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Title: Interfacial Analysis of (La0.6Sr0.4)(Co0.2Fe0.8)O3-δ Substrates Wetted by Ag-CuO

Abstract

Recently a new method of brazing has been developed to hermetically seal high-temperature, solid-state electrochemical devices, such as as oxygen and hydrogen separators, fuel gas reformers, solid oxide fuel cells, and chemical sensors. Based on a two-phase liquid composed of silver and copper oxide, brazing is conducted directly in air without the need of an inert cover gas or the use of surface reactive fluxes. A key issue in the development of this joining technique is understanding the effect of braze composition on wetting behavior. In the present paper we consider the wetting behaviors of two candidate braze filler materials, Ag-CuO and Ag-CuO-TiO2, on a protoypical mixed ionic/electronic conducting oxide substrate, lanthanum strontium cobalt ferrite [(La0.6Sr0.4)(Co0.2Fe0.8)O3-δ]. It was found that additions of CuO to silver exhibit a tremendous effect on both the wettability and joint strength characteristics of the subsequent braze relative to polycrystalline alumina substrates. The effect is particularly significant at low CuO content, with substantial improvements in wetting observed in the 1 – 8 mol% range. The corresponding strength of the brazed polycrystalline alumina joints appears to be maximized at a copper oxide content of 8 mol%, with a maximum room temperature flexural strength approaching that of monolithicmore » alumina. While further increases in oxide content lead to improved wetting on polycrystalline alumina, the effect on joint strength is deleterious. It appears that the formation of a continuous brittle copper-based oxide layer along the interface between the braze and alumina faying surface is responsible for the poor mechanical behavior observed in joints fabricated with higher CuO content brazes.« less

Authors:
; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
914698
Report Number(s):
PNNL-SA-41576
Journal ID: ISSN 0022-2461; JMTSAS; AA1510100; TRN: US200812%%242
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Journal of Materials Science, 40(9-10):2341-2348
Additional Journal Information:
Journal Volume: 40; Journal Issue: 9-10; Journal ID: ISSN 0022-2461
Country of Publication:
United States
Language:
English
Subject:
30 DIRECT ENERGY CONVERSION; BRAZING; COPPER OXIDES; COVER GAS; FLEXURAL STRENGTH; FUEL GAS; SOLID OXIDE FUEL CELLS; SUBSTRATES; WETTABILITY; lanthanum strontium cobalt ferrite, wetting, air brazing

Citation Formats

Weil, K Scott, Kim, Jin Yong Y, and Hardy, John S. Interfacial Analysis of (La0.6Sr0.4)(Co0.2Fe0.8)O3-δ Substrates Wetted by Ag-CuO. United States: N. p., 2005. Web. doi:10.1007/s10853-005-1956-1.
Weil, K Scott, Kim, Jin Yong Y, & Hardy, John S. Interfacial Analysis of (La0.6Sr0.4)(Co0.2Fe0.8)O3-δ Substrates Wetted by Ag-CuO. United States. doi:10.1007/s10853-005-1956-1.
Weil, K Scott, Kim, Jin Yong Y, and Hardy, John S. Sun . "Interfacial Analysis of (La0.6Sr0.4)(Co0.2Fe0.8)O3-δ Substrates Wetted by Ag-CuO". United States. doi:10.1007/s10853-005-1956-1.
@article{osti_914698,
title = {Interfacial Analysis of (La0.6Sr0.4)(Co0.2Fe0.8)O3-δ Substrates Wetted by Ag-CuO},
author = {Weil, K Scott and Kim, Jin Yong Y and Hardy, John S},
abstractNote = {Recently a new method of brazing has been developed to hermetically seal high-temperature, solid-state electrochemical devices, such as as oxygen and hydrogen separators, fuel gas reformers, solid oxide fuel cells, and chemical sensors. Based on a two-phase liquid composed of silver and copper oxide, brazing is conducted directly in air without the need of an inert cover gas or the use of surface reactive fluxes. A key issue in the development of this joining technique is understanding the effect of braze composition on wetting behavior. In the present paper we consider the wetting behaviors of two candidate braze filler materials, Ag-CuO and Ag-CuO-TiO2, on a protoypical mixed ionic/electronic conducting oxide substrate, lanthanum strontium cobalt ferrite [(La0.6Sr0.4)(Co0.2Fe0.8)O3-δ]. It was found that additions of CuO to silver exhibit a tremendous effect on both the wettability and joint strength characteristics of the subsequent braze relative to polycrystalline alumina substrates. The effect is particularly significant at low CuO content, with substantial improvements in wetting observed in the 1 – 8 mol% range. The corresponding strength of the brazed polycrystalline alumina joints appears to be maximized at a copper oxide content of 8 mol%, with a maximum room temperature flexural strength approaching that of monolithic alumina. While further increases in oxide content lead to improved wetting on polycrystalline alumina, the effect on joint strength is deleterious. It appears that the formation of a continuous brittle copper-based oxide layer along the interface between the braze and alumina faying surface is responsible for the poor mechanical behavior observed in joints fabricated with higher CuO content brazes.},
doi = {10.1007/s10853-005-1956-1},
journal = {Journal of Materials Science, 40(9-10):2341-2348},
issn = {0022-2461},
number = 9-10,
volume = 40,
place = {United States},
year = {2005},
month = {5}
}