Aging of gels

Bayerite (P-Aluminum Trihydroxide). Bayerite is rarely found in nature. It has been synthesized by several methods A pure product is prepared by the Schm b method (3) in wliich amalgamated aluminum reacts with water at room temperature. Other methods include rapid precipitation from sodium alurninate solution by CO2 gassing, aging of gels produced by neutrali2ation of aluminum salts with NH OH, and rehydration of transition rlio alumina. 

At the IV stage, the ageing of gels is accompanied by the transformation of coagulation bonds into condensation bonds, and by recondensation processes. 

Fig. 4. Thermograms of aged ferric oxide gel precipitated with sodium hydroxide. Age of gels given in days.

Aging of gel at low temperature shortens reaction time and decreases PSD and APS [28]. The mechanism is compatible with the surface gel model. At low temperature, due to low reactivity, builiding blocks are... 

The reactions that bring about gelation continue long after the gel point. In the next chapter we examine the long-term aging of gels, during which they may stiffen, coarsen, and shrink. 

A wet gel, by definition, consists of a continuous solid network, the pores of which contain a liquid phase. At the gel point however, unbound oligomers of various sizes or even monomeric species are still dissolved or dispersed in the pore liquid. This is important for the aging of gels (see below). 

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