KR0133455B1 - Manufacture of superconductor by using neodymium:yttrium alumina garnet laser - Google Patents

Abstract

The present invention relates to a method for preparing a superconducting ceramic material, in particular to a method of calcining a Y-Ba-Cu-O superconductor starting material under an oxygen atmosphere at room temperature using an Nd: YAG laser. Unlike the conventional method, the method according to the present invention has an advantage of shortening the process time as much as possible by using a laser instead of a furnace in the calcination step. In addition, since the crucible is not used, the possibility of introducing impurities by the reaction with the crucible and the difficulty in selecting the crucible material are excluded.

Description

Neodymium: Manufacturing method of superconductor using yttrium alumina garnet laser

1 is a schematic diagram of an apparatus that can be used in a laser calcination process according to the present invention.

2 is a graph showing an X-ray diffraction pattern of powder (a) calcined by the conventional method and powder (b) calcined by the method of the present invention,

3 is a graph showing the temperature dependence of the resistance of specimen (a) prepared by calcination by the conventional method and specimen (b) prepared by calcination by the method of the present invention.

4 is a graph showing the magnetization characteristics of specimens prepared by calcination by the conventional method and specimens prepared by calcination by the method of the present invention.

5 is a photograph showing the microstructure of a specimen prepared by calcining by a conventional method.

6 is a photograph showing the microstructure of a specimen prepared by calcining by the method of the present invention.

* Description of the symbols for the main parts of the drawings *

1: feed funnel 2: feed regulator

3: 2 stage vibrator 4: oxygen supply pipe

5: emission port 6: Nd: YAG laser

7: laser beam 8: lens

9: rotating table 10: beam absorption crucible

The present invention relates to a method of performing a calcination process, which is an essential step in the synthesis of superconductors, using a laser. More specifically, the present invention relates to a method of calcining superconductor powder using a low power neodymium: yttrium alumina garnet laser (Nd: YAG laser).

Since the discovery of oxide superconductors in 1986, research on new superconductors has been ongoing. Most oxide superconductors are made by mixing precursors consisting of nitrate (NO ₃ ), carbonate (CO ₃ ) and oxide (O ₂ ), calcining them and then subjecting them to press and sintering steps. Among them, the calcination step is to separate the powder mixture into gas phase and solid phase and to obtain a homogeneous mixture, and to use the furnace in spite of the process step which is essential and significant part in the synthesis of general ceramic materials including superconductor. There were several disadvantages that followed. In other words, it takes a lot of time, usually about 24 hours, to obtain the desired level of homogeneous mixture, and since the crucible is used as a supporter of the starting material, impurities are introduced by the reaction of the crucible and the starting material. The likelihood is high and, therefore, difficulties have arisen in the material selection of the crucible. In particular, the long process time has become one of the problems to be urgently improved considering the industrial applicability of the superconductor and the economic aspects required for mass production.

In this regard, Japanese Laid-Open Patent Publication No. Hei 1-1082945 (April 25, 1989) describes a method for producing a fluorescent material powder by calcining the raw material with a laser, but the method of preparing the raw material before laser calcining is disclosed. It is different from the present invention in terms of primary calcination at, reactor use, other process conditions, content and material itself. Also, mr. W. Chen et al. [1] Chen, P.A.A. Khan, KW Mukherjee, Journal of Material Science, Laser fabrication of Pb doped Bi-Sr-Ca-Cu-Osuperconductor] method for producing Pb-doped Bi-Sr-Ca-Cu-O superconductor using Nd: YAG laser Although described, not only does not have a detailed description of the process, the process itself is also different from the process of the present invention.

The present inventors have led to the present invention as a result of long-term research to develop a new calcination process using a laser to overcome the above-mentioned disadvantages.

Accordingly, an object of the present invention is not only to reduce the process time as much as possible compared to the conventional method, but also to eliminate the possibility of introducing impurities due to the reaction with the crucible, the difficulty of selecting the crucible material, neodymium: yttrium alumina garnet laser It is to provide a method of manufacturing a new superconductor using.

This object of the present invention can be achieved by the method of the present invention by mixing the starting materials for the production of superconductors in an oxygen atmosphere at room temperature, calcining the mixture using a neodymium: yttrium alumina garnet laser, and then pressing and sintering. have.

As a starting material of the superconductor material used in the present invention, Y ₂ O ₃ , BaCO ₃ and CuO may be used in a 1: 2: 3 molar ratio.

The calcination process according to the method of the present invention may be performed for 3 to 4 hours under a pulse energy of 2 to 3.0 J and a pulse rate of 100 to 200 pulses / second under an oxygen atmosphere at room temperature. More preferably, it may be performed for about 4 hours under a pulse energy of about 2.5 J and about 100 pulses / second under an oxygen atmosphere at room temperature.

Hereinafter, the calcination process of the present invention will be described in more detail with reference to FIG.

1 schematically illustrates an example of a calcination apparatus that may be used to manufacture a superconductor according to the method of the present invention. As shown in FIG. 1, the calcination apparatus can be divided into two parts, a supply section for supplying superconductor starting material and oxygen, and a calcination section for calcining and collecting the supply section. It consists of a regulator (2), an electric vibrator (3), an oxygen supply pipe (4) and a discharge port (5) of the supplied powder, and the calcining portion is a laser source (6), a lens (8), a longitudinal axis rotating table ( 9) and the beam absorption crucible 10 on the table. The starting material suitably mixed under an oxygen atmosphere at room temperature is first fed to the feed funnel 1, where the mixed powder is again horizontally in the path 7 of the laser beam defocused vertically by a two-stage electric vibrator 3. It is injected into the enemy and falls free. At this time, the ejection opening 5 is properly positioned so that the emitted powder reacts with the laser beam 7 at a predetermined distance from the focal point of the lens 8, and oxygen gas is also used to control the oxygen adjustment of the superconductor. Supplied through.

The calcined superconducting powder, which first interacted with the laser beam, is collected in a beam absorption crucible 10 on the longitudinal axis rotating table 9. This rotary table is designed to automatically rotate on the longitudinal axis to prevent the powder from being overexposed to the laser beam and melting. As the beam absorption crucible, it is preferable to use a carbon crucible (graphite mold) having good electrical and thermal characteristics as well as mechanical stability. Powders interacted with the laser are periodically withdrawn from the absorption crucible 10, combined and then ground to further homogenize. This reaction-recovery-grinding cycle can be continued until the desired laser-particle reactivity is obtained. Subsequent pressing and sintering processes can be carried out according to conventional methods.

The following examples are only intended to illustrate the present invention in more detail, and are not intended to limit the present invention, it is to be understood that there are many modifications and variations that are possible without departing from the spirit and scope of the present invention.

Example

Y ₂ O ₃ , BaCO ₃ and CuO were mixed in a molar ratio of 1: 2: 3 to prepare a YBa ₂ Cu ₃ O ₇ -x phase powder. Using the apparatus shown in FIG. 1, at room temperature, in an oxygen atmosphere, a pulsed energy of about 2.5 J and a pulse rate of 100 pulses / second were taken into the path of a vertically defocused 1.06 × 10 ⁻⁶ m beam of Nd: YAG laser. The mixed powder was injected by a two stage vibrator. 5.5 × 10 ⁻¹⁰ kg of powder was released per second from the feeder, and the powders interacted with the laser were collected in a carbon crucible of 6 × 10 ⁻² m in diameter. The powder was periodically withdrawn from the crucible and regrind, and the powder was recycled three times in reaction with the laser beam. It took about 4 hours based on 20 × 10 ⁻³ kg of starting material to obtain the desired homogeneous mixture. Subsequent pressurization and sintering steps in the furnace were carried out under conventional methods and conditions. For the purpose of comparison, conventional furnace-calcination processes are described in AK Singh, LE Richards, HA Hoff, V. Letourneau and CS Pande: J Appl. Phys, 63 (1988) 5805; and S. Nakahara, T. Boone, MF Yan, GJ Fisanick and DW Johnson Jr. : J. App1. Phys. 63 (1988) 451. The calcination and sintering conditions of the manufacturing method of the superconductor according to the present invention and the conventional manufacturing method are shown in Table 1 below.

TABLE 1

As can be seen from Table 1, it can be seen that the manufacturing time of the specimen subjected to the laser calcination process is reduced by 20 hours compared to the manufacturing process time of the specimen using a conventional furnace.

Test powders were exposed to Ni-filtered CuKα radiation for confirmation of structure and phase. As can be seen in FIG. 2, the X-ray diffraction pattern is almost identical for the powders that have undergone two different calcination processes, namely furnace-calcination and laser-calcination, especially in powders prepared according to the present invention. No influx of impurities or presence of molten phase due to the reaction was observed. Carbon diffusion was negligible.

Figure 3 shows the electrical properties of the final specimens prepared after different calcination treatments, measuring the electrical resistance with a conventional four-probe technique and graphically showing its temperature dependence. The superconducting critical temperature (Tc) of the two specimens is about 92 ° K, which shows the superconductivity of YBa ₂ Cu ₃ O ₇ -x. In particular, it can be seen that in the laser-calculated specimens, impurities or secondary phases generated during calcination did not affect the critical temperature.

Magnetic moments were measured on the two final specimens prepared as described above using a magnetic property measurement system (MPMS, model 2000 VHF SQUID, Quantum Design). As shown in FIG. 4, both specimens exhibit superconductivity, with the magnetization characteristic changing to zero at 92 ° K. In addition, it can be seen that this result is completely in agreement with the result of the electrical property (Tc).

Polarization microscopy and scanning electron microscopy were used to observe the microstructure of the final specimens subjected to the no-calcination process and the laser-calcination process (FIGS. 5 and 6, respectively). As can be seen from these figures, it can be seen that the fracture surface of the laser-calcined specimen has a larger pore size and a larger diameter than the specimen prepared using a conventional furnace. The current carrying capacity of the polycrystalline specimens is improved, resulting in an increase in the critical current density (Jc).

As described above, by calcination with a laser in accordance with the present invention has advantageous properties comparable to materials produced by conventional superconductor manufacturing processes, for example, having a high critical temperature (92 ° K) and a larger particle diameter. Superconductors can be manufactured in a much shorter process time.

Claims (2)

Starting materials for the production of superconductors are mixed under an oxygen atmosphere at room temperature, and the mixture is neodymium; A method of manufacturing a superconductor, which is calcined using a yttrium alumina garnet laser (Nd: YAG-laser), followed by pressing and sintering. The method of claim 1, wherein the starting material is a mixture of Y ₂ O ₃ , BaCO ₃ and CuO in a molar ratio of 1: 2: 3, and calcination is performed using a Nd: YAG laser with a pulse energy of 2 to 3.0 J and 100 To 3 to 4 hours under conditions of from 200 pulses / second.