Crystal centered

On the other hand, the formation of the high pressure phase is preceded by the passage of the first plastic wave. Its shock front is a surface on which point, linear and two-dimensional defects, which become crystallization centers at super-critical pressures, are produced in abundance. Apparently, the phase transitions in shock waves are always similar in type to martensite transitions. The rapid transition of one type of lattice into another is facilitated by nondilTusion martensite rearrangements they are based on the cooperative motion of many atoms to small distances. ... 

A mixture of lignosulfonates, alkali-treated brown coal, and minor amounts of organic silicon compounds (e.g., ethyl silicone) reduces the permeability of cements [1019]. The additives may interact with the crystallization centers of the cement slurry and form a gel system in its pores and capillaries, thus reducing the permeability of the cement and increasing its isolating capability. Furthermore, it is claimed that the additive retards the setting rate of cement up to 200° C and increases the resistance to corrosive media. 

Radiation interactions with a crystal center cause electrons to be raised to an excited state. 

Figure 1. The concentration, c(x) of the solute as a function of the distance, x from the crystal center.

Barite that is colorless is pure, but radiation damage centers commonly cause color. For example, 0 (in some blue crystals), SOJ (in some honey-yellow and blue crystals), and SO2 (in yellow crystals) centers have been identified in barite. 

A Miller indices faec on the from face of a cube would be (100). signifying that face intersects the o axis at I unit length from the center of the crystal, and is parallel to axes a2 and or intersects those axes at infinity. In this system, zero (0) is the numerical substitute for infinity. A (I I I) Miller indices face identifies that facial plane as intersecting each of the three crystallographic axes of that form at I unit length from the crystal center. 

The H-ZSM-5 coatings were tested for the one-step oxidation of benzene by nitrous oxide to phenol. The grids had a total area of 9 cm2, a wire diameter of 250 pm and a mesh size of 800 pm. Fifteen grids formed a stack separated by steel rings. By acid pretreatment of the grids, defects were generated which are known to become crystallization centers during the synthesis of the zeolite. 

Figure 50. Snapshots of oxygen incorporation experiments in Fe-doped SrTi03, recorded by in situ time and space resolved optical absorption spectroscopy.256 Rhs column refers to the corresponding oxygen concentration profiles, in a normalized representation. Top row refers a predominantly diffusion controlled case (single crystal), center row to a predominandy surface reaction controlled case (single crystal), bottom row to transport across depletion layers at a bicrystal interface.257,258 For more details on temperature, partial pressure, doping content, structure see Part I and Ref.257-259 Reprinted from J. Maier, Solid State Ionics, 135 (2000) 575-588. Copyright 2000 with permission from Elsevier.

The so-called cooperative Jahn-Teller effect is another occurance of the static distortions. Here, interaction, that is, cooperation between different crystal centers, make the phenomenon observable. Without interaction, the nuclear motion around each center would be independent and of a dynamic character. 

We have discussed in detail the cholesteric pitch and the cholesteric sense in polypeptide liquid crystals, centering around our own work, which had not been investigated much since Robinson had presented excellent works about a quarter of a century ago. We have show that compensation of the cholesteric sense caused by temperature and solvent can be consistently explained by the theory of Kimura et al., in which the intermolecular force is assumed as the sum of a repulsion of a hardcore with shape of a twisted rod and of dispersion forces of Maier-Saupe-Goossens type. 

In the Ewald construction (Figure 3.17), a circle with a radius proportional to 1/A and centered at C, called the Ewald circle, is drawn. In three dimensions it is referred to as the Ewald sphere or the sphere of reflection. The reciprocal lattice, drawn on the same scale as that of the Ewald sphere, is then placed with its origin centered at 0. The crystal, centered at C, can be physically oriented so that the required reciprocal lattice point can be made to intersect the surface of the Ewald sphere. 

The construction takes the form (in two dimensions) of a plot of surface energies as a function of directions using polar coordinates. For each plane a normal is defined, and then a perpendicular line segment where the normal strikes the energy curve. The distance of a given surface plane from the crystal center of mass turns out to be proportional to the surface energy of that plane. For particular directions corresponding to... 

As a result of mutual lapping of transparent defects in different layers (due to mismatch of transparent defects, and of crystallization centers in upper and lower layers of photomask) almost defect-free photomask is obtained. 

The equilibrium state for various faces of crystal is determined by the condition of Ap=const., which yields the Curie-Wulff expression, stating that the ratio of the free surface energy of a particular face to its distance from the crystal center is constant for all faces in equilibrium state, i.e. ... 

In agreement with both the Curie-Wulff expression and the above equation, the faces that bear the lowest energy have the largest area, and are the closest to the crystal center (Fig. 1-15). Conversely, the faces that are further away from the center have higher surface energy and are, therefore, less developed. 

The fact that the modulus of rigidity varies with Afn indicates that it is controlled by the number of crystallization centers per unit volume, while the breaking strength is controlled by the proportion of molecules which have more than one crystallization center per molecule. Thus, breaking strength is more dependent upon... 

When crystals are grown from a melt, the simultaneous growth of a great many crystallization centers must be prevented. The growing crystal should always be the coldest part of the surroimdings by being connected to a heat sink (a rod or a tube with good thermal conductivity). 

The growing of metal single crystals can be carried out via several methods. Tammann and Bridgman [12] have devised an apparatus for slow solidification of metallic melts. A tube filled with the melt is lowered slowly and at a uniform rate (e.g., by means of a clock mechanism) through a vertical, electrically heated tubular furnace. In order to force the crystallization process to occur at a fixed place and from only one crystallization center, the bottom of the tube is drawn out to a capillary point (Schubnikow Straumanis Cl2]. 

Activation of the crystal center 0.37-0.53 Degradation of defects in the interior of the crystal. 

---