Spongy particles

Fig. 7 SEM pictures representing A sample prq>ared at a concentratirai above 30 wt%, B the spongy particles obtained at 30 wt.% and C spheres corresponding to the Iowa concentrations of tinplate.

The morphology of powder particles electrodeposited from electrolytes with different Ni/Mo ion concentration ratios (1/0.3, 1/1, and 1/3) is shown in Figs. 8.29, 8.30, and 8.31. For the Ni/Mo ratio, 1/0.3 typical spongy particles were detected... 

Fig. 8.29 (a) Typical spongy particles electrodq)osited at the Ni/Mo = 1/0.3. (b) Cavity marked with arrow in (a) at higher magnification (Reprinted from Ref. [1] with kind permission from Springer)... 

As represented in Figure 4.11, for a given concentration by weight of silica in a sol, the volume fraction of the dispersed phase varies with (a) the volume of the ion atmosphere in the double layer surrounding each particle, and (b) the porosity or hydration of the particles. If the viscosity is measured at pH 2, where there is no charge on the particles, then it can be used to deduce how much water is bound to the surface of solid particles, or is held within spongy particles or aggregates, since such water must be considered as part of the dispersed phase. 

As can be seen they are in good agreement with the SEM results Fig. 2.28b ball-like particles Fig. 2.28c spongy particles Fig. 2.28d compact agglomerates. Although for Co powder different types of agglomerates are present, it is quite obvious that all Co powder... 

The polamation phenomena can be observed by methods similar to those described in the previous paragraphs. Differences between compact and spongy particles exhibit themselves in the colour of the scattered light ... 

In suspension processes the fate of the continuous liquid phase and the associated control of the stabilisation and destabilisation of the system are the most important considerations. Many polymers occur in latex form, i.e. as polymer particles of diameter of the order of 1 p.m suspended in a liquid, usually aqueous, medium. Such latices are widely used to produce latex foams, elastic thread, dipped latex rubber goods, emulsion paints and paper additives. In the manufacture and use of such products it is important that premature destabilisation of the latex does not occur but that such destabilisation occurs in a controlled and appropriate manner at the relevant stage in processing. Such control of stability is based on the general precepts of colloid science. As with products from solvent processes diffusion distances for the liquid phase must be kept short furthermore, care has to be taken that the drying rates are not such that a skin of very low permeability is formed whilst there remains undesirable liquid in the mass of the polymer. For most applications it is desirable that destabilisation leads to a coherent film (or spongy mass in the case of foams) of polymers. To achieve this the of the latex compound should not be above ambient temperature so that at such temperatures intermolecular diffusion of the polymer molecules can occur. 

To remove the essential oil from the peel of citrus fruits, the oil glands, which are located in the flavedo (the outer coloured portion of the peel), are ruptured by mechanical systems. The oil is washed away with a spray of water to produce an oil-in-water emulsion with small peel particles. To prevent absorption of the essential oil by the spongy albedo (the iimer white portion of the peel), this emulsion is passed through a screening device (finisher) of 0.5 to 0.7 mm in diameter, which removes the coarsest particles of the fruit peels [12]. 

PORE. I A minute cavity in epidermal tissue as in skin, leaves, or leather, having a capillary channel to the surface that permits transport of water vapor from within outward but not the reverse. 2. A void of interstice between particles of a solid such as sand minerals or powdered metals, that permits passage of liquids or gases through the material in either direction. I11 some structures, such as gaseous diffusion barriers and molecular sieves, the pores ate of molecular dimensions, i.e 4-10 A units. Such microporous structures are useful for filtration and molecular separation purposes in various industrial operations. 3. A cell in a spongy structure made by gas formation (foamed plastic) that absorbs water on immersion but releases it when stressed. 

There are various kinds of polytetrafluoroethylene. One is granular polymer consisting of spongy, white particles having a median size of about 600/l The specific surface of this polymer is on the order of 2 m2/g (determined by nitrogen adsorption and calculations by the method of Brunauer, Emmett, and Teller). Since this specific surface area is about 1700 times the observed outer surface of the particles, these measurements confirm the porous, spongelike structure that can be seen in the photomicrograph of a cross section of several particles in Fig. la. 

The parameters of the pore structure, such as surface area, pore volume, and mean pore diameter, can generally be used for a formal description of the porous systems, irrespective of their chemical composition and their origin, and for a more detailed study of the pore formation mechanism, the geometric aspects of pore structure are important. This picture, however, oversimplifies the situation because it provides a pore uniformity that is far from reality. Thorough attempts have been made to achieve the mathematical description of porous matter. Researchers discussed the cause of porosity in various materials and concluded that there are two main types of material based on pore structure that can be classified as corpuscular and spongy systems. In the case of the silica matrices obtained with TEOS and other precursors, the porous structure seems to be of the corpuscular type, in which the pores consist of the interstices between discrete particles of the solid material. In such a system, the pore structure depends on the pores mutual arrangements, and the dimensions of the pores are controlled by the size of the interparticle volumes (1). 

Because particles may be hard and smooth in one case and rough and spongy in another, one must express densities with great care. Density is universally defined as weight per unit volume. Three types of densities—true density, particle density, and bulk density—can be defined, depending on the volume of particles containing microscopic cracks, internal pores, and capillary spaces. 

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