Oriented precipitation

Figure 5.16. Difference in step patterns for the case in which (a) foreign particles or the same crystal particles with different orientation precipitate on a growing surface, and (b) in which the same crystal particles precipitate in the same orientation. The shaded side indicates the higher side of the steps, (c) Actual example of cases shown in (a) and (b), observed on a (0001) face of hematite.

It should be noted first that the mechanical properties of refractory metals and alloys are sensitive to minor impurities, such as O, C, and N levels, grain size and orientation, precipitates, dislocations, and other microstructural parameters. Moreover, impurity levels and microstractural states may change during high-temperature testing, which also influence the properties. Comparison of the mechanical properties is made in this section based on literature data, in which, however, details of the materials and testing information are unavailable in most cases. 

Dahmen U 1982 Orientation relationships in precipitation systems Acfa Metall. 30 63... 

Phenolics. PVP readily complexes phenolics of all types to some degree, the actual extent depending on stmctural features such as number and orientation of hydroxyls and electron density of the associated aromatic system. A model has been proposed (102). Complexation with phenoHcs can result in reduced PVP viscosity and even polymer-complex precipitation (103). 

Theories of the oxidation of tantalum in the presence of suboxide have been developed by Stringer. By means of single-crystal studies he has been able to show that a rate anisotropy stems from the orientation of the suboxide which is precipitated in the form of thin plates. Their influence on the oxidation rate is least when they lie parallel to the metal interface, since the stresses set up by their oxidation to the pentoxide are most easily accommodated. By contrast, when the plates are at 45° to the surface, complex stresses are established which create characteristic chevron markings and cracks in the oxide. The cracks in this case follow lines of pores generated by oxidation of the plates. This behaviour is also found with niobium, but surprisingly, these pores are not formed when Ta-Nb alloys are oxidised, and the rate anisotropy disappears. However, the rate remains linear it seems that this is another case in which molecular oxygen travels by sub-microscopic routes. 

Chitosan scaffolds were reinforced with beta-tricalciiun phosphate and calcium phosphate invert glass [177]. Along the same line, composites of Loligo beta-chitin with octacalcium phosphate or hydroxyapatite were prepared by precipitation of the mineral into a chitin scaffold by means of a double diffusion system. The octacalciiun phosphate crystals with the usual form of 001 blades grew inside chitin layers preferentially oriented with the 100 faces parallel to the surface of the squid pen and were more stable to hy-... 

Previously, we have proposed that SFG intensity due to interfacial water at quartz/ water interfaces reflects the number of oriented water molecules within the electric double layer and, in turn, the double layer thickness based on the p H dependence of the SFG intensity [10] and a linear relation between the SFG intensity and (ionic strength) [12]. In the case of the Pt/electrolyte solution interface the drop in the potential profile in the vicinity ofelectrode become precipitous as the electrode becomes more highly charged. Thus, the ordered water layer in the vicinity of the electrode surface becomes thiimer as the electrode is more highly charged. Since the number of ordered water molecules becomes smaller, the SFG intensity should become weaker at potentials away from the pzc. This is contrary to the experimental result. 

In places where the orientation of the boundary changed, small precipitates were observed. Their EELS spectrum (Figure 5.45) showed that they had a composition corresponding to the NiMo-8 phase. 

The shaking of protein solutions may lead to aggregation and precipitation as a result of several mechanisms, such as air oxidation, denaturation at the interface, adsorption to the vessel, or mechanical stress. These possibilities were systematically examined for solutions of human fibroblast interferon [50]. In this example, mechanical stress was identified as the causative factor in the inactivation. The proposed mechanism of inactivation by mechanical stress was through orientation of the asymmetrical protein in the... 

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