Thin mechanical stress

Fligh-tech ceramics withstand great mechanical stresses even thin structures and sharp edges are feasible with high reliability. This allows connecting the HT cables reliably to the ceramic part of the tubes directly. Many available resin systems bond easily to ceramics. 

Film Adhesion. The adhesion of an inorganic thin film to a surface depends on the deformation and fracture modes associated with the failure (4). The strength of the adhesion depends on the mechanical properties of the substrate surface, fracture toughness of the interfacial material, and the appHed stress. Adhesion failure can occur owiag to mechanical stressing, corrosion, or diffusion of interfacial species away from the interface. The failure can be exacerbated by residual stresses in the film, a low fracture toughness of the interfacial material, or the chemical and thermal environment or species in the substrate, such as gases, that can diffuse to the interface. 

If the gas diffusion between bubbles is reduced, the collapse of the bubbles is delayed by retarding the bubble size changes and the resulting mechanical stresses. Therefore single films can persist longer than the corresponding foams. However, this effect is of minor importance in practical situations. Electric effects, such as double layers, form opposite surfaces of importance only for extremely thin films (less than 10 nm). In particular, they occur with ionic surfactants. 

Because of its piezoelectric properties, synthetic CC-quartz is used for frequency control in electrical oscillators and filters and in electromechanical transducers. When mechanically stressed in the correct direction, CC-quartz develops an electric polarization. The opposite is also tme an applied electric field gives rise to a mechanical distortion in the crystal. Thin sections of quartz are cut to dimensions that produce the desired resonance frequency when subjected to an alternating electric field the vibrating crystal then reacts with the driving circuit to produce an oscillation that can be narrowly controlled. Quartz is ideal for this application because it is hard, durable, readily synthesized, and can be tuned to high accuracy, for example, quartz crystal clocks can be made that are stable to one part in 109. 

Molina-Aldareguia, J.M., Lloyd, S.J., Barber, Z.H., Blamire, M.G. and Clegg, WJ. (2000), In Materials Research Society Symposium Proceedings Thin Film Stresses and Mechanical Properties VIII, Vol. 594 (ed. Vinci, R., Kraft, O., Moody, N., Besser, P. and Shaffer, E. II), Materials Research Society, Boston, MA, pp. 9-14. 

As already pointed out earlier, in most cases the formation of chemical compounds is accompanied by considerable changes of the volume of reaction couples. Figure 1.8 represents the case where the layer occurrence reduces the total volume of the A-ApBq-B reaction system. This causes the displacement of that part of the specimen, where initial substances interact, relative to the other where they do not react with each other. A thin cut made throughout the entire depth of the specimen almost up to its ends makes it possible to reduce the mechanical stresses between the comparison and measurement parts. 

For transmission measurements, samples are typically pressed into thin wafers, whereas for measurements in diffuse reflection powders are used. To suppress regular reflection and particularly to work in a range in which F(p) is proportional to the concentration, samples often have to be diluted. The diluent should be a nonabsorbing standard that does not interact with the sample, and the mixing procedure should be nondestructive (some samples are sensitive to mechanical stress (Section 2.4)). 

The first mechanical problems of a fundamental nature may occur as soon as the thin film is deposited on the substrate, even before any further processing (as engraving for films intended for microelectronics). The film is far less rigid than the substrate at this point. In the absence of any external mechanical stress, the elastic interaction between film and substrate generates mechanical stresses. These are commonly referred to as internal stresses or residual stresses . The latter expression will be adopted in this chapter. The deposited film is thin and homogeneous, and the residual stresses are considered to be flat and constant through the thickness of the film. 

J.N. Glosli, J. Belak, and M.R. Philpott, in Thin Films Stresses and Mechanical Properties VI, eds. W.W. Gerberich, H. Gao, J.-E. Sundgren, and S.P. Baker, Materials Research Society Proceedings V436, Pittsburg (1996). 

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