Mehrdad Hassanzadeh

Quasi-ideal Nonlinear Electrical Behavior of Polycrystalline SnO2 Ceramic Varistors Doped with SiO2

The influence of SiO2 doping on the microstructure and electrical behavior of SnO2 varistors has been studied. The varistor effect was studied over a wide range from 10−9 A to 104 A. It is shown that the J(E) characteristic of SnO2 ceramics exhibits a nonlinear coefficient >100. The SiO2 doping also resulted in a sharp-abrupt upturn region in the I–V characteristic, indicating a single semiconductor junction behavior. The leakage current of the varistors is rather low, on the order of 10−10 S m−1. In the upturn region of operation where the curve departs from the nonlinear relation and approaches the value of the bulk resistivity of the material, the ceramic is characterized by a current density almost independent of the applied voltage. A very small amount of SiO2 causes large perturbations of the conventional thermionic emission observed in varistor ceramic materials.

MAX phase ternary carbide derived 2-D ceramic nanostructures [CDCN] as chemically interactive functional fillers for damage tolerant epoxy polymer nanocomposites

A 2-dimensional ceramic nanostructure was successfully processed out of nanolamellar 312 MAX phase ternary carbide, titanium silicon carbide, Ti3SiC2 (TSC), via a simple shear-induced delamination technique. It has been explored as a functional nanofiller for obtaining chemically homogeneous, low-friction, self-lubricating epoxy nanocomposites. The structural characterization of the MAX phase Carbide Derived Ceramic Nanostructure (CDCN) was carried out using Dynamic Light Scattering (DLS), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) analysis. Subsequently, CDCN was mixed with Araldite CY 225 (DGEBA) at different percentages and thermally cured using Aradur HY 925 hardener at 130 °C to make epoxy–Ti3SiC2 nanocomposites. The effect of CDCN-nanofiller was studied on epoxy rheology, glass transition temperature (Tg), thermal stability, flexural and compressive strengths, microhardness, dry sliding wear and friction properties. It was found that, unlike other ceramic fillers, CDCN chemically interacts with epoxy and readily dispersed in a polymer matrix without any deleterious structural defects. It resulted in the formation of physico-chemically homogeneous microstructures. Epoxy composites prepared with CDCN filler attained 50% more mechanical strength and hardness. Wear analysis trends indicate Ti3SiC2 nano reinforcement possibly formed a lubricating tribo-chemical film that decreases the wear rate and coefficient of friction. This work is significant in such a way that a novel nanofiller has been identified from MAX phase carbide family which offers a self-lubricating interface and produces mechanically reliable, damage tolerant epoxy composite for state-of-the-art engineering applications.

Comparison of epoxy and thermoplastic embedded pole regarding reliability and cost in air insulated switchgear

Recently embedded Vacuum Circuit Breakers (VCB) with thermoplastic have been introduced on the market. The substitution of epoxy resin by thermoplastic is of concern in ambient air insulated switchgear solutions. This paper reports a study performed for VCB embedded poles with two technologies: epoxy resin and engineering thermoplastic PA66. A comparison is made between both technologies reagarding reliability, long life tracking withstand, cost and environmental impact by performing a multi-criteria life cycle assessment.