Structure metallic glasses

Applications of epoxy-polysulfide adhesives primarily include structural assemblies requiring some degree of resilience. Epoxy-poly sulfides are used in bonding concrete for floors, airport runways, bridges and other concrete structures, metals, glass and ceramics, wood, rubber, and some plastics. They are particularly durable in outdoor applications where temperature extremes (freeze-thaw cycles) will be encountered. Epoxy-poly sulfides can be heavily filled without adversely affecting their properties. 

Fig. 1. Structures of (O) atoms and corresponding electron and x-ray diffraction patterns for (a) a periodic arrangement exhibiting translational symmetry where the bright dots and sharp peaks prove the periodic symmetry of the atoms by satisfying the Bragg condition, and (b) in a metallic glass where the atoms are nonperiodic and have no translational symmetry. The result of this stmcture is that the diffraction is diffuse.

Phenolic-neoprene contact cements are used for structural metal-metal bonding. especially where fatigue resistance and low temperature performance are important [209]. They are also used for bonding textiles, wood, rubbers, plastics, ceramics, and glass to metal and to one another. Solvent toxicity and flammability has greatly reduced the use of contact cements in the wood products industry. Water-based contact cements persist, but generally do not perform as well as the solvent systems, thus allowing market erosion by alternative binders. 

Avoiding structural failure can depend in part on the ability to predict performance for all types of materials (plastics, metals, glass, and so on). When required designers have developed sophisticated computer methods for calculating stresses in complex structures using different materials. These computational methods have replaced the oversimplified models of materials behavior relied in the past. The result is early comprehensive analysis of the effects of temperature, loading rate, environment, and material defects on structural reliability. 

Metallic glasses are alloys that have been cooled so rapidly that no crystal structure has had time to develop, for example, Pd-Si, Pd-Ge, Fe-Ge (Metglas). These materials are characterized by the absence of sharp lines in their X-ray spectra. 

The hardness shear modulus ratio in this case is similar to the one for metallic glasses. This suggests that the structure in the KCl-KBr solid solution is highly disordered i.e., glassy. 

Crystal approximants. Several crystalline phases contain more or less closely packed atomic assemblies (polyhedra, clusters) which have been considered fundamental constituents of several quasicrystals, metal glasses and liquids. Such crystalline phases (crystal approximants), as reported in the previous paragraph, are often observed in the same (or similar) systems, as those corresponding to the formation of quasicrystals and under similar preparation conditions. Crystalline phases closely related to the quasicrystals (containing similar building blocks) have generally complex structures as approximants to the ico-quasicrystals we may, for instance, mention the Frank-Kasper phases (previously described in 3.9.3.1). 

Newtonian Viscosity in Glasses. As we saw in Chapter 1, the structure of glasses is fundamentally different from metals. Unlike metals and alloys, which can be modeled as hard spheres, the structural unit in most oxide glasses is a polyhedron, often a tetrahedron. As a result, the response of a structural unit to a shear force is necessarily different in molten glasses than in molten metals. The response is also generally more complicated, such that theoretical descriptions of viscosity must give way completely to empirical expressions. Let us briefly explore how this is so. 

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