Crystallization time, reduced

Kumar et al. (298-300) reported a method wherein the crystallization time is significantly reduced. They found that addition of a small amount of oxyanion (e.g., H3PO4) to the TS-1 synthesis gel enhances the nucleation and crystallization... 

Prehydrolysis method. Investigation of influence of added oxyanions such as phosphate, perchlorate, arsenate, chlorate, bromate, etc. on rate of crystallization. The overall crystallization time in the presence of additives reduced by about five times compared to the conventional prehydrolysis method (7,8)... 

Installation of an agitator in an open-tank crystalliser gives smaller and more uniform crystals and reduces batch times. Because less liquor is retained by the crystals after filtration... 

Quartz Crystal Microbalance (QCM) in high pressure cell (Burgass et al., 2002 Mohammadi et al., 2003) Yes P, T (with P transducer, thermocouple in cell) Yes P, T vs. time Typically 6000 psi / diss. /diss Advantages mg samples so equilibration times (hence experimental time) reduced... 

Measurements of the specific surface area, SSA, of the products grown at various times indicate that the initial formation of a microcrystalline or amorphous precursor leads to a rapid increase in SSA. The development of these phases is also observed by scanning electron microscopy, and dissolution kinetic studies of the grown material have indicated the formation of OCP as a precursor phase ( , 7). The overall precipitation reaction appears to involve, therefore, not only the formation of different calcium phosphate phases, but also the concomitant dissolution of the thermodynamically unstable OCP formed rapidly in the initial stages of the reaction. In the presence of magnesium ion the overall rate of crystallization is reduced and lower Ca P ratios are observed for the first formed phases (51). 

As mentioned above, it is difficult to separate the influence of the crystal size and of the external surface on the shape-selectivity of zeohtes rigorously. Increasing the crystal size of the zeolite means at the same time reducing the influence of the external sur ce. For the industrial production it is desirable to operate with small crystal sizes. 

Fig. 11. Reduced crystallinity /) as a function of crystallization time for different tempea-tures. The system is an 80% palm stearin blend in sesame oil, cooling rate 30°C/min.

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