Search

link to homepage

Institute of Energy and Climate Research (IEK)

Navigation and service


Reactive air brazing to combine metallic and ceramic components

At IEK-2 RAB-brazing is used for several years, to integrate ceramic components into metallic frames for high temperature fuel cell application.

Most commercially available brazes for connecting ceramic with metallic components are so-called "vacuum-active brazes". Typically titanium or zirconium is used as reactive element. These metals have a high reduction potential at high temperatures and are able to remove oxygen from the surface of ceramic materials provided that the oxygen partial pressure of the surrounding atmosphere is sufficiently low. Consequently the activated surface is better wetted by the braze material (typically precious metals or nickel). Nevertheless vacuum-brazing is not suitable when the joining partners are made from materials that tend to be damaged by reducing atmospheres at high temperatures, for example high temperature fuel cells or gas separation membranes for CO2 free power plants.

A process known as Reactive Air Brazing (RAB) has become increasingly important in recent years and is an alternative to vacuum brazing. RAB-brazing has proven to be advantageous, since materials which are sensitive to reducing atmospheres or vacuum can be joined. The RAB-Process was developed from the "Direct copper bonding (DCB) method" which is known since the 60s. A RAB-braze is typically made of a precious metal (e.g. silver) matrix and a reactive component, in most cases CuO, which improves wetting on ceramic and oxidized metal surfaces. Therefore brazing can be processed in air. The additional costs of the precious metal based RAB-brazes compared to nickel based vacuum-brazes can potentially be compensated by lower processing and investment costs compared with vacuum brazing facilities.

At IEK-2 RAB-brazing is used for several years, to integrate ceramic components into metallic frames for high temperature fuel cell application. The investigations of RAB-brazed composites provide a basic understanding of the relationship between brazing-process, chemical composition and microstructure of the joining partners, as well as the interfacial strength and bonding behaviour. In addition to the study of composites in the initial state after brazing, degradation under exposition to high temperature and mechanical stress are a central aspect of the work carried out at IEK-2.


Servicemeu

Homepage