A-crystal modification

The fact that in HPLC only UV-active components are registered, whereas in titration all basic functional groups are detected constitutes a difference in specificity (quality) and sensitivity (quantity) of these two methods relative to a given impurity. See Fig. 4.17 (left). [Solvent A (water) behaves differently from the other four as can be seen from Fig. 4.17 (right). The material was known to exist in a crystal modification that theoretically contains 3.2% water, and moderate drying will most likely drive off only the excess Indeed, the best-dried batches are all close to the theoretical point (circle, arrow in Figs. 4.16-17), and not near zero. This is only partly reflected in Table 4.15, column A for this reason tabular and graphic information has to be combined. Solvent B, which is an alcohol, behaves more like water... 

Superconducting only in thin films or under high pressure in a crystal modification not normally stable. Critical temperatures for those elements from [32, Chapter 12]. 

The a- and (i-types of Copper Phthalocyanine Blue reign supreme among commercially available phthalocyanine pigments. There is also an increasing amount of interest in the phase-stabilized form of the a-crystal modification. Both modifications are also supplied as flocculation resistant types. 

The (3-lorm is obtained by dissolving crude quinacridone in any one of a variety of solvents (such as concentrated sulfuric acid/toluene or methylated sulfuric acid), followed by precipitation with water. The same end is achieved by dissolving the product in polyphosphoric acid, followed by rapid precipitation with ethanol at 45°C. The (3-product, however, is not pure and usually contains some a-crystal modification as well. 

Figure 12.17a shows the increment in thickness during the crystallization of one droplet that occurs at 33.6°C. Figure 12.17b shows the dependence of the crystallization temperature on the thickness of the droplets in a range of 0.5-7 nm. Both results support the hypothesis of the authors. The temperature-dependent AFM studies also showed that during heating scans, reorganization processes occur that transformed the PP from the smectic phase to the a-crystal modification. 

Ruthenium is a hard, white metal and has four crystal modifications. It does not tarnish at room temperatures, but oxidizes explosively. It is attacked by halogens, hydroxides, etc. Ruthenium can be plated by electrodeposition or by thermal decomposition methods. The metal is one of the most effective hardeners for platinum and palladium, and is alloyed with these metals to make electrical contacts for severe wear resistance. A ruthenium-molybdenum alloy is said to be... 

Samarium has a bright silver luster and is reasonably stable in air. Three crystal modifications of the metal exist, with transformations at 734 and 922oC. The metal ignites in air at about ISOoC. The sulfide has excellent high-temperature stability and good thermoelectric efficiencies up to llOOoC. 

Terbium is reasonably stable in air. It is a silver-gray metal, and is malleable, ductile, and soft enough to be cut with a knife. Two crystal modifications exist, with a transformation temperature of 1289oC. Twenty one isotopes with atomic masses ranging from 145 to 165 are recognized. The oxide is a chocolate or dark maroon color. 

A cmcial development for zinc phosphate coatings came in 1943 when it was found that more uniform and finer crystals would develop if the surface was first treated with a titanium-containing solution of disodium phosphate (6). This method of crystal modification is a prime reason for the excellent paint (qv) adhesion seen on painted metal articles. 

The cmde copper phthalocyanine must be treated to obtain a satisfactory pigment in regard to the crystal modification and optimal particle size... 

Forms of Boric Acid. Orthoboric acid, B(OH)3, formula wt, 61.83, crystaUi2es from aqueous solutions as white, waxy plates that are triclinic ia nature sp gi 4, 1.5172. Its normal melting poiat is 170.9°C, however, when heated slowly it loses water to form metaboric acid, HBO2, formula wt, 43.82, which may exist ia one of three crystal modifications. Orthorhombic HBO2-III or a-form d = 1.784 g/mL, mp = 176° C) forms first around 130°C and gradually changes to monoclinic HBO2-II or P-form (d = 2.045 g/mL, mp = 200.9° C). Water-vapor pressures associated with these decompositions foUow. To convert kPa to mm Hg, multiply by 7.5. 

Laser based mass spectrometric methods, such as laser ionization (LIMS) and laser ablation in combination with inductively coupled plasma mass spectrometry (LA-ICP-MS) are powerful analytical techniques for survey analysis of solid substances. To realize the analytical performances methods for the direct trace analysis of synthetic and natural crystals modification of a traditional analytical technique was necessary and suitable standard reference materials (SRM) were required. Recent developments allowed extending the range of analytical applications of LIMS and LA-ICP-MS will be presented and discussed. For example ... 

Figure 5.2 The modification of the electron energy distribution curve by the presence of diffraction limits in a crystal. The lower filled band is separated from upper unoccupied states in a semiconductor by a small energy difference, so that some electrons can be promoted to conduction by an increase in temperature...

Figure 6.4 Crystal structure of ar-tetragonal boron. This was originally thought to be B50 (4Bi2 + 2B) but is now known to be either B50C2 or B50N2 in which the 2C (or 2N) occupy the 2(b) positions the remaining 2B are distributed statistically at other vacant sites in the lattice. Note that this reformulation solves three problems which attended the description of the or-tetragonal phase as a crystalline modification of pure B ...

Let us consider a clathrate crystal consisting of a cage-forming substance Q and a number of encaged compounds ( solutes ) A, B,. . ., M. The substance Q has two forms a stable modification, which under given conditions may be either crystalline (a) or liquid (L), and a metastable modification (ft) enclosing cavities of different types 1,. . ., n which acts as host lattice ( solvent ) in the clathrate. The number of cavities of type i per molecule of Q is denoted by vt. For hydroquinone v — for gas hydrates of Structure I 1/23 and v2 = 3/23, for those of Structure II vx = 2/17 and v2 = 1/17. 

For the case of the crystallization from the amorphous phase, the blending with PPO for lower contents (less than 30wt%) favours the obtainment of the a" ordered modification with respect to the a disordered modification, which is obtained for the unblended polymer. For higher PPO contents the obtainment of the p form is favored [105]. This behavior would be simply due to the increases of the glass transition temperature, and hence of the crystallization temperature on heating, which correspond to increased PPO contents in the blends [105],... 

We now discuss the effects of finite chain length. The difficulties arise from the definition of a bulk free energy term, when the very nature of the chains constrains the crystal thickness to be finite. There are two different approaches to this problem the first to be considered is due to Hoffman et al. [31] and is a simple modification of the infinite chain case, but is somewhat lacking in theoretical justification the second, due to Buckley and Kovacs [23], aims to correct this deficiency and suggests that the interpretation of experimental data given by Hoffman s approach is misleading. 

The nucleation rate onto a crystal is determined by the flux onto an ensemble of substrates. As the nuclei should be widely separated for the nucleation approach to be valid, this does not appear to be unreasonable. However, the subsequent way in which this flux is used to determine the thickness and growth rate seems somewhat inconsistent as explained below. However, a modification of the derivations would satisfy this query, and it is not likely that this will greatly affect the results. 

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