Crystalline phase change

The endotherm at 192 °C is due to the fi-d crystalline phase change, and the exotherm at 276 °C is due to the violent decomposition of HMX. Thermal pre-ignition and ignition temperatures of explosive substances can be obtained from DTA and TGA thermograms. 

It was found that the temperature of the crystalline phase change from Y-AI2O3 to 0-AI2O3 increased by about 100°C-150°C when adding rare earth oxides as stabilizator. Even calcined to 1050°C, the (X-AI2O3 phase did not appear. 

The effects of rare earth oxides could be concluded from Table 3, 5 and 7 (a) to improve catalytic activity (b) to improve mobility of lattice oxygen in catalyst B and its activity for CO and HC conversion in a lower ratio of air/fuel (c) to improve thermal stability of support to resist crystalline phase change to a phase and maintain crushing strength and surface area. 

The piezoelectric effect stems from hydrogen and fluorine atoms in the VDF, which are positioned perpendicularly to the polymer backbone. Fig. 5.7A shows a typical molecular structure of PVDF with different crystalline phases (Chang et al., 2012). The piezoelectric performance of PVDF is dependent on the nature of the crystalline phase (Crossley et al., 2014). Typically, PVDF has three crystalline phases, namely a, p, and y, and it is the a-phase that typically forms in most situations. While it is polar p-phase that shows the strongest piezoelectric behavior so this material needs to be electrically poled using an electric field with the order of 100 MV m or mechanically stretched. A higher P-phase crystalline can lead to a higher piezoelectric coefficient Note that the copolymer of P(VDF-TrFE) [(CH2-CF2) -(CHF-CF2)ml crystallizes more easily into the P-phase due to steric factors (Furukawa, 1989). So, the most applied material in piezoelectric generator is P(VDF-TrFE). 

Physical changes and measurements. These include melting, crystalline phase changes, ehanges in liquid and liquid crystalline states and in polymers, phase diagrams, heat capacity, glass transitions (Tg), thermal conductivity, difftisivity, emissivity, etc. 

Seguela R (2002) Dislocation approach to the plastic deformation of semicrystalline polymers kinetic aspects for polyethylene and polypropylene. J Polym Sci B Polym Phys 40 593 Seguela R (2005) On the strain-induced crystalline phase changes in semi-crystalline polymers mechanisms and incidence on the mechanical properties. J Macromol Sci C Polym Rev 45 263-287... 

Perhaps, a more-or-less common diffusion mechanism is operative for these amorphous hydrides that is rather insensitive to the metal constituents or hydrogen stoichiometry. However, a decrease in with increasing hydrogen content is seen for glassy a-Zr2PdH samples which is opposite to the trend observed for the crystalline phases. Changes in the proton... 

For polyamide-montmorillonite nanocomposites, and ignoring all crystalline-phase changes that may be caused by silicate fillers," an adhesive interfacial adhesion of 107 mj/m, corresponding to an interfacial strength of 14 MPa. 

K. Shportko, S. Kremers, M. Woda, D. Lencer, J. Robertson, M. Wuttig, Resonant bonding in crystalline phase-change materials. Nat. Mater. 7, 653-658 (2008)... 

Semicrystalline PA Crystallization kinetics Stress between amorphous and crystalline phases Change in degree of crystallization... 

Generally, it is possible to obtain data from broad-band NMR spectroscopy that compares favorably with dynamic-mechanical measurements of polymers. The two types of data, NMR and dynamic-mechanical, complement each other in that, for some physical or chemical changes that occur in the polymer, both methods check each other or, alternatively, one method gives results which the other method cannot give. For example, both amorphous and crystalline phase changes can be detected by NMR and dynamic-mechanical measurements. Some crystalline melt transitions cannot be detected by NMR. In addition some secondary amorphous transitions in polymers cannot be detected by NMR. On the other hand, NMR is a more sensitive technique for determining side chain ro-... 

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