The lattice parameter of α-bronzes as a function of solute content: application to archaeological materials

The lattice parameter of Cu substitutional solid solution-α-phase-has been studied in relation with the solute content. The investigation was conducted on pure binary Cu-Sn, industrial Cu-Sn-Zn alloys and archaeological bronzes. Lattice parameters and elemental compositions of the α-phase have been determined by X-ray diffraction and X-ray spectrometry. A linear relation between the unit cell constant and the atomic tin equivalent content in the α-phase has been evidenced and characterised, in fair agreement with Vegard's law. Addition of lead and trace elements has no significant effect on the results. Therefore, the tin equivalent content of the α-phase can be determined from XRD evaluation of the lattice parameter. As a consequence, a new approach is proposed for setting composition standards in α-(Cu-Sn) and α-(Cu-Sn-Zn) bronzes and application to characterization of ancient bronzes is discussed.