Gel freezing

Figure 7. Electrophoretic patterns of proteins which are released from thyla-koids during freezing or exposure to 0°C in the presence of various solutes. The solute concentration before freezing is indicated under the gels. Freezing time was 3 hours at —25°C. After thawing, supernatant fluids from membranes were treated with sodium dodecylsulfate (SD) and mercaptoethanol then subjected to gel electrophoresis. Phe is sodium phenylpyruvate, Cap is sodium caprylate, lie is isoleucine. From Volger, Heber, and Berzborn (48).

Ding SQ, Zeng YP, Jiang DL (2007) Fabrication of mullite ceramics with ultrahigh porosity by gel freeze drying. J Am Ceram Soc 90 2276-2279... 

Aloe vera gel (freeze-dried) produced no toxic effects in rats from either acute or sub-chronic oral doses (l-64mg/kg p.o. twice daily). In mice or rats, the preserved or fresh gel failed to cause any toxicity at doses up to 20 g/kg p.o. or i.p., and no toxic effects were found from a dose of 5 g/kg p.o. per day for 45 days. Life-long dosing of a freeze-dried filet of the leaves at 1% of the diet also failed to produce any deleterious effects. ... 

Y.H. Huang, O.L. Jiang, and J.X. Zhang, et al., Fabrication of Transparent Yttria Ceramics Through Gel-freezing Dry Method, J.inorg.Maier., 23[6 1135-1140(2008). 

The fluid is formulated from a premium mineral od-base stock that is blended with the required additive to provide antiwear, mst and corrosion resistance, oxidation stabdity, and resistance to bacteria or fungus. The formulated base stock is then emulsified with ca 40% water by volume to the desired viscosity. Unlike od-in-water emulsions the viscosity of this type of fluid is dependent on both the water content, the viscosity of the od, and the type of emulsifier utilized. If the water content of the invert emulsion decreases as a result of evaporation, the viscosity decreases likewise, an increase in water content causes an increase in the apparent viscosity of the invert emulsion at water contents near 50% by volume the fluid may become a viscous gel. A hydrauHc system using a water-in-od emulsion should be kept above the freezing point of water if the water phase does not contain an antifreeze. Even if freezing does not occur at low temperatures, the emulsion may thicken, or break apart with subsequent dysfunction of the hydrauHc system. 

Gelation. A sol becomes a gel when it can support a stress elasticaUy, defined as the gelation poiat or gelation time, C A sharp iucrease ia viscosity accompanies gelation. A sol freezes ia a particular polymer stmcture at the gel poiat (27). This frozen-ia stmcture may change appreciably with... 

In general, derivatization increases solution and gel clarity, reduces the tendency to gel, improves water binding, increases freeze—thaw stabiHty, reduces the gelatinization temperature, increases peak viscosity, and reduces the tendency to retrograde. Combinations of substitutions are used to obtain desiredproperti.es for specific appHcations. 

Ereeze casting (59) is a hybrid of sHp casting, gel casting, and freeze drying in which a slurry is poured into a rigid mbber mold, frozen, and the frozen Hquid is removed by sublimation, ie, by freeze drying (see Cryogenics). 

Supercritical and Freeze Drying. To eliminate surface tension related drying stresses in fine pore materials such as gels, ware can be heated in an autoclave until the Hquid becomes a supercritical fluid, after which drying can be accompHshed by isothermal depressurization to remove the fluid (45,69,72) (see Supercritical fluid). In materials that are heat sensitive, the ware can be frozen and the frozen Hquid can be removed by sublimation (45,69). 

Distd, then repeatedly fractionally crystd by partial freezing. Immediately before use, the material was passed through a column containing Woelm silica gel (activity I) and Woelm alumina (neutral) in separate layers. 

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