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2. Single crystal growth of sodium sulfate heptahydrate 29 growth from center [mm] a time [s] growth from center [mm] b time [s] Fig. 2.10: Growth in the y1-direction for c 0 = 3.4 mole/kg (a) and c 0 = 2.5 mole/kg (b). The solid squares denote the experimental data, whereas the various curves reflect the model predictions. The diagrams in Fig. 2.10 show an example of fits of L y from Eq. (2.5) to the experimental results (y1-direction for 3.4 mole/kg (a) and 2.5 mole/kg (b)) obtained by assuming either a linear, parabolic, or exponential dependence of the growth rate on the supersaturation ratio, respectively. The best overall agreement is clearly achieved with a linear dependence (i.e., g = 1 in Eq. (2.5)). The kinetic parameters G k obtained from these fits are 6 µm/s for c 0 = 3.4 mole/kg and 1.3 µm/s for c 0 = 2.5 mole/kg. For the latter concentration, some discrepancies between model and experiment can be observed. The measured initial growth is much slower than predicted by the model. This discrepancy may be explained as follows. The interface-controlled growth rate is determined by the concentration at the crystal-solution interface. In the model, this concentration was approximated by the average concentration in the solution, which might
2. Single crystal growth of sodium sulfate heptahydrate 30 be an over-estimate, because the Rayleigh-Bernard convection discussed above is driven by a concentration gradient, which is absent if no crystal is growing. Initially, the growth of the crystal will consume the solute and drive the concentration of the adjacent solution towards the solubility limit, so that approaches unity and the growth slows down. This drop in concentration produces a density gradient that initiates convection. Therefore, the slow initial growth may reflect the time lag before convection actually starts. 2.8 Conclusion The growth rate of sodium sulfate heptahydrate has been measured in cooled droplets of solution. By combining non-destructive measurements of the concentration in a droplet with image analysis, the crystal growth could be studied in detail. The experimental data showed that the growth rate of sodium sulfate heptahydrate is controlled by the rate of attachment (adsorption) of ions at the crystal/liquid interface. The kinetic parameter G k ranges between 1 and 7 µm/s in drops of 50 to 100 µl at temperatures of 4.8 to 13 ◦ C.
Page 2 and 3: Sodium sulfate heptahydrate in weat
Page 4: To my family
Page 8 and 9: CONTENTS 1. Introduction . . . . .
Page 10 and 11: 1. INTRODUCTION 1.1 Introduction Sa
Page 12 and 13: 1. Introduction 11 This phenomenon
Page 14 and 15: 1. Introduction 13 1 2 initial mass
Page 16 and 17: 1. Introduction 15 However, our pre
Page 18 and 19: 2. SINGLE CRYSTAL GROWTH OF SODIUM
Page 20 and 21: 2. Single crystal growth of sodium
Page 32 and 33: 3. CRYSTALLIZATION UNDER WETTING/NO
Page 34 and 35: 3. Crystallization under wetting/no
Page 44 and 45: 4. NUCLEATION ON MINERAL SUBSTRATES
Page 46 and 47: 4. Nucleation on mineral substrates
Page 52 and 53: 5. SODIUM SULFATE HEPTAHYDRATE FORM
Page 54 and 55: 5. Sodium sulfate heptahydrate form
Page 62 and 63: 6. CRYSTALLIZATION OF SODIUM SULFAT
Page 64 and 65: 6. Crystallization of sodium sulfat
Page 72 and 73: M 6. Crystallization of sodium sulf
Page 74 and 75: 7. THERMODYNAMIC AND POROMECHANIC C
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7. Thermodynamic and poromechanic c
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8. NMR COMBINED WITH ACCELERATED WE
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8. NMR combined with accelerated we
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∆ 8. NMR combined with accelerate
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9. CONCLUSIONS AND OUTLOOK This cha
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9. Conclusions and Outlook 107 Soft
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APPENDIX: CALCULATION OF SALT CRYST
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Appendix: Calculation of salt cryst
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Bibliography 113 [15] L.M. Luquer,
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Bibliography 115 [47] D. Rosenblatt
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Bibliography 117 [78] H.P. Huinink,
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LIST OF PUBLICATIONS Published: •
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ACKNOWLEDGMENT This thesis would no
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CURRICULUM VITAE Tamerlan Saidov wa
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