Method for producing cubic boron nitride

Abstract

hBN is converted to cBN by keeping it under temperature and pressure conditions within the range of stability of cubic boron nitride, in the presence of a mixture of at least two compounds selected from amides and imides of Li, Ca and Mg, or in its copresence with at least one metal selected from elements of Groups Ia, IIa, IIIa, VIa, VIIa, VIII, IIb and IIIb.

We claim: 
     
       1. A method for producing cubic boron nitride, comprising keeping hexagonal boron nitride under temperature and pressure conditions within the range of stability of cubic boron nitride in the presence of a mixture of at least two compounds selected from the group consisting of amides and imides of Li, Ca and Mg, to convert said hexagonal boron nitride to cubic boron nitride. 
     
     
       2. A method according to claim 1, wherein said at least two amides and imides .[.are.]. compounds .Iadd.are .Iaddend.used such that the total number of metal atoms making up the compounds is 2 parts or more to 100 parts of the number of boron making up the hexagonal boron nitride. 
     
     
       3. A method according to claim 2, wherein said at least two amides and imides compounds are used such that the total number of the metal atoms making up the compounds is 5 to 50 parts to 100 parts of the number of boron atoms making up the hexagonal boron nitride. 
     
     
       4. A method according to claim 1, wherein said region of stability of cubic boron nitride is selected to have a temperature of 1100° C. or higher and a pressure of 3.8 GPa or higher. 
     
     
       5. A method according to claim 1, wherein .Iadd.a conversion rate is less than 100%, so that a composite lump comprising a mixture of hexagonal boron nitride and cubic boron nitride is formed, and .Iaddend.the method .Iadd.further .Iaddend.includes crushing the .[.converted cubic boron nitride.]. .Iadd.composite lump.Iaddend., then adding sodium hydroxide and water thereto and heating to selectively dissolve the hexagonal boron nitride, and then cooling, acid cleaning and filtering, so as to isolate the cubic boron nitride. 
     
     
       6. A method for producing cubic boron nitride, comprising keeping hexagonal boron nitride under temperature and pressure conditions within the range of stability of cubic boron nitride in the presence both of a mixture of at least two compounds selected from the group consisting of amides and imides of Li, Ca and Mg and of one or more metals selected from the group consisting of elements of Groups Ia, IIa, IIIa, VIa, VIIa, VIII, IIb and IIIb of the Periodic Table, to convert said hexagonal boron nitride to cubic boron nitride. 
     
     
       7. A method according to claim 6, wherein said at least two of amides and imides compounds of Li, Ca and Mg and said one or more metals from Groups Ia, IIa, IIIa, VIa, VIIa, VIII, IIb and IIIb are used such that the total number of the metal atoms making up the compounds and the latter metals is 2 parts or more to 100 parts of the number of boron making up the hexagonal boron nitride. 
     
     
       8. A method according to claim 7, wherein said at least two amides and imides compounds of Li, Ca and Mg and said one or more metals from Groups Ia, IIa, IIIa, VIa, VIIa, VIII, IIb and IIIb are used such that the total number of the metal atoms making up the compounds and the latter metals is 5 to 50 parts or more to 100 parts of the number of boron making up the hexagonal boron nitride. 
     
     
       9. A method according to claim 6, wherein said region of stability of cubic boron nitride is selected to have a temperature of 1100° C. or higher and a pressure of 3.8 GPa or higher. 
     
     
       10. A method according to claim 6, wherein .Iadd.a conversion rate is less than 100%, so that a composite lump comprising a mixture of hexagonal boron nitride and cubic boron nitride is formed, and .Iaddend.the method .Iadd.further .Iaddend.includes crushing the .[.converted cubic boron nitride.]. .Iadd.composite lump.Iaddend., and then adding sodium hydroxide and water thereto and heating to selectively dissolve the hexagonal boron nitride, and then cooling, acid cleaning and filtering, so as to isolate the cubic boron nitride. 
     
     
       11. A method for producing cubic boron nitride, comprising keeping hexagonal boron nitride under temperature and pressure conditions within the range of stability of cubic boron nitride in the presence of a single compound selected from the group consisting of amides of Ca and Mg and imides of Li, Ca and Mg, to convert said hexagonal boron nitride to cubic boron nitride. 
     
     
       12. A method according to claim 11, wherein said single amide or imide compound is used such that the total number of metal atoms making up the compound is 2 parts or more to 100 parts of the number of boron making up the hexagonal boron nitride. 
     
     
       13. A method according to claim 12, wherein said single amide or imide compound is used such that the total number of the metal atoms making up the compound is 5 to 50 parts to 100 parts of the number of boron atoms making up the hexagonal boron nitride. 
     
     
       14. A method according to claim 11, wherein said region of stability of cubic boron nitride is selected to have a temperature of 1100° C. or higher and a pressure of 3.8 GPa or higher. 
     
     
       15. A method according to claim 11, wherein .Iadd.a conversion rate is less than 100%, so that a composite lump comprising a mixture of hexagonal boron nitride and cubic boron nitride is formed, and .Iaddend.the method .Iadd.further .Iaddend.includes crushing the .[.converted cubic boron nitride.]. .Iadd.composite lump .Iaddend.and then adding sodium hydroxide and water thereto and heating to selectively dissolve the hexagonal boron nitride, and then cooling, acid cleaning and filtering, so as to isolate the cubic boron nitride. 
     
     
       16. A method for producing cubic boron nitride, comprising keeping hexagonal boron nitride under temperature and pressure conditions within the range of stability of cubic boron nitride in the presence both of a single compound selected from the group consisting of amides and imides of Li, Ca and Mg and of one or more metals selected from the group consisting of elements of Groups Ia, IIa, IIIa, VIa, VIIa, VIII, IIb and IIIb of the Periodic Table, to convert said hexagonal boron nitride to cubic boron nitride. 
     
     
       17. A method according to claim 16, wherein said single amide or imide compound of Li, Ca or Mg and said one or more metals from Groups Ia, IIa, IIIa, VIa, VIIa, VIII, IIb and IIIb are used such that the total number of the metal atoms making up the compound and the latter metals is 2 parts or more to 100 parts of the number of boron making up the hexagonal boron nitride. 
     
     
       18. A method according to claim 17, wherein said single amide or imide compound of Li, Ca or Mg and said one or more metals from Groups Ia, IIa, IIIa, VIa, VIIa, VIII, IIb and IIIb are used such that the total number of the metal atoms making up the compound and the latter metals is 5 to 50 parts or more to 100 parts of the number of boron making up the hexagonal boron nitride. 
     
     
       19. A method according to claim 16, wherein said region of stability of cubic boron nitride is selected to have a temperature of 1100° C. or higher and a pressure of 3.8 GPa or higher. 
     
     
       20. A method according to claim 16, wherein .Iadd.a conversion rate is less than 100%, so that a composite lump comprising a mixture of hexagonal boron nitride and cubic boron nitride is formed, and .Iaddend.the method .Iadd.further .Iaddend.includes crushing the .[.converted cubic boron nitride.]. .Iadd.composite lump.Iaddend., and then adding sodium hydroxide and water thereto and heating to selectively dissolve the hexagonal boron nitride, and then cooling, acid cleaning and filtering, so as to isolate the cubic boron nitride.