JPS6033796B2 - Electric furnace for crystal growth - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electric furnace that can be used to grow crystals such as ferrite single crystals that can be used as magnetic head materials for VTRs.

Bridgman (Br) is generally used to grow single crystals of ferrite.
A method called the idgman method is used.

In this method, a ferrite raw material placed in a Rubbo is melted in an electric furnace, and then a single crystal is grown while the Rubbo is slowly moved within the furnace where there is a temperature gradient, and then cooled and solidified. The internal structure of an electric furnace for crystal growth employed in the production of ferrite single crystals by the conventional Bridgman method is as shown in FIG. That is, this electric furnace includes a heat-resistant cylindrical alumina furnace core tube 1, a heater wire 2 made of platinum-platinum rhodium (Pt-Rh) or the like wound around the furnace core tube, and The crucible is composed of an alumina protection tube 3 and a heat insulating body 4. A crucible filled with raw materials is placed in an electric furnace at room temperature, and then the electric furnace is heated to exhibit the temperature distribution shown in Fig. 2. After melting the raw material in Rubbo 5 at the top of the core tube, crystals are grown in the process of slowly descending inside the furnace core tube, which has a temperature gradient as shown in the figure, and then this electric furnace is slowly cooled to room temperature. Single crystals are produced through cycles. This manufacturing method is
Since the electric furnace may be slowly cooled in a region with a temperature gradient, there is a risk of cracks in the grown single crystal, and in order to obtain a single crystal with a diameter of 50 mm and a length of 150 mm, The above-mentioned one cycle requires about 11 days, which has the drawback of extremely low production efficiency. The present invention provides an electric furnace in which a first electric furnace for melting a raw material and growing a single crystal from the melted raw material can be coupled to and separated from a second electric furnace for slowly cooling the grown crystal. When the grown crystal is brought into the second electric furnace using such an electric furnace, the second electric furnace is separated from the first electric furnace, and then the raw material is transferred to another second electric furnace. Another charged crucible is set and connected to the first electric furnace, and the first electric furnace is used to melt a new raw material and generate crystals from the melted raw material without cooling the first electric furnace. The purpose of the present invention is to enable the growth of single crystals, thereby making it possible to efficiently use the first electric furnace to efficiently produce high-quality single crystals.

FIG. 3 shows one embodiment of the electric furnace of the present invention, and this figure shows a vertically central cross-sectional view of a state in which a first electric furnace and a second electric furnace are combined.

The present invention will be explained below with reference to FIG. The second electric furnace D is combined or separated from the first electric furnace U'.
When they are combined, the furnace core tube 6 of the first electric furnace and the furnace core tube 7 of the second electric furnace are aligned, and the heating element 8 of the former and the heating element 9 of the latter are separated by an insulating spacer 10. Installed as follows. Note that 11, 12 and 13, 14 are the first
These are the protection tube and the heat insulating body of the second electric furnace, and these are also configured so that they match each other when they are combined. 1
Reference numeral 5 denotes a crucible filled with raw materials that can move in the axial direction within the furnace core tubes 6 and 7.

The heating element 8 of the first electric furnace is formed of a substantially cylindrical solid resistor that is externally mounted on the furnace core tube 6, and spiral grooves 8a, 8 that do not intersect with each other are formed on the outer periphery of the heating element 8.
b, and when a constant current is applied through electrodes 16, 16 provided at both ends divided by this groove, heat is generated.

The cross section of this heating element perpendicular to the axial direction is made larger as it goes downward, so that it exhibits the temperature distribution shown in area A in FIG. 4 when it generates heat. The upper part of the region A has sufficient heat generation to melt the raw material in the rubbo, and as it goes downward, it exhibits a temperature program suitable for crystal growth of the melted raw material. The heating element 9 of the second electric furnace is formed of a substantially cylindrical solid resistor that is externally mounted on the furnace core tube 7, and has spiral grooves 9a, which do not intersect with each other, on its outer periphery. 9b, and electrodes 17, 17 provided at both ends divided by this groove.
The heating element 9 of the second electric furnace is substantially the same as the heating element of the first electric furnace in that it generates heat when a constant current is applied through the heating element 9, but the temperature program of the heating element 9 of the second electric furnace is the same as that of the fourth electric furnace. It is configured as shown in area B in the figure.

That is, the temperature can be made uniform at a position in the furnace core tube of the second electric furnace where the rubbo can be installed. Next, a method for efficiently manufacturing a ferrite single crystal using such an electric furnace will be explained with reference to the models shown in FIGS. 5 to 7.

The temperature of the first electric furnace U is raised only during the first single crystal production so that it exhibits the temperature distribution shown in area A in FIG. 4, and thereafter it is controlled to always exhibit this temperature distribution.

In addition, the second electric furnace D exhibits a relatively flat temperature distribution when generating heat.
,,D2 is at room temperature, and in this state, the rubbo 15 containing the monkey material is set in one of the second electric furnaces, for example, D (FIG. 5). Next, the second electric furnace D is connected to the first electric furnace U while raising its temperature, and the two are combined. Thereafter, the Rubbo 15a is raised in the first electric furnace U until it reaches its maximum temperature, and the raw material in the Rubbo 15a is completely melted. Next, the rubbo 15a is lowered in the first electric furnace U at a predetermined crystal growth rate to grow a crystal. During this time, another rubbo 15b filled with raw materials is set in the other second electric furnace D2 (FIG. 6). After the crystal in Rubbo 15a has completed crystal growth in the first electric furnace U, Rubbo 15a is further lowered to a place where the temperature distribution in the second electric furnace ○ is flat. Next, the first electric furnace U and the second electric furnace D are separated, and the second electric furnace D is slowly cooled to room temperature to take out the crystals (actually, the Rubbo 15a is placed in the second electric furnace ○,
(take it out). On the other hand, the second electric furnace U, which is separated from the second electric furnace D, has another rubbo 15b set therein.
The electric furnace D2 is combined (Fig. 7).

Next, this rubbo 15b is moved from the second electric furnace D2 to the first electric furnace U, and the temperature is further increased to the maximum temperature in the first electric furnace to completely melt the raw material in the rubbo 15b. below,
The above steps are repeated to grow r-vertical crystals. In other words, by using the electric furnace of the present invention, the furnace body, which has a temperature gradient suitable for growing single crystals, can be heated without being cooled.
Only the furnace body with a relatively flat temperature distribution is heated one after another.
Crystal growth can be performed by repeated cooling, and therefore the production efficiency can be improved to more than twice that of conventional equipment. In other words, a single crystal of the above size can be obtained in about 5 days required for crystal growth. Although the object of the present invention can be achieved by using heater wires for each heating element of the first and second electric furnaces as in the conventional device, it is difficult to obtain the desired temperature distribution when using these heater wires. In particular, there is a drawback that the heating element itself may break due to its own heat when it generates heat, and it is desirable to employ a heating element such as the one of this embodiment because it can eliminate this drawback.

[Brief explanation of the drawing]

Fig. 1 is an internal configuration diagram of the conventional device, Fig. 2 is its temperature distribution diagram, Fig. 3 is a central vertical sectional view of the electric furnace according to the present invention in a connected state, Fig. 4 is its temperature distribution diagram, and Fig. 5 is its temperature distribution diagram. 6 and 7 are explanatory diagrams of the operational status of this electric furnace. Explanation of main drawing numbers U...First electric furnace, D...Second electric furnace, 6, 7... Furnace core tube, 8, 9... Heating element. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7

Claims (1)

[Scope of Claims] 1. A first electric furnace for melting raw materials and growing crystals from the melted raw materials, and a second electric furnace for slowly cooling the grown crystals can be connected and separated, and The first electric furnace includes a furnace core tube that can move a crucible filled with raw materials in the axial direction, and a furnace core tube that is externally covered and whose temperature distribution in the axial direction is lowered toward the entrance and exit of the crucible. The second electric furnace includes a heating element capable of melting the raw material on the side opposite to the entrance/exit side, and the second electric furnace includes a furnace core tube that can move the crucible in the axial direction, and an exterior of the furnace core tube. The second electric furnace is provided with a heating element that can substantially uniform the temperature therein, and the second electric furnace is insulated so that each furnace core tube coincides with the first electric furnace, and each heating element is insulated. An electric furnace for crystal growth, which is configured to be attached as shown in FIG. 1 and separated from the first electric furnace. 2. The heating element of the first electric furnace and the heating element of the second electric furnace are both solid heating elements that are substantially cylindrical and have grooves on their circumferential sides. Electric furnace for crystal growth.