JPH04183884A - Electrolytic cell - Google Patents

Abstract

PURPOSE:To produce gaseous NF3 safely over a long period of time by using Ni for the joining parts of electrode connecting rods which support electrode plates and supply electricity thereto and the electrodes at the time of producing the gaseous NF3 by a fused salt electrolysis method. CONSTITUTION:The gaseous NF3 is produced by executing an electrolysis in an electrolytic cell 1 using the fused salt electrolysis method to generate the gaseous NF3 and gaseous N2 from the anode 5 and gaseous H2 from the cathode 6. The material of the respective joint parts 7c, 7d where the anode connecting rod 7a and cathode connecting rod 7b respectively supporting the anode 5 and the cathode 6 come into contact with the anode 5 and the cathode 6 is formed of the Ni at this time. The respective joint parts 7c, 7d are prevented from being corroded by the HF vapor, etc., accompanied with the gases generated by these joint parts in this way. The gaseous NF3 is thus produced safely over a long period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an electrolytic cell used in the production of nitrogen trifluoride gas by molten salt electrolysis.

[Prior art and problems to be solved by the invention] Nitrogen trifluoride (NF3) gas is a dry etching agent for semiconductors and C
Demand has been increasing in recent years as a cleaning gas for VD equipment, and carbon tetrafluoride (C
It cannot be used unless it is a highly pure gas with low F4) content.

NF and gas are produced by various methods, among which molten salt electrolysis is used as an industrial production method because it has a good yield and is easier to mass produce than other methods. Furthermore, this method is the only way to obtain high-purity gas with low CF as mentioned above.
This is the most convenient manufacturing method.

The production of Nh gas by this molten salt electrolysis method uses the N If 4F It F system using acidic ammonium fluoride or ammonium fluoride and hydrogen fluoride as raw materials, and the N If 4F It F system using acidic potassium fluoride or potassium fluoride as raw materials. added K
This is carried out by electrolyzing a F-NH4F-HF based molten salt.

In the production of NF3 gas by this molten salt electrolysis method, NF3 gas and nitrogen (N2) gas are generated from the anode, and hydrogen (TLZ) gas is generated from the cathode. Both the so-called picture electrodes undergo a gas generation reaction. be. Therefore, if the NF3 gas generated from the anode and the H2 gas generated from the cathode mix, there is a safety problem that may cause an explosion. Therefore, in order to prevent this explosion, the electrolytic cell is provided with a partition plate to prevent the anode-generated gas and the cathode-generated gas from mixing in the gas phase, as shown in Figures 1 and 2. .

Further, in order to prevent corrosion and the partition plate itself from becoming an electrode, it is usually preferable to use a fluorine-based resin or to coat it with a fluorine-based resin.

Here, the anode is carbon (C) or nickel (Ni)
electrodes can be used, but as mentioned earlier,
Only Ni can be used to obtain high purity gas with low F4 content. However, when this Ni anode is used, there is a drawback that the Ni anode is slightly dissolved.

Once the electrodes immersed in the electrolytic bath are consumed and reduced by this dissolution, further electrolysis becomes difficult, so the anode must be replaced at regular intervals. In addition, in industrial terms, the period is from at least one month to several years at most.
It is usually replaced every three months to one year. Therefore, if the electrode connecting rod that connects to the electrode and the joint between the electrode plate and the electrode connecting rod do not have a lifespan equal to or longer than the electrode, the lifespan of these parts will become a bottleneck and efficient manufacturing will be impossible. Become.

On the other hand, any metal can be used for the cathode plate, and usually inexpensive iron is used. When used as an electrode, there is no consumption due to melting, so there is no need to replace the electrode, and the joint needs to have a lifespan equal to or longer than that of the anode.

Here, since the electrode connecting rod is also used for the purpose of conducting electricity to the electrode, metal is usually used. Further, the electrode and the electrode connecting rod are connected by using a joint such as a bolt/nut or by welding. Here, the temperature of the above-mentioned molten salt during electrolysis is most convenient if it is carried out at 100 to 130[deg.] C., because the operation is easy, the conductivity is good, and the current efficiency is also good.

However, in this NH, F-HF system, there is a vapor pressure of 1 (F) ammonia (N11.) at this temperature. The metal parts such as the joints between the electrodes and the electrode connecting rods are gradually corroded by the HF vapor accompanying the generated gas.After long-term use, we found that the joints between the electrodes and the electrode connecting rods were corroded. Corrosion is the most severe, and if commonly used metals such as iron or stainless steel are used for electrode connecting rods and joints, bolts and nuts and welded parts will corrode quickly and become thinner, causing electrode The electrode became detached from the electrode connecting rod because it could no longer withstand the weight of the metal, making it impossible to continue electrolysis.Also, as reported in the literature (Watanabe, Tasaka, Nakanishi, ``Electrochemistry 36.685 (196B)'') Similarly, long-term use was not possible.

Furthermore, even when copper, which has high electrical conductivity and corrosion resistance is used in IIF, a similar problem occurred due to corrosion caused by ammonia. In addition, the electrode may come off from the welding part and short circuit in the middle, and in extreme cases it may come into contact with the cathode and cause an explosion or fire. Thus, it was found that the distance between the joint between the electrode and the electrode connecting rod and the liquid level is an important issue for stable operation and safety.

As mentioned above, in the production of NF3 gas by molten salt electrolysis, it has been found that the materials of the electrode connecting rod and the joint between the electrode and the electrode connecting rod are very important for safe and stable operation. There have been almost no studies on the structure of the tank, and there are particularly few reports on the materials of the electrode connecting rods and the joints between the electrodes and the electrode connecting rods.

[Means to solve the problem]

In view of the above situation, the present inventors have developed an NF using molten salt electrolysis method.
As a result of various studies on the materials of the electrode rod that supports and conducts electricity to the electrode plate that performs electrolysis in the electrolytic cell for L gas production, and the joint part between the electrode plate and the electrode rod, we have found that the material The inventors discovered that NF3 gas could be produced safely and over a long period of time by limiting the amount of nickel to nickel, leading to the completion of the present invention.

That is, the present invention relates to an electrode connecting rod that supports an electrode plate for electrolysis and conducts electricity to the electrode plate in an electrolytic cell for producing nitrogen trifluoride gas by molten salt electrolysis. The present invention relates to an electrolytic cell characterized in that the material of the joint portion with the electrode connecting rod is nickel.

[Detailed Description of the Invention Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The most important aspect of the present invention is an electrode connecting rod that supports and conducts electricity to the electrode plate for electrolysis in an electrolytic cell for producing NF3 gas safely and over a long period of time. This is the material of the joint between the electrode plate and the electrode connecting rod.

FIG. 1 is a longitudinal sectional view showing an example of an electrolytic cell for producing NF3 gas suitable for carrying out the present invention, and FIG. 2 is a view taken along the line A-A'' in FIG.

In an electrolytic cell for producing Nh gas using the molten salt electrolysis method, the joint between the electrode and the electrode connecting rod is made by using a joint such as a bolt/nut or by welding. In the electrolytic cell of the present invention, as shown in FIGS. 1 and 2, the parts are joined by welding. Therefore, in this case, the term "joint part" as used in the present invention means the welding surface between the electrode and the electrode connecting rod. Note that even when a joint such as a bolt nut is used, it refers to the part where the electrode and the electrode connecting rod come into contact. Although the present invention can be effectively carried out in either case, since the effects are the same, the following explanation will be given only for the welded case shown in FIG.

In the present invention, the material of the anode connecting rod 7a and the joint portion 7C between the anode 5 and the anode connecting rod 7a is nickel. As mentioned above, in this case, the joint means the welding surface 7C between the anode 5 and the anode connecting rod 7a shown in FIG. Note that nickel must be similarly used for the material of the cathode connecting rod 7b and the joint portion 7d between the cathode 6 and the cathode connecting rod 7b.

In this case, only the anode 5 will be described, but the same applies to the cathode.

The materials of the anode connecting rod 7a of the electrolytic cell of the present invention and the joint portion 7C between the anode 5 and the anode connecting rod 7a are as described above. Anode connecting rod 7a and a joint 7c between the anode 5 and the anode connecting rod 7a
If the material is other than nickel, H generated from the electrolytic tank
Corrosion progresses rapidly due to the F vapor, and when used for a long period of time, the welded portion 7C gradually becomes thinner and becomes unable to withstand the weight of the anode 5, causing the anode 5 to come off from the anode connecting rod 7a.

Since the detached anode 5 can no longer function as an electrode,
It becomes impossible to continue electrolysis. That is, the production of NFff gas is stopped. These are serious problems in terms of stable operation. Furthermore, if the electrode is in the process of falling without the welded part coming off, a part of the anode 5 may come into contact with the cathode 6 and short circuit may occur, which in extreme cases may cause an explosion or fire. .

This is a very big safety problem and must be avoided at all costs.

[Example] Example I NP, F/IIF system (HF/NF4F molar ratio -1,8)
Using the molten salt shown in FIG. Using an electrolytic cell in which is nickel, the current is 25OA
When long-term continuous electrolysis was carried out at an anode average current density of 10 A/dm2, it was possible to safely produce NF3 gas over a long period of time without causing an explosion even after 3 months. Therefore, when the electrode was taken out from the electrolytic bath and the state of corrosion at the joint was observed, no corrosion had progressed, and the electrode was found to be usable.

Comparative Example 1 Anode connecting rod 7a and joint 7 between anode 5 and anode connecting rod 7a
Material of C, cathode connecting rod 7b, cathode 6 and cathode connecting rod 7
Electrolysis was performed in the same manner as in Example 1, except that the material of the joint portion 7d of b was iron.

As in Example 1, when main electrolysis was carried out with the aim of long-term continuous electrolysis for three months, the electrolytic sliding voltage showed an abnormality that increased sharply after about a week, so it was decided that it was impossible to continue electrolysis any further. As a result, the electrolysis was stopped immediately.

Then, when the electrode was taken out from the electrolytic bath 4 and the corrosion status of the joint was observed, it was found that the corrosion progressed and the anode 5 was just about to come off from the anode connecting rod 7a, and the connection between the anode 5 and the anode connecting rod 7a It was found that 7C had a poor contact and the electrolytic sliding voltage showed an abnormal value.

Comparative Example 2 Anode connecting rod 7a and joint 7 between anode 5 and anode connecting rod 7a
Material of C, cathode connecting rod 7b, cathode 6 and cathode connecting rod 7
Electrolysis was carried out in the same manner as in Example 1, except that the material of the joint portion 7d of b was stainless steel. Similar to Example 1, 3
When electrolysis was carried out with the aim of long-term continuous electrolysis, an abnormality was observed in which the electrolytic sliding voltage suddenly increased after about 3 weeks, so it was judged that it was impossible to continue electrolysis any longer and the electrolysis was immediately discontinued. Therefore, when we took the electrode out of the electrolytic bath and observed the corrosion status of the joint, we found that corrosion had progressed and the anode 5
It was found that the electrolytic sliding voltage showed an abnormal value due to a poor contact between the anode 5 and the anode connection rod 7a at the connecting portion 7C just before the anode was separated from the anode connection rod 7a.

Comparative Example 3 Anode connecting rod 7a and joint 7 between anode 5 and anode connecting rod 7a
Material of c, cathode connecting rod 7b, cathode 6 and cathode connecting rod 7
Electrolysis was performed in the same manner as in Example 1, except that the material of the joint portion 7d of b was brass.

As in Example 1, when main electrolysis was carried out with the aim of long-term continuous electrolysis for three months, an abnormality in which the electrolytic sliding voltage suddenly increased after about one week was observed, so it was judged that it was impossible to continue electrolysis any further. , immediately stopped electrolysis.

Therefore, when the electrode was taken out from the electrolytic bath and the corrosion status of the joint was observed, it was found that the corrosion had progressed and the anode 5 was just about to be detached from the anode connecting rod 7a.
It was found that the electrolytic sliding voltage showed an abnormal value due to poor contact at the connection part 7C of a.

Comparative Example 4 Anode connecting rod 7a and joint 7 between anode 5 and anode connecting rod 7a
Material of c, cathode connecting rod 7b, cathode 6 and cathode connecting rod 7
Electrolysis was performed in the same manner as in Example 1, except that the material of the joint portion 7d of b was copper.

As in Example 1, when main electrolysis was carried out with the aim of long-term continuous electrolysis for three months, an abnormality in which the electrolytic sliding voltage suddenly increased after about three weeks was observed, so it was judged that it was impossible to continue electrolysis any further. , immediately stopped electrolysis.

Therefore, when the electrode was taken out from the electrolytic bath and the corrosion status of the joint was observed, it was found that the corrosion had progressed and the anode 5 was just about to be detached from the anode connecting rod 7a.
It was found that the electrode sliding voltage showed an abnormal value due to a poor contact at the connection part 7c of a.

〔Effect of the invention〕

As explained in detail above, the present invention is an electrolytic cell for producing NF and gas by molten salt electrolysis, and includes an electrode connecting rod that supports an electrode plate for electrolysis and connects the electrode plate with electricity. By specifying the material of the joint part with the electrode connecting rod as nickel, it is possible to manufacture NF3 gas safely and over a long period of time.

That is, in the comparative example in which the material of the joint between the electrode plate and the electrode connecting rod is outside the scope of the present invention, it is insufficient to produce NF3 gas safely and over a long period of time. On the other hand, the embodiments in which the material of the joint between the electrode plate and the electrode connecting rod is within the scope of the present invention are clearly superior in that they can produce NF3 gas safely and over a long period of time. This is extremely significant for industrially producing the NF3 gas of the present invention.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing an example of an electrolytic cell for producing NFi gas suitable for implementing the present invention, and FIG. 2 is a view taken along the line AA' in FIG. In the figure, 1-1--electrolytic cell body, 2-111 fluorine resin plate, 3-111 cover plate, 4-111 electrolytic bath, 5-111 anode, 6----- Cathode, 7a---One anode connecting rod, 7b---One cathode connecting rod, 7cm---One joint with the anode connecting rod, 7d---One joint with the cathode connecting rod, 8a---One Anode insulation material, 8b---One cathode insulation material, 9a---One Anode connection rod fixing cap nut, 9b---
Cathode connecting rod fixing bag, 10--m partition plate, 11--1 partition plate fixing cover plate, 12--1 anode generated gas outlet pipe, 13--m-cathode generated gas outlet Pipe, 14---Backing, 15---Bolt and nut for cover plate, 16---Bolt for fixing corner plate, are not shown. Patent applicant Mitsui Toatsu Chemical Co., Ltd.

Claims (1)

[Claims] 1) In an electrolytic cell for producing nitrogen trifluoride gas by molten salt electrolysis, an electrode connecting rod that supports an electrode plate for electrolysis and connects electricity to the electrode plate, the electrode plate and the electrode connecting rod. An electrolytic cell characterized in that the material of the joint part with is nickel.