Prediction of the Molecular Structure of the Crystalline Interface

A morphology can be geometrically constructed by drawing planes with an orientation (hkl) having a disTable 2 Details of additive effects on product properties tance from the origin proportional to the growth rate. The central volume enclosed by the set of planes is the growth form. A face with a large growth rate is positioned far from the origin, and thus its surface area will be small. In contrast, a face with a small growth rate will be close to the origin and have a large surface area (Figure 4). This means that the morphology is determined by the slowest growing (hkl) faces and that a morphology prediction can be made if the relative growth rates of all the different (hkl) faces are known.

Figure 4 also shows the effect of a growth-retarding impurity. Before a crystal face can grow the adsorbed impurity has to be removed from the surface. This takes energy, and thus the growth rate decreases. When face-specific adsorption occurs, surface concentrations of the impurity vary from face to face. The growth retarding effect will then also vary from face-to-face. When face-specific adsorption occurs, the relative growth rates may change, as shown in Figure 4.

Nowadays there are several general prediction methods for vacuum morphologies. Here vacuum means that the influence of the solvent or the melt is not taken into account. Donnay and Harker's law states that the importance of a crystal face decreases with interplanar distance dhkl. A morphology can be predicted if the interplanar distance is assumed to be inversely proportional to the relative growth rate of the corresponding crystal face. A prediction method that takes into account the anisotropic energies in the

Effect on Interaction with Addition Effect on face product property - - -

Specific All faces Before During After Blocking Template face crystallization crystallization crystallization growth induced growth

Anticaking

Antiscaling Morphology Polymorphism Crystal size distribution x x

Figure 2 The interaction between the surface and the impurity is the key to the effect of the additive in the crystallization process. This effect translates to changes in the growth and nucleation behaviourofthe crystal compound, which in turn affect the crystal quality and process parameters and thus the product properties change.

Figure 2 The interaction between the surface and the impurity is the key to the effect of the additive in the crystallization process. This effect translates to changes in the growth and nucleation behaviourofthe crystal compound, which in turn affect the crystal quality and process parameters and thus the product properties change.

crystal unit cell is the attachment energy method. The attachment energy is defined as the energy release per growth unit upon adding a growth slice of thickness dhkl onto the corresponding crystal surface. The assumption that the attachment energy is linearly proportional to the relative growth rate of the corresponding crystal surface gives the morphology prediction.

Solar Panel Basics

Solar Panel Basics

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