Solid solution terms, 12-13 regular

We have already learned that metals may be deformed easily and we have explained this in terms of the absence of directional character in metallic bonding. In view of this principle, it is not surprising that two-element or three-element metallic crystals exist. In some of these, regular arrangements of two or more types of atoms are found. The composition then is expressed in simple integer ratios, so these are called metallic compounds. In other cases, a fraction of the atoms of the major constituent have been replaced by atoms of one or more other elements. Such a substance is called a solid solution. These metals containing two or more types of atoms are called alloys. 

The first two terms describe mechanical mixing of endmembers A and B, the third is the ideal solution mixing term, and the last term is the regular solution contribution, in which solid solution composition. (If a> is not so independent, the solution is not regular). The term (oNJ n in Eq. (1.39) is also sometimes called the excess Gibbs free energy of mixing, or AG (excess). 

Above about 900 °C all carbon steels form a non-magnetic interstitial solid solution of carbon in y iron, called austenite. The amount of carbon which can be taken up in solid solution is, "however, limited to about 17 per cent by weight, equivalent to 7 5 atomic per cent, and it is therefore clear that the number of carbon atoms is insufficient for them to be arranged in any regular way and that they must be distributed at random in the interstices of the structures. If more carbon is present the excess occurs as graphite, and in this case the system is usually described as cast iron . It is convenient to restrict the term steel to those systems in which the carbon content does not exceed 7-5 atomic per cent. 

In Chapter 6 we saw that the chemistry of sodium can be understood in terms of the special stability of the inert gas electron population of neon. An electron can be pulled away from a sodium atom relatively easily to form a sodium ion, Na+. Chlorine, on the other hand, readily accepts an electron to form chloride ion, Cl-, achieving the inert gas population of argon. When sodium and chlorine react, the product, sodium chloride, is an ionic solid, made up of Na+ ions and Cl- ions packed in a regular lattice. Sodium chloride dissolves in water to give Na+(aq) and C (aq) ions. Sodium chloride is an electrolyte it forms a conducting solution in water. 

CA of Polysaccharides. Polysaccharides adopt a wide variety of shapes that depend on their composition and their environment. In solution, polymers are almost always random coils that have local regions that might be similar to conformations that are found in the solid state. The chapter by Brant and Christ discusses conformations of polysaccharides in solutions both in terms of these local regions and by the overall shape of the random coil in terms of end-to-end distance, etc. The following discussion concerns only linear (unbranched) molecules, and refers only to regular polymers, i.e., those that have repeated sequences of monomeric residues located by screw-axis (helical) symmetry. 

Two models are frequently used to predict the activity coefficient of the solid the regular solution model (93) and the DLP (delta-lattice-parameter) model (94). With both models, the activity coefficient of component i, yf, is calculated in terms of the interaction parameter, ft, by the expression... 

McBain s term Sorption applies to all cases when a gas or solute is taken up by a solid. Adsorption means strictly the formation of a layer on an impermeable surface a sorption to penetration, or solution, into the interior. With the zeolites, there are pores of quite regular shape and size, only a few A. across. With charcoal there are irregular pores of similar size, as well as larger ones. Foreign substances, finding their way into these very fine pores may be said to be adsorbed on the walls of the pores, but as they permeate the whole structure of the solid more or less uniformly, they may equally be said to be absorbed by the solid. McBain avoids this difficulty simply by omission of the prefix. 

Now, let us return to the fluid mechanics problem of streaming flow past a solid sphere at small, but nonzero, Reynolds numbers. The objective is to see how the steady-state creeping-flow solution is modified if we consider the nonlinear terms in (7-2) for Re < 1. As we shall see, there is essentially the same problem of trying to obtain a solution of (7-2) in the form of a regular perturbation expansion as was encountered when we tried to obtain such a solution of the thermal problem for IP

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These are usually heat effects during dissolution of solids (and liquids) in solvents, and the ideal solution relation is modified by an energy term that takes into account heats of mixing. The term modifies the ideal solution equation to give the regular solution theory prediction of solubility... 

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