Chemistry of inorganic compounds – Boron or compound thereof – Binary compound
Patent
1991-03-11
1993-07-27
Lewis, Michael
Chemistry of inorganic compounds
Boron or compound thereof
Binary compound
51307, C01B 21064
Patent
active
052308731
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Cubic boron nitride is a known industrial abrasive. It is produced from hexagonal boron nitride, hBN, at high pressures and temperatures, very often under the influence of Mg, Li, Mg.sub.3 N.sub.2 and Li.sub.3 N as flux (catalyst), as described, for example, in U.S. Pat. No. 2,947,617. To obtain the cubic form of boron nitride, this crystal structure must be favored. This occurs on the one hand by the addition of selected active catalysts based on alkali metals, alkaline earth metals, lead, tin, antimony, or nitrides of these metals, and the like, and on the other hand by a directed slow cooling of the melt which favors the crystal growth. Typical crystal morphology for cBN is octahedral or tetrahedral. Typical crystal sizes range from about 20 up to 500 .mu. (0.02-0.5 mm), dependent on the production conditions.
Hexagonal boron nitride is used in industry in pressed and sintered bodies as a powder, paste or spray, e.g., to produce or line casting molds or also as a lubricant, as a temperature-resistant shaped material.
Cubic boron nitride, which is distinguished from hexagonal boron nitride by its higher temperature resistance and by its hardness, which lies only slightly below that of diamond, finds a use as a cutting grain in the tool and abrasive industry. A further form of boron nitride is known under the name "turbostratic boron nitride, tBN". It is used as a starting material for pressed bodies and for the production of cubic boron nitride.
In addition to these, up to now there has only been a so-called "amorphous boron nitride", synthesized by Sumiya et al., see Materials Research Bulletin, 18, pages 1203-1207, 1983; it is termed aBN-1 below, for the soft phase produced at normal atmospheric pressure. This aBN-1 is a boron nitride which no longer possesses any graphite-like layer structure, but consists of fragments of crystal lattice and is soft. Thus it is not established whether aBN-1 is really amorphous or whether it is only present in a finely-powdered state.
A suitable apparatus for producing the pressures and temperatures in order to produce cubic boron nitride from hexagonal boron nitride is described, for example, in U.S. Pat. No. 2,941,243.
SUMMARY OF THE INVENTION
There is at present a great industrial need for abrasives of greater hardness. The object of the invention is to supplement or widen the palette of the known abrasives with a new one.
According to the invention, an amorphous boron nitride (aBN-2) with a hardness corresponding to the hardness of diamond has been found. The boron nitride aBN2 according to the invention, of a structure which is amorphous by X-ray and electron beam determination, has a hardness sufficient to scratch diamond. It is characterized by an amorphous (internal) structure, i.e., non-crystalline arrangement of the atoms. Apart from this, the grains can however have a pseudomorphic form, i.e., the hexagonal or cubic form can still exist. The grains can also have a glassy external form. To distinguish it from the known boron nitride produced at normal pressure and called amorphous, termed aBN-1, the amorphous boron nitride according to the invention is termed aBN-2. The boron nitride according to the invention is amorphous by X-rays and electron beam.
According to the invention, amorphous boron nitride of high hardness can be produced from hexagonal or turbostratic boron nitride (BN) as starting material, at pressures exceeding 70 Kbar, preferably 75 Kbar or more, and at temperatures of at least 1650.degree. C. or higher, by complete melting of the boron nitride charged, in that the thus obtained boron nitride melt is quenched. The crystalline components contained in the starting material are, according to the invention, completely melted and receive by quenching the consistency of a metastable, supercooled melt, so that there result grains of completely amorphous boron nitride with X-ray and electron beam amorphous structure, termed aBN-2.
In carrying out the process, after melting, the heat supply is first shut off for quench
REFERENCES:
patent: 3192015 (1965-06-01), Wentorf, Jr.
patent: 4623408 (1986-11-01), Karamon et al.
patent: 4772575 (1988-09-01), Ota et al.
Metallic Glasses, American Society for Metals, 1978: pp. 9-12.
Wildenburg Jorg
Will Georg
Firna Siegfried Golz
Kalinchak Stephen G.
Lewis Michael
LandOfFree
Process for producing amorphous boron nitride of high hardness does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for producing amorphous boron nitride of high hardness, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for producing amorphous boron nitride of high hardness will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2340892