Electricity transmission and distribution networks : Ecodesign

Thermo-mechanically durable industrial polymer nanocomposites have great demand as structural components. In this work, highly competent filler design is processed via nano-modified of micronic SiO2/Al2O3 particulate ceramics and studied its influence on the rheology, glass transition temperature, composite microstructure, thermal conductivity, mechanical strength, micro hardness, and tribology properties. Composites were fabricated with different proportions of nano-modified micro-composite fillers in epoxy matrix at as much possible filler loadings. Results revealed that nano-modified SiO2/Al2O3 micro-composite fillers enhanced inter-particle network and offer benefits like homogeneous microstructures and increased thermal conductivity. Epoxy composites attained thermal conductivity of 0.8 W/mK at 46% filler loading. Mechanical strength and bulk hardness were reached to higher values on the incorporation of nano-modified fillers. Tribology study revealed an increased specific wear rate and decreased friction coefficient in such fillers. The study is significant in a way that the design of nano-modified mixed-matrix micro-composite fillers are effective where a high loading is much easier, which is critical for achieving desired thermal and mechanical properties for any engineering applications.

Purpose Polymers typically have intrinsic thermal conductivity much lower than other materials. Enhancement of this property may be obtained by the addition of conductive fillers. Nanofillers are preferred to traditional ones, due to their low percolation threshold resulting from their high aspect ratio. Beyond these considerations, it is imperative that the development of such new fillers takes place in a safe and sustainable manner. A conventional life cycle assessment (LCA) has been conducted on epoxy-based composites, filled with graphite nanoplatelets (GnP). In particular, this study focuses on energy requirements for the production of such composites, in order to stress environmental hot spots and primary energy of GnP production process (nano-wastes and nanoparticles emissions are not included). Methods A cradle-to-grave approach has been employed for this assessment, in an attributional modeling perspective. The data for the LCA have been gathered from both laboratory data and bibliographic references. A technical LCA software package, SimaPro (SimaPro 7.3), which contains Ecoinvent (2010) life cycle inventory (LCI) database, has been used for the life cycle impact assessment (LCIA), studying 13 midpoint indicators. Sensitivity and uncertainty analyses have also been performed. Results and discussion One kilogram of GnP filler requires 1,879 MJ of primary energy while the preparation of 1 kg of epoxy composite loaded with 0.058 kg of GnP 303 MJ. Besides energy consumption in the filler preparation, it is shown that the thermoset matrix material has also a nonnegligible impact on the life cycle despite the use of GnP: the primary energy required to make epoxy resin is 187 MJ, i.e., 62 % of the total energy to make 1 kg of composite. Conclusions Raw material extraction and filler and resin preparation phase exhibit the highest environmental impact while the composite production is negligible. Thermosetting resin remains the highest primary energy demand when used as matrix for GnP fillers. The result of the sensitivity analysis carried out on the electricity mix used during the GnP and the composite production processes does not affect the conclusions.

The influence of SiO2 doping on the microstructure and electrical behavior of SnO2 varistors has been studied. The varistor effect was studied over a wide range from 10 9 A to 104 A. It is shown that the J(E) characteristic of SnO2 ceramics exhibits a nonlinear coefficient>100. The SiO2 doping also resulted in a sharp-abrupt upturn region in the I-V characteristic, indicating a single semiconductor junction behavior. The leakage current of the varistors is rather low, on the order of 10 10 S m 1. In the upturn region of operation where the curve departs from the nonlinear relation and approaches the value of the bulk resistivity of the material, the ceramic is characterized by a current density almost independent of the applied voltage. A very small amount of SiO2 causes large perturbations of the conventional thermionic emission observed in varistor ceramic materials.

Nano/micro ceramic-filled epoxy composite materials have been processed with various percentage additions of SiO2, Al2O3 ceramic fillers as reinforcements selected from the nano and micro origin sources. Different types of filler combinations, viz. only nano, only micro, nano/micro, and micro/micro particles, were designed to investigate their influence on the thermal expansion, thermal conductivity, and dielectric properties of epoxy polymers. Thermal expansion studies were conducted using thermomechanical analysis that revealed a two-step expansion pattern consecutively before and after vitreous transition temperatures. The presence of micro fillers have shown vitreous transition temperature in the range 70-80°C compared with that of nano structured composites in which the same was observed as ~90°C. Similarly, the bulk thermal conductivity is found to increase with increasing percentage of micron-size Al2O3. It was established that the addition of micro fillers lead to epoxy composite materials that exhibited lower thermal expansion and higher thermal conductivity compared with nano fillers. Moreover, nano fillers have a significantly decisive role in having low bulk dielectric permittivity. In this study, epoxy composites with a thermal expansion coefficient of 2.5 × 10 5/K, thermal conductivity of 1.18W/m* K and dielectric permittivity in the range 4-5 at 1 kHz have been obtained. The study confirms that although the micro fillers seem to exhibit good thermal conductivity and low expansion coefficient, the nano-size ceramic fillers are candidate as cofillers for low dielectric permittivity. However, a suitable proportion of nano/micro-mixed fillers is necessary for achieving epoxy composites with promising thermal conductivity, controlled coefficient of thermal expansion and dielectric permittivity. Copyright © 2013 John Wiley & Sons, Ltd.

The complete oxidation kinetics of indium powder in air has been studied from thermogravimetric studies under isothermal conditions in the range 858-1173 K. The influence of particle size was analyzed in the 25-375 lm range. We succeeded in carrying out the full oxidation of the powders far above the indium-metal melting point (429.75 K) without apparent coalescence of the particles through the presence of a thin In2O3 layer which confines the liquid metal during the oxidation process. The apparent activation energy obtained from the Arrhenius law was 62.2 kJ mol-1.

This paper reports mesoscopic Monte Carlo simulations (in which a 'mesoscopic particle' corresponds to a group of atoms or molecules) of interfacial films in ZnO-Bi2O3 binary ceramics. We observe the formation of Bi2O3-rich interfacial phases at the surface of ZnO grains (surface amorphous films) or at the grain-boundary between ZnO grains (intergranular films). In qualitative agreement with the experimental results reported on premelting of ceramics, the thickness of these films increases as the temperature increases up to the eutectic temperature. Moreover, the Bi2O3 concentration in the surficial or intergranular films is found to be larger than in the bulk. These surficial films exhibit both some layering and lateral ordering.