Solid-Liquid Suspension Chapters

Coating development in the preceding Chapter 5.3.1 on APS can be described as the result of injecting the solid precursor powder by a stream of accelerated (inert) gas into the plasma jet, whereas SPS uses an injected liquid as the powder carrier (Figure 5.29). The introduction of the powder material into the plasma jet in form of a solid-liquid suspension via an atomizer allows the utilisation of very... 

Design methods for solid-liquid suspension were some of the first to be established (Zwietering, 1958), and this early work has withstood the test of time virtually unchanged. Solid-liquid mixing is discussed in Chapter 10, with design guidelines for ... 

The material presented in this chapter has been used by the author to study and predict the flow behavior of water and solid-liquid suspensions in a 10-mi-long pipeline between a processing plant and dock facility. I would tell you about it now, but that s another story, and this chapter is long enough already ... 

Disperse systems can be classified in various ways. Classification based on the physical state of the two constituent phases is presented in Table 1. The dispersed phase and the dispersion medium can be either solids, liquids, or gases. Pharmaceutically most important are suspensions, emulsions, and aerosols. (Suspensions and emulsions are described in detail in Secs. IV and V pharmaceutical aerosols are treated in Chapter 14.) A suspension is a solid/liquid dispersion, e.g., a solid drug that is dispersed within a liquid that is a poor solvent for the drug. An emulsion is a li-quid/liquid dispersion in which the two phases are either completely immiscible or saturated with each other. In the case of aerosols, either a liquid (e.g., drug solution) or a solid (e.g., fine drug particles) is dispersed within a gaseous phase. There is no disperse system in which both phases are gases. 

Sample levitation can be accomplished in different ways, one of which is by using ultrasonic energy. The phenomenon by which small samples of solids, liquids or suspensions can be levitated at the nodal points of a standing ultrasonic wave was first described by Bucks and Muller in 1933 [70]. The flexibility and potential of acoustic levitation in various fields are widely documented, mainly by studies in the analytical and bioanalytical fields [71-73]. Therefore, levitation can be considered a mature technique. Its development warrants inclusion of a dedicated section in this chapter to describe its fundamentals and compare the advantages and limitations of acoustic levitation with other levitation modes. The devices used for this purpose and the potential applications of each mode are also discussed. 

In operations such as crystallization or solid-catalysed liquid reactions, it is necessary to suspend solid particles in a relatively low viscosity liquid. This can be achieved in mechanically agitated vessels where the mixer is used to prevent sedimentation of the solids and to provide conditions suitable for good liquid-solid mass transfer and/or chemical reaction. If agitation is stopped the solids will settle out or float to the surface, depending upon the relative densities of the solid and liquid phases. The suspension of solids in mixing vessels and the design of mixing vessels for solid-liquid reactions are treated in Chapters 16 and 17 respectively. 

By implication, therefore, processes which are particularly dependent on turbulent eddies and their associated forces are likely to be well correlated by energy dissipation rate. Bubble formation (Chapter IS) and micromixing phenomena (Chapter 10), for instance, fall into this category. However, processes which are dependent on the anisotropic ntain flows and for which the non-homogeneous nature of stirred tanks turbulence is significant, e.g. solid suspension and solid-liquid mass transfer (Chapters 16 and 17), are not well correlated that way. 

On the other hand, elucidation of the typical components and different forms of the physical. systems that we call pharmaceutical suspensions requires previously to have an idea about the different types of suspensions, intimately related to their purpose and applications. Thus, most authors consider three main kinds of pharmaceutical suspensions (4-6). namely, orally administered, or. simply oral, suspensions externally applied (topical suspensions) and injectable or parenteral. Although strictly speaking, from the colloid science point of view, aerosols ore simply suspensions in which the dispersion medium is a gas and the di.spersed material is. solid, throughout this chapter we will primarily adhere to the more clussicul point of view that considers only solid/liquid dispersions under the denomination of suspensions. Their most significant features are displayed in Table I (see also Refs. 4-6). 

Liquid-liquid and solid-liquid dispersed systems are complicated forms from a physicochemical point of view, because of the presence of two phases. Their formulation therefore necessitates comprehension of fundamental aspects controlling the behavior of these systems. With this end in view, we begin this volume with theoretical considerations concerning pharmaceutical surfactants, formulation concepts, and emulsion properties, and the related know-how to attain them. As the text progresses, each chapter becomes more advanced and specific. Thermodynamic and kinetic aspects of suspension formulations, as well as... 

In the past few decades, plasma spray-coating techniques have been developed to cover orthopedic implants with protective and/or bioactive coatings. As introduced in Chapter 1, the plasma spray-coating method employs high temperature plasma jet to melt and spray a feedstock material onto a substrate to form a coating. The feedstock materials for plasma spray can be in the forms of solid, liquid or suspension [29,30]. For the fabrication of nanocoating on orthopedic implants, the commonly used solid... 

Most of the studies referred to in the previous discussion used two-phase (gas-liquid) systems. The considerations are substantially similar when the liquid jet ejector is to be used as a three-phase catalytic reactor, particularly because the catalyst loading commonly used in a venturi loop system is relatively low. In terms of mass transfer, besides gas-liquid mass transfer, solid-liquid mass transfer step assumes great importance. As discussed in Chapters 7A and 7B, factors relating to dispersion of the gas phase, suspension of solids, and concentration profile of the catalyst phase need to be addressed in the case of a three-phase reactor. 

This chapter will start with a short account of the general classification and description of polymeric surfactants. This is followed by a summary on then-solutions properties. The adsorption and conformation of polymeric surfactants at the solid-liquid interface will be discussed at a fundamental level and some experimental results will be presented to illustrate the prediction of the theories. The interaction energies between particles or droplets containing adsorbed polymeric surfactants will be briefly described. The final section will give some applications of polymeric surfactants in suspensions, emulsions, and multiple emulsions. 

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