Sediment stability

Granulated fly ash [6] can substitute for Portland cement to an extent of 40% to 60%. Fly ash is used in granulated form and has a moisture content around 10% to 20%. The formulation can be used for cementing oil and gas wells within a temperature range of 20° to 250° C. The solution has reduced water absorption and increased sedimentation stability. A formulation [1388] is shown in Table 18-2. Hydrosil (Aerosil) is used to increase the adhesion of the produced cement rock to the casing string. It also reduces the density and water absorption. 

N. A. Okishev, A. G. Ivanov, and I. V. Karpenko. Plugging solution for oil and gas wells with increased sedimentation stability—containing Portland cement, nitrile trimethyl phosphonic acid, polyoxyethylene, water-soluble cationic polyelectrolyte and water. Patent RU 2039207-C,1995. 

The type of chosen polymer and additives most strongly influences the rheological and processing properties of plastisols. Plastisols are normally prepared from emulsion and suspension PVC which differ by their molecular masses (by the Fickentcher constant), dimensions and porosity of particles. Dimensions and shape of particles are important not only due to the well-known properties of dispersed systems (given by the formulas of Einstein, Mooney, Kronecker, etc.), but also due to the fact that these factors (in view of the small viscosity of plasticizer as a composite matrix ) influence strongly the sedimental stability of the system. The joint solution of the equations of sedimentation (precipitation) of particles by the action of gravity and of thermal motion according to Einstein and Smoluchowski leads 37,39) to the expression for the radius of the particles, r, which can not be precipitated in the dispersed system of an ideal plastisol. This expression has the form ... 

Assessment of sediment stability serves to determine whether or not SQT studies need to be limited to superficial sediments (Chapman et al., 2002). Such assessments usually involve determining current flows required to resuspend sediments compared to worst case current flows or events such as 100-year storms at that site. 

As noted above, the SQT originally focused on sediment chemistry, toxicity, and community structure. It has been expanded to include bioaccumulation, sediment stability, CBR and TIE analyses. Schmidt et al. (2002) have provided a means for inclusion of data on habitat. Habitat is a key factor controlling the distributions of biota, which has been implicitly but not explicitly considered to date in the SQT (e.g., via measurements of sediment grain size and TOC). Habitat should be explicitly considered as part of the SQT in future. 

Povidone can also be used as a sedimentation stabilizer in ophthalmic suspensions. Mefenamic acid suspension is a typical example [492]. 

Pulsed sedimentation stabilization with laminar calcrete development... 

Usui, H. Saeki, T. Hayashi, K. Tamura, T. Sedimentation stability and rheology of coal water slurries. Coal Prep. 1997, 18, 201-214. 

Since the 1930s, Zostera stands recovered quite slowly, especially Zostera marina was shown to have reclaimed its former habitat only partially within 25 years after the disease (Den Hartog, 1970), whereas Zostera noltii recovered well. Schories et al. (2006a) argue that on one hand, the pool of plants from which reestablishment was nourished was quite small and, on the other hand, the habitat itself had changed by the absence of Zostera stands. For example, sediment stability was decreased after Zostera was eradicated and therefore... 

Figures 1 and 2 show the influence of ultrasonic treatment of aqueous dispersions of Ti02 and Fe203, respectively, on their sedimentation stability in the absence and presence of ethylhydroxyethylcellulose (EHEC). The particle size of obtained dispersions is given for Fe203 in Table 1 and for TiCC in Table 2.

The presence of EHEC in the system increases the stability of dispersions (compare curves 2 and 3 in Fig. 1 and 2), and particle size decreases from 1,2 mcm to 0,4 - 0,6 mcm. This is due to the formation of protective adsorption-solvation layers of the polymer on the pigment surface, which leads to an increase in aggregation and sedimentation stability of Ti02 and Fe203 dispersions. 

Figure 4 illustrates the influence of a polymer concentration on the stability of aqueous dispersions of pigment Ti02 (ultrasonic treatment time - 2 min). It is seen from the figure that with increasing the concentration of EHEC, sedimentation stability of dispersions increases. 

Rhoads, D. C., and Young, D. K. (1970). The influence of deposit-feeding organisms on sediment stability and community trophic structure. J. Mar. Res. 28, 150-178. 

In free disperse systems, in particular those with low concentration of dispersed phase, the nature of colloid stability and conditions under which the collapse occurs, are to a great extent dependent on thermal motion of dispersed particles, which may contribute to both stability and destabilization. For example, the necessary condition for sedimentation stability is sufficiently small particle size, so that the tendency of particles to distribute within the entire volume of disperse system due to the Brownian motion (an increase in entropy) would not be affected by gravity. As a quantitative criterion for the presence of noticeable amount of dispersed particles in equilibrium with a sediment one, for instance, may use the... 

In systems that initially reveal sedimentation stability, particle coagulation, as well as particle growth due to subsequent coalescence or isothermal mass transfer, may result in a loss of sedimentation stability. At the same time, coagulation may not necessarily be followed by phase separation due to sedimentation, as in the case when particle aggregation results in formation of continuous three-dimensional networks of particles that fill an... 

The emulsions were prepared on an ultrasonic disperser, coalescence stability was determined from the volume of the separated oil phase after 24 hours. As it is seen from Fig. 6.8, a complete coalescence stability of the emulsions is achieved at surfactant concentrations beyond the CMC. At the same time, the concentration at which the maximum coalescence stability is achieved is not sufficient to provide sedimentation stability of the emulsions. 

The maximum sedimentation stability is achieved at C > CMC. After the CMC, the emulsion droplet size decreases in accordance with the rate of interfacial tension decrease. Increase in sedimentation stability is observed in accordance with increasing degree of dispersity. 

These data proof the need of using surfactants at C CMC. The excessive bulk concentration of surfactants is required not only for an effective decrease of y but also for the formation of a protective adsorption layer after the abrupt increase in interfacial area caused by the growing number of small size droplets. Thus, emulsions formed with typical surfactants behave towards sedimentation stability similar to those stabilized by natural surfactants. In this respect the advantage becomes better understandable of the so-called true , i.e. micelle-forming, surfactants as compared to the surfactants unable to form aggregate. True surfactants not... 

Another technique to increase sedimentation stability of emulsions is viscosity control of the disperse phase. It is noted in [31—32, 35] that the viscosity of the disperse phase influences the stability of o/w emulsions. The effect of the disperse phase viscosity of various nature on the mean size d of the emulsion droplets is clearly seen from Fig. 6.9. The change of the nature of high-viscosity hydrocarbon component (decane, toluene, MS-20 oil) has no substantial effect... 

The surfactant concentration has a great effect on the decrease in the dispersity degree of the emulsions. An abrupt decrease in the droplet size becomes appreciable with addition of even small surfactant amounts—0.25% of ethoxylated alkylphenol. This dispersity increase unequivocally leads to an increase in sedimentation stability. 

Note that the minimum flocculation degree value is observed at the same surfactant ratios at which the minimum interfacial tension value is achieved. This makes clear the previously known facts about the increase of the emulsion stability at low y. This occurs, first of all, due to an appreciable decrease in the flocculation degree up to its complete suppression. These phenomena result in an increase in the sedimentation stability both for non-flocculated emulsions (dispersity increase) and partly flocculated emulsions (decrease in flock size and flocculation degree). 

Table 6.2 presents data on the sedimentation stability of emulsions stabilised by some typical nonionics as an example of efficiency of flocculation inhibition using chromium stearate additives as antiflocculant. 

Table 6.2. Effect of antiflocculation additive (CrStj) on sedimentation stability of water-Diesel fuel emulsions stabilised by nonionics...

One can see that surfactants like esters of monobasic alcohols and higher acids give water-in-hydrocarbon emulsions the sedimentation stability of which is 3—5 minutes. Application of an antiflocculation additive leads to a significant increase in sedimentation stability of up to 10 hours. Note that emulsions stabilised by a nonionic like Span have a high coalescence stability there is no aqueous serum separated as a continuous layer within several months. 

Satisfactory emulsion stability results are observed when using a three-component emulsifier B1215-6 (0.7 wt.%) + sorbitane oleate (0.3 wt.%) + chromium salts of C17—C20 synthetic fatty acids (0.1 wt.%). Such emulsions do not cream within 10 to 30 days, and their sedimentation stability is 30—50 hours. 

The t -potential and the surface charge of pigment particles in a polymer solution has a direct effect on the suspension stability [194]. Ultra-fine pigment particles (< 0.05 pm) were formed during dispersion, which both adsorb on larger pigment particles and are included in the latex structure. Here, a steric factor increases the sedimentation stability of the suspensions additionally. 

The stability improvement of Ti02 suspensions is important not only for water-based paints, but also for paints based on non-polar or low-polar solvents. It is shown in [208] that Ti02 powders modified with an anionic surfactant, e.g. sodium dodecyl sulphate, are dispersed to smaller sizes, and their sedimentation stability increases. The production of water-alkyd emulsions is inhibited due to low mechanical stability. These emulsions can easily break when exposed to shear forces such as those produced by pumps, and when intensively agitated during dispersion. [209] demonstrates that most stable emulsions can be obtained with alkyds showing high acid numbers, as well as with highly polymerised alkyds of low viscosities. 

Busch, W.H., and Keller, G.H. 1983. Analysis of sediment stability on the Peru-Chile continental... 

Whelan III, T., Coleman, J.M., Suhayda, J.N., and Garrison, L.E. 1975. The geochemistry of recent Mississippi River delta sediments—Gas concentration and sediment stability. Proceedings of the 7th Offshore Technology Conference. 3(2342) 71-84. 

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