Yasuchika Nagai

Mass spectrometric observation of vacuum treated oxygen free copper

Abstract To reduce the quantity of dissolved volatile gases in oxygen free copper (OFC), a vacuum treatment for molten copper is the most effective method. The application of vacuum degassing to a fully continuous casting plant was made and a successful mass production of OFC ingots has been achieved. Microscopic observation shows that the vacuum treated OFC meets the requirement of the standard specification of the ASTM-F-68 Class 1 for its low porosity count. Gas chromatographic analysis also reveals that it has 50% less contents of dissolved gas than the normally manufactured OFC. To investigate the gas desorption during ion bombardment, SIMS measurements for the vacuum treated OFC have been carried out. It is thought that most of the desorbed gas consists of hydrogen and oxygen, and that their amounts are less than half of those from normally manufactured OFC.

Electrical breakdown strength of oxygen-free copper electrodes under surface and bulk treatment conditions

Abstract The effects of heating electrodes, and diamond turning of these electrode surfaces to a mirror finish upon an electrical breakdown in a vacuum were investigated. The electrode material used was oxygen-free copper. It was found that the mirror finish obtained by diamond turning reduces the number of repetitive breakdowns to achieve higher hold-off voltages, (conditioning of the vacuum gaps by repetitive breakdowns). Heating the electrodes was effective in improving the breakdown strength after the conditioning process. A higher heating temperature produced a higher breakdown field. A breakdown field of about 250 MV/m was obtained for electrodes heated at 700 °C in a vacuum and then finished by diamond turning. It has been concluded that an improvement in the breakdown field by heating is due to a reduction of the gas contents rather than recrystallization.

Vacuum-breakdown properties of oxygen-free copper electrodes machined by diamond turning for mirror finish

The electrodes used in this investigation to experimentally evaluate the effect of diamond turning on electrical breakdown characteristics in vacuum were first roughly machined by turning, and then machined to a mirror finish by diamond turning. Residual stresses of the electrode surfaces were measured by an X-ray diffraction method before and after the diamond turning. Several electrodes were annealed in vacuum for one hour at 400 degree(s)C or 700 degree(s)C before the diamond turning. Vacuum breakdown experiments using impulse voltages with the wave form of 64/700 microsecond(s) revealed that the diamond turning improves breakdown strength, that the conditioning of vacuum gaps is achieved by only few tens of breakdowns, and that annealed electrodes have a better hold-off voltage capability.