Decomposition of Ag₂C₂O₄ in a spark plasma sintering apparatus: Morphological study and application for materials joining

Silver oxalate Ag₂C₂O₄ is an interesting compound from both fundamental and practical viewpoints. Decomposition of Ag₂C₂O₄ results in the formation of metallic silver, whose size and morphology can be tailored for different applications. In this work, we focused on the morphological features of silver that forms upon decomposition of Ag₂C₂O₄ in a spark plasma sintering (SPS) apparatus. While crystals heated in a conventional furnace decompose to produce silver in the form of a pseudomorph, decomposition induced by heating in a SPS chamber at a rate of 30 ºC·min^-1 via a pressureless process results in the formation of foam-like porous silver. Decomposition of Ag₂C₂O₄ was also carried out under pressure by placing the powder between copper plates and heating the assembly in a SPS die. A feasibility study has shown that Ag₂C₂O₄ powders can be used for joining copper plates in a fast process enabled by the SPS method. Joints formed by the SPS method at 300ºC and 13 MPa were formed by silver with 500-nm crystallites; the shear strength of the joints was 45 MPa.