Static plate crystallizer

The first group of commercially available equipment is based on the Hoechst Tropfapparat (sweating apparatus) patented more than 100 years ago. It is a solid layer equipment of the batch type with stagnant melts (only natural convection). These crystallizers are commercially available, for example, as the Proabd type (Befs) using tubes and as the static plate crystallizer from Sulzer Chemtech Ltd (see Figure 17.2). Both crystallizers feature cooled surfaces for crystallization of the melt. 

The cooled surface for the crystal growth of the solid layer is provided in the static plate crystallizer of Sulzer Chemtech Ltd by plates that are located in the stagnant melt. The melt feedstock is progressively crystallized by cooling the heat transfer surface. As the crystallization proceeds, the remaining melt becomes more and more impure. The crystallization process needs about 2-30 h. Subsequently, the remaining residual melt is allowed to drain by opening a valve at the bottom of the apparatus. A film of melt with residual composition, however, remains unfortunately on the crystal coat. This... 

Figure 17.2 Static plate crystallizer of Sulzer Chemtech Ltd. (reproduced with permission from Sulzer Chemtech Ltd).

Black elongated platelets of y-(EDT-TTF)[Ni(dmit)2] [28] were obtained after 1 month by conventional electrochemical crystallization of [(C4H9)4N][Ni(d-mit)2] in acetonitrile with EDT-TTF under galvano-static conditions. Single crystals of the y-salt were obtained using a larger amount of [(C4H9)4N][Ni(d-mit)2] than for the a-salt. The X-ray structural analysis of the black plate crystals of y-(EDT-TTF)[Ni(dmit)2]... 

Depending on the type of boundary and field, a force may act on the static interface. This can be seen from Figure 10-8. For the analysis, let us place the crystal between asymmetric capacitor plates. Without the field, the boundary (b) is surrounded by a symmetric (AX/AX) or an asymmetric (AX/AY) space charge. Thus, an inhomogeneous electric field exerts a force on the (dipolar) interface. The boundary... 

Since the unloaded QCM is an electromechanical transducer, it can be described by the Butterworth-Van Dyke (BVD) equivalent electrical circuit represented in Fig. 12.3 (box) which is formed by a series RLC circuit in parallel with a static capacitance C0. The electrical equivalence to the mechanical model (mass, elastic response and friction losses of the quartz crystal) are represented by the inductance L, the capacitance C and the resistance, R connected in series. The static capacitance in parallel with the series motional RLC arm represents the electrical capacitance of the parallel plate capacitor formed by both metal electrodes that sandwich the thin quartz crystal plus the stray capacitance due to the connectors. However, it is not related with the piezoelectric effect but it influences the QCM resonant frequency. 

Taylor and Thomas [91] proposed that apparently spontaneous explosions in solutions in which lead azide crystals are growing may be caused by the buildup and subsequent discharge of static electricity on the surface of the growing crystals [64, p. 123]. To test this hypothesis. Fox et al. carried out experiments [92] in which this charge was measured by forming a parallel plate condenser between the surface of the solution arfd a reference electrode a short distance away. Erratic charging effects were observed which in some cases led to explosion, an example of which is shown in Figure 9. 

For background information on infrared spectral changes with changes of phase such as might occur in the lubricant under shear, infrared emission spectra were obtained under static conditions at different temperatures. For this purpose, a small amount of liquid crystal was sandwiched between a KBr window and a stainless steel plate and emission spectra were obtained at different temperatures. The thickness of the layer was not determined but judging from the spectra, must have been about 1.0 pm. Stainless steel had to be used to avoid chemical reaction with acidic liquid crystal. 

Figure 6.2 Examples of static self-assembly, (a) Crystal structure of a ribosome, (b) Self-assembled peptide-amphiphile nanofibers, (c) An array of millimeter-sized polymeric plates assembled at a water/perfluorodecalin interface by capillary interactions, (d) Thin film of a nematic liquid crystal on an isotropic substrate, (e) Micrometer-sized metallic polyhedral folded from planar substrates, (f) A 3-D aggregate of micrometer plates assembled by capillary forces.

Both the Hoechst Tropfapparat and the Proabd are tube bundle crystallization equipment run in the same way, as mentioned above. In principle, every plate or tube bundle heat exchanger can be used as static solid layer crystallizer however, a few special geometrical considerations have to be obeyed. 

Some of the very early applications of CPL spectroscopy involved chiral polymeric systems. In particular, the CPL from achiral dye molecules dissolved in cholesteric liquid crystals has been used to probe chirality changes. CPL from chromophores attached to a chiral poly-amino acid may also be used to study exciton coupling between aromatic chromophores. In these polymeric systems, it is often observed that gijjjjj is quite large. In some cases it is so large, in fact, that detection using static quarter-wave plates is possible. 

---