Settling of dispersions

At the pouring temperature, the suppository mass should be sufficiently viscous to prevent the settling of dispersed particles during the filUng process. 

As shown in Figure 2, adsorption of dispersants on particle surfaces can increase 2eta potential further, enhancing electrostatic repulsion. Increased repulsion between particles is evidenced by lower viscosity in concentrated slurries, or decreased settling rates in dilute suspensions. The effect of added dispersants on settling of (anhydrous) iron oxide particles is shown in Figure 3. 

Fig. 3. Effect of dispersants on settling rate of 700 mg/L dehydrated iron oxide in water. Left, no dispersant. Right, 3 mg/L styrenesulfonate—maleic acid...

Thru a combination of sedimentation and transmission measurements, a particle size distribution can be found. Tranquil settling of a dispersion of non-uniform particles will result in a separation of particles according to size so that transmission measurements at known distances below the surface at selected time intervals, will, with Stokes law, give the concn of particles of known diameter. Thus, a size frequency distribution can be obtained... 

Particles of matter suspended in water that can be removed by filtration or prevented from settling for periods of time by the use of dispersants. 

Theoretically, electrokinetic processes should also occur in nondisperse systems, but then additional factors arise (vortex formation in the liquid, settling of the particles, etc.) which produce a strong distortion. Hence, electrokinetic processes can be regarded as one of the aspects of the electrochemistry of disperse heterogeneous systems. 

Ud Settling (terminal) velocity of dispersed phase in a decanter LT-1... 

The fineness characteristic of a powder on a cumulative basis is represented by a straight line from the origin to 100 per cent undersize at a particle size of 50 un. If the powder is initially dispersed uniformly in a column of liquid, calculate the proportion by mass which remains in suspension in the time from commencement of settling to that at which a 40 i m particle falls the total height of the column. It may be assumed that Stokes law is applicable to the settling of the particles over the whole size range. 

The main benefits of nondispersive solvent extraction over the conventional process are (1) it avoids the need of a settling stage for phase disengagement and the consequent risk of dispersed phase carryover (2) the value of the interfacial area per unit volume can be much higher than in a liquid-liquid dispersion as there is no risk of phase inversion and (3) the interfacial area is easily calculated and scale-up of the process is straightforward. 

The way to maximise the solids content of the slurry while keeping a reasonable viscosity is through the use of a dispersant. The dispersant helps maintain fine solid particles in a state of suspension, thus minimising their agglomeration or settling. The dispersant is generally a low molecular weight acrylic based polymer. For most applications, cost of dispersant is critical. 

Given time, water which exists as discrete droplets in finished fuel may coalesce into larger drops and settle by gravity from the fuel. Demulsifiers or dehazers can accelerate this process by functioning as a site for attraction of dispersed water. 

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