JPH04235229A - Production of high purity metallic chromium - Google Patents

Abstract

PURPOSE:To produce high purity metallic chromium minimal pin the contents of impurity metals, such as Fe, and nonmetallic impurities, such as S, O, and N. CONSTITUTION:First impurity metals, such as Fe, are removed by adding inorganic acid, such as hydrochloric acid, sulfuric acid, and nitric acid, or acetic acid to crushed crude metallic chromium, and, on the other hand, S, N, and O are degassed and removed by mixing carbon material or chromium carbide with the crude metallic chromium after acid cleaning and applying heating to the resulting mixture in vacuum or in an inert-gas atmosphere, by which respective impurities mentioned above can be removed as far as possible.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for producing high-purity metallic chromium, and relates to a method for producing metallic chromium with extremely low impurity contents, particularly S, O, and N, and low Fe content, and is particularly applicable to the electronics industry. This paper proposes an advantageous method for producing high-purity metallic chromium, which is suitable as a raw material for the production of corrosion-resistant and heat-resistant alloys (superalloys).

0002

[Prior Art] Generally, methods for producing metallic chromium include an electrolytic method in which Cr2(SO4)3 is electrolyzed, or a method for producing metallic chromium.
A thermite reduction method in which r2O3 is reduced by an aluminum thermite reaction is known. Metallic chromium produced by these conventional methods all contain S, O
, N content is high, and therefore it is unsuitable as a material for electronic materials and a material for high-purity superalloys, which require high purity.

[0003] That is, in the electrolytic method, as an electrolytic solution,
Because Cr2(SO4)3 is used, the resulting metal chromium contains 200 to 300 ppm of S, and because it is aqueous electrolysis, it contains 3000 to 5000 ppm of S.
It contains 200 to 500 ppm of O and 200 to 500 ppm of N.

On the other hand, regarding the thermite reduction method, sulfuric acid is used to precipitate the raw material Cr2O3, and most of the S in the raw material remains in metallic chromium during the reaction.
The S content can be as high as 200 to 400 ppm. Also, O
The content can be lowered by increasing the amount of reducing agent (aluminum) added.
In this case, excess aluminum remains in the metal chromium. Therefore, it is necessary to lower the aluminum content, resulting in an O content of 3000 to 4000pp.
It becomes high as m. Furthermore, the N content is also high at about 200 ppm.

[0005] Metallic chromium produced by each of the above conventional methods has a high content of S, O, and N, as described above. Therefore, in order to produce metallic chromium that can be used in fields such as electronic materials and high-purity superalloys, it is necessary to remove each of the impurity elements more thoroughly.

[0006] As a method for this purpose, methods of degassing such as a vacuum carbon reduction method or a hydrogen reduction method have been attempted.

That is, the vacuum carbon reduction method described above removes oxygen in metallic chromium as CO by adding carbon powder and, if necessary, an agglomerating agent to pulverized crude metallic chromium powder and heating the mixture in vacuum. The hydrogen atmosphere reduction method is a method for degassing oxygen by converting oxygen into H2O by heating crushed crude metal chromium powder in a hydrogen atmosphere.

[0008]

[Problems to be Solved by the Invention] However, these improved conventional methods have the disadvantage that it is difficult to uniformly mix metal chromium powder and carbon, and therefore, when the mixture is heated, it is difficult to remove oxygen. There were cases in which carbon was insufficient in some places, and carbon remained untreated in the product metal chromium.

Furthermore, in the case of these conventional methods, contamination by impurities from the crusher etc. during crushing cannot be avoided, and F
Another drawback was that the content of impurity metals such as e, Ni, and W increased.

It is an object of the present invention to provide an S
The content of impurities such as , N, and O is extremely low, and Fe
The objective is to establish a technology to produce high-purity metallic chromium with a low content.

[0011]

[Means for Solving the Problems] In order to achieve the above-mentioned purpose, that is, as a method for producing metallic chromium with extremely low impurity content, the present invention first crushes crude metallic chromium, and then adds hydrochloric acid and sulfuric acid to the crushed product. , Washing by adding an inorganic acid such as nitric acid or acetic acid, then removing impurity metals such as Fe mixed in by pulverization, and then adding either carbon material or chromium carbide to the washed crude metal chromium powder,
and/or add powder of easily sulfurized metals such as Sn, Cu, Ni, etc. to 1100 ml in vacuum or inert gas atmosphere.
By heating at a temperature of ~1500°C, S, N, O
This method is designed to produce high-purity metallic chromium with low chromium.

[0012] According to this method, the obtained metallic chromium has extremely low levels of impurities such as S, N, and O, and impurity metals such as Fe, resulting in a product that is well suited for the above-mentioned uses. .

[0013]

[Operation] It can be said that crude metal chromium obtained by the thermite method or electrolytic method is in an environment where impurity metals such as Fe are likely to be mixed in during the manufacturing stage. In addition, as mentioned above, when this crude metal chromium is crushed, Fe is also present in this crushing process.
When impurity metals such as , Ni, and W are mixed in, the content becomes even higher.

[0014] Moreover, such impurity metals cannot be removed by vacuum heating, so they are mixed into the product as they are.

Therefore, in the present invention, first, an inorganic acid such as hydrochloric acid, sulfuric acid, nitric acid, or acetic acid is added to the pulverized crude metal chromium to wash it, thereby removing Fe, etc. contained in the crude metal chromium. Start by removing impurity metals.

Next, S contained in the crude metal chromium,
By heat-treating impurities such as N and O in a vacuum or an inert gas atmosphere, they are gasified and removed by volatilization.

Now, in the method of the present invention, as a means for volatilizing and removing O, carbonaceous material,
In particular, a method is adopted in which chromium carbide is mixed and heated in vacuum or in an inert gas atmosphere.

In the reduction method in a vacuum or inert gas atmosphere as in the present invention, carbonaceous material or chromium carbide is added to remove oxygen from the crude metal chromium powder. As an example, C
r3C2, Cr7C3, Cr23C6, etc. are preferably used. Note that in the present invention, metallic chromium containing chromium carbide may be used instead of these chromium carbides. Therefore, in this case, chromium-containing carbide metal chromium is added and mixed as the chromium carbide.

[0019] In the present invention, chromium carbide is preferable because it has better reactivity than when using carbon powder, and when compared to carbon powder,
This is because oxygen and carbon can be mixed more uniformly. This eliminates uneven oxygen removal depending on location and no unreacted carbon remaining in the product, the reaction speed is fast, and it is also safer than deoxidation using hydrogen. This is because it is excellent.

[0020] The crude metal chromium powder used as the starting material in the method of the present invention is pulverized to 40 mesh or less. The reason why the powder is 40 mesh or less is to improve the contact between metallic chromium and easily sulfurized metal and increase reactivity.

Further, in the present invention, an easily sulfurized metal is mixed for the purpose of removing S, but it is preferable to mix S.
n, Ni, Cu, etc. These are metals that easily generate sulfides, and S in metal chromium powder
It reacts with SnS, NiS, and CuS and contributes to desulfurization.

When mixing the easily sulfurized metal powder with the crude metal chromium powder, a binder such as PVA is added in a stoichiometric amount necessary to remove the sulfur in the crude metal chromium as metal sulfide. That is, it is mixed in a molar ratio of 0.5 to 2.0 with respect to sulfur in the crude metal chromium. The reason why the mixing ratio is limited in this manner is that if the amount of easily sulfurized metal is added to the amount of sulfur, there will be a lot of sulfur remaining in the metal, whereas if it is added too much, the amount of easily sulfurized metal will remain in the metal, and the metal chromium will remain in the metal. This is because the purity of

[0023] Furthermore, the amount of chromium carbide powder or chromium metal powder containing chromium carbide added to the crude metal chromium powder is determined by the amount of chemical necessary to reduce oxygen in the crude metal chromium powder to carbon monoxide. Add stoichiometric amount. That is, the amount of carbon in the carbide is set at a molar ratio of 0.8 to 1.2 to the amount of oxygen in the crude metal chromium.

[0024] The prepared above mixture was heated at 110% in vacuum.
Heating is maintained at a temperature range of 0 to 1500°C. The reason for limiting the temperature is that if the temperature is lower than the above range, the reaction will be slow, while if it is too high, the evaporation loss of Cr will be large. Further, the degree of vacuum is preferably within the range of 0.1 to 2 torr, which is particularly effective in deoxidizing and denitrogenizing.

[0025]

[Example] Example 1 Crude metal chromium (1
00 kg) to an average particle size of 100 mesh using a ball mill.
It was crushed. Next, this pulverized material was mixed with nitric acid (concentration 25
%) solution for 2 hours.

After washing with water and drying, 290 g of chromium carbide powder and 90 g of Sn powder were added thereto, mixed, and a binder was added to form briquettes, which were then heat-treated in a vacuum at 1350° C. to obtain metallic chromium. The composition is shown in Table 1.

In this example, F in the crude metal chromium
e was initially 200 ppm, but after pulverization it became 280 ppm.
It had increased to 0 ppm. Therefore, if the product is heat treated without acid washing, 280%
It contained 0 ppm of Fe. However, when acid cleaning is performed as in the present invention, Fe in the product is removed at this point.
could be reduced to 200 ppm.

Furthermore, as for O, the content decreased as a result of adding chromium carbide.

It was also found that S content as low as 10 ppm was obtained.

From these results, according to the method of the present invention,
It was possible to obtain metallic chromium with extremely low impurity metals such as Fe, and also with low impurities such as S, N, and O.

[0031]

[Effects of the Invention] As explained above, according to the method of the present invention, it is possible to obtain high-purity metallic chromium, which contains very few impurity metals such as Fe and impurities such as S, N, and O, and is useful for electronic materials and super alloys. We can provide high-purity metallic chromium that is optimal for your application.

Claims (1)

[Claims] Claim 1. A method for producing high-purity metallic chromium by removing impurities from crude metallic chromium containing impurities, first pulverizing the crude metallic chromium;
Next, the pulverized product is washed with an inorganic acid or acetic acid, and then either carbonaceous material or chromium carbide and/or easily sulfurized metal are added to form a mixture, and this mixture is heated in a vacuum or an inert gas atmosphere. 1100-15
A method for producing high-purity metallic chromium, which comprises heating to a temperature of 0.000C.