JPS60131811A - Synthesis method of boron nitride - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed description of the invention (a) Technical field Cubic boron nitride (hereinafter referred to as Cl5N) has a hardness second only to diamond, and is widely used as an artificially synthesized abrasive grain for grinding iron-based materials. It is being Recently, synthesis technology has advanced and single crystal powders of 2o/go US mesh size can now be synthesized.

The advantage of CBN over diamond is that it is less reactive with ferrous metals. Single crystal diamonds weighing more than 1 carat and having a diameter of 6 mm or more have already been successfully synthesized under ultra-high pressure. In recent years, the demand for ultra-precision machining technology has increased, and tools using diamond single crystals are widely used, but as mentioned above, these ultra-precision machining tools cannot be performed due to their reactivity with iron-based materials. However, there was a desire to develop a tool material to replace diamond.

The present invention relates to a method for synthesizing large CBN single crystals with good reproducibility, which can also be used for such applications.

(b) Prior art and its problems CBNO synthesis usually uses hexagonal boron nitride (hereinafter referred to as hBN) as a raw material, and uses alkali metals, alkaline earth metals, or their nitrides as catalysts at ultra-high pressures and high temperatures. It is done under 1. Commonly used catalysts are Li, Mg
, ca, Li3N, Mg4N2, Ca3
It is N2 grade. During synthesis, a mixture of hBN and these catalyst materials is filled into a container, placed in an ultra-high pressure apparatus, and heated and pressurized to the stable region of CBN shown in FIG. In such a method, natural nucleation of CIIIN occurs and a large number of fine CBN single crystals are obtained. Single crystals of powdered CB and N up to a 20/80 US mesh size, that is, about 0.7 mm, are produced industrially.

Historically, attempts have been made to grow large single crystals. For example, in JP-A-57-156899, the solvent "'C-S
'r3112N4 + B a B B 2 CBNO by 1111 degree difference method using CBN with seed crystal binding
An example of single crystal growth is shown.

An example of single crystal growth using the temperature difference method under ultra-high pressure is already widely known for diamond. (For example, USP3,
297,407) In the case of CBN, boron nitride is used as a raw material, and if there is a solvent that dissolves it appropriately, it is possible to grow large single crystals by taking advantage of changes in solubility due to temperature differences. A number of experiments were carried out using seed crystals with a diameter of 0.7 mm placed in a low-temperature area, but no satisfactory results were obtained. The biggest problem is that in most cases, the seed crystal is dissolved in the solvent first, resulting in the production of a large number of CBNs due to spontaneous nucleation, making it impossible to obtain large, high-quality single crystals.

(/→Constitution of the Invention In the growth of CBN single crystals, it was found that prevention of dissolution of the seed crystal was a major problem, so various measures were taken to save the seed crystal. For example, in JP-A-57-156399, the seed crystal Fe-, 10% hlj alloy thin plate is coated with S to prevent melting
A method is adopted in which the r B B 2 N 4 is inserted between the aqueous medium and the CBN seed crystal. However, even with this method, dissolution of the seed crystal could not be completely prevented. This seems to be because the Fe-J alloy has solubility in CBN.

The dissolution of the seed crystal is thought to be due to the heating of the system under ultra-high pressure and the solvent dissolving the saturated concentration of boron nitride before CBN growth begins on the seed crystal. From this point of view, the principle of the present invention is to prevent dissolution of the seed crystal CBN by adding boron nitride to the solvent in advance, in addition to the seed crystal, at a concentration below the predicted saturation concentration under the synthesis temperature and pressure conditions. It is. By using this method, dissolution of the seed crystal can be almost prevented by using a solvent pre-contained with an appropriate amount of boron nitride, and it is possible to grow a large CIIN single crystal only from the seed crystal. It became.

This method is very simple and gives highly reproducible results. The nitrided #llI raw material used in the present invention is hBN.
, CBN, WBN (wurtzite boron nitride? or amorphous boron nitride, etc.) The crystal form does not matter.

However, choose one with the highest purity possible. In the experiment, CB
Good results were obtained when using a mixture of N or CBN and I+RN.

As solvent substances, boronitrides of alkali metals or alkaline earth metals, each represented by M-38N or riML112N4, can be used. Especially Li3BN2,
Ca3B2N4.

The eutectic composition of each solvent with boron nitride should be below.

If it exceeds this range, CBN will precipitate into the solvent. In most cases, when the amount added was less than 0.5 molt, clear dissolution of the seed crystals was observed.

This will be explained in more detail below with reference to Examples.

Example C 1 CBN powder with an average particle size of about 50 μm and I+BN powder were mixed in a weight ratio of 1:1 and pressed. L+3BN
2 powder fchBN powder 0*0.5*I, B*6t
8) A mixed powder containing v% was prepared. 4 in Figure 2
A CBN seed crystal with a diameter of about 0.7 ttun, a solvent, raw materials CIIIN, and an hBNO embossing body were placed in a 14-piece sample chamber. This was placed in a Velsito type loading pressure device and heated and pressurized at 53 Kb to bring the temperature of the raw material section to 1650° C., and after maintaining this condition for 24 hours, it was taken out. bBN addition amount of 0 or 8 molti of solvents are all 1g of diameter.
The following CBN was produced, and in the case where the amount of hBN added was 0, the seed crystals were dissolved. In other cases, CBN single crystals with a diameter of about 8 am were grown from seed crystals.

Example 2 Using Ca3B2N4 and Mg3B2N4 as solvents, 11BN was added in the same manner as in Example 1 to prepare a sample. Other conditions were the same as in Example 1, and the CaBB2N4-based aqueous medium was 531 (b, the temperature of the raw material part was 1600°C, the Mg3B2N4
In the case of a system aquatic medium, it is the same at 51 Kb (the conditions were set at 1600°C and held for 24116 hours. As a result, 1+BN
Seed crystals disappeared in all solvents to which CBN was not added, and CBN was formed at the bottom of the solvent.

Example 3 Ll 3BN2, S r3B2N4, h BN
were mixed at a cell ratio of 645:32.3:3.2 to prepare a solvent. CBN powder is used as the raw material boron nitride,
Further, a CBN single crystal with a diameter of 0.7 mm was used as a seed crystal. When kept at a pressure of 52 Kb and a temperature of 1550°C for 24 hours, C with a good morphology of about 3 mg in diameter was formed only on the seed crystal.
A BN single crystal was growing.

[Brief explanation of the drawing]

FIG. 1 is a temperature and pressure phase diagram of boron nitride for explaining the CBN single crystal synthesis conditions of the present invention. The second boron stability region is shown. l: Pyrofluorite Nureep 2: Graphite heater 3: Nitriding? 1ljll Raw material 4: Solvent 5: CBN seed crystal 6: Platinum bed bed 7: hBN sintered body 8: Ta container

Claims (1)

[Claims] (1) Using boron nitride as a raw material, alkali metal MaBN2
Boron nitride expressed in the form, cubic crystal nitride using an oil medium containing 0.5 mole or more of boron nitride mixed or dissolved in an amount less than the eutectic composition of alkaline earth metal boronitride. Using a single crystal of boron as a seed crystal, the bulk of the raw material boron nitride and the bulk of the solvent substance are brought into contact under pressure and temperature conditions where cubic boron nitride is stable and the entire system is maintained at a temperature above the melting point of the solvent substance. The seed crystal is placed in contact with the solvent substance at a position away from the contact surface, and the cubic crystal is placed on the seed crystal while keeping the temperature of the seed crystal part relatively lower than the temperature of the contact point between the raw material and the solvent substance. A method for synthesizing #jl nitride to grow type boron nitride.