Hexagonal-cubic transition

The curve peak maximas depend on the particle size, moisture content, and thermal history of the sample. For the hexagonal - cubic transition, two peaks at 409 and 413 K, respectively, were observed. 

Using the so-called "block copolymers (a block of Na A-monomers at one end is covalently bonded to a block of Nb B-monomers) one can also realize the analogy of order-disorder phenomena in metallic alloys with polymers one observes transitions from the disordered melt to mesophases with various types of long range order (lamellar, hexagonal, cubic, etc ). We shall not consider these phenomena here further, however... 

Fig. XVII-8.—Phase equilibrium diagram for the system Cu-Zn, in which a number of phases of variable composition arc formed, mixtures of the phases being stable between the regions of stability of the pure phases. The phase a is face centered cubic, as Cu is, j8 is body centered, 7 is a complicated structure, e and r) are hexagonal. The transition between and /S is an order-disorder transition, /3 being disordered, and /8 ordered, as discussed in the following chapter.

Fig. 11 Phase transitions in mesoporous solids a-d, lamellar-hexagonal e-f, hexagonal-cubic. The circular objects around the surfactant assemblies are the metal-oxo species (from Neeraj and...

PROP Colorless hexagonal crystals. Undergoes hexagonal to cubic transition. Mp 350°. Very sol in H2O sol in EtOH. 

The thermodynamic properties of hexagonal AIN and cubic transition metal nitrides and carbides are known, but for the calculation of the ranges of metastability of the cubic and hexagonal phases in the AlN-MeN or AlN-MeC systems, the energy differences for the transitions from the stable to the metastable structures, e.g. MeNj i, —> MeN and AlNi, —> AlN b primary importance. In addition, the... 

AOT Acrylamide/JV,J T -methy- lenebisacrylamide Lamellar, hexagonal, cubic No phase transition Not characterized - [49]... 

Allyldodecyl dimethyl-ammonium bromide Micellar, hexagonal, cubic, lamellar No phase transitions Partially polymerized, 11-40% conversion, increased phase stabilities [50]... 

The effect of added oil on the phase behavior of the Ci2(EO) -water system was investigated as a function of EO chain length at 25°C [296]. When decane is added to the system Ci2(EO)3-water, the lamellar to reverse hexagonal Hu transition takes place, while in the system decane-Ci2(EO)7 water, the normal hexagonal Hi to hydrophilic discrete cubic Ii transition occurs. These phenomena may be interpreted by considering the two ways in which oil may affect the system [296] ... 

The monoclinic to cubic transition for Bk203 also appears to be irreversible , while the hexagonal-monoclinic transition is readily reversible. This transition behavior is typical for the first four transplutonium sesquioxides. 

Individual samples may contain two or more bicontinuous mesophases these exhibit a distinct, sharp interface separating isotropic, viscous mixtures visible in a transparent ampoule. Transitions between bicontinuous mesophases can also occur with small temperature changes. The transitions are first-order, and exhibit a small latent heat of transition typically less than O.OlkJ/mol, compared with ca.lkJ/mol for (Type 2) bicontinuous-(reversed) hexagonal transitions and slightly less for lamellar-bicontinuous cubic transitions. 

Lee HH, Jeong WY, Kim JK, Ihn KJ, Komfield JA, Wang ZG, Qi S (2002) Orientational proliferation and successive twining from thermoreversible hexagonal-body-centered cubic transition. Macromolecules 34 785-794... 

Figure 1.9 Total energy versus volume (both per ZnO formula unit) for the three phases zinc blende (squares), wurtzite (diamonds), and rocksalt (circles). The zero of energy is the sum of the total energies of an isolated Zn and an isolated O atom. The hexagonal/cubic phase transition occurs at pT = 8.57CPa. (After Ref [20].)...

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