KR100636415B1 - Manufacturing method of cubic boron nitride - Google Patents

Abstract

The present invention relates to hexagonal boron nitride under stable temperature and pressure range conditions of cubic boron nitride in the presence of at least one compound selected from amides, imides, and carbides of alkali and alkaline earth metals as well as silicon and / or boron sources. It relates to a conversion method for converting to cubic boron nitride.

Description

Method for producing cubic boron nitride

The present invention relates to an improved manufacturing method for producing cubic boron nitride (cBN) from hexagonal boron nitride (hBN).

Since cubic boron nitride has a second hardness after diamond in terms of hardness and is very chemically stable, its importance is gradually recognized in grinding, polishing and cutting of materials. In the method for producing cubic boron nitride, various methods have been proposed, but a known production method which is widely used industrially is a method of producing cubic boron nitride in a solvent (catalyst) at a high temperature of 1400 to 1600 ° C. and about 4.5 to 6.0 GPa. It converts into cubic boron nitride under high pressure. Known solvents (catalysts) well known in this process are known, for example, boron nitride and nitrides of alkali metals and alkaline earth metals, as in US Pat. No. 3,772,428.

Nevertheless, the cubic boron nitride obtained by using the solvent (catalyst) has low toughness and heat resistance, so that the exposure to high temperatures causes a significant decrease in the strength of the abrasive powder or the grinding of the abrasive powder. In addition, the cubic boron nitride obtained using the solvent (catalyst) is irregularly shaped or almost spherical and vulnerable to the development of a self-shaped surface.

The present invention relates to an improved process for producing cubic boron nitride from hexagonal boron nitride.

The present invention to solve the above problems, (1) in the presence of (i) at least one compound selected from the group consisting of carbides, amides, imides of alkali metals and alkaline earth metals, and (ii) in the presence of a silicon source, Or (2) at least one compound selected from the group consisting of (i) amides of alkali metals and alkaline earth metals, imides, (ii) carbides of alkali metals and alkaline earth metals, and ( iii) at least one compound selected from the group consisting of (i) carbides, amides, imides of (i) alkali metals and alkaline earth metals in the presence of a boron source, and (ii) silicon sources and (iii) boron Converting hexagonal boron nitride to cubic boron nitride while maintaining the hexagonal boron nitride in the presence of a circle under stable temperature and pressure range conditions of the cubic boron nitride It relates to a method for producing cubic boron nitride.

(1) The cubic boron nitride of the present invention obtained in the presence of (i) at least one compound selected from the group consisting of carbides, amides, and imides of alkali metals and alkaline earth metals and (ii) silicon sources is characterized by toughness and heat resistance. This is improved. (2) at least one compound selected from the group consisting of (i) amides of alkali metals and alkaline earth metals, imides, and (ii) carbides of alkali metals and alkaline earth metals, and (iii ) The cubic boron nitride of the present invention obtained in the presence of a boron source has a sharp edges due to the development of its shape and excellent cutting ability. (3) the cubic crystal of the present invention obtained in the presence of (i) at least one compound selected from the group consisting of carbides, amides, and imides of alkali and alkaline earth metals, (ii) silicon sources and (iii) boron sources Boron nitride not only improves cutting performance but also improves both toughness and heat resistance.

Hexagonal boron nitride used as a starting material may be used commercially available hexagonal boron nitride powder. Oxygen impurities incorporated in the form of boron oxide or the like delay the conversion from hexagonal boron nitride to cubic boron nitride, and therefore a raw material with low oxygen content is desired. The hexagonal boron nitride of the present invention is not particularly limited in particle size, but is preferably 150 mesh or less. If the particle size is too large, the reactivity with the solvent (catalyst) may be low.

Amides, imides, and carbides of alkali metals and alkaline earth metals are also preferably low in oxygen, like hexagonal boron nitride used as starting materials. The particle size is not particularly limited, but generally 1 mm or less is preferred. If the particle size of these compounds is too large, the reactivity with hexagonal boron nitride becomes low.

Amides and imides of alkali metals and alkaline earth metals used in the present invention are basically

LiNH ₂ , NaNH ₂ , KNH ₂ , RbNH ₂ , CsNH ₂ ,

Li ₂ NH, Na ₂ NH, K ₂ NH, Rb ₂ NH, Cs ₂ NH,

Be (NH ₂ ) ₂ , Mg (NH ₂ ) ₂ , Ca (NH ₂ ) ₂ , Sr (NH ₂ ) ₂ , Ba (NH ₂ ) ₂ ,

BeNH, MgNH, CaNH, SrNH, BaNH, etc.

Carbide of alkali metal and alkaline earth metal used in the present invention is basically

Li ₂ C ₂ , Na ₂ C ₂ , K ₂ C ₂ , Rb ₂ C ₂ , Cs ₂ C ₂ ,

Be ₂ C, BeC ₂ , MgC ₂ , Mg ₂ C ₃ , CaC ₂ , SrC ₂ , BaC ₂ , and the like.

However, similar effects can also be obtained by using solid solutions, complexes, and nonstoichiometric compounds of these compounds.

The silicon and boron sources used in the present invention are Si, B ₄ Si, Si ₃ N ₄ , B, B ₄ C, SiC, metal silicides, metal silicofluorolides, metal silicohydrides, metal silicon nitrides, organic Silicon compounds, metal borosilicates, metal borohydrolides, metal borohydrides, ammonium borohydrolides, ammonium silolipolides, and the like.

Preferred carbides, amides and imides of alkali metals and alkaline earth metals are carbides, amides and imides of lithium, magnesium and calcium. Carbides, amides, and imides of alkali metals and alkaline earth metals other than lithium, magnesium, and calcium are cubic crystals of hexagonal boron nitride at higher temperatures and higher pressures than those of lithium, magnesium, or calcium carbides, amides, and imides. Can be converted to boron nitride. Cubic boron nitride obtained by using carbides, amides and imides of lithium, magnesium or calcium is much superior in terms of grinding ratio and required grinding power than those obtained by other amides, imides or carbides.

Preferred combinations of amides of alkali metals and alkaline earth metals, at least one first compound of imides with at least one second compound of alkali metals and alkaline earth metal carbides, include amides of lithium, magnesium and / or calcium and / or Or a combination of one or more of imides and one or more of lithium, magnesium and / or calcium carbide. When amides, imides, and carbides of alkali and alkaline earth metals other than lithium, magnesium, and calcium are converted from hBN to cBN, they are converted only at higher temperatures and higher pressures for amides or imides of lithium, magnesium, or calcium. Can be. CBN, which can be obtained using amides, imides or carbides of alkali and alkaline earth metals other than lithium, magnesium and calcium, has a higher grinding ratio and required than that obtained by amides, imides or carbides of lithium, magnesium or calcium. Grinding force is somewhat inferior

A particularly preferred combination is a combination of LiNH ₂ and CaC ₂ . Since this combination can obtain cubic boron nitride having excellent transparency and few defects, it is possible to obtain cubic boron nitride having very excellent properties by the silicon source and the boron source under relatively low temperature and low pressure.

Preferred silicon and boron sources are Si and B. This is easy to handle, easy to purchase, and high in reactivity, and thus can produce a desired effect even in a relatively short reaction time.

The present invention provides a composition comprising (1) at least one compound selected from amides, imides and carbides of (i) alkali metals and alkaline earth metals, and (ii) in the presence of a silicon source or (2) (i) alkali metals and At least one compound selected from amides of alkaline earth metals, imides, and at least one compound selected from (ii) carbides of alkali metals and alkaline earth metals, and (iii) in the presence of a boron source, or (3 (i) at least one compound selected from amides, imides and carbides of alkali metals and alkaline earth metals, and (ii) from silicon and (iii) from boron. . According to the preparation method of the present invention, hBN can be converted to cBN having excellent toughness and heat resistance as well as well-developed shape and sharp edges as a result of the solvent (catalyst) effect of the compound.

In general, it is understood that hBN reacts with various additives and acts as a solvent or a catalyst so that the conversion of cBn proceeds, and likewise, the present invention also acts in the same manner.

The amount of at least one compound selected from amides, imides, or carbides of alkali metals and alkaline earth metals used in the present invention is a metal atom constituting the additive with respect to 100 parts of boron atoms constituting hBN (number of hBN molecules). The total number of is 0.1-30 parts, More preferably, it is 0.5-20 parts. If the amount of the additive is less than 0.1 part, the effect of such an additive cannot be sufficiently exerted, and the cBN production is reduced. If the amount of the additive exceeds 30 parts, the obtained cBN includes a mammal consisting of several components of the additive, thereby reducing the polishing performance.

The ratio of at least one compound selected from carbides of alkali metals and alkaline earth metals to at least one compound selected from amides and imides of alkali metals and alkaline earth metals is 70 as the atomic ratio of the metal elements constituting each compound. : 30-5: 95, More preferably, it is 50: 50-5: 95.

If the ratio of at least one compound selected from carbides of alkali metals and alkaline earth metals to at least one compound selected from amides and imides of alkali metals and alkaline earth metals is greater than 70:30, the resulting cubic crystal Black mammals are formed in boron nitride to reduce the polishing performance. If the ratio is 5:95 or less, the solvent (catalyst) effect of one compound selected from amides and imides of alkali metals and alkaline earth metals is too high, resulting in irregular cubic boron nitride particles. The polishing performance is also lowered.

The amount of the silicon source is preferably 0.01 to 0.8 parts of silicon atoms, more preferably 0.025 to 0.3 parts with respect to 100 parts of hexagonal boron nitride molecules. If the addition amount of the silicon source is less than 0.01 part, the addition effect of the silicon source cannot be sufficiently exerted, and if it exceeds 0.8 part, the yield of cubic boron nitride is reduced.

The amount of the boron source is preferably from 0.05 to 15 parts of boron atoms, more preferably from 0.1 to 5 parts with respect to 100 parts of hexagonal boron nitride molecules. If the addition amount of the boron source is less than 0.05 part, the addition effect of the boron source cannot be sufficiently exhibited. If the addition ratio of the boron source is more than 15 parts, the yield of cubic boron nitride is reduced.

As a preferred method of combining the above additives and hexagonal boron nitride, these powders may be mixed together or arranged so that the layers of hexagonal boron nitride and the additives are alternately stacked in the reaction vessel.

In practice, the hBN and the additives are preferably filled separately or in a reaction vessel and then filled at a pressure of about 1-2 t / cm ² . This has the effect of improving the ease of handling of the crude powder and at the same time improving the productivity by reducing the amount of shrinkage in the reaction vessel.

The granules of cubic boron nitride may be previously bonded to the molded body or the laminate as a seed, and as a nucleus, the added fine cBN particles may promote crystal growth of cubic boron nitride. Such an implementation is included in the present invention. In this case, the seed particles may be applied with additives of the carbides, amides and / or imides of the present invention.

The reaction vessel is a high temperature, high pressure generator capable of holding crude powders (hBNs and additives) or their molded bodies under temperature and pressure conditions in the stabilization range of cBN. This stabilization (temperature and pressure) range is described in P. Bundy, RH Wentorf, J. Chem. Phys., 38 (5), 1144-1149, (1963), and in most cases minimum temperatures and pressures of 1100 ° C. and 3. 8 GPa are effective, but this is not the case with additives (solvent, catalyst) It may vary depending on the type and combination. The holding time is not particularly limited and in most cases, about 1 second to 6 hours in order to achieve a desired conversion rate.

hBN is converted to cBN by maintaining the above stabilization range, and if the temperature and pressure conditions are very high, a conversion rate of nearly 100% can be obtained. In general, however, synthetic ingots comprising a mixture of hBN and cBN are obtained.

The synthetic ingots are ground and separated into cBN. The separation method used is described in Japanese Patent Laid-Open No. 49-27757, for example, after pulverizing the synthetic ingot to 5 mm or less, preferably 1 mm or less, sodium hydroxide and a small amount of water are added and about 300 After heating at a temperature of < RTI ID = 0.0 > C, < / RTI >

EXAMPLE

Various additives or elements in the amounts shown in the table below in hexagonal boron nitride, which is 0.2% by weight of metallic impurities, 0.8% by weight of oxygen and particles of 150 mesh or less as impurities other than alkali metals and alkaline earth metals. Metal was added. The amount of the additive shown in the table represents the ratio of the total number of metal atoms constituting the added additive or elemental metal to 100 parts of the number of hexagonal boron nitride. This mixture was adjusted to a pressure of 1.5 ton / cm ² in the reaction vessel shown in FIG. 1 to prepare a 26 mm x 32 mmh molded body.

In the reaction vessel shown in Fig. 1, the outer wall 1 of the vessel is made of plecides as a voltage element and is cylindrical, and inside it is provided a heater 2 composed of graphite cylinders and a plecides 8 as a diaphragm material. Further, conductive steel rings 3 and conductive steel plates 4 are provided at the ends of the upper and lower portions of the container, respectively, and sintered alumina plates 5 and chloroplast 6 as voltage bodies are provided therein. The space enclosed by the sinter rock 6 and the sinter rock 8 as a diaphragm is used as a holding compartment 7 for receiving the reaction raw materials.

In this reaction vessel, the molded product shown above was treated for 10 minutes under the conditions shown in the table.

Cubic boron nitride is a mortar or the like, and the specimen prepared by grinding up to about 1 mm or less is added with sodium hydroxide and a small amount of water, heated at 300 ° C., cooled, washed with distilled water and hydrochloric acid, filtered, and then filtered. It can isolate | separate (purify) by drying.

The cubic boron nitride thus obtained was adjusted to 120/140 based on JIS-B 4130, and the "toughness index" and "thermal toughness indes" were measured.

"Toughness index" means a certain amount of sample and one steel ring that pass through a 139 μm sieve specified in correspondence with the granule powder 120/140 and remain in a 107 μm sieve in a 2 ml volumetric capsule for a fixed time (30.0 ± 0.3 sec.) After grinding, screen the screen with a specified 90μm sieve to display the remaining weight of the sample on this sieve as a fraction of 100.

The term “heating toughness index” was measured in the same manner as the toughness index except that the sample was calcined at 1050 ° C. in air for 1 hour, washed with dilute hydrochloric acid, and dried.

The higher the measured toughness index, the higher the toughness of the ground powder, and the higher the measured toughness index, the higher the heat resistance of the ground powder.

Using the hexagonal boron nitride thus obtained, a grinding wheel bonded by vitreous was made. This grinding wheel has the following composition and appearance.

Particle size of cBN # 120/140

Concentration 100 (25% Grinding Wheel Ratio)

Porosity 30% by volume

Bonding rate 25% by volume

Filler (White Alundum WA # 200) 30%

Appearance of grinding wheel 205 mmø and 5 mmU 76.2H

Cubic boron nitride was mixed with borosilicate glass and filler, molded into a shape of about 5 mm × 3 mm × 30 mm and fired for 10 hours at a temperature of 1050 ° C. in air. The fired body was bonded to the outer surface of the aluminum wheel to prepare a grinding wheel.

Grinding tests on the resulting grinding wheel were carried out using a planar grinding machine under the following conditions:

Wet Flat Cross Grinding

Peripheral speed of grinding wheel 1500 m / min

Table speed 15 m / min

Feed rate 2 mm / pass

Setting depth 20 μm

Grinding Material SKH-51

The grinding ratios (grinding / grinding wear) and the power used here were measured and shown in the table below.

A portion of the obtained converted ingot was crushed in mortar and the rotation of cubic boron nitride (111) and hexagonal boron nitride (002) using CuK α-rays using an X-ray power diffraction instrument. The conversion rate to cubic boron nitride was obtained from the line intensity ratio.

table

According to the present invention, hexagonal boron nitride can be converted into cubic boron nitride having an excellent shape.

1 is a cross-sectional view of a reaction vessel used when converting hexagonal boron nitride to cubic boron nitride in an embodiment.

<Description of Signs of Major Parts of Drawings>

1: outer wall of container 2: heater

3: steel ring 4: steel plate

5: alumina plate 6, 8: lamellar

7: storage room

Claims (16)

(1) at least one compound selected from the group consisting of (i) carbides, amides and imides of alkali and alkaline earth metals and (ii) in the presence of a silicon source, or (2) at least one compound selected from the group consisting of (i) amides and imides of alkali metals and alkaline earth metals, (ii) at least one compound selected from the group consisting of carbides of alkali metals and alkaline earth metals, and (iii ) In the presence of a boron source, or (3) in the presence of at least one compound selected from the group consisting of (i) carbides, amides and imides of alkali and alkaline earth metals, (ii) silicon sources and (iii) boron sources, While maintaining the hexagonal boron nitride under conditions where the cubic boron nitride is stable at a temperature and pressure range, A method for producing cubic boron nitride, characterized by converting hexagonal boron nitride into cubic boron nitride. 2. The conversion according to claim 1, wherein the conversion is performed in the presence of (i) at least one compound selected from the group consisting of carbides, amides and imides of alkali and alkaline earth metals and (ii) silicon sources. Method for producing phosphorus cubic boron nitride. The method of claim 1, wherein the conversion is selected from the group consisting of (i) at least one compound selected from amides and imides of alkali metals and alkaline earth metals, and (ii) carbides of alkali metals and alkaline earth metals. A process for producing cubic boron nitride, characterized in that it is carried out in the presence of at least one compound and (iii) a boron source. The method according to claim 1, wherein the conversion is performed by (i) at least one compound selected from the group consisting of carbides, amides and imides of alkali metals and alkaline earth metals, (ii) silicon sources and (iii) boron sources. Method for producing cubic boron nitride, characterized in that carried out in the presence. The total number of metal atoms constituting the at least one compound selected from the above amides, imides, and carbides with respect to the number of hexagonal boron nitride molecules is 0.1-30. Method for producing cubic boron nitride characterized in that it is used in an amount to be added. The total number of metal atoms constituting the at least one compound selected from the above amides, imides, and carbides is 0.5 to 20 with respect to 100 parts of hexagonal boron nitride molecules. Method for producing cubic boron nitride characterized in that it is used in an amount to be added. The method of claim 1, wherein the ratio of the at least one carbide to the at least one amide, the imide, or a combination thereof is 70:30 to 5:95 based on the total number of metal atoms constituting the compound. Method for producing cubic boron nitride characterized in that. The method according to claim 7, wherein the ratio of the at least one carbide to the at least one amide, the imide, or a combination thereof is 50:50 to 5:95 based on the total number of metal atoms constituting the compound. Method for producing cubic boron nitride characterized in that. The method for producing cubic boron nitride according to claim 1, wherein the silicon source is used in an amount such that the total number of silicon atoms constituting the silicon source is 0.01 to 0.8 parts with respect to 100 parts of hexagonal boron nitride molecules. The method for producing cubic boron nitride according to claim 9, wherein the silicon source is used in an amount such that the total number of silicon atoms constituting the silicon source is 0.025 to 0.3 parts with respect to 100 parts of hexagonal boron nitride molecules. The method for producing cubic boron nitride according to claim 1, wherein the boron source is used in an amount such that the total number of boron atoms constituting the boron source is 0.05 to 15 parts with respect to 100 parts of hexagonal boron nitride molecules. The method for producing cubic boron nitride according to claim 11, wherein the boron source is used in an amount such that the total number of boron atoms constituting the boron source is 0.1 to 5 parts with respect to 100 parts of hexagonal boron nitride molecules. The method of claim 1, wherein the stability range of the cubic boron nitride is selected to have a temperature of at least 1100 ° C. and a pressure of at least 3. 8 GPa. The method according to claim 1, wherein a mass containing converted cubic boron nitride and non-converted hexagonal boron nitride is obtained, and then the mass is pulverized, and sodium hydroxide and water are added, followed by heating to selectively dissolve the hexagonal boron nitride. And then cooled, washed with acid and filtered to separate cubic boron nitride. The method for producing cubic boron nitride according to claim 1, wherein the at least one compound which is an amide, an imide and a carbide is at least one of amides, imides and carbides of lithium, magnesium and calcium. The method for producing cubic boron nitride according to claim 1, wherein a combination of LiNH ₂ and CaC ₂ is used or a combination of LiNH ₂ and CaC ₂ is used together with a silicon source, a boron source or a combination thereof.