S. Savoie

Electrical properties analysis of micro and nano composite epoxy resin materials

This work deals with the study of micro and nanosilica filled epoxy resin samples carried out in the framework of CIGRE WG D1.24 cooperative test program. This program focused on chemical, electrical and electrostatic properties of epoxy based nanodielectrics for electrical engineering applications. Epoxy based samples filled with micro and/or nanoparticles of silica were characterized by transmission electron microscopy, dielectric spectroscopy, conduction current and space charge measurements. These mutually complementary techniques were used to examine the effect of the size and quantity of silica particles on the electrical properties of the analyzed materials. The analysis of charge injection, polarization, trapping and conduction phenomena has allowed the modeling of dielectric behavior of the studied materials under multiple stresses. The Schottky Injection and Space Charge Limited Current models were studied to explain conduction phenomena. A composition of micro and nano-sized silica particles accumulating the smallest amount of space charge is also proposed.

Hydrophobic fluorinated carbon coatings on silicate glaze and aluminum

Abstract Hydrophobic, adherent, and strong coatings would be desirable for the glazed porcelain insulators and aluminum conductors of electric power grids. Micron-thick films consisting of fluorinated carbon (CFx) on top of adherence layers (a-C:H on Si or Cr) were deposited on insulator pieces and aluminum, using a benign Ar/C2H2/C3F8 chemistry in a dual magnetron sputtering/plasma-enhanced chemical vapor deposition system. A wide range of process parameters was explored: pressure from 1 to 67 Pa, substrate r.f.-induced d.c. offset from –50 to –1000 V, and different gas ratios. Advancing and receding contact angle measurements, X-ray photoelectron spectroscopy, optical and atomic force microscopy, micro- and nano-indentation, and scratch testing were performed. Contact angles as large as 130° were obtained. The film F content was

An Experimental Evaluation of the Temperature Gradient in Solid Oxide Fuel Cells

The use of solid oxide fuel cells SOFCs 1,2 as efficient energyconverter devices rests on their high working temperature. These ceramic fuel cells generally operate between 800 and 1000°C, although a major research effort is put forward to reduce their operation below 800°C for reducing manufacturing costs and improving cell lifetime. Depending on the selected range of temperature, a SOFC system would allow for either cogeneration or bottoming cycle, which add significantly to the overall power-generation efficiency. The high operating temperature of SOFC affords, in principle, for the direct use of hydrocarbon fuels by means of their catalytic conversion to carbon monoxide and hydrogen. The most economical way to convert these fuels is to proceed through direct internal reforming DIR, as it is observed in tubular or planar designs, or through catalytic partial oxidation CPOX, which is at the basis of the functioning of single-chamber SOFC SC-SOFC. However, both DIR and CPOX may lead to high temperature variations along the fuel cell. In the case of direct reforming of methane, a significant cooling at the inlet of the fuel cell is expected due to the fast kinetics of the endothermic reforming reaction, especially over conventional Ni– yttria-stabilized zirconia YSZ cermet. 3 It then aggravates the tem

Post-heat treatment effect on the dielectric response of epoxy samples

In the present experiment, the dielectric response of various types of epoxies was investigated in the frequency and time domain. The samples consisted of nanostructured epoxy microcomposites and reference microcomposites. Water ingression at the fabrication step and/or at measuring time is known to affect the dielectric response of materials such as epoxy. Prior to measurement, some samples were submitted to 160°C during 48 hours under vacuum. Heating the epoxy sample under vacuum was found to have a substantial effect on dielectric properties specially when the microcomposite was nanostructured. In the nanodielectric case, pre-treatment conditions could produce a drop in the dielectric constant, about 5% at around 10-2 Hz. This observation would be consistent with the removal of the polarisability associated with water molecules.

Dielectric and thermal properties of boron nitride and Silica epoxy composites

Samples containing only submicrometric filler (BN), only nanometric filler (Silica) and both fillers were prepared by gravity moulding. A pure epoxy sample was also prepared to quantify the enhanced properties. Glass transition temperatures were measured by Differential Scanning Calorimetry. Dielectric Breakdown data were analysed using the Weibull statistical method and Dielectric Spectroscopy was used at low and high voltage to measure the samples permittivity. The glass transition temperature is decreased by BN presence but not by nanosilica. At ambient temperature, the β relaxation peak is not affected by nanoparticles nor by applied voltage. Strangely, the sample containing the two nanoparticles type is not affected compared to pure epoxy. On dielectric spectra, a supplementary relaxation peak for samples containing nanosilica is present. This peak is associated with the interphase between nanosilica and polymer.

Water as a Digression Relative to the Dielectric Response in the Frequency Domain for Polymer Composites

The presence of water in insulating solids is known to affect the dielectric properties. Although relaxation processes evolved with the excitation frequency and temperature, further characteristics unfold when contaminant with a high dielectric constant, such as water is involved. When the material consists of a microcomposite, and especially in the advent of incorporation of nanofillers, it is speculated that water molecules may intervene in several different manners. In order to investigate further the potential digression caused by water, dielectric spectroscopy was used on prepared composite specimen. Different types of epoxy microcomposites exhibiting a high content of quartz, i.e. 60% wt., were prepared. The effects due to the variation of the water content and presence of nanostructures (nanoclay) on the dielectric response will be discussed. With a weight intake of 0.2% of water, the capacity of the epoxy microcomposite exhibits a slight increase (2%) at lower frequencies and losses are found to increase while a shift towards higher frequencies occurs.

Dielectric study with epoxy-based nanostructured microcomposites containing silica

Material samples were prepared consisting of silica particles in an epoxy matrix. The generic compound contained a large amount of micrometric silica (e.g. 60% wt.) and a few % of nanosilica. Investigation of the microstructure of the samples showed that indeed the microcomposites exhibited a nanostructured morphology. Dielectric spectroscopy was used to compare the behavior of materials differing in composition. Posttreatment using heat was necessary to obtain a reproducible dielectric response. Dielectric features linked to the material compositions were annotated. For the case of 65-% total wt. silica, it was found that when the nanophase varies from 0 to 5%, the increase in the dielectric constant could fluctuate by as much as 10% in the low-frequency range.

Electrical conductivity of graphene-based epoxy nanodielectrics

Graphene-based epoxy nanocomposites have been produced by the ultrasonication of graphene oxide (GO), chemically modified GO and through two-phase extraction of GO water solution. All the samples have been post-cured and the thermal treatment provided a thermal in situ reduction of GO into the epoxy reticulated matrix. Electrical conductivity of the samples has been measured showing different behavior depending on both the nanofiller and the production procedure employed. Sample with 0.5 wt% of GO shows conductivity values 80 times higher than the neat epoxy.

Preparation and dielectric behavior of epoxy resin containing graphene oxide

Graphene oxide (GO) and chemically modified graphene oxide have been dispersed in low amount (until 0.5 wt%) into epoxy resin. Comparing the dielectric responses of the polymer nanocomposites with those of neat epoxy, no significantly changes were noted. Relevant differences were recorded after a post-curing heating treatment able to reduce the dispersed GO to more conductive graphene. Neat epoxy and epoxy samples with chemically modified GO had usually a small decrease on permittivity while GO samples showed an increase of about 10% of the value previously observed. This behavior will be connected with chemical properties of the nanofiller.

Tribo-Mechanical Properties of HVOF Deposited Fe3Al Coatings Reinforced with TiB2 Particles for Wear-Resistant Applications

This study reveals the effect of TiB2 particles on the mechanical and tribological properties of Fe3Al-TiB2 composite coatings against an alumina counterpart. The feedstock was produced by milling Fe3Al and TiB2 powders in a high energy ball mill. The high-velocity oxy-fuel (HVOF) technique was used to deposit the feedstock powder on a steel substrate. The effect of TiB2 addition on mechanical properties and dry sliding wear rates of the coatings at sliding speeds ranging from 0.04 to 0.8 m·s−1 and loads of 3, 5 and 7 N was studied. Coatings made from unreinforced Fe3Al exhibited a relatively high wear rate. The Vickers hardness, elastic modulus and wear resistance of the coatings increased with increasing TiB2 content in the Fe3Al matrix. The wear mechanisms strongly depended on the sliding speed and the presence of TiB2 particles but were less dependent on the applied load. This study reveals the effect of TiB2 particles on the mechanical and tribological properties of Fe3Al-TiB2 composite coatings against an alumina counterpart. The feedstock was produced by milling Fe3Al and TiB2 powders in a high energy ball mill. The high-velocity oxy-fuel (HVOF) technique was used to deposit the feedstock powder on a steel substrate. The effect of TiB2 addition on mechanical properties and dry sliding wear rates of the coatings at sliding speeds ranging from 0.04 to 0.8 m·s−1 and loads of 3, 5 and 7 N was studied. Coatings made from unreinforced Fe3Al exhibited a relatively high wear rate. The Vickers hardness, elastic modulus and wear resistance of the coatings increased with increasing TiB2 content in the Fe3Al matrix. The wear mechanisms strongly depended on the sliding speed and the presence of TiB2 particles but were less dependent on the applied load. This study reveals the effect of TiB2 particles on the mechanical and tribological properties of Fe3Al-TiB2 composite coatings against an alumina counterpart. The feedstock was produced by milling Fe3Al and TiB2 powders in a high energy ball mill. The high-velocity oxy-fuel (HVOF) technique was used to deposit the feedstock powder on a steel substrate. The effect of TiB2 addition on mechanical properties and dry sliding wear rates of the coatings at sliding speeds ranging from 0.04 to 0.8 m·s−1 and loads of 3, 5 and 7 N was studied. Coatings made from unreinforced Fe3Al exhibited a relatively high wear rate. The Vickers hardness, elastic modulus and wear resistance of the coatings increased with increasing TiB2 content in the Fe3Al matrix. The wear mechanisms strongly depended on the sliding speed and the presence of TiB2 particles but were less dependent on the applied load. This study reveals the effect of TiB2 particles on the mechanical and tribological properties of Fe3Al-TiB2 composite coatings against an alumina counterpart. The feedstock was produced by milling Fe3Al and TiB2 powders in a high energy ball mill. The high-velocity oxy-fuel (HVOF) technique was used to deposit the feedstock powder on a steel substrate. The effect of TiB2 addition on mechanical properties and dry sliding wear rates of the coatings at sliding speeds ranging from 0.04 to 0.8 m·s−1 and loads of 3, 5 and 7 N was studied. Coatings made from unreinforced Fe3Al exhibited a relatively high wear rate. The Vickers hardness, elastic modulus and wear resistance of the coatings increased with increasing TiB2 content in the Fe3Al matrix. The wear mechanisms strongly depended on the sliding speed and the presence of TiB2 particles but were less dependent on the applied load. This study reveals the effect of TiB2 particles on the mechanical and tribological properties of Fe3Al-TiB2 composite coatings against an alumina counterpart. The feedstock was produced by milling Fe3Al and TiB2 powders in a high energy ball mill. The high-velocity oxy-fuel (HVOF) technique was used to deposit the feedstock powder on a steel substrate. The effect of TiB2 addition on mechanical properties and dry sliding wear rates of the coatings at sliding speeds ranging from 0.04 to 0.8 m·s−1 and loads of 3, 5 and 7 N was studied. Coatings made from unreinforced Fe3Al exhibited a relatively high wear rate. The Vickers hardness, elastic modulus and wear resistance of the coatings increased with increasing TiB2 content in the Fe3Al matrix. The wear mechanisms strongly depended on the sliding speed and the presence of TiB2 particles but were less dependent on the applied load. This study reveals the effect of TiB2 particles on the mechanical and tribological properties of Fe3Al-TiB2 composite coatings against an alumina counterpart. The feedstock was produced by milling Fe3Al and TiB2 powders in a high energy ball mill. The high-velocity oxy-fuel (HVOF) technique was used to deposit the feedstock powder on a steel substrate. The effect of TiB2 addition on mechanical properties and dry sliding wear rates of the coatings at sliding speeds ranging from 0.04 to 0.8 m·s−1 and loads of 3, 5 and 7 N was studied. Coatings made from unreinforced Fe3Al exhibited a relatively high wear rate. The Vickers hardness, elastic modulus and wear resistance of the coatings increased with increasing TiB2 content in the Fe3Al matrix. The wear mechanisms strongly depended on the sliding speed and the presence of TiB2 particles but were less dependent on the applied load.