Low-temperature oxidation effects on the morphological and structural properties of hexagonal Zn nanodisks

Ambient-atmosphere oxidation in the temperature range of 90-450 C was performed over Zn films composed by well-faceted hexagonal nanodisks, which were deposited by thermal evaporation. Morphological and structural properties of oxidized Zn nanodisks were studied by scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and Raman scattering measurements. It was found that Zn nanodisks keep its original shape only when they are annealed at 90 or 150 C. Smooth oxidation ocurred only on the rectangular faces of Zn nandodisks heated at 150 C. Thermal oxidation at 250 C favored growth of ZnO nanoneedles over the surface of the Zn nanodisks. Hexagonal-shape of Zn nanodisks was transformed completely into a complex morphology composed by different shaped particles, with further increase in oxidation temperature to 450 C

CW-laser induced microchannels in dye-polymethacrylic acid films

In this work we report on the formation of microchannels on dye-polymethacrylic acid films using a cw-laser. A focalized beam of a He-Ne laser (632.8 nm emission line) was used to form microchannels on the films. It was found that there exists a laser power density threshold for a pit formation that depends on the dye concentration. The dimensions of the laser-induced channels are dependent on the laser power density. Microchannel formation in the transparent polymethacrylic acid films was not observed. Green colored films were obtained by the spin coating technique from a polymethacrylic acid solution mixed with commercial dye°R . All the films obtained presented four absorption bands at 607, 636, 677 and 713 nm. These results show that this material could be applied in microfluidic devices

Synthesis and Thermal Cross-Linking Study of Partially-aminated Epoxidized Linseed Oil

The reaction of diamines or triamines with epoxidized oils leads to different reactions of intra/intermolecular cross-linking and the disruption of the ester linkage. However, by controlling the reaction conditions of temperature, stoichiometry and catalyst, production of oxirane rings without cross-linking and/or disruption of ester group can be achieved. In this work, the synthesis of cross-linking aminated-epoxidized linseed oil resins in two stages is presented. The first one started with epoxidized linseed oil (55.4%) which was subjected to a partial aminolysis using three different amines (ethylenediamine, p-xylylenediamine and triethylenetetramine) and a ZnCl 2 catalyst. Products were characterized by FT-IR, 1H-NMR and DSC. In the second stage, the thermal cross-linking reaction (thermal cure) for obtaining cross-linked polymers was studied by calorimetry using isothermal experiments. These results were extrapolated for producing sheet molding thermally cross-linked polymers

Polymer concretes: A description and methods for modification and improvement

Portland cement concrete (PCC) has been successful in many applications. However, since the 1960s technological investigations concerning modifications of concrete by polymeric materials have been conducted. Attention has been focused on concretes in which the continuous phase is some kind of polymeric resin and the discrete phase is some type of mineral aggregate. Such composite materials are known as Polymer concrete (PCt) and boast several advantages such as higher strength and a shorter curing process. In spite of these advantages, there are deficiencies that could be addressed by fiber incorporation into PCts, however this kind of approach is not typical. Here we acquaint readers with the nature of polymer concretes as these materials have not yet gained wide recognition. We describe recent developments regarding the influence of fiber reinforcements on PCts. The curing process is a critical concern in dealing with polymer concretes as it is with Portland cement concrete. Studies on the effects of gamma ionizing radiation on the curing process and on final properties of PCts are ongoing. Developments in this area are also described here. In particular, the effects of gamma irradiation on the mechanical properties are discussed. Notably, improvements of the Young's modulus E described here have wider implications and may be indicative of improvements or modifications to other properties not directly tested. Specifically, the modifications to the Young's modulus can be a defining measure of whether one will obtain a ductile or more brittle concrete

Polymer concrete reinforced with luffa fibers: Effect of gamma radiation

The interest of many research groups regarding manufacture of composite materials by using natural fibers is increasing world-wide. The main objectives involve the improvement of mechanical properties, mainly those related to resistance and elasticity. In the present study in a first stage, polymer concrete specimens were elaborated by using an unsaturated polyester resin, silica sand and luffa fibers; after, they were gamma irradiated at different doses and their mechanical properties were evaluated. Two different silica particle sizes (0.15 mm and 0.6 mm), and four different luffa fiber concentrations (0.3, 0.6, 0.9 and 1.2 wt%) were used, as well as 50 and 100 kGy of radiation dose. The results show a gradually diminution of compressive strength and modulus of elasticity when adding luffa fiber concentration. Nevertheless, such mechanical features are increasing when polymer concrete is gamma irradiated

Photoluminescent colloidal Cu@C-NPs suspensions synthesized by LASL

In this work we report the synthesis of photoluminescent carbon-coated copper nanoparticles (Cu@C-NPs) based colloidal suspensions, using the laser ablation of solids in liquids technique (LASL). LASL experiments were carried out by ablating a Cu solid target immersed in acetone as the liquid medium with ns-laser pulses (1064 nm) of a Nd-YAG laser. In all experiments the per pulse laser fluence and the repetition rate frequency were kept constant and the ablation time was varied. The as obtained Cu@C-NPs suspensions were optically characterized with absorption and photoluminescence spectroscopies. Raman spectroscopy was used to give evidence of the carbon shell deposited around the Cu NPs. TEM results showed that 10 nm spheroids Cu@CNPs were obtained. The as obtained Cu@C-NPs suspensions displayed out a PL emission band similar to that for carbon nanoparticles suspensions obtained by the same technique. We have found that the blue-green PL emission band intensity is mainly dependent on the ablation and aging time of the samples. The Cu@C-NPsbased colloidal suspensions can be proposed as multifunctional due to its absorbance and emission properties.SIEA-UAE

Effect of thermal treatment on Zn nanodisks

Metallic Zn nanodisks with hexagonal morphology were obtained onto glass substrate under vacuum thermal evaporation. A thermal characterization of Zn nanodiks showed a lower oxidation temperature than source powder Zn. Different thermal treatment on Zn nanodisks played an important role on the morphology, crystal size and surface vibrational modes of ZnO. The growth of ZnO nanoneedles started at the edge of metallic zinc hexagonal structures according with SEM images, the higher temperature the longer needles were grown. XRD diffractogram confirmed the wurtzite structure of ZnO with metallic nuclei. A wide band between 530 and 580 cm−1 of Raman scattering corresponded at surface vibrational modes not observed at higher temperature