A palladium-free gallium-based alloy: analysis of composition and microstructure

Objectives. To study the microstructure of a palladium-free gallium-based alloy (Galloy®) before and after mixing to identify the metallic phases produced by the setting reaction and assess the quantitative elemental analysis of the phases present. Methods. The Galloy® powder was analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM) and the particle size distribution was determined using a high resolution particle size analyzer. Cylindrical test specimens were mechanically condensed in accordance with ISO 1559: 1986 for XRD, energy dispersive spectroscopy (EDS) and SEM analyses of the set alloy. Disc shaped specimens were prepared by manual condensation to compare the width of the reaction zone with specimens condensed mechanically. Results. The Galloy® powder consisted of spherical particles varying between 0.1 and 40 μm in diameter which contained a network of grooves and clefts extending deep within the substance of the particles. The reaction zone appeared ‘grainy’ and ‘fragmented’ compared with the well defined reaction zone previously observed for Pd-containing gallium-based alloys. The student t-test indicated the width of reaction zone varied significantly (P<0.001) with method of specimen fabrication. Significance. The significantly larger reaction zone in the manually condensed specimens was possibly due to failure of the condensation technique to force out excessive liquid alloy present in the triturated mass. The surface topography of the Pd-free Galloy® powder particles could be responsible for the characteristically fragmented and ill-defined reaction zone observed in the set material compared with the well defined reaction zone previously observed for Pd-containing gallium-based alloys.