R. Veillette

Nanostructured polymer microcomposites: A distinct class of insulating materials

Experimental evidence was produced and gathered to demonstrate the distinct nature of nanostructured polymer microcomposites. The case of a polymer composite consisting of a high-content of micrometric quartz with a small adjunct of nanoclay is discussed. Emphasis is put on dielectric behavior studies while some results on thermal characteristics are presented. Overall results strongly support the potential of this class of insulating material for electrotechnical applications.

Structural and electronic properties of the LiNiPO4 orthophosphate

Microcrystalline LiNiPO4 powders have been prepared by solid-state reaction using various precursors. Characterization of the structure and morphology of powders was performed using XRD, SEM, HRTEM, Raman, and FTIR. The electronic properties of materials were investigated by SQUID and ESR. The LiNiPO4 material adopts the olivine-like structure (Pnma S.G.). Analysis of the Raman and FTIR spectra figures out, with the aid of a molecular vibration model, the bonding between NiO6 octahedral and (PO4)3− tetrahedral groups. The electronic configuration and the local cationic arrangement are confirmed by magnetic susceptibility and electron spin resonance spectroscopy.

Nanodielectric surface performance when submitted to partial discharges in compressed air

Bulk samples of a nanodielectric material were synthesized. This insulating material consisted of a mix of epoxy resin, a SiO/sub 2/ load and a percent fraction of inorganic nanoparticles. The aim of the present experiment was to determine the performance of the nanodielectric surface when exposed to partial discharges as compared to that of an epoxy containing only the micrometric SiO/sub 2/ load. A discharge situation featuring a triple-junction condition was used. Low-intensity discharges were produced along a gap formed by the interface between compressed air and the bulk sample. The material containing a small amount of nanoparticles was found to resist much more the present discharge conditions, showing an improved performance as compared to that observed in the case of the epoxy without nanoclay.

Polymer composites with a large nanofiller content: a case study involving epoxy

A situation involving a polymer nanocomposite containing a large amount of inorganic filler was studied. An epoxy nanocomposite with a content of 20% wt of nanosilica was used. Emphasis was put on imaging at the nanoscale and some dielectric responses were measured using dielectric spectroscopy. Using Transmission Electron Microscopy (TEM) in a High-Angle Annular Dark Field (HAADF) scanning mode, an area of less than 4 nm around an isolated particle was imaged and found to have a very low atomic number. With Atomic Force Microscopy (AFM) in peak-force mode agglomerates were clearly imaged. With respect to the dielectric response, no interfacial relaxation peak was observed. In presence of some agglomeration, the real part of the permittivity was found to be decreased by the addition of the nanofiller. Higher-field measurements unravelled nonlinear variations of the conduction versus an applied field. It was shown that the use of a large filler concentration resulted in greater interphase overlapping between the nanoparticles.

On the degree of exfoliation affecting the corona performance of a nanodielectric surface

Samples of a nanodielectric material were synthesized. This bulk material was a mix of epoxy resin, a SiO2 load and a small fraction of inorganic nanoparticles. The present experiment aimed at determining the effect of the degree of exfoliation on the performance of the nanodielectric surface when exposed to partial discharges. It was found that when the degree of intercalation/exfoliation of the nanoclay is low, the nanodielectric surface did not exhibit superior performance compared to that not containing nanoclay.

Dielectric design of LDPE properties: With the help of double-core Si/SiO 2 and Carbon Black

Low-density Polyethylene (LDPE) was modified by using simultaneously 2 additives. Each additive had a specific attribute. Silicon was used. Using TEM with EELS, it was proved first that the passivated version constituted a double core consisting of Si surrounded by a nanometric layer of amorphous Silica (SiO2). Thus Si brought the possibility of an enlarged dielectric storage capacity with a barrier controlling the electrical charge movement (via SiO2). Silicon was used in conjunction with Carbon Black (CB) and produced, upon some conditions, enlarged dielectric storage yet with intempestive conversion to a conducting state. At low voltage, LDPE containing 5 wt% CB and 3% or 0.25% Si remained insulating materials. During breakdown conditions with a 2 kV/s rise, only the composite containing 0.25 wt% CB and 3 wt% Si exhibited insulating conditions. These results draw attention to the importance of performing material system evaluation under dynamical conditions.

Polymer composites having large content of nanofiller: A case study involving epoxy

The situation where the polymer nanocomposite contains a large amount of organic filler was studied. An epoxy nanocomposite having a content of 20% wt of nanosilica was used. Emphasis was put on imaging at nanoscale and some dielectric responses were measured using dielectric spectroscopy. Using HAAD mode, an area of less than 4 nm surrounding an isolated particle was imaged and found to have a very low atomic number. Only with AFM in peak-force mode that agglomerates were clearly detected. Relative to the dielectric response, no interfacial relaxation peak was observed. In spite of some agglomeration, the real part of the permittivity was found to be increased by the adjunct of the nanofiller.

Secondary Electron Yield at High Voltages up to 300 keV

Secondary electrons (SE), emitted from bombardment of a matter with energetic particles such as electrons, ions, or protons, are conventionally defined as those with a kinetic energy of 50 eV or less. The parameter describing SE emission is called SE yield, δ, which defines as the number of SEs produced by each incident particle. The SE micrograph, which reveals the surface of materials, is the most widely used imaging mode for scanning electron microscopy (SEM). Recently, SE detectors have been installed on scanning transmission electron microscopes (STEM), as it augments the ability of imaging surface features to a bright-field or dark-field STEM image, which essentially reveal bulk information of a very thin specimen. The benefit of simultaneous imaging of surface (SE) and transmitted electrons (TE) at atomic-scale has been demonstrated in materials science research [1], such as learning the degradation mechanism of battery materials [2] and morphological evolution of catalysts during in situ heating [3].

High Capacity and High Efficiency Maple Tree-Biomass-Derived Hard Carbon as an Anode Material for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are in the spotlight because of their potential use in large-scale energy storage devices due to the abundance and low cost of sodium-based materials. There are many SIB cathode materials under investigation but only a few candidate materials such as carbon, oxides and alloys were proposed as anodes. Among these anode materials, hard carbon shows promising performances with low operating potential and relatively high specific capacity. Unfortunately, its low initial coulombic efficiency and high cost limit its commercial applications. In this study, low-cost maple tree-biomass-derived hard carbon is tested as the anode for sodium-ion batteries. The capacity of hard carbon prepared at 1400 °C (HC-1400) reaches 337 mAh/g at 0.1 C. The initial coulombic efficiency is up to 88.03% in Sodium trifluoromethanesulfonimide (NaTFSI)/Ethylene carbonate (EC): Diethyl carbonate (DEC) electrolyte. The capacity was maintained at 92.3% after 100 cycles at 0.5 C rates. The in situ X-ray diffraction (XRD) analysis showed that no peak shift occurred during charge/discharge, supporting a finding of no sodium ion intercalates in the nano-graphite layer. Its low cost, high capacity and high coulombic efficiency indicate that hard carbon is a promising anode material for sodium-ion batteries.

Hydrophobic performance of SiCO coating on polycarbonate assessed by a dielectric method

Experimental evidence was produced and gathered to demonstrate the performance of a submicrometric-sized SiCO coating on polycarbonate. Identification and morphology of the deposit were established using micro-Raman spectroscopy and Transmission Electronic Microscopy, respectively. The amorphous- phase deposit of submicrometric thickness, on average of 825 nm, was found to succeed in changing the polymer properties when submitted to high humidity. In these conditions, the dielectric permittivity of the coated polymer, especially the real part, was found to be less than that of the bare polymer surface due clearly to the presence of H2O. Thus, this coating was found to be hydrophobic.