Dependence of Vacuum Electrical Breakdown Field and Field Enhancement Factor on the Number of Apertures Drilled in Small Electrodes

Dark current based on field emission current is considered to be a factor causing the vacuum electrical breakdown between multiaperture acceleration grids in the JT‐60 negative ion source. In this paper, we focus on field enhancement factor, which is a key parameter of field emission from the electrode. Vacuum breakdown testing for small‐sized electrodes simulating the multiaperture acceleration grids of the negative ion source was performed. We found the field enhancement factor and breakdown field for multiaperture electrodes, and we investigated the dependence of each parameter on the number of apertures. The results revealed that an increase in the average field enhancement factor after the end of conditioning resulting from an increase in the number of apertures led to a decrease in the dielectric strength of the multiaperture electrodes.     

Role of Water Vapor in Crystallite Growth and Tetragonal-Monoclinic Phase Transformation of ZrO2

The role of water vapor in crystallite growth and the tetragonal-to-monoclinic phase transformation of ZrO₂ was studied using three specially prepared samples: an ultrafine powder of monoclinic ZrO₂ obtained by hydrolysis of ZrOCI₂, an aggregated powder of tetragonal ZrO₂ obtained by thermal decomposition of Zr(OH)₄ under reduced pressure, and an ultrafine powder of tetragonal ZrO₂ obtained by thermal decomposition of zirconyl acetate dispersed in caramel. The samples were heat-treated up to 1000°C in dry and wet atmospheres saturated with water vapor at 90°C. It was found that water vapor markedly accelerated crystallite growth for both monoclinic and tetragonal ZrO₂ and facilitated the tetragonal-to-monoclinic phase transformation. Water vapor increases surface diffusion and thus enhances crystallite growth and decreases surface energy, which leads to stabilization of the tetragonal phase.     

EIGENVECTOR METHOD IN MULTICRITERIA OUTRANKING RELATIONS

Most complex decision problems involve conflicts among multiple criteria and uncertain and imprecise data. The (fuzzy) outranking relation model that was introduced by Roy can tackle such complex situations. The present paper proposes a new ranking procedure based on the eigenvector in multicriteria outranking relations. The properties of the eigenvector method in ordinary outranking relations are investigated. Then, the eigenvector method is compared to that of qualification by several examples. Finally, we compare the eigenvector method with the distillation method in ELECTRE III in fuzzy outranking relations. The results of the two methods did not exhibit significant differences. The eigenvector method turns out useful, because it can promote a complementary viewpoint.     

Effects of Bismuth Sesquioxide on the Characteristics of ZnO Varistors

The nonlinearity of ZnO varistors is significantly influenced by the Bi₂O₃ and Sb₂O₃ contents, as well as by the phase composition of the Bi₂O₃. Degradation of the current-voltage characteristics due to the applied voltage is not always lowered by the β—γ transition of the Bi₂O₃ phase. Lattice parameter determinations and stress analyses suggest that the Bi₂O₃-rich phase in multigrain junctions causes mechanical strain at the grain boundary which may play an important role in the current-voltage characteristics of ZnO varistors.     

ESTIMATION OF DAILY INTAKE OF FOUR KINDS OF TRIHALOMETHANE BY JAPANESE HOUSEWIVES

Duplicate portions of the daily meals consumed by 30 housewives were collected for 3 consecutive days in the cities of Nagoya and Yokohama in Japan.
Meals were analyzed for chloroform, bromodichloromethane (BDCM), chlorodibromomethane (CDBM) and bromoform by using a purge-trap procedure. The average concentration (and the range) of these four kinds of trihalomethane in each of the 24 h duplicate meals were, chloroform 19.6±18.1 ppb(n.d.-106.8 ppb), BDCM 0.3±0.3 ppb(n.d.-1.7 ppb), CDBM 0.1±0.2 ppb(n.d.-0.6 ppb) and bromoform 0.5±1.3 ppb(n.d.-8.1 ppb).
The mean daily dietary intake of the four kinds of trihalomethane by housewives were, chloroform 40.0±25.4 μg, BDCM 0.6±0.5 μg, CDBM 0.3±0.3 μg and bromoform 0.9±1.3 μg.     

Grain Growth and Phase Transformation of Titanium Oxide During Calcination

Additions of NiO, CoO, MnO₂, Fe₂O₃, and CuO promote the anatase-rutile transformation and grain growth of TiO₂. Additions of Na₂O and WO₃ retard the transformation and have no effect on the grain growth. The addition of MoO₃ strongly promotes the grain growth but has only a slight effect on the phase transformation. Both the grain growth and transformation are promoted slightly by Cr₂O₃. The transformation is significantly affected by the method of preparing TiO₂. The grain size of TiO₂ heated in H₂ exceeds that of TiO₂ heated in O₂, in air, in argon, and in vacuum. The rate of transformation decreases with an increase in the partial pressure of oxygen of the atmosphere.     

Sintering of High-Purity Nickel Oxide

The results of an investigation of densification and grain growth during the sintering of high-purity NiO in various atmospheres are presented. The sintering of NiO powders is divided into three stages. Grain growth during the third stage follows the empirical equation D ²= K t, where D is the average grain diameter, K a rate constant, t the sintering time. The activation energy of grain growth was found to be 55 kcal. per mole. The shrinkage and weight loss during the sintering process in vacuum were larger than in argon, air, and oxygen. Grain growth during sintering also differed with the sintering atmosphere. It was concluded that the sintering process is not explained reasonably by the theory of a semiconductor.