JPH0791664B2 - Method for electrolytic production of nitrogen trifluoride - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION INDUSTRIAL FIELD The present invention is, in the electrolytic production of NF _3, by the presence of nickel fluoride ammonium complex into molten ammonium acid fluoride, high in current efficiency of NF ₃ product The anodic dissolution of the nickel electrode while maintaining it is 1 /
The present invention relates to a method for electrolytically producing nitrogen trifluoride that suppresses the amount to 3 to 1/5, extends the electrode life 3 to 5 times, and economically performs electrolytic operation.

Conventional technology Nitrogen trifluoride has been used as a dry etching gas for microfabrication of megabit class VLSI or as a cleaning gas for cleaning the inner wall of a CVD device with plasma in line with the rise of the electronics industry. It is a useful gas for special materials, which is attracting attention as a reforming gas and is expected to grow in demand in the future.

The manufacturing method of nitrogen trifluoride is roughly classified into a chemical method and an electrolytic method. The chemical method is as follows:
Known methods include a method of blowing NH ₃ and F ₂ , a method of reacting a solid metal fluoride ammoranium complex with F _2, and the like. On the other hand, in the electrolysis method, for example, molten ammonium acid fluoride is used as an electrolytic solution, and (1) graphite (graphite) is used as an anode for electrolysis.

(2) Method of electrolyzing nickel as an anode (Glemser,
et.al, Chem.Ber., 99, 371 (1966)) and the like, have long been known, in recent years, as a method for producing a nitrogen trifluoride high purity, reviewed electrolysis method using a nickel as an anode Is coming.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention Regarding the conventionally known electrolysis method, in (1), the fluorinated graphite is generated on the surface of the graphite electrode, so that the anodic effect occurs, and the trifluoride generated Carbon tetrafluoride, which comes from the electrode material, is mixed in nitrogen, and it is highly purified as a product.
It is difficult to obtain NF ₃ , and in (2), the nickel electrode is consumed due to anodic dissolution, and the electrode must be replaced regularly. It was a reality.

In view of the circumstances in the first half of the present invention, it is an object of the present invention to suppress the anodic dissolution of a nickel electrode, extend the life of the electrode, and advantageously provide a method for industrially producing high-purity nitrogen trifluoride that is not contaminated by carbon tetrafluoride. I am trying.

Means for Solving the Problems In order to achieve the above object, as a result of repeated various studies, the present inventors have found that in a molten ammonium acid fluoride electrolytic solution,
It was found that the presence of the nickel fluoride ammonium complex can very effectively suppress the anodic dissolution of the nickel electrode, and completed the present invention.

That is, the gist of the present invention is to provide nickel fluoride ammonium salt, NH ₄ N in a molten acidic ammonium fluoride electrolytic solution.
The presence of iF ₃ and / or (NH ₄ ) ₂ NiF _{4 in the range} of 0.001 to 2.0 wt%, preferably 0.01 to 0.2 wt% suppresses the anodic dissolution amount of the Ni electrode to 1/3 to 1/5, 3-5 electrode life
The purpose of the present invention is to provide an economically advantageous method for doubling the cost of industrial electrolytic production of NF ₃ . As a method of allowing the nickel fluoride ammonium complex to exist in the electrolytic solution, (1) a method of generating a complex in the electrolytic solution by performing preliminary electrolysis for a long time using a nickel electrode (2) nickel fluoride ammonium complex Another method is to separately prepare and add it to the electrolytic solution.

When the method (1) is adopted, the object is achieved by carrying out preliminary electrolysis for 50 to 100 hours or more. Considering the consumption of the nickel electrode, for example, a method of separately preparing an electrolytic solution that has been subjected to preliminary electrolysis, or using a electrolytic cell having a structure having a separate nickel electrode for preliminary electrolysis, the preliminary electrolysis is performed. The method of doing it is advantageous. Whether the method (1) or the method (2) described below is selected may be selected in consideration of the scale of the production of nitrogen trifluoride, economic efficiency, and the like.

Next, the case of using the method (2) will be described.

An example of the preparation of the nickel fluoride ammonium complex to be added is shown below.

The nickel fluoride ammonium complex is added to molten ammonium acid fluoride in an amount of 0.001 to 2.0 wt%, preferably 0.01 to 0.2 wt%, prior to the start of electrolysis. If the concentration of the additive is lower than the above concentration, the effect of suppressing the anodic dissolution of nickel is difficult to manifest, and the addition of an excessive amount of the additive is meaningless because the amount of the nickel fluoride ammonium complex dissolved reaches saturation. The form of addition may be powdery or lumpy, but powdery is more preferable in order to make it uniformly exist in the electrolytic solution. The electrolysis conditions are those of the known mesophilic method,
That is, molten ammonium acid fluoride electrolytic solution (hydrofluoric acid concentration 40 to 60 wt%) can be performed at a temperature of 100 to 150 ° C., by adding additives such as the structure of the electrolytic cell and the shape of the nickel electrode,
There are no restrictions.

EXAMPLES The present invention will be specifically described with reference to the following examples.

[Example 1] 100 g of commercially available nickel fluoride (NiF ₂ purity 99.9%) and 75 g of acidic ammonium fluoride (NH ₄ F-HF purity 99%) were thoroughly mixed and the surroundings could be heated with a heater made of Ni. Reactor (1 ^B x
500 ^mmL ) and the temperature was kept at 110 ° C. HF / in reactor
Flow N ₂ mixed gas (HF approx. 50 vol%) at a flow rate of 3 / hr, and
Reacted for hours. Then, the reactor was sealed under the same atmosphere, the reaction temperature was raised to 160 ° C., and the reaction was carried out at the same temperature for 5 days. After the reaction was completed, the temperature was lowered in an HF / N ₂ gas stream, the temperature was returned to room temperature, the inside of the reactor was replaced with N _2, and the product was taken out.

The product was crushed, the residual ammonium acid fluoride was washed with formamide, further washed with diethyl ether, and then dried at 80 ° C. for 20 hours in a dry nitrogen atmosphere.

The obtained product was 125 g, and was identified by X-ray diffraction to be NH ₄ NiF ₃ containing a trace amount of NiF ₂ .

[Example 2] 1.8 kg of molten ammonium acid fluoride having a hydrofluoric acid concentration of about 52 wt% was charged into an electrolytic cell made of Teflon having a volume of 1.5, and the temperature was kept at 120 ° C. To this, 1.5 g of the nickel fluoride ammonium complex prepared in Example 1 was added, and 25 mA / cm ^{2 with} the plate-like nickel in the electrolytic solution immersion portion 66 cm ² as the anode.
Constant current electrolysis was carried out at a current density of ² for 75 hours continuously.

After the electrolysis was completed, the Ni electrode was taken out, and the loss of electricity due to anodic dissolution determined from the weight change before and after electrolysis was 0.75%.

The current efficiency of nitrogen trifluoride generation during electrolysis was maintained at 60% or more.

Example 3 1.8 kg of molten ammonium acid fluoride having a hydrofluoric acid concentration of about 52 wt% was charged into the same electrolytic cell as in Example 2, and the temperature was kept at 120 ° C. Preliminary electrolysis was performed at a constant current at a current density of 20 mA / cm ² for 100 hours continuously using a plate-like nickel of 66 cm ^{2 in} the electrolytic solution immersion portion as an anode.

After completion of the preliminary electrolysis, the electrode was replaced with another nickel plate having the same shape, and this was used as an anode, and constant current electrolysis was continuously performed at a current density of 25 mA / cm ² for 70 hours.

After the completion of electrolysis, the loss of electricity due to anodic dissolution was determined in the same manner as in Example 2, and the result was 0.95%. Also, during electrolysis, NF
The current efficiency of ₃ generation was kept above 60%.

Comparative Example 1 Electrolysis was performed continuously for 75 hours under the same electrolysis conditions as in Example 2 without adding the nickel fluoride ammonium complex.

After the completion of electrolysis, the loss of electricity due to anodic dissolution was determined as in Example 2, and the result was 2.8%.

The current efficiency of NF ₃ generation during electrolysis was maintained at 60% or more.

As described above, the present invention suppresses anodic dissolution of nickel to 1/3 to 1/5 by adding a nickel fluoride ammonium complex to molten acidic ammonium fluoride,
That is, by extending the life of the nickel electrode 3 to 5 times, the frequency of replacement of the expensive nickel electrode can be reduced.
It is intended to provide a method capable of carrying out an industrial electrolytic operation economically extremely advantageously.

Claims (1)

[Claims] 1. A method for producing nitrogen trifluoride in which a molten ammonium acid fluoride electrolytic solution is electrolyzed with a nickel anode,
A method for electrolytically producing nitrogen trifluoride, characterized in that 0.001 to 2.0% by weight of nickel fluoride ammonium complex is present in the electrolytic solution.