Material instability

Gurtin, M.E. (ed.) (1984) Phase Transformations and Material Instabilities in Solids (Academic Press, Orlando) (Proceedings of a conference eonducted by the Mathematics Research Center, University of Wisconsin). 

These examples illustrate that, for many materials, the water content can be relatively high without leading to any material instability dmring shelf life, which depends on the water-bonding capacity of the material. When water is strongly retained, the water activity and thus the amount of free water will be low. It must be mentioned that this is quite contradictory to some former and still presently reported assumptions that the water content of CRMs should generally not exceed a rather low value, e.g. around 3 % for long-term stability of RMs. 

Apart from liquid-liquid transitions, liquid-vapor transitions in aqueous electrolyte solutions have played a crucial role in debates on ionic criticality [142-144], The liquid-vapor transition is usually associated with a mechanical instability with diverging density fluctuations, while liquid-liquid transitions are associated with a material instability with diverging concentration fluctuations. This requires, however, that both regimes are well-separated. Their interference can lead to complex phase behavior with continuous transitions from liquid-liquid demixing to liquid-gas condensation [9, 145, 146]. It is then not trivial to define the order parameter [147-149]. 

For applications in the thermistor area, one can point out the broad range of / values as well as the high values of aT obtainable with a-Si H. On the other hand, the many problems related to material instabilities, aging of the structure, and intrinsic and excess 1//noise should not be underestimated. The removal of these drawbacks is of primary importance in determining the industrial interest of thermistors made of a-Si H. 

The two systems containing potassium nitrate and ammonium sulfate each have a region of partial miscibility. Adding a third constant to the Wilson equation allows correlation of such systems. The results are shown in Table II and Figure 2. (The broken line of Figure 2 is a feature of systems which show material instability. A graph of molar free energy... 

In addition to these impediments to rheological measurements, some complex fluids exhibit wall slip, yield, or a material instability, so that the actual fluid deformation fails to comply with the intended one. A material instability is distinguished from a hydrodynamic instability in that the former can in principle be predicted from the constitutive relationship for the material alone, while prediction of a flow instability requires a mathematical analysis that involves not only the constitutive equation, but also the equations of motion (i.e., momentum and mass conservation). 

Doi and Edwards 1979). The predicted shear thinning is so severe that as the shear rate increases, the shear stress r y is pre,dicted to pass through a maximum and then decrease. with further increases in y (see Fig. 3-33). Hence, at each shear stress there are at least two values of the shear rate. This, it is predicted, should lead to material instabilities—that is, apparent slip phenomena, such as spurt, sometimes observed in flow through capillaries (see Section 3.7.5.3). 

Experimentally, melts of low polydispersity that do not overtly spurt, slip, or succumb to other material instabilities will typically show steeply decreasing values of the viscosity and first normal stress coefficient in the shear-thinning region. Menezes and Graessley (1980) reported that t] oc y ° y i- at large y. These dependencies... 

Theories for material instabilities or slip in highly entangled melts and solutions are still under active development. 

Ghoniem N. M., Computational Methods for Mesoscopic, Inhomogeneous Plastic Deformation, to appear in Proceedings of the Latin American Summer School on Materials Instabilities,... 

Slemrod, M. Dynamics of first order phase transitions. In Phase Transformations and Material Instabilities in Solids, ed. M. Gurtin, Academic Press New York (1984) 163-203. 

The ultimate goal is a reversible bottom-up, top-down approach, based on first principles QM, to characterize properties of materials and processes at a hierarchy of length and timescales. This will improve our ability to design, analyze, and interpret experimental results, perform model-based prediction of phenomena, and to control precisely the multi-scale nature of material systems for multiple applications. Such an approach is now enabling us to study problems once thought to be intractable, including reactive turbulent flows, composite material instabilities,... 

Unfortunately, owing to experimental difficulties, interfacial measurements in molten salts often need to be made at solid metal substrates, and these give rather less reliable results.For example, the agreement between the reported values of the minimum capacitance for both solid and liquid metals tends to be quite poor. This may be ascribed to melt impurities, especially water and, at the higher temperatures, spurious parallel components arising from materials instabilities. However, progress has been achieved in a number of experimentally difficult situations, notably in the alumina-cryolite melt system which is so important in aluminum production. 

It is worth noting that both Pd-aUoy and sUica-based membranes present some problem about material instability in the WGS environment. The Pd-aUoy membranes can be negatively affected by surface carbonization, sulfur poisoning, and hydrothermal embrittlement, whereas the amorphous silica-based membranes can show some degradation caused by the condensation reaction of sUanol in hydrothermal conditions (Tang et al., 2010). In particular, the siliceous MFI-type zeolite membranes, constituted by a crystalline microporous zeolite membrane, in recent years have been seen as attractive candidates for the WGS reaction because of the high-temperature hydrogen separation and for their intrinsic sulfur tolerance and hydrothermal stability. 

Another cause of material instability in MLBs is the excessive material movement that occurs if the laminating temperature exceeds the glass transition temperature Tg of the laminate resin. On the other hand, if the laminating temperature remains below the Tg of the resin, there is minimal dimensional variation of the base material, as the resin is still in its linear expansion phase. This explains the need for use of high-T resins in the PWB industry. 

Dewell, G. and Borckmans, R, in Pattern Defects and Materials Instabilities, edited by D. Walgraef and N. Ghoniem (Kluwer Academic Publishers, Hingham, MA, 1990). 

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