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Title: Film breakdown and nano-porous Mg(OH)2 formation from corrosion of magnesium alloys in salt solutions

In this paper, small angle neutron scattering (SANS) and scanning transmission electron microscopy (STEM) were used to study film formation by magnesium alloys AZ31B (Mg-3Al-1Zn base) and ZE10A (Elektron 717, E717: Mg-1Zn + Nd, Zr) in H2O and D2O with and without 1 or 5 wt% NaCl. No SANS scattering changes were observed after 24 h D2O or H2O exposures compared with as-received (unreacted) alloy, consistent with relatively dense MgO-base film formation. However, exposure to 5 wt% NaCl resulted in accelerated corrosion, with resultant SANS scattering changes detected. The SANS data indicated both particle and rough surface (internal and external) scattering, but with no preferential size features. The films formed in 5 wt% NaCl consisted of a thin, inner MgO-base layer, and a nano-porous and filamentous Mg(OH)2 outer region tens of microns thick. Chlorine was detected extending to the inner MgO-base film region, with segregation of select alloying elements also observed in the inner MgO, but not the outer Mg(OH)2. Modeling of the SANS data suggested that the outer Mg(OH)2 films had very high surface areas, consistent with loss of film protectiveness. Finally, implications for the NaCl corrosion mechanism, and the potential utility of SANS for Mg corrosion, are discussed.
Authors:
 [1] ;  [1] ; ;  [1] ;  [1] ;  [2] ;  [1] ;  [1] ;  [1] ;  [3]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Central Metallurgical Research and Development Inst. (CMRDI), Cairo (Egypt)
  3. Magnesium Elektron North America (MENA), Madison, IL (United States)
Publication Date:
OSTI Identifier:
1185706
Grant/Contract Number:
AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Journal of the Electrochemical Society
Additional Journal Information:
Journal Volume: 162; Journal Issue: 4; Journal ID: ISSN 0013-4651
Publisher:
The Electrochemical Society
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS); High Flux Isotope Reactor (HFIR)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office (EE-3V)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE