JPS6247437A - Manufacture of metallic chromium with very low nitrogen content - Google Patents

Abstract

PURPOSE:To stably manufacture metallic chromium with very low nitrogen content by charging metallic chromium containing nitrogen as impurity into an atmospheric heat-treatment furnace, maintaining it in a high-temp. vacuum atmosphere, introducing a nonoxidizing gas and adjusting the furnace pressure to a specific value. CONSTITUTION:The metallic chromium, containing nitrogen as impurity, in massive, crushed or pulverized state made by a fire refining or hydrometallurgy method is charged into the heat-treatment furnace with airtight atmosphere and maintained at about 1,100-1,700 deg.C under the vacuum atmosphere. Subsequently, the nonoxidizing gas (Ar, He, H2, CH4, etc.) is introduced into the furnace continuously or intermittently and the furnace pressure is adjusted to 3.75X10<-3>-0.22Pa, which is maintained for about 5-15hr. In this way, the metallic chromium having a nitrogen content as impurity, as low as <= about 0.00005wt% can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing ultra-low nitrogen metal chromium. More specifically, the present invention relates to a method for producing ultra-low nitrogen metallic chromium by dry refining metallic chromium containing nitrogen as an impurity using an atmospheric heat treatment furnace.

When metal chromium is used as an alloy component, it has a remarkable effect on imparting heat resistance, corrosion resistance, and wear resistance to the alloy, so it is often used as an additive component to nickel, cobalt, iron, etc. In recent years, it has also been widely used as a material in so-called dry plating fields such as vacuum evaporation and ion plating, and in the semiconductor field. Especially in these fields, there is a strong demand for ultra-low nitrogen products.

[Conventional technology]

The manufacturing methods for metallic chromium can be broadly divided into pyrometallurgy and hydrometallurgy. In the pyrometallurgical method, the clinker obtained by roasting chromium ore with alkali oxidation is extracted as raw material, chromate sodium 1) Umushi Valley 1. It is typified by the so-called thermite method, in which metallic chromium is obtained by reducing chromium oxide obtained by repeating recrystallization, purification, and chromic acid anhydride with aluminum or the like. On the other hand, the hydrometallurgical method is typified by an electrolytic method in which chromium ore is reduced with carbon, the obtained high carbon ferrochrome is dissolved in sulfuric acid, and this is electrolytically reduced to obtain metallic chromium.

Although the nitrogen content of metallic chromium produced by these manufacturing methods is relatively high, it is still desired to produce a low-nitrogen product.

As a method for purifying and removing nitrogen from total chromium, there is the LCH method (Japanese Patent Laid-Open No. 52-22889). This is 0a
-C! aC4 or Mg-MgC1q flux,
This is a method to purify the nitrogen in metallic chromium to a very high level of purity.

However, since this method has limitations on the particle size of the raw material and uses flux, some of its components remain in the metal chromium. In addition, the operation is somewhat complicated as it involves a dry process and a wet process.

[Problem that the invention seeks to solve]

As mentioned above, the conventional manufacturing method for metallic chromium contains a small amount of nitrogen as an impurity, making it difficult to use in the dry plating field.

In the semiconductor field, applications for metallic chromium with as little nitrogen content as possible are desired. In addition, conventionally known purification and removal methods for nitrogen have drawbacks such as complicated operations and the use of additives, which inevitably leads to the contamination of new impurities.

The present inventors completed the present invention as a result of intensive research in search of a method for removing nitrogen from metallic chromium that eliminates these drawbacks.

[Means for solving problems]

That is, in the present invention, metallic chromium containing nitrogen as an impurity is charged into an airtight atmosphere heat treatment furnace, maintained in a high-temperature vacuum atmosphere, and a non-oxidizing gas is continuously or intermittently introduced into the furnace. The pressure inside the furnace was 575×1O-s-α22 Pa
The present invention provides a method for producing ultra-low nitrogen metal chromium, which is characterized by adjusting the nitrogen content to chromium.

The present invention uses metallic chromium produced by pyrometallurgy or hydrometallurgy as a starting material, charges it into an airtight atmospheric heat treatment furnace, maintains it in a high-temperature vacuum atmosphere,
It is characterized by continuously or intermittently introducing a small amount of non-oxidizing gas to control Cr loss, promote denitrification, and stably remove nitrogen from metallic chromium down to an extremely small amount. .

The raw material used in the present invention may be any shape and particle size of metallic chromium obtained from pyrometallurgy or hydrometallurgy, including lumps, coarsely crushed products, and finely crushed products. This is because nitrogen diffusion in chromium particles is rate-determining in a high-temperature vacuum atmosphere, and the removal rate is extremely fast. Atmospheric heat treatment is carried out in the vacuum atmosphere of a furnace at a treatment temperature of 1100°C to 1700°C, preferably 1200°C to 1500°C, but a non-oxidizing gas, such as Ar, Introducing a small amount of He, Hl, CH4, etc.
The condition is maintained under reduced pressure adjustment at 5 x 10-'' to cL22 Pa for 5 to 15 hours. This is because metal chromium has a relatively high vapor pressure in a high-temperature vacuum atmosphere, so Cr loss cannot be controlled. The non-oxidizing gas may be introduced continuously during the process, or intermittently during the first or second half of the process. May be introduced.

〔Effect of the invention〕

Metal chromium from which the nitrogen component has been purified and removed according to the present invention is not contaminated with other contaminants, and the nitrogen content in metal chromium is refined to an extremely small amount of ctooos weight t% or less, and can be used as a material for dry plating and semiconductor fields. It is durable enough for use. In addition, since the process is a dry purification method, it is extremely simple and industrially superior.

〔Example〕

Next, in order to explain the present invention more specifically, examples will be given.

Example 1 A lump of metallic chromium containing nitrogen (L037 heavy ill) produced by a pyrometallurgical method was coarsely crushed with a jaw crusher and sized to a particle size of 20 to 30%.This was used as a raw material and subjected to atmospheric heat treatment. Load it into the furnace and use an oil rotary pump.
The inside of the furnace was made into a vacuum atmosphere and the temperature was raised. Processing temperature is 15
The treatment was carried out at 00°C2 for a holding time of 10 hours, and during the holding time, Ar gas was introduced into the furnace, and the furnace pressure was adjusted to a reduced pressure of α04 Pa. After the holding time, Ar
The introduction of gas was stopped and vacuum cooling was performed. As a result, the amount of nitrogen in metallic chromium was [10,005 weight-t].

Example 2 A method wet tank 1 was manufactured (metallic chromium containing 1025% by weight of nitrogen was ground into a finely ground product with a particle size of 32Mθ8h or less. After adding a small amount and mixing, it was press-molded at 1t/crI to form a cylindrical molded body with a diameter of 30%; The temperature was charged at 1400"C and held for 5 hours. Ar gas was introduced into the furnace for 2 hours from the start of the holding time, and 7.
The treatment was carried out under a controlled pressure of 5×10 −′ Pa, and then the Ar gas was stopped and the vacuum atmosphere was maintained for 5 hours.

After the holding was completed, it was cooled in a vacuum atmosphere. the result,
The amount of nitrogen in metallic chromium was 0.0002% by weight.

Claims (3)

[Claims] (1) Metal chromium containing nitrogen as an impurity is charged into an airtight atmosphere heat treatment furnace, maintained in a high-temperature vacuum atmosphere, and non-oxidizing gas is continuously or intermittently introduced into the furnace,
A method for producing ultra-low nitrogen metal chromium, which comprises adjusting the furnace pressure to 3.75×10^-^3 to 0.22 Pa. (2) The ultra-low-concentration metal chromium containing nitrogen as an impurity is a lump product, a coarsely crushed product, or a finely crushed product manufactured by a pyrometallurgical method or a hydrometallurgical method. Method for producing nitrogen metal chromium. (3) Non-oxidizing gas is Ar, He, H_2 or CH_4
A method for producing ultra-low nitrogen metal chromium according to claim (1) or (2).