Metallized-film capacitors have the property, even under high continuous voltage, to self-heal i.e., to clear a defect in the dielectric. The self-healing process is a consequence of a transient arc discharge. It has been previously shown that during the discharge, due to Joule effect, the metal is vaporized until the arc extinguishes. The discharge duration has been found to be inversely proportional to the mechanical pressure applied on the layers of metallized films making up a capacitor. The aim of this study is to understand the physical processes involved in this spontaneous extinction of the arc discharge. Emission spectroscopy has been used to provide information about the physical properties (temperatures, electronic and neutral particles densities, etc.) of the plasma induces by a self-healing. An analysis, based on the broadenings and shifts of Al atomic lines, of the experimental light spectra obtained has shown that the self-healing process leads to the generation, from the vaporized metal, of a high-density and relatively weakly ionized aluminum plasma. The plasma density increases with the pressure applied on the film layers and, consequently, the density power needed to extend the plasma zone increases as well and the arc discharge goes out faster as experimentally observed.

Articles you may be interested inViscosity measurement of nanoimprint lithography resists with a rheological nanoindenter Effect of fluoroalkyl substituents on the reactions of alkylchlorosilanes with mold surfaces for nanoimprint lithography J.Polymer selection and critical dimension control across the wafer are key parameters for the nanoimprint lithography technique. This nanotechnology requires polymers having a low glass transition temperature T g combined with a good etch resistance. In this work, three different polymers have been evaluated. The influence of the temperature and pressing time is analyzed to clarify the correlation between polymer behavior and printing uniformity as a function of the pattern density. Measurements of the polymer residual thickness show that the printing uniformity is strongly correlated with the thermal properties of the polymer.

Core double-shell cobalt/graphene//polystyrene nanocomposites (Co/C//PS) were synthesized by in situ sonochemical polymerization technique. Commercial Co/C nanoparticles are used and successfully lead to gram-scale production of processable nanocomposite. Synthesized Co/C//PS nanocomposites result in homogeneous and dense dispersion of particles with or without additional polymeric matrix. They showed improved thermal properties such as higher initial degradation temperatures and a significant increase of glass transition temperature (i.e. 10 to 12°C) in contrast to neat PS. These results suggest that covalent bonding occurs between PS and graphene shell, and may be promoted by two surface reactions: "grafting from" when monomer is pre-immobilized on graphene and grows to polymer, and "grafting to" when presynthesized polymer is immobilized on graphene. Both mechanisms are compared and explained. HR-TEM observations revealed polymer shells of 4 to 5 nm covering Co/C nanoparticles or at least small aggregates. However, the number of layer of the graphene shell which consists of 6 to 8 regular layers on raw particles decreases to 3, this layer reduction can be explained by a partial amorphization of graphene occurring during the polymerization. Nevertheless, Co particles are still efficiently protected from oxidation as final Co/C//PS nanocomposites are able to sustain high mass-magnetization (i.e. ~ 49 emu/g for 94 % wt Co/C). First indications of satisfying mechanical cohesion are also shown by the formation of two relevant nanocomposites shapes (film and disk). In conclusion, in situ polymerization is a powerful synthesis method to produce processable high-magnetization nanocomposites.