Diffraction methods crystal growth

In a typical zeolite synthesis, the first definite evidence for a successful reaction is the appearance of crystals of the product. As noted above (section 6.1), this signal for the end of the induction period is dependent upon the method of detection most commonly a combination of visual inspection or microscopy with X-ray diffraction. Thereafter, crystal growth can be monitored by the same techniques and the resulting S-shaped growth curve of bulk crystallinity against time is by far the most commonly reported measurement of zeolite crystallisation kinetics (fig- 2). 

Confinement effects may also be employed to characterize the nucleation and growth of porous materials [211]. The underlying mechanisms of self-assembly and crystallization of these complex heterogeneous systems may be traced by solid state NMR methods well before their detection by diffraction methods. 

Diffraction methods, which are beyond doubt the most informative approach, are at the same time the most cumbersome. It should also be stressed that, although this approach may allow the complete structure of a molecule to be given in the gas or solid phase, in practice nonvolatility, instability, and difficulties inherent in crystal growth, of the samples may interfere significantly. Where, however, these difficulties are overcome the results obtained are profitable whatever the effort invested. 

This method typically results in disordered materials as the fast precipitation does not allow for ordered crystal growth. The researchers foimd that this method produced amorphous catalysts (as shown by electron diffraction) that had very high specific activities relative to those of the traditionally produced materials. 

One of the most commonly applied SR-based scattering methods is powder X-ray diffraction, usually accompanied by Rietveld profile fitting of the diffraction pattern (e.g., Hazemann et al. 1991 Parise 1999 Lee et al. 2001). Special in situ reaction cells have been designed to study crystal growth and phase transformations in aqueous solutions at ambient to moderate temperatures ( 200°C) using X-ray diffraction (Cahill et al. 1998). Such cells have been used to study pyrite growth from aqueous solutions (Cahill et al. 

The details of the polymer crystallization process can be quite complicated. Practically, one may not care about the details of crystal nucleation and the linear crystal growth rates, but just want to characterize the overall crystallization kinetics. The degree of crystallization process can be roughly defined as crystallinity, regardless of their detailed crystal morphologies. The conventional methods to characterize the crystallinity include DSC, X-ray diffraction and dilatometer. Depending on the measured quantity, crystallinity is also separated into the weight crystallinity... 

There are several methods available for the study of bulk crystallization, including dilatometry, differential scanning calorimetry, and x-ray diffraction. Optical microscopy is the most versatile method for the study of crystallization since the use of a trinocular permits the simultaneous measurement of bulk crystallization (using transmitted light intensity) and of crystal growth kinetics using direct observation. 

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