High crystallisation

Although its main use is still the identification of crystalline phases, X-ray diffraction is also the most used technique for the determination of the location of extraframework cations. XRD is well suited to perform structural characterisation of dehydrated zeolites since the framework is highly crystallised and the extraframework cations are often heavy elements. 

At high crystallisation temperatures, the high molar mass polymer crystallised alone. Data for the fold surface free energy obtained from linear growth rate data supported the view that the nature of the fold surface of the dominant lamellae was related only to the molar mass of the crystallising component and was not affected by the composition of the melt. 

Fig. 13. Micrographs indicating crystal thickness distribution at high crystallisation temperatures...

The disadvantage of this approach is that the resulting oxides are not highly crystallised because heat treatment cannot be conducted at a temperature above about 400 °C, where structural collapse occurs. This soft method has not been applied for ordered mesoporous crystalline late transition metal (such as Cu, Co, Ni and Fe) oxides. As a rare case, preparation of mesoporous nickel or iron oxide was reported. However, nickel oxide has an amorphous wall and iron oxide (crystalline y-Fe203) has disordered wormhole mesopores. ... 

The other method for preparing ordered mesoporous materials is the so-called hard template method using hard mesoporous silica or replicated carbon templates. The metal precursors are filled into hard templates. In this method, heat treatment can be performed at a higher temperature without structural collapse and highly crystallised materials can be obtainedl ° ] (Figure 3.6). 

It is interesting to note that in just these situations, i.e. tension at 0 0° for an oriented polymer, and for a highly crystallised material, extended tie molecules may be expected to influence the deformation (cf. Refs. 69-79). No firm interpretation can be offered, however, at this preliminary stage of the study. Croll points out that it is not possible with constant strain-rate data alone to distinguish by visual inspection between polymers which obey eqn. (19) and those which belong to the class typified by Fig. 22 and so for these purposes creep measurements are more definitive. 

Poly(e-caprolactone) (PCL) consists of sequences of methylene units separated by ester groups and is one member of the general series of aliphatic polyesters 2 which have different methylene to carbonyl ratios, i.e. have different values of n. In these structures there is little steric hindrance to rotation about main-chain bonds and, in consequence, amorphous PCL has a low glass-transition temperature and is soft and rubbery. Regularity in its molecular structure renders PCL highly crystallisable and the crystalline entities reinforce the material and enhance its mechanical properties. 

PCL is a highly crystallisable polymer which can crystallise in the pure state or in blends. The crystallisation of PCL and its resulting morphology in the crystalline state accord with classical patterns of polymer crystallisation. 

In order to predict values of Tg of mixtures it is necessary to have the correct values of Tg of the constituents. Because of the highly crystallisable nature of PCL it is difficult to obtain an unambiguous value of Tg for this polymer but it is possible to obtain an estimate of Tg by the use of modified forms of Eqs. (21) or (22) see below. 

Rebillat, F., Guette, A., Espitalier, L. (1998). Oxidationresistance of SiC/SiC micro and mini-composites with a highly crystallised BN interphase. Journal of the European Ceramic Society, 75(13), 1809-1819. doi 10.1016/S0955-2219(98)00120-4. 

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