JP3400842B2 - Method for producing cubic boron nitride - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an improved method for synthesizing cubic boron nitride from hexagonal boron nitride.

[0002]

2. Description of the Related Art Cubic boron nitride has hardness second only to diamond and chemical stability surpassing that of diamond, and demand for grinding, polishing and cutting materials is increasing. Various methods for producing cubic boron nitride have been devised, but the best known and widely used industrially are solvents (catalysts).
Hexagonal boron nitride in the presence of about 5.5 GPa, 1600
It is a method of converting into cubic boron nitride at a high temperature and high pressure of about ℃. In this case, as a solvent (catalyst), conventionally, a nitride of an alkali metal or an alkaline earth metal, or a boronitride is often used. Of these, lithium-based solvents (catalysts)
Has been thoroughly investigated, and particularly lithium nitride and lithium boronitride are considered to be effective solvents (catalysts) (see, for example, US Pat. No. 3,772,428).

[0003]

However, when the above-mentioned solvent (catalyst) is used, a sufficient yield cannot be obtained, and therefore the above-mentioned method is not yet industrially sufficiently satisfactory. In view of the above-mentioned circumstances, it is an object of the present invention to provide a method for converting cubic boron nitride from hexagonal boron nitride at a high conversion rate.

[0004]

Means for Solving the Problems The present invention which achieves the above-mentioned object is provided in the presence of one or more compounds selected from amides and imides of elements of the groups Ia and IIa of the periodic table or in the groups Ia and IIa of the periodic table. 1 selected from elemental amides and imides
More than one compound and periodic table Ia, IIa, IIIa, VIa,
In the presence of both of one or more metals selected from the group VIIa, VIII, IIb, IIIb elements, hexagonal boron nitride
There is provided a method for producing cubic boron nitride, which is characterized in that the cubic boron nitride is converted to cubic boron nitride while being maintained under a temperature and pressure condition within a stable region of cubic boron nitride.

Commercially available hexagonal boron nitride (hBN) powder can be used as the starting material, hexagonal boron nitride.
Oxygen impurities mixed in the form of boron oxide may delay the conversion of hBN to cubic boron nitride (cBN), and a raw material having a small amount of oxygen is desirable. The particle size is not particularly limited, but generally 150 mesh or less is suitable. This is because if the particle size is too large, the reactivity with the solvent (catalyst) may decrease.

[0006] The present invention, the conversion from hBN to cBN,
At least one of amides and imides of Group Ia and IIa elements
In the presence of one compound, or at least one compound selected from the group consisting of amides and imides of group Ia, IIa and Ia, II
a, IIIa, VIa, VIIa, VIII, IIb, IIIb Group 1 or more metals selected from the presence of both. It was found that the conversion rate is dramatically improved by carrying out the conversion in the presence of these compounds or in the presence of a metal with them. Generally h
It is considered that BN acts as a solvent or a catalyst that reacts with an alkali metal, an alkaline earth metal or a compound thereof to promote the reaction to cBN, and also in the amide or imide compound of the present invention or in combination with the metal. It is also believed to act as a solvent or catalyst.

In the present invention, the periodic table is of long-period type, and the elements of each group are as follows. Ia: Li, Na, K, Rb, Cs, Fr IIa: Be, Mg, Ca, Sr, Ba, Ra III a: Sc, Y, lanthanoid element (atomic number 57 to
71), actinide elements (atomic numbers 89 to 103) VIa: Cr, Mo, W VIIa: Mn, Tc, Re VIII: Fe, Co, Ni, Ru, Rh, Pd, Os, I
r, Pt IIb: Zn, Cd, Hg III b: B, Al, Ga, In, Tl Ia, IIa group amide, imide (hereinafter, simply referred to as amide, imide), Ia, IIa, IIIa, VIa,
The metal selected from the group VIIa, VIII, IIb, and IIIb elements is preferably one having a small amount of oxygen impurities as in the case of the raw material hBN, and generally, a powder of 150 mesh or less is used.

The amount of amide, imide or amide, and imide and metal used is such that the number of metal atoms constituting the additive (amide, imide or amide, imide and metal) is based on 100 parts of boron atoms constituting hBN. The total amount is 2 parts or more, and more preferably 5 to 50 parts. If the amount of the additive is less than 2 parts, a sufficiently high conversion rate to cBN cannot be obtained.
If the amount is less than the amount, it takes a long time to obtain a sufficient conversion rate. On the other hand, even if it exceeds 50 copies, the conversion rate will not improve, so
It is uneconomical and neither is preferable.

One or more compounds selected from amides and imides of the elements of group Ia and IIa and Ia, IIa, IIIa and VI
a, VII a, VIII, IIb, IIIb 1 element selected from
When used in combination with one or more metals, the ratio between them can be arbitrarily selected, but the atomic ratio of the metal elements is 95: 5 to 5: 5.
It is preferably between 5:95. If it deviates from this range, the effect of simultaneously adding the above-mentioned compound and metal will not be sufficiently exhibited, and as a result it will be difficult to obtain a sufficiently high conversion rate.

When amide and imide are used in combination with a metal, cBN can be obtained at a high conversion rate under a lower temperature and pressure as compared with the case where only amide and imide are used. As a mode in which the above-mentioned additive and the hexagonal boron nitride coexist, it suffices to mix these powders, and it is preferable that the hexagonal boron nitride layer and the additive layer are alternately laminated in the reaction vessel. It may be placed in.

In practice, after mixing hBN and amide, imide or amide, or imide and metal, or separately, molding at a pressure of about 1 to ² t / cm ² , and then filling the reaction vessel. Is preferred. This is because the handleability of the raw material powder is improved, and the amount of shrinkage in the reaction vessel is reduced, so that the productivity is improved. The reaction vessel may be any high-temperature and high-pressure generator capable of holding the raw material powder (hBN and additives) or a molded product thereof under the temperature and pressure conditions in the stable region of cBN. This stable region (temperature, pressure) is FP Bundy, RH Wentorf, J. Chem. Phys.
8 (5), pp. 1144-1149 (1963). Generally, a temperature and pressure with a lower limit of 1100 ° C. and 3.8 GPa are effective, but the additive (solvent, catalyst) Depending on the type and combination, 1100 ℃,
It is possible to convert to cBN even at 3.8 GPa or less. The holding time is not particularly limited and may be until the desired conversion rate is achieved, but it is generally about 1 second to 6 hours.

By holding in the above stable region, hB
N is converted to cBN, and it is possible to obtain a conversion rate close to 100% by making the temperature and pressure conditions extremely high, but generally, a synthetic mass composed of a mixture of hBN and cBN is obtained. Crush the synthetic mass and isolate cBN. As the isolation method, the method described in JP-B-49-27757 can be used. For example, after crushing the synthetic mass to 5 mm or less, preferably 1 mm or less, sodium hydroxide and a small amount of water are added. When heated to about 300 ° C., hBN is selectively dissolved. Therefore, after cooling this, cBN is obtained by washing with acid and filtering. If the metal used as the additive remains, it can be removed using hydrochloric acid, nitric acid, or the like.

[0013]

Example 1 A hexagonal boron nitride having a grain size of 150 mesh or less and containing 0.8% by weight of oxygen as impurities and 0.2% by weight of metal impurities other than alkali metals and alkaline earth metals constitutes the same compound. 20 parts of lithium amide as an atomic ratio of lithium was added to and mixed with 100 parts of boron atoms. 26mmφ × 32mm with pressure of 1.5 ton / cm ²
The molded body of h was housed in the reaction container shown in FIG.

In the reaction container shown in FIG. 1, the outer wall 1 of the container is used.
Is made into a cylindrical shape by pyrophyllite as a pressure transfer body, inside which a heater 2 made of a graphite cylinder and a pyrophyllite 8 as a partition material are arranged.
Further, a current-carrying steel ring 3 and a current-carrying steel plate 4 are respectively arranged on the upper and lower ends of the container, and a sintered alumina plate 5 and a pyrophyllite 6 as a pressure transmitting body are arranged on the inner side thereof. A space surrounded by the pyrophyllite 6 and the pyrophyllite 8 as a partition material is a storage chamber 7 for storing the reaction raw material.

In this reaction vessel, the above-mentioned molded body was subjected to 4.5 GPa.
It was treated at 1400 ° C. for 10 minutes. This sample was crushed in a mortar, and the conversion ratio from the intensity ratio of the diffraction lines of cubic boron nitride (111) and hexagonal boron nitride (002) to CuKα rays to cubic boron nitride was measured using an X-ray powder diffractometer. Was 84%.

Samples crushed to a size of 1 mm or less in a mortar, etc.
Cubic boron nitride was isolated by adding sodium hydroxide and a small amount of water, heating to 300 ° C., cooling, washing and filtering with distilled water, hydrochloric acid, etc., and drying the filtered residue. Purification). Example 2 Hexagonal boron nitride was added to 20 parts by weight of magnesium amide as an atomic ratio of magnesium with respect to 100 parts as boron atoms constituting the same compound, and cubic boron nitride was synthesized and evaluated in the same manner as in Example 1. As a result, the conversion rate to cubic boron nitride was 88%.

Example 3 Hexagonal boron nitride was added in an amount of 20 parts by weight of calcium amide as an atomic ratio of calcium to 100 parts by weight of boron atoms constituting the same compound, and cubic boron nitride was added in the same manner as in Example 1. When synthesized and evaluated, the conversion rate to cubic boron nitride was 82%.

Example 4 Hexagonal boron nitride was added in the same manner as in Example 1 except that 20 parts of lithium imide was added as an atomic ratio of lithium to 100 parts of boron atoms constituting the same compound. When synthesized and evaluated, the conversion rate to cubic boron nitride was 83%.

Example 5 Hexagonal boron nitride was added in an amount of 20 parts by weight of magnesium imide as an atomic ratio of magnesium to 100 parts by weight of boron atoms constituting the same compound, and cubic boron nitride was added in the same manner as in Example 1. When synthesized and evaluated, the conversion rate to cubic boron nitride was 85%.

Example 6 Hexagonal boron nitride was added in an amount of 20 parts by weight of calcium imide in an atomic ratio of calcium to 100 parts by weight of boron atoms constituting the same compound, and cubic boron nitride was added in the same manner as in Example 1. When synthesized and evaluated, the conversion rate to cubic boron nitride was 85%.

Example 7 As in Example 1, hexagonal boron nitride was added in an amount of 10 parts each of lithium amide and magnesium amide as an atomic ratio of lithium and magnesium to 100 parts of boron atom constituting the same compound. When cubic boron nitride was synthesized and evaluated in the above manner, the conversion rate to cubic boron nitride was 93%.

Comparative Example 1 Hexagonal boron nitride was added in an amount of 20 parts by weight of lithium nitride in an atomic ratio of lithium to 100 parts by weight of boron atoms constituting the same compound, and cubic boron nitride was added in the same manner as in Example 1. When synthesized and evaluated, the conversion rate to cubic boron nitride was 7%.

Comparative Example 2 Hexagonal boron nitride was added in the same manner as in Example 1 except that 20 parts of lithium boronitride was added in an atomic ratio of lithium to 100 parts of boron atoms constituting the same compound. When was synthesized and evaluated, the conversion rate to cubic boron nitride was 14%.

Comparative Example 3 Hexagonal boron nitride was added to 20 parts by weight of Mg in an atomic ratio of 100 parts as boron atoms constituting the same compound, and cubic boron nitride was synthesized and evaluated in the same manner as in Example 1. As a result, the conversion rate to cubic boron nitride was 54%. Example 8 100 parts of hexagonal boron nitride containing 0.8% by weight of oxygen as impurities and 0.2% by weight of metal impurities as boron atoms constituting the same compound, and 10 parts of lithium amide as an atomic ratio of lithium, 1 as the atomic ratio of magnesium
0 part was weighed and mixed. This was molded into a compact of 26 mmφ × 32 mmh at a pressure of 1.5 ton / cm ² and was housed in the reaction vessel shown in FIG. 1 in the same manner as in Example 1.

In this reaction vessel, the above-mentioned molded body was placed at 4.0 GPa.
It was treated at 1200 ° C. for 10 minutes. This sample was crushed in a mortar and converted into cubic boron nitride by an X-ray powder diffractometer using the intensity ratio of the diffraction lines of cubic boron nitride (111) and hexagonal boron nitride (002) to CuKα rays. The rate was 96%.

Example 9 100 parts of hexagonal boron nitride as a boron atom constituting the same compound, 10 parts of lithium amide as an atomic ratio of lithium and 10 parts of lithium as an atomic ratio were weighed and mixed. When cubic boron nitride was synthesized and evaluated using this in the same manner as in Example 8, the conversion rate to cubic boron nitride was 73%.

Example 10 100 parts of hexagonal boron nitride as a boron atom constituting the same compound, 10 parts of lithium amide as an atomic ratio of lithium and 10 parts of chromium as an atomic ratio were weighed and mixed. Using this, a cubic boron nitride was synthesized and evaluated in the same manner as in Example 8. As a result, the conversion rate to cubic boron nitride was 80%.

Example 11 100 parts of hexagonal boron nitride as a boron atom constituting the same compound, 10 parts of lithium amide as an atomic ratio of lithium and 10 parts of manganese as an atomic ratio were weighed and mixed. When cubic boron nitride was synthesized and evaluated using this in the same manner as in Example 8, the conversion rate to cubic boron nitride was 81%.

Example 12 100 parts of hexagonal boron nitride as a boron atom constituting the same compound, 10 parts of lithium amide as an atomic ratio of lithium and 10 parts of iron as an atomic ratio were weighed and mixed. Using this, a cubic boron nitride was synthesized in the same manner as in Example 8,
When evaluated, the conversion rate to cubic boron nitride is 79%.
Met.

Example 13 100 parts of hexagonal boron nitride as a boron atom constituting the same compound, 10 parts of lithium amide as an atomic ratio of lithium, and 10 parts of cobalt as an atomic ratio were weighed and mixed. Using this, a cubic boron nitride was synthesized and evaluated in the same manner as in Example 8. As a result, the conversion rate to cubic boron nitride was 80%.

Example 14 100 parts of hexagonal boron nitride as a boron atom constituting the same compound, 10 parts of lithium amide as an atomic ratio of lithium and 10 parts of nickel as an atomic ratio were weighed and mixed. When cubic boron nitride was synthesized and evaluated using this in the same manner as in Example 8, the conversion rate to cubic boron nitride was 88%.

Example 15 100 parts of hexagonal boron nitride as a boron atom constituting the same compound, 10 parts of lithium amide as an atomic ratio of lithium and 10 parts of zinc as an atomic ratio were weighed and mixed.
Using this, a cubic boron nitride was synthesized and evaluated in the same manner as in Example 8. The conversion rate to cubic boron nitride was 8
It was 5%.

Example 16 100 parts of hexagonal boron nitride as a boron atom constituting the same compound, 10 parts of lithium amide as an atomic ratio of lithium, and 10 parts of aluminum as an atomic ratio were weighed and mixed. Using this, a cubic boron nitride was synthesized and evaluated in the same manner as in Example 8. As a result, the conversion rate to cubic boron nitride was 72%.

Example 17 100 parts of hexagonal boron nitride as a boron atom constituting the same compound, 10 parts of lithium amide as an atomic ratio of lithium and 10 parts of lanthanum as an atomic ratio were weighed and mixed. When cubic boron nitride was synthesized and evaluated using this in the same manner as in Example 8, the conversion rate to cubic boron nitride was 76%.

Example 18 100 parts of hexagonal boron nitride as a boron atom constituting the same compound, 10 parts of lithium amide as an atomic ratio of lithium, and 10 parts of cerium as an atomic ratio were weighed and mixed. Using this, a cubic boron nitride was synthesized and evaluated in the same manner as in Example 8. As a result, the conversion rate to cubic boron nitride was 77%.

Example 19 100 parts of hexagonal boron nitride as a boron atom constituting the same compound, 10 parts of lithium amide as an atomic ratio of lithium and 10 parts of praseodymium as an atomic ratio were weighed and mixed. When cubic boron nitride was synthesized and evaluated using this in the same manner as in Example 8, the conversion rate to cubic boron nitride was 78%.

Example 20 100 parts of hexagonal boron nitride as a boron atom constituting the same compound, 10 parts of lithium amide as an atomic ratio of lithium and 10 parts of neodymium as an atomic ratio were weighed and mixed. Using this, a cubic boron nitride was synthesized and evaluated in the same manner as in Example 8. As a result, the conversion rate to cubic boron nitride was 77%.

Example 21 100 parts of hexagonal boron nitride as a boron atom constituting the same compound, 10 parts of lithium amide as an atomic ratio of lithium, and 10 parts of samarium as an atomic ratio were weighed and mixed. When cubic boron nitride was synthesized and evaluated using this in the same manner as in Example 8, the conversion rate to cubic boron nitride was 76%.

Example 22 100 parts of hexagonal boron nitride as a boron atom constituting the same compound, 10 parts of lithium amide as an atomic ratio of lithium, and 10 parts of gadolinium as an atomic ratio were weighed and mixed. When cubic boron nitride was synthesized and evaluated using this in the same manner as in Example 8, the conversion rate to cubic boron nitride was 76%.

Example 23 100 parts of hexagonal boron nitride as a boron atom constituting the same compound, 10 parts of lithium amide as an atomic ratio of lithium, 10 parts of magnesium as an atomic ratio, and 5 parts of nickel as an atomic ratio. It was taken and mixed. When cubic boron nitride was synthesized and evaluated using this in the same manner as in Example 8, the conversion rate to cubic boron nitride was 95%.

Example 24 100 parts of hexagonal boron nitride as a boron atom constituting the same compound, 10 parts of lithium amide as an atomic ratio of lithium, 10 parts of magnesium amide as an atomic ratio of magnesium, and manganese as an atomic ratio. 5 parts were weighed and mixed. When cubic boron nitride was synthesized and evaluated using this in the same manner as in Example 8, the conversion rate to cubic boron nitride was 86%.

Example 25 100 parts of hexagonal boron nitride as a boron atom constituting the same compound, 10 parts of lithium imide as an atomic ratio of lithium, and 10 parts of magnesium as an atomic ratio were weighed and mixed. Using this, a cubic boron nitride was synthesized and evaluated in the same manner as in Example 8. As a result, the conversion rate to cubic boron nitride was 74%.

Comparative Example 4 100 parts of hexagonal boron nitride as a boron atom constituting the same compound and 10 parts of lithium nitride as an atomic ratio of lithium were weighed and mixed. Using this, a cubic boron nitride was synthesized and evaluated in the same manner as in Example 8. As a result, the conversion rate to cubic boron nitride was 0%.

Comparative Example 5 100 parts of hexagonal boron nitride as a boron atom constituting the same compound and 10 parts of lithium boronitride as an atomic ratio of lithium were weighed out and mixed. Using this, a cubic boron nitride was synthesized and evaluated in the same manner as in Example 8. As a result, the conversion rate to cubic boron nitride was 0%.

Comparative Example 6 100 parts of hexagonal boron nitride as a boron atom constituting the same compound and 10 parts of magnesium as an atomic ratio were weighed and mixed. Using this, a cubic boron nitride was synthesized and evaluated in the same manner as in Example 8. As a result, the conversion rate to cubic boron nitride was 0%.

[0046]

According to the present invention, in the method for synthesizing cubic boron nitride using hexagonal boron nitride as a raw material, the conversion rate can be significantly improved.

[Brief description of drawings]

1 shows a cross section of a reaction vessel used to convert hBN to cBN in the examples.

[Explanation of symbols]

1 ... Container outer wall 2 ... heater 6,8 ... Pyrophyllite 7 ... accommodation room

Continuation of front page (56) Reference JP-A-59-92974 (JP, A) JP-A-62-108716 (JP, A) JP-A-62-289230 (JP, A) JP-A-48-55900 (JP , A) JP-A-4-126541 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B01J 3/06 C04B 35/583

Claims (2)

(57) [Claims] 1. Maintaining hexagonal boron nitride in the presence of one or more compounds selected from amides and imides of elements of groups Ia and IIa of the periodic table under temperature and pressure conditions within the stable region of cubic boron nitride. Then, a method for producing cubic boron nitride, which comprises converting to cubic boron nitride. 2. A periodic table Ia, IIa and at least one compound selected from amides and imides of elements of group Ia and periodic table Ia, II.
a, IIIa, VIa, VIIa, VIII, IIb, IIIb elements, at least one metal selected from hexagonal boron nitride in the presence of both, the temperature and pressure in the stable region of cubic boron nitride A method for producing cubic boron nitride, which is characterized in that the cubic boron nitride is converted to cubic boron nitride while being held under the conditions.