Processing Sonogels

Before proceeding with the operation, the energy provided by the electrostrictive device of the ultrasonic apparatus is calibrated by the temperature increase of a fixed volume (v) of distilled water while applying ultrasound by the relationship 

the energy density delivered by the ultrasounds per unit volume will be  

Typical K- v values range from 50 to 100 W [18,40-43]. Many factors can affect these K values, such as room temperature, catalyst, molar ratios of wateifTEOS, soWent/TEOS, beaker diameter and volume, horn tip immersion in the liquid solution and its diameter. 

The basic procedure for the preparation of a silica gel (M = Si) in the laboratory follows four steps. 

The corresponding mixture of the silicon alkoxide (typically, TEOS) and acidic water is placed in a double-volume beaker and a two-phase system is formed with the alkoxide above the water. The water must be acidic because the hydrolysis of 

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Ballarin et al. used sonogel-carbon composite electrodes containing CoPc for the oxidation of cysteine The catalytic process is mediated by the generation of the Co Pc species. Oxidation of sulfide ion was catalyzed by microcrystals of CoPc immobilized at a surface of paraffin impregnated graphite electrode. Filanovsky reported the use of a carbon electrode prepared by hand pressing carbon powder mixed with CoPc and a polymer solution (poly(methyl methacrylate)) in dichloromethane, followed by evaporating the dichloro-methane, for the analysis of mercaptoethanol in petroleum and cysteine in human urine with detection limits of 8 x 10 M for the former and 2 x 10 M for the latter . 

It is possible to apply the sonogel approach in the field of OIHM based on ormosils (Chap. 13). This approach to these materials incorporates an organic phase, very commonly PDMS, in the inorganic precursor (TEOS or TMOS) sol in combination with sonication of the precursors, producing a sono-ormosil (also called hard ormosil) after gelation [41, 57-59]. The processing and properties of sono-ormosils and derived materials have been recently reviewed [60, 61]. 

Zarzycki J (1992) Sonogels - development and perspectives. In Ulhmann DR and Ulrich DR (eds) Ultrastructure processing of advanced materials, Wiley, New York... 

Einarsmd M.A. light gels by conventional drying. J. Non-Cryst. Sohds. 1998 225 1-7 Esquivias L, Zarzycki J. Sonogels an altranative method in sol-gel processing. In Ultrastructure ftocessing of Advanced ceramics, JT). Mackenzie, D.R, Ulrich, eds. New York John Wiley, 1988, pp. 255-270... 

While the relationship between ultrasound and fiber formation is not whoUy understood, cavitation (bubble formation, growth, and collapse) and the local changes in temperature and pressure that accompany this process are likely to be important. However, the breadth of experimental observations in sonogelation (see below) suggests that more than one phenomenon which can affect supramolecular aggregation is at work. 

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