Enhanced High-Temperature DC Dielectric Performance of Crosslinked Polyethylene with a Polystyrene Pinning Structure

In this paper, we propose a method on improving direct current (DC) dielectric performance by designing a polystyrene (PS) pinning crosslinked polyethylene (XLPE) for the application of insulation materials on high voltage direct current (HVDC) extruded cable. Electrical experimental results show that the addition of PS (1–5 phr, parts per hundreds of resin) can significantly reduce DC conductivity and increase DC breakdown strength of XLPE in the test temperature range of 30–90 °C. Microstructure investigation shows PS distributed as particles could participate in the formation of a crosslinking network with the help of a crosslinking agent, thus forming a polymer pinning structure at the interface between XLPE and PS. It is believed that such a special design strengthens the structure of XLPE, which leads to the improved DC dielectric performance at elevated temperatures. Our findings may contribute a new solution for developing HVDC cable insulation materials.

Effects of Microstructure on the Electrical Conductivity of SrCo0.8Fe0. 2O3_δ

ABSTRACTThe effect of microstructure on the electrical conductivity of SrCO0.8Fe0.2O3_δ (SCFO) was investigated in air using a four-point dc method. In the test temperature range of 200 to 900 °C, the electrical conductivity of this material was observed to increase with the increase of the average grain size in the lower temperature region where the conductivity increases with the increase of the temperature. The activation energy is decreased with the increase of the grain size in this region, 0.04 ± 0.004 ev for 4.1μm sample and 0.01 ± 0.001 ev for 14.8 μm sample. When temperature is further increased, the conductivity of this material decreases with the increase of the temperature, and the grain size effect becomes less noticeable.

The Effect of Heat Treatment on the Room Temperature and Elevated Temperature Fracture Toughness Response of Alloy 718

The effect of heat treatment on the JIC fracture toughness behavior of Alloy 718 was characterized at room temperature, 427°C and 538°C. Two different heat treatments were used: the conventional (ASTM A637) treatment, and a modified heat treatment designed to improve the toughness of Alloy 718 base metal and weldments. The elastic-plastic JIC fracture toughness response of the modified Alloy 718 was found to be superior to the JIC behavior exhibited by the conventional material over the entire test temperature range. Metallographic and fractographic examinations of Alloy 718 fracture surfaces revealed that the inferior fracture resistance of the conventional superalloy was attributed to the presence of coarse δ precipitates throughout the conventional matrix. The increased fracture toughness response of the modified Alloy 718 was related to the dissolution of coarse δ precipitates during the high temperature solution anneal employed in the modified treatment.