Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Crystallization, cold reversibility

The crystal compositions vary, depending on the transport agent used, from TiB,4,y (Ij) and TiBj <,4 (TeCl4). At process temperatures > 1000°C and with I2, the transport direction is reversed. Crystals grow in the cold zone of the tube, but only microscopic needle-like crystals are obtained. ... [Pg.280]

Palladium hydride is a unique model system for fundamental studies of electrochemical intercalation. It is precisely in work on cold fusion that a balanced materials science approach based on the concepts of crystal chemistry, crystallography, and solid-state chemistry was developed in order to characterize the intercalation products. Very striking examples were obtained in attempts to understand the nature of the sporadic manifestations of nuclear reactions, true or imaginary. In the case of palladium, the elfects of intercalation on the state of grain boundaries, the orientation of the crystals, reversible and irreversible deformations of the lattice, and the like have been demonstrated. [Pg.636]

Problems caused by wax which has already formed in fuel cannot be reversed unless the fuel is warmed to temperatures above the fuel cloud point. Warming will dissolve wax crystals. Upon further cooling, the modifier will then function and inhibit wax-related problems such as wax deposition onto interior surfaces of cold fuel lines and plugging of fuel filters. [Pg.150]

Quinazoline is a solid which crystallizes in the form of leaflets from petroleum ether (mp 48-48.5 °C) and can be distilled without decomposition (bp 241 °C/764 Torr, 120-121 "C/17-18 Torr). It is steam-volatile and sublimes readily under vacuum. It is freely soluble in water giving an alkaline reaction and is also soluble in various organic solvents. Quinazoline hydrochloride monohydrate has a melting point of 127-128°C [cf. that of its picrate (mp 188-190°C)]. In aqueous solutions the cation of quinazoline undergoes reversible water addition across the N3 —C4 double bond. This phenomenon is known as covalent hydration".Quinazoline is stable in cold dilute acid and alkali solutions but it decomposes when these solutions... [Pg.2]

From Fig. 3, it may be seen that lowering of the temperature to 60-70 will cause separation of amylopectin. In general, this phase separation takes the same route as that for the amylose (except for the peculiar, morphological phenomena of the latter). As crystallization is much slower for the branched fraction of starch, the critical temperature of phase separation is sufficiently high to permit the existence of a coherent, liquid phase for short periods of time. The fact that freshly obtained amylopectin precipitate is soluble in cold water, whereas, after several hours, it is completely insoluble in cold water can only be interpreted as being the result of crystallization. In accordance with this conclusion, it is to be noted that this phenomenon is perfectly reversible. [Pg.324]

The reverse of sublimation is often called deposition. Molecules in the gaseous state become part of the surface of a crystal. Energy is released in the exothermic process. The energy released in deposition is equal to the energy required for sublimation. A common example of deposition is the formation of frost on exposed surfaces during a cold night when the temperature is below freezing. In a laboratory, you may see iodine gas deposit as solid crystals onto the surface of a sealed container. [Pg.402]

This reaction is reversed at the cold end of a sealed ampule, and thus solid material is deposited. For good crystal growth, very low gradients ( 5°C/cm) must be used . This results in low growth rates in addition, there seems to be a ripening phenomenon, in which the reaction slows with time, leaving facets so perfect that nucleation is inhibited at these low supersaturations. [Pg.400]


See other pages where Crystallization, cold reversibility is mentioned: [Pg.347]    [Pg.152]    [Pg.1993]    [Pg.7]    [Pg.115]    [Pg.49]    [Pg.617]    [Pg.248]    [Pg.164]    [Pg.1007]    [Pg.78]    [Pg.60]    [Pg.558]    [Pg.109]    [Pg.232]    [Pg.87]    [Pg.111]    [Pg.103]    [Pg.218]    [Pg.531]    [Pg.558]    [Pg.653]    [Pg.222]    [Pg.340]    [Pg.795]    [Pg.144]    [Pg.325]    [Pg.1751]    [Pg.152]    [Pg.319]    [Pg.299]    [Pg.248]    [Pg.3092]    [Pg.68]    [Pg.85]    [Pg.408]    [Pg.2162]    [Pg.43]    [Pg.309]    [Pg.309]    [Pg.703]    [Pg.704]    [Pg.106]   
See also in sourсe #XX -- [ Pg.255 , Pg.256 , Pg.268 ]




SEARCH



Cold crystallization

Cold-crystallized

Crystallization reversible

© 2024 chempedia.info