Weathering and Thermal Aging of Ultraviolet-Cured Polymer Films

Six different formulations were developed with an urethane acrylate oligomer (Ebcryl 264) in combination with a carboamide monomer (N-vinyl pyrrolidone) and a difunctional acrylated monomer (tripropylene glycol di-acrylate) in the presence of some filler (talc) and a plasticizer (diallyl phthalate). Thin polymer films prepared out of these formulations under ultraviolet radiation were characterized. The change of optical absorption of these films between 240 and 380 nm as a result of weathering and thermal aging was studied. The absorption spectra shifted toward higher wavelengths for thermal and weathering treatments. Loss of tensile strength (T _s) and elongation (E _b) was also investigated. The loss was observed to be dependent on the nature of formulations.     

Study of the water uptake and internal defects of jute‐reinforced polymer composites with a digital neutron radiography technique

The water‐uptake behavior of jute fabric and its composites with polycarbonate and polypropylene was monitor by a digital neutron radiography technique. The thermal neutron radiography facility of neutron transmission radiography (NEUTRA) at spallation source (SINQ) of the Paul Scherrer Institute was used for this work. The internal defects, such as voids, cracks, and inhomogeneity, of the composites were studied. The water‐uptake behavior of the jute fiber was also studied with a digital neutron radiography technique. The natural jute fiber showed higher water absorption than the composites. No voids or inclusions in these composites were observed. Moreover, both the jute and polymer were uniformly distributed and well mixed with the polymer matrix. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Atmospheric dispersion modeling for an accidental release from the Pakistan Research Reactor-1 (PARR-1)

Atmospheric dispersion modeling and radiation dose calculations have been performed for a postulated accidental airborne radionuclide release from the Pakistan Research Reactor-1 (PARR-1) appropriate to a power upgrade to 10 MW. Estimates of releases for various radionuclide groups are based upon US-NRC regulatory guide 1.183. Committed Effective Doses (CEDs) to the public at various downwind distances were calculated using a health physics computer code “HotSpot” developed at the Lawrence Livermore National Laboratory, University of California, USA. The doses were calculated for various atmospheric stability classes, viz., Pasquill categories A–F with site-specific averaged meteorological conditions. The meteorological data on atmospheric stability conditions, mean wind speed and the frequency distribution of wind direction based on data collected near the reactor site have also been analyzed and are presented here.The results indicate that a person located within a downwind distance of about 500 m from the reactor would receive more than the permissible CED under the analyzed severe accident scenario. Analysis of one typical year of wind data indicates that the predominant wind direction is East–North East (ENE), which occurs at the site for more than 15% of the time.     

Electrode kinetics of ethanol oxidation on novel CuNi alloy supported catalysts synthesized from PTFE suspension

An understanding of the kinetics and mechanism of the electrochemical oxidation of ethanol is of considerable interest for the optimization of the direct ethanol fuel cell. In this paper, the electro-oxidation of ethanol in sodium hydroxide solution has been studied over 70:30 CuNi alloy supported binary platinum electrocatalysts. These comprised mixed deposits of Pt with Ru or Mo. The electrodepositions were carried out under galvanostatic condition from a dilute suspension of polytetrafluoroethylene (PTFE) containing the respective metal salts. Characterization of the catalyst layers by scanning electron microscope (SEM)–energy dispersive X-ray (EDX) indicated that this preparation technique yields well-dispersed catalyst particles on the CuNi alloy substrate. Cyclic voltammetry, polarization study and electrochemical impedance spectroscopy were used to investigate the kinetics and mechanism of ethanol electro-oxidation over a range of NaOH and ethanol concentrations. The relevant parameters such as Tafel slope, charge transfer resistance and the reaction orders in respect of OH⁻ ions and ethanol were determined.     

Electrolytes for solid oxide fuel cells

The high operating temperature of solid oxide fuel cells (SOFCs), as compared to polymer electrolyte membrane fuel cells (PEMFCs), improves tolerance to impurities in the fuel, but also creates challenges in the development of suitable materials for the various fuel cell components. In response to these challenges, intermediate temperature solid oxide fuel cells (IT-SOFCs) are being developed to reduce high-temperature material requirements, which will extend useful lifetime, improve durability and reduce cost, while maintaining good fuel flexibility. A major challenge in reducing the operating temperature of SOFCs is the development of solid electrolyte materials with sufficient conductivity to maintain acceptably low ohmic losses during operation. In this paper, solid electrolytes being developed for solid oxide fuel cells, including zirconia-, ceria- and lanthanum gallate-based materials, are reviewed and compared. The focus is on the conductivity, but other issues, such as compatibility with electrode materials, are also discussed.     

Crystallographic and magnetic properties of the spinel type solid solution Zn0.4Co0.6AlxFe2−xO4 (0≤x≤1)

The spinel system Zn_0.4Co_0.6Al_xFe_2−xO₄ (x=0.0, 0.25, 0.50, 0.75, and 1.0) has been prepared in air at 1300 °C by standard solid state sintering method. X-ray and neutron powder diffraction measurements have been performed to characterize the materials. The crystal structure of the system has been found out by refining neutron diffraction data and cubic symmetry corresponding to the space group Fd3m has been confirmed for all the samples of the series. Zn and Al ions exclusively enter into the tetrahedral (A) and octahedral (B) sites, respectively, while Co and Fe ions are distributed over both the A and B sites for the whole compositional range investigated. With increasing x, the occupation of Co gradually increases in A site and that in B site decreases, and the Fe ions gradually decrease in both the sites. The lattice constant decreases and the oxygen position parameter increases with increasing Al content in the system. The moment distributions in the two sublattices for different compositions have also been determined. The magnetization measurements show that the saturation magnetization and the Néel temperature decreases with increasing Al contents and the coercivity decreases initially and then increases when x>0.75.     

Surface treatment of coir (Cocos nucifera) fibers and its influence on the fibers’ physico-mechanical properties

Coir, an important lignocellulosic fiber, can be incorporated in polymers like polyacrylate in different ways for achieving desired properties and texture. But its high level of moisture absorption, poor wettability and insufficient adhesion between untreated fiber and the polymer matrix lead to debonding with age. In order to improve the above qualities, adequate surface modification is required. In our present work, fiber surface modification by ethylene dimethylacrylate (EMA) and cured under UV radiation. Pretreatment with UV radiation and mercerization were done before grafting with a view to improve the physico-mechanical performance of coir fibers’. The effects of mercerization on shrinkage and fiber weight losses were monitored at different temperature and alkali concentration. We observed that, fiber shrinkage is higher at low temperature and 20% alkali treated coir fibers yielded maximum shrinkage and weight losses. It was found that higher shrinkage of the polymer grafted fiber showed enhanced physico-mechanical properties. The grafting of alkali treated fiber shows an increase of polymer loading (about 56% higher) and tensile strength (about 27%) than 50% EMA grafted fiber. The fiber surface topology and the tensile fracture surfaces were characterized by scanning electron microscopy and were found improved interfacial bonding to the modified fiber–matrix interface.