Recrystallization and crystal growth

The properties described above have important consequences for the way in which these skeletal tissues are subsequently preserved, and hence their usefulness or otherwise as recorders of dietary signals. Several points from the discussion above are relevant here. It is useful to ask what are the most important mechanisms or routes for change in buried bones and teeth One could divide these processes into those with simple addition of new non-apatitic material (various minerals such as pyrites, silicates and simple carbonates) in pores and spaces (Hassan and Ortner 1977), and those related to change within the apatite crystals, usually in the form of recrystallization and crystal growth. The first kind of process has severe implications for alteration of bone and dentine, partly because they are porous materials with high surface area initially and because the approximately 20-30% by volume occupied by collagen is subsequently lost by hydrolysis and/or consumption by bacteria and the void filled by new minerals. Enamel is much denser and contains no pores or Haversian canals and there is very, little organic material to lose and replace with extraneous material. Cracks are the only interstices available for deposition of material. 

LR Fleischer, JM Tobin. Growth of transition metal carbide single crystals by recrystallization n. Transition metal carbide recrystallization and crystal growth. J Cryst Growth 8 243, 1971. 

It was proposed to use the thermodynamics of small systems and Avrami equations to describe the formation processes of carbon nanostmctures during recrystallization (graphitization) [6, 7]. These equatiorrs are successfully applied [8] to forecast permolecular stmctures and prognosticate the conditions on the level of parameters resulting in the obtaining of nanostmctures of definite size and shape. The equation was also used to forecast the formation of fibers [9]. The application of Avrami equations in the processes of nanostmcture formation a) embryo formation and crystal growth in polymers [8... 

A solution containing 105.0 g (31 mmol) of tetrabutylammonium hydrogen sulfate (recrystallized once from acetone) in 150 mL of triply distilled water is placed in a plastic beaker (500 mL) and placed in an ice th to cool. Then a solution of 95% HFSO3 (18.8 mL, 31 mmol) (Aldrich) is added dropwise with stirring. A white precipitate immediately forms. This precipitate is filtered and washed with copious amounts of ice-cold triply distilled water until the wash solution shows pH near 7.0. The precipitate is then dried and twice recrystallized from ethyl acetate to yield 9 g (8% of theoretical yield) of colorless, platelike crystals of very pure [CH3(CH2)3]4NFS03 (mp = 179-180°C). A neutral salt of very high purity is essential for any electrocrystallization portions of this synthesis, otherwise spurious reactions occur and crystal growth fails. 

Many phase transformations such as nucleation and crystal growth from a melt, solid-state recrystallization during annealing, austenitic to ferritic transformation in steels, etc. are stochastic events because they involve either liquid- or solid-phase nucleation and therefore must be treated in terms of probabilities as done in Chapter 11. Let Vq be the total volume of the material, Vj be the volume of the transformed material, and Vu be the volume of material that has not yet been transformed. Recall from Poisson statistics that the probability of no events occurring in a given time is exp (expected number of events in that time). In this case the expected volume to be transformed is kt" where k and n may be specified by models of the transformation mechanism or may be determined empirically. Therefore, the fraction of trarrsformed matter at time t can be written as... 

The habit of pharmaceutical compounds has been used for purposes of identification, although the method can only be reliably used when the crystallization solvent used to generate the test crystals is carefully controlled. Since the faces of a crystal must reflect the internal structure of the solid, the angles between any two faces of a crystal will remain the same even if the crystal growth is accelerated or retarded in one direction or another. Toxicologists have made extensive use of microscopy following multiple recrystallization, and they have developed useful methods for compound identification [5]. 

The growth kinetics describes the nucleation processes on the atomic scale. Thermally activated processes as adsorption, desorption, and diffusion at the surface and in the volume, nucleation, and crystallization/ recrystallization determine the film structure and can be controlled by the substrate temperature and the growth rate. Using a diagram ln(J ) over 1/ T, R being the deposition rate and T the growth temperature, three different growth modes (epitaxial, polycrystalline, and amorphous) can be... 

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