Reversible colour change in Ag-Zn alloy ribbon

Abstract

The reversibility of a colour change and its relationship to the phase transformation of Ag-50 at % Zn alloy ribbon produced by the twin-roller type melt-quenching method were investigated by spectral reflectivity measurements and X-ray diffractometry. This ribbon turns pink-coloured on quenching from a temperature above 560 K, and turns silver-coloured on ageing between 423 and 553_K. By alternating these heat treatments, either of the two colours can be acquired around room temperature interchangeably. The spectral reflectivity also changes with respect to the colour change. The pink-coloured alloy shows a CsCl structure which is the metastableβ ₁ phase. The silver-coloured alloy shows a hexagonal structure which is the ζ equilibrium phase. Therefore, the colour change between pink and silver is due to the solid-state phase transformation betweenβ, andζ caused by heat treatment.[/p]