Solid properties, control

During the course of the last century, it was realized that many properties of solids are controlled not so much by the chemical composition or the chemical bonds linking the constituent atoms in the crystal but by faults or defects in the structure. Over the course of time the subject has, if anything, increased in importance. Indeed, there is no aspect of the physics and chemistry of solids that is not decisively influenced by the defects that occur in the material under consideration. The whole of the modem silicon-based computer industry is founded upon the introduction of precise amounts of specific impurities into extremely pure crystals. Solid-state lasers function because of the activity of impurity atoms. Battery science, solid oxide fuel cells, hydrogen storage, displays, all rest upon an understanding of defects in the solid matrix. 

Within the subsurface zone, two hquid phase regions can be defined. One region, containing water near the solid surfaces, is considered the most important surface reaction zone. This near solid phase water, which is affected by the sohd phase properties, controls the diffusion of the mobile fraction of the solute adsorbed on the solid phase. The second region constimtes the free water zone, which governs liquid and chemical flow in the porous medium. 

Figure 3.5 shows the organized mesoporous structure of one of these materials. The wide variety of organic molecules with self-assembling properties allows for the synthesis of a myriad of solids with controlled porosity. Cationic surfactants, like the hexadecyltrimethylammonium used to synthesize MCM-41 [26], or three-block copolymers (hydrophilic-hydrophobic-hydrophilic) are two good examples. 

Elliott J.A.W. and Ward C.A., Statistical Rate Theory and the Material Properties Controlling Adsorption Kinetics. In RUDZINSKI W., STEELE W.A., ZGRABLICH G.. (eds.) Equilibria and Dyrutmics of Gas Adsorption on Heterogeneous Solid Surfaces (Elsevier New York, 1997), pp.285-333. 

The drying kinetics (rate of drying, and hence required drying time) also depend strongly on solids properties, particulany particle size and porosiW. The surface area/mass ratio and the internal pore structure control the extent to which an operation is diffusion-limited, i.e., diffusion into and out of the pores of a given solids particle, not through the voids among separate particles. 

I. INTRODUCTION C. Control of solid properties IV. C yD-BASED SITE-SPECIHC... 

The habit of crystals obtained from an industrial crystallization process can have a major impact on a number of important properties relating to the slurry and the dry product. Crystal habit will affect the rheological properties of the suspension, the filtration or centrifugation efficiency, the bulk density of the solid, and the flow properties of the solid. The control of crystal habit (along with crystal size distribution) is, therefore, an important part of industrial crystallization processes. 

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