Etching Techniques for Gold-Containing Ag3Sn Alloys and Amalgams*

Argon-ion etching and various other chemical etchants were applied to conventional and gold-containing dental alloys and amalgams. The polished and etched specimens were studied by optical and/or electron optical methods and by energy-dispersive x-ray spectroscopy. Chemical etchants, though effective, have the disadvantage of accentuating surface scratches. This, in turn, causes difficulty in the accurate determination of microstructure. Argon-ion etching, on the other hand, was found to clearly reveal microstructural details as well as minute features of the solidification process. Any surface irregularities in this case were not revealed. Although argon-ion etching was successful for the conventional and the gold-containing Ag~Sn annealed alloys, it caused sufficient specimen heating to drive off high-vapor-pressure mercury compounds and hence was unsuitable for amalgams. A double cyanide chemical etchant was found to clearly reveal 3' grains and matrix phases 3't and 3'2 in the conventional amalgam but revealed only 3' grains and (Au-Sn) rings surrounding the y grains in the gold-containing amalgam. After further etching in 30% nitric acid, the gold-containing amalgam revealed 3'] and Au-Sn phases between the boundary regions of the 3, grains.