Metal-ceramic interactions

Very little is known theoretically about the metal-oxide interface although a rather limited number of first principles theoretical studies have dealt with the general problem of metal-ceramic interaction. The aim of this section is to discuss some fundamental aspects of the bonding of metal clusters deposited on the surface of simple binary oxides, in particular MgO and AI2O3. 

Kingery, W. D., Metal-ceramic interactions IV, Absolute measurements of metal-ceramic interfacial energies, J. Am. Ceram. Soc., 37, 42-45, 1954. 

In many catalytic systems, nanoscopic metallic particles are dispersed on ceramic supports and exhibit different stmctures and properties from bulk due to size effect and metal support interaction etc. For very small metal particles, particle size may influence both geometric and electronic structures. For example, gold particles may undergo a metal-semiconductor transition at the size of about 3.5 nm and become active in CO oxidation [10]. Lattice contractions have been observed in metals such as Pt and Pd, when the particle size is smaller than 2-3 nm [11, 12]. Metal support interaction may have drastic effects on the chemisorptive properties of the metal phase [13-15]. Therefore the stmctural features such as particles size and shape, surface stmcture and configuration of metal-substrate interface are of great importance since these features influence the electronic stmctures and hence the catalytic activities. Particle shapes and size distributions of supported metal catalysts were extensively studied by TEM [16-19]. Surface stmctures such as facets and steps were observed by high-resolution surface profile imaging [20-23]. Metal support interaction and other behaviours under various environments were discussed at atomic scale based on the relevant stmctural information accessible by means of TEM [24-29]. 

Metal-ceramic interface interactions wetting and interfacial energies... 

The phenomena which occur in metal-ceramic interface interactions are of great importance in catalysis. There are two types of interactions those which depend on the epitaxy between the metal and the support and those which are independent of it. Strong metal-support interactions are described by the term SMSI. 

In the following example, we examine the role of different gases and metal-support interactions in metal-particle catalysts supported on the so-called nonwetting or irreducible ceramic oxides by dynamic EM. The direct observations provide powerful insights into the role of gas environments in catalytic reactions and in the regeneration of supported metallic catalyst particles. 

In situ ETEM permits direct probing of particle sintering mechanisms and the effect of gas environments on supported metal-particle catalysts under reaction conditions. Here we present some examples of metals supported on non-wetting or irreducible ceramic supports, such as alumina and silica. The experiments are important in understanding metal-support interactions on irreducibe ceramics. 

Theoretical methods offer the opportunity to explore structure-property relationships in ideal metal-ceramic interfaces. Ultimately, improved understanding of the causal sequence leading to a particular interface structure and set of properties would enable further optimization of manufacturing parameters. Atomistic modeling constitutes the perfect laboratory in this respect. Within the limits of the specific approximations used for interatomic interactions, physical properties may be resolved to arbitrary accuracy and competing effects may be separated. 

Kinetic Monte Carlo and hyperdynamics methods have yet to be applied to processes involved in thermal barrier coating failure or even simpler model metal-ceramic or ceramic-ceramic interface degradation as a function of time. A hindrance to their application is lack of a clear consensus on how to describe the interatomic interactions by an analytic potential function. If instead, for lack of an analytic potential, one must resort to full-blown density functional theory to calculate the interatomic forces, this will become the bottleneck that will limit the size and complexity of systems one may examine, even with multiscale methods. 

The basic requirement in biosensor development is ascribed to the successful attachment of the recognition material, a process governed by various interactions between the biological component and the sensor interface. Advanced immobilization technologies capable of depositing biologically active material onto or in close proximity of the transducer surface have been reported. In this context, the choice of a biocompatible electrode material is essential. The material surfaces (support) include almost all material tjrpes metals, ceramics, polymers, composites and carbon materials [8]. In most cases, when a native material does not meet all the requirements for... 

The analytical requirements in IC processing equal or surpass those of any other industry and present a formidable problem to the analyst. The fabrication of a semiconductor device Involves interaction of materials, processes and environment to produce a complex, geometrical configuration of many materials. When processed through to the package level a typical IC is a composite of semiconductors, metals, ceramics and polymers containing over a dozen distinct materials. 

The morphology of the metal-ceramic interface depends upon the type of interaction that has occurred. If only physical interaction has occurred, the structure of the metal and ceramic is unchanged. However, if a chanical reaction occurs, the morphology is affected depending upon whether solid-solid or solid-liquid reactions occur and if new interfacial phases are formed. The formation of new interfacial phases alters not only the microstructure but also the physical and mechanical properties. These interfacial phases or reaction product layers are a consequence of the reactions needed to cause wetting of the ceramic. One can consider the reaction product layers as chemical bridges between the metal and ceramic. 

Hierarchy can be described in analogy to rope (stretched polymer molecules in domains that make up nanofibers, combined to microwhiskers, bundled into fibers that are spun into yarn that is twined to make up the rope). Wood and tendon are biological examples that have six or more hierarchical levels. Compared to these, fiber-reinforced matrix composites made up of simple massive fibers embedded in a metallic, ceramic, or polymer matrix are primitive. Hierarchical inorganic materials, as discussed in Chapter 7, can be made with processes for fractal-like solid products spinodal decomposition, diffusion-limited growth, particle precipitation from the vapor, and percolation. Fractal-like solids have holes and clusters of all sizes and are therefore hierarchical if the interactions... 

Because the AMB process uses copper sheets as the metallization, the electrical and thermal performances are identical to that of DEC. It should be noted that the ceramic interaction with the active metal in the braze material has a high thermal conductivity and can be neglected in most thermal analyses. 

From the materials point of view, many stacks consist of ceramics and metals. Ceramics may exhibit oxygen nonstoichiometry and change their volume in a complicated manner as functions of temperature and pressure. On the other hand, metals and alloys can be deformed under stresses/loads. When those two materials are utilized tmder a long-term operation at constant temperature or under frequent thermal cycles, mechanical interactions between two materials become important... 

---