Temperature, reaction crystallization

In pigments, 2irconium sHicate serves as the host lattice for various chromophores, such as vanadium, praseodymium, iron, etc. Zirconium sHicate crystals are usuaHy formed in situ during pigment preparation by a high temperature reaction of Zr02 and Si02 ... 

The cloudiness of ordinary ice cubes is caused by thousands of tiny air bubbles. Air dissolves in water, and tap water at 10°C can - and usually does - contain 0.0030 wt% of air. In order to follow what this air does when we make an ice cube, we need to look at the phase diagram for the HjO-air system (Fig. 4.9). As we cool our liquid solution of water -i- air the first change takes place at about -0.002°C when the composition line hits the liquidus line. At this temperature ice crystals will begin to form and, as the temperature is lowered still further, they will grow. By the time we reach the eutectic three-phase horizontal at -0.0024°C we will have 20 wt% ice (called primary ice) in our two-phase mixture, leaving 80 wt% liquid (Fig. 4.9). This liquid will contain the maximum possible amount of dissolved air (0.0038 wt%). As latent heat of freezing is removed at -0.0024°C the three-phase eutectic reaction of... 

A considerable amount of research has been conducted on the decomposition and deflagration of ammonium perchlorate with and without additives. The normal thermal decomposition of pure ammonium perchlorate involves, simultaneously, an endothermic dissociative sublimation of the mosaic crystals to gaseous perchloric acid and ammonia and an exothermic solid-phase decomposition of the intermosaic material. Although not much is presently known about the nature of the solid-phase reactions, investigations at subatmospheric and atmospheric pressures have provided some information on possible mechanisms. When ammonium perchlorate is heated, there are three competing reactions which can be defined (1) the low-temperature reaction, (2) the high-temperature reaction, and (3) sublimation (B9). 

The Avrami—Erofe ev equation, eqn. (6), has been successfully used in kinetic analyses of many solid phase decomposition reactions examples are given in Chaps. 4 and 5. For no substance, however, has this expression been more comprehensively applied than in the decomposition of ammonium perchlorate. The value of n for the low temperature reaction of large crystals [268] is reduced at a 0.2 from 4 to 3, corresponding to the completion of nucleation. More recently, the same rate process has been the subject of a particularly detailed and rigorous re-analysis by Jacobs and Ng [452] who used a computer to optimize curve fitting. The main reaction (0.01 < a < 1.0) was well described by the exact Avrami equation, eqn. (4), and kinetic interpretation also included an examination of the rates of development and of multiplication of nuclei during the induction period (a < 0.01). The complete kinetic expressions required to describe quantitatively the overall reaction required a total of ten parameters. 

Some compounds with network structures are synthesized by high-temperature reactions of metals with elemental sulfur [2, 8]. Rauchfuss et al. exploited the low-temperature synthesis of metal polysulfides by the reaction of metals with elemental sulfur in strong donor solvents. The reaction of copper powder with Ss in pyridine gives a copper polysulfide cluster Cu4(S5)2(-py)4 as orange crystals (Scheme 10) [45]. Furthermore, zinc powder reacts... 

A stannaketenimine has been synthesized by the low-temperature reaction of a diarylstannylene with mesityl isocyanide.87 The stannaketenimine is thermally stable, crystals being obtained by sublimation at 40°C/0.01 mmHg. In this case, the stannylene acts as the Lewis acid for formation of the adduct and, along with the stannenes described above, covers the full range of bonding modes available to the stannenes. 

N-Phenylhydroxylamine (11 g., 0.10 mole)2 (Note 1) and N-phenylmaleimide (17.4 g., 0.10 mole)3 are suspended in 40 ml. of ethanol contained in a 200-ml. Erlenmeyer flask. To the mixture is added immediately (Note 2) 8.98 g. (11.2 ml., 0.124 mole) of freshly distilled w-butyraldehyde. An exothermic reaction ensues, and the mixture spontaneously heats to the boiling point. A clear slightly yellow solution results which, upon cooling, deposits an almost colorless crystalline cake. The mixture is allowed to stand in the ice box for 1 day it is then filtered through a Buchner funnel, and the crystals are washed twice with 25-ml. portions of ice-cold ethanol. The yield of air-dried product, m.p. 99-101°, is 31-32 g. (92-95%). For further purification the crude material is dissolved in 60 ml. of boiling ethanol on the steam bath, and the resulting solution is allowed to cool slowly to room temperature. If crystallization does not spontaneously begin in 5-10 minutes, it can then be induced by... 

The zwitterion X5-spirosilicate bis[2,3-naphthalendiolato][2-(dimethylammonio)phe-nyl]silicate (56 isolated as 57 = 56-1/2 MeCN) was synthesized by reaction of [2-(dimethylamino)phenyl]dimethoxyorganosilanes with 2,3-dihydroxynaphthalene in acetonitrile at room temperature. Reaction of 57 or of [2-(dimethylamino)phenyl]trimetho-xysilane with water in acetonitrile yielded the cage-like silasesquioxane 58 (R = 2 — Me2NCgH4). The crystal structures of 57 and 58 were studied by X-ray diffraction. In addition, 57 and 58 were characterized by solid-state 29Si CPMAS NMR142 (Figure 34). 

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