JPS606914B2 - Method for producing tantalum carbide crystals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing tantalum carbide crystals having a uniform composition.

More specifically, the present invention relates to a method for producing a tantalum carbide crystal having a uniform composition even in the starting end and the final weave of the crystal. Tantalum 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 crystals as field emitter materials is being considered.

Furthermore, because this substance exhibits a golden color due to its composition (C/Ta>0.9), it can be expected to be used as a decorative item. Tantalum carbide (TaCx) crystals are produced by the flux method, gas phase method, plasma method, etc., but the crystals are produced by supporting both ends of a compaction rod with a holder and using a heating source such as a high frequency to condense it. A method (hereinafter referred to as the FZ method) in which a part of the body rod is melted and the sintered body rod is moved in a pressurized inert gas atmosphere using a heating source such as high frequency waves (hereinafter referred to as the FZ method) produces high-purity and relatively large crystals. Since ra
Attempts have been made to grow Cx crystals.

However, TaCx has a very wide non-stoichiometric region (0.7
<x<1), crystals grown by the conventional FZ method are
The composition in the length direction of the crystal rod changed, and it was not possible to obtain a crystal with a uniform composition in the length direction.

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 provides a method for producing tantalum carbide crystals having a uniform composition by the FZ method.

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 Figure 1, 1' shaft ~
2 is a holder, 3 is a bran solid rod, 4 is a TaC crystal rod, 5 is a melting zone, and 6 is an RF coil. Length 10 to 20
The end of the cm sintered rod 3 is melted by induction heating by generating high frequency from an RF coil 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 10 c/h. The direction of movement may be either up or down. An inert gas is used as the atmosphere, usually argon, helium, or a mixture thereof. The pressure is usually 2 to 3 p atm, preferably 5 to 2 p atm.If the pressure is lower than this, there will be little effect on suppressing evaporation and discharge, and if the pressure is higher than this, heat loss due to convection will occur. This is not preferable because it increases the size of the crystal.The composition of the fusion zone is determined by determining the liquid phase composition that coexists with crystals having the desired composition from a phase diagram.

At that time, this material has a high melting point and "carbon evaporates so intensely that it forms an initial melting zone in an instant, or carbon from the tie rods on both sides of the initial melting zone evaporates by the time it forms." , it is necessary to negate the change in composition due to evaporation of carbon by adding carbon by the amount of evaporation and attaching the composition to the tip of the supply rod. A TaC single crystal having a constant composition can be obtained by preventing the composition change due to the large amount of carbon present.
In addition, the composition of the supply rod uses supply rods with various compositions,
In each case, perform the FZ method using the melt zone composition as the liquid phase composition,
The composition of the supply rod may be selected based on the crystal composition obtained. In the present invention, the method of performing the FZ method with a melting zone composition rod present in the melting zone is as follows: {1} The sintered rod is divided into two parts, and the raw material supplying solid rod (first carbon is added) is placed in the lower part of the sintered rod. A method in which a melting zone composition rod is placed at the top (adding an appropriate amount), and the melting zone composition rod at the top is first melted to generate a melting zone, and the dawn concretion rod is moved upward.

Another method is to reverse the upper and lower rods and move them downward. '2} Provide the supply sintered body rods on the upper and lower sides, sandwich the melt zone composition rod or the amount of carbon plate and metal tantalum that will become the melt zone composition when melted, first melt the melt zone part, and then supply the sintered body. A method of moving the rod either up or down.

(3) When the normal FZ method is carried out, as the melt zone moves, the composition of the melt zone approaches the composition of the coexisting liquid phase.

Therefore, when the molten zone is moved sufficiently and the fusion zone composition matches the coexisting liquid phase composition, the fusion zone is solidified, and this is used to instantly form a fusion zone using the method of {1). A method for growing crystals having a composition such as The crystal growth conditions are such that by giving rotation to the upper and lower shafts, it is possible to promote the candle worship of the fusion zone and facilitate the zone pass.

Since tantalum carbide has a wide non-stoichiometric region, the feed sintered rods used in the present invention are prepared in various compositions.

For example, a sintered rod having a desired composition can be produced by mixing tantalum metal or carbon for emission spectroscopy with commercially available tantalum carbide powder. The higher the purity of the raw material, the better, and it is usually at least 9% by weight, preferably at least 9% by weight. The average particle size is preferably 10 or less. The shape of the cord body rod is a square column (for example, 10 x 10 x 20 x 3, 15 x 15 x low x 3)
)" A cylinder (for example, IOC x 15 columns) is usually used, but any shape may be used.

As for 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 lt/
It is. Next, the molded body is sintered.

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

The sintering is carried out under a vacuum or inert gas atmosphere, and any type of sintering furnace may be used, but a high-frequency fusion heating furnace is convenient. The density of the rod is between 45% and 75%.It is normal for the chemical composition of the Akatsuki body to deviate to some extent during the sintering process, so in order to strictly control it, the composition of the sintered body should be analyzed and the compound composition It is preferable to have a correspondence between the sintering composition and the tantalum carbide crystal.Tantalum carbide crystals grown under these conditions are polycrystalline from the end of the grain to one skin, but beyond that, they are a single grain. The terminal portion is a single crystal.

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. Furthermore, it was found that the impurities contained in this substance were purified by evaporation during growth because their vapor pressure was higher than that of this substance.

The method of the present invention exhibits its true value when applied to the growth of crystals having a composition other than the composition exhibiting the highest melting point.

To explain based on Figure 2, which shows part of the phase diagram of the TaC-C system, according to the subordinate method, in order to form a melt zone using a feed rod with a composition of x, it is necessary to reach a temperature of L. It is necessary to raise the temperature. On the other hand, according to the method of the present invention, since the composition of the part forming the melt zone is x2 of the liquid phase composition coexisting therewith, the melt zone can be formed at a temperature of T.

Specifically, in the conventional method, it was necessary to raise the temperature to nearly 400,000, but with the method of the present invention, it was necessary to raise the temperature to 3,400 to 3,400.
A melting zone can be sufficiently formed at a temperature of 3500 oo. In this way, at a temperature of 30,000○ or more, an additional 500
Raising the temperature above oo requires a lot of energy and causes problems such as discharge and other problems, but the method of the present invention does not cause such problems. Also,
According to the method of the present invention, since the composition does not change during the movement of the melting zone, the adjustment of the heating power is small, and the movement of the melting zone becomes more stable, so that a high-quality crystal can be obtained.

In addition, there is no change in the composition of the resulting tantalum carbide crystal at the end, center, or end, and it is easy to obtain a material with a substantially uniform composition. It has an excellent effect of producing crystals. Example In order to obtain a crystal rod having a composition of C/Ta=0.95, the composition must be constantly changed to C/Ta=1 during the fusion zone movement.
．． It is necessary to keep it close to one hill.

Therefore, in order to obtain a predetermined composition from the time of initial melting zone formation, a graphite disk of approximately 0.1 hour was inserted between the upper and lower dawn structures, and that portion was melted to form a melting zone. However, the composition near the fusion zone of the feeding rays has changed significantly by the time it is formed due to carbon evaporation. Therefore, a melting zone was formed by the above method using supply rods of each composition, and the melting zone was moved at a speed of 1.5 cm/h. The starting end and the ending end of the obtained crystal rod were analyzed for composition, and the relationship shown in FIG. 3 was obtained. Due to this, C
To obtain a crystal strand of /Ta=0.95, the starting end of the feeding strand should be C/Ta=2.0, and the remaining part should be C/Ta=1.4.
I realized what I needed to do. By using a dawning rod whose composition had been changed only at the tip, with a carbon disc sandwiched between them, growth was carried out under the same conditions as before: PHe = 1 pressure, 1.5 skins/h.

There is no free carbon in the obtained crystal comb, and the supplied carbon at the starting, central, and terminal ends is 5.94 and 5.94, respectively.
．． The compositions were 97 and 6.0% by weight, and C/Ta=0.946, 0.951, and 0.955, respectively. Furthermore, as a result of analyzing the periphery and center of the crystalline
/Ta=0.952, 0.957, and it was found that the entire crystalline obtained had an almost uniform composition.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of the FZ method, and FIG. 2 is a part of the phase diagram of the HfC-C system. 1: shaft, 2: holder, 3: supply sintered rod,
4: TaC crystalline, 5: melting zone, 6: RF coil, A: liquidus line, B: solidus line, C: eutectic point. Figure 3 shows a supply rod single crystal (
(starting end, end end) composition relationship is shown. ○: Starting end ○: Ending end black (solid areas indicate free carbon was observed). Younger brother” Zutsumu 2 Zutsumu 3

Claims (1)

[Claims] 1. In a method of manufacturing tantalum carbide crystals by supporting both ends of a sintered body rod with a holder and heating it with a heat source while moving the sintered body rod under a pressurized inert gas atmosphere, the supply sintered body rod is The composition is the solid phase component of the tantalum carbide crystal to be obtained, plus tantalum or carbon components generated from the melt zone during melting, and the composition of the supplied sintered body rod is added to the solid phase component of the tantalum carbide crystal to be obtained. A sintered body composition containing as much carbon as is evaporated at the start of melting is attached, and a melting zone of a liquid phase component coexisting with a solid phase component of the tantalum carbide crystal to be obtained is installed in the melting zone. 1. A method for producing tantalum carbide crystals, characterized by forming tantalum carbide crystals.