Papers by Keyword: Zr Additions

Abstract: The effects of the addition of Y or both Y and Zr to Bi-Mn-Co-Sb-Si-Cr-Ni-added ZnO varistors on the varistor voltage and the tolerance characteristics of electrical degradation were investigated. The deterioration of the tolerance characteristics of electrical degradation by the addition of Y was probably caused by an increase in the number of willemite (Zn2SiO4)-type particles or a decrease in the number of spinel (Zn2.33Sb0.67O4)-type particles, but this deterioration was reduced by adding Zr. Moreover, the reduction in the average ZnO grain size due to the addition of Y was a major factor in the increased varistor voltage, and the ZnO grain growth was inhibited by the formation of an un-known compound after adding Y. The varistor voltage of a varistor with 2 mol% added Y increased by approximately 50% compared to a varistor with no Y added.

Abstract: Two Al-Mg-Mn alloys having similar compositions but with and without Zr addition were subjected to equal channel angular pressing (ECAP) at 350°C using route BC and a 90° die, followed by water quenching or air cooling. A series of annealing experiments were conducted at various temperatures from 400°C to 460°C on the water-quenched alloys. Fine structures with grain size of approximately 1~2μm were obtained in these alloys after 6 passes. The water-quenched alloy containing Zr exhibited finer structure compared with the Zr-free alloy in the same cooling condition, which was due to the existence of Al3Zr dispersoids. And in the air cooling condition, it was found that in the Zr-free alloy static recovery occurred, and in partial regions some small grains without dislocation inside appeared suggesting the occurrence of static recrystallization. This demonstrated a fairly restored structure. However, the microstructure of the alloy containing Zr kept stable during the air cooling process. In addition, in the annealing experiments, secondary recrystallization took place in the Zr-free alloy annealed at 410°C for 1h, while the alloy containing Zr kept stable up to 460°C. TEM observation showed that the Al3Zr dispersoids pinned the motion of the grain boundaries, thereby the secondary recrystallization and grain growth were inhibited.

Abstract: Addition of Ti and Zr to high-pressure (HP) synthesized MgB2 results in an increase of critical current density of the material due to the absorption of impurity hydrogen coming most likely from the materials of a high-pressure cell. The results of the studies of structure, critical current density, trapped field and mechanical characteristics are discussed. High-pressure synthesized MgB2 (with Ti additions) blocks were for the first time used in a SC electromotor at 20 K and demonstrated the efficiency similar to that of MT-YBCO bulk (at the same working temperature).