Electrical glass/ceramic sealing

Conversion of glass to a polycrystalline ceramic is accompanied by increased strength (two to four times), increased fracture toughness (two to four times), increased electrical resistivity (10 times), increased deformation temperature (200-400°C), increased abrasion resistance, and increased thermal shock resistance. All these factors contribute to many applications for glass ceramics dinnerware, cooking utensils, stove tops, radomes, hermetic seals to metals, building materials, and so on. 

The E-design stack, shown in Fig. lA, consists of a relatively thick metallic interconnect with machined gas channels on both sides and a metallic picture frame for the cell, brazed to the interconnect by a metal solder. Sealing is obtained by glass ceramic sealants applied to the planar cell and frame surfaces using an automated dispenser. A fine Ni-mesh is spot-welded to the fuel side of the interconnect in order to improve the electrical contact between interconnect and anode substrate. On the air side usually a lanthanum cobaltite (LC) contact layer is sprayed onto the ribs of the interconnect. 

Lithium disilicate glass-ceramics demonstrate a relatively high linear coefficient of thermal expansion of approximately 105 x 10 K h This property is favorable for the fabrication of special composite materials, e.g., for sealing to metal substrates in the electrical industry (Beall 1993). 

The central element of the solid oxide fuel cell stack is the SOFC cell which consists of the fuel electrode (anode), the oxygen electrode (cathode), and the ionconducting electrolyte. To reach the desired electrical voltage, single cells are stacked (cf. Fig. 21.11). They are separated by interconnects (plates) and sealed by glass ceramics. 

An increasing number of household appliances use electronic controls (see Fig. 3.25). Cooktops especially take advantage of touch inputs. They preserve the smooth look and the sealed easy-to-clean surface. Glass ceramic is suitable because of its electrical and optical properties. 

Relative ease of hermetic sealing by having the electrical leads cast into molten glass ( glass-to-metal seal ) in ceramic ( ceramic-to-metal seal ), or embedded into thermosetting plastic ... 

Effective sealing of SOFC components is critical for efficient and effective operation and metallic, metal-ceramic composite and ceramic based seals are not ideal [23, 24]. Glass based sealants are typically recognised to be the best candidate due to their excellent electrical, mechanical and chemical stability in both oxidising and reducing environments properties at high temperature [25]. 

For the electrical contacts in many cases the metallic container is one pole and a glass-to-metal seal (or ceramic-to-metal seal) the other. The container may also have to be potential free then both contacts are made from the glass-to-metal seals. 

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