JPH0232237B2 - CHITANTANCHITSUKABUTSUNOTANKETSUSHONOSEIZOHO - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for producing a single crystal of titanium carbonitride. Titanium carbonitride has a high melting point of titanium carbide (3100
It is a material that combines the characteristics of high hardness (Vickers hardness: 3000Kg/mm ² ) with the high melting point (2950℃) and high toughness of titanium nitride, and is used as a cermet for various cutting tools, wear-resistant parts, etc. It is put into practical use. Since its work function is lower than that of heat-resistant metals (W, Mo, etc.) and it is chemically stable, this single crystal is promising as an electronic material, especially as a field emitter material. Prior Art The following method is known as a method for producing crystals of titanium carbonitride (TiC _X N _Y ). (1) A solid phase reaction method in which a mixed powder of TiC and TiN is heated to high temperature in an inert atmosphere. (2) A gas phase reaction method in which TiCl ₄ , hydrocarbons, and nitrogen gas are transported using hydrogen or other carrier gas, and thermally decomposed on a high-temperature substrate to precipitate titanium carbonitride. However, the solid phase reaction method (1) is a powder synthesis method, and has the drawback that only polycrystalline products can be obtained. (2)
Although acicular or columnar crystals can be obtained using the gas phase reaction method, the crystals are very small and have the disadvantage that they cannot be used for purposes other than polycrystalline films. As described above, production of a single crystal of titanium carbonitride has heretofore been practically impossible. OBJECTS OF THE INVENTION The object of the present invention is to provide a method for producing large-sized, high-quality titanium carbonitride single crystals that could not be obtained using conventional methods. Another object of the present invention is to provide a method for producing a titanium carbonitride single crystal that can be used as a field emitter material. Structure of the Invention In order to achieve the above object, the present inventors attempted to grow a single crystal of titanium carbonitride by a floating zone method (hereinafter abbreviated as FZ method). However, if the FZ method is simply carried out using a sintered body rod of titanium carbonitride, the evaporation of nitrogen and/or titanium nitride will be intense, and the target
It was not possible to grow a single crystal of TiC _X N _Y composition. In order to solve this problem, we conducted further research and found that by appropriately controlling the composition of the rod of the supplied sintered body, the composition of the melt, and the partial pressure of nitrogen gas in the atmosphere, single crystals of titanium carbonitride can also be grown. I was able to find out what could be done. The present invention was completed based on this knowledge. Summary of the Invention A method for growing a single crystal by supporting a sintered rod with a holder and moving the sintered rod while heating and melting a part of the rod in a pressurized inert gas atmosphere. The composition of the melting zone is obtained by changing the composition of the body rod to a composition in which nitrogen and carbon components that evaporate from the melting zone are added to the solid phase components of the titanium carbonitride crystal to be obtained. The composition of the liquid phase component coexisting with the solid phase component of the titanium carbonitride crystal, and a total pressure of 2 to 100, having a nitrogen gas partial pressure of 0.1 to 10 times the equilibrium dissociation pressure of the titanium carbonitride.
A method for producing a single crystal of titanium carbonitride, which is characterized by growing a crystal by forming a molten zone in a pressurized atmosphere of an inert gas at atmospheric pressure. The FZ method used in the method of the present invention will be explained based on the drawings. Figure 1 is a conceptual diagram of the FZ method equipment. As the device, for example, a high-pressure type crystal growth furnace manufactured by ADL is used. In FIG. 1, 1 is a shaft, 2 is a holder, 3 is a sintered rod, 4 is a crystal rod, 5 is a melt zone, and 6 is an RF coil. For example, the end of sintered rod 3 with a length of 10 to 20 cm
A high frequency is generated from the RF coil 6 to cause induction heating and melting to form a melt zone 5, and the sintered rod 3 held in the holder 2 is slowly moved to grow the crystal. At this time, the moving speed of fusion zone 5 is 0.5 to 5
cm/h is appropriate. 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 evaporation of the sample and to suppress electrical discharge between the RF coil and between the coil and the sample. Gas pressure is usually 2~
The pressure is 100 atmospheres, preferably 5 to 50 atmospheres. If the pressure is lower than 2 atm, there is almost no effect of suppressing evaporation and discharge, and if it is higher than 100 atm, heat loss due to convection increases, which is not preferable. Furthermore, helium is more effective than argon in suppressing discharge between the coils and between the coil and the sintered body rod. This is thought to be because the ionization potential of helium is higher than that of argon. However, even if the FZ method was simply performed using a sintered rod of titanium carbonitride, the desired single crystal of TiC _X N _Y composition could not be obtained. Therefore, the following experiment was conducted to find the correspondence between the solidus line and the liquidus line, and the correspondence between the liquid phase composition and the gas phase composition. First, under pressure of a nitrogen and helium mixed gas having a predetermined nitrogen gas partial pressure, the composition was determined.
Using _{a TiC}
Make a crystal rod, and define the starting and ending parts of this crystal rod,
The carbon content and nitrogen content of the solidified melt zone and sintered body were analyzed. Through this analysis, the solid phase composition of titanium carbonitride and the liquid phase composition coexisting therewith were determined. In addition, similar experiments were carried out by changing the composition of the sintered rod, and the solid phase composition and liquid phase composition coexisting therewith were determined. Furthermore, the gas phase composition inside the furnace was analyzed. next,
Similar experiments were carried out by varying the partial pressure of nitrogen gas, and the correspondence between the liquid phase composition and the coexisting solid phase composition and gas phase composition was investigated. As a result, the crystal composition differs from that of the supplied sintered rod due to evaporation from the melt zone during melting, so the composition of the supplied sintered rod is determined by the solid phase of the titanium carbonitride crystal to be obtained. It is necessary to add nitrogen and carbon components that evaporate from the melting zone during melting, and the composition of the melting zone must be such that it coexists with the solid phase components of the titanium carbonitride crystal to be obtained. It has been found that it is necessary to have a composition of liquid phase components that Furthermore, it has been found that controlling the gas composition and nitrogen gas partial pressure in the atmosphere is important in growing single crystals of titanium carbonitride. In other words, the nitrogen gas partial pressure is equal to the equilibrium dissociation pressure (calculated value) of titanium carbonitride.
It has been found that single crystals can be obtained only when the total pressure is 0.1 to 10 times higher and the total pressure is 2 to 100 atm, preferably 5 to 50 atm. The equilibrium dissociation pressure of titanium carbonitride is calculated by the following formula based on the phase equilibrium of the TiC _X N _Y +C (solid) + _N2 (gas) system. RTln (X/Y・K _N /K _C・(P _N2 ) ^1/2 ) = ΔG゜_f,TiN −ΔG゜_f,TiC However, R: Gas constant T: Absolute temperature K _N : Nitrogen partition coefficient K _C : Carbon partition coefficient P _N2 : Nitrogen gas partial pressure ΔG゜_{f, TiN} : Standard free energy of formation of TiN (liquid) ΔG゜_{f, TiC} : Standard free energy of formation of TiC (liquid). When the nitrogen gas partial pressure is less than 0.1 times the equilibrium dissociation pressure, the evaporation of nitrogen from the melt zone is intense, and not only is the amount of nitrogen dissolved in solid solution in the crystal small;
(Approximately 10% of the nitrogen content of the sintered rod) Cracks occur, making it difficult to grow single crystals. If the pressure exceeds 10 times the equilibrium dissociation pressure, insoluble precipitates will form on the surface of the melting zone, making it difficult to move the sintered rod while heating and melting it, making it impossible to obtain a single crystal. FIG. 2 shows the relationship between the composition of the single crystal to be obtained in the present invention and the nitrogen partial pressure. The shaded area in the figure is the required nitrogen gas partial pressure. Furthermore, if the total pressure is lower than 2 atmospheres, titanium carbonitride evaporates rapidly, and the evaporated material adheres to the coil, causing discharge and making it difficult to grow a single crystal. Furthermore, when the total pressure exceeds 100 atmospheres, heat loss due to convection increases. 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 rod is divided into two parts, the sintered rod to be supplied is in the lower part, and the melt zone composition is in the upper part. First, the upper melt zone composition rod is melted to form a melt zone,
A method of moving the sintered rod upward.
Another method is to reverse the upper and lower rods and move them downward. (2) Supply sintered body rods are provided on the upper and lower sides, and a melt zone composition rod or titanium carbide, titanium nitride, carbon plate, and metal titanium plate in an amount that will give a melt zone composition are sandwiched between them, and the melt zone portion is first melted. , a method in which the supplied sintered body rod is moved either up or down. (3) When the normal FZ method is performed, as the melt zone moves, the composition of the melt zone approaches the composition of the coexisting liquid phase. Therefore, when the melting zone is moved sufficiently and the melting zone composition matches the coexisting liquid phase composition, the melting zone is solidified, and this is used to grow crystals of the corresponding composition by method (1). can be mentioned. During crystal growth, rotation is applied to the upper and lower shafts to promote agitation of the melt zone and facilitate zone passing. The supply sintered body rod used in the present invention is
It can be made by mixing titanium metal and carbon with commercially available titanium carbide and titanium nitride powders. The higher the purity of the raw material, the better, usually 98% by weight.
Above, preferably 99% by weight or more. The average particle size is preferably 10 μm or less. The shape of the sintered rod is a prism (for example, 10×10×
200mm ³ , 15×15×100mm ³ , cylinder (for example, 10φ×
150 mm ³ or the like is usually used, but any shape may be used. As a molding method, in order to obtain a molded product with uniform density,
Preferably, a rubber press is used. The molding pressure is usually 1 t/cm ² . 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 performed in a vacuum or inert gas atmosphere, 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 55-75%. Example 1 Commercially available TiC powder (total carbon 19.45% by weight, free carbon 0.05% by weight) and TiN powder (nitrogen 21.1% by weight)
After mixing in the specified ratio, the diameter is 10mmφ and the length is 150mm.
Two cylinders of mm and 50 mm were rubber press molded.
This was sintered in vacuum at 2000°C for 30 minutes. The composition of the obtained sintered body was TiC _0.08 N _0.09 . Next, based on the results of preliminary experiments, carbon for emission analysis was mixed with the TiC powder and TiN powder,
A sintered body rod for forming a melt zone having a TiC _1.10 N _0.01 composition was produced by sintering in the same manner as described above. Two sintered rods having the TiC _0.88 N _0.09 composition were supported by a holder, and a TiC _1.10 N _0.01 composition was sandwiched between them. The equilibrium dissociation pressure was calculated to be 0.18 atm, so the total pressure
Under pressure of a nitrogen-helium mixed gas of 10 atmospheres and P _{N 2} 0.55 atmospheres, the sintered body rod for forming a melt zone was melted to form a melt zone, and the upper and lower rods were slowly moved downward. The rotation speed is 5 rpm, and the movement speed is
33 mm/hr and 25 mm/hr. As a result, the upper rod melted into the melt zone, while a titanium carbonitride single crystal was grown in the lower part. The composition analysis of the starting end, center, and end of the single crystal obtained was as shown in Table 1.

[Table] As shown by this result, a homogeneous single crystal with a composition of TiC _0.86 N _{N 0.05} was obtained. Example 2 Composition of supplied sintered rod, TiC _0.87 N _0.10 Composition of sintered rod for forming melting zone, TiC _1.13 N _0.005 Nitrogen partial pressure P _N2 0.20 atm Total pressure 10 atm Same as Example 1 Single crystals were grown. A homogeneous and high-quality single crystal with a TiC _0.88 N _0.02 composition as shown in Table 1 was obtained. Example 3 Composition of sintered rod to be supplied, TiC _0.69 N _0.27 Composition of sintered rod for forming melt zone, TiC _0.66 N _0.06 Nitrogen partial pressure P _N2 5 atm Total pressure 30 atm under the conditions of Example 1 and Single crystals were grown in the same manner. A single crystal with a composition of TiC _0.71 N _0.18 as shown in Table 1 was obtained. Effects of the Invention According to the method of the present invention, an excellent effect of obtaining a large, high-quality single crystal with a uniform composition, which could not be obtained by conventional methods, can be achieved. In addition, a single crystal that can be used as a field emitter material can be provided.

[Brief explanation of drawings]

Figure 1 shows the floating zone method (FZ method)
FIG. 2 shows a relationship diagram between the composition of a desired single crystal of titanium carbonitride and the nitrogen partial pressure required for crystal growth. 1: Shaft, 2: Holder, 3: Sintered rod, 4: TiC _X N _Y crystal rod, 5: Melting zone, 6: High frequency induction heating coil.

Claims (1)

[Claims] 1. A method of growing a single crystal by supporting a sintered rod with a holder and moving the sintered rod while heating and melting a part of the sintered rod under a pressurized inert gas atmosphere. The composition of the titanium carbonitride crystal to be obtained is determined by adding nitrogen and carbon components that evaporate from the melting zone during melting to the solid phase components of the titanium carbonitride crystal to be obtained. A total pressure 2 having a composition of a liquid phase component coexisting with a solid phase component of the carbonitride crystal, and having a nitrogen gas partial pressure of 0.1 to 10 times the equilibrium dissociation pressure of the titanium carbonitride.
A method for producing a single crystal of titanium carbonitride, which is characterized by growing a crystal by forming a molten zone in an inert gas pressurized atmosphere of ~100 atmospheres.