Divided solid, definition

The estimation of the surface area of finely divided solid particles from solution adsorption studies is subject to many of the same considerations as in the case of gas adsorption, but with the added complication that larger molecules are involved whose surface orientation and pore penetrability may be uncertain. A first condition is that a definite adsorption model is obeyed, which in practice means that area determination data are valid within the simple Langmuir Equation 5.23 relation. The constant rate is found, for example, from a plot of the data, according to Equation 5.23, and the specific surface area then follows from Equations 5.21 and 5.22. The surface area of the adsorbent is generally found easily in the literature. 

The amount of surface-active agent present may be so small that no measurable change in any physical property, including interfacial tension, can be detected. This is particularly true if the agent is a finely divided solid (El). Lindland and Terjesen (L4) showed that, after a definite but small concentration of surfactant had been used, further additions caused but little change in terminal velocity. 

This term is restricted here to equipment in which finely divided solids in suspension interact with gases. Solids fluidized by liquids are called slurries. Three phase fluidized mixtures occur in some coal liquefaction and petroleum treating processes. In dense phase gas-solid fluidization, a fairly definite bed level is maintained in dilute phase systems the solid is entrained continuously through the reaction zone and is separated out in a subsequent zone. 

As is the case in most discussions of interfacial systems and their applications, definitions and nomenclature can play a significant role in the way the material is presented. The definition of an emulsion to be followed here is that they are heterogeneous mixtures of at least one immiscible liquid dispersed in another in the form of droplets, the diameters of which are, in general, greater than 0.1 (.m. Such systems possess a minimal stability, generally defined rather arbitrarily by the application of some relevant reference system such as time to phase separation or some related phenomenon. Stability may be, and usually is, enhanced by the inclusion of additives such as surfactants, finely divided solids, and polymers. Such a definition excludes foams and sols from classification as emulsions, although it is possible that systems prepared as emulsions may, at some subsequent time, become dispersions of solid particles or foams. 

An emulsion is a heterogeneous system, consisting of at least one immiscible liquid intimately dispersed in another in the form of droplets, whose diameter, in general, exceeds 0.1 micron (italics ours) . He has further opined that such systems possess a minimal stability, which may be accentuated by such additives as surface active agents, finely divided solids etc. [1]. The presence of a surface active agent (see below, and also Chapter 2) obviously makes the system tri-component. More recently, Dickinson [2] accepted the traditional definition of an emulsion as an opaque, heterogeneous system of two immiscible liquid phases ( oil and water ) with one of the phases dispersed in the other as droplets of microscopic or colloidal size . In spite of Becher s contention that the dispersed phase is a liquid, it has been commented that the difference between a liquid-in-liquid emulsion and a solid particle dispersion in a liquid is not entirely distinct [2]. Further, in an emulsion, the dispersed phase itself can be an emulsion, so that this multiple emulsion can be of the types water-in-oil-in water or oil-in-water-in-oil [3,4]. We can also have more than one dispersed phase in a continuous phase, e.g. two kinds of aqueous solution in oil for very short periods before collision and coalescence, which is a very important route for synthetic reactions. Examples of the varieties of emulsions relevant to solid particle preparation will be cited and discussed in later Chapters. 

We suppose that the Gibbs dividing surface (see Section III-5) is located at the surface of the solid (with the implication that the solid itself is not soluble). It follows that the surface excess F, according to this definition, is given by (see Problem XI-9)... 

The material on solids drying is divided into two subsections, Solids-Drying Fundamentals, and Sohds-Drying Equipment. In this introductory part some elementary definitions are given. In solids-gas contacting equipment, the solids bed can exist in any of the following four conditions. 

This book is divided into three parts the first part covers the fundamental aspects, which should form the backbone of any course. As is evident from the title I consider electrochemistry to be a science of interfaces - the definition is given in the introduction -, so I have treated the interfaces between a metal or a semiconductor and an electrolyte solution, and liquid-liquid interfaces. I have not considered solid... 

Commercial Plastisols, Accdg to definition given in Ref 2, a plastisol is a liquid dispersion of finely divided resin in a plasticizer. It is usually 100% solid with no volatiles when volatile content exceeds 5% of the total wt it is called organosol. When the plastisol is heated, the plasticizer solvates the resin particles, and the mass gels. With continued application of heat the mass fuses to become a conventional thermoplastic material... 

When describing liquid surfaces, the surface tension was of fundamental importance. If we try to extend the definition of surface tension to solids, a major problem arises [324], If the surface of a liquid increases, then the number of surface atoms increases in proportion. For a solid surface this plastic increase of the surface area is not the only possible process. Usually more important is an elastic increase of the surface area. If the solid surface is increased by mechanically stretching, the distance between neighboring surface atoms changes, while the number of surface atoms remains constant. The change in surface area is commonly described in terms of the surface strain. The total surface strain etot is given by the change in surface area divided by the whole surface area detot = dA/A. The surface strain may be divided into a plastic strain dep and an elastic strain dse so that dstot = dep + dee. 

For porous solids such as coal, there are five different density measurements true density, apparent density, particle density, bulk density, and in-place density. The true density of coal is the mass divided by the volume occupied by the actual, pore-free solid in coal. However, determining mass of coal may be deemed as being rather straightforward, but determining volume presents some difficulties. Volume, as the word pertains to a solid, cannot be expressed universally in a simple definition. Indeed, the method used to determine volume experimentally, and subsequently, the density, must be one that applies measurement rules consistent with the adopted definition. 

Figure 4.11 Definition of the solid angle fi0 of a point source Q accepted by the entrance slit S of a sector CMA. Two cross-cuts are shown (a) for a plane containing the symmetry axis of the analyser, (b) for a plane perpendicular to this axis. The principal ray starting at Q is shown together with the angular spreads from the finite acceptances in A and Acp. If expressed in spherical coordinates, the slit S has a width b = r2 A and a length i = i ,2 + A

Example 10.9 used two different definitions of the catalyst density and at least two more definitions are in common usage. The value pc = 367 refers to the reactor average density. It is quite low in the example because so much of the reactor volume is empty. Normally, the reactor would be packed almost completely, and the reactor average density would approach the bulk density. The bulk density is what would be measured if the catalyst were dumped into a large container and gently shaken. The bulk density is not stated in the example, but it would be about 800 kg/m3 for the catalyst pellets prior to grinding. The catalyst will pack to something less than the bulk density in a small-diameter tube. The pellet density in the example is 1120 kg/m3. It is the mass of a catalyst pellet divided by the external volume of the pellet. The final density is the skeletal density of the pellet. It is the density of the solid support and equals 1120/(1 — 0.505) = 2260 kg/m3 for the example catalyst. The various densities fall in the order... 

According to the IUPAC definition, porous materials ate divided into three different classes, depending on their pore sizes. Mesoporous materials are described as materials whose pore diameters lie in the range between 2 and 50 nm. Solids with a pore diameter below 2 nm or above 50 nm belong to the class of micro- and macroporous materials, respectively. 

See, for example, Chap. 2 in G. Sposito, The Surface Chemistry of Soils, Oxford University Press, New York, 1984. The location of an interface is a molecular-scale concept that macroscopic definitions like Eq. 4.1 cannot make precise. That the interface is likely to be located within three molecular diameters of the periphery of an adsorbent solid is sufficient detail for the application of the concepts in the present section. See D. H. Everett, op. cit.,1 for additional discussion of the interface to which Eq. 4.1 applies (known technically as a Gibbs dividing surface). 

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