JPS5957996A - Manufacture of niobium carbide crystal body - Google Patents

Abstract

PURPOSE:To obtain an NbC crystal body having a uniform composition by adding a component corresponding to Nb or C which is evaporated from a melt zone during melting to the solid phase component of an NbC crystal to be manufactured to prepare the composition of a rod of a sintered body to be fed and by forming a melt zone of a liq. phase component coexisting with the solid phase component of the NbC crystal to be manufactured at the melt zone section. CONSTITUTION:Both ends of a rod 3 of a sintered body is supported by holders 2, and an NbC crystal body is manufactured by heating the rod 3 with a heating source 6 such as a high frequency heating source in an inert gaseous atmosphere under pressure while moving the rod 3. The composition of the rod 3 is composed of the solid phase component of an NbC crystal to be manufactured and a component corresponding to Nb or C which is evaporated from a melt zone 5 during melting, and a melt zone of a liq. phase component coexisting with the solid phase component of the NbC crystal to be manufactured is formed at the melt zone section.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a niobium carbide crystal having a uniform composition. More specifically, the present invention relates to a method for producing a niobium carbide crystal having a uniform composition even at the starting end and the terminal end (t)11 of the crystal. .

Niobium carbide has a high melting point, high hardness, and high air conductivity, and its work function is lower than that of heat-resistant metals (W, Mo, etc.), and it is chemically stable. from,
Recently, the use of crystalline materials as electronic materials and special field emitter materials has been investigated.

Conventionally, niobium carbide (NbCx) crystals have been produced using the Flacne method, vapor phase method, and Norasma method. A method in which a part of the sintered rod is melted and the sintered rod is moved in a pressurized inert gas atmosphere while using high frequency waves or the like as a heating source (hereinafter referred to as the FZ method) is a high-purity and relatively large-scale method. Since crystals can be obtained, attempts have been made to grow NbCX crystals.

However, NbCXTt has a very wide non-stoichiometric region (0
, 7 < It was not possible to obtain crystals with a uniform composition. Therefore, it has not been possible to determine the best composition for using Cγ+'F 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 niobium carbide crystals having a uniform composition by the I='Z method.

The method of the present invention (the FZ method used here) will be explained based on the drawings.

FIG. 1 is a conceptual diagram of an apparatus for the FZ method using the method of the present invention. For example, a high-pressure crystal growth furnace manufactured by AlJL is used as the apparatus. In Fig. 1, j3 is the shaft, 2 is the boulder, and 23 is the sintered rod.
4 is NbC crystal 47k, 5 is a melt zone, and 6 is a 1F coil.

The end of the sintered rod 3 having a length of 10 to 20α is melted by induction heating at °C 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 wlb. The moving direction may be any direction below L. An inert gas is used as the atmosphere, usually Norgon, Heliun, or a mixture thereof. The atmospheric gas is used mainly to suppress triggering of the sample and to suppress discharge between the RF co-coil and between the coil and the sample.It is usually 2 to 30 atmospheres, preferably 5 to 20 atmospheres. 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.

(The composition of the melt zone has the desired composition.) The composition of the liquid phase that coexists with the crystal is determined from the phase diagram and determined as that composition.

At that time, this material has a high melting point and evaporates rapidly, so either an initial melting zone is formed in an instant, or carbon (or Niobium) evaporates, so it is necessary to add carbon (or niobium) to the tip of the supply rod by the amount of evaporation to cancel out the composition change due to evaporation of C1 carbon (or niobium).Also, the composition of the supply rod is Feed rods with various compositions are used, and each time the melt zone composition is used as the liquid phase composition to feed F under predetermined conditions.
The composition of the supply rod may be determined from the crystal composition obtained by carrying out the Z method.

In the present invention, a melting zone composition rod is present in the melting zone section described in +iiJ. (added carbon or niobium in advance),
+-: Set the fusion zone composition rod to sr+, firstly, the upper t, i
11! A method in which a band composition rod is exposed to a bath to generate a melting zone, and the sintered body opening and closing point are moved in this direction.

Another method is 1-, where the opening of the C is reversed and the C is moved downward.

+21 111G supply sintered compact rod is provided, and between them (
After melting the melting zone #11 +1v, rod or the amount of carbon 1i- or niobium that will make the melting zone composition when melted, and melting the melting zone #11 +1v, put the supplied sintered compact rod under either of L. Direction (Movement +1 (How to make IJ.

(8) If the normal ISZ method is used, the zone will move (
Eventually, the melt zone composition approaches the coexisting liquid phase composition. Therefore, the melting zone is moved by 1 minute, and when the melting zone composition matches the coexisting liquid phase by +t JJy, the melting zone is solidified, and this is used to strain -114G by the method (1). , a method of forming a melt zone and growing a crystal with a corresponding composition.

Conditions for crystal growth are listed in section 7 above. By applying two rotations of the throat G, agitation of the melting zone can be promoted and zone bathing can be facilitated.

Since niobium carbide has a wide non-stoichiometric region, the supply sintered rods used in the present invention are prepared in various types with t, +1 composition. For example, a sintered rod can be made by mixing commercially available niobium carbide powder (niobium metal or carbon for emission spectroscopy).The higher the purity of the raw material, the better, and usually 98 weight 11
% or more], preferably 99% or more. It is preferable that the average particle size is 10 tt or more.

The shape of the sintered rod is a rectangular column (for example, 10 x 10
200 m4.15X15Xi00J), a cylinder (for example, 10φx150 J); As a first step method, it is preferable to use a rubber press in order to obtain a molded product with uniform acoustic intensity. The molding pressure is usually 1 t/i.

Next, the molded body is sintered. Sintering is usually 1500-2400
C. for 0.3 to 6 hours. The sintering atmosphere is vacuum,
The sintering is performed using an 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 45-75%
Furthermore, it is normal for the chemical composition of the sintered body to deviate somewhat during the sintering process, so in order to strictly control it, it is necessary to analyze the composition of the sintered body and check the correspondence between the blended composition and the sintered composition. A niobium carbide crystal grown under such conditions, where it is preferable to leave the crystal with C, is polycrystalline at 1 cm'i from the starting point, but beyond that it grows into one dalein, and at the end, it grows into a single crystal. It is a crystal. Observation of the cleavage plane at the center, and inspection using the X-ray method and X-ray Lawe method revealed that it was a high quality single crystal.The impurities that can damage this material are 1! (+
In comparison, it was found that because of its high vapor pressure, it is purified through evaporation during growth.

The method of the present invention exhibits its true value when applied to the growth of crystals having compositions other than those exhibiting the highest melting point. NbC-
7. Figure 2 shows part of the phase diagram of the C system. To explain this in terms of the conventional method, a melt zone is formed using a feed rod having a composition of Xl (this requires raising the temperature to a temperature of T).

On the other hand, according to the method of the present invention, the composition of the part forming the melt zone is X of the liquid phase composition coexisting with the melt zone.
A melt zone can be formed at a temperature of 1. Specifically, in the conventional method, it was safe to raise the temperature to nearly 3600°C, but with the method of the present invention, a melting zone can be sufficiently formed at a temperature of 3300°C.
At a temperature above 00℃, raise the temperature to 300℃ or higher (this requires a lot of energy and the discharge wire
However, the method of the present invention does not cause such problems.

In addition, according to the method of the present invention, since the composition does not change during the melting and 11F transition, the heating and IC power 11i are small, which increases the woman's lAJ' and band transfer ability, resulting in high-quality crystals. You get a body. Moreover, there is no change in the composition of the resulting niobium carbide crystal at the starting end, center, and end, and it is easy to obtain a material having a substantially uniform composition. It has an excellent effect of obtaining crystals.

<Example 2> In order to grow a single crystal with an arbitrary uniform composition in the entire composition range of NbCx (0,7<x<1), it is necessary to find the compositional relationship between the crystal and the melt zone. Must be.

The composition of the 41st melt zone is as described above (page 4).
This can be determined based on the phase diagram that has already been reported. On the other hand, the composition of the sintered body was determined from the relationship (FIG. 3) by examining the crystal composition of 'C obtained in a steady state using sintered rods having compositions of 4 and 11.

NbC...+5. NbCo, s7. NbCo7
The s crystal rod was grown based on the phase diagram and Figure 3. The growth conditions were Pll = 10 atm F, growth rate 1.25 cm.
/h, L Fshi1. The speed was 8 times per minute in the opposite direction.

b) When growing NbC1195 crystal bales, the initial melt zone composition is C/Nb key 1.2, and the sintered body composition is C/Nb
= L, 17. A: The crystal rod that was separated was made up of a constant portion of 1.

) NbCo, s7 crystal rods were grown in the same way, with the initial fusion zone set to C/Nb key 0.99, and the sintered rod composition set to C/Nb.
= 0.96 - [, conducted. The composition of the obtained crystal is c/Nb at the beginning, center, and end, respectively.
= o, s 74. o, s 74. The composition was constant: o, s73. .

C) The crystal rod growth of NbCo7s is carried out in the melting zone.
[The composition was set to 0.7 in C/Nb, and the sintering 4.9 composition was set to C/Nb.
Nl)-〇, 73. Obtained crystal rod starting end I6;
Then, a crystal rod with a constant C/Nb=0.752.0.755 was obtained at the final part.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of the FZ method, and FIG. 2 is a part of the Nb-C phase diagram. 1: Shaft, 2: Holter, 3: Supply sintered rod, 4: NbC crystal pellet, 5:
Melting zone, 6: it F coil, A:
liquidus line, 13: solidus line, C: eutectic point. Figure 3 shows the composition of the sintered rod and the steady state f7Q from the sintered body.
11) shows the relationship with the crystal composition. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] (1,) Support both ends of the sintered rod with holders,
A method of producing a niobium carbide crystal by moving the sintered body in a pressurized inert gas atmosphere F and heating it with a heating source such as a high frequency. The solid phase component of the niobium carbide crystal to be obtained is added with the component of niobium or carbon that evaporates from the melting zone during melting, and the melting zone G is the internal phase of the crystal of niobium carbide to be obtained. A method for producing niobium carbide crystals, characterized by forming a melt zone consisting of a liquid phase component coexisting with other components.