Corrosion behavior of metals and alloys in downstream environment of microwave plasma with CF4/O2 gas mixture

Eiji Ohtsuki, Atsushi Nakafuji, Noboru Akao, Nobuyoshi Kara, Matsuho Miyasaka, Katsuhisa Sugimoto

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)

Abstract

The corrosion characteristics of metals (Al, Ti, Cr, Fe, Co, Ni, Cu, Mo, Ta, and W), stainless steels (SUS304 and 316), and a Ni-based alloy (Alloy 600) in a downstream reactor of CF4-11%O2 plasma have been studied. The mass change and penetration depth of the specimens were measured after corrosion tests at temperatures in the range of 298 to 573 K. The surfaces of the specimens were examined using Auger electron spectroscopy (AES) with Ar+ ion sputtering. It was found that metals such as Ti, Cr, Mo, Ta, and W suffered from corrosion leading to a decrease in mass, and their corrosion rates increased with rising test temperature. At 573K, Fe and the stainless steels showed an increase in mass, while Al, Co, Ni, Cu, and Alloy 600 no change in mass. The results of AES analysis exhibited that the corroded surface of Cr, Mo and Ta was covered with a thin film of parent metal oxyfluorides, and that of W with a thin oxide film. Thin films of metal fluorides were formed on Co, Ni and Cu. Thicker films consisting of metal fluorides and oxyfluorides existed on Fe and stainless steels. In the downstream environment of CF4/O2 plasmas, metal fluorides are thermodynamically favored for all the metals examined. The vapor pressures of MoF6, TaF5 and WF6 in the temperature range of 298 to 573K are high enough to evaporate when they are formed. Therefore, the corrosion of metals and alloys in the downstream environment of CF4/O2 plasmas is primarily controlled by the rates of reactions with fluorine atoms, which are generated in the plasmas, and the vapor pressures of metal fluorides formed by the reactions.

Original languageEnglish
Pages (from-to)136-145
Number of pages10
JournalZairyo to Kankyo/ Corrosion Engineering
Volume47
Issue number2
DOIs
Publication statusPublished - 1998

Keywords

  • Auger electron spectroscopy
  • CF/O plasma
  • Corrosion
  • Fluorine atom
  • Metal fluoride
  • Metal oxyfluoride
  • Pure metal
  • Stainless steel

ASJC Scopus subject areas

  • Surfaces, Coatings and Films
  • Metals and Alloys
  • Electrochemistry
  • Materials Chemistry

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