Solid State Phase Transitions

Fig. 4. DSC-trace of octamethyltetra-siloxane showing the melting transition at 298 K and a solid state phase transition at 262 K. Heating rate lOK/ min. (Ref. 10))...

Solid-state phase transitions can be distinguished according to Buerger in the following manner ... 

Solid-state phase transitions usually take place at a slower rate than solution-mediated phase transitions because the motion of the molecules is restricted in the solid state. Processing stresses such as grinding [28], heating [28], humidity... 

Metallic tin has many allotropic forms rhombic white tin (also called /3-tin) is stable at temperatures above 13 °C, whereas the stable form at lower temperatures is cubic grey tin (also called a-tin). A transition such as tin(white) tin ey) is called a solid-state phase transition. 

Bicyclopropylidene (1) with its melting point of -10.4°C undergoes a solid state phase transition at -40.2°C with AH = 0.038 kcal/mol, and the two polymorphous structures possess different structural parameters (Table 2) [85,86]. A similar behavior was also observed for me50-bis(bicyclopropylidenyl) meso-87 [56]. The structure of meso-S represents essentially a combination of the two bicyclopropylidene units the central bond length h (1.494 A, Table 2) which is practically the same as that in bicyclopropyl (1.492 A) indicates the absence of any strong electronic interaction between the two bicyclopropylidene units in meso-S which should thus react independently of each other. 

Fig. 5 The typical DSC diagram for solid state phase transition with latent heat red plot) or without latent heat blue plot). The scale is not the same in general the curve for a second-order transition blue plot) is associated with smaller changes of heat capacity (and therefore more difficult to detect)...

Herbstein EK (2006) On the mechanism of some first-order enantiotropic solid-state phase transitions from Simon through Ubbelohde to Mnyukh. Acta Crystallogr B 62 341-383... 

Mnyukh Yu (2001) Fundamentals of solid state phase transitions, ferromagnetism and ferroelectricity. First Books New York... 

Vadas, E.B., Toma, P, and Zogra, G. (1991). Solid-state phase transitions initiated by water vapor sorption of crystalline L-660,711, a leukotriene PeceptorantagonislJharm. Res., 8 148-155. 

Fig. IV.2. Temperature dependence i>(79Br) in K2ReBr6. The three solid state phase transitions in the temperature range between 240 °K < T < 280 °K are clearly recognized...

With the structure determination of triethylboroxin (Figure 1) we focused on the geometry of the six-membered ring. After detecting a solid-state phase transition we were attracted by the mechanism of the change of the assembly of the molecules in the crystal lattice [5], totally disregarding the geometry of the attached ethyl... 

Wide Angle Scattering During Crystallization and Solid State Phase Transitions... 

R. Solid-state phase transitions of AG337, an antitumor... 

There are two solid state phase transitions, both associated with electronic-magnetic phenomena. The adopted temperature of the a-B transition is = 411 3 K (15). Our analysis of the adopted C data yields = 0.398 kcal mol in view of... 

Fig. 39 XRPD patterns obtained before (left) and after (right) a solid-state phase transition (seen as the endothermic peak at 160°C in the DSC trace above). 

Solid-state phase transitions of salts have been studied by fitting the pressure and internal energy of each phase to an equation of state and determining the temperature for which AG = 0 at each pressure. Simulations for each solid-state phase are performed separately in the NVE ensemble.[158] In general, the thermodynamic -integration method discussed in Sec. 4.1 can be used to study solid-state phase transitions as well. 

Solid-state phase transitions often involve deformation of the unit cell along with rearrangements of the molecules inside the unit cell. Therefore a simple constant-pressure simulation which allows only isotropic expansion or contraction of the unit cell may not be able to reproduce all of the aspects of a solid-state phase transition. The technique of Parrinello and Rahman [160] introduces a time-dependent metric tensor in the Lagrangian of the system, which allows changes of both volume and shape of the xmit cells. As such, simple solid-state phase transitions can be directly simulated with this technique. However, this method cannot be used for solid phases with very different unit cells.[145] The orientational order-disorder transitions in the solid state in some cases occur with little change in the unit cell parameters or molecular rearrangements. These orientational transitions are suitable for the Parrinello-Rahman technique.[161]... 

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