Recebido em 2/2/99; aceito em 16/6/99 THE ULTRASOUND EFFECT ON CHEMISTRY REACTIONS. Unusual chemical phenomenon associated with ultrasound is on account of cavitation effect. The ultrasound increase the rate and yield of chemical reaction on account of its ability to emulsify liquids. When the ultrasound is used in metallic catalyst reaction the activity of catalyst is increased because the ultrasound clean the surface of catalyst. Sonogels have a fine porosity and large specific surface improving different properties. This paper deals with ultrasound phenomenon and gives some examples of reactions and properties where this radiation takes an important role.
A novel porous silica matrix has been prepared from Pyrex glass, using hydrothermal treatment under saturated‐steam condition. This process makes it possible to obtain, in one step, a silica support formed of a homogeneously distributed and interconnected macropore microstructure. The new matrix contains silanol groups that can be used in reactions of surface modification to provide a hybrid material and a selective macrofiltration membrane, and also it can improve chemical inertness. The porous matrix is noncrystalline as obtained and, after thermal treatment at temperatures higher than 950°C, exhibits an X‐ray pattern characteristic of α‐cristobalite and low volume contraction. The present samples were characterized by scanning electron microscopy, mercury intrusion porosimetry, nitrogen adsorption‐desorption isotherms, infrared spectroscopy, X‐ray powder diffractometry, atomic absorption, and high‐resolution solid‐state nuclear magnetic resonance. The results present a new way of producing a macroporous silica matrix.
Recebido em 10/1/96; aceito em 23/9/96 MICROWAVE OVEN MODIFICATIONS FOR LABORATORY APPLICATIONS. Domestic microwave oven was modified for laboratory applications. Electronic system was made for controlling magnetron irradiation time. Exhaustion and air circulation systems were installed to clean the internal oven atmosphere during operation. The cavity walls were coated with aluminized thermal paint to avoid chemical corrosion. These modifications allowed the usage of the oven for drying and processes using reflux.
The present work demonstrates preparation of magnetic nanoparticles by a novel method. Magnetic nanoparticles with potential for biomedical and environmental applications were obtained by homogeneous coprecipitation method sonochemically assisted. The effect of ultrasonic cavitation on changing the reaction environment was studied. The chemical reaction media used here was very similar to those used for Sono-Fenton process. The ultrasonic energy has driven the growth of particles; smaller diameter nanoparticles were obtained by applying a higher power. For the first time, it was demonstrated the iron oxide nanoparticles synthesis at pH lower than 6.
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