JPH10265935A - Ultra-high vacuum vessel and ultra-high vacuum parts - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain an ultra-high vacuum in a short time from the atm. pressure and the repetitively open the state to the atm. by forming thin oxidized layers of titanium and more particularly the oxidized layers having a dense crystalline structure on the surfaces to be exposed to vacuum of a ultra-high vacuum vessel and ultra-high vacuum parts made of the titanium or titanium alloy. SOLUTION: The ultra-high vacuum vessel and ultra-high vacuum parts to be used under about 10<-8> Pa are made of the titanium the titanium alloy contg. or aluminum, vanadium, etc., and further the thin oxidized layers of the titanium are formed on their surfaces to be exposed to the vacuum. the oxidized layers of the titanium preferably have the dense crystalline structure and the thickness thereof are preferably 10 to 60 nm above the thickness of the natural oxidized layers of several nm. The oxidized layers of the titanium are formable by heat treating the vessel and parts made of, for example, the titanium etc., to about 450 deg.C in an oxygen atmosphere after pickling.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrahigh-vacuum container and an ultrahigh-vacuum part made of titanium or a titanium alloy, particularly to an ultrahigh-vacuum container requiring baking, and a high-temperature vacuum of 200 ° C. or more. Such ultra-high vacuum container and ultra-high vacuum component.

[0002]

2. Description of the Related Art Conventionally, ultrahigh vacuum vessels have been made of stainless steel or aluminum alloy. Ultra-high vacuum components are also generally made of stainless steel except for special heat-resistant metals.

[0003]

In general, the evacuation process of a vacuum vessel once exposed to the atmosphere includes (1) a process in which the pressure decreases exponentially depending on the volume, and (2) adsorption during release to the atmosphere. The process in which water and other gas species are desorbed and the pressure is determined. (3) The gas released from the inside of a vacuum vessel or vacuum component material, reaching the surface and being released into vacuum is released under pressure. (4) Finally, it is said that the gas permeating from the atmosphere goes through four processes of determining the pressure (FIG. 1). Since the initial process of exponentially decreasing the pressure is as short as several minutes in a normal vacuum vessel of several tens of liters to about 100 liters, these vacuum vessels are quickly brought to an ultra-high vacuum of 10 ^-8 Pa or less. In order to
It is important to shorten the steps (2) and (3). That is, the gas species adsorbed on the surface is quickly desorbed,
In addition, it is necessary to reduce gas released from inside the material due to diffusion.

[0004] In order to provide energy for desorbing the gas species adsorbed on the surface, baking of a vacuum apparatus is usually performed, and it is desirable to perform the baking at a high temperature unless the characteristics of the material are impaired. In recent years, there has been a report that the properties of a film formed by forming a film at a high temperature by sputtering or the like are improved, and a vacuum treatment at a high temperature is often performed.

[0005] As a material for vacuum containers and vacuum parts for that purpose, aluminum alloys are not suitable for softening at 200 ° C or higher. On the other hand, stainless steel can be used even at a high temperature of 200 ° C. or more, but the research by the present inventors (M. Minato
And Y. Itoh, Vacuum, Vol. 47, No. 6-8, pp. 683-686
(1996)) shows that increasing the temperature releases hydrogen at a constant rate, and that the higher the temperature of stainless steel, the greater the release of hydrogen. For this reason, a vacuum device made of a stainless steel vacuum container or a stainless steel vacuum component does not readily decrease in pressure at high temperatures and needs to reach an ultra-high vacuum region for 20 minutes.
Heat baking at 0 to 250 ° C. for 24 hours or more is required.

According to the study by the present inventor, when the temperature is increased, the release rate of hydrogen is lower in the case of titanium than in the case of stainless steel, and the ratio increases as the temperature increases. know. For example, 250
For stainless steel when evacuated to ° C., the hydrogen release rate is 12.2 times the hydrogen release rate for titanium. Therefore, if a titanium vacuum container or a vacuum component is used, the pressure can be expected to decrease quickly because the hydrogen release is low in a low pressure region where diffusion is rate-determining.

In manufacturing a structure using commercially available titanium, mechanical cutting, glass bead blasting, and chemical polishing with an acid are generally applied as surface processing methods. However, there are the following problems when attempting to manufacture a titanium vacuum container by these methods. That is, when the gas release from the inner surface of the surface-treated container was examined, the latter half of the exhaust (gas release rate of 2 × 10 ^{In the} region (lower than ⁻⁶ Pa · m / s), the gas release rate was lower than that in the case of stainless steel surface-treated by electrolytic polishing, but the region (gas) corresponding to the exhausting process (2) Release rate is 2
The gas release in the range of × 10 ⁻⁶ Pa · m / s or more) was equal to or higher than that of stainless steel subjected to electrolytic polishing. In order to shorten the total evacuation time, the surfaces of the vacuum container and
It was found that it was necessary to modify the surface so that the adsorbed gas was easily desorbed.

An object of the present invention is to provide an ultrahigh vacuum vessel and an ultrahigh vacuum component which can solve the above-mentioned drawbacks of the prior art and can achieve an ultrahigh vacuum state in a shorter time than atmospheric pressure. is there.

[0009]

The thickness of the natural oxide layer formed on the surface of titanium is about several nm. According to the research of the present inventors, a titanium oxide layer is further formed thereon. As a result, it has been found that a surface that can be quickly desorbed in a heated vacuum, particularly for water, can be realized, and the present invention has been completed. The ultrahigh-vacuum container and ultrahigh-vacuum part made of titanium or a titanium alloy of the present invention have a thin titanium oxide layer formed on the surface exposed to vacuum. The titanium oxide layer preferably has a dense crystal structure.

The thickness of the titanium oxide layer is 10 to 60 n.
m is desirable. Lower limit of oxide layer thickness is 10
The reason why the thickness is set to nm is that a new oxide layer having a thickness greater than the thickness of the natural oxide layer of titanium is required, and the thickness that can be controlled by the oxidation treatment is 10 nm or more. Also,
The reason for setting the upper limit of the thickness of the oxide layer to 60 nm is that the gas release rate increases as the thickness of the oxide layer increases,
This is because the thickness of the oxide layer is such that a gas release rate lower than that in the case where only the natural oxide layer is formed can be obtained. The provision of an oxide layer having a thickness within this range is effective for realizing ultra-high vacuum in a shorter time than atmospheric pressure.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

(Example 1) A sample (CP) having a naturally oxidized layer on its surface after pickling treatment using a set of five 100 × 80 × 2t plates of pure titanium (JIS type 2), and pickling After the treatment, the sample was heated in an oxygen atmosphere (450 ° C.), and the thickness of the oxide layer was changed by changing the heating time.
1, S2 and S3) at 200 ° C.
The gas release rate during heating for 4 hours and cooling for 24 hours was measured using the conductance modulation method, and the gas release rate during heating was examined. The oxide layers of S1, S2 and S3 have a thickness of XPS
According to observation, they were 17.9 nm, 42.7 nm and 183.1 nm, respectively, and the outgassing rate was C
P: 8.06 × 10 ⁻⁸ Pa · m / s, S1: 2.7 × 1
0 ⁻⁸ Pa · m / s, S2: 4.27 × 10 ⁻⁸ Pa · m /
s, S3: 1.33 × 10 ⁻⁷ Pa · m / s. These results are shown in FIG.

As the thickness of the oxide layer increased, the rate of outgassing during heating increased. This is because the surface structure of titanium is roughened by the progress of oxidation, the adsorption area is increased, and the absolute amount of the adsorbed gas is increased even if the desorption speed is high. Therefore, the thickness of the titanium oxide layer is set to 10 to 60 nm.
This is desirable for achieving ultra-high vacuum in a short time. (Example 2) Inner diameter 3 with pure titanium (JIS type 2)
A vacuum container having a volume of 98 liters, a height of 417 mm and an internal volume of 55 liters was manufactured. After washing the entire surface of the container with an acid, an evacuation experiment was performed. At this time, the natural oxide layer of titanium is formed on the inner surface of the vacuum vessel. The baking temperature was 250 ° C. The exhaust curve in this case is shown by a dotted line in FIG. As is clear from this figure,
The pressure 8 hours after evacuation from the atmosphere was 6.52 × 10 ⁻⁸ Pa.

After the pickling, the vacuum vessel is heated in an argon atmosphere containing 8% oxygen (450 ° C., 2 hours) to form an oxide layer of 20 nm on the inner surface of the vessel, and under the same exhaust conditions as above. Evacuated. The formed oxide layer had a dense crystal structure. The exhaust curve at this time is shown by a solid line in FIG. The pressure 8 hours after exhaust from the atmosphere is 8.
The pressure was 8 × 10 ⁻⁹ Pa, which was lower than that of the case where only the natural oxide layer was formed, by almost an order of magnitude, indicating that the ultrahigh vacuum was reached in a short time.

Although pure titanium is used in the above embodiment, a titanium alloy containing aluminum or vanadium (for example, 6
% Aluminum and 4% vanadium, etc.), as in the case of pure titanium, hydrogen gas emission is low as in pure titanium. Therefore, a vacuum container or a vacuum component is manufactured using this material, and a thin titanium film is formed on the surface exposed to the vacuum. When the oxide layer is formed, the same result as in the case of pure titanium can be obtained. In the above embodiment, high-temperature heating in an oxygen atmosphere was performed to obtain an oxide layer of titanium.
Or even if an oxide layer is formed on the surface exposed to vacuum by oxygen ion implantation of titanium surface, plasma oxidation, etc.
The same result is obtained.

[0016]

According to the ultrahigh vacuum vessel and the ultrahigh vacuum component of the present invention, the ultrahigh vacuum state can be achieved in a shorter time than the atmospheric pressure, and the apparatus can be repeatedly opened to the atmosphere.

[Brief description of the drawings]

FIG. 1 is a diagram showing a rate-determining process during evacuation of a normal vacuum vessel exposed to the atmosphere.

FIG. 2 is a graph showing the relationship between the thickness of an oxide layer of titanium and the rate of gas release from the surface.

FIG. 3 is a graph showing an evacuation curve of the vacuum vessel of the present invention and a vacuum vessel having only a natural oxide layer of titanium.

Claims (3)

[Claims] An ultra-high vacuum vessel and an ultra-high vacuum component made of titanium or a titanium alloy, wherein a thin titanium oxide layer is formed on a surface exposed to a vacuum. Ultra high vacuum parts. 2. The ultra-high vacuum vessel and the ultra-high vacuum component according to claim 1, wherein the titanium oxide layer has a dense crystal structure. 3. The thickness of the titanium oxide layer is 10 to 60.
The ultrahigh vacuum vessel and the ultrahigh vacuum component according to claim 1 or 2, wherein the ultrahigh vacuum container and the ultrahigh vacuum component have a thickness of 1 nm.