Formation of Boron Carbide-Boron Nitride Carbon Compositions

Formation of Boron Carbide-Boron Nitride Carbon Compositions
May 18, 2017 | Source: U.S. Patent and Trademark Office, pdfpiw.uspto.gov, 28 February 2017, Keller et al.

The present disclosure is generally related to synthesis of boron carbide and boron nitride.

Boron carbide is a highly refractory material that is of great interest for both its structural and electronic properties. Of particular importance are its low density, high-temperature stability, high hardness, high chemical stability, high cross-section for neutron capture, and excellent high-temperature thermoelectric properties. Boron carbide, in conjunction with other materials, also finds use as ballistic armor (including body or personal armor) where the combination of high hardness, high elastic modulus, and low density give the material an exceptionally high specific stopping power to defeat high velocity projectiles.

While boron carbide powders are easily made by the direct reaction of the elements at high temperatures, new synthetic methods that allow the formation of pure boron carbide in processed shaped forms are necessary for many potential applications. For commercial use, B.sub.4C powders usually need to be milled and purified to remove metallic impurities.

In common with other non-oxide materials, boron carbide is difficult to sinter to full density, with hot pressing or sinter hot isostatic pressing (HIP) being required to achieve greater than 95% of theoretical density. Even using these techniques, in order to achieve sintering at realistic temperatures (e.g. 1900-2200.degree. C.), small quantities of additives such as fine carbon or silicon carbide are usually required.

At present, attempts to form boron carbide or boride nitride have resulted in either powders or films. This is because these methods rely on the reaction between boron oxide and already formed carbon for B.sub.4C under an argon atmosphere and a boron oxide and a nitrogen sources (ammonia or urea) for BN under a nitrogen atmosphere. When these mixtures are heated at elevated temperatures, the result is the formation of the designated carbide or nitride as a powder in a classic nucleation-and-growth scheme. The microsized powder ceramic product must then be heated under high pressure and at temperature over 2000.degree. C. to consolidate to a hard shaped component, which is very brittle due to the grain boundaries.

Disclosed herein is a composition comprising nanoparticles of boron carbide and a carbonaceous matrix. The composition is not in the form of a powder.

Also disclosed herein is a composition comprising boron and an organic component. The organic component is selected from an organic compound having a char yield of at least 60% by weight and a thermoset made from the organic compound.

Also disclosed herein is a method comprising combining boron and an organic compound having a char yield of at least 60% by weight to form a precursor mixture.