Electrical Conduction in Thin-Film Polypropylene Capacitors

Thin polypropylene films have played a strategic role in recent years because they are the dielectric of choice for high-energy-density and high-power-density DC-link capacitors, and have been extensively used in renewable energy and electric mobility applications. Currently, these capacitors operate at temperatures of up to 105 °C with electric fields of up to 200 V/µm, allowing high efficiency due to their low dissipation figures compared to other capacitor technologies. The rapid evolution of green energy applications demands higher energy and power density, with expected operating temperatures and electric fields of up to 115 °C and above 250 V/µm, respectively. Under such conditions, the insulation resistance of the capacitor becomes a key factor, as it may start to contribute to the dissipation of energy. A correct understanding of conduction phenomena within the dielectric is necessary for the design of new high-performance capacitors based on polypropylene film with reduced conduction losses. The scope of this review is to present and evaluate the theoretical and experimental works on thin biaxially oriented polypropylene (BOPP) films for capacitor applications with a focus on electrical conductivity at high electric field and temperature

Inertizzazione di rifiuti industriali attraverso processi di geopolimerizzazione

L’incenerimento dei rifiuti solidi urbani (RSU) produce ogni anno tonnellate di ceneri leggere che, a differenza delle ceneri derivanti dalla combustione di carbone, contengono grandi quantità di sostanze tossiche come ad esempio i metalli pesanti. Una tecnica di solidificazione/stabilizzazione nota come geopolimerizzazione viene proposta con il fine di legare chimicamente e fisicamente le ceneri in una matrice solida, in modo da ridurre la mobilità degli inquinanti in esse contenuti. È quindi presentato uno studio della stabilità chimica di geopolimeri con un rapporto Si/Al di 1.8-1.9 e Na/Al di 1.0, sintetizzati per attivazione alcalina di metacaolino e aggiunta di ceneri da elettrofilro e filtro a maniche in concentrazione 20%. Il processo di consolidamento a temperatura ambiente è stato valutato attraverso test di cessione in acqua, come previsto dalla norma UNI 10802. Il rilascio di metalli, determinato tramite ICP-AES, ricade nei limiti imposti per legge per lo smaltimento in discarica per rifiuti non pericolosi

A new environmentally friendly process for the recovery of gold from electronic waste

A new method for the recovery of preciousmetals, in particular gold, from electronic waste is proposed.This work focused on the research of an easilyrenewable etching agent, in order to make an environmentallyfriendly process possible. Two well knownhydrometallurgical etching agents, FeCl3 and CuCl2, wereevaluated in terms of efficiency and kinetics, testingsolutions with different concentration of etchant andhydrochloric acid. The recovery of spent etching solutionswas evaluated: promising results were found in the case ofCuCl2, which can be completely restored by oxidation ofthe cuprous chloride formed during the etching usingatmospheric oxygen

The effects of carboxylic acids on the aqueous dispersion and electrophoretic deposition of ZrO2

The agglomeration, electrokinetic properties and electrophoretic deposition behaviour of aqueous suspensions of ZrO2 with carboxylic acid additives were studied in comparison with conventional pH adjustment. It was found that citric acid imparted negative zeta-potential values and electrosteric stabilisation to particles in suspensions at all pH levels. The examination of additions of carboxylic acids to ZrO2 suspensions revealed that these reagents cause a sharp drop in zeta-potential at distinct addition levels, which correspond to surface saturation of the particles with negatively charged carboxylate groups. Adsorption cross sections of citric acid, EDTA and oxalic acid were evaluated from these results, showing that both citric acid and EDTA coordinate to ZrO2 surfaces by two carboxylate groups while oxalic acid is coordinated by one group. The use of carboxylic acids was shown to facilitate superior electrophoretic deposition in comparison with zeta-potential modification by conventional pH adjustment through improved suspension stability. \ua9 2011 Elsevier Ltd

Combination of electrophoretic deposition and microwave-ignited combustion synthesis for the preparation of ceramic coated intermetallic-based materials

Electrophoretic deposition (EPD) was used to deposit sub-micrometric ZrO2 particles on metallic powder compacts belonging to the systems Ni + Al and Ti + Al, which were used as deposition electrodes in the EPD cell. After EPD, combustion synthesis (CS) of such reactive electrodes was ignited in a microwave single-mode applicator, operating at a frequency of 2.45 GHz, in order to obtain in a single step the synthesis of the desired intermetallic phase (substrate) and the sintering of the previously deposited ceramic particles (or coating). Experimental results demonstrate that the excess heat released during the formation of nickel and titanium aluminides by CS can be exploited not only to self-sustain and self-propagate the reaction front along the substrate, but also to rapidly sinter the coating obtained by EPD. The innovative procedure here proposed is a promising strategy in order to obtain, in a single step, high temperature intermetallic-based materials, protected by well adhered ceramic coatings

Anodic aqueous electrophoretic deposition of titanium dioxide using carboxylic acids as dispersing agents

The dispersion of anatase phase TiO2 powder in aqueous suspensions was investigated by zeta-potential and agglomerate size analysis. The iso-electric point (IEP) of anatase was determined to be at pH 2.8 using monoprotic acids for pH adjustment. In comparison, it was found that the use of carboxylic acids, citric and oxalic, caused a decrease in zeta-potential through the adsorption of negatively charged groups to the particle surfaces. The use of these reagents was shown to enable effective anodic electrophoretic deposition (EPD) of TiO2 onto graphite substrates at low pH levels with a decreased level of bubble damage in comparison with anodic EPD from basic suspensions. The results obtained demonstrate that the IEP of TiO2 varies with the type of reagent used for pH adjustment. The low pH level of the IEP and the ability to decrease the zeta-potential through the use of carboxylic acids suggest that the anodic EPD of anatase is more readily facilitated than cathodic EP

Chemical stability of geopolymers containing municipal solid waste incinerator fly ash

Municipal solid waste incinerators every year produce tons of fly ashes which, differently from coal fly ashes, contain large amounts of toxic substances (heavy metals, dioxins, furans). The stabilization/solidification (S/S) technology known as geopolymerization is proposed with the purpose to bond physicallyand chemically incinerator fly ashes (IFA) in a solid matrix, in order to reduce pollutant mobility. The chemical stability of geopolymers with Si/Al ratio of 1.8–1.9 and Na/Al ratio of 1.0, synthesized by alkali activation of metakaolin and the addition of 20 wt% of two different kinds of IFA, is presented. The concentration of the alkaline solution, water to solid ratio and curing process have been optimized. The room temperature consolidation of IFA containing geopolymers has been tested for leachability in water for 1 day, accordingly to EN 12457 regulation and extended to 7 days to increase the water attack on solid granules. Leachable metals in the test solution, determined by ICP_AES, fall within limit values set by regulation for non-dangerous waste landfill disposal. Geopolymeric matrix evolution with leaching time has been also evaluated in terms of pH and electrical conductivity increase in solution

Electrochemically assisted grafting of asymmetric alkynyl(aryl)iodonium salts on glassy carbon with focus on the alkynyl/aryl grafting ratio

Glassy carbon (GC) surfaces are functionalized exploiting the electrochemical reduction of asymmetric iodonium salts of the general formula [4-Zsingle bondC6H4single bondI+single bondCtriple bond; length of mdashC(CH2)4Cl, Z = NO2, Br, F, H, or CH3]. The range of Z groups was selected aiming to examine the Carylsingle bondI bond energy as a function of the “electron withdrawing/electron donating” ability of the Z-group, with the ultimate purpose of controlling the alkynyl/aryl grafting ratio. The electroreduction mechanism and the characteristics of the grafted surface are studied by means of cyclic voltammetry and X-ray photoelectron spectroscopy. It is shown that the alkynyl/aryl grafting ratio decreases with the increasing electron withdrawing nature of Z, which induces a weakening of the Carylsingle bondI bond. Ab initio DFT vertical electron affinities (EAv) allowed to rationalize the electroreduction potentials of both the bulk and surface functionalised redox couples. Moreover, the alkynyl/aryl grafting ratio is assessed, at a molecular level, on the basis of ab initio DFT potential energy surfaces

The Effects of Carboxylic Acids on the Aqueous Dispersion and Electrophoretic Deposition of ZrO2

The agglomeration, electrokinetic properties and electrophoretic deposition behaviour of aqueous suspensions of ZrO2 with carboxylic acid additives were studied in comparison with conventional pH adjustment. It was found that citric acid imparted negative zeta-potential values and electrosteric stabilisation to particles in suspensions at all pH levels. The examination of additions of carboxylic acids to ZrO2 suspensions revealed that these reagents cause a sharp drop in zeta-potential at distinct addition levels, which correspond to surface saturation of the particles with negatively charged carboxylate groups. Adsorption cross sections of citric acid, EDTA and oxalic acid were evaluated from these results, showing that both citric acid and EDTA coordinate to ZrO2 surfaces by two carboxylate groups while oxalic acid is coordinated by one group. The use of carboxylic acids was shown to facilitate superior electrophoretic deposition in comparison with zeta-potential modification by conventional pH adjustment through improved suspension stability

The Effects of Firing Conditions on the Properties of Electrophoretically Deposited Titanium Dioxide Films on Graphite Substrates

Thick anatase films were fabricated on graphite substrates using a method of anodic aqueous electrophoretic-deposition using oxalic acid as a dispersant. Thick films were subsequently fired in air and in nitrogen at a range of temperatures. The morphology and phase composition were assessed and the photocatalytic performance was examined by the inactivation of Escherichia coli in water. It was found that the transformation of anatase to rutile is enhanced by the presence of a graphite substrate through reduction effects. The use of a nitrogen atmosphere allows higher firing temperatures, results in less cracking of the films and yields superior bactericidal performance in comparison with firing in air. The beneficial effects of a nitrogen firing atmosphere on the photocatalytic performance of the material are likely to be a result of the diffusion of nitrogen and carbon into the TiO2 lattice and the consequent creation of new valence band states