Silver dissolution and precipitation in an Na ₂ O–ZnO–B ₂ O ₃ metallization paste glass

Abstract Thermally stimulated interactions between silver and glass, that is, silver dissolution as Ag ⁺ and precipitation as Ag ⁰ were studied in two glass series of molar target composition x Ag ₂ O–(19 − x )Na ₂ O–28ZnO–53B ₂ O ₃ with x = 0, 0.1, 0.5, 5 and (19Na ₂ O–28ZnO–53B ₂ O ₃ )+ y Ag ₂ O with y = 0.01, 0.05. These act as model for low‐melting borate glasses being part of metallization pastes. The occurrence of metallic silver precipitates in melt‐quenched glass ingots demonstrated that silver dissolved only in traces (< 0.01 mol%) in the glasses. The dissolved silver was detected by means of Raman spectroscopy and energy‐dispersive X‐ray spectroscopy. Increasing x in the batch could not lead to a significant increase of the silver ion fraction in the glass as possible in binary silver borate glasses. In situ observation of heated AgNO ₃ mixed with the base glass frit in a hot stage microscope showed that Ag ⁰ precipitation occurs already at the solid state. At higher temperatures, small droplets of liquid silver were found to move freely within the melt, whereas coalescence caused a stepwise increase of their size. These results contribute to the understanding of formation of silver precipitates in metallization pastes described in the literature.