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7.3. Experimental section 101of a gel yields consistent results [126, 134]. The gel time of the sol-gel solutions wasnot systematically measured. However, the occurrence of gelation of each solution wasverified by casting part of each solution in transparent vessels and checking the abilityof the solution to flow 24 hours after preparation. All solutions gelled within 24 hours.The solutions prepared using the pH = 9.25 buffer gelled relatively fast within minutesor hours, depending on the TMOS concentration, and much faster than the solutionsprepared with the diluted buffer (pH = 8.8). In the remainder of this work the degree ofaging of the gels refers to combined curing and aging time of the gels with respect to theinstant the solutions were prepared.Gelling solutions, that were prepared as described above for the gel rods, were imbibedinto the dry rock samples followed by complete immersion in the solution for ten seconds.The imbibition, driven by capillary rise, was initiated by slowly lowering the sandstoneplates into the solution, such that the shortest dimension of the plates was directedvertically. The saturation of a sandstone plate was indicated by a color change of the rocksurface as the solution imbibed, and was completed within ten seconds. Subsequently,the rock samples were tightly wrapped in several layers of aluminum foil. Plastic foilwas wound around the aluminum. This way the evaporation of the gelling solution ordrying of the resulting gel near the rock surface was minimized and the aluminum couldeasily be removed from the treated rock samples. For each TMOS concentration andpH used (see Table 7.3) two separate rock samples were prepared in order to check thereproducibility. Similar exchange procedures used for the gels were applied to the rocksamples. First the rock samples were immersed in pure ethanol for an extended periodto arrest the curing. Next the samples were put into a mixture of ethanol and glycerol(50 vol%) to exchange part of the ethanol in the pores with glycerol. Finally, the sampleswere immersed in glycerol for several days in order to maximize the exchange of the poreliquid with glycerol. With respect to the overall pore volume of the rock samples theexcess volume of the glycerol was about 25 to 1. The use of a high-viscosity liquid suchas glycerol was necessary in order to prevent the hydrodynamic relaxation from being toofast with respect to the temporal resolution and accuracy of the beam bending method,since the rocks have high moduli on the order of 10 GPa.7.3.3 Beam bending setupAn extensive description of the beam bending apparatus is given in Ref. [128]. Twoequivalent set-ups were used, both of which were situated in an incubator. The firstset-up (see Figure 7.2) was used for the gel measurements, which were done at roomtemperature. The temperature was stable during each run with fluctuations smaller than1 ◦ C. The second set-up was used for the rock sample measurements. The temperaturewas controlled to 26 ± 0.5 ◦ C. Each set-up contains a stainless steel bath which was filledwith ethanol for the gel measurements and glycerol for the rock sample measurements.The gel samples were aligned at a fixed position using V-notch supports consisting of 6.35-mm-diameter rollers set at an angle of 90 ◦ with respect to each other, and forming 45 ◦angles with the horizontal plane. The pushrod, comprising an iron core and stainless steelhammerhead end was mounted onto the load cell. The load cell (SENSOTEC), with acapacity of ± 50 g, was mounted onto the stepper motor (UltraMotion). The displacement
102 7. Permeability reduction in porous materials by in situ formed silica gelof the pushrod was monitored through a linear-variable differential transformer (LVDT,Macrosensors). The span (L) of the supports was 110 mm. The sandstone plates weresupported by two different stainless steel supports. One consisted of a recessed ball, theother of a pivoting cylinder. This configuration was chosen to prevent torsion. The spanin this case was 150 mm. A round-tipped pushrod (diameter = 6.3 mm) was used to bendthe plates. A load cell with a capacity of ± 1000 g was mounted onto the stepper motor.In addition a 1000 g counter-weight was mounted on the pushrod.Fig. 7.2: Photo of beam bending set-up. A rectangular beam is placed in the bath.The rock samples and gel rods were put in the bath at least 30 minutes in advanceof the bending experiment in order to equilibrate thermally and mechanically. Duringbending deflections of about 1 or 1.5 mm were applied to the gels, whereas a deflection ofabout 35 µm was applied to the rock samples. The small deflection for the rock sampleswas chosen because of the limited load capacity of the system and in order to preventthe rock samples from cracking or breaking. Due to the small deflection with respect tothe surface roughness – the grain size of the sandstone is on the order of 50 to 500 µm– the bending measurement is sensitive to the effect of slipping of the pushrod at thesurface or slipping of the rock on the supports. Test measurements indicated that thiseffect occurred by yielding unrealistically low moduli (E p ) for some samples and scatteredresults when a sample was repeatedly measured. Therefore the samples were preloadedwith a net load of about 100 g prior to the equilibration period to promote a more stablesettling of the rock and pushrod. The total load upon deflection is on the order of 1 kg.7.4 Results and discussion7.4.1 GelsGel propertiesFour series of gel rods were prepared. The TMOS concentration was varied in series Iand IV. The concentration was kept fixed in series II and III, but extra salt, in the formof sodium-chloride (NaCl), was added in various concentrations, C S , up to 80 mMolal.The effect of additional salt on the gel properties was investigated in consideration of
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TWO-PHASE REACTIVE TRANSPORTOF AN O
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Dit proefschrift is goedgekeurd doo
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4. The effect of pH on mass transfe
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Samenvatting . . . . . . . . . . .
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2 1. Introductionproducerbarrierlow
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4 1. IntroductionTwo inter-European
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Part ITwo-phase bulk systems7
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10 2. Coupled mass transfer and sol
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0+,44 4. The effect of pH on mass t
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46 4. The effect of pH on mass tran
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48 4. The effect of pH on mass tran
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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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