Corrosion Behavior of Sputter- Deposited W-Cr-(4-15)Ni Alloys in Nacl and Naoh Solutions
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Central Department of Chemistry
Abstract
The synergistic effect of chromium addition in the sputter-deposited amorphous or nanocrystalline W-Cr-(4-15)Ni alloys is studied in 0.5 M NaCl and alkaline NaOH solutions at 25oC, open to air using immersion tests and electrochemical measurements. In 0.5 M NaCl solution, the addition of chromium to W-Cr-(4-15)Ni alloys containing 42-75 at % chromium increases the corrosion resistance and makes the open circuit potential more noble so as to show higher corrosion resistance than those of alloy-constituting elements (that is, tungsten, chromium and nickel). The corrosion rates of all the examined W-Cr-(4-15)Ni alloys are almost same (that is, about 2-3 x 10-3 mm/y) and are about one order of magnitude lower than that of tungsten and even lower than that of chromium metal after prolonged immersion in 0.5 M NaCl solution. In 1 M NaOH solution, the corrosion rates of the W-Cr-(4-15)Ni alloys (about 2-5 x 10-3 mm/y) are about two orders of magnitude lower than that of tungsten and nearly one order of magnitude lower than that of chromium metal. The open circuit potential of the W-Cr-(4-15)Ni alloys is generally increased with increasing chromium content in different concentrations of NaOH solutions. The open circuit potentials of all the examined W-Cr-(4-15)Ni alloys are in more noble direction in 0.5 M NaCl solution than that in 1 M NaOH solution. The passivity of the W-Cr-(4-15)Ni alloys is increased with decreasing the concentration of NaOH solutions at 25oC.