Please use this identifier to cite or link to this item: http://hdl.handle.net/10397/31814
Title: Nature of surface layer and electrochemical behavior of NaOH hydrothermally treated NiTi alloy
Authors: Shi, P
Cheng, FT
Man, HC 
Keywords: Electrochemical impedance spectroscopy
Hydrothermal treatment
NaOH
NiTi
Resistance
Issue Date: 2004
Source: Journal of materials science and technology, 2004, v. 20, no. 2, p. 185-188 How to cite?
Journal: Journal of Materials Science and Technology 
Abstract: 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)2 instead 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.
URI: http://hdl.handle.net/10397/31814
ISSN: 1005-0302
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