Cermet films

Another example of the use of HFFMR was a study of granular cermet films, (Fe5oCo5o)x-(Al203)i-x, that are also of interest for data storage. The original measurements at X-band found that the concentration dependence of the effective anisotropy field deviated from the solid solution law. Experiments at 94 GHz showed that this was shown an artefact, due to the low field for resonance at X-band. At 94 GHz the relationship between anisotropy and composition was found98 to be linear for all x. 

Granqvist, C.G., Hunderi. O. Conductivity of inhomogeneous materials Effective-medium theory with dipole-dipole interaction. Phys. Rev. B 18, 1554-1561 (1978) Optical properties of Ag-SiO2 cermet films A comparison of effective-medium theories. Phys. Rev. B 18, 2897-2906 (1978)... 

Although this work only evaluated the performance of the anode electrode, a complete fuel cell is envisioned that would be cofired into the LTCC, consisting of the required cavities for fuel storage, channels, and wick structures for fuel deliver, a porous Ag structure for the electrodes, separated by a cavity with nanoporous surfaces that will allow the PEM organics to be added after firing and polymerized in situ. This work only considers the development of the porous cermet films for the Ag-based anode structure. 

Cermet thick-fihn materials, a combination of glass ceramic and metal (hence the name cermet). Cermet films are designed to be fired in the range 850 1000°C. 

Cermets. Resistor films of this type are usually either mixtures of precious metals (e.g., Ag or Au) and glass frit or mixtures of PdO and glass frit. Cermet resistive inks are made by mixing a cermet powder with an organic vehicle of suitable viscosity. This mixture can be screened onto a substrate and cured by firing. Resistor films are typically 0.25 to 2.0 mils thick, and usually they do not require an overglaze for protection. Cermet films are sufficiently hard and abrasion resistant to be used as slide resistors in potentiometers. Since thick cermet films are not very sensitive to substrate surface roughness, special surface preparation usually are not necessary. 

The resistance of a cermet film is determined by the metal-to-glass ratio. For example, the resistance of lead-borosilicate glass and either Ag or Au changes by five orders of magnitude with a few percent change in metal content (see Fig. 2.56), whereas either Pd or Pd -I-Ag glass mixtures are much less sensitive therefore, they are more easily reproduced on a production basis. The addition of silver to palladium improves the temperature coefficient of resistance and decreases the electrical noise and resistivity of the films (see Table 2.23). 

The conductivity mechanism in cermet films is not well understood however, the available evidence indicates that conduction occurs hy chains or networks of touching conductive particles embedded in an insulating matrix. In these films, the temperature coefficient of resistance varies from negative at low temperatures to positive at high temperatures. 

In this section the attention of the reader is called to some particular problems the surface analyst may encounter in analyzing thin surface films treated by various particle beams, essentially in the sputtering regime (from I to 5 keV). In the following subsections some representative studies will be presented in which it is demonstrated how the effects of particle bombardment on surface chemistry can be evaluated, mainly by XPS, for various inorganic compounds (e.g., TiN layers, metal oxides, Cr-O-Si cermet films) and polymeric materials (e.g., polysulfone, polyimide and poly(organosiloxanes)). 

For ceramic resistor use, cermet and Ta2N films have been used since the time of the early hybrid integrated circuits (ICs). A cermet film is produced by mixing a metal and ceramic, for instance, Cr-SiO, Cr-MgFj, and Au-SiO. The Cr-SiO (SiO 25-90%) film is generally used because of its stable properties and its specific resistance of 3.1 X 10 to 4.3 X 10 Q cm. 

Cermet or carbon friction matenals operate at substantially higher temperatures than the normal automotive or tmck materials. Still the wear rates of these materials increase with the brake temperature. One unique feature of these materials is the formation of a glazed friction film at high temperatures that reduces the wear rate and stabilizes the friction level. Without this glazed layer the wear rate is usually very high. 

I.V. Yentekakis, Y. Jiang, S. Neophytides, S. Bebelis, and C.G. Vayenas, Catalysis, Electrocatalysis and Electrochemical Promotion of the Steam Reforming of Methane over Ni Film and Ni-YSZ cermet Anodes, Ionics 1, 491-498 (1995). 

Silver films and Ag-CaO-SragOg cermets were chosen as the anodic electrocatalysts because of their high electrical conductivity, which is necessary for electrocatalytic operation, and also because of their high (>95%) selectivity to Cg hydrocarbons at very low (<2%) CH conversions [9]. 

Ni-YSZ cermets deposited by RF sputtering (230 nm) were found to have micro-structural features consisting of columnar grains 13 to 75 nm long and 9 to 22 nm wide, and showed good adhesion to the YSZ layer on which they were deposited [128], In a three-layer Ni-YSZ-Ni film deposited on NiO by RF sputtering in another study, the YSZ layer exhibited a columnar structure with some pinholes [129], Microstructural and electrochemical features of Pt electrodes patterned by lithography on YSZ have also been studied [130,131]. 

The multilayer sensor structure consists of cermet and polymer based layers sequentially deposited on a 96% alumina ceramic substrate using a thick film screen printing process. The cermet layers are of ceramic-metal composition which require firing at a temperature of 850°C and the polymer layers are cured at temperatures below 100°C. Layout of this multilayer sensor structure is shown in Figure 1. 

The heart of this system is an yttria-stabilized zirconia, Zr(Y)0 film, which acts as a solid electrolyte, allowing high conductivity for 0 ions at about 1,000°C. The fuel electrode is a porous Ni/ZrO cermet, which serves both as the electrocatalyst and as the current collector. Actually, electrocalalysis is no longer a problem at such elevated temperatures, and different fuels, including H, regular fossil fuels, and even CO, can be used. The air (oxygen) electrode is a... 

Use Additive (with tungsten carbide) in making cutting tools and other parts subjected to thermal shock, arc-melting electrodes, cermets, coating dies for metal extrusion (0.2 mil film by vapor deposition). 

Theoretical modeling of porous cermets can be ascribed to two general approaches simulating random packing of particles (Monte Carlo simulations) and via macroscopic averaged models in terms of corrugated layers covered by a thin electrolyte film or vice versa (Sunde, 1997). 

In thick-film technology (layer thickness > 1 pm), roll or tampon printing methods well known in the porcelain industry are suitable for applying layers of defined geometry on the green ceramic. The thickness is controlled by precise adjustment of the paste viscosity and solid content. To provide an adequate three-phase boundary, zirconia is added to the platinum to form a cermet (ceramic-metal compound). 

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