5 times to 5.0 times, depending on the treatment time. The value of R of all the samples became steady within a period of less than 15 h. Results of the present study indicate that alkaline treatment leads to the growth of an insulating layer on NiTi, but the method is not suitable for the surface modification of NiTi implants due to the enhanced Ni content in the surface layer.
Original languageEnglish
Pages (from-to)185-188
Number of pages4
JournalJournal of Materials Science and Technology
Issue number2
Publication statusPublished - 1 Mar 2004


  • Electrochemical impedance spectroscopy
  • Hydrothermal treatment
  • NaOH
  • NiTi
  • Resistance

ASJC Scopus subject areas

  • Ceramics and Composites
  • Mechanics of Materials
  • Mechanical Engineering
  • Polymers and Plastics
  • Metals and Alloys
  • Materials Chemistry


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