Structural characterisation and corrosion resistance of Ga-precious metal alloys formed by liquid–solid reaction at room temperature

An attempt to eliminate Hg from dental amalgams was made by substituting it with low melting Ga-based alloys, liquid at room temperature. However more information is needed on the influence of alloy composition and their questioned corrosion resistance. In this paper the reaction of some liquid Ga alloys and some solid precious metal alloys with different nobility was studied. Structural features, hardness and corrosion resistance of the obtained composite materials were investigated as a function of composition of the starting alloys, liquid/solid ratio and different mixing methods. Every combination of the solid precious metal powders and the liquid Ga-alloys gives rise to similar composite materials. The structure always consists of unreacted solid alloy particles embedded in a complex matrix composed of many reaction phases. The formation of some phases depends on the composition of the solid alloy, others originate all the time; however their topography and morphology may be different as well as their compositional range. The high porosity generally present in the composite materials markedly affects hardness values; nevertheless some prepared materials reach hardness comparable with the one of commercial amalgams. The nobility of the solid alloy and porosity percentage play a determinant role on the corrosion behaviour. In all cases the low corrosion resistance of the experimented materials may be attributed to a galvanic coupling between the reaction intermediate phases and the unreacted liquid alloy remained inside the pores.