Identification of coating of Ammonium Sulfate dust with DMSO by NMR

In order to confirm that the dust particles of Ammonium Sulfate are really coated with DMSO, the coated crystals were subjected to 1H-NMR study in D2O solvent. In the NMR spectrum (Fig. 3), we observe a sharp peak at ro

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Fig. 3. NMR spectrum of DMSO-coated Ammonium Sulfate crystals.

Fig. 3. NMR spectrum of DMSO-coated Ammonium Sulfate crystals.

6 4.683, because of the presence of H2O as an impurity along with D2O. The other peak at 6 2.60 is due to DMSO. This clearly shows that Ammonium Sulfate dust particulates are actually coated with DMSO.

4.4. Variation of crystal count and dimension with seeding temperature in case of DMSO-coated Ammonium Sulfate

The variation of crystal count with seeding temperature for the second experiment is presented in Fig. 4. The modal value of dimension of all the crystals measured in 80 fields of view of the microscope at a seeding temperature is also presented in the same figure. The crystal count and modal value of dimension have significant consistency with the variation of seeding temperature. Like the previous experiment, the seeding temperature was varied from —22.0°C to 0°C. The most dominant distinction between the two experiments is in the count of crystals. The crystal count has gone up many folds particularly at the peak values, though the crystal dimension remained almost unaltered. The highest peak in the crystal count occurred at — 21.0° C, which is the eutectic temperature of DMSO and water combine. The second highest peak in crystal count occurred at —18.2°C, which is the eutectic temperature of Ammonium

Fig. 4. Variation of crystal count and modal value of crystal dimension with seeding temperature in case of DMSO-coated Ammonium Sulfate.

Sulfate and water combine. However, the first crystal count was almost twice the second count. Beyond the temperature of the second peak toward 0°C, the count gradually goes down.

The modal dimension of crystal count has two distinct peaks coincident with the two peak temperatures in the crystal count. But, the two peaks in the modal value attain almost the same height. There is a distinct third peak in the modal value around — 8°C; the reason of its existence is not at all clear.

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