Microstructures of high copper amalgams after corrosion in various solutions

Five copper rich amalgam systems were studied to detect corrosion induced microstructural changes after immersion in various solutions for 2.5 years. The solutions were artificial saliva, 10 times concentrated artificial saliva, and a one to one ratio of 1% Na₂S and Ringer's solution. Surface corrosion products were removed by metallographic polishing and microstructures were studied by SEM/EDS and x-ray diffraction. Preferential corrosion attack occurred in the eta prime Cu₆Sn₅ reaction product in both blended and single particle systems. Copper appeared to be preferentially released, resulting in insoluble tin containing corrosion products. In addition, phase mixtures of copper and tin containing products were often found in the corroded samples. In more concentrated solutions the extent of corrosion was more pronounced. The corrosion process also enhanced the gamma 1 to beta 1 transformation.