Chapter 15 - Silica Membranes Sealing in High Temperatures

Abstract

Silica membranes and membrane reactor are developed for high temperature separation of hydrogen from other gas. The ceramic membrane performances depend not only on the separation and permeation properties of the membrane layer but on its mechanical integrity as well. A seal glass should have a combination of desired thermal, chemical, mechanical, and electrical properties in order to seal cell components and stacks and prevent gas leakage. There are currently only a few accepted methods of sealing of high temperature ceramic membrane, none of which fully meet the design requirements. Seals need to withstand many thermal cycles during separation or reaction operation. Thermal expansion coefficients must be between the metal seal, support, and ceramic membrane, because during cooling down from operation temperatures, residual thermal stresses will build up in the seals. It is due to the thermal expansion mismatch between the sealing material and adjacent components. There are three methods for sealing the ceramic membranes at high temperatures. The first technique is based on soldering or brazing of an alloy such as Ti-Au-Cu or Ni-Ag-Cu alloys. The second technique uses soft and relatively inert metals such as silver and gold, for sealing. The third technique uses glass or ceramics as the seal.