Aging equilibrium

An understanding of the concept of secular equilibrium is also important for such age determinations using U-Th series radionuclides. Owing to the longevity of Th, and the number of parent atoms remains essentially... 

The sequence just outlined provides a salutary lesson in the nature of explanation in materials science. At first the process was a pure mystery. Then the relationship to the shape of the solid-solubility curve was uncovered that was a partial explanation. Next it was found that the microstructural process that leads to age-hardening involves a succession of intermediate phases, none of them in equilibrium (a very common situation in materials science as we now know). An understanding of how these intermediate phases interact with dislocations was a further stage in explanation. Then came an nnderstanding of the shape of the GP zones (planar in some alloys, globniar in others). Next, the kinetics of the hardening needed to be... 

Nowick (1996) has outlined the researches done on crystal defects during the period 1949-1959 and called this the "golden age of crystal defects . A recent, very substantial overview (Kraftmakher 1998) admirably surveys the linkage between vacancies in equilibrium and thermophysical properties of metals this paper includes a historical table of 32 key papers, on a wide range of themes and techniques, 1926-1992. 

The calculated results are demonstrated in Figs. 7a and 7b [25, 33). The system maintained at T—1.85 is subject to down quenching with a temperature step AT = 0.05 and isothermal aging is followed at each temperature to equilibrate the system. After reaching the equilibrium at T =1.5, the operation is reversed up to T =1.85. In Fig. 7a, one sees that the resultant relaxation time is shortened with decreasing temperature and... 

Another problem associated with sodium appears in the form of sodium chloride. Chlorides tend to reactivate aged metals by redistributing the metals on the equilibrium catalyst and allowing them to cause more damage. 

Bone maintenance during adulthood is dependent on the equilibrium between bone formation by osteoblast cells and bone resorption by osteoclast cells. Bone loss with age is linked to increased osteoclast activity compared to... 

Figure 6. Schematic representation of the model used by Williams et al. (1986) to calculate the age of the Oldoinyo Lengai (Tanzania) caibonatite magma. The model assumes an instantaneous Ra-Th fractionation produced by the exsolution of a carbonatite melt from a nephelinite parental magma in radioactive equilibrium for both Ra-Th pairs. The existence of Ra- Th disequihbria indicates that the fractionation occurred shortly before eruption, and thus the ( Tla/ °Th) ratios have not significantly changed since the exsolution. By assuming the same Ra-Th fractionation for both pairs, the ( Ra/ °Th) in the carbonatite gives the ( Ra/ h) ratio just after the exsolution, and its age can then be calculated from the equation ...

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