Structure and Properties of Silver Borate Glasses

Clear glasses form in the system Ag 2 O‐B 2 O 3 up to about 35 mol% (65 wt%) Ag 2 O. Infrared absorption, thermal expansion, and density data indicated an analogy to the Na 2 O‐B 2 O 3 system. Pentaborate‐triborate group pairs appear to be formed on addition of Ag 2 O to B 2 O 3 up to 20 mol% Ag 2 O and diborate groups from 20 to 33 mol% Ag 2 O. This interpretation is supported by the comparison of the infrared absorption spectra of quenched and crystallized glasses. One crystallization product, Ag 2 O‐4B 2 O 3 , was identified previously. A new compound starts to appear at 28 mol% Ag 2 O. The theory that silver is generally present as a network modifier like sodium was substantiated by the comparison of the molar volume of sodium and silver borate glasses. Above 27 mol% Ag 2 O some atomic silver is assumed to be present; below 15 mol%, exploratory studies indicate a two‐phase structure within an immiscibility gap. A low‐temperature internal friction peak in the glasses up to 28 mol% Ag 2 O corresponds to the alkali peak in other glasses; a high temperature peak appearing in the 34 mol% Ag 2 O glass is associated with the appearance of nonbridging oxygen in the system.