Induction brazing BaCo0.7Fe0.2Nb0.1O3-δ membrane tubes to steel supports with Ag-based filler in air

An induction brazing process has been developed to seal BaCo0.7Fe0.2Nb0.1O3-δ (BCFN) membrane tubes to metal supports using Ag-Cu alloy in air. The closed-one-end BCFN membrane tubes with an outer diameter of 16 mm and a length of 560 mm were prepared by slip casting. The thermal expansion behaviors of the BCFNO membrane, Ag braze and 310S stainless steel were characterized. A sleeve joint was optimized to reduce the stresses caused by the mismatching in thermal expansions. Ag-1 mol%Cu braze was chosen as brazing filler duo to its good wettability for both the membranes and the metal substrates and thin and continuous reaction layers. Based on the characteristics of the BCFN membrane, a temperature schedule was exploited to successfully achieve the induction brazing of the BCFN membrane tubes to the 310S supports using Ag-1 mol%Cu in air. The entire time needed is about 80 min. The brazed assemble subjected to 15 thermal cycles still exhibits no degradation in joint hermeticity and stable oxygen permeation flux. The result indicates that induction brazing can efficiently join large membrane tubes with high thermal expansion to their metal supports.