Crystal, habit chloride

Therefore we have two extremes in crystal habit in sodium chloride, the octahedron and the skeleton, the prevailing shape depending upon the relative rates of growth in different directions in the crystal lattice. The common cube shape is formed when a balance in the two rates of growth prevails. 

In addition to crystal size and size distribution, the shape of the crystal product might also be important. The term crystal habit is used to describe the development of faces of the crystal. For example, sodium chloride crystallizes from aqueous solution with cubic faces. On the other hand, if sodium chloride is crystallized from an aqueous solution... 

Shotton, E. Obiorah, B.A. The effect of particle shape and crystal habit on properties of sodium chloride. J. Pharm. Pharmacol. 1973, 25 (SuppL 37), 43. 

Impurities often have a profound effect on crystal habit. Adsorption of an impurity on faces of a crystal may retard the growth of certain crystal faces, and these will therefore become prominent in the final crystal, as described earlier (see Figure 2.7). For example, sodium chloride ... 

Although the angles between faces remain constant, the relative sizes of faces may vary from crystal to crystal. This behaviour is described as crystal habit, and the growth of the same substance from different solutions can result in different shapes. For example, sodium chloride crystals grown in water are cubic, but if urea is added to the water they become octahedral (a regular octahedron and a cube have the same overall symmetry). 

Changes in the solvent used or the presence of an impurity can also profoundly affect the crystal habit. Figure 2.17 shows the effect of aluminum fluoride on the habit of anhydrous calcium sulfate. The impurity transforms the needle-like habit to a cubic looking crystal. Figure 2.18 demonstrates the effect of urea on sodium chloride crystals. A large amount of qualitative information exists on the effect of impurities on crystal habit (Mullin 1993 ... 

Another example of control of crystal habit and size of cefinatilen hydrochloride hydrate (3, Scheme 24.2) with a habit modifier, an impurity, has been reported recently. It has been demonstrated that concentration of a related substance, a diphenyl methyl substitution at the N3 position in the triazole (4) (formed during deprotection of trityl and diphenyl methyl group (5) with AICI3 and anisole in methylene chloride at elevated temperature) is critical for formation of the particular crystal habit. 

The existing method for preparing crystalline zirconium phosphate is firstly to precipitate the amorphous form from a mixture of phosphonic acid and zirconyl chloride and secondly to reflux the amorphous form in 12M phosphoric acid for several days after washing the amorphous form free of chloride. This gives the a-form. Not only is this a time consuming process, but the amorphous form is difficult to filter. We aimed to develop a one step process to the crystalline material by using crystal habit modifiers. 

The addition of crystal habit modifiers to the original phosphoric acid/zirconyl chloride solution gave catalysts which were mainly crystallinein less than one hour but still had some amorphous character (Figure 8). 

The relative development of different types of faces of a crystal may differ for a given solute crystallizing. Sodium chloride crystallizes from aqueous solutions with cubic faces only. In another case, if sodium chloride crystallizes from an aqueous solution with a given slight impurity present, the crystals will have octahedral faces. Both types of crystals are in the cubic system but differ in crystal habit. The crystallization in overall shapes of plates or needles has no relation to crystal habit or crystal system and usually depends upon the process conditions under which the crystals are grown. 

The new niobium phases with Nb(II,IV), K and F ions were obtained on cathode by molten salts electrolysis of the system K2NbOp5 +FLINAK. These phases never are produced by electrolysis in the chloride molten system. Niobium phase with similar crystal habit and K ions in composition has been reported by E.Christensen et al [1]. We initiated the present investigation in order to define some individual characteristics of the phases. The aims of our study are following (a) identification of the niobium phases (b) determination of their atomic structure (c) analysis of their transformations under washing out a cathodic product with acid water solution and under the action of the KCl+NaCl melt. 

The effect of the crystal habit-forming impurities, raffinose, dextrose, and potassium chloride on the growth of sucrose crystals from various seeds has been studied. A mechanism for the oxidation of o-galactose by Nessler s reagent in alkaline media via the enediol has been proposed on the basis of kinetic measurements. The reaction is zero-order with respect to Hg" and first-order with respect to galactose. The rate is inversely proportional to the concentration of iodine ion. 

HNS is a thermally-stabie expiosive and a nucieant for improving the crystallization habit of TNT in expiosive formulations such as composition B. in the presence of excess TNT, the chloride yieids 2,2, 4,4, 6,6 -hexanitrobibenzyl (HNBB) which can be oxidized to HNS according to the equation ... 

Sodium chloride and sodium cyanide are isomorphous and form an unintermpted series of mixed crystals. The ferrocyanide ion has a marked effect on the habit of sodium cyanide crystallized from aqueous solution (50). Sodium cyanide and sodium carbonate form a molten eutectic at approximately 53 wt % sodium carbonate and 465°C. The specific conductivity of molten 98% sodium cyanide is 1.17 S /cm (51). 

Why do we get differences in crystal shape or habit This may be a matter of directional rates of growth. Factors affecting directional rates will then affect the habit. Directional rates of growth can be illustrated with a relatively simple crystal structure, that of sodium chloride. 

However, in recent years it has been shown that single crystals and dispersed materials are not so different as to hinder fruitful comparisons of results from the separate fields (22,23). It has been shown that when proper synthesis and sintering procedures are adopted, oxide and chloride microparticles are obtained that can assume the crystalline habits of very well-defined polyhedra and consequently can expose facelets with regularity not significantly different from that of single crystals (22, 23). 

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