Seeding point

These CaC03 crystal nuclei then provide seeding points for silicate precipitation. 

The nature of silicate scaling is often complex and can involve the nucle-ation of calcium carbonate crystals (which tends to provide seeding points for silicate precipitation) and magnesium hydroxide (which can form at the heat-transfer surfaces, especially at cathodic sites where localized pH levels may exceed 10.0, then reacting with colloidal silica from the bulk water to form silicate scale). 

Finally, one of the most interesting extensions of DTI is the potential to track fibers [ in vivo MR tractography (Bammer et al. 2003 Mori and van Zijl 2002)], by using the information on anisotropic directionality contained in the diffusion tensor. With these mathematically complex methods, it has become possible to track fibers from an initial set of seed points, which can be used to track the pyramidal tract or corpus callosum as shown in Fig. 7.5b. 

Instramentation for control of seed point and growth/nucleation processing is discussed. 

Another key variable in batch cooling is seeding. The difficulty is in determining the seed point, which is ideally when the batch temperature first crosses the saturation curve. However, this temperature can be affected by batch-to-batch variations in several factors, including the actual concentration of the material to be crystallized, as well as by impurities that can affect the solubility. If the seed is added at a temperature above the solubility temperature, some or all of it can dissolve, resulting in uncontrolled nucleation. If the seed is added at a temperature too far below saturation, the product may have already nucleated. In either case, the increase in nucleation could result in a decrease in impurity rejection and/or a change in particle size distribution and other physical attributes. 

This issue, determining the point of seeding, is common to crystallization by cooling, as well as solvent removal by concentration, and by antisolvent addition. As such, seed point determination merits discussion of various methods. 

Online, in-situ instrumentation to measure product composition has been developed to successfully determine the seed point, and is being utilized in an increasing number of crystallization operations. Image analysis or photographic methods may be useful in... 

Issues High slope of temperature versus solubility curve High nucleation rate results in wide PSD Seed point is difficult to define... 

In the modified procedure, the organic solution was distilled under vacuum until the batch concentration exceeded the solubihty limit. In order to avoid undesited spontaneous nucleation, seed was charged at this point and the batch was aged to develop a seed bed. Following the seed age, toluene was fed and THF was distilled continuously under vacuum while maintaining the same batch volume. On completion of the distillation, additional hexane was added to minimize product loss in the mother hquor. The key parameters for this process are construction of the solubility map, determination of the seeding point, and control of the solvent evaporation rate to release the supersatrrration at the proper rate. 

Figure 8-7 A concentration profile for a controlled crystallization by evaporation (revised procedure) with seeding and a seed age in Example 8-1. The seeding point was much closer to the solubihty curve, and sufficient seed aging was given to release the supersaturation before further distillation.

Goals To demonstrate the effect of seeding point and addition of reactant on nucleation and filtration rate... 

Issues Seeding point, linear versus controlled addition, nucleation, filtration rate... 

In this example, the impact of seeding point and addition mode of MSA are presented. 

The influence of the initial MSA/EtOAc charge prior to seeding on the filtration flux is illustrated in Table 10-3. By reducing the percentage of MSA before seeding, the degree of supersaturation is decreased, and therefore the amount of secondary nucleation is reduced. The seed point in the 5%... 

Seeding point determine method/timing of seeding as suggested in Chapter 5 and from observation. Maintaining amount, size, timing of seed addition, and point of addition, test as follows ... 

The samples were spotted on 1 cm x 10 cm strips (Gelman Sciences, Inc., Ann Arbor, MI, USA) the mobile phase used was 75% aqueous methanol. Uncomplexed Ho stays at the origin or seeding point (7 f = ().() 0.2), and Ho labelled biomolecules migrate with the solvent front (7 f = 0.9). 

It turns out that the interactive setting of seed points and visualization... 

Partitioning the items into k initial clusters or specif3dng k initial mean values as seed points. 

Run the sequential algoiithni to obtain an estimate of the number of routes k. We can also retain the k seeds obtained by the sequential algorithm. Alternatively, once one has obtained an estimate of the number of routes, one can use some other heuristic to generate the seeds. A representative method is the seed-point-generation procedure of Fisher tmd Jaikumar (1981). The result of tins process is a set of k rontes that start from the depot, visit their respective seeds, and return to the depot. 

The variation of the maximum allowable undercooling A max with the cooling rate 6 for aqueous solutions of ammonium sulphate (Mullin, Chakraborty and Mehta, 1970) is shown in Figure 5.11. The lines for seeded and unseeded solutions are not parallel the seeded points lie approximately 1.5-2 °C below the unseeded. The slopes of the lines for seeded and unseeded solutions are approximately 2.6 and 6.4, respectively, which indicates that the mechanisms of primary and secondary nucleation are different. The best straight lines through the data yield the relationships... 

Region oriented Image patch No Low It was not selected because requires manual interaetion to obtain the seed point that must be planted, also segmentation ean be sensitive to noise, partial volume effects can cause separate regions to become connected. 

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