Formation of the main atmospheric zinc end products:: NaZn4Cl(OH)6SO4•6H2O, Zn4SO4(OH)6•nH2O and Zn4Cl2(OH)4SO4•5H2O in [Cl-] [SO42-] [HCO3-] [H2O2] electrolytes

The composition of new accelerated zinc corrosion electrolytes has been derived from the chemistry of atmospheric pollutants. Zinc plated specimens were exposed to these solutions and the growth of the corrosion products has been studied by means of scanning electron microscopy, X-ray microanalysis and grazing incidence X-ray diffraction. First, the main atmospheric zinc end products were identified according to different natural environments, i.e. NaZn4Cl(OH)(6)SO4. 6H(2)O for a marine atmosphere, Zn4SO4(OH)(6). nH(2)O for a rural environment and Zn4Cl2(OH)(4)SO4. 5H(2)O developed in industrial and urban atmospheres. Then, the corrosion sequences were established for the 3 electrolytes able to reproduce mechanisms close to the atmospheric corrosion sequences of zinc when it is exposed to marine, rural, urban and industrial atmospheres. Accelerated corrosion tests performed in such electrolytes would advantageously replace cyclic automobile test solutions by improving the resemblance between accelerated corrosion results and natural ones. (C) 1999 Elsevier Science Ltd. All rights reserved.