JPS5812239B2 - Method for manufacturing zirconium carbide crystals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a zirconium carbide single crystal having a uniform composition.

More specifically, the present invention relates to a method for producing a zirconium carbide single crystal having a uniform composition even at the starting and ending ends of the single crystal.

Zirconium carbide has a high melting point, high hardness, and high electrical conductivity, has a lower work function than heat-resistant metals (W, Mo, etc.), and is chemically stable, so it has recently been used as an electronic material, especially The use of single crystals as field emitter materials is being considered.

Conventionally, zirconium carbide ZrCx crystals have been produced by flux method, gas phase method, Bernoulli method, etc., but both ends of a sintered rod are supported with holders and a sintered rod is produced using a heating source such as high frequency. A method in which a part of the crystal is melted and a sintered body is moved under a pressurized inert gas atmosphere while using high frequency waves as a heating source (hereinafter referred to as the FZ method) can obtain relatively large crystals with high purity. , attempts have been made to grow ZrCx single crystals.

However, ZrCx has a very wide non-stoichiometric region (0.6
<x<1), the crystal grown by the conventional FZ method changes the composition in the length direction of the crystal rod due to the principle of the FZ method, resulting in a crystal with a uniform composition in the length direction. I couldn't get it.

Therefore, it has not been possible to determine the best composition for use as a field emitter material, and it has not been put to practical use as a field emitter material.

The present invention uses the FZ method to produce zirco carbide with a uniform composition in the longitudinal direction.
The purpose of the present invention is to provide a method for producing a single crystal of aluminum.

Another object of the present invention is to provide a method for producing a zirconium carbide single crystal that can be used as a field emitter material.

The FZ method used in the method of the present invention will be explained based on the drawings.

FIG. 1 is a conceptual diagram of an apparatus for the FZ method used in the method of the present invention.

As the apparatus, for example, a high-pressure crystal growth furnace manufactured by ADL is used.

In FIG. 1, 1 is a shaft, 2 is a holder, 3 is a sintered body rod, 4 is a ZrC crystal rod, 5 is a melt zone, and 6 is an RF coil.

The end of the sintered rod 3 with a length of 10 to 20 cm is melted by induction heating by generating high frequency from the RF coil 6 to form a melt zone 5, and the sintered rod 3 held in the holder 2 is slowly moved. to grow crystals.

At this time, the moving speed of the melting zone 5 is suitably 0.5 to 5 cm/h.

The direction of movement may be either up or down.

The atmosphere is an inert gas, usually argon, helium or a mixture thereof.

The atmospheric gas is mainly used to suppress sample evaporation and to
Used to suppress electrical discharge between coils and between coil and sample.

The pressure is usually 2 to 30 atm, preferably 5 to 20 atm.

If the pressure is lower than this, there is almost no effect of suppressing evaporation and discharge, and if the pressure is higher than this, heat loss due to convection becomes large, which is not preferable.

Zirconium carbide crystals grown under these conditions are polycrystalline up to 3 cm from the starting point, grow into a single grain in the center, and are single crystal covered with a polycrystalline outer layer at the end. .

Observation of the cleavage plane at the center, and inspection by etching and X-ray Laue methods revealed that it was a single crystal of good quality.

However, as a result of analyzing the carbon contained in the starting and ending parts of the crystal rod, it was found that there was a clear difference in the carbon content.

For example, as shown in Comparative Example 1, the composition C/Zr=0.9
The carbon content at the beginning and end of a 6 cm long crystal rod grown from the sintered body Rondo of No. 8 was 10.
54% by weight (bonded carbon 10.49% by weight), total carbon 10
．． 82% by weight (bonded carbon 10).

It was found that there was a clear difference at 77% by weight).

Furthermore, as a result of testing in the same manner using sintered compact Rondo of each composition and examining the deviation in composition of the obtained crystal rods, it was found that C
If the composition is other than around /Zr=0.83, it will be anharmonically melted (the coexisting solid phase and liquid phase have different compositions), and if the composition is anharmonically melted, the crystals will be grown using the FZ method. It was concluded that compositional fluctuation is essentially an unavoidable problem.

Therefore, the following experiment was conducted to find the correspondence between the solidus line and the liquidus line.

First, using a ZrC sintered rod with a particular composition,
A crystal rod several centimeters in length was produced using the FZ method.

The carbon content of the starting end, end, solidified melt zone, and sintered body of this crystal rod was analyzed.

From the results of this analysis, the solid phase composition of zirconium carbide and the liquid phase composition coexisting therewith were determined.

Next, the same experiment was conducted with different compositions of the sintered rods to determine the solid phase composition and the liquid phase composition coexisting with this.

FIG. 2 shows the solidus line B and liquidus line A obtained in this manner.

Point C indicates the eutectic point.

(@The degree axis is on an arbitrary scale.

) From FIG. 2, it can be seen how much the liquid phase composition should be in order to obtain a crystal with a certain composition.

For example, it was found that in order to obtain a crystal with a composition of C/Zr=0.93, the melt zone composition should be set to C/Zr=1.15.

Furthermore, the composition of the sintered body Rondo changes due to intense evaporation from the melt zone during melting.

Therefore, it is essential to change the composition of the sintered body Rondo to compensate for this.

This change in the composition of the melt zone due to evaporation can be obtained by performing the FZ method using a sintered rod of a certain composition and changing the composition of the melt zone to a liquid phase composition corresponding to the composition of the sintered rod from Figure 2. This can be determined from the changes in composition.

Specifically, for example, as shown in Comparative Example 2, C/Zr=
Using a 0.98 sintered body Rondo, the melt zone composition was set to C/Zr = 1.7 from Figure 2, and the FZ method was performed. The composition is, respectively,
The carbon content is reduced to C/Zr=0.992, 0.949, 0.928.

The composition of the melt zone also changes from 1.7 to 1.263 (the value of the solidified melt zone composition of Comparative Example 2), and the composition changes due to evaporation from the melt zone, so it is uniform. It was found that it was not possible to obtain crystal rods of the composition.

In the present invention, the composition of the supplied sintered body Rondo is such that the solid phase component of the zirconium carbide crystal to be obtained is added with a component of Zr or C that evaporates from the melting zone during melting, and the composition of the zirconium carbide crystal to be obtained is By forming a melting zone consisting of a liquid phase component coexisting with a single phase component of the zirconium carbide crystal, the conventional drawbacks could be solved.

In the present invention, the method of performing the FZ method with a melt zone composition rod present in the melt zone is as follows: (1) The sintered body rod is divided into two, the lower part is the material supplying sintered body rod, and the upper part is the melt zone. A method in which the compositional rondo is first melted to form a fusion zone, and the sintered body rondo is moved upward.

Another method is to reverse the upper and lower rondo and move them downward.

(2) Supply sintered body rondos are provided on the upper and lower sides, and a fusion zone composition rondo or a carbon plate and metal zirconium in an amount that becomes a fusion zone composition when melted are sandwiched between them, and after first melting the fusion zone portion,
A method of moving the supplied sintered body Rondo either up or down.

(3) When the normal FZ method is performed, as seen in Comparative Example 1, as the melt zone moves, the melt zone composition approaches the coexisting liquid phase composition.

Therefore, when the melting zone is moved sufficiently and the melting zone composition matches the coexisting liquid phase composition, the melting zone portion is solidified, and this is used to grow crystals of the corresponding composition by method (1).

can be mentioned.

The crystal growth conditions are similar to those in the normal FZ method.

At this time, by giving rotation to the upper and lower shafts, stirring of the melt zone can be promoted and the zone pass can be facilitated.

Since zirconium carbide has a wide non-stoichiometric region, the supplied sintered body rond used in the present invention is prepared with various compositions.

For example, a sintered body rondo having a desired composition can be produced by mixing zirconium metal or carbon for emission spectroscopic analysis with commercially available zirconium carbide powder.

The raw material purity is preferably higher, and is usually 98 weight ratio or higher, preferably 99 weight ratio or higher.

The average particle size is preferably 10 μm or less.

The shape of the sintered body Rondo is a square column (for example, 10×10
X200mm3, 15X15X100m'), a cylinder (for example, 10φxl50mm''), etc. are usually used, but any shape may be used.

As the molding method, it is preferable to use a rubber press in order to obtain a molded product with uniform density.

The molding pressure is usually 1 t/cm2. Next, the molded body is sintered.

Sintering is usually performed at 1500 to 2400°C for 0.3 to 6 hours.

The sintering atmosphere is vacuum or inert gas, and any type of sintering furnace may be used, but a high-frequency induction heating furnace is convenient.

The density of the sintered rod obtained under these conditions is 55
~75chi.

Note that it is normal for the chemical composition of the sintered body to deviate somewhat during the sintering process, so to strictly control it, it is necessary to analyze the composition of the sintered body and establish a correspondence between the blended composition and the sintered composition. is preferred.

When using the method of the present invention, there is no change in the composition of the resulting zirconium carbide single crystal at the starting end, center, and end, and a substantially uniform composition can be easily obtained, and the desired composition can be easily obtained. It has an excellent effect of producing high-quality, large-sized crystals.

Example In order to obtain a crystal rod having a composition C/Zr=0.93,
Composition C/Zr=0.98, diameter approximately 10 mm, length 15 cm
A cylindrical sintered body rond was made and this was used as a supply sintered body rond.

From FIG. 2, it can be seen that the liquid phase composition corresponding to the composition of the sintered body Rondo is C/Zr=1.15, so commercially available Zr
C/Zr2 1.15 carbon for emission spectroscopy is added to the C raw material powder.
The mixture was mixed so as to have the following properties, sintered in vacuum at 2000°C for 30 minutes, and used for forming a melt zone.

The FZ method was performed by placing the supplied sintered body rond at the bottom and the fusion zone forming sintered body rond at the top.

That is, first, a part of the sintered body Rondo for forming a melting zone was melted to generate a melting zone, and then the Rondo was slowly moved upward.

The supplied sintered body rod gradually melted into the melting zone, while crystal rods grew in the melting zone stop.

The movement speed of Rondo was 1cm/h, and the movement was carried out for about 7 hours.

Note that the rond was rotated at 10 rpm, and the atmosphere was He at 10 atm.

The bound carbon contents at the starting end, center, and end of the obtained crystal rod were 10.90, 10.87, and 10.93 by weight, respectively.

In terms of composition, C/Zr=0.932, 0.9, respectively.
27.0.932, the entire bar was of almost uniform composition.

Comparative Example 1 Using commercially available raw material powder with C/Zr=0.98, Example 1
A supply sintered body rod was prepared under the same conditions as in Example 1, and crystals were grown using the FZ method under the same conditions as in Example 1.

The bonded carbon contents at the starting end and the ending end of the obtained crystal rod with a length of 6 cm were 0.891 and 0.917, respectively.

In terms of composition, C/Zr is 0.895 and 0.921, respectively.
The composition of the solidified melt zone was C/Zr21,115.

That is, it had a non-uniform composition.

Comparative Example 2 Using a supplied sintered body Rondo with a composition of C/Zr=0.98,
The FZ method was carried out under the same conditions as in Example 1, with the melt zone composition set at C/Zr=1.7.

The bound carbon contents of the starting end, center, and end of the obtained crystal rod were 12.14, 11.14, and 10.92 by weight, respectively.

In terms of composition, C/Zr is 1.049 and 0.952, respectively.
, 0.931, and the composition of the solidified melt zone C/Zr=1
．． It was 263.

Thus, the crystal rod had a non-uniform composition.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of the FZ method, and FIG. 2 is a phase diagram of the ZrC-C system. 1 shaft, 2: holder, 3: supply sintered body rod,
4: ZrC crystal rod, 5: melting zone, 6: RF coil, A two liquidus line, B: solidus line, C two eutectic point.

Claims (1)

[Claims] 1 In a method of manufacturing a zirconium carbide single crystal by supporting both ends of a sintered body with a holder and heating it with a heating source such as a high frequency while moving the sintered body in a pressurized inert gas atmosphere, the supplied sintering process is performed. The composition of the solid iron is such that the solid phase component of the zirconium carbide crystal to be obtained is added with a component of Zr or C that evaporates from the melting zone during melting, and the composition of the zirconium carbide crystal to be obtained is added to the melting zone. A method for producing a zirconium carbide single crystal, characterized by forming a melt zone consisting of a liquid phase component coexisting with a solid phase component of the crystal.