Suspensions small solid particles

SUSPENSION. A liquid medium having small, solid particles uniformly dispersed through it. 

Dust may be defined as suspension in air or other gases, of small solid particles ranging from ca 0.05 to 1000 microns in size. Mrs is usually water or other liq in the form of particles floating or falling in the atmosphere. Vapor is a term applied to a gas that is at a temp below its critical temp, which can, therefore, be condensed by pressure alone... 

One type of colloidal system has been chosen for discussion, a system in which the solid metal phase has been shrank in three dimensions to give small solid particles in Brownian motion in a solution. Such a colloidal suspension consisting of discrete, separate particles immersed in a continuous phase is known as a sol. One can also have a case where only two dimensions (e.g., the height z and breadth y of a cube) are shrank to colloidal dimensions. The result is long spaghettihke particles dispersed in solution—macromolecular solutions. 

Microcarriers are small solid particles (kept in suspension by stirring) upon which cells may grow as a monolayer. They confer the advantage of large scale suspension cultures on anchorage dependent cells. They thus offer the following advantages. 

Spray drying. A suspension of small solid particles in water is sprayed as a fine mist into a stream of hot air. The water evaporates, larger solid particles settle out of the air and are removed by a conveyor, and fine suspended particles are separated from the air by a bag filter or cyclone separator. Dried milk is produced in this manner. 

Narrowing of NMR lines has been observed in colloidal suspensions of ultrafine particles, presumably by Brownian motion. A suggestion related to this principle is to take small solid particles into a liquid medium and induce sufficient reorientational motion of these particles to produce narrowing (Satoh and Kimura 1990). Ultrasound induces translational motion and collisions of the particles produce rotation. This sonically induced narrowing has been observed for Al in aluminium sulphate, with the advantage that no spinning sidebands were observed (Homer et al. 1991). The experiment depends on the frequency and the power of the ultrasound and the liquid medium. Although the first reports of this approach appeared in 1989 there have been few developments in this field. 

Anyway, bridging by adsorbed polymers will often depend on the history of the system. Consider a dispersion of small solid particles that tend to aggregate. To stabilize the suspension, an adsorbing polymer is added that can give a maximum surface excess Tpiateau of 6 mg m-2. If the specific particle surface area A is lm2 per ml and 3 mg of a suitable surfactant polymer is added per ml, a r value of at most 3 mg per m2 can result. This value is on the low side, but the particles are nevertheless stabilized apparently, polymer chains stick out far enough into the solvent to cause steric repulsion. Assume now that to 1 ml of the suspension 6 mg of polymer is added and that subsequently 1 ml of suspension without polymer is added. 

Ideal for sprays containing small solid particles mixed inside liquid (a suspension spray)... 

A colloidal sol is a suspension of very small solid particles in a continuous liquid medium. Colloidal sols are quite stable and show the Tyndall effect (light scattering by particles in a colloid). They can be quite stable. Examples include blood, pigmented ink, and paint. Colloidal sols can change their viscosity quickly if they... 

Aerosol Suspension of small solid particles and/or liquid droplets in a gas, usually air. 

Colloids or sols can be made (a) by peptizing small particles in a solvent, which means that the suspended solid particles are given a surface charge that prevents them from coagulating and keeps them in a stable suspension, a sol or (b) by growing small solid particles from a solution of molecules, e.g., hydroxides from hydrolized halides, or by polymerization from a solution of monomers. 

For small solid particles whose density is approximately equal to that of the liquid, once suspended they continue to move with the liquid. The suspension behaves like a single-phase liquid at low solid concentrations the mixing operation is more like blending than solid suspension. For heavier solid particles, their velocities will be different from that of the liquid. The drag force on the particles caused by the liquid motion must be sufficient and directed upward to counteract the tendency of the particles to settle by the action of gravity. 

Spray drying is a very common process, in which a liquid feed-typically a suspension, an emulsion, or a solution-is atomised within a heated drying chamber. By evaporation of the solvent small solid particles are obtained, which may be the final... 

There are many kinds of systems with interfacial effects that are of practical interest. Such systems have a large surface area per unit mass and either consist of very small particles or have an extremely irregular surface. Surface effects can dominate in determining the behavior of such systems. Colloids are suspensions of small solid particles in a liquid medium. Aerosols are suspensions of fine solid or liquid particles in a gas and are important in atmospheric chemistry and physics. A number of solids with large... 

Another method widely used for controlled S5mthesis of multifunctional ceramics is the sol-gel, that is used for the S3mthesis of a colloidal suspension where the dispersed phase is a solid and the dispersion medium is liquid, and is called sol. Therefore, there is the formation of a dual phase material a solid body that is occupied by a solvent, i.e., moist gel. The initiator compounds, commonly called precursors, consist of a metal surrounded by many connections and typically are inorganic salts or organic compounds. The two precursors undergo two chemical reactions at sol preparation hydrolysis and condensation, which resulted from the addition of an acid or base catalyst to form small solid particles or clusters in a liquid (aqueous solvent) [32,33]. The sol-gel method provides homogenous mixtures of cations on an atomic... 

Filter aids as well as flocculants are employed to improve the filtration characteristics of hard-to-filter suspensions. A filter aid is a finely divided solid material, consisting of hard, strong particles that are, en masse, incompressible. The most common filter aids are applied as an admix to the suspension. These include diatomaceous earth, expanded perlite, Solkafloc, fly ash, or carbon. Filter aids build up a porous, permeable, and rigid lattice structure that retains solid particles and allows the liquid to pass through. These materials are applied in small quantities in clarification or in cases where compressible solids have the potential to foul the filter medium. 

Colloidal suspensions are systems of small mesoscopic solid particles suspended in an atomic liquid [1,2]. We will use the term colloid a little loosely, in the sense of colloidal particle. The particles may be irregularly or regularly shaped (Fig. 1). Among the regular shapes are tiny spherical balls, but also cylindrical rods or flat platelets. As the particles are solid, fluctuations of their form do not occur as they do in micellar systems. Not all particles in a suspension will, in general, have the same form. This is an intrinsic effect of the mesoscopic physics. Of course in an atomic system, say silicon, all atoms are precisely similar. One is often interested in the con-... 

In order to achieve uniform solid suspension or pickup of solid particles off the bottom, the upward velocities of the fluid streams in all portions of the vessel must exceed the terminal setding velocity of the particular particles. This can be determined by small scale tests. 

An ophthalmic suspension should use the drug in a microfine form usually 95% or more of the particles have a diameter of 10 pm or less. This is to ensure that the particles do not cause irritation of the sensitive ocular tissues and that a uniform dosage is delivered to the eye. Since a suspension is made up of solid particles, it is at least theoretically possible that they may provide a reservoir in the cul-de-sac for slightly prolonged activity. However, it appears that this is not so, since the drug particles are extremely small, and with the rapid tear turnover rate they are washed out of the eye relatively quickly. 

Transition from liquid behavior to solid behavior has been reported with fine particle suspensions with increased filler content in both Newtonian and non-Newtonian liquids. Industrially important classes are rubber-modified polymer melts (small rubber particles embedded in a polymer melt), e.g. ABS (acrylo-nitrile-butadiene-styrene) or HIPS (high-impact polystyrene) and fiber-reinforced polymers. Another interesting suspension is present in plasticized polyvinylchloride (PVC) at low temperatures, when suspended PVC particles are formed in the melt [96], The transition becomes evident in the following... 

If the solid particles are very small (e.g., typically less than 100 /xm) and/or not tremendously denser than the fluid, and/or the flow is highly turbulent, the mixture may behave as a uniform suspension with essentially continuous properties. In this case, the mixture can be described as a pseudo singlephase uniform fluid and the effect of the presence of the particles can be... 

Another trend that has received considerable recent attention is the decomposition of metal clusters under controlled conditions on solid supports or on liquid suspensions, which generates small metallic particles of specific size, struc-... 

Fluidized beds have also been used for generating suspensions of solid particles with diameters in the range of 0.5-40 gm. Air flows through the fluidized bed, which contains beads kept suspended by the motion of the air dust injected into the bed is broken up into small particles and carried out with the air flow (Raabe, 1976). 

Pyrotechnic smoke is basically an aerosol, that is, a suspension of small solid or liquid particles in a gaseous medium. The small particles of smoke are formed due to the heat of chemical reaction between oxidizer and fuel (exothermic... 

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