Cermet Fabrication

I igure 6.5 Micrograph of anode-supported thin electrolyte cell structure. On either side of the dense electrolyte is a fine-structured functional layer for the electrocatalytic promotion of the electrotle reactions. The full thickness of the cathode layer is imaged, but only a. small. section of the anode. substrate (bottom). (Reproduced by courtesy of the Research Centre. JiVich (h /.)).) 

5 Anode Behaviour Under Steady-State Conditions 

The details of the electrode reactions and associated polarisations are discussed in Chapter 9. In this and the next two sections, anode behaviour under various conditions is described. 

I igure 6.6 Overpotential referred to e iuilihrium (AU) determined by Nernst conditions. Reaction order m as determined for hydrogen. iiiHj, with l ny ) = 0.05 bar. at temperatures ( ) 725°C and (A) 950°C. indicates a change of limiting reaction mechanism. 

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FIGURE 2.5 Electrical conductivity versus Ni volume fraction for Ni-YSZ cermets fabricated using different starting materials, as labeled in the graph. (From Ivers-Tiffee, E. et al., Berichte der Bunsen-Gesellschaft fur Physikalische Chemie, 94 978-981, 1990. Permission pending.)... 

Grahl-Madsen L, Larsen PH, Bonanos N, Engell J, and Linderoth S. Mechanical strength and electrical conductivity of Ni-YSZ cermets fabricated by viscous processing. J Mater Sci 2006 41 1097-1107. 

Composite membranes also employ dense cermets fabricated by sintering together mixed powders of metal and ceramic [10-12], Examples include powders of Pd and its alloys sintered with powders of perovskites [11,12], niobium sintered together with AI2O3 [12], and nickel sintered with proton-conducting perovskites. Layers of dense cermets, 25-100 xm thick, are supported by porous ceramic tubes. Cermets employing chemically reactive metals, Nb, Ta, U, V, Zr, and their alloys, are typically coated with Pd and alloys thereof [11,12],... 

The principle of additive strength can be applied equally, regardless of the type of composite material. Composite materials can be broadly classified as laminates, reinforced plastics, cermets, fabrics, and filled composites. Each class of composite materials has its own particular strengths and weaknesses and its own methods of production, although there is some crossover in the areas of application. 

There are a number of informative reviews on anodes for SOFCs [1-5], providing details on processing, fabrication, characterization, and electrochemical behavior of anode materials, especially the nickel-yttria stabilized zirconia (Ni-YSZ) cermet anodes. There are also several reviews dedicated to specific topics such as oxide anode materials [6], carbon-tolerant anode materials [7-9], sulfur-tolerant anode materials [10], and the redox cycling behavior of Ni-YSZ cermet anodes [11], In this chapter, we do not attempt to offer a comprehensive survey of the literature on SOFC anode research instead, we focus primarily on some critical issues in the preparation and testing of SOFC anodes, including the processing-property relationships that are well accepted in the SOFC community as well as some apparently contradictory observations reported in the literature. We will also briefly review some recent advancement in the development of alternative anode materials for improved tolerance to sulfur poisoning and carbon deposition. 

Jiang SP, Callus PJ, and Badwal SPS. Fabrication and performance of Ni/3% mol% Y203-Zr02 cermet anodes for solid oxide fuel cells. Solid State Ionics 2000 132 1-14. 

Misono T, Murat, K, Fukui T, Chaichanawong J, Sato K, Abe H et al. Ni-SDC cermet anode fabricated from NiO-SDC composite powder for intermediate temperature SOFC. J. Power Sources 2006 157 754—757. 

While high temperatures do not severely limit fabrication of Ni—YSZ cermets, they can impact the way in which other composite electrodes are made. This is well-known for cathodes, where the most commonly used material is a composite of YSZ and Sr-doped LaMnOs (LSM). The primary reason for using LSM, rather than materials such as Sr-doped LaFeOs (LSF) or LaCoOs (LSC) that exhibit a better performance, is that LSM—YSZ mixtures can be... 

Unfortunately, it appears that this method cannot be applied to the fabrication of Cu cermets due to the low melting temperatures of CuO and CU2O. For lower sintering temperatures, it is likely that the electrolyte powder within the electrode does not become connected, either to itself or to the electrolyte. 

Another application concerning the liquid-metal-cooled fast breeder reactors (LMFBR) was studied as development of advanced control rod materials for FBR (22). Fabrication tests and out-of-pile measurements were made of B4C/Cu cermet to obtain high-performance neutron absorber materials for LMFBR. A coating layer of Cu was formed on the surface of B4C/Cu powder, and then the coated B4C... 

Medical sources are fabricated with remotely operated, specially designed machines (8). The fabrication process involves production of Pt - 10% Ir-clad wire with a californium oxide-palladium cermet core. The wire is swaged and drawn to size, cut to length, and welded in a Pt - 10% Ir capsule. Nominally, medical sources contain from 0.3 yg 252cf in an individual seed (Figure 8) to 30 yg 252cf in an applicator tube (Figure 7). 

Ni-GDC cermet not only lowered the operating temperature of SOFC but also allowed the use of CH4 as a fuel. The direct use of CH4 or hydrocarbon provides a number of significant advantages elimination of the use of reformer, improvement of the energy efficiency, and reduction in fabrication cost. Table 3 summarizes the performance of SOFC for the direct oxidation of hydrocarbon fuels. ... 

In the frame of the PACT project, irradiation of several kilograms of Np-237 to produce Pu-238 was planned for the years after 1973. A test irradiation of ca. 180 g Np-237 was initiated by the Alkem company in 1970. The neptunium was fabricated by Alkem into target rods containing pellets of a 10 % NpO -iron-cermet. The targets were irradiated in the BR-2 reactor at Mol, Belgium, for about 2 months, and were then cooled for 9 months before processing in the Milli. 

Cermets, which are mixtures of ceramic and metal powders, heat treated and compressed. (4) Fabrics, e.g., woven combinations of wool or cotton and a synthetic fiber. (5) Filled composites in which a bonding material, i.e., linseed oil, resin, or asphalt, is loaded with a filler in the form of flakes or small particles examples are linoleum, glass flake-plastic mixtures for battery cases, and asphalt-gravel road-surfacing mixtures. 

One of the objective of this research is to fabricate diamond- gradually dispersed cermets by the combination technique of SHS for short time processing and following dynamic compaction for densification. The other is to support for the fabrication by the calculation of residual stress based on graded structure of diamond in the matrix. 

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