Supplementary crystallization

Several commercial grades are available fine crystals of 99 to 100% purity, large crystals, pressed lumps, rods, and granular material. Double-Decomposition Methods. Double-decomposition processes all iavolve the reaction of sodium chloride, the cheapest chlorine source, with an ammonium salt. The latter may be suppHed directiy, or generated in situ by the reaction of ammonia and a supplementary iagredient. Ammonium chloride and a sodium salt are formed. The sodium salt is typically less soluble and is separated at higher temperatures ammonium chloride is recovered from the filtrate by cooling. 

Pontikis, V. (1993) Crystal surfaces melting and roughening, in Supplementary Volume 3 of the Encyclopedia of Materials Science and Engineering, ed. Cahn, R.W. (Pergamon press, Oxford), p. 1587. 

Selected area diffraction (SAD) combined with microscopy is an important supplementary tool to X-ray diffraction in crystal structure analysis. SAD has the additional advantage of giving the correlation between morphology and crystal structure whenever single crystals are too small for single-crystal X-ray analysis. 

An introduction to crystal structures and nomenclature is given in the Supplementary Material Section SI. 

X-ray diffraction allows the dimensions of the unit cell to be accurately measured. If the structure type of the material is known, the ideal cell contents are also known. Thus, the unit cell of a crystal of composition M2O3 that adopts the corundum structure contains 12 M atoms and 18 O atoms (Supplementary Material, SI). This readily allows the theoretical density of a solid to be calculated. The weights of all of the atoms in the cell are added, and this is divided by the cell volume. 

In metallic and many semiconducting crystals, the valence electrons are delocalized throughout the solid, so that antisite defects are not accompanied by prohibitive energy costs and are rather common. For example, an important defect in the semiconducting material GaAs, which has the zinc blend structure (Supplementary Material SI), is the antisite defect formed when an As atom occupies a Ga site. 

A Schottky defect in a crystal consists of a cation and anion vacancy combination that ensures overall electroneutrality in the crystal (Section 1.9). The estimation of the configurational entropy change in creating a population of Schottky defects in a crystal can be obtained in the same way as that of a population of vacancies in a monatomic crystal. The method follows that given in Section 2.1 for the equilibrium concentration of vacancies in a monatomic crystal and is set out in detail in Supplementary Material S4. 

The estimation of the number of Frenkel defects in a crystal can proceed along lines parallel to those for Schottky defects by estimating the configurational entropy (Supplementary Material S4). This approach confirms that Frenkel defects are thermodynamically stable intrinsic defects that cannot be removed by thermal treatment. Because of this, the defect population can be treated as a chemical equilibrium. For a crystal of composition MX, the appropriate chemical equilibrium for Frenkel defects on the cation sublattice is... 

Following the method set out in Supplementary Material S4, derive a formula for the number of Schottky defects in a crystal of formula MX2. 

The disruption to the crystal introduced by a dislocation is characterized by the Burgers vector, b (see Supplementary Material SI for information on directions in crystals). During dislocation motion individual atoms move in a direction parallel to b, and the dislocation itself moves in a direction perpendicular to the dislocation line. As the energy of a dislocation is proportional to b2, dislocations with small Burgers vectors form more readily. 

Acceptor doping, as in lithium oxide doping of nickel oxide, produces p-type thermistors. The situation in nickel-oxide-doped Mn304 is similar but slightly more complex. This oxide has a distorted spinel structure (Supplementary Material SI), with Mn2+ occupying tetrahedral sites and Mn3+ occupying octahedral sites in the crystal, to give a formula Mn2+[Mn3+]204, where the square parentheses enclose the ions in octahedral sites. The dopant Ni2+ ions preferentially occupy... 

Quenching the vapour with cold air in the chamber may increase the rate of heat removal although excessive nucleation is likely and the product crystals will be very small. Condenser walls may be kept free of solid by using internal scrapers, brushes, and other devices, and all vapour lines in sublimation units should be of large diameter, be adequately insulated, and if necessary, be provided with supplementary heating to minimise blockage due to the buildup of sublimate. One of the main hazards of air-entrainment sublimation is the risk of explosion since many solids that are considered safe in their normal state can form explosive mixtures with air. All electrical equipment should therefore be flame-proof, and all parts of the plant should be efficiently earthed to avoid build-up of static electricity. 

The structures of iron oxides have been determined principally by single crystal X-ray diffraction or neutron diffraction with supplementary information coming from infrared spectroscopy, electron diffraction and high resolution electron microscopy. A few years after the first successful application of X-ray diffraction to crystal structure determination, this technique was used to establish the major features of the structures of magnetite (Bragg, 1915 Nishikawa, 1915) and hematite (Bragg Bragg, 1918). 

Diffuse scattering, which nearly always occurs during a diffraction experiment however, represents a potentially rich source of dynamic information supplementary to that obtainable from the Bragg reflections. Many protein crystals exhibit diffuse... 

Abstract This chapter comments on the motivations and the methods of crystallographic studies at low temperature. Cry-crystallography is a brunch of Crystallography, a science that is too often confused with a technique. On the other hand, the scientific background to study crystal phases at low temperature is here provided, together with a survey of many possible techniques that provide complementary or supplementary information. Several apphcations are discussed, in particular in relation with highly accurate studies like electron density determination or phase transition mechanisms. 

Optically uniaxial crystals may be tetragonal, hexagonal, or trigonal. If it is possible to recognize a shape characteristic of a particular system this information is useful supplementary evidence but it must be emphasized that the refractive index values by themselves are usually sufficient for identification. 

The X-ray crystal data are often used in relation to solution chemistry, and the general question of the identity of the species in solution and those present in the crystals has to be considered, since rapid interconversion between different bridged species is frequently seen for both chromium(III) and cobalt(III). Supplementary solution measurements are therefore generally required in order to be reasonably certain that the solid-state structure corresponds to the structure in solution. 

Factors like volatility of the substance, size and complexity of the molecules, and parameter correlation affect the limits of applicability of ED and MW. X-ray crystallography, on the other hand, has become a routine tool for structure elucidation (structure now in Ruzicka s interpretation), and geometrical data are often not printed in the journal but are deposited as supplementary material. Structural data of free molecules are available in printed form14 and in a database at the University of Ulm17, and crystal-phase data are found in the Cambridge Structural Database18 (CSD). 

Rather recently, we have studied the solid-state structure of various polymers, such as polyethylene crystallized under different conditions [17-21], poly (tetramethylene oxide) [22], polyvinyl alcohol [23], isotactic and syndiotactic polypropylene [24,25],cellulose [26-30],and amylose [31] with solid-state high-resolution X3C NMR with supplementary use of other methods, such as X-ray diffraction and IR spectroscopy. Through these studies, the high resolution solid-state X3C NMR has proved very powerful for elucidating the solid-state structure of polymers in order of molecules, that is, in terms of molecular chain conformation and dynamics, not only on the crystalline component but also on the noncrystalline components via the chemical shift and magnetic relaxation. In this chapter we will review briefly these studies, focusing particular attention on the molecular chain conformation and dynamics in the crystalline-amorphous interfacial region. 

Experimental-4] Typical experiment of preferential crystallization11 To a 50 mL flask were added ( )-a-(m-hydroxyphenyl)glycine (HPG) (6.2g, 37.1 mmol), (+)-HPG (0.20 g, 1.2 mmol), methanesulfonic acid (2.07g, 21.6 mmol) and water (30 mL) which was heated and dissolved to give a clear solution. The solution was then cooled and inoculated with seed crystals (25 mg). Slurry was cooled over iced water for 2 hours and the deposited crystals were filtered to afford (+)-HPG with 98%ee (0.57g). To a mother liquor was supplementary added ( )-HPG and the same operations were repeated to afford (+)-HPG with 98% ee (0.85 g). 

Within a given crystal system, a supplementary subdivision is necessary to be made, in order to produce the 14 Bravais lattices. In this regard, it is necessary to make a distinction between the following types of Bravais lattices, that is, primitive (P) or simple (S), base-centered (BC), face-centered (FC), and body-centered (BoC) lattices [1-3]. 

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