JPH03226568A - Metal vapor generator - Google Patents

Abstract

PURPOSE:To allow the efficient supply of the energy of an electron beam and metal vapor by inserting grounding wires into the metallic raw material housed in a crucible for evaporation and the side wall of the crucible to stabilize the surface potential of the raw material and the irradiation of the electron beam. CONSTITUTION:This metal vapor generator is provided with the crucible 2a for evaporation housing the metallic raw material 3 and an electron gun 9 in a vacuum vessel. The above mentioned electron gun 9 heats the above mentioned metallic raw material 3 to melt and evaporate. The grounding wire 13 for the raw material is inserted into the above mentioned raw material 3 as well the grounding wire 14 for the crucible is embedded into the side wall of the above-mentioned crucible 2a.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Field of Application) The present invention relates to a metal vapor generator that generates metal vapor, and in particular to a metal vapor generator that reduces surface charges floating on the surface of a molten metal raw material. The present invention relates to a metal vapor generator that can stably and economically obtain metal vapor by keeping the surface potential of a metal raw material constant and stabilizing the irradiation position of a heating electron beam.

(Prior art) Isotope separation equipment, semiconductor manufacturing equipment, optical mirror manufacturing equipment, etc. include processes for separating and vapor depositing specific metal components, and are equipped with various metal vapor generators. There is.

FIG. 4 is a cross-sectional view showing an example of the configuration of a conventional metal vapor generating device constituting an isotope separation device. This metal vapor generator consists of a vacuum container 1 that airtightly houses the evaporator main body, and various devices that make up the evaporator main body. A crucible 2 for use is arranged, and a metal raw material 3, which is an isotope metal, is accommodated in this crucible 2 for evaporation. The evaporation crucible 2 is housed in a water cooling hearth 4 to prevent damage due to overheating, and a large number of cooling water pipes 5 are buried in the water cooling hearth 4.

In addition, in order to prevent the transfer of heat from the raw metal 3 to the evaporation loop 2 direction, and from the evaporation loop 2 to the water cooling hearth 4.
In order to prevent the transfer of heat in the direction, heat-resistant coating layers 6.7 having heat insulating properties such as Z r 203 and Y 203, for example, are formed on the inner and outer surfaces of the evaporating loop 2, respectively.

On the other hand, an electron gun 9 that emits an electron beam 8 for heating the metal raw material 3 in the evaporation crucible 2 is provided adjacent to the evaporation crucible 2 .

Further, above the evaporation crucible 2, a vapor recovery mechanism 10 is provided, which is formed by alternately arranging negative electrodes and positive electrodes.

Common methods for heating the metal raw material 3 include heating by induction heating and heating by electron beam irradiation, but the latter method has particularly good thermal efficiency, so it is suitable for isotope separation processes, etc. Suitable for evaporating large quantities of metal raw materials, such as in

Specific evaporation and separation operations will be explained below. An electron beam 8 emitted from an electron gun 9 is deflected by a deflection magnetic field and irradiated onto the surface of the metal raw material 3 housed in the evaporation melt 2 .

The metal raw material 3 irradiated with the electron beam 8 at the irradiation point P is heated to a high temperature, evaporates through a molten state, and continuously forms a vapor flow 11 of the isotopic metal. This steam flow 1
As a result of being irradiated with selective excitation laser light (not shown) at 1, specific isotope atoms that are characterized by recovery in the vapor flow 11 are selectively excited and ionized. Ionized isotopes are
The vapor is introduced into the vapor recovery mechanism 10 provided at the top of the vacuum container 1, and only the ionized isotope is deflected toward the recovery electrode and adsorbed and recovered.

At this time, the metal raw material 3 in the evaporation crucible 2 melts and generates a vapor flow 11 from the molten liquid surface, while the evaporation crucible 2
Convection 12 is generated inside as shown by the arrow. However, the heat-resistant coating layer 6 formed on the inner and outer surfaces of the evaporation crucible 2.
7 prevents heat from moving outside, and the irradiated electron beam 8 is effectively utilized. On the other hand, if the evaporation crucible 2 is heated rapidly, the evaporation crucible 2 may be damaged by the thermal shock. is cooled.

(Problems to be Solved by the Invention) However, in the conventional metal vapor generator shown in FIG. 4, heat-resistant coating layers are formed on the inner and outer surfaces of the evaporation crucible in order to prevent heat loss. Since this heat-resistant coating layer generally has heat insulating properties as well as insulating properties, both the evaporation crucible and the metal raw material are maintained in an electrically insulated state. Therefore, when a heating electron beam is irradiated onto a metal raw material housed in an evaporation crucible, floating charges are accumulated on the surface of the metal raw material over time. The distribution of these floating charges changes due to the convection of the molten metal, and the floating charges create an electric field, which bends the trajectory of the electron beam. Therefore, the irradiation point of the electron beam cannot be maintained at a predetermined position, making it difficult to stably generate metal vapor, and the efficiency of using the energy of the electron beam is reduced.

The present invention has been made to solve the above problems, and by grounding the electrically insulated evaporation crucible and metal raw material, it is possible to prevent the accumulation of stray charges and prevent heating operations using electron beams. An object of the present invention is to provide a metal steam generator that can be continuously operated in a stable state and has improved heating efficiency.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention provides an evaporation crucible containing a metal raw material and an electron gun that fires an electron beam that heats, melts and evaporates the metal raw material. The metal vapor generator housed in a container is characterized in that a raw material ground is inserted into the metal raw material, and a crucible ground is buried in the side wall of the evaporation crucible.

(Function) According to the metal vapor generator having the above configuration, when the electron beam is irradiated, the metal raw material is heated and gradually melted from the vicinity of the irradiation point. At this time, floating charges accumulated on the surface of the molten metal raw material are grounded through a raw material ground inserted into the metal raw material.

Therefore, the surface potential of the molten metal raw material is always kept constant, so there is no fluctuation in the irradiation point of the electron beam, making it possible to stably supply metal vapor, and the trajectory and irradiation point of the electron beam are Since it is limited to a narrow fixed area, the energy utilization efficiency of the electron beam increases and the heating efficiency of the metal raw material can be significantly improved.

Furthermore, even if the heating temperature is further increased and the heat-resistant coating layer and the raw material ground formed on the inner surface of the evaporation crucible melt or disappear due to erosion, resulting in direct contact between the molten metal raw material and the evaporation crucible, Floating charges are grounded through a crucible ground buried in the side wall of the evaporation crucible.

Therefore, even when the operating temperature is set over a wide range, floating charges are always grounded, so stable electron beam irradiation is possible over a long period of time, and metal vapor can be stably and efficiently supplied.

(Example) Next, an example of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a sectional view of essential parts showing an embodiment of a metal vapor generator according to the present invention. The features of the device of the present invention are as follows:
The only difference is that the evaporation crucible and the metal raw material are provided with grounding equipment, and the other components are the same as in the conventional example. Therefore, the same elements as those in the conventional example shown in FIG. 4 are given the same reference numerals, and redundant explanation thereof will be omitted.

That is, the metal vapor generator according to the present embodiment includes an evaporation crucible 2a containing a metal raw material 3, and an electron gun 9 that emits an electron beam 8 that heats, melts and evaporates the metal raw material 3. In the metal vapor generator housed in the evaporation crucible 2a, a raw material earth 13 is inserted into the metal raw material 3, and a crucible earth 14 is buried in the side wall of the evaporation crucible 2a.

The raw material earth 13 is a large-diameter earth rod 15 that is inserted into the metal raw material 3 and does not melt even when the metal raw material 3 is melted.
A small diameter ground wire 16 is branched at the upper end of the ground rod 15 and is disposed so as to pass through the gap between the metal raw material lumps.
It consists of

Here, examples of materials for forming the ground rod 15 and the ground wire 16 include tantalum (Ta) and tungsten (W).
) etc., which have a higher melting point than the metal raw material, are used. Raw material earth 13 and crucible earth 1
4 are each grounded.

The state in which the bulk metal raw material 3 is initially filled into the evaporation crucible 2a is as shown in FIG. In this state, earth rod 1
Even if only the grounding rod 5 is inserted, the grounding rod 15 and the bulk metal raw material 3 will not come into contact with each other, and there is a risk that the grounding function will not be exhibited.

Therefore, a thin and flexible ground wire 16 with bendability is arranged so as to pass through the gap between the metal raw material blocks.

As a result, even in the initial stage of heating by the electron beam 8, the grounding wire 16 comes into contact with any of the metal raw material lumps near the irradiation point P, so there is little risk that the grounding function will be impaired.

In the initial stage of heating, the metal raw material lump located at the irradiation point P is irradiated with the electron beam 8 and gradually melts. Floating charges accumulated on the surface of the molten metal raw material are grounded via the ground wire 16. Therefore, the potential on the molten metal surface is kept constant, and metal vapor can be generated in a stable state with little variation in the irradiation point.

By the way, when using this metal vapor generator to perform an operation to separate uranium isotopes, for example, the heating temperature is 30°C.
The equipment is operated under severe conditions of 0.00 or more. On the other hand, uranium has the property of chemically corroding other metals under high-temperature conditions, and small-diameter ground wires and heat-resistant coatings made of high-melting point metals such as tantalum and tungsten can only be used at temperatures below the melting point. In some cases, it is eroded and disappears. This state is as shown in FIG. 2, and during the middle stage of heating, the ground wire 16 immersed in the molten metal raw material 3a is chemically eroded or melted and disappears.
Resulting in. However, since the large-diameter ground rod 15 remains, the floating charges on the surface of the molten metal raw material 3a are grounded via this ground rod 15.

When the heating temperature is further increased from the state shown in FIG. 2, the state shown in FIG. 3 is reached. That is, the large-diameter earth rod 15 melts or melts due to erosion, and the evaporation crucible 2
Even if the heat-resistant coating layer 6 formed on the inner surface of a is eroded and melted, the floating charges will damage the molten metal raw material 3a that has soaked into the heat-resistant coating layer 6 and the main body of the evaporator 2a, which has conductivity. It then reaches the crucible ground 14 and is grounded outside the device. Therefore, the device can always be operated in a stable state where stray charge accumulation occurs.

In this way, the floating charges are grounded via at least one of the raw material ground 13 and the crucible ground 14 depending on the operating temperature of the apparatus. If the heat-resistant coating layer 6 formed on the inner surface of the evaporation crucible 2a is eroded by the molten metal raw material, the thickness of the grounding rod 15 is such that the molten metal raw material permeates into the heat-resistant coating layer 6 and has conductivity. The thickness is set to withstand up to the point where it starts to come into direct contact with the inner surface of the evaporation crucible 2a.

As described above, according to the apparatus of this embodiment, since the electrically insulated metal raw material 3 and the evaporation crucible 2a are each provided with grounding equipment, there is no risk of floating charges accumulating on the surface of the molten metal. Therefore, the trajectory of the electron beam 8 is stabilized and the irradiation point P is also held in a fixed position, so that metal vapor can be stably generated and the heating efficiency of the metal raw material is also greatly improved.

In this embodiment, a small-diameter high-melting point metal wire is used as the ground wire 16, but even if a thin plate-like or mesh-like wire is laid on the inner surface of the evaporation crucible 2a instead of the ground wire 16, A similar effect can be obtained.

〔Effect of the invention〕

As explained above, according to the metal vapor generator according to the present invention, when the electron beam is irradiated, the metal raw material is heated and gradually melted from the vicinity of the irradiation point. At this time, floating charges accumulated on the surface of the molten metal raw material are grounded through a raw material ground inserted into the metal raw material.

Therefore, the surface potential of the molten metal raw material is always kept constant, so it is possible to stably supply metal vapor without fluctuations in the electron beam irradiation point, and the electron beam trajectory and irradiation point can be kept constant. Since it is limited to a narrow fixed area, the energy utilization efficiency of the electron beam increases and the heating efficiency of the metal raw material can be significantly improved.

Furthermore, even if the heating temperature is further increased and the heat-resistant coating layer and the raw material ground formed on the inner surface of the evaporation crucible melt or disappear due to erosion, resulting in direct contact between the molten metal raw material and the evaporation crucible, Floating charges are grounded through a crucible ground buried in the side wall of the evaporation crucible.

Therefore, even when the operating temperature is set over a wide range, floating charges are always grounded, making it possible to stably irradiate the electron beam over a long period of time and efficiently supply metal vapor.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the main part showing an embodiment of the metal steam generator according to the present invention, FIG. FIG. 4 is a cross-sectional view of a main part showing a state in which most of the metal vapor is molten, and FIG. 4 is a cross-sectional view showing an example of the configuration of a conventional metal vapor generator. 1... Vacuum container, 2, 2a... Evaporation crucible, 3.
...Metal raw material, 3a... Molten metal raw material, 4... Water cooling hearth, 5... Cooling water pipe, 6.7... Heat resistant coating layer, 8... Electron beam, 9... Electron gun, 10
...Steam recovery mechanism, 11...Steam flow, 12...Convection, 13...Earth for raw materials, 14...Earth for crucible, 15...Earth rod, 16...Earth wire, P...
・Irradiation point.

Claims (1)

[Claims] A metal vapor generating device in which an evaporation crucible containing a metal raw material and an electron gun that fires an electron beam that heats, melts and evaporates the metal raw material are housed in a vacuum container,
A metal vapor generator characterized in that a raw material earth is inserted into the metal raw material, and a crucible earth is buried in a side wall of the evaporation crucible.