Gelled layer

Slush molding Used to create hollow, flexible items. A quantity of plastisol is poured into a heated female mold, causing gelling of the plastisol directly in contact with the heated surfaces. The excess plastisol is poured off and the gelled layer is allowed to fuse. After fusing, the finished item is removed from the mold. 

HEC Coherent tablets with gelled layer formed only with few grades... 

Dispersion of polymeric viscosifiers is often difficult because the initial contact of the untreated polymer with water results in very rapid hydration of the outer layer of particles which creates a sticky, rubbery exterior layer that prevents the interior particles from contacting water. The net effect is formation of what are referred to as nfish eyes" or "gel balls." These hamper efficiency by lowering the viscosity achieved per pound of gelling agent and by creating insoluble particles that can restrict flow both into the formation and back out of it. The normal remedy for this behavior... 

Button cells consist of cathode and anode cans (used as the terminals), powdered zinc anode, containing gelled electrolyte and the corrosion inhibitor, separator with electrolyte, thin (0.5 mm) carbon cathode with catalyst and PTFE, waterproof gas-permeable (teflon) layer and air distribution layer for the even air assess over the cathode surface. Parameters of battery depend on the air transfer rate, which is determined by quantity and diameters of air access holes or porosity of the gas-diffusion membrane. Air-zinc batteries at low rate (J=0,002-0,01C at the idle drain and J= 0,02-0,04C at the peak continuous current) have flat discharge curves (typical curve is shown by Figure 1). 

From Equation 2.2, it can be seen that the viscosity of the slip plays an important role. It regulates the formation rate of the gel layer and helps to prevent the slip from penetrating the support pore system. In the colloidal suspension route the evolution of the viscosity during the solvent extraction is slow during the very first steps of the process and drastically increases just before gelling. With the polymeric gel route a more gradual increase of the viscosity is observed. In both cases the evolution of the viscosity can be modified by the addition of binders to the sol slip . Different kind of binders are chosen depending on the nature of the solvent, the compatibility with the precursors and the viscosity of the system. 

Characteristic microstructural properties of TiOj membranes produced in this way are given in Table 2.5. Mean pore diameters of 4-5 nm were obtained after heat treatment at T < 500°C. The pore size distribution was narrow in this case and the particle size in the membrane layer was about 5 nm. Anderson et al. (1988) discuss sol/gel chemistry and the formation of nonsupported titania membranes using the colloidal suspension synthesis of the type mentioned above. The particle size in the colloidal dispersion increased with the H/Ti ratio from 80 nm (H /Ti = 0.4, minimum gelling volume) to 140 nm (H /Ti " — 1.0). The membranes, thus prepared, had microstructural characteristics similar to those reported in Table 2.5 and are composed mainly of 20 nm anatase particles. Considerable problems were encountered in membrane synthesis with the polymeric gel route. Anderson et al. (1988) report that clear polymeric sols without precipitates could be produced using initial water concentrations up to 16 mole per mole Ti. Transparent gels could be obtained only when the molar ratio of H2O to Ti is < 4. Gels with up to 12 wt.% T1O2 could be produced provided a low pH is used (H /Ti + < 0.025). 

To overcome the poor mechanical properties of polymer and gel polymer type electrolytes, microporous membranes impregnated with gel polymer electrolytes, such as PVdF. PVdF—HFP. and other gelling agents, have been developed as an electrolyte material for lithium batteries.Gel coated and/ or gel-filled separators have some characteristics that may be harder to achieve in the separator-free gel electrolytes. For example, they can offer much better protection against internal shorts when compared to gel electrolytes and can therefore help in reducing the overall thickness of the electrolyte layer. In addition the ability of some separators to shutdown... 

Numerous asymmetric membranes were prepared under various conditions and their cross-section was examined by SEM. Typical of the results are those shown in Figure 5 for the membrane cast from 70 30 THF-formamide and gelled in IPA. Close inspection of Figure 5 reveals a thin, relatively dense skin supported by a microporous layer. The support layer contains macrovoids, the cause of which is presently under investigation. 

The cross-sections of two typical cylindrical cells are shown in Fig. 3.9. In Fig. 3.9(a) a D-size unit used for flashlights and similar applications is shown a large capacity alarm cell is shown in Fig. 3.9(b). The electrolyte or paste separator in Fig. 3.9(a) is a relatively thin layer of electrolyte solution immobilized in a gel or microporous separator. Different manufacturers favour different forms of separator. These range from gelled... 

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