KR100406385B1 - Method for refining niobium alloy having ultra-high purity - Google Patents

Abstract

PURPOSE: A method for refining niobium alloy having ultra-high purity is provided which is applied to superconductor through getter agent and a new heat treatment in which refining is performed within a short period of time by simple operation. CONSTITUTION: The method comprises a step of covering a niobium alloy(5) to be refined with a foil formed of Ti, covering the Ti foil(3) with a Mo foil again, and charging the niobium alloy covered with the Ti foil and the Mo foil into a quartz tube(1) so that it is vacuum sealed in the quartz tube; a step of forming a getter agent deposition layer(7) by depositing Ti on the surface of the niobium alloy using the Ti foil as a getter agent by heat treating the quartz tube in the temperature range of 1,100 to 1,190 deg.C for 10 to 24 hours; and a step of removing a thin film deposited on the surface of the niobium alloy by rapidly cooling the quartz tube, wherein the quartz tube is vacuumed to 10¬-2 torr or less, wherein the getter agent is deposited to a thickness of 20 μm or more on the surface of the niobium alloy, and wherein the thin film is removed by impregnating the thin film deposited on the surface of the niobium alloy with a mixed solution of NH3 and HF.

Description

Refining method of ultra high purity niobium material

The present invention relates to a method for refining niobium or niobium-based alloys suitable for superconductors, and more particularly, to a method for refining ultra-high purity niobium materials through new heat treatment and a getter.

Niobium (Nb) is the material with the highest superconductivity critical temperature (Tc) among the metals. MR1 is present in the form of a single metal (Nb), an alloy (Nb-Ti) or an intermediate compound (Nb ₃ Sn, Nb ₃ Al) of A15 structure. It is a metal that is applied to numerous fields such as magnetic levitation trains. In particular, an electron accelerator (Cavity), which is an essential equipment for recent nuclear physics research, uses niobium as a superconducting material as an application of superconductivity. Niobium's superconducting performance for this purpose is affected by chemical changes such as the concentration of invasive or substituted impurities remaining therein and physical changes such as grains and dislocations. Among these physical and chemical effects, niobium needs some material conditions to fully function as a superconductor, one of which is an electron flow generated around impurities, particularly oxygen and nitrogen, or around lattice deformations. Minimize the heat generated by the resistance of To minimize the heat generation, impurities in niobium are extremely low and internal lattice defects must be sufficiently removed. In other words, the higher the purity in the nature of the superconductor, the higher the use value. At present, efforts are being made to obtain the correlation between niobium purity and superconductivity in various countries of the world, and at the same time, efforts to obtain ultra high purity niobium are increasing.

Zone melt refining, one of the high purity niobium manufacturing methods proposed to date, uses the solubility difference between the liquid phase and solid phase impurities of niobium. Part of the sample using high density energy such as electron beam under high vacuum Is melted and the melt is slowly moved to another part to collect impurities at one end of the sample. However, the proposal suggests that the sample must be heated to a high temperature and undergo a molten state, so that the sample may have a strong affinity with oxygen or nitrogen such as metals such as titanium (Ti), zirconium (Zr), tantalum (Ta) or niobium (Nb). Application requires close control of the vacuum atmosphere. Therefore, the ultra high vacuum [10 ^-9 mbar or less, UHV (Ultra High Vacuum) must be maintained, the molten portion must be moved at a low speed, there is a disadvantage that the melter must be operated for a long time under high vacuum.

Another proposal is to heat niobium to 2500-2600 ° C. under ultra-high vacuum (UHV) to allow oxygen and nitrogen to escape into the vacuum. However, like the above refining, there is a disadvantage in that heat treatment is performed for a long time at a high temperature.

A more important problem with the above proposals is the purity of niobium material after finishing the refining work. In order to apply the niobium material mainly used as an electron accelerator material such as a superconductor, the concentration of impurities is required to be refined to 1 ppm or less. As shown in Table 1, representative oxygen, nitrogen, and In addition, it can be seen that the impurity concentration of 450 ppm or more cannot be applied as a superconductor requiring high purity.

TABLE 1

Accordingly, the present invention has been proposed to solve the above problems, and an object thereof is to provide a method for refining niobium material having ultra high purity while processing in a short time by a simple operation at a low heat treatment temperature.

1 is a schematic diagram for refining niobium material

Figure 2 is a schematic diagram showing the phenomenon occurring in the vacuum-sealed quartz tube during heating

3 is a cross-sectional EMPA photograph of a titanium deposition layer deposited on the niobium surface

* Description of the symbols for the main couples in the drawings

1.quartz 2.molybdenum sheet

3. Getter Jane thin plate 4. Sponge getter

5. Niobium material 6. Diffusion and movement of oxygen and nitrogen

7. Getter deposition layer 8. Transfer of getter (Ti) vapor

The present invention comprises the steps of wrapping the niobium material to be refined with a thin sheet of Ti material, wrapping the thin plate again with a Mo thin plate and loading it into a quartz tube for vacuum sealing;

Heat-treating the quartz tube in a range of 1100-1190 ° C. for 10-24 hours to deposit Ti as a getter on the surface of the niobium material; And

Thereafter, quenching the quartz tube to remove the thin film deposited on the surface of the niobium material; It relates to a refining method of ultra-high purity niobium material comprising a.

Hereinafter, the present invention will be described in detail.

The present invention is characterized by providing a method of removing residual oxygen in a metal using a getter agent having a stronger affinity by focusing on the affinity between oxygen and nitrogen between the metals as one of the methods of increasing niobium purity. In addition, it provides a method of coating the surface of the niobium sample more simply using a quartz tube and a getter agent.

First, a method for coating a surface of niobium material with a getter will be described with reference to FIG. 1. The niobium material 5 is wrapped with a thin plate 3 serving as a getter, and if there is a getter tube, the niobium material may be placed in the tube. The niobium material 5 and the getter thin plate 3 positioned as described above are wrapped with the molybdenum thin plate 2 as shown in FIG. In addition, in addition to the getter thin plate (3) in the tube formed of the molybdenum thin plate (2) in order to pay for the evaporation of the getter agent from more getter thin plate (3), the sponge getter agent (4) pulverized in addition to the deposition effect Is large. The niobium material 5 formed as described above is charged in a quartz tube 1 to avoid contact with outside air, evacuated to 10 ⁻² torr, and heated with an oxygen + propane gas torch to vacuum seal. If the degree of vacuum does not satisfy 10 ⁻² torr or less, oxygen and the like remain in the quartz tube, which is not preferable.

In addition, the heat treatment should be carried out at a temperature above the reheating temperature of the niobium material and below the temperature where the vacuum sealing container is not deformed. The reason for heat treatment above reheating temperature is that recrystallization occurs, and oxygen and nitrogen, which have received sufficient driving force, can diffuse and move toward the getter deposited on the surface. In addition, the reason why the vacuum sealing vessel should be carried out at a deformation temperature or less is that in the present invention, a quartz tube was used as the vacuum sealing vessel. When the temperature exceeds 1200 ° C., the quartz tube is softened and vacuum-sealed. This is because the purpose of the container to block the niobium material from the outside and to sink inwards is eliminated. Therefore, the heat treatment is preferably performed for 10-24 hours in the temperature range of 1100-1190 ℃. If the heat treatment time is less than 10 hours, oxygen and nitrogen of the niobium material may not sufficiently move to the getter agent, and if the heat treatment time exceeds 24 hours, the vacuum sealing container may be deformed or cracks may occur.

Next, the transfer of oxygen, nitrogen, and getter agent evaporation and deposition occurring between the niobium material and the ketter agent in the quartz tube by the heat treatment will be described with reference to FIG. 2.

When the heat treatment is carried out, the getter agent is evaporated from the thin plate 3, for example, in the case of a thin plate made of Ti, Ti is evaporated and deposited on the surface of the niobium material 5. Play a role. The deposition thickness of the getter agent at this time should be 20 µm or more. If the deposition thickness of the getter is less than 20 µm, oxygen and nitrogen, which migrate from the niobium material, cannot be sufficiently absorbed.

Oxygen and nitrogen, which have received sufficient diffusion driving force at a high temperature, diffuse the inside of the niobium material 5 and diffuse and move toward the getter 7 deposited on the surface. As described above, the diffusion movement 6 of oxygen and nitrogen is transferred to the getter 7 deposited on the niobium material 5 as follows. In general, the residual oxygen and nitrogen in the metal diffuses to a lower concentration. If the concentration of oxygen and nitrogen is lowered, the remaining oxygen and nitrogen diffuse out to the outside. It can be removed.

Therefore, in order to keep the concentration of external oxygen or nitrogen low, a getter agent, which serves as a deoxidation and denitrification agent that strongly absorbs oxygen and nitrogen, is required. That is, if a metal having a higher affinity with oxygen and nitrogen than the niobium to be refined is attached to the surface, oxygen and nitrogen will move and be absorbed by this metal.

The conditions which should be provided as a getter agent which plays the above role are as follows.

1. More affinity for oxygen and nitrogen than niobium.

2. Niobium has a slower diffusion rate than oxygen or nitrogen.

3. High vapor pressure

Thermodynamic and diffusion rate calculations revealed that the preferred metals satisfying the above getter conditions were titanium and were used for niobium high purity.

In addition, after the deposition of the getter by heat treatment as described above, the quartz tube is quenched and opened to extract niobium material. In order to extract the niobium material from being deformed, the sample is extracted with NH ₃ + HF solution (NH ₃ : HF = 1). (1, 50%) to melt the deposited titanium sheet, sponge titanium and titanium deposited on the surface of niobium.

Hereinafter, the embodiment of the present invention will be described in detail.

Example 1

After the niobium material was dissolved in an electron beam, the oxygen and nitrogen contents and other impurity concentrations were as shown in Table 1, and the niobium ingot was cut and processed into a niobium material having a wire shape as shown in FIG. 1 (a). It was made into the comparative example (1). The niobium material was wrapped in a titanium thin plate, a sponge titanium and a molybdenum thin plate, and vacuum-sealed in a quartz tube.

Vacuum encapsulation of the quartz tube is a commonly used method, and exhausted to 10 ^-2 torr, and then heated and encapsulated with an oxygen + propane gas torch.

The quartz tube as a vacuum rod prepared as described above was charged to a furnace, and the temperature was raised to 1190 ° C. for 10 hours to form a titanium deposition layer of about 150 μm. After the heat treatment, the quartz tube was quenched and opened to extract a sample. In order to extract the sample without deformation, the sample was put in NH ₃ + HF solution (NH ₃ : HF = 1: 1, 50%) to melt the adhered titanium sheet, sponge titanium, and titanium deposited on the surface of niobium. 1). The purity of the niobium material carried out as described above was evaluated, and the results are shown in Table 2 below. Niobium produced by the present invention was shown to be of very high purity, and could not be evaluated by the conventional oxygen nitrogen extraction method due to exceeding the lower limit of analysis, and the current residual resistivity ratio (Electrical Residual), which is a recent evaluation method of ultra-pure metal materials. Resistivity Ratio, RRR = ρ _at273K / ρ _at4.2K ).

TABLE 2

As shown in Table 2, Inventive Example (1) was found to have an ultra-high purity as compared to Comparative Example (1) with an electrical residual resistance ratio of 1000. In addition, the rapid recrystallization occurs at the heat treatment temperature, the oxygen and nitrogen diffusion rate is also sufficiently high, the heat treatment for about 10 hours 1.45-2mm dia. Oxygen and nitrogen remaining in the niobium material in the form of wires were diffused to the titanium deposition layer and almost completely removed.

On the other hand, during the heat treatment in the practice of the present invention, the thin titanium plate or sponge titanium in the quartz tube evaporated slowly to fill the inside of the quartz tube. Such titanium vapor was deposited on the surface of niobium, and titanium deposited on the surface was able to diffuse and penetrate into the niobium material by maintaining a high temperature for a long time, but its penetration rate is very slow compared to the diffusion rate of oxygen and nitrogen. It was as small as On the other hand, niobium may diffuse into the titanium deposition layer, but the diffusion rate may be negligible because the diffusion rate is very slow. 3 shows a cross section of titanium deposited on a niobium material. As shown in FIG. 3, it was found that titanium was deposited on the entire surface of the niobium material.

As described above, the present invention has the effect of being applicable to a superconductor or the like by providing a new heat treatment for refining in a short time by a simple operation and a refining method of ultra-high purity niobium material through a getter agent.

Claims (4)

Wrapping the niobium material to be refined with a thin plate made of Ti, wrapping the thin plate made of Ti again with a Mo plate, and then charging the vacuum in a quartz tube; Heat-treating the quartz tube in a range of 1100-1190 ° C. for 10-24 hours to deposit Ti as a getter on the surface of the niobium material; And Thereafter, quenching the quartz tube to remove the thin film deposited on the surface of the niobium material; Refining method of ultra-high purity niobium material comprising a. The method of claim 1, wherein the vacuum conditions in the quartz tube are 10 ^-2 torr or less. The method of claim 1, wherein the getter deposited on the surface of the niobium material is 20 µm or more in thickness. The method of claim 1, wherein the thin film removal is performed by impregnation with NH ₃ + HF solution.