Translucent aluminum oxide, a crystalline substance, has transmittivity of some 90%, high corrosion resistance, and high stability in alkali metal vapor at high temperature and pressure, in addition to the high mechanical strength and thermal resistance which are the specific properties of conventional alumina ceramic.
By this new substance being utilized for a discharge tube and the sodium vapor pressure being increased, a sodium-vapor lamp has been developed, which is smaller than conventional and produces white light with a wide spectral band and the luminous efficiency of about 100 lm/W.
This new substance-to-metal sealing is very difficult. The writers sealed this new substance to Ti by reactive alloying method utilizing Ti-Ni. Particularly, paying, attention, to sealing time and the surface condition of this new substance in sealing, we investigated those influences on seal strength and the vacuum tightness, and observed and examined the sealed part by the microscope and the X-ray microanalyzer.
Gained results are as follows.
(1) By reactivealloying method utilizing Ti-Ni, it is possible to seal in vacuum-tight this new substance to Ti.
(2) Sealing surface which is flat and slightly rough, is good to obtain the vacuum tightness.
(3) At sealing temperature of 1000°C, seal strength approaches the saturation condition in 10 minutes to seal, and the seal strength is about 150 kg/cm².
(4) In the sealed part, the triangular and the lustrous crystal constructions are observed, these parts seem to be Ti₂Ni phase.
(5) In the sealing part of this new substance to Ti, three boundary layers are observed. Ti, Ni and Al elements show their own peculiar diffusion distribution in these layers. In this part, a solid solution or a compound of Ti-Al-Ni-O system and Ti-Al-O system is formed, and the combination between this new substance and Ti seems to be completed.

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Ultimate pressure vs input characteristics of a Hickman pump, containing Octoil-S and DC-705 as working fluids, have been observed as a function of an operating period and a backing pressure. It is shown that in both cases of using these two oils the characteristics vary markedly, in a way characteristic of each oil, as the pump is operated for several hundreds hours. It is confirmed that the important pressure-limiting factors are back-diffusion of gases from fore-vacuum and thermal decomposition of impurity or unstable component in the oil as well as an outgassing of the system. In case of DC-705, the lowest pressure is obtainable for an input where pumping of the oil occurs continuously. Pressure burst due to pumping is, however, not observed for each boiler except for a nonvolatile-reserving boiler over an entire region of input tested. The lowest ultimate pressure is not affected by changing a backing pressure from 10^-3 to 10^-6 torr as long as an input is optimum. The lowest pressure obtained is 4 × 10^-1 torr without cooling a trap. Very good heat-resistant property of DC-705 has been suggested from these experiments.

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