Nucleation, crystal fundamentals

I. V. Markov, Crystal Growth for Beginners Fundamentals of Nucleation, Crystal Growth and Epitaxy (World Scientific, Singapore, 1994). 

Markov, I.V., Crystal growth for beginners Fundamentals of nucleation, crystal growth, and epitaxy. World Scientific, Singapore, 1995. 

The study of nucleation is fundamental to the understanding of crystallization. Heterogeneous and homogeneous nucleation, are terms proposed [5] to differentiate nucleation within a receptive and an inert environment. In the context of electrocrystallization, the terms can be apphed to phase formation at preferred sites on the electrode surface and phase formation at surfaces without such sites, respectively. Figure 3.1 [6] illustrates heterogeneous nucleation and shows a scanning electron microscopy (SEM) image of the nuclei of nickel formed on a scratched surface, and on indents. 

To further improve performances, nanometric fillers are widely investigated for embedding in the polymeric matrix. Especially in foams, they can improve cell nucleation, crystallization kinetics, and elongational viscosity (fundamental for the production of a fine cellular structure). 

Polymer crystallization is of great theoretical and practical significance and an extensive literature has been published that spans many decades. Some of the classic textbooks that have reviewed fundamental aspects of polymer crystallization are those by Wunderlich [1-3], Mandelkern [4,5], Schultz [6], Gedde [7], and Hiemenz and Lodge [8]. More specialized books review recent literature highlight controversies on polymer nucleation, crystallization theories, and simulation and also present new experimental results on multiphasic materials [9-13]. 

As has already been noted, polymerization is a common output of high-pressure reactions. The kinetics of solid-state pressure-induced polymerizations have been treated within the nuclei growth [see eq. (17)] model. These reactions, as we will discuss in Section IV, are a typical example of how the crystal structure plays a fundamental role in sohd-state chemistry. Kinetic data of polymerizations are usually analyzed according to Eq. (17) by inserting an additional parameter fo accounting for the nucleation step ... 

Batch crystallizers are often used in situations in which production quantities are small or special handling of the chemicals is required. In the manufacture of speciality chemicals, for example, it is economically beneficial to perform the crystallization stage in some optimal manner. In order to design an optimal control strategy to maximize crystallizer performance, a dynamic model that can accurately simulate crystallizer behavior is required. Unfortunately, the precise details of crystallization growth and nucleation rates are unknown. This lack of fundamental knowledge suggests that a reliable method of model identification is needed. 

Etherton studied the growth and nucleation kinetics of gypsum crystallization from simulated stack gas liquor using a one-liter seeded mininucleator with a Mixed Suspension Mixed Product Removal (MSMPR) configuration for the fines created by the retained parent seed. The effect of pH and chemical additives on crystallization kinetics of gypsum was measured. This early fundamental study has been the basis for later CSD studies. 

Crystal stmcture prediction by computer has made great steps forward in the last 10 years, with progress toward consistent success in blindfold tests. Fundamental uncertainties still remain, due to the unknown role of nucleation kinetics and to the neglect of temperature effects in the calculations. Success or failure still depends to some extent on hardly predictable factors and on the extent to which the experimental polymorph screening has been carried out. Presently, some of the best computational tools are not yet available to the general community of solid state scientists, being implemented in commercial, strictly copyrighted software. 

Nucleation and Growth (Round 1). Phase transformations, such as the solidification of a solid from a liquid phase, or the transformation of one solid crystal form to another (remember allotropy ), are important for many industrial processes. We have investigated the thermodynamics that lead to phase stability and the establishment of equilibrium between phases in Chapter 2, but we now turn our attention toward determining what factors influence the rate at which transformations occur. In this section, we will simply look at the phase transformation kinetics from an overall rate standpoint. In Section 3.2.1, we will look at the fundamental principles involved in creating ordered, solid particles from a disordered, solid phase, termed crystallization or devitrification. 

The basic science behind nucleation and forces between materials have been treated in Chapter 1. For those interested in this section, it is assumed that this basic science is (more or less, at least) understood. However, the basics treated in Chapter 1, while important to an understanding of film (as opposed to isolated crystal) formation, are not enongh by themselves to provide a phenomenological explanation of film formation. We would ideally like to be able to predict in advance, from fundamental principles, whether a particular bath formulation will result in adherent films or not. We cannot However, if we cannot reliably predict adhesion, we can at least choose conditions so that the probability of adhesion is good. 

At the most fundamental level, monolayers of surfactants at an air-liquid interface serve as model systems to examine condensed matter phenomena. As we see briefly in Section 7.4, a rich variety of phases and structures occurs in such films, and phenomena such as nucleation, dendritic growth, and crystallization can be studied by a number of methods. Moreover, monolayers and bilayers of lipids can be used to model biological membranes and to produce vesicles and liposomes for potential applications in artificial blood substitutes and drug delivery systems (see, for example, Vignette 1.3 on liposomes in Chapter 1). 

Boistelle, R. 1988. Fundamentals of nucleation and crystal growth. In Crystallization and Polymorphism of Fats and Fatty Acids (N. Garti, K. Sato, eds.), pp. 189-226, Marcel Dekker Inc., New York. 

He started to work at the Chemical Faculty of Sofia University where he became a professor and the head of the Department of Physical Chemistry, in 1947. Kaishev founded the Institute of Physical Chemistry of the Bulgarian Academy of Sciences in 1958, and helped to establish the Central Laboratory of Electrochemical Power Sources [i]. Kaishev started to collaborate with - Stran-ski in Berlin in 1931 [iii] and became his assistant in Sofia in 1933. They laid the fundamentals of the crystal growth theory. They proposed the first kinetic theory of the two-dimensional nucleation and growth. The spiral type growth during electrocrystallization was first observed by Kaishev on silver [iii]. On the history of the creation of the molecular-kinetic theory of crystal growth see [iv]. 

Refs. [i] Toschev S, Milchev A, Stoyanov S (1972) J Crystal Growth 13/14 123 [ii] Gunawardena, GA, Hills G), Scharifker BR (1981) J Elec-troanal Cheml30 99 [iii] Milchev A, Tsakova V (1985) Electrochim Acta 30 133 [iv] Milchev A (2002) Electrocrystallization fundamentals of nucleation and growth. Kluwer, Boston... 

Crystallization can occur from melts, solutions, or vapors. Since crystallization from aqueous solutions is most pertinent to chemical engineering, this aspect of the general topic is stressed in the following presentation. Historical and descriptive material are minimized. The fundamental principles underlying solubility, nucleation, and crystal growth are presented first, followed by a brief discussion of their application in modem practice, so that the reader may be apprised of recent significant advances in the design and operation of crystallization equipment. 

In Chapter 6, precipitation from a solvent was discussed. This subject, which includes nucleation and crystal growth, has the same fundamentals as precipitation from the melt. Crystal growth mechanisms are summarized in Table 16.11. These mechanisms include diffusion. 

In order to decrease dispersion in particle size during electrodeposition, two important principles should be taken into account. Firstly, the crystal seed formation has to occur spontaneously, thus preventing progressive nucleation. Secondly, the crystal growth has to be conducted at a slow rate, that is, at low overpotential. Penner et al. [22-26] has elucidated the importance and coherence of these fundamental principles. 

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