Crystallization induction time

Fig.1. Determination of crystallization induction times by baseline deviation (A) and linear extrapolation to the time axis (B).

Precipitation Conditions. The amount of aluminium dissolved in the synthetic Bayer liquors studied here is in excess of the solubility of the Al(OH)3 polymorphs, and solid will precipitate out if the solutions are simply left for a sufficiently long period of time, referred to as ageing (4 - 48 hours, depending on conditions). The ageing period included the crystallization induction time and some precipitation, but the rate of precipitation can be increased by partially neutralising the alkali hydroxide by the addition of carbon dioxide or acid, or by the addition of seed crystals. 

Two methods were used to measure crystallization induction times polarized light microscopy and laser polarized light turbidimetry, as described in Herrera et al. [5]. This polarized light laser turbidimetric technique (setup shown diagra-matically in Fig. 10) was developed by our group. 

Independently of the measuring method employed, the overall crystallization kinetics can be characterized by the crystallization induction time and the crystallization half-time. More detailed analysis is frequently per-... 

Isothermal crystallization of a polymer is frequently characterized by the induction time and the crystallization half-time. The crystallization induction time is the time that elapses from the moment when the desired crystallization temperature is reached to the onset of crystallization, characterized by the formation of the first nuclei. The crystallization half-time is the time when relative crystallinity reaches 0.5. More detailed analyses of the isothermal crystallization are usually based on the Avrami-Evans theory. Equation (7.10) yields ... 

In addition to induction time measurements, several other methods have been proposed for determination of bulk crystallization kinetics since they are often considered appropriate for design purposes, either growth and nucleation separately or simultaneously, from both batch and continuous crystallization. Additionally, Mullin (2001) also describes methods for single crystal growth rate determination. 

KNUDSEN J c, ANTANUSE H s, RisBO j and SKIBSTED L H (2002) Induction time and kinetics of crystallization of amorphous lactose, infant formula and whole milk powder as studied by isothermal differential scanning calorimetry, Milchwissenschaft, 57, 543-546. 

The induction times to the beginning of crystallization at lower temperatures of 90 - 120 °C. 

Table 5.2 Half -times and induction times (in min) for different PET samples when crystallized isothermally from the melt [26]. From Wick, G., Characterization of PET polymer for bottle manufacturing, presentation given at the Society of Plastics Engineers Benelux Seminar, 20-21 May, 1980, Amsterdam, and reproduced with permission of KoSa GmbH Co. KG...

Synthesis of Zeolite A. Zeolite A was crystallized from a batch of overall composition 2.5 Na20-Al203-1.7 SiO2-150 H20 at 60, 75, and 90°C (10). The same system was seeded with zeolite A crystals of 0.5-5 /zmeter size at an initial conversion level of 25% and crystallized at 60°C. As with the crystallization of zeolite X from seeded systems, the data were treated by ignoring the presence of seed crystals. The crystallization curves are shown in Figure 8. During the induction time period in the unseeded system, crystallization was taking place at a slow rate in the seeded system, both at 60°C. After this slow crystallization period the crystallization rate reached 22% per hour at the 50% conversion level... 

Flo. 16. Induction time for the isomerization of 1-butene on cut single crystal catalyst of MoS2 (14,37). 1-Butene (25 torr) was added first, followed by the addition of H2 (75 torr) at 100 C. 

Fig. 22. Selective hydrogen mixing between C2H4 and C2D4 during induction time Tor the isomerization of m-2-butene-d0, and superimposed hydrogen scrambling between C2D4 and cis-2-butene-dQ after the induction time on cut single crystal catalyst of MoS2 at 100°C (8,14).

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