Interconnect ceramic

Zhou X-L, Ma J-J, Deng F-J, Meng G-Y, and Liu X-Q. A high performance interconnecting ceramic for solid oxide fuel cells (SOFCs). Solid State Ionics 2006 177 3461-3466. 

Zhou X, Deng F, Zhu M, Meng G, and Liu X. Novel composite interconnecting ceramics LaojCao jCrOj j/ Cc02Sm08O 9 for solid oxide fuel cells. Mater. Res. Bull. 2007 42 1582-1588. 

Interconnect The property requirements for the interconnect ceramic are the most demanding. The conductivity should be as high as possible and, ideally, 100% electronic. This is necessary to reduce internal resistance and to avoid severe problems which would arise were ionic space-charge polarization (see Section 2.7.1) to develop. 

Directed Oxidation of a Molten Metal. Directed oxidation of a molten metal or the Lanxide process (45,68,91) involves the reaction of a molten metal with a gaseous oxidant, eg, A1 with O2 in air, to form a porous three-dimensional oxide that grows outward from the metal/ceramic surface. The process proceeds via capillary action as the molten metal wicks into open pore channels in the oxide scale growth. Reinforced ceramic matrix composites can be formed by positioning inert filler materials, eg, fibers, whiskers, and/or particulates, in the path of the oxide scale growth. The resultant composite is comprised of both interconnected metal and ceramic. Typically 5—30 vol % metal remains after processing. The composite product maintains many of the desirable properties of a ceramic however, the presence of the metal serves to increase the fracture toughness of the composite. 

S.3.2 Sol-Gel Encapsulation of Reactive Species Another new and attractive route for tailoring electrode surfaces involves the low-temperature encapsulation of recognition species within sol-gel films (41,42). Such ceramic films are prepared by the hydrolysis of an alkoxide precursor such as, Si(OCH3)4 under acidic or basic condensation, followed by polycondensation of the hydroxylated monomer to form a three-dimensional interconnected porous network. The resulting porous glass-like material can physically retain the desired modifier but permits its interaction with the analyte that diffuses into the matrix. Besides their ability to entrap the modifier, sol-gel processes offer tunability of the physical characteristics... 

Ceramic boards are currently widely used in high-performance electronic modules as interconnection substrates. They are processed from conventional ceramic precursors and refractory metal precursors and are subsequently fired to the final shape. This is largely an art a much better fundamental understanding of the materials and chemical processes will be required if low-cost, high-yield production is to be realized (see Chapter 5). A good example of ceramic interconnection boards are the multilayer ceramic (MLC) stractures used in large IBM computers (Figure 4.11). These boards measure up to 100 cm in area and contain up to 33 layers. They can interconnect as many as 133 chips. Their fabrication involves hundreds of complex chemical processes that must be precisely controlled. 

FIGURE 4.11 Cross-section of the IBM Multilayer Ceramic interconnection package. Various layers in this interconnection device are shown. Copyright 1982 by International Business Machines Corporation. Reprinted with permission. 

The micro channels were prepared with a cutter in a ceramic tape [70,71]. Sealings served to ensure liquid tightness. Each end of the stack of five ceramic layers was clamped between two blocks, allowing a reversible interconnection. 

Interconnects are formed into the desired shape using ceramic processing techniques. For example, bipolar plates with gas channels can be formed by tape casting a mixture of the ceramic powder with a solvent, such as trichloroethylene (TCE)-ethanol [90], Coating techniques, such as plasma spray [91] or laser ablation [92] can also be used to apply interconnect materials to the other fuel cell components. 

The difficulty and high cost of the fabrication of ceramic interconnect materials is their primary disadvantage and has led to recent emphasis on metallic interconnects, which will be discussed in the next section. 

In addition to the aforementioned interactions with the surrounding gas environments, metallic interconnects also interact with adjacent components at their interfaces, potentially causing degradation of metallic interconnects and affecting the stability of the interfaces. One typical example is the rigid glass-ceramic seals, in particular those made from barium-calcium-aluminosilicate (BCAS) base glasses [205-209], FSS interconnect candidates have been shown to react extensively with... 

The aforementioned requirements on surface stability are typical for all exposed areas of the metallic interconnect, as well as other metallic components in an SOFC stack e.g., some designs use metallic frames to support the ceramic cell. In addition, the protection layer for the interconnect or in particular the active areas that... 

Sakai N, Yokokawa H, Horita T, and Yamaji K. Lanthanum chromite-based interconnects as key materials for SOFC stack development. Int. J. Appl. Ceram. Technol. 2004 l 23-30. 

Nishiyama H, Aizawa M, Sakai N, Yokokawa H, Kawada T, and Dokiya M. Property of (La,Ca)Cr03 for interconnect in solid oxide fuel cell (part 2). Durability. J. Ceram. Soc. Japan 2001 109 527-534. 

Hatch well CE, Sammes NM, Tompsett GA, and Brown IWM. Chemical compatibility of chromium-based interconnect related materials with doped cerium oxide electrolyte. J. Eur. Ceram. Soc. 1999 19 1697-1703. 

Zhong Z. Stoichiometric lanthanum chromite based ceramic interconnects with low sintering temperature. Solid State Ionics 2006 177 757-764. 

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