Untitled - Technische Universiteit Eindhoven

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4.4. Results and discussion 490.625 °C50 °C0.50.4T 2[s]0.30.20.10.00.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7x mFig. 4.3: T 2 of the 2 H content in the methanol-D 2 O calibration mixtures.fraction of methanol. The temperature is indicated in the legend.x m is the moleTable 4.2: Transverse relaxation time T 2 of deuterium in aqueous buffers and of deuteriumin calibration gel samples. φ g Tis the initial volume fraction of TMOS mixed withwater to prepare the gels.φ g TT 2 [s]no buffer pH = 2.95 pH = 5.50 pH = 9.4825 ◦ C 50 ◦ C 25 ◦ C 50 ◦ C 25 ◦ C 50 ◦ C 25 ◦ C 50 ◦ C0.00 0.389 0.647 - 0.652 - 0.642 - 0.6520.10 0.123 0.073 0.060 0.048 0.028 0.025 0.047 0.0770.20 0.066 0.037 0.029 0.018 0.021 0.018 0.013 0.0170.30 0.053 0.030 0.025 0.014 0.018 0.015 0.0084 0.00810.40 0.038 0.026 0.019 0.011 0.016 0.013 0.0077 0.0057
50 4. The effect of pH on mass transfer and gelation1008025 °C50 °C1/T 2[s -1 ]60402000.0 0.1 0.2 0.3 0.4φ TgFig. 4.4: Reciprocal transverse relaxation time (relaxivity) of deuterium in the acid-catalyzedgels (pH = 2.95). The solid curves indicate the obtained fits using Eq. 4.6 and theapproximation for f s .estimate f s . Furthermore, the approximation φ m = 0.2φ g Twas used, which is based on fullhydrolysis and condensation of the initial TMOS content. Typical experimental valuesof the surface area of aero-gels, with which the dilute wet gels are compared, are on theorder of 1000 m 2 g −1 [99], so we choose A = 1000 m 2 g −1 for the calculation of f s . Themonolayer thickness λ equals 1.5 Å. The bulk relaxation time T 2,b of the water-methanolmixture in the pores, which is a function of φ g T, is derived from the calibration resultsof the water-methanol mixtures together with the calculation of the final water-methanolratio in the gels. The resulting fits for the acid-catalyzed gels are shown in Figure 4.4.It can be observed that the reciprocal relaxation times increase roughly linearly withφ g T . The obtained surface relaxation times T 2,s are listed in Table 4.3. The transverserelaxation times T 2,s are on the order of 0.1 to 1 ms. The estimated fraction f s variedbetween 0.0067 and 0.028.4.4.2 Two-phase bulk experimentsConcentration profilesThe average TMOS concentration in the oleic phase in the two-phase bulk experimentswas determined by measuring T 1 of the oleic phase [88]. For this purpose calibrationsof T 1 for TMOS/Isopar V mixtures were made (see Figure 4.5), which clearly showed amonotonous increase of T 1 with increasing TMOS concentration and temperature withinthe temperature range considered (15–55 ◦ C). From the derived volume fraction of TMOSin oil the number of TMOS molecules n o in the oleic phase was calculated. The results offour bulk experiments, done at 25 ◦ C with varying pH of the aqueous phase and with an
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TWO-PHASE REACTIVE TRANSPORTOF AN O
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Dit proefschrift is goedgekeurd doo
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114 8. Model of reactive transport
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132 9. Concluding remarks and outlo
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-142 Appendix A, - C D *, - D
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144 Appendix Awhere S 0 is a consta
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146 Appendix AThe 0.95 Tesla scanne
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148 Appendix B
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150 Appendix CwhereΩ A (θ) = −2
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152 Appendix C
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154 Appendix D
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156 Appendix Eand equal to zero in
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158 Appendix EAs the saturations, d
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160 Bibliography[12] B. Vinot, R. S
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162 Bibliography[40] M. D. Mantle a
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164 Bibliography[70] F. J. M. van d
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166 Bibliography[97] K. Yoshida, A.
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168 Bibliography[127] G. W. Scherer
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170 Bibliography
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172 Summaryand gelation rates. The
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174 Samenvattingwaterfase. De T 1 v
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176 List of publications
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178 Dankwoordimmer opgewekte stemmi
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Prior to the speech, Harald Cramér
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