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Surface preparation for high purity alumina ceramics enabling direct brazing in hydrogen atmospheres

United States Patent

November 13, 2001
View the Complete Patent at the US Patent & Trademark Office
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The present invention relates to a method for preparing the surface of a high purity alumina ceramic or sapphire specimen that enables direct brazing in a hydrogen atmosphere using an active braze alloy. The present invention also relates to a method for directly brazing a high purity alumina ceramic or sapphire specimen to a ceramic or metal member using this method of surface preparation, and to articles produced by this brazing method. The presence of silicon, in the form of a SiO.sub.2 -containing surface layer, can more than double the tensile bond strength in alumina ceramic joints brazed in a hydrogen atmosphere using an active Au-16Ni-0.75 Mo-1.75V filler metal. A thin silicon coating applied by PVD processing can, after air firing, produce a semi-continuous coverage of the alumina surface with a SiO.sub.2 film. Room temperature tensile strength was found to be proportional to the fraction of air fired surface covered by silicon-containing films. Similarly, the ratio of substrate fracture versus interface separation was also related to the amount of surface silicon present prior to brazing. This process can replace the need to perform a "moly-manganese" metallization step.
Cadden; Charles H. (Danville, CA), Yang; Nancy Yuan Chi (Lafayette, CA), Hosking; Floyd M. (Albuquerque, NM)
Sandia Corporation (Albuquerque, NM)
09/ 606,823
June 28, 2000
FEDERALLY SPONSORED RESEARCH The United States Government has rights in this invention pursuant to Department of Energy Contract No. DE-AC04-94AL85000 with Sandia Corporation.