The sonochemical reaction between Zn(NO 3 ) 2 and hexamethylenetetramine (HMT) resulted in different products depending on amounts of Zn(II) cations in the aqueous solution. Crystalline phase pure ZnO nanoparticles were obtained by using 0.05 M Zn(NO 3 ) 2 -HMT. This single phase was formed by low power sonication for 20 min in an ultrasonic bath at ambient conditions and its morphology did not change for the next 60 min. Higher concentrations of precursors (0.1 and 0.5 M) led to a mixture of zinc compounds including plate-like Zn 5 (OH) 8 (NO 3 ) 2 (H 2 O). In contrast, a mixed phase ZnO/Zn 5 (OH) 6 (CO 3 ) 2 and a single phase Zn 5 (OH) 6 (CO 3 ) 2 were formed when the precursor concentrations were decreased to 0.01 and 0.005 M, respectively. The resulting infrared absorption and ultraviolet/visible emission were dependent on the phases and defects in these zinc compounds.

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Physical properties of polyurethane (PU) can be modified for desired applications by adding appropriate fillers. In this work, cobalt (Co) powder of average diameter 2 μπι was filled in PU elastomers synthesized by a reaction between polyol and diisocyanate. Variation of Co loading (0, 20,40 and 60 wt.%) modified thermal properties of PU composites in terms of the shift in a melting temperature and the increase in heat absorption. From DC hysteresis loops, PU/Co composites exhibited ferromagnetic properties with improved magnetizations by the increase in Co loading. On the other hand, the coercive field was almost unvaried. For high frequency electromagnetic behaviors, the complex electrical permittivity (ε-je") and magnetic permeability (μ'-]μ") were sensitive to the frequency from 10 MHz up to 100 MHz and reached the modest values in the regime between 100 MHz and 1 GHz. At each frequency, the real part of permeability and permittivity of PU were raised by the inclusion of Co fillers. While the thermal behaviors were explained using the interaction between Co clusters and the PU matrix, the electromagnetic properties can be understood by taking into the account of interactions between Co clusters at high loading levels.

Zinc oxide nanoparticles were synthesized using a commercial ultrasonic homogenizer in a sonochemical reaction between 0.05 M zinc nitrate and hexamethylenetetramine. The solutions in glass vessels of varying shapes i.e. cube, cylinder and sphere were sonicated with a 45 W 20 kHz ultrasonic pulse for 60 min under ambient conditions. The crystalline ZnO phase was confirmed by powder X-ray diffraction and scanning electron microscopy with average particle diameters around 70 nm from the three different vessels. These ZnO particles were smaller than those previously synthesized in ultrasonic baths and sonoreactors.

Hexagonal zinc oxide (ZnO) nanotubes were synthesized from 0.05 M zinc nitrate hexahydrate [Zn(NO 3 ) 2 ·6H 2 O] and hexamethylenetetramine (C 6 H 12 N 4 ) by a sonochemical method under ambient conditions. White precipitates, obtained after ultrasonic irradiation for 60 min, were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectroscopy (PL). The ZnO crystals had a tubular structure ³500 nm in length with a hexagonal cross section for both the inner and outer walls. The room temperature PL spectrum of ZnO nanotubes exhibited an ultraviolet (UV) emission peak, a sharp violet peak and a further broad visible band centered at 650 nm.©2011 The Ceramic Society of Japan. All rights reserved.Key-words : ZnO nanotubes, Sonochemical method, Photoluminescence, Near band-edge recombination, Oxygen vacancy [Received February 17, 2011; Accepted March 29, 2011] Micro-and nano-scale tubular structures have attracted extensive interest due to their unique hollow morphology with space confined transport properties, large surface area and potential applications in nanotechnology. Since the discovery of carbon nanotubes, 1) such structures have been fabricated using many different compounds including zinc oxide (ZnO). ZnO microtubes with well faceted surfaces have been successfully synthesized by chemical solution techniques, 2) thermal evaporation, 3) hydrothermal methods, 4) and direct microwave heating. 5)With the rapid development in ultrasonic sonochemistry, a variety of chemical reactions can acquire energy from the process of acoustic cavitations driven by ultrasound waves involving the formation, growth and implosive collapse of bubbles in the liquid.6) The process is generally simple and requires low-cost setups with moderate energy demand. The sonochemical method is therefore a real alternative for producing ZnO of varying morphologies. Ultrasound pretreatments prior to solution synthesis and an ultrasonically assisted 2-step polyol process have previously been shown to enable the formation of ZnO tubes.2),7)In this work, ZnO hexagonal nanotubes were prepared by a sonochemical method. Their morphological and optical properties were then examined.Reagent grade zinc nitrate hexahydrate [Zn(NO 3 ) 2 ·6H 2 O] and hexamethylenetetramine (C 6 H 12 N 4 ) powders (²99.0% in purity) were used as starting materials without any pretreatment. The solution, 0.05 M in Zn(NO 3 ) 2 ·6H 2 O and C 6 H 12 N 4 in 50ml deionized water, was prepared and stirred for 10 min with heating up to 50°C until a stable viscous white colloid formed. The colloid was then transferred to a vertical cylindrical glass vessel and placed in a 30W ultrasonic reactor. It was sonicated at 35 kHz for 1 h under ambient conditions. During the ultrasonic irradiation, the temperature of the colloid rose to approximately 70°C. After the reaction was complete, the white precipitate was collected by filtration and thoroughly rinsed with distilled water and ethanol. Finally, the precipitate was dried in an oven a...

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