Microbubbles phenol

The following polymeric materials have been used as ablative materials for specific applications phenolics, phenyl silanes, nitrile phenolics, nitrile rubber, silicones, epoxy polyamide, and novolac epoxies. Fillers and reinforcements are used in ablative formulations to improve performance and reduce thermal conductivity. Common ablative fillers are glass, siUca, and quartz cloth carbon and graphite cloth microbubbles (phenolic, silica, and glass) and asbestos fiber. 

Li et al. [76] confirmed that efficacy of phenol degradation depends on microbubble formation. In their experiments, they observed no change in phenol concentration if micro-bubble formation was stopped. The phenol decomposition rate was found maximum in the case when O2 was passed in the solution due to highest micro-bubble formation followed by air and N2 respectively. 

Hence, the formation of microcells in the structure of phenolic foams is due to the fact that, at a certain str e of foaming (region III), thermodyramic conditions are created for the liberation of gas from the oversaturated mixture (formation of a new portion of bubbles). These bubbles expand according to the same laws as bubbles formed at point A, but they do not attain the same sizes as the macrobubbles. This is ascribed to the fact that at point C the viscosity of the foam system has in-aeased to mch an extent that the ps pressure in ail bubbles (both macro- and microbubbles) is insufficient to cause a further expansion and the foam does not rise further. 

Phenolic microbubbles generally yield lower-strength syntactic foams than do glass microbubbles of equal density. As bubble density decreases, relative strengths also decrease (7). The most important factor for use as deep-submergence buoys is the rate of water absorption under a given hydrostatic load. 

Table 13.10. Changes in the phenol content of a Madiran wine after 5 months of oxygen microbubbling at two different doses (Moutounet et al., 1996)...

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