Wet and dry accelerated aging tests in a spray chamber to understand the effects of acid rain frequencies on bronze corrosion

We have conducted controlled laboratory experiments using a series of bronze alloys exposed to frequent, repeated wet and dry cycles, to simulate frequent acid rain exposure and study the resultant corrosion processes in bronze artifacts exposed to an outdoor urban environment. To simulate rainwater and condensation, a spray chamber for the corrosion tests was assembled, which delivered homogeneous vapor diffusion and drop deposition. Three bi-component bronzes, with 3%, 7% and 20% tin content, were subjected to seven days of controlled wet and dry cycles, and analyzed at precise intervals. Electrochemical impedance spectroscopy and spectrocolorimetry results were combined to show the different phases of corrosion. The patinas on all three samples at the end of the exposure period were studied with scanning electron microscopy to show the morphology of corrosion products; they were also analyzed by X-ray diffraction. The sample containing 7% tin produces a patina that is unstable and frequently dissolved. Partial patina dissolution also occurs during exposure for the 3% tin sample, but the effects are less pronounced. Because it reacts the least with the environment, the 20% tin sample demonstrates intermediate behavior (between the 7% and the 3% tin samples). However, the patina is less protective than the 3% tin sample patina