No abstract

The dielectric and mechanical properties of standard (PEI), nanoscale-filled and microscale-filled varnishes are detailed and analyzed in this communication. Fumed silica (10nm and 400nm) have been tested as a filler. A particular attention has been paid to Partial Discharge Inception Voltage, Lifetime under pulse voltage and bonding strength which are crucial for varnish to be used in rotating machines fed by inverters.

No abstract

Radiofrequency glow discharge coupled to optical emission spectrometry (RF-GD-OES) is a wellknown analytical technique for bulk, surface and depth profiling and can be applied in the direct analysis of conductors, semiconductors and non-conductors, however for the latter case limits still exist. The problem is related to the low power deposited in the plasma due to a voltage drop developing inside the material. The voltage transfer coefficient, defined as the ratio between the peak voltage at the front and at the back of the sample. This depends on the sample capacitance, which itself is dependant on the material surface, thickness and permittivity. In order to improve the analysis of such non-conductive materials, thin conductive top layers are deposited on both sides of the sample which increases their voltage transfer coefficient. The aim of this work is to study the influence of these thin layers on the optical and electrical signals measured for the samples with varying thickness and diameter. Additionally, the influence of applying a magnetic field during the GD analysis has been evaluated as an attractive option in order to obtain higher sputtering rates, together with better ionisation and excitation efficiencies and as a consequence give improved emission intensities.

In radiofrequency glow discharge emission spectrometry (RF-GDOES), the excitation voltage used to create the plasma is applied to the back or front end of the sample to be analyzed. In this paper we focus on back-applied voltage systems (a configuration that represents about half of the instruments available on the market), and on applied voltage problems (the power coupling efficiency and materials analysis are beyond the scope of this study). In the RF-GDOES of nonconductive samples, a voltage drop develops inside the material. The voltage transfer coefficient is defined as the ratio between the peak voltage in front of the sample (facing the plasma) and the peak voltage applied to the back of the sample. In this work, we show that it is possible to increase the voltage transfer coefficient by increasing the capacitance of the sample. The capacitance of a given nonconductive material depends on its surface, its thickness and its permittivity. Increasing the voltage transfer coefficient permits higher power deposition in the plasma. This study is based on an electrical equivalent circuit for the discharge device, which takes into account the sample and reactor capacitances as well as the voltage probes used for the measurements. This circuit, when modeled by a commercial electrical circuit simulator, gives the voltage transfer coefficient as a function of the sample capacitance. Different approaches to increasing the sample capacitance and their influence on the voltage transfer coefficient are presented and related to the 750.4 nm argon line intensity, which is correlated to the electron density.