Search results for "conductivity"
showing 10 items of 1988 documents
Insulating Building Components Made from a Mixture of Waste and Vegetal Materials: Thermal Characterization of Nine New Products
2021
Nowadays, energy efficiency and sustainability are the fulcra of building policies. These policies promote the use of new technologies and materials that can reduce the primary energy involved and the environmental costs of construction, guarantying at the same time a high level of comfort for the building’s occupants. Synergy between previous construction techniques and the use of new materials should be pursued by employing materials with a low environmental impact and optimal thermal insulation properties. Within this framework, new materials derived from the agriculture sector, and waste or recycling products from the industrial/agricultural sectors have been studied. The aim of this pa…
Effect of sheep wool fibres on thermal-insulation and mechanical properties of cement matrix
2015
The use of sheep wool as reinforcement of cement in order to produce mortar or plaster involves several advantages for environment and energy. Moreover, in several regions it is treated as a waste and, consequently, its employ is characterized by low cost. Aim of this paper is to evaluate the influence of wool fibres on thermal conductivity and mechanical properties of cement. The samples were prepared using wool fibres, obtained from a breed of Sicilian sheep, with three different length (i.e. 1 mm, 6 mm and 20 mm). Moreover, in order to evaluate the influence of fibre content, the samples were prepared by varying the fibres weight fraction up to maximum level. The thermal conductivity of …
Nanocarbon broadband analysis, temperature dependent dielectric properties and percolation thresholds
2013
The results of a broadband dielectric investigation of multi-walled CNT (MWCNT)/epoxy resin composites in wide temperature range from room temperature to 450 K are reported. Far below the percolation threshold (0.25 wt% MWCNT) the dielectric properties of the composite are mostly determined by alpha relaxation in pure polymer matrix. Close to the percolation threshold the composite shows the negative temperature coefficient (NTC) effect in the temperature region, where the pure polymer matrix becomes conductive. The activation energy increases with the MWCNT concentration far below the percolation threshold and decreases close to it (1.5 wt% MWCNT). The dielectric analysis of the MWCNT/epox…
Multiscale Approach in Studying the Influence of Annealing Conditions on Conductivity of TiO2 Nanotubes
2015
Titanium oxide nanotubes (NTs) have attracted much attention during last decade due to their special characteristics such as one-dimensional highly ordered geometry with large surface area and good chemical and optical stability.
Influence of heteropolyacid in enhancing proton conductivity of chitosan membranes for H2/O2 Fuel Cells
2016
To promote Proton Exchange Membrane Fuel Cells (PEMFCs) commercialization, large research effort has been devoted in developing new polymer electrolytes that can replace the usually employed proton conductors, e.g. Nafion®, with other membranes of comparable performances but lower cost. Chitosan (CS)-based membrane electrolyte is currently studied as alternative candidate for PEMFC application. Several works have shown that Heteropolyacids (HPAs) can be used to prepare Chitosan polyelectrolytes (PECs) to be employed as proton exchange membrane in low temperature fuel cell. In previous works [1-3] we have shown that CS/PTA membranes, prepared using alumina porous medium for the slow release …
On some issues in the computational modelling of spacer-filled channels for membrane distillation
2017
Abstract This study addresses issues which arise in the computational and experimental modelling of flow and heat/mass transfer in membrane distillation and other processes adopting spacer-filled channels (either planar or spiral wound), but have not been sufficiently clarified in the literature so far. Most of the argumentations presented are based on original computational results obtained by the authors by finite volume simulations; some literature results are also considered. The questions addressed regard the choice of scales for the reduction of data and the definition of dimensionless numbers ( Re , f , Nu , Sh ); the definition of average heat or mass transfer coefficients; the comb…
Electrochemical treatment of real wastewater with low conductivity
2018
In the last years, many efforts have been devoted to the development of electrochemical processes for the effective treatment of wastewater contaminated by organic pollutants resistant to conventional biological processes and/or toxic for microorganisms [1–5]. It was shown that some electrochemical approaches, including the direct anodic oxidation at suitable anodes such as boron-doped diamond (BDD) and/or electro-Fenton (EF) at suitable operating conditions and cells [1–6] could allow treating effectively a very large number of organic pollutants. However, most of the investigations were performed using synthetic wastewater. Hence, it is now mandatory to study the problems connected to the…
Improving the understanding of the melting behaviour of Mo, Ta, and W at extreme pressures
2004
We discus existent conflicts between experimentally measured and theoretically calculated melting curves of Mo, Ta, and W. By assuming that vacancy formation plays a fundamental role in the melting process, an explanation for the measured melting curves is provided. Furthermore, we show that the Lindemann law fits well all the measured melting curves of bcc transition metals if the Grueneisen parameter is written as a power series of the interatomic distance. For completeness, we examine possible reasons for current disagreements between shock-wave and DAC experiments. To solve them, we propose the existence of an extra high P-T phase for Mo, Ta, and W
Numerical investigation of the influence of EM-fields on fluid motion and resistivity distribution during floating-zone growth of large silicon singl…
2001
The floating-zone-process with needle-eye inductor is a complex process with many coupled parameters that have nonlinear influence on the process stability and resistivity distribution in the silicon single crystal. To fulfill the requirements of semiconductor industry for tighter specification of resistivity distribution, additional means like magnetic fields can be used to reach a more homogeneous resistivity distribution without disturbing process stability. The current paper analyses the influence of static and alternating fields on the fluid motion and macroscopic and microscopic resistivity profile by means of numerical calculations. It is found that with a lower frequency of the HF-i…
Proton conducting composite electrolytes based on antimonic acid
1997
Abstract This report concerns a composite proton electrolyte suitable for use in electrochromic devices. The electrolyte consists of nanosize pyrochlore antimonic acid particles suspended in a poly(vinyl acetate) matrix by a gel route. It was found possible to substitute the antimonic acid by inert oxides of aluminum and silicon, thus making the electrolyte less harmful to the oxide electrodes of the electrochromic devices without considerably decreasing the conductivity. The proton conductivity of the antimonic acid electrolyte was ∼10 −4 S/cm at room temperature, practically independent of its amount of absorbed water.