JPH0371493B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to a method for producing high purity zirconium, and particularly to a production method suitable for obtaining high purity zirconium. [Background of the Invention] Zirconium currently used as a material for nuclear reactors is produced by the Kroll process.
The process of manufacturing zirconium by the Kroll method is, for example, “ASTM
MANUAL ON ZIRCONIUM AND
HAFNIUM”Chapter 4-Production
As shown in Techniques, (1) the raw material zircon sand Zr(Hf)SiO ₄ is primary chlorinated, and Zr
Make (Hf) _Cl4 . (2) Change the primary chloride to oxychloride Zr(Hf)OCl ₄ and separate zirconium and hafnium by countercurrent extraction. (3) After the precipitated zirconium is roasted and sintered, it is subjected to secondary chlorination to form secondary chloride ZrCl ₄ . (4) Sublimate the secondary chloride ZrCl ₄ and reduce it in a reduction furnace to pure zirconium.
(5) After separating the magnesium used as a reducing agent by distillation, it is crushed into zirconium sponges with a diameter of several millimeters. The above is the manufacturing process of zirconium sponge for nuclear reactors, but below is ASTM B-352-
Shows the chemical composition standard shown in 79GradeR60001. Aluminum 75ppm or less, Boron 0.5ppm or less, Cadmium 0.5ppm or less, Carbon 270ppm or less, Cobalt 20ppm or less, Chromium 200ppm or less,
Copper 50ppm or less, iron 1500ppm or less, hafnium
100ppm or less, magnesium 20ppm or less, manganese 50ppm or less, molybdenum 50ppm or less, nickel
70ppm or less, silicon 120ppm or less, tin 50ppm or less, tungsten 100ppm or less, uranium 3.5ppm or less, niobium 100ppm or less, titanium 50ppm or less, hydrogen 25ppm or less, nitrogen 80ppm or less. Zirconium produced by the Kroll method is currently used as a zirconium alloy material for fuel cladding tubes in nuclear reactors, but recently, as shown in Japanese Patent Application Laid-Open No. 51-69795, A zirconium liner tube, in which a pure zirconium liner is lined inside a cladding tube made of a zirconium alloy, has been proposed as a fuel cladding tube. Zirconium liner tubes are considered to perform better with fewer impurities in the liner, given their original purpose of preventing stress corrosion cracking. By the way, although zirconium produced by the Kroll method has relatively high purity, it has a large tolerance for impurity elements such as iron, chromium, carbon, and silicon, and zirconium produced by the Kroll method usually contains iron.
It contains 500 to 1200 ppm, 100 to 200 ppm of chromium, and 1000 to 1500 ppm of other impurity elements in total. In order to obtain even higher purity zirconium,
There is a conventional method for manufacturing zirconium crystal bars. This is a thermal decomposition method of zirconium iodide, in which zirconium and iodine are reacted at approximately 400℃.
High purity zirconium is obtained by making zirconium iodide and thermally decomposing it at 1400℃. However, this method cannot be mass-produced due to the unique manufacturing method, and the manufacturing cost is extremely high. Therefore, it is essential to improve the performance of zirconium liner tubes by somehow lowering the impurity content of zirconium sponge obtained by the Kroll method to increase its purity. [Object of the Invention] The present invention has been made in view of the above, and its object is to provide a method for producing high-purity zirconium that can obtain high-purity zirconium by removing impurities contained in a zirconium sponge. Our goal is to provide the following. [Summary of the Invention] The feature of the present invention is that a zirconium sponge is immersed in an alcohol solution containing halogen, and then
The main feature is that many impurity elements present in the grain boundaries are removed by cleaning and vacuum heat treatment. [Embodiment of the Invention] An embodiment of the manufacturing method of the present invention will be described in detail below with reference to FIGS. 1 to 3. Halogen elements include chlorine, bromine, fluorine, iodine, etc. In the present invention, by immersing a zirconium sponge in an alcohol solution containing halogen, the spaces between the crystal grains of polycrystalline zirconium are eroded by atomic halogen. We focused on the cause of grain boundary embrittlement. In other words, many impurity elements in zirconium are present at grain boundaries, so if the grain boundaries are selectively removed, pure zirconium remains and zirconium of substantially high purity can be obtained. . In short, grain boundaries, impurity segregation layers, inclusions, etc. present at grain boundaries are chemically and physically removed, resulting in highly pure zirconium. Among the impurity elements, the elements that have a small amount of solid solution with respect to zirconium are iron, chromium, carbon, silicon,
Nickel, etc. These are contained in relatively large amounts in the zirconium sponge produced by the Kroll method, and reducing their content will significantly improve the purity. In this way, since the impurity element to be removed has a small solid solution amount with respect to zirconium, it is convenient to remove it by existing in large quantities at the grain boundaries. In the method of the present invention, the purpose of heating in vacuum is to evaporate and remove halides produced by grain boundary reactions. For example, zirconium iodide (ZrI ₄ ) has a high vapor pressure (10 ^-5 Torr at 850K), so it can be removed sufficiently by commonly used vacuum heat treatment. FIG. 1 is a process diagram of the present invention. 1 is the raw material zirconium sponge, 2 is immersion in an alcohol solution containing halogen, 3 is cleaning of the raw material sponge after immersion, and 4 is heat treatment in vacuum. When obtaining high purity zirconium powder, ,
Crushing is performed in Step 5, and powder is obtained in Step 6. In the present invention, since zirconium sponge is used as a raw material, grain boundary reaction with the solution is effectively carried out during immersion, and the purification effect is large. Furthermore, the zirconium sponge obtained by this method is characterized by being more porous and easily crushed. The zirconium obtained by the above method can be used as a zirconium material for a nuclear reactor after undergoing ordinary steps such as melting, forging, and rolling. Next, specific examples will be described. Using the zirconium materials shown in Table 1, the optimum immersion time was first investigated under the following conditions. Solution: methanol-iodine (1% by weight) Soaking time: 24, 35, 48, 60, 80, 100, 120, 140,
Heat treatment in vacuum at room temperature for 160 hours; 600℃ at 6×10 ^-7 Torr for more than 3 hours to crush the zirconium material.
The fracture surface was observed using a scanning electron microscope.

[Table] Note: Unit is weight%
As a result, as shown in Figure 2, the immersion time was
Within 100 hours, most of the fracture surfaces are intragrain fractures, but
After 120 hours or more, grain boundary fracture surfaces appeared, and smooth zirconium crystal grains with almost all precipitates of impurity elements Fe and Cr removed were observed. Next, the zirconium sponge 7 containing the impurities shown in Table 2 was immersed in a methanol-iodine (1% by weight) solution 9 in a container 8 for 140 hours as shown in FIG. As shown in the figure, the zirconium sponge 7 after immersion was transferred to pure water 11 in an ultrasonic cleaner 10 and ultrasonically cleaned for about 2 hours.
Next, it was heated at 600° C. for 3 hours in a vacuum (1×10 ⁻⁷ Torr).

〔Effect of the invention〕

As explained above, according to the present invention, without using expensive crystal verzirconium,
This method has the effect of producing high-purity zirconium using a simple method.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the steps of the method for producing high-purity zirconium of the present invention, FIG. 2 is a diagram showing the relationship between immersion time and grain boundary fracture surface area in the process of the present invention,
FIG. 3 is an explanatory diagram of the dipping method and the cleaning method in the method for producing high-purity zirconium of the present invention. 7... Zirconium sponge, 9... Methanol-iodine solution, 10... Ultrasonic cleaner, 11...
...Cleaning liquid.

Claims (1)

[Claims] 1. A method for producing high-purity zirconium, characterized in that in the zirconium purification process, a zirconium sponge is immersed in an alcohol solution containing halogen for a predetermined period of time or more, and then washed and subjected to vacuum heat treatment. . 2. The method for producing high-purity zirconium according to claim 1, wherein the alcohol solution is a methanol-iodine solution, and the predetermined time is 120 hours or more.