JPS623406Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a crucible holder for supporting a crucible used in an electric furnace for crystal growth.

Manganese-zinc ferrite single crystals used in magnetic heads for VTRs and the like are usually produced by the Bridgeman method. In this Bridgeman method, a crucible filled with raw materials is transferred at a predetermined speed in a furnace with a predetermined temperature distribution to grow seed crystals in the crucible, but if the temperature distribution in the furnace is not smooth, It has been said that it is difficult to successfully produce single crystals with a desired crystal orientation. On the other hand, the crucible support method for transferring the crucible in the furnace is to insert a heat-resistant recrystallized alumina tube (crucible holder) into the furnace from the bottom of the furnace, and place a platinum or platinum rhodium crucible on top of it. Two methods are used: the method of supporting the crucible, and the method of attaching a platinum-rhodium suspension wire to the crucible from the top of the furnace and suspending it from the top, but when producing large single crystals, the former method is used because it is more stable. There are many things.

FIG. 1 shows a model diagram of an electric furnace using a conventional crucible holder, together with the temperature distribution on the crucible surface. In the figure, 1 is an alumina furnace core tube;
2 is a platinum crucible that moves up and down within this furnace core tube, and 3 is a crucible holder. Further, characteristics 4 and 5 indicate the temperature distribution on the crucible surface expressed by the temperature scale 6. The crucible 2 has a cylindrical shape with a conical (funnel) lower part, and is further provided with a tube 7 at the lower end into which a seed crystal is placed. The lower end of the tube 7 is sealed (for example, by crushing) to prevent the seed crystal from falling. The crucible receiver 3 is a cylindrical body made of alumina, and the inner diameter 8 of the head is smaller than the outer diameter 9 of the crucible 2, so that the lower part 2A of the crucible is accommodated in the cylindrical body as shown in the figure. There is. The lower part of this crucible holder 3 is supported by a base 10, and this base 10 is connected to a drive mechanism 11.
Accordingly, the crucible holder 3 and the crucible 2 are connected to the furnace core tube 1.
I'm trying to move it up and down inside.

In the Bridgeman method, when no external airflow is applied to the furnace core tube 1, the temperature distribution on the crucible surface becomes smooth as shown by the broken line characteristic 5, so the probability of changing the crystal direction of the single crystal to be grown is small and desirable. However, when growing Mn--Zn ferrite single crystals, the oxygen partial pressure decreases, so there is a drawback that it is difficult to stably produce crystals with a constant composition ratio. Therefore, in the conventional example, oxygen gas is applied from below the furnace core tube 1 as shown by the arrow 12 to obtain ferrite with a stable composition ratio. By the way, when this oxygen gas hits the lower part of the crucible 2, that part is partially cooled and comes to exhibit a temperature distribution as shown by the solid line characteristic 4 in the figure. In other words, since heat is removed between points A and B in the figure by the cold oxygen gas, and heat is retained between points B and C by the crucible holder 3, there is an inflection point near point B. This results in an uneven temperature distribution. Therefore, during the crystal growth process, the portion at point B becomes partially supercooled, and another crystal that is different from the crystal direction of the seed is likely to be generated.

The present invention was made with this drawback in mind.
It is an object of the present invention to provide a crucible holder in which the smoothness of the temperature distribution on the crucible surface is not easily disturbed even when airflow is applied from the outside in order to grow crystals with a stable composition ratio. That is, the present invention provides a cylindrical crucible holder having a head in which the conical lower part is inscribed in order to support a cylindrical crucible whose lower part is formed into a conical shape. It is an object of the present invention to provide a crucible holder characterized by having a through hole provided near the head of the crucible in order to provide airflow to the crucible portion placed in the crucible.

FIG. 2 is a schematic diagram of an electric furnace equipped with the crucible holder of the present invention, together with the temperature distribution on the crucible surface. In the figure, the other components except for the crucible holder are substantially the same as those of the corresponding figures shown in FIG. 1, and therefore the explanation thereof will be omitted.

The crucible holder 20 is a cylindrical body made of alumina, and includes a head 21 that receives the conical part 2A of the crucible 2, and a head 21 that is arranged near the head and that connects the conical part 2A inside the crucible holder. The crucible holder is provided with a plurality of through holes 22 for applying airflow from below on the outside, and the lower end 23 is connected to the base 10 as in FIG.
It is connected to the drive mechanism 11 via. head 2
The inner diameter 24 of the crucible 2 is made slightly smaller than the outer diameter 9 of the crucible 2, and the ribs 25 adjacent to the plurality of through holes 22 are enlarged to some extent, so that the entire weight of the crucible 2 filled with raw materials is sufficiently It is designed to be supported.

A raw material 30 is charged into the crucible 2 supported by the crucible holder 20, and the crucible 2 is raised from below the furnace core tube 1 by the drive mechanism 11. The furnace controls a heating element (not shown) so that the temperature distribution on the crucible surface becomes as shown in the figure. This position can be determined by detecting the temperature at point C (crystallization temperature of the raw material, for example 1620° C.) with a thermocouple (not shown) placed near the lower end of the crucible 2 (upper end of the pipe). At this position, all the raw materials in the crucible 2 are melted, and by lowering the crucible receiver 20 at a predetermined speed by the driving device 11, crystals that follow the crystal orientation of the seed crystal in the pipe 7 are grown. . During this growth process, oxygen gas is introduced from below, and this oxygen gas is applied almost uniformly to the inner and outer conical portions 2A and 2B of the crucible holder 20, so that the surface of the crucible is coated as shown in FIG. Since no refraction point of the temperature distribution occurs, the above-mentioned adverse effects due to this refraction phenomenon do not occur (see Temperature Distribution Characteristics 26 also included).

As mentioned above, the crucible holder of the present invention stably receives the crucible from the bottom for growing large-sized single crystals, and at the same time, the temperature inside the furnace is higher than that in the furnace in order to obtain single crystals with a stable composition ratio. Even if low-temperature gas (oxygen gas in the case of ferrite) is introduced into the crucible, this fluid will not cause sudden changes in the temperature distribution on the crucible surface, making it possible to stably produce single crystals with a high yield. It is possible and practical.

[Brief explanation of the drawing]

FIG. 1 shows a model diagram of an electric furnace equipped with a conventional crucible holder, and FIG. 2 shows a schematic configuration diagram of an electric furnace equipped with a crucible holder according to the present invention. Explanation of main drawing numbers 2... Crucible, 20... Crucible holder, 21... Head, 22... Through hole.

Claims (1)

[Scope of utility model registration request] The conical lower part is arranged to be movable up and down in the furnace core tube and is for supporting the circularly formed lower part of the cylindrical crucible which is exposed to the airflow flowing from the bottom to the top in the furnace core tube. In a cylindrical crucible receiver having a head in which a relatively small-diameter portion of A crucible holder characterized by having a plurality of through holes provided along the axial direction.