Crystalline turbostratic boron nitride powder and method for producing same

Abstract

Turbostratic boron nitride (t-BN) powder having excellent sinterability. A mixture of boric acid anhydride and urea is charged in a reaction vessel together with alkali-borate, heated step by step in the vessel in an nonoxidizing gas atmosphere of one atmospheric pressure or above, and kept at a temperature from 850° C. to 950° C. to yield an intermediate product formal substantially of an amorphous boron nitride powder (first reaction step). Then the intermediate product is heated and kept at a temperature from 1200° C. to 1400° C. to crystallize crystalline t-BN, and the product is purified by washing with water and aqueous solution to obtain pure crystalline t-BN powder.

1. A method for producing a crystalline turbostratic boron nitride, comprising:
 providing a mixture of a substantially amorphous boron nitride and an alkali-borate fluxing agent, and  
 crystallizing said amorphous boron nitride to said crystalline turbostratic boron nitride in the presence of an effective amount of said alkali-borate fluxing agent in a non-oxidizing atmosphere comprising an atmosphere within a vessel of a closed or quasi-closed state.  
 
     
     
       2. The method of  claim 1 , wherein said crystallizing is carried out by heating said mixture at a temperature of about 1500° C. or below for a time period until said amorphous boron nitride is substantially crystallized to said crystalline turbostratic boron nitride. 
     
     
       3. The method of  claim 1 , wherein said crystallizing is carried out at a temperature from 1200° C. to 1400° C. 
     
     
       4. The method of  claim 1 , wherein said alkali-borate comprises sodium borate and/or hydrate thereof. 
     
     
       5. The method of  claim 1 , wherein said alkali-borate in said mixture ranges from 0.01% to 20% by weight. 
     
     
       6. The method of  claim 1 , further comprising:
 purifying the crystalline turbostratic boron nitride by washing with an aqueous cleaning liquid to remove impurities after forming the crystalline turbostratic boron nitride.  
 
     
     
       7. A crystalline turbostratic boron nitride, wherein said crystalline turbostratic boron nitride has a (   001   )  diffraction peak in an X - ray powder diffraction diagram with Cu Kα X - ray which corresponds to the [ 002 ] diffraction peak of hexagonal boron nitride,      said  (   001   )  diffraction peak having a dominant peak defined by two straight flank lines, and being located between  20  and  30  degrees of  2 θ and rising from a substantially flat portion of said X - ray diffraction diagram; and        said crystalline turbostratic boron nitride exhibits a combined  (   10   )  diffraction peak in the X - ray powder diffraction diagram around the site of [ 100 ] and [ 101 ] diffraction peaks of hexagonal boron nitride,        said combined  (   10   )  diffraction peak having a peak at a site which corresponds to the site of [ 100 ] diffraction of hexagonal boron nitride and exhibiting substantially no recognizable diffraction peak which corresponds to the [ 101 ] diffraction peak of hexagonal boron nitride.     
     
     
       8. The crystalline turbostratic boron nitride as defined in  claim 7 , wherein said combined (   10   )  diffraction peak has a shoulder and a sloped foot portion following the shoulder on a larger angle side of  2 θ where the [ 101 ] diffraction peak of hexagonal boron nitride appears.   
     
     
       9. The crystalline turbostratic boron nitride as defined in  claim 7 , wherein said ( 001 ) diffraction peak is the ( 001 ) diffraction peak shown in  FIG. 7  of Drawings, and said combined ( 10 ) diffraction peak is the ( 10 ) diffraction peak shown in  FIG. 7  of Drawings. 
     
     
       10. The crystalline turbostratic boron nitride as defined in  claim 7 , wherein said crystalline turbostratic boron nitride has a primary particle size of approximately from  0 . 1  to  0 . 4  μm. 
     
     
       11. The crystalline turbostratic boron nitride as defined in  claim 7 , wherein said crystalline turbostratic boron nitride has a primary particle size in the order of  0 . 2  to  0 . 3  μm. 
     
     
       12. The crystalline turbostratic boron nitride as defined in  claim 7 , wherein said turbostratic boron nitride has an X- ray powder diffraction peak which corresponds to a [ 004 ] diffraction of hexagonal boron nitride having a half peak - height width of  0 . 6 ° or below in  2 θ.   
     
     
       13. The crystalline turbostratic boron nitride as defined in  claim 7 , wherein said turbostratic boron nitride has an X- ray powder diffraction peak which corresponds to a [ 004 ] diffraction of hexagonal boron nitride having a half peak - height width of  0 . 5 ° or below in  2 θ.   
     
     
       14. A crystalline turbostratic boron nitride, wherein said crystalline turbostratic boron nitride has a (   001   )  diffraction peak in an X - ray powder diffraction diagram with Cu Kα X - ray which corresponds to the [ 002 ] diffraction peak of hexagonal boron nitride,      said  (   001   )  diffraction peak having a dominant peak defined by two straight flank lines, and being located between  20  and  30  degrees of  2 θ and rising from a substantially flat portion of said X - ray diffraction diagram;        said crystalline turbostratic boron nitride exhibits a combined  (   10   )  diffraction peak in the X - ray powder diffraction diagram around the site of [ 100 ] and [ 101 ] diffraction peaks of hexagonal boron nitride,        said combined  (   10   )  diffraction peak having peak at a site which corresponds to the site of [ 100 ] diffraction of hexagonal boron nitride and exhibiting substantially no recognizable diffraction peak which corresponds to the [ 101 ] diffraction peak of hexagonal boron nitride; and        said turbostratic boron nitride comprises primary particles having a substantially spherical shape.     
     
     
       15. The crystalline turbostratic boron nitride as defined in  claim 14 , wherein said combined (   10   )  diffraction peak has a shoulder and a sloped foot portion following the shoulder on a larger angle side of  2 θ where the [ 101 ] diffraction peak of hexagonal boron nitride appears.   
     
     
       16. The crystalline turbostratic boron nitride as defined in  claim 14 , wherein said ( 001 ) diffraction peak is the ( 001 ) diffraction peak shown in  FIG. 7  of Drawings, and said combined ( 10 ) diffraction peak is the ( 10 ) diffraction peak shown in  FIG. 7  of Drawings. 
     
     
       17. The crystalline turbostratic boron nitride as defined in  claim 14 , wherein said crystalline turbostratic boron nitride has a primary particle size of approximately from  0 . 1  to  0 . 4  μm. 
     
     
       18. The crystalline turbostratic boron nitride as defined in  claim 14 , wherein said primary particles have a size in the order of  0 . 2  to  0 . 3  μm. 
     
     
       19. The crystalline turbostratic boron nitride as defined in  claim 14 , wherein said turbostratic boron nitride has an X- ray powder diffraction peak which corresponds to a [ 004 ] diffraction of hexagonal boron nitride having a half peak - height width of  0 . 6 ° or below in  2 θ.   
     
     
       20. The crystalline turbostratic boron nitride as defined in  claim 14 , wherein said turbostratic boron nitride has an X- ray powder diffraction peak which corresponds to a [ 004 ] diffraction of hexagonal boron nitride having a half peak - height width of  0 . 5 ° or below in  2 θ.