Crystal Type

Polymer Melting poiut, °C Crystal type Helix type Crystalline density, g/cm ... 

Definition of process objectives Generation of separation core structure Selection of separation sequence and unit operations Addition of further units to the process structure Selection of crystallizer type... 

In the case of crystallization and suspended solid fouling, the process is usually of type A. However, when the fouling is of the crystallization type with a pure compound crystallizing out, the fouling approaches type B and the equipment must be cleaned at frequent intervals. 

Plastics can be used to make erasable printing media by a number of different techniques. Photo changing dyes could be incorporated into the structure of the plastics. The printer could change the dye to the colored form to read, and the material can be bleached with another unit that would reverse the photo coloring process. An ionic type plastic can be incorporated into the plastics and used to color the printed area by the use of an indicator type reaction with an organic acid or base. Another method would be to use a thermal printer in conjunction with liquid crystal type materials that would alter the state of the liquid crystals in the printed areas. Applying heat and electrical fields to the printed sheet would erase the printing. 

Side and expanded views of hexagonal and cubic close-packed crystal types. In the hexagonal close-packed structure, spheres on both sides of any plane are in the same positions, and the third layer is directly above the first. In the cubic close-packed structure, layers take up three different positions, and the fourth layer is directly above the first. 

It is noteworthy that the HRTEM cannot distinguish core and shell even by combining X-ray or electron diffraction techniques for some small nanoparticles. If the shell epitaxially grows on the core in the case of two kinds of metals with same crystal type and little difference of lattice constant, the precise structure of the bimetallic nanoparticles cannot be well characterized by the present technique. Hodak et al. [153] investigated Au-core/Ag-shell or Ag-core/Au-shell bimetallic nanoparticles. They confirmed that Au shell forms on Ag core by the epitaxial growth. In the TEM observations, the core/shell structures of Ag/Au nanoparticles are not clear even in the HRTEM images in this case (Figure 7). 

There is almost no degree of freedom in the choice of the crystallizer type Crystallization in fine chemicals manufacture is usually carried out in jacketed stirred tanks. Coils can also be used to enhance cooling, but crystals are often formed on their surface. This encrustation results in a large increase of the thermal resistance, and, consequently, a decrease of the cooling capability of the tank. Any roughness of inner surfaces of the tank can be a germ for crystals, particularly the cooled surfaces. Therefore, crystallizers are often made with polished cooled surfaces. 

Massive barite crystals (type C) are also composed of very fine grain-sized (several xm) microcrystals and have rough surfaces. Very fine barite particles are found on outer rims of the Hanaoka Kuroko chimney, while polyhedral well-formed barite is in the inner side of the chimney (type D). Type D barite is rarely observed in black ore. These scanning electron microscopic observations suggest that barite precipitation was controlled by a surface reaction mechanism (probably surface nucleation, but not spiral growth mechanism) rather than by a bulk diffusion mechanism. 

Fig. 4.13 Combined magnetic hyperfine interaction for Fe with strong electric quadrupole interaction. Top left, electric quadrupole splitting of the ground (g) and excited state (e). Top right first-order perturbation by magnetic dipole interaction arising from a weak field along the main component > 0 of the EFG fq = 0). Bottom the resultant Mossbauer spectrum is shown for a single-crystal type measurement with B fixed perpendicular to the y-rays and B oriented along...

Fig. 4.14 Magnetically perturbed quadrupole spectra simulated for powder distributions of the EFG (Vzz > 0) with an applied field B = 4T which is fixed in the laboratory system perpendicular to the y-beam/ The value of the quadrupole splitting is kept constant at AEq = +4 mm s For negative quadrupole splitting (V z < 0), the spectra would be inverted on the velocity scale. Note the difference in relative intensities for the spectrum for ry = 0 and the single-crystal type spectrum given in Fig. 4.13. Similar patterns are obtained for B y...

In conclusion of this Section let us dwell on another important topic related to possible from our stand-point classification of sensors on crystal type of adsorbent. 

Phospholipids, which are one of the main structural components of the membrane, are present primarily as bilayers, as shown by molecular spectroscopy, electron microscopy and membrane transport studies (see Section 6.4.4). Phospholipid mobility in the membrane is limited. Rotational and vibrational motion is very rapid (the amplitude of the vibration of the alkyl chains increases with increasing distance from the polar head). Lateral diffusion is also fast (in the direction parallel to the membrane surface). In contrast, transport of the phospholipid from one side of the membrane to the other (flip-flop) is very slow. These properties are typical for the liquid-crystal type of membranes, characterized chiefly by ordering along a single coordinate. When decreasing the temperature (passing the transition or Kraft point, characteristic for various phospholipids), the liquid-crystalline bilayer is converted into the crystalline (gel) structure, where movement in the plane is impossible. 

The discussion so far is for low temperatures that is, temperatures below the Debye temperatures of each crystal type. There is little excitation of individual atoms below the Debye temperature. Above the Debye temperature, the temperature is associated with thermal activation and plays a much more important role, as will be discussed later. 

Details of the calculation of Madelung constants for all of the common types of crystals are beyond the scope of this book. When the arrangement of ions differs from that present in NaCl, the number of ions surrounding the ion chosen as a starting point and the distances between them may be difficult to determine. They will most certainly be much more difficult to represent as a simple factor of the basic distance between a cation and an anion. Therefore, each arrangement of ions (crystal type) will have a different value for the Madelung constant. The values for several common types of crystals are shown in Table 7.3. 

Predict the crystal type for each of the following using the radius ratio (a) K2S (b) NH4Br (c) CoF2 (d) TiF2 (e) FeO. 

Fig. 2.12. Left transient anisotropic reflectivity change of the (001) surface of single crystal type Ha diamond. Inset shows the FT spectrum of the oscillation, demonstrating a narrow peak of the optical phonon at 40THz. Right pump and probe polarizations to detect the optical phonon. Adapted from [50]...

Microscopically, the crystal type depends on the method of preparation of halcinonide. Slabs, either 2 to 4, 5 to 10, or 10 to 15 microns square, were found in three lots of halcinonide, intermingled with needle-like (acicular) crystals 5 to 10 microns long.27... 

The specific influence of the rosin is suggested to happen due to an increased solubility of the sodium compound by micellization and to the formation of less stable mixed crystal-type lakes [2],... 

P.R.206 is a mixed crystal type and consists of unsubstituted quinacridone and quinacridone quinone. The ratio between the two components as well as the crystal modification is not yet known. P.R.206 affords a very dull, yellowish shade of red, referred to as maroon. The pigment is considerably weaker than perylene pigments. All commercially available types of P.R.206 are more or less transparent and are used mostly in metallic finishes for automobiles, to which they lend reddish shades of copper. The pigment is often found to be difficult to disperse. The finishes frequently exhibit rheological problems, especially at high pigment concentration. 

Of the four nonlinear crystal types investigated in this paper (figure 20), bulk KNbOs was superior in terms of generated blue average power (11.8 mW) and generated beam quality. KNbOs is also less susceptible to the observed saturation and subsequent decrease in SHG efficiency observed in both waveguide crystals. 

---