Mechanosynthesized and ultra-fast quenched AgI–Ag2O–B2O3 materials with high AgI contents

The 78AgI, 16.5Ag2O, and 5.5B2O3 mol% powder mixture, ultra-fast quenched 78AgI-16.5Ag2O-5.5B2O3 glass containing α-AgI crystalline precipitates and pristine AgI were ball-milled at a high rotation speed. For all the materials, the processing did not cause formation of α-AgI phase, in contrary, it prompted α to β phase transition of the α-AgI precipitates in the glass. Nanosize scale β/γ-AgI grains were detected both in the milled powder mixture and in the glass but not in the pristine AgI powder.The decrease of α to β phase transition temperature was observed for the milled materials during cooling from 170 °C, ca. 10 °C, 60 °C and 75 °C respectively for the AgI powder, the powder mixture and the glass. Stabilization of the α-AgI to low temperatures was related to the nanosize scale β/γ-AgI grains. The work demonstrates, that although it is not possible to stabilize α-AgI in pure silver iodide powder by ball-milling, nevertheless it is achievable for mixtures with high AgI contents.

► Ball-milling of pristine AgI (β/γ-AgI) does not lead to formation of α-AgI.
► Milling at a high speed forms nanoparticles of β-AgI in AgI, Ag2O, and B2O3 mixture.
► Mechanosynthesis of AgI, Ag2O and B2O3 mixture does not form α-AgI.
► α-AgI phase is stable down to 75 °C in fast quenched and then milled in a borate glass.